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   15230篇
  免费   1107篇
  国内免费   4篇
  16341篇
  2024年   14篇
  2023年   92篇
  2022年   170篇
  2021年   375篇
  2020年   269篇
  2019年   346篇
  2018年   417篇
  2017年   339篇
  2016年   534篇
  2015年   868篇
  2014年   879篇
  2013年   1100篇
  2012年   1326篇
  2011年   1206篇
  2010年   807篇
  2009年   740篇
  2008年   900篇
  2007年   884篇
  2006年   780篇
  2005年   717篇
  2004年   679篇
  2003年   561篇
  2002年   559篇
  2001年   156篇
  2000年   102篇
  1999年   133篇
  1998年   183篇
  1997年   140篇
  1996年   91篇
  1995年   92篇
  1994年   101篇
  1993年   86篇
  1992年   67篇
  1991年   58篇
  1990年   58篇
  1989年   47篇
  1988年   43篇
  1987年   34篇
  1986年   30篇
  1985年   40篇
  1984年   50篇
  1983年   29篇
  1982年   38篇
  1981年   28篇
  1980年   18篇
  1979年   18篇
  1978年   17篇
  1976年   14篇
  1975年   17篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
FTA® cards were used for long‐term storage of avian blood samples. Blood DNA was extracted by a simple method and used in PCR for sex identification of adult and nestling Great Grey Shrikes Lanius excubitor.  相似文献   
3.
4.
5.
6.
7.
Assessing small mammal diversity is a common procedure, which usually employs widespread standard techniques, for gathering information for a wide range of studies. Traditional methods, however, may be biased against capturing arboreal marsupials, such as Dromiciops gliroides, an endemic marsupial currently considered a rare species in the Patagonian temperate rainforest due to the low abundances reported previously. I tested a new capturing methodology to assess the small mammal diversity of an old-growth forest in Patagonia, based on a randomized and balanced design, which incorporated a combination of different trap types, bait types, and placement heights. The proposed methodology included four trap types (two for live-capturing: wire-mesh and Sherman traps, and two sign-recording traps for tracks and hair), two types of bait (banana and rolled oats), and two trap placements (ground level and 1.5–2.5 m above the ground). Trap type, bait type, and height of placement all had significantly different effects on capturing and detecting rodents or marsupials; environmental variables at the trap location also affected the ability to detect rodents and marsupials. Traditional methods used for sampling small mammals performed well for rodents but are not effective for capturing marsupials and vice versa, showing species-specific sampling protocols. There is no single combination of trap-bait-height capable to assess the entire small mammal community, but the combination of the most effective protocol for rodents and the most effective protocol for marsupials guarantee better results.  相似文献   
8.
9.
In the River Lobos-Ucero and its tributary the River Avión-Milanos (Duero basin, Old Castile, Central Spain), two limestone streams fed by aquifers, the population of brown trout, as compared with the populations of other European streams, shows a high growth rate, high condition coefficients, short life-span and early age at first maturity. Gonad cycle was also studied. Size distributions of unshed eggs exhibit a dynamic activity with a bi-modal distribution from June onwards, spawning occurred in the last days of November. Fecundity (F) can be predicted from trout length (L, mm) according to the equation: F= –646.47+5.6167 · L. Numbers and standing crop of trout range from 18 to 3903 ind. ha–1 and 3.6 to 452.9 Kg ha–1, reaching higher values in the sites close to the aquifers. Egg production had values of 22.4 and 18.0 eggs m–2 in the Rivers Ucero and Avión-Milanos respectively. Some factors suggested as regulators of these demographical characteristics are discussed in the light of recent literature.  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