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   2379篇
  免费   151篇
林业   58篇
农学   49篇
基础科学   12篇
  221篇
综合类   440篇
农作物   98篇
水产渔业   148篇
畜牧兽医   1331篇
园艺   51篇
植物保护   122篇
  2022年   18篇
  2021年   19篇
  2020年   29篇
  2019年   35篇
  2018年   33篇
  2017年   30篇
  2016年   35篇
  2015年   24篇
  2014年   42篇
  2013年   106篇
  2012年   77篇
  2011年   85篇
  2010年   54篇
  2009年   49篇
  2008年   74篇
  2007年   87篇
  2006年   84篇
  2005年   79篇
  2004年   84篇
  2003年   74篇
  2002年   77篇
  2001年   74篇
  2000年   69篇
  1999年   58篇
  1998年   24篇
  1997年   21篇
  1996年   26篇
  1993年   20篇
  1992年   37篇
  1991年   62篇
  1990年   44篇
  1989年   43篇
  1988年   42篇
  1987年   32篇
  1986年   59篇
  1985年   54篇
  1984年   32篇
  1983年   28篇
  1980年   28篇
  1979年   33篇
  1978年   32篇
  1975年   21篇
  1974年   29篇
  1973年   27篇
  1972年   36篇
  1971年   37篇
  1970年   29篇
  1969年   17篇
  1967年   23篇
  1966年   17篇
排序方式: 共有2530条查询结果,搜索用时 0 毫秒
1.
Wilson EO 《Science (New York, N.Y.)》1985,228(4707):1489-1495
Studies on the social insects (ants, bees, wasps, and termites) have focused increasingly on sociogenesis, the process by which colony members undergo changes in caste, behavior, and physical location incident to colonial development. Caste is determined in individuals largely by environmental cues that trigger a sequence of progressive physiological restrictions. Individual determination, which is socially mediated, yields an age-size frequency distribution of the worker population that enhances survival and reproduction of the colony as a whole, typically at the expense of individuals. This "adaptive demography" varies in a predictable manner according to the species and size of the colony. The demography is richly augmented by behavioral pacemaking on the part of certain castes and programmed changes in the physical position of colony members according to age and size. Much of what has been observed in these three colony-level traits (adaptive demography, pacemaking, and positional effects) can be interpreted as the product of ritualization of dominance and other forms of selfish behavior that is still found in the more primitive insect societies. Some of the processes can also be usefully compared with morphogenesis at the levels of cells and tissues.  相似文献   
2.
3.
Neurophysiology     
  相似文献   
4.
Four groups of five Romney lambs were treated by plunge dipping with one of four registered organophosphorus flystrike preventatives. Untreated lambs acted as controls. The sheep were challenged at weekly intervals with larval implants of organophosphate-susceptible and -resistant strains of Lucilia cuprina. All four treatments provided 19-21 weeks protection against susceptible larvae but chlorfenvinphos provided the longest protection (16-17 weeks), followed by propetamphos (15-16 weeks), dichlofenthion (10-13 weeks) and diazinon (9-13 weeks), against the resistant strain.  相似文献   
5.
6.
The effect of soil water potential on the respiration of microorganisms in soil was studied. Bacterial respiration decreased rapidly below ?3 bar; at -20 bar it was very slight. The most rapid decline occurred above ? 6 bar. The respiration of a mixed population of microorganisms, however, was maintained at a fairly high level between ?8 and ?30 bar but subsequently declined until at ?50 bar it became negligible. At potentials below ?50 bar, additions of glucose caused no increase in respiration. The sensitivity of bacteria to relatively small negative potentials was probably due to their restricted movement as the soil pores drained.  相似文献   
7.
8.
9.
Objective To assess the effectiveness of a detomidine infusion technique to provide standing chemical restraint in the horse. Design Retrospective study. Animals Fifty‐one adult horses aged 9.5 ± 6.9 years (range 1–23 years) and weighing 575 ± 290.3 kg. Methods Records of horses presented to our clinic over a 3‐year period in which a detomidine infusion was used to provide standing chemical restraint were reviewed. Information relating to the types of procedure performed, duration of infusion, drug dosages and adjunct drugs administered was retrieved. Results Detomidine was administered as an initial bolus loading dose (mean ± SD) of 7.5 ± 1.87 µg kg?1. The initial infusion rate was 0.6 µg kg?1 minute?1, and this was halved every 15 minutes. The duration of the infusion ranged from 20 to 135 minutes. Twenty horses received additional detomidine or butorphanol during the procedure. All horses undergoing surgery received local anesthesia or epidural analgesia in addition to the detomidine infusion. A wide variety of procedures were performed in these horses. Conclusions Detomidine administered by infusion provides prolonged periods of chemical restraint in standing horses. Supplemental sedatives or analgesics may be needed in horses undergoing surgery. Clinical relevance An effective method that provides prolonged periods of chemical restraint in standing horses is described. The infusion alone did not provide sufficient analgesia for surgery and a significant proportion of animals required supplemental sedatives and analgesics.  相似文献   
10.
Highly conserved protective epitopes on influenza B viruses   总被引:1,自引:0,他引:1  
Identification of broadly neutralizing antibodies against influenza A viruses has raised hopes for the development of monoclonal antibody-based immunotherapy and "universal" vaccines for influenza. However, a substantial part of the annual flu burden is caused by two cocirculating, antigenically distinct lineages of influenza B viruses. Here, we report human monoclonal antibodies, CR8033, CR8071, and CR9114, that protect mice against lethal challenge from both lineages. Antibodies CR8033 and CR8071 recognize distinct conserved epitopes in the head region of the influenza B hemagglutinin (HA), whereas CR9114 binds a conserved epitope in the HA stem and protects against lethal challenge with influenza A and B viruses. These antibodies may inform on development of monoclonal antibody-based treatments and a universal flu vaccine for all influenza A and B viruses.  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