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   288016篇
  免费   19341篇
  国内免费   52篇
  2021年   2593篇
  2020年   2120篇
  2019年   2401篇
  2018年   4980篇
  2017年   4777篇
  2016年   5975篇
  2015年   6277篇
  2014年   7494篇
  2013年   10508篇
  2012年   12443篇
  2011年   12435篇
  2010年   8511篇
  2009年   7000篇
  2008年   10672篇
  2007年   10753篇
  2006年   10273篇
  2005年   9374篇
  2004年   9527篇
  2003年   8933篇
  2002年   8702篇
  2001年   10775篇
  2000年   10407篇
  1999年   8133篇
  1998年   2635篇
  1997年   2337篇
  1996年   2211篇
  1995年   2031篇
  1992年   6123篇
  1991年   6233篇
  1990年   6180篇
  1989年   6112篇
  1988年   5690篇
  1987年   5318篇
  1986年   4885篇
  1985年   5120篇
  1984年   4130篇
  1983年   3323篇
  1982年   2289篇
  1979年   3583篇
  1978年   2800篇
  1977年   2565篇
  1976年   2484篇
  1975年   3048篇
  1974年   3385篇
  1973年   3351篇
  1972年   2946篇
  1971年   2817篇
  1970年   2400篇
  1969年   2345篇
  1968年   2205篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
991.
992.
Mild micrococcal nuclease treatment of rat and mouse nuclei and fractionation were based on the method of Tata and Baker. Three chromatin fractions, S, P1, P2, were separated, and for each of these fractions the sensitivity to the DNase 1 action was determined. The relative content in these fractions of non-transcribed DNA sequences was established by hydridization with a mouse satellite DNA, and the relative content of transcribed DNA sequences--by hydridization with DNA synthesised on the total poly (A) mRNA. None of the fractions displayed the properties characteristic of active chromatin.  相似文献   
993.
994.
The phylogenetic relationships among the wall lizards of the Podarcis hispanicus complex that inhabit the south-east (SE) of the Iberian Peninsula and other lineages of the complex remain unclear. In this study, four mitochondrial and two nuclear markers were used to study genetic relationships within this complex. The phylogenetic analyses based on mtDNA gene trees constructed with ML and BI, and a species tree using *BEAST support three divergent clades in this region: the Valencia, Galera and Albacete/Murcia lineages. These three lineages were also corroborated in species delimitation analyses based on mtDNA using bPTP, mPTP, GMYC, ABGD and BAPS. Bayesian inference species delimitation method (BPP) based on both nuclear data and a combined data set (mtDNA + nuclear) showed high posterior probabilities for these three SE lineages (≥0.94) and another Bayesian analysis (STACEY) based on combined data set recovered the same three groups in this region. Divergence time dating of the species tree provided an estimated divergence of the Galera lineage from the other SE group (Podarcis vaucheri, (Albacete/Murcia, Valencia)) at 12.48 Ma. During this period, the Betic–Rifian arc was isolated, which could have caused the isolation of the Galera form distributed to the south of the Betic Corridor. Although lizards from the Albacete/Murcia and Galera lineage are morphologically similar, they clearly represent distinct genetic lineages. The noteworthy separation of the Galera lineage enables us to conclude that this lineage must be considered as a new full species.  相似文献   
995.
Galactose-1-phosphate uridylyltransferase (uridine diphosphoglucose: α-d-galactose-1-phosphate uridylyltransferase, EC 2.7.7.12) has been purified 4000-fold from human placenta in four chromatographic steps using DEAE-cellulose, hydrocylapatite, ethyliminohexylagarose, and Sephacryl S-200. The specific activity of the homogeneous enzyme was 56 units/mg protein. The placental enzyme consists of two similar subunits, each of molecular weight about 48,000. The placental enzyme was similar to published results for the red cell enzyme (V. P. Williams, Arch. Biochem. Biophys., 1978, 191, 182–191) with respect to subunit molecular weight, electrophoretic migration, and immunological properties. The more purified fractions of the placental enzyme invariably contained a glycoprotein which was removed in the gel filtration step. After this glycoprotein was removed, the enzyme was very labile and only about 20% of the catalytic activity was recovered.  相似文献   
996.
997.
Natural heparin complexes proved to activate the anticoagulation system. The obtained experimental data convincingly confirm that glutamic acid alone, and particularly in a complex with heparin, has a considerable preventive potential and efficiently protects experimental animals with induced diabetes mellitus.  相似文献   
998.
999.
1000.
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