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   2941篇
  免费   340篇
  国内免费   1篇
  2022年   23篇
  2021年   31篇
  2020年   21篇
  2019年   35篇
  2018年   30篇
  2017年   38篇
  2016年   49篇
  2015年   66篇
  2014年   99篇
  2013年   142篇
  2012年   139篇
  2011年   151篇
  2010年   110篇
  2009年   93篇
  2008年   127篇
  2007年   149篇
  2006年   134篇
  2005年   120篇
  2004年   121篇
  2003年   124篇
  2002年   151篇
  2001年   80篇
  2000年   64篇
  1999年   65篇
  1998年   40篇
  1997年   35篇
  1996年   31篇
  1995年   32篇
  1994年   40篇
  1993年   30篇
  1992年   51篇
  1991年   51篇
  1990年   44篇
  1989年   59篇
  1988年   53篇
  1987年   42篇
  1986年   55篇
  1985年   50篇
  1984年   60篇
  1983年   27篇
  1982年   33篇
  1981年   28篇
  1980年   23篇
  1979年   25篇
  1978年   28篇
  1977年   19篇
  1976年   24篇
  1973年   27篇
  1972年   22篇
  1970年   21篇
排序方式: 共有3282条查询结果,搜索用时 15 毫秒
1.
2.
3.
1. Species interactions in tightly bound ecological mutualisms often feature highly specialised species' roles in which competitive exclusion may preclude multi‐species coexistence. Among the 800 fig (Ficus) species, it was originally considered that each was pollinated by their own wasp (Agaonidae). However, recent investigations show that this ‘one‐to‐one’ rule often breaks down, as fig species regularly host multiple agaonids but in ways suggesting that competitive processes still mediate biodiversity outcomes. 2. A phenological survey was conducted of the fig–fig wasp pair, Ficus microcarpa and its associated pollinating wasp, alongside its sister species, the cheating wasp, in Xishuangbanna, China. 3. Reproductive output underwent extreme seasonal variation. Seed and pollinator production fell markedly during cooler, drier months, although high levels of fig production continued. However, this resource was predominantly utilised by the cheater species, which offers no pollination services. Pollinators and cheaters rarely co‐occur, suggesting that temporal coexistence is constrained by competition for access to figs. 4. The overall findings indicate periodic rearrangements of mutualism dynamics, probably resulting from a strongly seasonal environment. Sympatric co‐occurrence may result from a window of opportunity for a functionally divergent agaonid, potentially due to constraints on the main pollinator in adapting to variable year‐round conditions that prevent competitive exclusion.  相似文献   
4.
From experience in the Northampton/Kettering area 9 to 10% of all patients in a general hospital requiring care in an intensive therapy unit were aged 12 years or under. Fifty-nine children were admitted to the intensive therapy unit of Northampton General Hospital between May 1967 and August 1969. Of these, 22 had been injured in road traffic accidents, five were surgical emergencies, five had meningitis, four status epilepticus, and four respiratory infections.All of the 30 families interviewed were in favour of their child being admitted to the unit, and none considered that the experience had had any lasting adverse psychological effect on the child. It is suggested that certain carefully selected child patients do benefit from the facilities of an intensive therapy unit, and for this reason such units must be designed, equipped, and staffed with this in mind.  相似文献   
5.
Andrew C. Harper 《CMAJ》1980,123(5):400-401
  相似文献   
6.
Abstract The effectiveness of immunofluorescence flow cytometry and cell sorting to detect, quantify and separate indigenous bacterial populations present in low concentrations in sewage outflow was investigated. Preparatory experiments for targeted recovery revealed indigenous, immunoglobulin-G-binding particles present at low levels in sewage outflow samples taken from Coniston Water. Fluorescence-activated cell sorting of this population was employed to enrich for these particles, which were confirmed as bacterial cells. This cell population comprised approximately 23% of the total plate count on MacConkey agar before cell sorting, rising to approximately 95% after sorting. These results corresponded to cell densities of less than 5% of the total plate count on R2A agar. Taxonomic tests suggested the bacterium to be Ochrobactrum anthropi .  相似文献   
7.
8.
9.
The HsdS and HsdM polypeptides of the type IC restriction enzyme EcoR124 have been purified independently and used in a set of gel retardation experiments to determine the minimum requirements for sequence-specific recognition of DNA by this enzyme. The HsdS polypeptide alone is able to bind to DNA in a sequence-specific manner. In addition, whilst the presence of the HsdM polypeptide gives rise to a stimulation of DNA binding by the HsdS subunit it is not clear whether, under the conditions of the experiments reported here, the HsdS subunit maintains the same interactions with the HsdM subunits observed in the absence of DNA.  相似文献   
10.
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