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   17036篇
  免费   898篇
  国内免费   17篇
林业   828篇
农学   558篇
基础科学   122篇
  2505篇
综合类   2663篇
农作物   911篇
水产渔业   950篇
畜牧兽医   8309篇
园艺   197篇
植物保护   908篇
  2020年   161篇
  2019年   182篇
  2018年   310篇
  2017年   365篇
  2016年   261篇
  2015年   198篇
  2014年   316篇
  2013年   664篇
  2012年   497篇
  2011年   620篇
  2010年   428篇
  2009年   410篇
  2008年   628篇
  2007年   552篇
  2006年   513篇
  2005年   453篇
  2004年   420篇
  2003年   429篇
  2002年   369篇
  2001年   486篇
  2000年   475篇
  1999年   373篇
  1998年   180篇
  1997年   201篇
  1996年   156篇
  1995年   192篇
  1993年   164篇
  1992年   280篇
  1991年   313篇
  1990年   307篇
  1989年   312篇
  1988年   289篇
  1987年   246篇
  1986年   295篇
  1985年   253篇
  1984年   209篇
  1983年   207篇
  1979年   250篇
  1978年   165篇
  1977年   155篇
  1975年   171篇
  1974年   234篇
  1973年   215篇
  1972年   251篇
  1971年   230篇
  1970年   203篇
  1969年   192篇
  1968年   158篇
  1967年   160篇
  1966年   161篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The effect of endotoxin induced fever on the steady state concentration of sulphadimethoxine in pigs has been studied.Sulphadimethoxine 20 mg/kg b.wt. was injected at 9 a.m. in an ear vein each day for eleven days. From day 6 until the end of the experiment, endotoxin fromEscherichia coli 1.5 g/kg b.wt. was injected at 9 a.m. and at 3 p.m. The plasma concentration versus time curves were calculated by means of a computer program, assuming a two-compartment model. During the endotoxin injections the plasma concentrations were simulated and compared with those calculated.It was not possible to show any clinically significant changes in pharmacokinetics of sulphadimethoxine after the start of endotoxin injections.  相似文献   
52.
53.
Chicks monocolonized by either salmonellae or pathogenic strains of Escherichia coli had persistent and undiminished colonization of all levels of the gastrointestinal tract and frequently had bacteremia during test periods ranging to 35 days. Poults monocolonized by salmonellae or Arizona hinshawii 7:"1,7,8 developed a similar pattern of colonization. Conventionally reared chicks and poults had rather variable colonization by these pathogens, and it was most persistent in the ceca. Groups treated with a native protective microflora were infrequently colonized. Differences in colonization are explainable by lack of competing bacteria in the monocolonized group and by various degrees of protection provided by microflora colonizing the other groups.  相似文献   
54.
A fossil land mammal, apparently the first found in Antarctica, belongs to the extinct marsupial family Polydolopidae. The fossils were recovered from rocks about 40 million years old on Seymour Island, in the northern Antarctic Peninsula. The newly discovered marsupials support theories that predicted their former presence in Antarctica and strengthen proposals that Australian marsupials perhaps originated from South American species that dispersed across Antarctica when Australia still was attached to it, prior to 56 million years ago.  相似文献   
55.
Two enzyme-linked immunosorbent assays (ELISA), one based on a mouse anti-Trypanosoma brucei group-specific monoclonal antibody and the other on rabbit anti-Trypanosoma evansi polyclonal antibodies, have been evaluated for their ability to detect circulating trypanosome antigens in camel sera as a means for the diagnosis of T. evansi infections. All 91 sera from a negative control camel herd from Kenya gave negative antigen-ELISA results in the monoclonal antibody-based ELISA and only 2 of them (2.2%) gave false positive results in the polyclonal antibody-based ELISA. In subsequent analyses of sera from infected camels (as determined by mouse inoculation), the monoclonal antibody-based ELISA detected antigens in 90 (83.3%) out of the 108 sera tested. This percentage was lower for the polyclonal antibody-based ELISA which was able to detect antigens in 67 (60.9%) out of the 110 sera tested. The two tests detected probably different antigens and when the results were combined, 99 out of 107 (92.5%) sera were shown to be ELISA positive. In a survey involving 316 camels from the Gao and Nara areas, in Mali, a high proportion of animals tested were antigen positive (43.5 and 42.9%, respectively for the mono- and polyclonal antibody-based ELISA) compared to only 22 (7.0%) diagnosed by the parasite detection techniques. Thus, these immunoassays were at least six times more sensitive than the haematocrit centrifugation technique. As a large proportion of cases may be antigen positive but parasite negative, these two of "surra" immunoassays should be used in routine diagnosis in addition to the parasite detection techniques in the dromedary camel.  相似文献   
56.
Coprinites dominicana gen.nov., spec.nov. (Coprinaceae) found in amber from the Dominican Republic is the earliest known gilled mushroom, the first fossil fleshy agaric determinable, and the only kiiown fossil "mushroom" (Agaricales) from the tropics. This find is of significance with respect to the evolutionary development of the Basidiomycetes. Because the appearance of this fossil is quite modern, it suggests that mushrooms as a group probably arose much earlier than the early to mid-Tertiary.  相似文献   
57.
58.
1. A method of freezing semen of individual males was adapted for use under farm conditions using an automated freezing apparatus.

2. An insemination programme to produce high fertility and hatchability with semen which had been deep frozen for 2 months was devised.

3. Over 90% fertile eggs with a 90% hatch of all eggs set was obtained with frozen and thawed semen over a period from the 2nd to the 12th day after the first of four inseminations. The persistency of fertility was also tested and 93, 86.6 and 30.7% of the eggs were fertile during days 2 to 6, 2 to 8 and 9 to 15 after the last insemination.

4. Corresponding with the high fertility rate, chicks were produced by every hen that was inseminated and from every male whose semen was frozen and stored. The implications for future breeding practices of this successful result are discussed.  相似文献   

59.
Summary Serological investigation by the indirect haemagglutination test forToxoplasma antibodies was carried out in a flock of dairy goats. Antibody titres ranging from 1:4 to 1:1,024 were found in 34% of 371 apparently healthy animals. High antibody titres of 1:256 suggestive of recent infection were noted in 18 (4.9%) animals including 13 nannies. The occurrence of a number of non-brucella abortions associated with high serological titres and the isolation of the parasite from the brain tissues of an aborted foetus suggestedToxoplasma as a probable aetiologic factor. Sera having significant levels of haemagglutinating antibodies (1:128) were also found positive to the card agglutination test. Epidemiological aspects and the public health potential of subclinical toxoplasmosis in dairy goats are discussed.
Infecciones Y Abortos En Cabras Lecheras Debido AToxoplasma
Resumen Se realizaron investigaciones serológicas de toxoplasmosis mediante la prueba indirecta de hemaglutinación en un rebaño de cabras lecheras. Se encontraron títulos de 1:4 a 1:1024 en 34% de 371 animales aparentemente sanos. Títulos de 1:256 sugestivos de infecciones recientes, se encontraron en 18 (4.9%) animales, incluyendo 13 hembras paridas. La ocurrencia de un significativo número de abortos no asociados con brucela, títulos serológicos altos de toxoplasmosis y el aislamiento del parásito del cerebro de fetos abortados, sugiere que eltoxoplasma es el factor etiológico más importante. Se discuten aspectos epidemiológicos de importantcia para la salud pública, relacionados con el potencial de la toxoplasmosis (subclínica) en cabras lecheras.

Toxoplasmose Et Avortement Chez Les Chevres Latiteres
Résumé Des investigations sérologiques par la méthode de l'agglutination indirecte pour rechercher des anticorps toxoplasmiques ont été faites sur un troupeau de chèvres laitières. Des anticorps ont été mis en évidence chez 34 p.100 des 371 animaux apparemment sains à des titres allant de 1:4 à 1:1024. Des titres élevés d'anticorps atteignant 1:256 ont été relevés chez 18 (soit 4,9 p.100) des animaux comprenant 13 chèvres, ce qui fait penser à une infection récente.L'existence de nombre d'avortements non-brucelliques associés avec des titres sérologiques élevés et l'isolement du parasite des tittus cérébraux d'un foetus avorté suggerent que les Toxoplasmes en ont probablement été le facteur étiologique. Des sérums ayant des taux significativement élevés d'anticorps agglutinants (1:128) ont également été reconnus comme positifs par le test d'agglutination en EAT. Les aspects épidémiologiques et le danger potentiel pour l'homme de ces cas subcliniques de toxoplasmose chez les chèvres laitières sont discutés.
  相似文献   
60.
1. Dry rabbit excreta were found to contain 188.1 g crude protein, 6.6 g non‐protein nitrogen, 0.3 g ammonia, 89.8 g moisture, 8.0 g ether extractives, 135.2 g crude fibre, 266.9 g ash and 19.18 MJ gross energy/kg. Methionine and lysine contents were 3.95 and 4.29 g/100 g protein, respectively.

2. In one experiment, 0, 50, 100 or 200 g rabbit excreta/kg were substituted for maize in a broiler diet. Chickens receiving the diet containing 200 g rabbit excreta/kg gained significantly less weight to 8 weeks of age than those receiving other diets.

3. In a second experiment, 0, 100, 150 or 200 g rabbit excreta/kg were substituted primarily for maize in a broiler diet to provide equal energy and protein contents. Weight gains to 8 weeks of birds receiving these diets did not differ significantly. The uncorrected metabolisable energy content of the excreta was 9.15 MJ/kg.

4. There were no gross pathological changes in the birds fed on the experimental diets.  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