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   148832篇
  免费   7824篇
  国内免费   84篇
林业   6214篇
农学   4366篇
基础科学   933篇
  16665篇
综合类   28320篇
农作物   5713篇
水产渔业   6747篇
畜牧兽医   77104篇
园艺   1766篇
植物保护   8912篇
  2018年   1857篇
  2017年   1982篇
  2016年   1858篇
  2015年   1669篇
  2014年   1890篇
  2013年   5639篇
  2012年   3756篇
  2011年   4622篇
  2010年   3014篇
  2009年   2965篇
  2008年   4552篇
  2007年   4271篇
  2006年   4018篇
  2005年   3785篇
  2004年   3825篇
  2003年   3810篇
  2002年   3693篇
  2001年   4501篇
  2000年   4523篇
  1999年   3483篇
  1998年   1501篇
  1997年   1514篇
  1995年   1717篇
  1994年   1586篇
  1993年   1535篇
  1992年   3163篇
  1991年   3439篇
  1990年   3330篇
  1989年   3385篇
  1988年   3084篇
  1987年   3083篇
  1986年   3276篇
  1985年   3191篇
  1984年   2598篇
  1983年   2419篇
  1982年   1573篇
  1981年   1500篇
  1979年   2370篇
  1978年   1941篇
  1977年   1654篇
  1976年   1641篇
  1975年   1688篇
  1974年   2155篇
  1973年   2185篇
  1972年   2145篇
  1971年   2024篇
  1970年   1946篇
  1969年   1793篇
  1968年   1500篇
  1967年   1570篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Acute viral hepatitis was diagnosed in five California sea lions (Zalophus californianus) stranded along the Los Angeles coast. Light microscopy revealed large nuclear inclusion bodies in hepatocytes. Electron microscopy provided evidence that these inclusion bodies were composed of adenovirus-like virions. Attempts to grow the virus in cell culture systems were unsuccessful.  相似文献   
942.
943.
944.
The data on health problems from visual livestock inspection at an auction mart in Saskatchewan during a two year period were tabulated for swine, cattle and calves. The major conditions seen in swine were underweight animals, infectious diseases or congenital abnormalities. Infectious diseases such as Hypoderma spp. infestations, ringworm or eye infections were the primary troubles in older cattle. Young calves demonstrated a predominance of congenital (herniation) and infectious (enteritis or navel infection) diseases.  相似文献   
945.
946.
947.
Birth difficulty and poor lamb vigour are significant causes of perinatal lamb mortality. In this study we investigated whether sheep breeds differing in appearance, muscularity and selection history also had differences in dystocia and lamb vigour, and considered some of the factors that may contribute to the variation in these traits. Data were collected at birth from a total of 3252 lambs of two terminal sire breeds selected for lean growth (Suffolk [S], n = 500 and Texel [T], n = 1207), from a Hill breed (Scottish Blackface [B], n = 610), which has been mainly selected for hardiness, and a crossbred (Mule × T [M], n = 935) representing a maternal line. For each lamb the degree of assistance at delivery, lamb presentation, amount of assistance to achieve successful sucking, sex, litter size and birth weight were recorded. T lambs required the most, and B and M lambs the least assistance at birth, S lambs were intermediate (% lambs assisted: T = 55.7, S = 30.7, B = 22.7, M = 24.9, P < 0.001). T and S lambs were equally likely to be malpresented at birth (29% of births) and more likely to be malpresented than B or M lambs (20%; P < 0.001). In T and S breeds lambs requiring veterinary assistance at delivery were mainly heavy and singleton lambs, whereas in B and M breeds these were exclusively low birth weight lambs in multiple litters. Although heavier lambs needed greater birth assistance, T lambs were lighter than S and M lambs, but heavier than B lambs (birth weight (kg): S = 4.66, M = 4.56, T = 4.32, B = 3.67, P < 0.001). S lambs were more likely to require assistance with sucking than other breeds, and T lambs also required more assistance than B or M lambs (% lambs assisted to suck: S = 56.0, T = 31.6, M = 19.8, B = 18.4, P < 0.001). Heavier lambs were more likely to suck unaided than lighter lambs (P < 0.001). The data suggest that the two terminal sire breeds, selected narrowly for greater productivity (muscle growth and conformation), are more likely to experience birth difficulty and poorer lamb vigour than the breed selected for hardiness, or the cross breed. Whether these effects arise as a consequence of genetic selection (e.g. for specific lamb conformation), or as a result of management practices to achieve selection goals (e.g. increased intervention at lambing) is unknown. Specific actions to improve birth difficulty and lamb vigour, such as including these traits in the selection index, would be beneficial in improving the welfare of ewes and lambs of the terminal sire breeds.  相似文献   
948.
Blood from calves infected with Theileria annulata and T parva was freed from host cell elements and the piroplasms liberated from the red cells by ammonium chloride lysis. Lysates of the purified piroplasms and control host cell material were examined electrophoretically for several enzymes. Zymograms stained for glucose phosphate isomerase showed distinct differences between the host cell enzyme pattern and parasite enzyme patterns. The isoenzyme pattern of T annulata piroplasms differed from the isoenzyme pattern of T parva piroplasms.  相似文献   
949.
While both Brucella abortus and Yersinia enterocolitica IX have O antigens in common, they differ significantly with respect to motility. Thus Br abortus is always non-motile while Y enterocolitica is motile when grown at room temperature. The presence of yersinia H agglutinins in serum can be shown to be evidence of previous exposure to Y enterocolitica. These agglutinins are not generated by brucella infection. A rapid H agglutination test will serve to provide this differentiation without interference from cross-reacting O antigens.  相似文献   
950.
Glanzmann thrombasthenia (GT) is characterized by a defect of platelet aggregation. This autosomal recessive genetic disorder is caused by an abnormality of the platelet glycoprotein receptors alpha IIb or beta III. Recently, we identified a horse with clinical and pathological features of GT. The aim of this study was to describe this case of GT at the molecular level. A point mutation from G to C in exon 2 of ITGA2B causing a substitution of the expected amino acid arginine 72 (Arg(72)) by a proline (Pro(72)) was encountered. This amino acid change may result in abnormal structural conformations that yield an inactive alpha IIb subunit. The genomic DNA analysis showed that this horse was homozygous for the missense mutation.  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