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   7172篇
  免费   643篇
  国内免费   3篇
  7818篇
  2023年   42篇
  2022年   83篇
  2021年   151篇
  2020年   94篇
  2019年   116篇
  2018年   144篇
  2017年   156篇
  2016年   243篇
  2015年   370篇
  2014年   420篇
  2013年   528篇
  2012年   534篇
  2011年   517篇
  2010年   325篇
  2009年   297篇
  2008年   432篇
  2007年   432篇
  2006年   388篇
  2005年   353篇
  2004年   366篇
  2003年   329篇
  2002年   318篇
  2001年   68篇
  2000年   53篇
  1999年   76篇
  1998年   83篇
  1997年   62篇
  1996年   69篇
  1995年   53篇
  1994年   37篇
  1993年   49篇
  1992年   45篇
  1991年   34篇
  1990年   31篇
  1989年   31篇
  1988年   25篇
  1987年   25篇
  1986年   20篇
  1985年   30篇
  1984年   34篇
  1983年   33篇
  1982年   32篇
  1981年   28篇
  1980年   17篇
  1979年   14篇
  1978年   27篇
  1977年   18篇
  1976年   18篇
  1974年   15篇
  1973年   14篇
排序方式: 共有7818条查询结果,搜索用时 0 毫秒
951.
Aza-analogues of Acyclovir were obtained from N-(2-pivaloyloxyethyl)-N-(pivaloyloxymethyl)-p-toluenesulfonamide via a one-pot base silylation/nucleoside coupling procedure. The antiviral activities of all aza-nucleosides in vitro against a variety of viruses were evaluated. None of these compounds displayed any specific antiviral effects.  相似文献   
952.
The use of real-time reporters has accelerated our understanding of gene expression in vivo. This study examined the feasibility of a luciferase-based reporter to image spatiotemporal changes in fetal gene expression in utero. We chose to monitor Period1 (Per1) because it is expressed broadly in the body and plays a role in circadian rhythmicity. Using rats carrying a Per1::luc transgene, we repetitively imaged fetuses in utero throughout gestation. We found that bioluminescence was specific to transgenic pups, increased dramatically on embryonic day 10 (10 days after successful mating), and continued to increase logarithmically until birth. Diurnal fluctuations in Per1 expression were apparent several days prior to birth. These results demonstrate the feasibility of in utero imaging of mammalian gene expression, tracking of fetal gene expression from the same litter, and early detection of mammalian clock gene expression. We conclude that luciferase-based reporters can provide a sensitive, noninvasive measure of in utero gene expression.  相似文献   
953.
Gao  Jian  Hu  Shengnan  Yang  Cheng  Liu  Zhengwen  Jeppesen  Erik 《Hydrobiologia》2022,849(16):3597-3606
Hydrobiologia - Shelter availability is one of the key features governing crayfish habitat quality. It can directly influence crayfish’s individual survival of by lowering the risk of...  相似文献   
954.
Environmental Biology of Fishes - Ex situ conservation comprises some of the oldest and best-known conservation methods and it has been applied for different fish stocks. This study describes...  相似文献   
955.
956.
957.
958.
959.

Background

The domestic dog is a rich resource for mapping the genetic components of phenotypic variation due to its unique population history involving strong artificial selection. Genome-wide association studies have revealed a number of chromosomal regions where genetic variation associates with morphological characters that typify dog breeds. A region on chromosome 10 is among those with the highest levels of genetic differentiation between dog breeds and is associated with body mass and ear morphology, a common motif of animal domestication. We characterised variation in this region to uncover haplotype structure and identify candidate functional variants.

Results

We first identified SNPs that strongly associate with body mass and ear type by comparing sequence variation in a 3 Mb region between 19 breeds with a variety of phenotypes. We next genotyped a subset of 123 candidate SNPs in 288 samples from 46 breeds to identify the variants most highly associated with phenotype and infer haplotype structure. A cluster of SNPs that associate strongly with the drop ear phenotype is located within a narrow interval downstream of the gene MSRB3, which is involved in human hearing. These SNPs are in strong genetic linkage with another set of variants that correlate with body mass within the gene HMGA2, which affects human height. In addition we find evidence that this region has been under selection during dog domestication, and identify a cluster of SNPs within MSRB3 that are highly differentiated between dogs and wolves.

Conclusions

We characterise genetically linked variants that potentially influence ear type and body mass in dog breeds, both key traits that have been modified by selective breeding that may also be important for domestication. The finding that variants on long haplotypes have effects on more than one trait suggests that genetic linkage can be an important determinant of the phenotypic response to selection in domestic animals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1702-2) contains supplementary material, which is available to authorized users.  相似文献   
960.
Selenium is a candidate treatment for liver tumour prevention in chronic liver disease. In this study, we have studied selenium uptake, distribution and accumulation in rats provided with water containing tumour-preventive doses of sodium selenite for 10 weeks. Male Fischer 344 rats were given drinking water containing 1 μg/mL or 5 μg/mL sodium selenite. Selenium levels were monitored in serum and liver tissue over the 10-week period, and the kinetics of induction of the redox-active cytosolic selenoenzyme thioredoxin reductase were followed. Selenite exposure via drinking water caused a dose-dependent increase in blood and liver selenium levels, with plateaus at 6 and 8 weeks, respectively. These plateaus were reached at the same level of selenium regardless of dose, and no further accumulation was observed. A selenium-dependent increase in the activity of TrxR1 in parallel with the increase in liver selenium levels was also seen, and the induction of TrxR1 mRNA was seen only during the first three days of treatment, when the levels of selenium in the liver were increasing. Sodium selenite at 1 and 5 μg/mL did not affect body weight or relative liver mass. We concluded that long-term treatment with selenite did not cause accumulation of selenium and that the activity of TrxR1 in the liver rose with the selenium levels. We therefore suggest that sodium selenite at doses up to 5 μg/mL could be used for long-term tumour prevention.  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