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   1094篇
  免费   77篇
  国内免费   1篇
  1172篇
  2023年   8篇
  2022年   18篇
  2021年   27篇
  2020年   20篇
  2019年   14篇
  2018年   18篇
  2017年   31篇
  2016年   36篇
  2015年   33篇
  2014年   59篇
  2013年   63篇
  2012年   66篇
  2011年   75篇
  2010年   42篇
  2009年   36篇
  2008年   60篇
  2007年   50篇
  2006年   40篇
  2005年   34篇
  2004年   53篇
  2003年   31篇
  2002年   25篇
  2001年   25篇
  2000年   30篇
  1999年   33篇
  1998年   15篇
  1996年   8篇
  1995年   10篇
  1994年   9篇
  1993年   10篇
  1992年   8篇
  1991年   15篇
  1990年   7篇
  1989年   7篇
  1988年   11篇
  1987年   12篇
  1986年   7篇
  1985年   5篇
  1984年   9篇
  1983年   10篇
  1982年   8篇
  1981年   6篇
  1979年   10篇
  1977年   6篇
  1976年   7篇
  1975年   11篇
  1974年   13篇
  1972年   4篇
  1970年   7篇
  1969年   3篇
排序方式: 共有1172条查询结果,搜索用时 15 毫秒
11.
Two new compounds G and H isolated from the roots of Costus speciosus have been characterized as 8-hydroxytriacontan-25-one and Me tritriacontanoat  相似文献   
12.
O. Babalola  R. Lal 《Plant and Soil》1977,46(2):337-346
Summary A series of factoral experiments involving the effects of gravel concentration in the subsoil horizon, the effect of inter-gravel bulk density, the depth of the surface soil above the gravel horizon and the interaction between soil moisture regime and gravel concentration, on growth and development of maize roots were conducted in the greenhouse. Increasing sub soil gravel concentration decreased the total porosity and the available waterholding capacity. Though the root growth of maize seedlings was adversely affected by gravel concentration above 20 per cent, lower concentration of gravels had a beneficial effect on roots. The root development and the leaf concentration of N, P and K improved with increasing depth of surface soil above the gravel horizon. The symptoms of mechanical impedance, such as thickening of root tips and profuse branching behind the tip were commonly observed on the root axis penetrating the gravelly horizon. re]19750916  相似文献   
13.
Rats withdrawn from continuous morphine infusion showed reliable occurrence of withdrawal body shakes. This sign of narcotic withdrawal was inhibited by the neuroleptic drug, (+) butaclamol. (?) Butaclamol was inactive. (+) Butaclamol activity was not antagonized by naloxone (5 mg/kg). The anti-withdrawal mechanism of (+) butaclamol is discussed in terms of effects on dopamine and narcotic receptors.The butyrophenone neuroleptic, haloperidol, has been used successfully to reduce signs of narcotic withdrawal in laboratory animals (1–4) and human addicts (5). Other neuroleptics of the butyrophenone type also show anti-withdrawal action (6, 7). The mechanism of action of these neuroleptics in blocking narcotic withdrawal is not understood. Butaclamol is a new neuroleptic drug that is available in two enantiomers and only (+) butaclamol possesses neuroleptic activity (8–10). Because of its demonstrated stereo-specificity in producing its pharmacological action, we employed this drug to establish specificity of action of neuroleptics in blocking narcotic withdrawal.  相似文献   
14.
15.
16.
17.
Plant Cell, Tissue and Organ Culture (PCTOC) - A method for in vitro screening and selection of drought (moisture stress) tolerant mango calli was developed. Poly ethylene glycol (PEG) (Molecular...  相似文献   
18.
19.
20.
In the present investigation, daily variations in plasma levels of melatonin, testosterone and estradiol-17β were analysed in the tropical freshwater catfish, Clarias batrachus during early and late-preparatory, pre-spawning, late-spawning and post-spawning phases of its annual reproductive cycle. Plasma melatonin levels exhibited a significant circadian rhythm during all the reproductive phases but peaks were invariably at night. The amplitude of melatonin was high during the early-preparatory phase and low in the pre-spawning phase. Testosterone also displayed significant rhythm during all the studied phases except post spawning phase. Estradiol-17β revealed diurnal rhythm only during preparatory and pre-spawning phases. The peak in the levels of plasma testosterone and estradiol-17β were recorded during the photophase. During the late-preparatory phase, the rhythm of testosterone coincided with the rhythm of estradiol-17β.  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