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   4064篇
  免费   284篇
  4348篇
  2023年   27篇
  2022年   71篇
  2021年   102篇
  2020年   53篇
  2019年   73篇
  2018年   76篇
  2017年   83篇
  2016年   135篇
  2015年   191篇
  2014年   204篇
  2013年   272篇
  2012年   294篇
  2011年   293篇
  2010年   152篇
  2009年   142篇
  2008年   265篇
  2007年   227篇
  2006年   187篇
  2005年   180篇
  2004年   193篇
  2003年   137篇
  2002年   168篇
  2001年   66篇
  2000年   55篇
  1999年   50篇
  1998年   28篇
  1997年   30篇
  1996年   20篇
  1995年   17篇
  1994年   16篇
  1993年   24篇
  1992年   53篇
  1991年   44篇
  1990年   35篇
  1989年   35篇
  1988年   31篇
  1987年   24篇
  1986年   15篇
  1985年   28篇
  1984年   33篇
  1983年   18篇
  1982年   13篇
  1981年   19篇
  1980年   18篇
  1979年   14篇
  1978年   16篇
  1976年   18篇
  1975年   14篇
  1974年   11篇
  1971年   11篇
排序方式: 共有4348条查询结果,搜索用时 15 毫秒
171.
172.
Ayurveda is a holistic medical system of traditional medicine, and Triphala is one of the most popular formulations in Ayurveda. Triphala is composed of three kinds of herb, Terminalia chebula, Terminalia bellirica, and Emblica officinalis. Since Triphala is shown to exhibit a protective activity against ionizing radiation in mice, we investigated its activity in HeLa cells. We found that Triphala showed the protective effects against X-radiation and bleomycin, both of which generate DNA strand breaks, in HeLa cells. Further, Triphala efficiently eliminated reactive oxygen species (ROS) in HeLa cells. Thus, the antioxidant activity of Triphala would likely play a role in its protective actions against X-radiation and bleomycin because both agents damage DNA through the generation of ROS. These observations suggested that the radioprotective activity of Triphala can be, at least partly, studied with the cells cultured in vitro. The simple bioassay system with human cultured cells would facilitate the understanding of the molecular basis for the beneficial effects of Triphala.  相似文献   
173.
Trolox, a water‐soluble vitamin E analogue has been used as a positive control in Trolox equivalent antioxidant capacity and oxygen radical antioxidant capacity assays due to its high antioxidative effect. In this study, the ex vivo antioxidative effects of Trolox and its concentration in blood and brain microdialysates from rat after administration were evaluated by newly established semi‐microflow injection analysis, chemiluminescence detection and HPLC‐UV. In the administration test, the antioxidative effect of Trolox in blood and brain microdialysates after a single administration of 200 mg/kg of Trolox to rats could be monitored. The antioxidative effects in blood (12.0 ± 2.1) and brain (8.4 ± 2.1, × 103 antioxidative effect % × min) also increased. Additionally, the areas under the curve (AUC)s0–360 (n = 3) for blood and brain calculated with quantitative data were 10.5 ± 1.2 and 9.7 ± 2.5 mg/mL × min, respectively. This result indicates that Trolox transferability through the blood–brain barrier is high. The increase in the antioxidative effects caused by Trolox in the blood and brain could be confirmed because good correlations between concentration and antioxidative effects (r ≥ 0.702) were obtained. The fact that Trolox can produce an antioxidative effect in rat brain was clarified. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
174.
Primary open angle glaucoma (POAG) is a complex disease and is one of the major leading causes of blindness worldwide. Genome-wide association studies have successfully identified several common variants associated with glaucoma; however, most of these variants only explain a small proportion of the genetic risk. Apart from the standard approach to identify main effects of variants across the genome, it is believed that gene-gene interactions can help elucidate part of the missing heritability by allowing for the test of interactions between genetic variants to mimic the complex nature of biology. To explain the etiology of glaucoma, we first performed a genome-wide association study (GWAS) on glaucoma case-control samples obtained from electronic medical records (EMR) to establish the utility of EMR data in detecting non-spurious and relevant associations; this analysis was aimed at confirming already known associations with glaucoma and validating the EMR derived glaucoma phenotype. Our findings from GWAS suggest consistent evidence of several known associations in POAG. We then performed an interaction analysis for variants found to be marginally associated with glaucoma (SNPs with main effect p-value <0.01) and observed interesting findings in the electronic MEdical Records and GEnomics Network (eMERGE) network dataset. Genes from the top epistatic interactions from eMERGE data (Likelihood Ratio Test i.e. LRT p-value <1e-05) were then tested for replication in the NEIGHBOR consortium dataset. To replicate our findings, we performed a gene-based SNP-SNP interaction analysis in NEIGHBOR and observed significant gene-gene interactions (p-value <0.001) among the top 17 gene-gene models identified in the discovery phase. Variants from gene-gene interaction analysis that we found to be associated with POAG explain 3.5% of additional genetic variance in eMERGE dataset above what is explained by the SNPs in genes that are replicated from previous GWAS studies (which was only 2.1% variance explained in eMERGE dataset); in the NEIGHBOR dataset, adding replicated SNPs from gene-gene interaction analysis explain 3.4% of total variance whereas GWAS SNPs alone explain only 2.8% of variance. Exploring gene-gene interactions may provide additional insights into many complex traits when explored in properly designed and powered association studies.  相似文献   
175.
An inducible expression vector, pSH19, which harbors regulatory expression system PnitA-NitR, for streptomycetes was constructed previously. Here, we have modified pSH19 to obtain shuttle vectors for Streptomyces-E. coli by introducing the replication origin of a plasmid for E. coli (ColE1) and an antibiotic-resistant gene. Six inducible shuttle vectors, pESH19cF, pESH19cR, pESH19kF, pESH19kR, pESH19aF, and pESH19aR, for Streptomyces-E. coli, were successfully developed. The stability of these vectors was examined in five different E. coli strains and Streptomyces lividans TK24. The stability test showed that the pSH19-derived shuttle vectors were stable in E. coli Stbl2 and S. lividans TK24. Heterologous expression experiments involving each of the catechol 2,3-dioxygenase, nitrilase, and N-substituted formamide deformylase genes as a reporter gene showed that pESH19cF, pESH19kF, and pESH19aF possess inducible expression ability in S. lividans TK24. Thus, these vectors were found to be useful expression tools for experiments on both Gram-negative and Gram-positive bacterial genes.  相似文献   
176.
Extracellular glutamate concentration is a critical determinant of neuronal cell fate. We recently demonstrated that HT22 murine hippocampal cell viability was reduced by exposure to high concentrations of glutamate, whereas low concentrations promoted cell survival. Extracellular signal-regulated kinase (Erk)1/2 activation by glutamate is important for both glutamate-induced cell death and survival. In this study, we investigated the role of glutamate-induced or hydrogen peroxide (H2O2)-induced Erk1/2 activation in HT22 cell fate determination. Glutamate and H2O2 treatment similarly induced early (<1 h) Erk1/2 phosphorylation regardless of concentration. On the other hand, persistent Erk1/2 phosphorylation (16–24 h) was observed only in the presence of excess glutamate. Only the latter contributed to glutamate-induced cell death, which involved metabolic glutamate receptor 5. Our findings suggest that glutamate concentration modulates two distinct phases of Erk1/2 activation, which can explain the glutamate concentration-dependent determination of HT22 cell fate.  相似文献   
177.
The first synthesis of the (9R,13R)-stereoisomer of LDS1, a flower-inducing oxylipin isolated from Lemna paucicostata, has been achieved from a known allylic alcohol by a seven-step sequence that involves the Horner–Wadsworth–Emmons olefination to construct its full carbon framework and an enzymatic hydrolysis of a penultimate methyl ester intermediate to provide the target molecule.  相似文献   
178.
179.
Extremophiles - The stability of dimeric cytochrome c′ from a thermophile, as compared with that of a homologous mesophilic counterpart, is attributed to strengthened interactions around the...  相似文献   
180.
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