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   195125篇
  免费   8609篇
  国内免费   9647篇
  213381篇
  2024年   240篇
  2023年   1418篇
  2022年   3263篇
  2021年   5513篇
  2020年   3778篇
  2019年   4680篇
  2018年   15090篇
  2017年   12973篇
  2016年   11421篇
  2015年   7204篇
  2014年   8106篇
  2013年   8570篇
  2012年   13817篇
  2011年   20931篇
  2010年   16814篇
  2009年   12723篇
  2008年   15042篇
  2007年   16004篇
  2006年   4700篇
  2005年   3972篇
  2004年   3907篇
  2003年   3717篇
  2002年   3031篇
  2001年   2118篇
  2000年   1852篇
  1999年   1693篇
  1998年   1042篇
  1997年   1022篇
  1996年   950篇
  1995年   821篇
  1994年   793篇
  1993年   646篇
  1992年   837篇
  1991年   654篇
  1990年   473篇
  1989年   450篇
  1988年   371篇
  1987年   357篇
  1986年   266篇
  1985年   286篇
  1984年   163篇
  1983年   178篇
  1982年   100篇
  1981年   85篇
  1980年   61篇
  1979年   77篇
  1977年   59篇
  1975年   61篇
  1972年   295篇
  1971年   294篇
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
51.
52.
Systems biology is an approach to explain the behaviour of a system in relation to its individual components. Synthetic biology uses key hierarchical and modular concepts of systems biology to engineer novel biological systems. In my opinion the next step in biology is to use molecule-to-phenotype data using these approaches and integrate them in the form a periodic table. A periodic table in biology would provide chassis to classify, systematize and compare diversity of component properties vis-a-vis system behaviour. Using periodic table it could be possible to compute higher-level interactions from component properties. This paper examines the concept of building a bio-periodic table using protein fold as the fundamental unit.  相似文献   
53.
Ferruh Aşçi 《Biologia》2009,64(6):1146-1149
In this study, the structural characteristics, unique features, various organ measurements of males and females of the water mite Atractides (Atractides) turcicus sp. n. from Turkey are described. In addition, the study compares their characteristics with related species.  相似文献   
54.
55.
A general in vitro cloning system was established for four Helleborus species: H. argutifolius, H. foetidus, H. niger and H. orientalis. The plant material was introduced in vitro from axillary buds. A Murashige and Skoog (MS)—based medium (Murashige and Skoog 1962) was used supplemented with 2% (w/v) sucrose, 2-isopentenyladenine (2-iP) and 6-benzylaminopurine (BA). Multiplication rates depended on the genotype and varied from 1.3 for H. foetidus till 3.8 for H. niger. The first results showed that the rooting phase could be done ex vitro. Rooting was induced by a drench for one week in a solution of indole-3-butyric acid (IBA -3 mg l−1) and 1-naphthaleneacetic acid (NAA-1 mg l−1) at 5°C.  相似文献   
56.
57.
Acidic lipase finds its commercial values in medical applications and bioremediation of food wastes. In this work, approaches for rapid screening of lipase-producing bacteria were developed and the feasibility assessment of the screening methods was performed. From food waste samples, the proposed screening procedures allowed isolation of sixteen pure bacterial strains expressing higher lipase activity at acidic pH (pH 6.0) than at alkaline pH (pH 9.0). To enhance the accuracy of lipase activity determination under acidic conditions, a novel assay procedure was also developed by deactivating lipase activity by microwave treatment prior to back titration. This additional step could minimize interferences arising from residual lipase activity during conventional direct back-titration methods in measuring lipase activity at acidic pH. Using the four strategies proposed in this work, the best acidic-lipase-producing isolate was obtained by strategy C (SSC) and was identified as Aeromonas sp. C14, displaying an optimal lipase activity of 0.7 U/ml at an acidic pH of 6.0.  相似文献   
58.
A Melanesian variant of the genetic disease α-thalassemia has recently been shown to be due to a single-nucleotide polymorphism located between the adult α-globin genes and their enhancers. The finding that this mutation creates a novel promoter provides support for a mechanism of gene regulation by facilitated chromatin looping.  相似文献   
59.
Starfish waste has been shown to be an effective compost material not only in the promotion of plant growth but also in terms of having insecticidal activity. In the present study, plant growth regulation by chemicals from starfish was examined. The aqueous fraction from a hot water extract of the starfish Asterias amurensis Lütken showed plant-growth activity, while the aqueous fraction from a methanol extract inhibited growth of Brassica campestris. The lipophilic fraction from the methanol extract also exhibited a plant growth-promoting effect. The active components from each extract were identified. Asterubine from the hot water extract promoted plant growth. A ceramide from the lipophilic fraction showed root growth promoting effect, and three glucocerebrosides had promotive effects on the entire plant. Asterosaponins were identified as the main growth inhibitors in the aqueous fraction of the methanol extract. These active compounds from starfish waste could be analyzed as potential plant growth regulators in agricultural applications in the future.  相似文献   
60.
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