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   96551篇
  免费   581篇
  国内免费   885篇
  98017篇
  2023年   16篇
  2022年   41篇
  2021年   70篇
  2020年   52篇
  2019年   51篇
  2018年   11874篇
  2017年   10696篇
  2016年   7528篇
  2015年   721篇
  2014年   453篇
  2013年   490篇
  2012年   4500篇
  2011年   13089篇
  2010年   12151篇
  2009年   8397篇
  2008年   10001篇
  2007年   11538篇
  2006年   435篇
  2005年   709篇
  2004年   1161篇
  2003年   1196篇
  2002年   945篇
  2001年   271篇
  2000年   180篇
  1999年   51篇
  1998年   46篇
  1997年   48篇
  1996年   40篇
  1995年   29篇
  1994年   42篇
  1993年   52篇
  1992年   38篇
  1991年   48篇
  1990年   18篇
  1989年   23篇
  1988年   33篇
  1987年   27篇
  1984年   41篇
  1983年   38篇
  1982年   22篇
  1980年   29篇
  1978年   25篇
  1977年   27篇
  1975年   19篇
  1974年   22篇
  1973年   16篇
  1972年   250篇
  1971年   282篇
  1965年   17篇
  1962年   28篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.

Background  

We have previously shown that supernatant from Candida albicans (CA) culture contains a Secretory Interleukin (IL)-12 Inhibitory Factor (CA-SIIF), which inhibits IL-12 production by human monocytes. However, the effect of CA-SIIF on secretion of other cytokines by monocytes is unknown, and detailed characterization of this factor has not been performed.  相似文献   
32.
'15N signatures of fossil peat were used to interpret past ecosystem processes on tectonically active subantarctic Macquarie Island. By comparing past vegetation reconstructed from the fossil record with present-day vegetation analogues, our evidence strongly suggests that changes in the '15N signatures of fossil peat at this location reflect mainly past changes in the proportion of plant nitrogen derived from animal sources. Associated with uplift above sea level over the past 8,500 years, fossil records in two peat deposits on the island chronicle a change from coastal vegetation with fur and elephant seal disturbance to the existing inland herbfield. Coupled with this change are synchronous changes in the '15N signatures of peat layers. At two sites 15N-enriched peat '15N signatures of up to +17‰ were associated with a high abundance of pollen of the nitrophile Callitriche antarctica (Callitrichaceae). At one site fossil seal hair was also associated with enriched peat '15N. Less 15N enriched '15N signatures (e.g. -1.9‰ to +3.9‰) were measured in peat layers which lacked animal associated C. antarctica and Acaena spp. Interpretation of a third peat profile indicates continual occupation of a ridge site by burrowing petrels for most of the Holocene. We suggest that 15N signatures of fossil peat remained relatively stable with time once deposited, providing a significant new tool for interpreting the palaeoecology.  相似文献   
33.
34.
The number of orientation, feeding and social calls emitted by pipistrelle batsPipistrellus pipistrellus Schreber, 1774 andP. pygmaeus Leach, 1825 was recorded throughout the night at eight different sites. Social calls were unaffected by weather variables, whereas orientation calls and feeding buzzes were both significantly affected by cloud and temperature conditions. The number of emissions of each call type was significantly different between sites, indicating that the bats used different sites for different activities. Significant positive correlations between all three combinations of call types occurred only during the middle of the night, corresponding with the nadir of flying insects. This suggests that bats were engaged in activities other than feeding at this time, such as territory protection or mate attraction.  相似文献   
35.
We propose a technique for separating the climatic signal which is contained in two tree-ring parameters widely used in dendroclimatology. The method is based on the removal of the relationship between tree-ring width (TRW) and maximum latewood density (MXD) observed for narrow tree rings from high latitudes. The new technique is tested on data from three larch stands located along the northern timberline in Eurasia. Correlations were calculated between the temperatures of pentads (five consecutive days), TRW chronologies and MXD chronologies calculated according to the standard and proposed methods. The analysis confirms the great importance of summer temperature for tree radial growth and tree-ring formation. TRW is positively correlated with the temperature of four to eight pentads (depending on the region) at the beginning of the growth season, but MXD as obtained by the standard technique is correlated with temperature over a much longer period. For maximum density series from which the relationship between MXD and TRW has been removed (MXD′), there is a clear correlation with temperatures in the second part of the growing season. These results are consistent with the known dynamics of tree-ring growth in high latitudes and mechanisms of tree-ring formation.  相似文献   
36.
37.
38.
39.
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   
40.
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   
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