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   77106篇
  免费   4257篇
  国内免费   40篇
林业   3676篇
农学   2659篇
基础科学   513篇
  9917篇
综合类   12453篇
农作物   2810篇
水产渔业   4131篇
畜牧兽医   38930篇
园艺   1089篇
植物保护   5225篇
  2019年   722篇
  2018年   1214篇
  2017年   1264篇
  2016年   1219篇
  2015年   1058篇
  2014年   1297篇
  2013年   2877篇
  2012年   2482篇
  2011年   2992篇
  2010年   1962篇
  2009年   1965篇
  2008年   3013篇
  2007年   2812篇
  2006年   2740篇
  2005年   2481篇
  2004年   2543篇
  2003年   2487篇
  2002年   2381篇
  2001年   2431篇
  2000年   2422篇
  1999年   1983篇
  1998年   960篇
  1997年   863篇
  1996年   824篇
  1995年   906篇
  1994年   880篇
  1993年   808篇
  1992年   1552篇
  1991年   1571篇
  1990年   1694篇
  1989年   1535篇
  1988年   1471篇
  1987年   1365篇
  1986年   1403篇
  1985年   1365篇
  1984年   1153篇
  1983年   1046篇
  1982年   647篇
  1979年   1023篇
  1978年   809篇
  1977年   732篇
  1976年   686篇
  1975年   729篇
  1974年   774篇
  1973年   846篇
  1972年   808篇
  1971年   754篇
  1970年   731篇
  1969年   744篇
  1967年   658篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Three strip test kits which measure calcium and/or magnesium in mares' mammary secretions were compared and assessed for their accuracy in:- 1) measuring these electrolytes compared to standard laboratory measurements, and 2) predicting the time of parturition. Daily samples of mammary secretions were obtained pre-partum from 35 Thoroughbred mares and allocated a score. Measurement of mammary secretion calcium and/or magnesium by the strip tests and laboratory methods correlated significantly (P less than 0.001). The results obtained for prediction of parturition were analysed by two methods. Method i) indicated that the majority of mares had a maximum score on the day of birth. However, the second method of analysis included all prepartum scores and this demonstrated that maximum scores occurred on more occasions prior to the day of birth than on the day of birth itself. The number of nights spent attending mares, and the percentage of occasions when foaling was missed, were also calculated for given strip test scores. The results indicate that the test kits are not particularly accurate in predicting time of parturition although they are a reliable means of measuring mammary secretion calcium and/or magnesium. It is suggested that the test kits may be more helpful by indicating when it is not necessary to attend mares at night.  相似文献   
52.
The ultrastructure of sarcocysts of macro- and microscopic species of Sarcocystis was compared from naturally infected water buffalo from India. Grossly visible sarcocysts had walls consisting of cauliflower-like villar protrusions, typical of S. fusiformis. The sarcocyst wall of the microscopic species of Sarcocystis was 6.4 microns thick and consisted of tightly packed conical villar protrusions that were 9.6 microns long and 3.7 microns wide at the base. At approximately 3 microns above the base, the distal two-thirds of the villar protrusion became conical shaped and was bent laterally at an angle of 45 degrees to the sarcocyst surface. The granular layer beneath the villar protrusions was 0.9 microns thick. In S. levinei the granular layer was 1.9 microns thick, the villar protrusions were narrow and it had a highly undulating primary cyst wall. Whether the microscopic S. levinei-like sarcocysts of Indian and Malaysian water buffalo are distinct species of Sarcocystis will require further investigation.  相似文献   
53.
Calcium fluxes were measured, in vivo, in both directions across the ovine reticulorumen wall of four sheep when the luminal potassium concentration was either 30 mmol litre-1 or 90 mmol litre-1. Neither fluxes were affected by an increased potassium concentration although net magnesium absorption was decreased (PO less than 0.05) and the transmural potential difference was increased (P less than 0.01) under these conditions. The results obtained suggest that, unlike magnesium, calcium is transported bidirectionally across ovine ruminal tissue independently of the transmural potential difference across the rumen wall.  相似文献   
54.
55.
Summary Virulent rinderpest virus was detected by immunoperoxidase staining of microtitre bovine kidney cell cultures within 24 to 48 hours of inoculation with prescapular lymph node and spleen homogenates from experimentally infected steers. Rinderpest virus specific cytopathic effects were evident from 48 hours in microtitre plates and from 72 hours in rolled tube cultures. Nasal and ocular secretions collected from cattle naturally infected with rinderpest and inoculated into bovine kidney cell cultures did not readily yield cytopathic virus in both tubes and microtitre plates, but immunoperoxidase staining of microtitre cultures on the fourth day of inoculation detected replication of virus in cultures inoculated with ocular and nasal secretions from seven of 17 cattle tested.
Resumen Se detectó el virus virulente de mediante la tinción con inmunoperoxidasa de cultivos de células de ri?ón bovino en bandejas de microtitulación, después de la inoculación de estos con suspensiones homogenizadas de ganglios linfáticos preescapulares y de bazo provenientes de novillos infectados experimentalmente. El efecto citopático del virus de la peste bovina fue evidente desde las 48 horas en bandejas de microtitulación y desde las 72 horas en tubos de cultivo giratorios. Secreciones oculares y nasales colectadas de ganado infectado en forma natural con la peste bovina e inoculadas en cultivos de células de ri?ón bovino, no mostraron efecto citopático fácilmente en tubos giratorios o bandejas de microtitulación, pero la tinción de las bandejas con inmunoperoxidasa reveló replicación del virus a partir del cuarto día de inoculación con secreciones oculares y nasales en siete de los 17 animales examinados.

Résumé Un virus bovipestique virulent a été décelé par le test de coloration à l'immunoperoxydase de cellules rénales bovines en culture dans des plaques de microtitrage et infectées 48 heures plus t?t avec des homogénats de ganglions lymphatiques et de rate provenant de bouvillons infectés expérimentalement. Les effets cytopathogènes du virus étaient évidents au bout de 48 h dans les plaques de microtitrage et 72 h dans les tubes en rollers. Les sécrétions nasales et oculaires prélevées sur du bétail infecté naturellement par la peste bovine et inoculées sur des cellules rénales bovines n'ont pas toujours montré d'effet cythopathogène aussi bien dans les tubes que dans les plaques de microtitrage. Cependant, la coloration à la peroxydase au jour 4 après l'inoculation a permis de déceler la présence de virus dans 7 cas sur 17.
  相似文献   
56.
As anaerobic sampling and culture techniques improved, the documented prevalence of anaerobic bacteria in periodontal disease has increased. The anaerobic bacteria have become more well-known in humans and consequently in dogs, since this species is a major model in periodontal studies. A review of the literature related to anaerobic flora is described.  相似文献   
57.
The contamination of poultry in the Netherlands with Salmonella enteritidis was tested. For this, different methods (detection of S. enteritidis in faecal samples of 25 g; detection of S. enteritidis in cloacal swabs; detection of S. enteritidis by serological testing of antibodies in serum) were compared for their efficiency to detect S. enteritidis in flocks of poultry. Testing of faecal samples clearly yielded the best results. This method was used in a transmission study, in which 14 flocks descending from a contaminated primary mother flock were screened for the presence of S. enteritidis. The method was also used for screening 49 flocks of laying hens and 52 flocks of broiler chickens throughout the Netherlands. From the transmission study it became clear that S. enteritidis, phage type 2 (Dutch phage set) was isolated both from the mother flock and from five of the descendent flocks. Screening of poultry flocks for the presence of salmonella revealed that salmonella was present in 47% of the layer flocks and in 94% of the broiler flocks. S. enteritidis was isolated from 15% of the flocks screened.  相似文献   
58.
The practice of small animal theriogenology is rewarding, but frustrations exist concerning technologic advances as compared with other species. Reproductive clinicians striving to practice good quality medicine readily identify topics of common concern: causes that are not identified or therapeutics that are not available or applicable. Improved collaboration among theriogenologists specializing in small animal practice is evidenced by growing attendance at national and international scientific meetings, increased scientific publications, and internet communications.  相似文献   
59.
An ammonium sulfate fraction of Taenia hydatigena cyst fluid (ThFAS) was further fractionated by hydrophobic interaction chromatography, using alkylagarose and omega-amino alkylagarose columns, in an effort to isolate and purify a specific diagnostic antigen in the ThFAS preparation. The less than 12 kDa antigen was found to have an affinity for immobilized alkanes with chain length of six carbons or greater. The antigen was recovered in an ethylene glycol eluate from a hexylagarose column then analyzed by Western blot; it reacted with bovine and human cysticercosis infection sera and with specific monoclonal antibodies but not with control sera or fascioliasis infection sera. When the eluate was used as coating antigen in a plate ELISA assay no false positive reactions were seen in sera from cattle infected with Fasciola hepatica; false positive reactions were observed for the unfractionated ThFAS antigen preparation.  相似文献   
60.
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