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   1283篇
  免费   198篇
  国内免费   894篇
  2023年   33篇
  2022年   69篇
  2021年   59篇
  2020年   75篇
  2019年   91篇
  2018年   27篇
  2017年   43篇
  2016年   44篇
  2015年   70篇
  2014年   89篇
  2013年   96篇
  2012年   136篇
  2011年   137篇
  2010年   113篇
  2009年   111篇
  2008年   152篇
  2007年   111篇
  2006年   113篇
  2005年   83篇
  2004年   94篇
  2003年   75篇
  2002年   75篇
  2001年   44篇
  2000年   40篇
  1999年   29篇
  1998年   12篇
  1997年   18篇
  1996年   12篇
  1993年   9篇
  1990年   7篇
  1989年   8篇
  1988年   9篇
  1987年   7篇
  1985年   13篇
  1982年   6篇
  1979年   7篇
  1978年   7篇
  1977年   6篇
  1974年   6篇
  1971年   6篇
  1965年   10篇
  1963年   12篇
  1959年   8篇
  1958年   16篇
  1957年   18篇
  1956年   17篇
  1955年   20篇
  1954年   17篇
  1953年   15篇
  1949年   7篇
排序方式: 共有2375条查询结果,搜索用时 15 毫秒
1.
2.
Studies on larval population densities and adult emergence rates of the Brugian filariasis vectors Mansonia bonneae Edwards and Ma. dives Schiner were conducted in freshwater swamp forest bordering the Sadong River, Serian District, Sarawak, East Malaysia, during 1984-85. Three species of aquatic host-plants in the Family Araceae were identified as supporting immature stages of the Ma. bonneae/dives complex. Proportions of positive plants were 4.7%, 6.5% and 3.4% with 6.4 +/- 2.6, 7.3 +/- 2.8 and 10.1 +/- 1.1 larvae per positive plant, respectively, for the plant species Homalomena cordata Schott, H. rostrata Griffiths and Hydrostemma motleyi (Hook. f.) Mabberley. These data indicate no significant preferences between the three types of host-plant. Detailed monitoring of the host-plant H. cordata revealed no significant monthly fluctuations in larval density per plant nor the proportion of positive plants. 11.6% of larvae were Ma. dives and 88.4% were Ma. bonneae. Mean daily yields of Ma. bonneae/dives adults per square metre of H. cordata vegetated water surface were 0.45 males plus 0.57 females during the wet season (December-February) compared with 0.2 males plus 0.31 females during the dry season (June-August). Thus output of adults per plant was approximately halved, and suitable breeding areas were further reduced, during the dry season. By extrapolation from these rates, a crude mean estimate for productivity of Ma. bonneae/dives females is 1.6 million per hectare per annum in swamp forest habitats vegetated with any of the host-plants studied.  相似文献   
3.
4.
Abstract 1. Crypsis is one of the main defences that insects use to avoid predators, and both the juveniles and adults of many geometrid moths are remarkable in their ability to blend into different host backgrounds. The larvae of Synchlora frondaria have two methods to achieve crypsis: phenotypic plasticity in colouration that enable them to hide more effectively on their host plants, and a self‐decorating behaviour whereby the larvae camouflage themselves with materials from their host plants. 2. Larvae of Synchlora frondaria reared on three different host plants showed systematic differences in relative growth rate, survivorship and larval colouration. 3. Larval colouration varied across diet treatments in a way that was consistent with diet‐induced phenotypic plasticity, and larvae also exhibited characteristic decorating behaviour on all three hosts. 4. Larvae showed highest survivorship on Heterotheca subaxillaris (Asteraceae), and had significantly higher relative growth rates on H. subaxillaris (Asteraceae) and Lantana camara (Verbenaceae) than on Bejaria racemosa (Ericaceae). 5. Synchlora frondaria provides an example of a species where both decorating behaviour and phenotypic plasticity in larval colouration produce a cryptic form that is remarkably responsive to its background.  相似文献   
5.
6.
Abstract— Glutamine transaminase from rat brain was shown to occur in the mitochondrial fraction, whereas the ω-amidase was shown to occur in the soluble fraction. Both enzymes were also found to be widely distributed throughout human brain tissue. Specific activities for the glutamine transaminase and ω-amidase in the parietal cortex of one individual at 5 h post mortem were 8 and 53 μmol per hour per gram of tissue, respectively. Rat brain glutamine transaminase was shown to be identical to that of the liver mitochondrial enzyme. Improved assays for glutamine transaminase and ω-amidase activities in crude tissue homogenates are described. The possible physiological importance of glutamine transaminase and its potential role in the encephalopathy of hepatic disease are discussed.  相似文献   
7.
目的对virB2基因编码蛋白进行分析,为virB2基因及其编码蛋白功能提供实验依据。方法利用多种生物学软件以及网站对VirB2蛋白的结构和功能进行分析预测,VirB2蛋白序列通过基因推导获得并由生物公司合成,然后通过免疫动物实验制备鼠抗VirB2蛋白多克隆抗体,同时设计进行VirB2蛋白细胞毒试验(MTT法)。结果virB2基因编码蛋白属于疏水性蛋白,为鞭毛样结构,有较强的细胞毒作用。结论对VirB2蛋白的结构和功能进行了分析预测,证明VirB2蛋白在H.pylori相关的致病性特别是引起胃黏膜炎症方面起到一定的作用,能够为研究H.pylori致病机制提供帮助。  相似文献   
8.
目的探讨通过随访观察金双歧辅助治疗小儿扁桃体炎患儿的远期效果。方法选取2013年1月至2014年7月在本院儿科住院诊断为扁桃体炎患儿300例,采用随机数字表法,按入院先后顺序分为对照组和观察组,对照组常规给予抗生素(包括抗病毒药)和(或)对症治疗;观察组在对照组治疗的基础上,给予金双歧口服辅助治疗,出院后继续服用金双歧4周;两组患儿分别在出院后1个月、2个月、3个月均进行电话随访,3个月后均通过家庭访视进行观察,比较两组患儿出院后发生呼吸道感染和肠道感染的差异。结果观察组患儿在出院后3个月内呼吸道感染和肠道感染的发生率低于对照组,差异具有统计学意义(P0.05)。结论出院扁桃体炎患儿继续服用金双歧,可提高患儿机体免疫力,降低呼吸道和肠道感染的发生率;随访为观察患儿出院后健康状态,进行健康指导以及收集资料的重要手段。  相似文献   
9.
2M NaCl-insoluble fraction of rat ventral prostatechromatin(residual proteins)contain proteins able tointeract specifically with androgen-receptor complex andis,therefore,a part of the acceptor complex.Amongresidual proteins,a 97 KDa protein has been found whichbinds signifieantly to a genomic fragment containingan androgen-regulated gene coding for a 22 KDa protein.The biological significance of this binding in androgenaction need to be further studied. A mini-plasmid clone containing 22 KDa proteincoding sequence was cloned into Charon 4A genomiclibrary from which a 5.7 Kb genomic fragment wasisolated,identified by hybridization with a 5' and a 3'cDNA probes,and shown to contain the 5' flankingsequence.Restriction enzyme treatment of this fragmentyielded a 4.7 Kb restriction fragment representingthe 5' upstream region and a 1.0 Kb containing part ofthe coding sequence.Deletion studies indicated that the97 KDa protein bound only to a subclone of about 300 bpsegment.Furthermore,gel shifting experiment supportedits DNA-prptein binding.  相似文献   
10.
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