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   2313篇
  免费   225篇
  国内免费   1篇
  2021年   31篇
  2020年   24篇
  2019年   29篇
  2018年   32篇
  2017年   16篇
  2016年   43篇
  2015年   87篇
  2014年   106篇
  2013年   134篇
  2012年   115篇
  2011年   128篇
  2010年   86篇
  2009年   65篇
  2008年   108篇
  2007年   115篇
  2006年   100篇
  2005年   116篇
  2004年   102篇
  2003年   85篇
  2002年   83篇
  2001年   42篇
  2000年   36篇
  1999年   42篇
  1998年   32篇
  1997年   18篇
  1996年   24篇
  1995年   20篇
  1994年   17篇
  1993年   27篇
  1992年   37篇
  1991年   22篇
  1990年   18篇
  1989年   26篇
  1988年   23篇
  1987年   15篇
  1985年   21篇
  1984年   19篇
  1983年   23篇
  1982年   28篇
  1981年   24篇
  1980年   28篇
  1979年   22篇
  1978年   22篇
  1977年   20篇
  1976年   15篇
  1975年   15篇
  1974年   18篇
  1973年   18篇
  1971年   25篇
  1970年   14篇
排序方式: 共有2539条查询结果,搜索用时 78 毫秒
101.
102.
103.
The pistillate flowers of Arceuthobium show a high degree of uniformity and structural simplicity. Because of their simplicity certain structures such as the carpel and the placenta have been difficult to interpret. From this study, the placenta is interpreted as a composite structure consisting of two united ovules fused basally with the tissues of the receptacle. Pollen tube penetration of the placenta at its tip, development of the zygote at the distal pole, and early endosperm formation at the basal pole of the former megagametophyte indicate that the ovule is orthotropous. A theoretical interpretation of gynoecial phylogeny in Arceuthobium is discussed.  相似文献   
104.
A new cyanogenic glycoside isolated from pods of Acacia sieberiana var. woodii has been shown by chemical and spectroscopic methods to be (2S)-2-[(6-O-α-l-arabinopyranosyl-β-d-glucopyranosyl)oxy]-3-methylbut-3-enenitrileo. Acid-catalysed hydrolysis of the glycoside afforded arabinose and proacacipetalin, and base-catalysed double-bond migration gave 2- [(6-O-α-l-arabinopyranosyl-β- d-glucopyranosyl)oxy ]-3-methylbut-2-enenitrile.  相似文献   
105.
LncRNA and miRNA are key molecules in mechanism of competing endogenous RNAs(ceRNA), and their interactions have been discovered with important roles in gene regulation. As supplementary to the identification of lncRNA‐miRNA interactions from CLIP‐seq experiments, in silico prediction can select the most potential candidates for experimental validation. Although developing computational tool for predicting lncRNA‐miRNA interaction is of great importance for deciphering the ceRNA mechanism, little effort has been made towards this direction. In this paper, we propose an approach based on linear neighbour representation to predict lncRNA‐miRNA interactions (LNRLMI). Specifically, we first constructed a bipartite network by combining the known interaction network and similarities based on expression profiles of lncRNAs and miRNAs. Based on such a data integration, linear neighbour representation method was introduced to construct a prediction model. To evaluate the prediction performance of the proposed model, k‐fold cross validations were implemented. As a result, LNRLMI yielded the average AUCs of 0.8475 ± 0.0032, 0.8960 ± 0.0015 and 0.9069 ± 0.0014 on 2‐fold, 5‐fold and 10‐fold cross validation, respectively. A series of comparison experiments with other methods were also conducted, and the results showed that our method was feasible and effective to predict lncRNA‐miRNA interactions via a combination of different types of useful side information. It is anticipated that LNRLMI could be a useful tool for predicting non‐coding RNA regulation network that lncRNA and miRNA are involved in.  相似文献   
106.
107.
Media preparation for perfusion cell culture processes contributes significantly to operational costs and the footprint of continuous operations for therapeutic protein manufacturing. In this study, definitions are given for the use of a perfusion equivalent nutrient feed stream which, when used in combination with basal perfusion medium, supplements the culture with targeted compounds and increases the medium depth. Definitions to compare medium and feed depth are given in this article. Using a concentrated nutrient feed, a 1.8-fold medium consumption (MC) decrease and a 1.67-fold increase in volumetric productivity (PR) were achieved compared to the initial condition. Later, this strategy was used to push cell densities above 100 × 106 cells/ml while using a perfusion rate below 2 RV/day. In this example, MC was also decreased 1.8-fold compared to the initial condition, but due to the higher cell density, PR was increased 3.1-fold and to an average PR value of 1.36 g L−1 day−1 during a short stable phase, and versus 0.46 g L−1 day−1 in the initial condition. Overall, the performance improvements were aligned with the given definitions. This multiple feeding strategy can be applied to gain some flexibility during process development and also in a manufacturing set-up to enable better control on nutrient addition.  相似文献   
108.
During male–male competition, evolution can favor alternative reproductive tactics. This often results in a dominant morph that holds a resource, such as a nest for egg laying, which competes with a smaller sneaker morph that reproduces by stealing fertilizations. The salinity environment can influence male growth rates, for example, via osmoregulatory costs, which in turn may influence the use of sneaker tactics for small males competing for mating opportunities. Salinity can also affect sperm directly; however, little is known of how salinity influences sneaker tactics through sperm performance. We sampled males of the invasive round goby (Neogobius melanostomus) from two environments, a freshwater river and a brackish estuary. This fish has two male morphs: nest‐holding dark males and non‐nest‐holding light males. We examined the role of water salinity of 0, 8, and 16 on sperm performance and found that for estuarine males, a salinity of 0 reduced sperm velocity compared to a salinity of 8 and 16. Riverine males had low velocity in all salinities. Sperm viability also decreased by over 30% in 0 salinity, compared to 8 and 16, for fish from both environments. Gobies produce ejaculate contents in specialized glands that could in theory shield sperm in an adverse environment. However, gland contents did not improve sperm performance in our tests. Body mass and age estimates indicate that riverine males invested more in somatic growth compared to estuarine males. Estuarine light morph males had a high enough gonadosomatic index to indicate sneaker tactics. We propose that when sperm performance is low, such as for the riverine males, sneaker tactics are ineffective and will be selected against or phenotypically suppressed. Instead, we interpret the increased investment in somatic growth found in riverine males as a life‐history decision that is advantageous when defending a nest in the next reproductive season.  相似文献   
109.
110.
Molecular and Cellular Biochemistry - Plasma-derived extracellular vesicles (EV) can serve as markers of cell damage/disease but can also have therapeutic utility depending on the nature of their...  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