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   20605篇
  免费   1791篇
  国内免费   1605篇
  24001篇
  2024年   55篇
  2023年   275篇
  2022年   591篇
  2021年   956篇
  2020年   750篇
  2019年   884篇
  2018年   900篇
  2017年   638篇
  2016年   909篇
  2015年   1325篇
  2014年   1592篇
  2013年   1573篇
  2012年   1889篇
  2011年   1709篇
  2010年   1136篇
  2009年   972篇
  2008年   1042篇
  2007年   941篇
  2006年   892篇
  2005年   747篇
  2004年   662篇
  2003年   667篇
  2002年   558篇
  2001年   342篇
  2000年   276篇
  1999年   273篇
  1998年   197篇
  1997年   154篇
  1996年   155篇
  1995年   144篇
  1994年   122篇
  1993年   80篇
  1992年   98篇
  1991年   89篇
  1990年   82篇
  1989年   64篇
  1988年   37篇
  1987年   33篇
  1986年   48篇
  1985年   41篇
  1984年   14篇
  1983年   16篇
  1982年   14篇
  1981年   15篇
  1980年   6篇
  1979年   8篇
  1976年   4篇
  1972年   6篇
  1971年   4篇
  1969年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Kumar  P. S.  Ling  C. Y.  Zhou  Z. B.  Dong  Y. L.  Sun  C. L.  Song  Y. X.  Wong  N. K.  Ju  J. H. 《Microbiology》2020,89(4):483-492
Microbiology - Marine actinobacteria particularly from marine environments are believed to be inexhaustible sources of biologically active molecules for biomedical and industrial applications. We...  相似文献   
52.
Abstract

Two new nickel (II) triphenylphosphine complexes derived from tridentate aroylhydrazone ligands [H2L1 = 2-hydroxy-3-methoxybenzylidene)benzohydrazone and H2L2 = N′-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzoylhydrazone] and triphenylphosphine were prepared and their molecular structures were determined by single crystal X-ray diffraction analysis. Both nickel(II) complexes showed slightly distorted square planar geometry with one tridentate aroylhydrazone ligand coordinated through ONO donor atoms and one triphenylphosphine ligand coordinated to the nickel center through the phosphorus atom. DNA interaction studies indicated that both complexes possessed higher affinity to herring sperm DNA (HS-DNA) than the corresponding free aroylhydrazone ligand. Molecular docking investigations showed that both complexes could bind to DNA through intercalation of the phenyl rings between adjacent base pairs in the double helix. Meanwhile, bovine serum albumin (BSA) binding studies revealed the complexes could effectively interact with BSA and change the secondary structure of BSA. Further pharmacological evaluations of the synthesized complexes by in vitro antioxidant assays demonstrated high antioxidant activity against NO· and O2˙? radicals. The anticancer activity of each complex was assessed through in vitro cytotoxicity assays (CCK-8 kit) toward A549 and MCF-7 cancer cell and normal L-02 cell lines. Significantly, the Ni(II) complex derived from H2L1 ligand was found to be more effective cytotoxic toward MCF-7cancerous cell with the IC50 value equaled 9.7?μM, which showed potent cytotoxic activity over standard drug cisplatin.

Abbreviations A549 human lung carcinoma cell

BSA bovine serum albumin

CCK-8 Cell Counting Kit-8

DFT density functional theory

DNA deoxyribonucleic acid

DPPH˙ 2,2-diphenyl-1-picrylhydrazyl

H2L1 2-hydroxy-3-methoxybenzylidene)benzohydrazone N′-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzoylhydrazone

H2L2 N′-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzoylhydrazone

HOMO highest occupied molecular orbital

IC50 the 50% activity

L-02 human normal liver cell

LOMO lowest unoccupied molecular orbital (LUMO)

MCF-7 human breast carcinoma cell

NO˙ nitric oxide

O2˙? superoxide anion

SOD superoxide dismutase

Communicated by Ramaswamy H. Sarma  相似文献   
53.
Yao  Hanhan  Liu  Chenshan  Lin  Dehai  Liu  Sheng  Lin  Zhihua  Dong  Yinghui 《Molecular biology reports》2020,47(2):1257-1264
Molecular Biology Reports - Leucine aminopeptidase 3 (LAP3) is an important proteolytic enzyme that catalyzes the hydrolysis of leucine residues from the amino termini of protein or peptide...  相似文献   
54.
Zhang  Huan  Sun  Gaigai  Lin  Zhihua  Yao  Hanhan  Dong  Yinghui 《Molecular biology reports》2020,47(12):9579-9593
Molecular Biology Reports - High ammonia can inhibit the survival and growth, and even cause mortality of razor clam (S. constricta). The accumulation of ammonia to lethal concentrations in some...  相似文献   
55.
56.
Uridine, a pyrimidine nucleoside, has been proposed to be a potential signaling molecule in the central nervous system. The understanding of uridine release in the brain is therefore of fundamental importance. The present study was performed to determine the characteristics of basal and morphine-induced uridine release in the striatum of freely moving mice by using the microdialysis technique. To ascertain whether extracellular uridine was derived from neuronal release, the following criteria were applied: sensitivity to (a) K+ depolarization, (b) Na+ channel blockade and (c) removal of extracellular Ca2+. Uridine levels were not greatly affected by infusion of tetrodotoxin (TTX) and were unaffected by either Ca2+-free medium or in the presence of EGTA (a calcium chelator), suggesting that basal extracellular uridine levels were maintained mainly by non-vesicular release mechanisms. In addition, both systemic and local application of morphine increased striatal uridine release. The morphine-induced release was reversed by naloxone pretreatment, but was unaffected by TTX or EGTA infusion. Moreover, co-administration of morphine and nitrobenzylthioinosine (NBTI, an inhibitor of nucleotide transporter) produced increases of uridine levels similar to that produced by NBTI or morphine alone, suggesting a nucleotide transporter mechanism involved. Taken together, these findings suggest that morphine produces a μ-opioid receptor-mediated uridine release via nucleoside transporters in a TTX- and calcium-independent manner.  相似文献   
57.
58.
A variety of epidemiologic studies have focused on the association between macrophage migration inhibitory factor (MIF) gene − 173G/C polymorphism and inflammatory bowel disease (IBD). However, results in different studies have been inconsistent. In order to derive a more precise estimation of the associations, we performed this meta-analysis and systematic searches of electronic databases PubMed and Web of Science (up to April 30, 2013). Based on our search criteria, a total of seven eligible studies concerning the MIF − 173G/C polymorphism and IBD risk were included in the final meta-analysis, comprising 2162 IBD cases and 2134 controls. Significant association was found between MIF − 173G/C polymorphism and the risk of IBD when all studies were pooled into the meta-analysis (for C allele vs. G allele: OR = 1.25, 95% CI = 1.12–1.41, p = 0.000; for C/C vs. G/G: OR = 1.71, 95% CI = 1.23–2.39, p = 0.002; for C/C + G/C vs. G/G: OR = 1.24, 95% CI = 1.09–1.42, p = 0.002; for C/C vs. G/C + G/G: OR = 1.67, 95% CI = 1.20–2.33, p = 0.002). Heterogeneity and publication bias did not exist in the overall comparisons. The present meta-analysis suggests an association between the MIF − 173G/C polymorphism and IBD risk. However, due to few studies and the selection bias existed in some studies, the results should be interpreted with caution.  相似文献   
59.
60.
We report a case of subcutaneous phaeohyphomycosis due to Phialophora verrucosa in a 64-year-old Chinese farmer suffering from CD4+ lymphopenia. He presented with diffuse and infiltrated plaques involving the entire face including the eyes, neck, occiput, and extending to the dorsal regions of his torso. The patient is notable for the discrete multifocal nature of the illness in the absence of disseminated infection and rarity of P. verrucosa as a cause of subcutaneous phaeohyphomycosis.  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