首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2864篇
  免费   187篇
  国内免费   113篇
  2024年   7篇
  2023年   37篇
  2022年   90篇
  2021年   120篇
  2020年   106篇
  2019年   102篇
  2018年   94篇
  2017年   90篇
  2016年   125篇
  2015年   161篇
  2014年   182篇
  2013年   194篇
  2012年   256篇
  2011年   237篇
  2010年   146篇
  2009年   121篇
  2008年   156篇
  2007年   139篇
  2006年   119篇
  2005年   112篇
  2004年   99篇
  2003年   81篇
  2002年   77篇
  2001年   33篇
  2000年   26篇
  1999年   28篇
  1998年   10篇
  1997年   11篇
  1996年   9篇
  1995年   6篇
  1994年   12篇
  1993年   10篇
  1992年   18篇
  1991年   11篇
  1990年   14篇
  1989年   10篇
  1988年   10篇
  1987年   4篇
  1986年   7篇
  1985年   8篇
  1984年   7篇
  1983年   4篇
  1982年   10篇
  1981年   5篇
  1980年   5篇
  1979年   8篇
  1978年   12篇
  1977年   10篇
  1976年   7篇
  1969年   3篇
排序方式: 共有3164条查询结果,搜索用时 107 毫秒
1.
2.
This study was designed to determine if the known decrease in slow axonal transport of proteins in the sciatic nerve of experimentally diabetic rats is related to altered phosphorylation of neurofilament proteins (NFPs). Rats were rendered diabetic with 50 mg/kg of streptozotocin, i.p. At 3 and 6 weeks later, NFPs were prepared from spinal cord. The in vivo phosphorylation state of NFPs was examined by using phosphate-dependent (RT97) and -independent (RMd09) antibodies against high-molecular-mass NFPs on Western blots. Neurofilament-associated kinase activity was also measured in vitro by incubation of NFPs with [32P]ATP. Phosphorylation of all three NFPs (high, medium, and low molecular mass) occurred, as confirmed by gel electrophoresis and autoradiography. At 30 min of incubation, protein-bound radioactivity in NFPs from diabetic animals was reduced to 86.7 +/- 3.4 and 54.3 +/- 19.6% of that in nondiabetic animals at 3 and 6 weeks of diabetes, respectively (p less than 0.001 and p less than 0.05, respectively). NFPs were also incubated with acid phosphatase and rephosphorylated. Results showed that the increased in vivo phosphorylation contributed to the decreased in vitro phosphorylation. Extraction of protein kinases and addition back to the NFPs revealed, in addition, a reduced activity in the diabetic animals of the protein kinases measured in vitro.  相似文献   
3.
4.
Molecular and Cellular Biochemistry - Excitation–contraction coupling in normal cardiac function is performed with well balanced and coordinated functioning but with complex dynamic...  相似文献   
5.
A series of new chiral thiosemicarbazones derived from homochiral amines in both enantiomeric forms were synthesized and evaluated for their in vitro antiproliferative activity against A549 (human alveolar adenocarcinoma), MCF‐7 (human breast adenocarcinoma), HeLa (human cervical adenocarcinoma), and HGC‐27 (human stomach carcinoma) cell lines. Some of compounds showed inhibitory activities on the growth of cancer cell lines. Especially, compound 17b exhibited the most potent activity (IC50 4.6 μM) against HGC‐27 as compared with the reference compound, sindaxel (IC50 10.3 μM), and could be used as a lead compound to search new chiral thiosemicarbazone derivatives as antiproliferative agents. Chirality 27:177–188, 2015. © 2014 Wiley Periodicals, Inc.  相似文献   
6.
The 40 kd lambda Integrase protein is shown to contain two autonomous DNA binding domains with different sequence specificities. Competition experiments in which the binding activity of Int is assayed through nuclease protection demonstrate the functional independence of the two DNA recognition specificities. Proteolytic cleavage of Int and footprinting analysis of the resulting two major peptides allow the physical separation and identification of two DNA binding domains: an amino-terminal peptide that interacts with "arm-type" sites and a carboxy-terminal peptide that binds to "core-type" sequences. In addition, the data suggest that the two domains can bind DNA simultaneously, consistent with a model in which Integrase would link two disparate DNA sequences.  相似文献   
7.
Summary Snake flask experiments were carried out as a preliminary study of fat formation byTrichoderma reesei (formallyviride) QM 9123 using a glucose based medium. The maximum quantity of fat production was 16% of the dry weight. The pH of the medium, as much as its composition, appeared to influence the quantity of fat that was produced. The fatty acids formed by the hydrolysis of the fats were found to be mainly unsaturated, with the 182 (linoleic) acid predominating.  相似文献   
8.
Anti-Trypanosoma cruzi epimastigote antibodies (anti-epi) from pooled and individual sera from patients with chronic Chagas' disease were purified on immunoaffinity columns of epimastigotes antigens (epi) coupled to activated Sepharose 4B. SDS-PAGE analysis of purified anti-epi preparations showed only the presence of human IgG H and L chains. These antibodies preparations showed similar Western blotting profiles as the sera pools from which they originated. The main polypeptides recognized by anti-epi had apparent molecular masses 31, 46, 51, 75 and 85 kDa. No difference in these patterns were detected between anti-epi from pooled sera of cardiac (anti-epiC) and indeterminate (anti-epiI) clinical forms. Anti-epi preparations (20 to 60 micrograms/ml) of pooled and individual sera stimulated proliferation of homologous and autologous PBMN or T-lymphocyte-enriched population. The stimulatory ability was dependent upon the PBMN-anti-epi combinations. There is no direct correlation between the level of PBMN response to epi and anti-epi stimuli. Comparison of the stimulatory activities of anti-epiC vs anti-epiI on PBMN of either cardiac or indeterminate group of patients indicate that anti-epiC is significantly more active than anti-epiI (p less than 0.025). These data demonstrate the presence of auto-anti-idiotypic-T cells in chagasic patients and lead to the possibility that idiotype/anti-idiotype interactions may play a role in determining the pathogenesis of chagasic cardiopathy.  相似文献   
9.
Summary This study investigates the effects of anticancer drugs and immunomodulating agents on the release of interleukin-6 (IL-6) from lipopolysaccharide-stimulated human peripheral blood mononuclear leucocytes in vitro. The addition of non-cytotoxic concentrations of Adriamycin (doxorubicin), vincristine and 4-OOH-cyclophosphamide (the in vitro active analogue of cyclophosphamide) resulted in suppression of IL-6 release. The drugs bleomycin, FK156 [d-lactoyl-l-alanyl--d-glutamyl-(l)-meso-diaminopimelyl-(l)-glycine], FK565 [heptanoyl--d-glutamyl-(l)-meso-diaminopimelyl-(d)-alanine] and the immunosuppressive agent cyclosporin A did not alter the release of IL-6 in the same experimental system.  相似文献   
10.
A new saponin, leucasin, has been isolated from Leucas nutans and characterized on the basis of chemical investigation and spectroscopic studies as 3-O-[β- -glucopyranosyl(1→2)β- -glucopyranosyl]2,3β-dihydroxylup-20(29)-ene. Lupeol palmitate, sitosterol and stigmasterol were also isolated.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号