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   236718篇
  免费   14488篇
  国内免费   659篇
林业   23305篇
农学   13951篇
基础科学   2952篇
  41517篇
综合类   15973篇
农作物   17160篇
水产渔业   16501篇
畜牧兽医   91044篇
园艺   6230篇
植物保护   23232篇
  2021年   2454篇
  2020年   2855篇
  2019年   3623篇
  2018年   3890篇
  2017年   4215篇
  2016年   4706篇
  2015年   4307篇
  2014年   5672篇
  2013年   16279篇
  2012年   5835篇
  2011年   7641篇
  2010年   7215篇
  2009年   7844篇
  2008年   6955篇
  2007年   6028篇
  2006年   6716篇
  2005年   5933篇
  2004年   5792篇
  2003年   5582篇
  2002年   4961篇
  2001年   5736篇
  2000年   5330篇
  1999年   5063篇
  1998年   4130篇
  1997年   4183篇
  1996年   3921篇
  1995年   4443篇
  1994年   3833篇
  1993年   3559篇
  1992年   4005篇
  1991年   4265篇
  1990年   3955篇
  1989年   3875篇
  1988年   3430篇
  1987年   3467篇
  1986年   3259篇
  1985年   3632篇
  1984年   3461篇
  1983年   3223篇
  1982年   2737篇
  1981年   2651篇
  1980年   2609篇
  1979年   2927篇
  1978年   2630篇
  1977年   2448篇
  1976年   2320篇
  1975年   2130篇
  1974年   2235篇
  1973年   2180篇
  1971年   1926篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
954.
955.
A total of 123 rabies virus isolates from various geographical areas in Canada were characterized by a panel of 43 anti-nucleocapsid monoclonal antibodies. Four major antigenic groups are found in terrestrial mammals: "Canadian Arctic" from Ontario, Quebec and the Northwest Territories; "south-eastern Georgian Bay" from Ontario; "south mid-central skunk" from Alberta, Saskatchewan and Manitoba; and "Brook's, Alberta skunk" from a restricted area in Alberta. Bat isolates can be divided into 4 major antigenic groups: "B-1" in Eptesicus fuscus from Ontario; "B-2" in a variety of bat species from British Columbia eastward into Ontario; "B-3" in Myotis spp. from Ontario and New Brunswick; and "B-4" in E. fuscus from Alberta and Saskatchewan. A single case of bat to horse transmission of rabies virus is recorded. These street isolates are compared with isolates of fixed virus. Epidemiological aspects are discussed.  相似文献   
956.
957.
958.
Four infectious agents were isolated from the ticks Ixodes ricinus (L.) collected in the recreational area and park-forest of Prague. On the basis of cultivation, staining, biochemical, serologic properties, pathogenicity for animals and histological tests they were identified as Francisella tularensis with the following features: they are short, gram-negative rods of approximate dimensions of 0.3 X 0.8 micron, growing in enriched media after 3-4 day incubation at 37 degrees C. They form small circular, at first transparent, later greyish turbid colonies with regular rims. They are little active biochemically. They are susceptible to streptomycin and some broad spectrum antibiotics. They react positively with tularemic serum, but in lower titres than those in which this serum reacts with standard antigen. The microbes are highly pathogenic for mice, guinea-pigs, young rats, in which a massive bacteriemia occurs before death, but they do not kill rabbits. They multiply well in chick embryo, but do not grow in cell or tissue cultures. The most important histologic changes were observed in liver and spleen of mice. No pathologic changes were found in brain, lungs, heart, kidneys. Necroses were found in liver and in their marginal zones the microbes were present. Conspicuous were changes in numerous hepatocytes which became enlarged due to microbial multiplication and finally transformed into "sacs" packed with microbes. Histological and electronoptical examination showed that these are intracellular parasites fringed with a light lytic zone. Discussed is the problem to what extent the properties of the isolated strains are typical of F. tularensis as well as the importance of their detection from the aspect of epidemiology and differential diagnostics.  相似文献   
959.
Data are presented on the occurrence of Braconidae (Hymenoptera parasitica) parasitizing insects associated with forest and ornamental trees and shrubs in Israel. Fifty-five genera of plants are listed, the richest in braconid fauna being tamarisk (9 species); acacia, pistachio and poplar (8 species each); carob and oak (7 species each). Of the 95 species of insect hosts mentioned, 53 are Lepidoptera, mostly Gelechiidae (7 species), Pyralidae (6 species), Noctuidae (5 species), Gracillariidae, Tortricidae, Geometridae, Lymantriidae and Lycaenidae (3 species each); 44 are Coleoptera, mostly Cerambycidae (13 species), Scolytidae (12 species), and Bostrichidae (9 species); three are Diptera. Of the 92 species of braconids listed, of which only 65 have been fully named, 56 develop in Lepidoptera, mostly Noctuidae (15 species), Gelechiidae (11 species) and Pyralidae (9 species); 33 species develop in Coleoptera, mostly Cerambycidae (12 species, Bostrichidae (10 species) and Scolytidae (5 species); and three species develop in Diptera. Thirty-eight species are new to the fauna of Israel; at least three of them are new to science,viz., Gnaptodon, Gildoria andDendrosotinus titubatus Papp.  相似文献   
960.
Diflubenzuron, PH 60-38, PH 6043, penfluron (PH 60-44), PH 6045, triflumuron, chlorfuazuron (IKI-7899), teflubenzuron (CME 134), XRD473 and Dowco 439 were tested for their efficacy against the larvae of the spiny bollworm,Earias insulana (Boisd.), in laboratory experiments. The compounds were incorporated at different concentrations in an artificial diet and 5-day-old larvae were introduced and grown on the treated diets until pupation and adult emergence. Teflubenzuron was active at 0.1 ppm, chlorfuazuron at 0.75 ppm and PH 60-38 at 10 ppm; triflumuron and diflubenzuron were active only at 50 ppm; all the rest of the compounds were even less active. When cotton bolls were dipped in teflubenzuron and offered to 6-day-old larvae in the laboratory, only 4% and 10% of the larvae penetrated inside the bolls treated with 50 and 25 ppm a.i., respectively, whereas 68% penetrated inside untreated bolls.  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