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   3429篇
  免费   268篇
  国内免费   4篇
  2023年   15篇
  2022年   23篇
  2021年   47篇
  2020年   42篇
  2019年   41篇
  2018年   56篇
  2017年   39篇
  2016年   103篇
  2015年   146篇
  2014年   179篇
  2013年   216篇
  2012年   268篇
  2011年   262篇
  2010年   149篇
  2009年   144篇
  2008年   177篇
  2007年   204篇
  2006年   180篇
  2005年   175篇
  2004年   116篇
  2003年   143篇
  2002年   118篇
  2001年   37篇
  2000年   33篇
  1999年   28篇
  1998年   35篇
  1997年   34篇
  1996年   22篇
  1995年   26篇
  1994年   17篇
  1993年   34篇
  1992年   34篇
  1991年   41篇
  1990年   30篇
  1989年   28篇
  1988年   37篇
  1987年   30篇
  1986年   29篇
  1985年   19篇
  1984年   26篇
  1983年   22篇
  1982年   23篇
  1981年   16篇
  1980年   15篇
  1979年   27篇
  1978年   19篇
  1977年   17篇
  1975年   15篇
  1972年   17篇
  1971年   16篇
排序方式: 共有3701条查询结果,搜索用时 218 毫秒
91.
Encompassing some of the major hotspots of biodiversity on Earth, large mountain systems have long held the attention of evolutionary biologists. The region of the Qinghai‐Tibet Plateau (QTP) is considered a biogeographic source for multiple colonization events into adjacent areas including the northern Palearctic. The faunal exchange between the QTP and adjacent regions could thus represent a one‐way street (“out of” the QTP). However, immigration into the QTP region has so far received only little attention, despite its potential to shape faunal and floral communities of the QTP. In this study, we investigated centers of origin and dispersal routes between the QTP, its forested margins and adjacent regions for five clades of alpine and montane birds of the passerine superfamily Passeroidea. We performed an ancestral area reconstruction using BioGeoBEARS and inferred a time‐calibrated backbone phylogeny for 279 taxa of Passeroidea. The oldest endemic species of the QTP was dated to the early Miocene (ca. 20 Ma). Several additional QTP endemics evolved in the mid to late Miocene (12–7 Ma). The inferred centers of origin and diversification for some of our target clades matched the “out of Tibet hypothesis’ or the “out of Himalayas hypothesis” for others they matched the “into Tibet hypothesis.” Three radiations included multiple independent Pleistocene colonization events to regions as distant as the Western Palearctic and the Nearctic. We conclude that faunal exchange between the QTP and adjacent regions was bidirectional through time, and the QTP region has thus harbored both centers of diversification and centers of immigration.  相似文献   
92.
BCL2 family proteins are important regulators of mitochondrial outer membrane permeabilization (MOMP). In recent years, BCL2 family proteins have also been linked to the regulation of mitochondrial bioenergetics and dynamics. Given their overexpression in breast cancer cells, we sought to explore whether two key members of this family, BCL2 and BCL(X)L impacted on mitochondrial fusion/fission processes. By employing a single cell imaging and RNA sequencing we found that overexpression of BCL2 or BCL(X)L increases mitochondrial dynamics and alters the expression profile of genes involved in this process. Collectively, our data show that overexpression of BCL2 proteins regulates mitochondrial dynamics in breast cancer tumor cells.  相似文献   
93.
Biodiversity and Conservation - Across Europe, calcareous grasslands become increasingly fragmented and their quality deteriorates through abandonment and land use intensification, both affecting...  相似文献   
94.
95.
96.
Cluster Computing - The cloud evolved into an attractive execution environment for parallel applications, which make use of compute resources to speed up the computation of large problems in...  相似文献   
97.
98.
Crop model‐specific biases are a key uncertainty affecting our understanding of climate change impacts to agriculture. There is increasing research focus on intermodel variation, but comparisons between mechanistic (MMs) and empirical models (EMs) are rare despite both being used widely in this field. We combined MMs and EMs to project future (2055) changes in the potential distribution (suitability) and productivity of maize and spring wheat in South Africa under 18 downscaled climate scenarios (9 models run under 2 emissions scenarios). EMs projected larger yield losses or smaller gains than MMs. The EMs’ median‐projected maize and wheat yield changes were ?3.6% and 6.2%, respectively, compared to 6.5% and 15.2% for the MM. The EM projected a 10% reduction in the potential maize growing area, where the MM projected a 9% gain. Both models showed increases in the potential spring wheat production region (EM = 48%, MM = 20%), but these results were more equivocal because both models (particularly the EM) substantially overestimated the extent of current suitability. The substantial water‐use efficiency gains simulated by the MMs under elevated CO2 accounted for much of the EM?MM difference, but EMs may have more accurately represented crop temperature sensitivities. Our results align with earlier studies showing that EMs may show larger climate change losses than MMs. Crop forecasting efforts should expand to include EM?MM comparisons to provide a fuller picture of crop–climate response uncertainties.  相似文献   
99.
100.
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