全文获取类型
收费全文 | 3400篇 |
免费 | 261篇 |
出版年
2023年 | 16篇 |
2022年 | 32篇 |
2021年 | 93篇 |
2020年 | 50篇 |
2019年 | 53篇 |
2018年 | 85篇 |
2017年 | 70篇 |
2016年 | 104篇 |
2015年 | 160篇 |
2014年 | 181篇 |
2013年 | 216篇 |
2012年 | 255篇 |
2011年 | 249篇 |
2010年 | 176篇 |
2009年 | 156篇 |
2008年 | 217篇 |
2007年 | 224篇 |
2006年 | 187篇 |
2005年 | 175篇 |
2004年 | 159篇 |
2003年 | 132篇 |
2002年 | 120篇 |
2001年 | 52篇 |
2000年 | 48篇 |
1999年 | 48篇 |
1998年 | 27篇 |
1997年 | 28篇 |
1996年 | 17篇 |
1995年 | 23篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 30篇 |
1991年 | 23篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1985年 | 19篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1978年 | 4篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1968年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有3661条查询结果,搜索用时 156 毫秒
131.
Betekhtin Alexander Pinski Artur Milewska-Hendel Anna Kurczynska Ewa Hasterok Robert 《Plant Cell, Tissue and Organ Culture》2019,137(2):343-357
Plant Cell, Tissue and Organ Culture (PCTOC) - The morphogenic callus (MC) of Fagopyrum tataricum contains a large amount of flavonoids, especially rutin, and exhibits a high level of antioxidant... 相似文献
132.
J. Eduardo Fajardo Rojan Shrestha Nelson Gil Adam Belsom Silvia N. Crivelli Cezary Czaplewski Krzysztof Fidelis Sergei Grudinin Mikhail Karasikov Agnieszka S. Karczyńska Andriy Kryshtafovych Alexander Leitner Adam Liwo Emilia A. Lubecka Bohdan Monastyrskyy Guillaume Pagès Juri Rappsilber Adam K. Sieradzan Celina Sikorska Esben Trabjerg Andras Fiser 《Proteins》2019,87(12):1283-1297
With the advance of experimental procedures obtaining chemical crosslinking information is becoming a fast and routine practice. Information on crosslinks can greatly enhance the accuracy of protein structure modeling. Here, we review the current state of the art in modeling protein structures with the assistance of experimentally determined chemical crosslinks within the framework of the 13th meeting of Critical Assessment of Structure Prediction approaches. This largest-to-date blind assessment reveals benefits of using data assistance in difficult to model protein structure prediction cases. However, in a broader context, it also suggests that with the unprecedented advance in accuracy to predict contacts in recent years, experimental crosslinks will be useful only if their specificity and accuracy further improved and they are better integrated into computational workflows. 相似文献
133.
Jasminder Sahi Michael P. Wiggins Gil B. Gibori Thomas J. Layden Mrinalini C. Rao 《Journal of cellular physiology》1996,168(2):276-283
To determine if calcium-dependent secretagogues directly act on epithelial cells to elicit CI− secretion, their effects on CI− transport and intracellular Ca2+ concentrations ([Ca2+]i) were determined in primary cultures of rabbit distal colonic crypt cells. The Cl− sensitive fluorescent probe, 6-methoxyquinolyl acetoethyl ester, MQAE and the Ca2+-sensitive fluorescent probe, fura-2AM were used to assess Cl− transport and [Ca2+]i, respectively. Basal Cl− transport (0.274 ± 0.09 mM/sec) was inhibited significantly by the Cl− channel blocker diphenylamine-2-carboxylate (DPC, 50 μM, 0.068 ± 0.02 mM/sec; P < 0.001) and the Na+/K+/2Cl− cotransport inhibitor furosemide (1 μM, 0.137 ± 0.04 mM/sec; P < 0.01). Ion substitution studies using different halides revealed the basal influx to be I− > F− ≥ Cl− > Br−. DPC inhibited I− influx by ∼50%, F− influx by 80%, Cl− influx by 85%, and Br− influx by 90%. Furosemide significantly inhibited influx of Br− (84%) and Cl− (81%) but not of F− and I−. The effects of agents known to alter biological response by increasing [Ca2+]i in other epithelial systems were used to stimulate Cl− transport. Cl− influx in mM/second was stimulated by 1 μM histamine (0.58 ± 0.05), 10 μM neurotensin (2.07 ± 0.32), 1 μM serotonin (1.63 ± 0.28), and 0.1 μM of the Ca2+ ionophore A23187 (2.05 ± 0.40). The Cl− permeability stimulated by neurotensin, serotonin, and A23187 was partially blocked by DPC or furosemide added alone or in combination. Histamine-induced Cl− influx was significantly inhibited by only furosemide. Indomethacin blocked histamine-stimulated Cl− permeability but had no effect on the actions of the other agents. These studies, focusing on isolated colonocytes without the contribution of submucosal elements, reveal that (1) histamine stimulates Cl− transport by activating the Na+/K+/2Cl− cotransporter via a cyclooxygenase-dependent pathway; (2) neurotensin, serotonin, and A23187 activate both Cl− channels and the cotransporter, and their actions are cyclooxygenase-independent. © 1996 Wiley-Liss, Inc. 相似文献
134.
135.
Svio S. Costa Leticia A. B. Lago Artur Silva Diego A. das Graas Jernimo Lameira Rafael A. Baraúna 《Genetics and molecular biology》2022,45(1)
Bacteriocins are antimicrobial peptides expressed by bacteria through ribosomal activity. In this study, we analyzed the diversity of bacteriocin-like genes in the Tucuruí-HPP using a whole-metagenome shotgun sequencing approach. Three layers of the water column were analyzed (photic, aphotic and sediment). Detection of bacteriocin-like genes was performed with blastx using the BAGEL4 database as subject sequences. In order to calculate the abundance of bacteriocin-like genes we also determined the number of 16S rRNA genes using blastn. Taxonomic analysis was performed using RAST server and the metagenome was assembled using IDBA-UD in order to recover the full sequence of a zoocin which had its three-dimensional structure determined. The photic zone presented the highest number of reads affiliated to bacteriocins. The most abundant bacteriocins were sonorensin, Klebicin D , pyocin and colicin. The zoocin model was composed of eight anti-parallel β-sheets and two α-helices with a Zn2+ ion in the active site. This model was considerably stable during 10 ns of molecular dynamics simulation. We observed a high diversity of bacteriocins in the Tucuruí-HPP, demonstrating that the environment is an inexhaustible source for prospecting these molecules. Finally, the zoocin model can be used for further studies of substrate binding and molecular mechanisms involving peptidoglycan degradation. 相似文献
136.
G Barja de Quiroga M Lopez-Torres P Gil 《Comparative biochemistry and physiology. A, Comparative physiology》1989,92(4):581-588
1. During the development of D. pictus larvae (Amphibia) in normoxia, selenium (Se) GSH-Px increased whereas non-Se GSH-Px did not change. 2. Acclimation to 60 or 100% O2 did not change Se GSH-Px or non-Se GSH-Px. 3. Hyperoxia did not change tissue peroxidation (TBA-RS) confirming the good capacity of D. pictus tadpoles for O2-adaptation. 4. Since hyperoxic induction of catalase (CAT) has been previously described in D. pictus tadpoles, it is concluded that CAT is more important than both GSH-Px for the establishment of O2-adaptation. 5. Increases of Se GSH-Px, SOD and CAT, are probably important for adaptation to the change from aquatic to aerial environment during metamorphosis in normoxia. 6. Chronic exposure to 100% O2 enormously reduced the lung size of D. pictus larvae. 相似文献
137.
Brooke M. Helfer Anthony Balducci Aaron D. Nelson Jelena M. Janjic Roberto R. Gil Pawel Kalinski I. Jolanda M. de Vries Eric T. Ahrens Robbie B. Mailliard 《Cytotherapy》2010,12(2):238-250
Background aimsDendritic cells (DC) are increasingly being used as cellular vaccines to treat cancer and infectious diseases. While there have been some promising results in early clinical trials using DC-based vaccines, the inability to visualize non-invasively the location, migration and fate of cells once adoptively transferred into patients is often cited as a limiting factor in the advancement of these therapies. A novel perflouropolyether (PFPE) tracer agent was used to label human DC ex vivo for the purpose of tracking the cells in vivo by 19F magnetic resonance imaging (MRI). We provide an assessment of this technology and examine its impact on the health and function of the DC.MethodsMonocyte-derived DC were labeled with PFPE and then assessed. Cell viability was determined by examining cell membrane integrity and mitochondrial lipid content. Immunostaining and flow cytometry were used to measure surface antigen expression of DC maturation markers. Functional tests included bioassays for interleukin (IL)-12p70 production, T-cell stimulatory function and chemotaxis. MRI efficacy was demonstrated by inoculation of PFPE-labeled human DC into NOD-SCID mice.ResultsDC were effectively labeled with PFPE without significant impact on cell viability, phenotype or function. The PFPE-labeled DC were clearly detected in vivo by 19F MRI, with mature DC being shown to migrate selectively towards draining lymph node regions within 18 h.ConclusionsThis study is the first application of PFPE cell labeling and MRI cell tracking using human immunotherapeutic cells. These techniques may have significant potential for tracking therapeutic cells in future clinical trials. 相似文献
138.
139.
Rodrigo L Hernández AF López-Caballero JJ Gil F Pla A 《Chemico-biological interactions》2001,137(2):123-137
Studies on the localization of paraoxonases (PON's) are of interest because of its involvement in both the detoxication of activated organophosphorus pesticides and in the prevention of peroxidative damage to phospholipids and cholesteryl-esters in LDL and HDL particles and cell membranes during the atherogenic process. In the present study, we have investigated the cellular localization of PON1 by immunohistochemistry in different rat tissues. The protein was mainly detected in the endothelial lining of every tissue studied (liver, kidney, lung and brain). Besides, it was found in hepatocytes from the centrolobular region of the liver, in the glomeruli and basal pole of the proximal convoluted tubule of the kidney, in cells from bronchiolar epithelium and type I pneumocytes of the lung, and in leptomeningeal cells, ependymal cells and ventricular side of choroid plexus cells of the brain. However, neurons and glia lacked immunostaining. After 3-methylcholanthrene induction an increase in the intensity of immunostaining was observed in the same areas, as well as an additional staining in midzonal hepatocytes. On the basis of the tissue distribution observed for PON1, it is proposed that this enzyme might have a function related to the inactivation of oxidative stress by-products (either at a cellular level or blood-vessel wall) and other environmental chemicals. At present it has not yet been established whether the paraoxonase detected in the various tissues is truly a product of the PON1 gene or could represent products of the PON2 or PON3 genes. 相似文献
140.
Lamrabet Y Bellogín RA Cubo T Espuny R Gil A Krishnan HB Megias M Ollero FJ Pueppke SG Ruiz-Sainz JE Spaink HP Tejero-Mateo P Thomas-Oates J Vinardell JM 《Molecular plant-microbe interactions : MPMI》1999,12(3):207-217
We mutagenized Sinorhizobium fredii HH103-1 with Tn5-B20 and screened about 2,000 colonies for increased beta-galactosidase activity in the presence of the flavonoid naringenin. One mutant, designated SVQ287, produces lipochitooligosaccharide Nod factors (LCOs) that differ from those of the parental strain. The nonreducing N-acetylglucosamine residues of all of the LCOs of mutant SVQ287 lack fucose and 2-O-methylfucose substituents. In addition, SVQ287 synthesizes an LCO with an unusually long, C20:1 fatty acyl side chain. The transposon insertion of mutant SVQ287 lies within a 1.1-kb HindIII fragment. This and an adjacent 2.4-kb HindIII fragment were sequenced. The sequence contains the 3' end of noeK, nodZ, and noeL (the gene interrupted by Tn5-B20), and the 5' end of nolK, all in the same orientation. Although each of these genes has a similarly oriented counterpart on the symbiosis plasmid of the broad-host-range Rhizobium sp. strain NGR234, there are significant differences in the noeK/nodZ intergenic region. Based on amino acid sequence homology, noeL encodes GDP-D-mannose dehydratase, an enzyme involved in the synthesis of GDP-L-fucose, and nolK encodes a NAD-dependent nucleotide sugar epimerase/dehydrogenase. We show that expression of the noeL gene is under the control of NodD1 in S. fredii and is most probably mediated by the nod box that precedes nodZ. Transposon insertion into neoL has two impacts on symbiosis with Williams soybean: nodulation rate is reduced slightly and competitiveness for nodulation is decreased significantly. Mutant SVQ287 retains its ability to form nitrogen-fixing nodules on other legumes, but final nodule number is attenuated on Cajanus cajan. 相似文献