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   6536篇
  免费   584篇
  国内免费   5篇
  7125篇
  2023年   37篇
  2022年   56篇
  2021年   96篇
  2020年   74篇
  2019年   112篇
  2018年   110篇
  2017年   84篇
  2016年   159篇
  2015年   295篇
  2014年   302篇
  2013年   337篇
  2012年   458篇
  2011年   431篇
  2010年   291篇
  2009年   286篇
  2008年   388篇
  2007年   377篇
  2006年   358篇
  2005年   321篇
  2004年   326篇
  2003年   323篇
  2002年   244篇
  2001年   99篇
  2000年   64篇
  1999年   101篇
  1998年   102篇
  1997年   70篇
  1996年   65篇
  1995年   75篇
  1994年   59篇
  1993年   62篇
  1992年   56篇
  1991年   50篇
  1990年   59篇
  1989年   44篇
  1988年   41篇
  1987年   33篇
  1986年   40篇
  1985年   32篇
  1984年   47篇
  1983年   35篇
  1982年   43篇
  1981年   40篇
  1980年   30篇
  1979年   31篇
  1978年   30篇
  1977年   29篇
  1975年   23篇
  1974年   39篇
  1973年   25篇
排序方式: 共有7125条查询结果,搜索用时 0 毫秒
1.
2.
3.
During the process optimisation of glucoamylase production by Aspergillus awamori, cell morphology was controlled at such a state that spore aggregation was completely prevented. Samples from five fermentations on complex media using either glucose or starch as carbon source were characterised with a Bohlin CS rheometer. The experimental data were conveniently described in terms of the power law model.  相似文献   
4.
Saturation and competitive binding analyses demonstrated the presence of a high affinity (KD = 0.92 nM), specific antiestrogen binding site (AEBS) in rat liver microsomes and at least 75% of total liver AEBS was recovered in this fraction. When microsomes were further separated into smooth and rough fractions, AEBS was concentrated in the latter. Subsequent dissociation of ribosomes from the rough membranes revealed that AEBS was associated with the membrane and not the ribosomal fraction. Antiestrogen binding activity could not be extracted from membranes with 1 M KCl or 0.5 M acetic acid but could be solubilized with sodium cholate. These data indicate that AEBS is an integral membrane component of the rough microsomal fraction of rat liver.  相似文献   
5.
Estimation of chitin deposition in the pupal and adult cuticles of adult Drosophila melanogaster during the pupal period is described. The timing of the periods of chitin deposition is compared with that deduced by previous workers using electron microscopy. The hypothesis that lethalcryptocephal mutant homozygotes are unable to evert their cephalic complexes at pupation because of excess chitin deposition is examined. The data obtained show no evidence that the mutation has any effect on chitin deposition.  相似文献   
6.
7.
Bacteriophage which produce either clear or turbid center plaques have been isolated for native isolates of Caryophanon latum.  相似文献   
8.
9.
10.
The use of plantations to manage extensive tracks of deforested lands in the tropics is a conservation strategy that has recently received considerable attention. Plantation trees can promote seed dispersal by attracting dispersers and creating favorable site conditions, leading to increased germination and establishment of indigenous trees. Subsequently, plantation trees can be harvested for profit or left to senesce, leaving a native tree community. We evaluated the effect of vine, grass, and shrub cutting (weeding) over a 3‐year period on regeneration of indigenous trees subsequent to the removal of plantation softwoods in Kibale National Park, Uganda. Counter to what would be expected if weeding released trees from competition, we found no difference in the total number of stems or in the stems greater than 10 cm diameter at breast height between control and weeded plots; there were more stems greater than 1 cm diameter at breast height in the control plots. For species found in both control and weeded plots, the maximum size of individuals did not differ. At the end of the study, 61 species were found in the control plots and 43 species were found in the weeded plots, and in both types of plots the three most abundant species were the same. The number of species and stems classified as early or middle successional species did not differ between weeded and control plots. The fact that weeding did not promote regeneration of indigenous trees after the removal of plantation trees illustrates the importance of evaluating and field‐testing potential management options.  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