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   11538篇
  免费   874篇
  国内免费   4篇
  12416篇
  2022年   62篇
  2021年   92篇
  2020年   61篇
  2019年   94篇
  2018年   105篇
  2017年   128篇
  2016年   171篇
  2015年   231篇
  2014年   309篇
  2013年   644篇
  2012年   537篇
  2011年   530篇
  2010年   367篇
  2009年   343篇
  2008年   525篇
  2007年   542篇
  2006年   495篇
  2005年   502篇
  2004年   518篇
  2003年   535篇
  2002年   489篇
  2001年   456篇
  2000年   468篇
  1999年   374篇
  1998年   141篇
  1997年   145篇
  1996年   116篇
  1995年   122篇
  1994年   120篇
  1993年   105篇
  1992年   268篇
  1991年   243篇
  1990年   234篇
  1989年   233篇
  1988年   228篇
  1987年   188篇
  1986年   198篇
  1985年   167篇
  1984年   119篇
  1983年   134篇
  1982年   111篇
  1981年   75篇
  1980年   77篇
  1979年   123篇
  1978年   73篇
  1977年   74篇
  1975年   56篇
  1973年   58篇
  1972年   53篇
  1970年   50篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
13.
14.
A new phosphorylating agent, S-(N-monomethoxytritylaminoethyl)-O-(O-chlorophenyl) phosphorothioate, was prepared and reacted with a 5'-hydroxyl group of an oligonucleotide using 1-mesitylene-sulfonyl-3-nitrotriazole (MSNT) as a condensing agent. After base labile protecting groups were removed, the partially deprotected oligonucleotide was separated on a reversed phase column and converted to the oligonucleotide with an aminoethyl or a phosphoryl group at the 5'-end by treatment with 80% acetic acid or iodine-water, respectively. The syntheses of ppT, pppT, A5'pp5'T and A5'ppp5'T were also performed by treatment of 5'-O-(N-monomethoxytritylaminoethylthiophosphoryl) thymidine with tri-n-octylammonium salt of phosphoric acid, pyrophosphoric acid, pA and ppA, respectively.  相似文献   
15.
16.
Attention is increasingly being given to genetic resources in the deep seabed beyond the limits of national jurisdiction owing to their considerable potential scientific and economic value. At the same time, there are concerns that the increased demand for these genetic resources may result in their unsustainable collection or even in the extinction of species in the deep seabed. At present there is no specific legal framework governing these resources in international law. Thus, this article explores the relevant rules of international law applicable to the conservation and sustainable use of genetic resources in the deep seabed.  相似文献   
17.
The upper limb nerves of 8 human embryos (Carnegie stages 13-21) were studied by reconstruction. In stage 13, upper limb nerves (C5-T1) extended from the spinal cord. In stage 14, these nerves united to form the nascent brachial plexus. In stages 16 and 17, the median nerve, the radial nerve and the ulnar nerve entered into the hand plate. In stages 20 and 21, the upper limb nerves were observed in an orientation and arrangement similar to those in the adult.  相似文献   
18.
19.
20.
For the purpose of determining the most reasonable lying posture for pregnant women, we investigated the lying positions of both 247 non-pregnant women and 302 pregnant women during sleep. As for the rate of each position during the entire period of observation, 33.2% of the non-pregnant women were in the supine position, 41.2% in the lateral position, 18.4% in Sims' position and 7.1% in the prone position. In the pregnant group, the rate of supine position, simple lateral position and Sims' position was 34.2%, 52.2% and 12.7%, respectively, but the rate of the prone position was limited to 0.8%. All of the gravidas assuming the prone position were at less than 16 weeks of gestation. Non-pregnant women could sleep in a variety of positions, but pregnant women could assume the prone position during sleep only in the stage when the abdomen is not yet prominent or distended. Pregnant women were restricted significantly, either consciously or unconsciously, with progress in gestation.  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