全文获取类型
收费全文 | 696篇 |
免费 | 39篇 |
专业分类
735篇 |
出版年
2022年 | 5篇 |
2021年 | 21篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 18篇 |
2015年 | 25篇 |
2014年 | 18篇 |
2013年 | 23篇 |
2012年 | 40篇 |
2011年 | 36篇 |
2010年 | 28篇 |
2009年 | 16篇 |
2008年 | 31篇 |
2007年 | 31篇 |
2006年 | 35篇 |
2005年 | 32篇 |
2004年 | 22篇 |
2003年 | 23篇 |
2002年 | 20篇 |
2001年 | 22篇 |
2000年 | 25篇 |
1999年 | 18篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1966年 | 3篇 |
1960年 | 4篇 |
排序方式: 共有735条查询结果,搜索用时 0 毫秒
51.
Saad M. Alshahrani Wenli Lu Jun-Bom Park Joseph T. Morott Bader B. Alsulays Soumyajit Majumdar Nigel Langley Karl Kolter Andreas Gryczke Michael A. Repka 《AAPS PharmSciTech》2015,16(4):824-834
The aim of this study was to evaluate a novel combination of Soluplus® and hypromellose acetate succinate (HPMCAS-HF) polymers for solubility enhancement as well as enhanced physicochemical stability of the produced amorphous solid dispersions. This was accomplished by converting the poorly water-soluble crystalline form of carbamazepine into a more soluble amorphous form within the polymeric blends. Carbamazepine (CBZ), a Biopharmaceutics Classification System class II active pharmaceutical ingredient (API) with multiple polymorphs, was utilized as a model drug. Hot-melt extrusion (HME) processing was used to prepare solid dispersions utilizing blends of polymers. Drug loading showed a significant effect on the dissolution rate of CBZ in all of the tested ratios of Soluplus® and HPMCAS-HF. CBZ was completely miscible in the polymeric blends of Soluplus® and HPMCAS-HF up to 40% drug loading. The extrudates were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and dissolution studies. DSC and XRD data confirmed the formation of amorphous solid dispersions of CBZ in the polymeric blends of Soluplus® and HPMCAS-HF. Drug loading and release of CBZ was increased with Soluplus® (when used as the primary matrix polymer) when formulations contained Soluplus® with 7–21% (w/w) HPMCAS-HF. In addition, this blend of polymers was found to be physically and chemically stable at 40°C, 75% RH over 12 months without any dissolution rate changes.KEY WORDS: carbamazepine, hot-melt extrusion, HPMCAS-HF, Soluplus®, stability 相似文献
52.
Jayant Arora John M Hickey Ranajoy Majumdar Reza Esfandiary Steven M Bishop Hardeep S Samra C Russell Middaugh David D Weis David B Volkin 《MABS-AUSTIN》2015,7(3):525-539
There is a need for new analytical approaches to better characterize the nature of the concentration-dependent, reversible self-association (RSA) of monoclonal antibodies (mAbs) directly, and with high resolution, when these proteins are formulated as highly concentrated solutions. In the work reported here, hydrogen exchange mass spectrometry (HX-MS) was used to define the concentration-dependent RSA interface, and to characterize the effects of association on the backbone dynamics of an IgG1 mAb (mAb-C). Dynamic light scattering, chemical cross-linking, and solution viscosity measurements were used to determine conditions that caused the RSA of mAb-C. A novel HX-MS experimental approach was then applied to directly monitor differences in local flexibility of mAb-C due to RSA at different protein concentrations in deuterated buffers. First, a stable formulation containing lyoprotectants that permitted freeze-drying of mAb-C at both 5 and 60 mg/mL was identified. Upon reconstitution with RSA-promoting deuterated solutions, the low vs. high protein concentration samples displayed different levels of solution viscosity (i.e., approx. 1 to 75 mPa.s). The reconstituted mAb-C samples were then analyzed by HX-MS. Two specific sequences covering complementarity-determining regions CDR2H and CDR2L (in the variable heavy and light chains, respectively) showed significant protection against deuterium uptake (i.e., decreased hydrogen exchange). These results define the major protein-protein interfaces associated with the concentration-dependent RSA of mAb-C. Surprisingly, certain peptide segments in the VH domain, the constant domain (CH2), and the hinge region (CH1-CH2 interface) concomitantly showed significant increases in local flexibility at high vs. low protein concentrations. These results indicate the presence of longer-range, distant dynamic coupling effects within mAb-C occurring upon RSA. 相似文献
53.
Jesudason R Sato S Parameswaran H Araujo AD Majumdar A Allen PG Bartolák-Suki E Suki B 《Biophysical journal》2010,99(9):3076-3083
Many fundamental cellular and extracellular processes in the body are mediated by enzymes. At the single molecule level, enzyme activity is influenced by mechanical forces. However, the effects of mechanical forces on the kinetics of enzymatic reactions in complex tissues with intact extracellular matrix (ECM) have not been identified. Here we report that physiologically relevant macroscopic mechanical forces modify enzyme activity at the molecular level in the ECM of the lung parenchyma. Porcine pancreatic elastase (PPE), which binds to and digests elastin, was fluorescently conjugated (f-PPE) and fluorescent recovery after photobleach was used to evaluate the binding kinetics of f-PPE in the alveolar walls of normal mouse lungs. Fluorescent recovery after photobleach indicated that the dissociation rate constant (koff) for f-PPE was significantly larger in stretched than in relaxed alveolar walls with a linear relation between koff and macroscopic strain. Using a network model of the parenchyma, a linear relation was also found between koff and microscopic strain on elastin fibers. Further, the binding pattern of f-PPE suggested that binding sites on elastin unfold with strain. The increased overall reaction rate also resulted in stronger structural breakdown at the level of alveolar walls, as well as accelerated decay of stiffness and decreased failure stress of the ECM at the macroscopic scale. These results suggest an important role for the coupling between mechanical forces and enzyme activity in ECM breakdown and remodeling in development, and during diseases such as pulmonary emphysema or vascular aneurysm. Our findings may also have broader implications because in vivo, enzyme activity in nearly all cellular and extracellular processes takes place in the presence of mechanical forces. 相似文献
54.
Bryan E. Hoffman Tonie M. Newman‐Tarr Anna Gibbard Shen Wang Charles Hanning Michael A. Pratta Ryan J. Boyle Sanjay Kumar Manas K. Majumdar 《Journal of cellular physiology》2010,222(3):695-702
Chondrocytes, the only cell type present in articular cartilage, regulate tissue homeostasis by a fine balance of metabolism that includes both anabolic and catabolic activities. Therefore, the biology of chondrocytes is critical for understanding cartilage metabolism. One major limitation when studying primary chondrocytes in culture is their loss of phenotype. To overcome this hurdle, limited attempts have been made to develop human chondrocyte cell lines that retain the phenotype for use as a good surrogate model. In this study, we report a novel approach to the establishment and characterization of human articular cartilage‐derived chondrocyte cell lines. Adenoviral infection followed by culture of chondrocytes in 3‐dimensional matrix within 48 h post‐infection maintained the phenotype prior to clonal selection. Cells were then placed in culture either as monolayer, or in 3‐dimensional matrix of alginate or agarose. The clones were characterized by their basal gene expression profile of chondrocyte markers. Based on type II collagen expression, 21 clones were analyzed for gene expression following treatment with IL‐1 or BMP‐7 and compared to similarly stimulated primary chondrocytes. This resulted in selection of two clones that retained the chondrocyte phenotype as evidenced by expression of type II collagen and other extra‐cellular matrix molecules. In addition, one clone (AL‐4‐17) showed similar responses as primary chondrocytes when treated with IL‐1 or BMP‐7. In summary, this report provides a novel procedure to develop human articular cartilage‐derived chondrocyte cell lines, which preserve important characteristics of articular chondrocytes and represent a useful model to study chondrocyte biology. J. Cell. Physiol. 222: 695–702, 2010. © 2009 Wiley‐Liss, Inc. 相似文献
55.
Rat intestinal UDPgalactose: N-acetylglucosaminyl(beta 1----4)galactosyltransferase activity was studied as to its intestinal and villus-to-crypt distribution, and then purified and characterized. Rapid UDPgalactose hydrolysis was noted in the duodenum and jejunum; little to no breakdown was detected in the distal ileum, cecum and proximal colon. Product analysis suggested that UDPgalactose hydrolysis was due to nucleotide-sugar pyrophosphatase and galactose-1-phosphate phosphatase activities; ileum appeared to have little of the first activity and none of the latter. An aboral gradient of galactosyltransferase activity was noted, activity being 3-4-fold higher in the ileum, cecum and proximal colon. Total homogenate exogenous acceptor galactosyltransferase activities showed no villus-crypt differences but activity measured with intact isolated cells demonstrated higher activity with crypt cells; this was particularly evident in the ileum. Galactosyltransferase activity was purified from ileal-colonic mucosa. An over 4000-fold purification with 75 percent yield was achieved. Only one band of approx. 70-75 kDa was noted on sodium dodecyl sulfate polyacrylamide electrophoresis. As with other eukaryotic galactosyltransferase activities, there was an absolute requirement for Mn2+; the concentration required for half maximal activity was only 2.5 microM and higher concentrations did not inhibit. The Km for UDPgalactose was 30 microM. 相似文献
56.
A K Roy B Chatterjee K V Rao C V Murty F H Sarkar D Majumdar 《Journal of steroid biochemistry》1987,27(4-6):1129-1134
Androgen-dependent synthesis of alpha 2u globulin in the rat liver has been used in our laboratory as a model for studying the effect of sex hormones on hepatic gene expression. alpha 2u Globulin is a group of low molecular weight (Mr approximately 18,000) male specific urinary proteins synthesized and secreted by hepatocytes. In the male rat hepatic synthesis of alpha 2u globulin begins at puberty (approximately 40 days), reaches a peak level (approximately 20 mg/day) at about 75 days and declines during old age. Androgens can induce alpha 2u globulin in ovariectomized female rats in vivo and in the liver perfusion system in vitro. However, both prepubertal and senescent (greater than 800 days) male rats not only do not produce alpha 2u globulin but are also refractory to androgen administration. alpha 2u Globulin is coded by a multigene family comprising about 20-30 gene copies per haploid genome. All of these gene copies seem to express translationally active mRNAs giving rise to individual isoforms of alpha 2u globulin. Appearance and disappearance of the cytoplasmic androgen-binding protein (CAB) correlates with the androgen responsiveness of hepatocytes. Photoaffinity labeling of the hepatic cytosol shows that the biologically active binding protein, found in the cytosol of the mature male rat liver, has a molecular weight of 31 kDa. A molecular transition of the 31-kDa CAB to a biologically inactive 29-kDa form may be the basis of hepatic androgen insensitivity during prepuberty and senescence. 相似文献
57.
Majumdar S Lamothe B Aggarwal BB 《Journal of immunology (Baltimore, Md. : 1950)》2002,168(6):2644-2651
Thalidomide ([+]-alpha-phthalimidoglutarimide), a psychoactive drug that readily crosses the blood-brain barrier, has been shown to exhibit anti-inflammatory, antiangiogenic, and immunosuppressive properties through a mechanism that is not fully established. Due to the central role of NF-kappaB in these responses, we postulated that thalidomide mediates its effects through suppression of NF-kappaB activation. We investigated the effects of thalidomide on NF-kappaB activation induced by various inflammatory agents in Jurkat cells. The treatment of these cells with thalidomide suppressed TNF-induced NF-kappaB activation, with optimum effect occurring at 50 microg/ml thalidomide. These effects were not restricted to T cells, as other hematopoietic and epithelial cell types were also inhibited. Thalidomide suppressed H(2)O(2)-induced NF-kappaB activation but had no effect on NF-kappaB activation induced by PMA, LPS, okadaic acid, or ceramide, suggesting selectivity in suppression of NF-kappaB. The suppression of TNF-induced NF-kappaB activation by thalidomide correlated with partial inhibition of TNF-induced degradation of an inhibitory subunit of NF-kappaB (IkappaBalpha), abrogation of IkappaBalpha kinase activation, and inhibition of NF-kappaB-dependent reporter gene expression. Thalidomide abolished the NF-kappaB-dependent reporter gene expression activated by overexpression of TNFR1, TNFR-associated factor-2, and NF-kappaB-inducing kinase, but not that activated by the p65 subunit of NF-kappaB. Overall, our results clearly demonstrate that thalidomide suppresses NF-kappaB activation specifically induced by TNF and H(2)O(2) and that this may contribute to its role in suppression of proliferation, inflammation, angiogenesis, and the immune system. 相似文献
58.
Shant J Bhattacharyya S Ghosh S Ganguly NK Majumdar S 《Experimental parasitology》2002,102(3-4):178-186
In this study we have reported the detailed characterization of a 58 kDa excretory-secretory product (ESP) of Giardia lamblia. The method of purification has been simplified which has improved the purification fold as well as the yield of the ESP. The binding efficacy of disialoganglioside (GD2) to the purified ESP was found to be maximum among all other gangliosides used. The N-terminal sequence of the immunoreactive 29 kDa peptide obtained from partial tryptic digest of the ESP was found to be AD-FVPQVST. The IgG against the purified ESP (IgGES) showed cross-reactivity with the binding subunit of the commercially available cholera toxin and also with two protein bands of western cottonmouth moccasin snake toxin. The ESP could accumulate fluid in the intestine of sealed adult mice and also induce morphological changes in HEp-2 cells. The crude extract of G. lamblia trophozoites preincubated with Escherichia coli revealed 8-fold augmentation in the cytopathic activity on HEp-2 cells as compared to that of crude preparation from trophozoites only. 相似文献
59.
Jonojit Roy Soumi Naha Madhumita Majumdar Nirmalya Banerjee 《Plant Cell, Tissue and Organ Culture》2007,90(1):31-39
An efficient method of mass propagation of Dendrobium chrysotoxum Lindl. was developed using a shoot-tip culture system. Both direct and callus-mediated formation of protocorm-like bodies
(PLBs) occurred from the basal cut surface of explants. Frequency of callusing was best in the presence of 2 μM thidiazuron
(TDZ) or N6-benzylaminopurine (BAP). The callus exhibited complete hormone autonomy for growth and differentiation of PLBs and was maintained
for 18 months without any exogenous growth regulators, an aspect important for minimising somaclonal variation. However, the
rate of callus growth and PLB formation varied with application of cytokinin and auxin. In addition, the callus exhibited
a differential sensitivity to the exogenous cytokinins. While BAP promoted callus growth and PLB differentiation, TDZ was
inhibitory to callus mediated PLB formation and caused extensive necrosis of callus. Although α-naphthaleneacetic acid (NAA)
had no significant effect on the induction of callus, subsequent growth was best in its presence. Using a 3-month subculture
period, a 69-fold increase in callus weight was achieved with 0.5 μM NAA, while as many as 133 PLBs could be obtained per
100 mg callus in the presence of 1 μM NAA. For direct PLB formation, the optimum cytokinin dosage was dependent upon the type
of cytokinin used. While TDZ was most effective at a concentration of 1 μM (15 PLBs per explant), for similar PLB yield the
application of 8 μM BAP was essential. 相似文献
60.
Ermolenko DN Majumdar ZK Hickerson RP Spiegel PC Clegg RM Noller HF 《Journal of molecular biology》2007,370(3):530-540
Protein synthesis is believed to be a dynamic process, involving structural rearrangements of the ribosome. Cryo-EM reconstructions of certain elongation factor G (EF-G)-containing complexes have led to the proposal that translocation of tRNA and mRNA through the ribosome, from the A to P to E sites, is accompanied by a rotational movement between the two ribosomal subunits. Here, we have used F?rster resonance energy transfer (FRET) to monitor changes in the relative orientation of the ribosomal subunits in different complexes trapped at intermediate stages of translocation in solution. Binding of EF-G to the ribosome in the presence of the non-hydrolyzable GTP analogue GDPNP or GTP plus fusidic acid causes an increase in the efficiency of energy transfer between fluorophores introduced into proteins S11 in the 30 S subunit and L9 in the 50 S subunit, and a decrease in energy transfer between S6 and L9. Similar anti-correlated changes in energy transfer occur upon binding the GTP-requiring release factor RF3. These changes are consistent with the counter-clockwise rotation of the 30 S subunit relative to the 50 S subunit observed in cryo-EM studies. Reaction of ribosomal complexes containing the peptidyl-tRNA analogues N-Ac-Phe-tRNAPhe, N-Ac-Met-tRNAMet or f-Met-tRNAfMet with puromycin, conditions favoring movement of the resulting deacylated tRNAs into the P/E hybrid state, leads to similar changes in FRET. Conversely, treatment of a ribosomal complex containing deacylated and peptidyl-tRNAs bound in the A/P and P/E states, respectively, with EF-G.GTP causes reversal of the FRET changes. The use of FRET has enabled direct observation of intersubunit movement in solution, provides independent evidence that formation of the hybrid state is coupled to rotation of the 30 S subunit and shows that the intersubunit movement is reversed during the second step of translocation. 相似文献