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   3373篇
  免费   275篇
  国内免费   2篇
  2023年   17篇
  2022年   38篇
  2021年   62篇
  2020年   38篇
  2019年   41篇
  2018年   51篇
  2017年   48篇
  2016年   88篇
  2015年   146篇
  2014年   164篇
  2013年   223篇
  2012年   247篇
  2011年   263篇
  2010年   185篇
  2009年   180篇
  2008年   243篇
  2007年   239篇
  2006年   214篇
  2005年   209篇
  2004年   208篇
  2003年   170篇
  2002年   180篇
  2001年   56篇
  2000年   33篇
  1999年   35篇
  1998年   37篇
  1997年   28篇
  1996年   21篇
  1995年   26篇
  1994年   13篇
  1993年   15篇
  1992年   10篇
  1991年   13篇
  1990年   11篇
  1989年   7篇
  1988年   10篇
  1987年   4篇
  1986年   5篇
  1985年   10篇
  1984年   6篇
  1983年   11篇
  1982年   12篇
  1981年   8篇
  1980年   2篇
  1979年   3篇
  1978年   5篇
  1977年   5篇
  1976年   4篇
  1973年   2篇
  1968年   1篇
排序方式: 共有3650条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
The influence of both predator and prey size on the shift from a pulling to a drilling predatory response was examined in the intertidal octopus Octopus dierythraeus, using an experimental program. Additionally, selective drilling, where particular regions of the prey are targeted, was examined for a variety of bivalve and gastropod prey. O. dierythraeus always initially attempted to pull bivalves apart. Shells that were eventually drilled were always subjected to significantly more pulling attempts than those that could be pulled apart, indicating that octopus are willing to expend more energy to access the flesh quickly. There was no defined threshold where bivalve size caused an octopus to switch from a pulling to a drilling response. Instead, there was a broad size range where the octopus could adopt either handling method and it varied for each individual. Octopus may only able to pull open bivalves before the molecular ratchet or ‘catch’ mechanism that many bivalves possess is engaged. This might explain the lack of a relationship between either octopus or bivalve size and the success of pulling, as it is likely that when the bivalves were presented to individual octopus they were either setting the ‘catch’ mechanism, or had already engaged it. O. dierythraeus demonstrated selective drilling on a variety of molluscan prey, with penetration sites differing between prey species. O. dierythraeus targeted the valve periphery, which was the thinnest part of the shell, therefore minimizing handling time. O. dierythraeus always drilled gastropods, but did not target the thinnest regions of the shells, with drill site varying according to the morphology of the prey. Elongate species with pronounced aperture lips were drilled in the apical region, close to the columella on the side of the opercula whereas nonelongate species were drilled immediately above the aperture. The location of drilling sites may represent a trade-off between targeting the most effective places to inject paralyzing secretions and the mechanically simplest places to drill.  相似文献   
7.
Extracellular production of a heat-stable somatic antigen (HSSA) by Bacillus thuringiensis subsp. dendrolimus strain T84A1-A [flagellar (H) serotype 4a: 4b] was serologically detected. In Ouchterlony tests, the HSSA antiserum gave single precipitin lines against both untreated and heat-treated culture supernatants. These two precipitin lines fused completely. When colonies of strain T84A1-A were grown on nutrient agar plates containing the homologous HSSA antiserum, precipitin halos were formed around the colonies. Of 27 type strains of B. thuringiensis subspecies tested, only the type strains of B. thuringiensis subsp. sotto (H serotype 4a: 4b) and B. thuringiensis subsp. israelensis (H serotype 14) formed [precipitin halos on nutrient agar plates containing antiserum against the HSSA of strain T84A1-A.  相似文献   
8.
Abstract The methyl-CoM reductase from Methanothrix soehngenii was purified 18-fold to apparent homogeneity with 50% recovery in three steps. The native molecular mass of the enzyme estimated by gel-fitration was 280 kDa. SDS-polyacrylamide gel electrophoresis revealed three protein bands corresponding to M r 63 900, 41 700 and 30 400 Da. The methyl-coenzyme M reductase constitutes up to 10% of the soluble cell protein. The enzyme has K m apparent values of 23 μM and 2 mM for N -7-mercaptoheptanoylthreonine phosphate (HS- HTP = component B ) and methyl-coenzyme M (CH3CoM) respectively. At the optimum pH of 7.0 60 nmol of methane were formed per min per mg protein.  相似文献   
9.
10.
Herpes simplex virus type 1 polypeptide ICP4 bends DNA.   总被引:5,自引:1,他引:4       下载免费PDF全文
  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