全文获取类型
收费全文 | 8403篇 |
免费 | 577篇 |
国内免费 | 106篇 |
专业分类
9086篇 |
出版年
2022年 | 73篇 |
2021年 | 161篇 |
2020年 | 75篇 |
2019年 | 95篇 |
2018年 | 116篇 |
2017年 | 94篇 |
2016年 | 139篇 |
2015年 | 209篇 |
2014年 | 255篇 |
2013年 | 411篇 |
2012年 | 451篇 |
2011年 | 438篇 |
2010年 | 260篇 |
2009年 | 246篇 |
2008年 | 307篇 |
2007年 | 327篇 |
2006年 | 318篇 |
2005年 | 284篇 |
2004年 | 251篇 |
2003年 | 248篇 |
2002年 | 261篇 |
2001年 | 195篇 |
2000年 | 200篇 |
1999年 | 171篇 |
1998年 | 82篇 |
1997年 | 85篇 |
1996年 | 80篇 |
1995年 | 76篇 |
1994年 | 74篇 |
1993年 | 72篇 |
1992年 | 180篇 |
1991年 | 159篇 |
1990年 | 160篇 |
1989年 | 145篇 |
1988年 | 124篇 |
1987年 | 144篇 |
1986年 | 123篇 |
1985年 | 155篇 |
1984年 | 147篇 |
1983年 | 145篇 |
1982年 | 110篇 |
1981年 | 92篇 |
1979年 | 136篇 |
1978年 | 95篇 |
1977年 | 100篇 |
1976年 | 76篇 |
1975年 | 90篇 |
1974年 | 91篇 |
1973年 | 85篇 |
1972年 | 96篇 |
排序方式: 共有9086条查询结果,搜索用时 15 毫秒
991.
Anumula KR 《Glycobiology》2012,22(7):912-917
Assays were developed using the unique labeling chemistry of 2-aminobenzoic acid (2AA; anthranilic acid, AA) for measuring activities of both β1-4 galactosyltransferase (GalT-1) and α2-6 sialyltransferase (ST-6) by high-performance liquid chromatography (HPLC) with fluorescence detection (Anumula KR. 2006. Advances in fluorescence derivatization methods for high-performance liquid chromatographic analysis of glycoprotein carbohydrates. Anal Biochem. 350:1-23). N-Acetylglucosamine (GlcNAc) and N-acetyllactosamine were used as acceptors and uridine diphosphate (UDP)-galactose and cytidine monophosphate (CMP)-N-acetylneuraminic acid (NANA) as donors for GalT-1 and ST-6, respectively. Enzymatic products were labeled in situ with AA and were separated from the substrates on TSKgel Amide 80 column using normal-phase conditions. Enzyme units were determined from the peak areas by comparison with the concomitantly derivatized standards Gal-β1-4GlcNAc and NANA-α2-6 Gal-β1-4GlcNAc. Linearity (time and enzyme concentration), precision (intra- and interassay) and reproducibility for the assays were established. The assays were found to be useful in monitoring the enzyme activities during isolation and purification. The assays were highly sensitive and performed equal to or better than the traditional radioactive sugar-based measurements. The assay format can also be used for measuring the activity of other transferases, provided that the carbohydrate acceptors contain a reducing end for labeling. An assay for glycoprotein acceptors was developed using IgG. A short HPLC profiling method was developed for the separation of IgG glycans (biantennary G0, G1, G2, mono- and disialylated), which facilitated the determination of GalT-1 and ST-6 activities in a rapid manner. Furthermore, this profiling method should prove useful for monitoring the changes in IgG glycans in clinical settings. 相似文献
992.
Purushotham Reddy S Chinnababu B Shekhar V Kumar Reddy D Bhanuprakash GV Velatoor LR Venkateswara Rao J Venkateswarlu Y 《Bioorganic & medicinal chemistry letters》2012,22(12):4182-4184
A simple, highly efficient and stereoselective synthetic route has been developed for synthesis of alpinoid-C (1) and its analogues (2, 3 and 4) from commercially available starting materials by using Wittig olefination, Sharpless asymmetric epoxidation, Grubbs cross metathesis as key steps. All the compounds showed moderate anti-proliferative activity against human leukemia/carcinoma (U-937, THP-1, COLO-205 and HepG2) and mouse melanoma (B16-F10) cancer cell lines. Compounds 3 and 4 are found to be most potent with an IC(50) of 7.53 μM and 32.26 μM on THP-1, 11.12 μM and 7.21 μM on COLO-205 cell lines, respectively. 相似文献
993.
Durón SG Lindstrom A Bonnefous C Zhang H Chen X Symons KT Sablad M Rozenkrants N Zhang Y Wang L Yazdani N Shiau AK Noble SA Rix P Rao TS Hassig CA Smith ND 《Bioorganic & medicinal chemistry letters》2012,22(2):1237-1241
The overproduction of nitric oxide during the biological response to inflammation by the nitric oxide synthase (NOS) enzymes have been implicated in the pathology of many diseases. By removal of the amide core from uHTS-derived quinolone 4, a new series highly potent heteroaromatic-aminomethyl quinolone iNOS inhibitors 8 were identified. SAR studies led to identification of piperazine 22 and pyrimidine 32, both of which reduced plasma nitrates following oral dosing in a mouse lipopolysaccharide challenge assay. 相似文献
994.
Semi-synthesis and bio-evaluation of polybrominated diphenyl ethers from the sponge Dysidea herbacea
Srikanth Reddy T Suryakiran N Narasimhulu M Ramesh D Chinni Mahesh K Sai Krishna A Kavitha P Venkateswara Rao J Venkateswarlu Y 《Bioorganic & medicinal chemistry letters》2012,22(14):4900-4906
The sponge Dysidea herbacea was collected from the Mandapam Coast, Tamilnadu, India. Isolated gram quantities of hydroxylated polybrominated diphenyl ether (HO-PBDE) and semi-synthesized a series of new PBDEs derivatives and tested them for antibacterial and cytotoxic activities. 相似文献
995.
996.
Chrysanthemum L. (Asteraceae-Anthemideae) is a genus with rapid speciation. It comprises about 40 species, most of which are distributed in East Asia. Many of these are narrowly distributed and habitat-specific. Considerable variations in morphology and ploidy are found in this genus. Some species have been the subjects of many studies, but the relationships between Chrysanthemum and its allies and the phylogeny of this genus remain poorly understood. In the present study, 32 species/varieties from Chrysanthemum and 11 from the allied genera were analyzed using DNA sequences of the single-copy nuclear CDS gene and seven cpDNA loci (psbA-trnH, trnC-ycf6, ycf6-psbM, trnY-rpoB, rpS4-trnT, trnL-F, and rpL16). The cpDNA and nuclear CDS gene trees both suggest that 1) Chrysanthemum is not a monophyletic taxon, and the affinity between Chrysanthemum and Ajania is so close that these two genera should be incorporated taxonomically; 2) Phaeostigma is more closely related to the Chrysanthemum+Ajania than other generic allies. According to pollen morphology and to the present cpDNA and CDS data, Ajania purpurea is a member of Phaeostigma. Species differentiation in Chrysanthemum appears to be correlated with geographic and environmental conditions. The Chinese Chrysanthemum species can be divided into two groups, the C. zawadskii group and the C. indicum group. The former is distributed in northern China and the latter in southern China. Many polyploid species, such as C. argyrophyllum, may have originated from allopolyploidization involving divergent progenitors. Considering all the evidence from present and previous studies, we conclude that geographic and ecological factors as well as hybridization and polyploidy play important roles in the divergence and speciation of the genus Chrysanthemum. 相似文献
997.
Synthesis of norbornene derived phosphonate (1), poly-d-lysine (2), and phopholipid (3) monomers and their complete characterizations are studied. Ring-opening metathesis polymerizations (ROMP) of monomers (1-3) produce well-defined copolymers, CP(1) and CP(2). (1)H NMR along with FT-IR spectroscopy characterization confirms the copolymer formation, while gel permeation chromatography (GPC) analysis suggests the formation of polymers with fairly narrow molecular weight distributions. Upon following the well-known ligand exchange methods these copolymers produce CdSe-bound copolymers, CP(3) and CP(4). Dynamic light scattering and transmission electron microscopy measures the size of these CdSe bound copolymers, while (31)P NMR suggests the formation of CP(3) and CP(4). The results from the experiments of these copolymers on Neuro2A cells suggest that the novel PDL-anchored nanomaterial show their ability to polarize neuronal growth and differentiation. 相似文献
998.
Vapor-induced transformations of docetaxel anhydrous (form D(A)) under ambient conditions have been studied using methanol, ethanol, and water as the solvent media. The online vapor-induced transformations were monitored by powder X-ray diffractometry. New solid forms (solvates/hydrates/anhydrous) of docetaxel anhydrous were obtained in stoichiometric ratios which were characterized completely using powder X-ray diffraction, differential scanning calorimeter, thermogravimetric analysis, and spectroscopic ((13)C solid-state nuclear magnetic spectroscopy, solution (1)H NMR, and Fourier transform infrared) techniques. The new forms namely methanol solvate (D(M)), ethanol solvate (D(E)), monohydrate (D(MH)), trihydrate (D(TH)), and anhydrous (D(AN-I) and D(AN-II)) were identified through structural analysis. 相似文献
999.
Insight into the processing dynamics and other neurophysiological properties of different hippocampal subfields is critically important for understanding hippocampal function. In this study, we compared shifts in the center of mass (COM) of CA3 and CA1 place fields in a familiar and completely novel environment. Place fields in CA1 and CA3 were simultaneously recorded as rats ran along a closed loop track in a familiar room followed by a session in a completely novel room. This process was repeated each day over a 4-day period. CA3 place fields shifted backward (opposite to the direction of motion of the rat) only in novel environments. This backward shift gradually diminished across days, as the novel environment became more familiar with repeated exposures. Conversely, CA1 place fields shifted backward across all days in both familiar and novel environments. Prior studies demonstrated that CA1 place fields on average do not exhibit a backward shift during the first exposure to an environment in which the familiar cues are rearranged into a novel configuration, although CA3 place fields showed a strong backward shift. Under the completely novel conditions of the present study, no dissociation was observed between CA3 and CA1 during the first novel session (although a strong dissociation was observed in the familiar sessions and the later novel sessions). In summary, this is the first study to use simultaneous recordings in CA1 and CA3 to compare place field COM shift and other associated properties in truly novel and familiar environments. This study further demonstrates functional differentiation between CA1 and CA3 as the plasticity of CA1 place fields is affected differently by exposure to a completely novel environment in comparison to an altered, familiar environment, whereas the plasticity of CA3 place fields is affected similarly during both types of environmental novelty. 相似文献
1000.
Rao RK Riffel P Meyer M Kettnaker PJ Lemke A Haneder S Schoenberg SO Michaely HJ 《PloS one》2012,7(2):e32613