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   96014篇
  免费   4076篇
  国内免费   51篇
林业   7862篇
农学   3710篇
基础科学   530篇
  11455篇
综合类   16561篇
农作物   5200篇
水产渔业   5257篇
畜牧兽医   40983篇
园艺   1995篇
植物保护   6588篇
  2018年   3589篇
  2017年   3629篇
  2016年   2100篇
  2015年   943篇
  2014年   1094篇
  2013年   2888篇
  2012年   2657篇
  2011年   4356篇
  2010年   3462篇
  2009年   2563篇
  2008年   3503篇
  2007年   3794篇
  2006年   2156篇
  2005年   2127篇
  2004年   2006篇
  2003年   2113篇
  2002年   1908篇
  2001年   2333篇
  2000年   2357篇
  1999年   1916篇
  1998年   724篇
  1997年   723篇
  1995年   868篇
  1993年   723篇
  1992年   1515篇
  1991年   1570篇
  1990年   1679篇
  1989年   1662篇
  1988年   1545篇
  1987年   1485篇
  1986年   1545篇
  1985年   1538篇
  1984年   1263篇
  1983年   1159篇
  1982年   782篇
  1981年   722篇
  1979年   1259篇
  1978年   989篇
  1977年   866篇
  1976年   813篇
  1975年   920篇
  1974年   1208篇
  1973年   1250篇
  1972年   1262篇
  1971年   1190篇
  1970年   1108篇
  1969年   1012篇
  1968年   873篇
  1967年   915篇
  1966年   848篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Ohne Zusammenfassung Bergleiche Auguftheft diefer Bl?tter, in melchem gleichfalls auf die Wichtigfeit diefes Qegenftandes hingemiefen murde. Die Red.  相似文献   
73.
74.
75.
76.
77.
78.
Crystalluria results from oversaturation of urine with crystallogenic substance. However, oversaturation may occur as a result of in vitro as well as in vivo events. The microscopic appearance of crystals only represents a tentative identification of their composition because variable conditions associated with their formation, growth, and dissolution may alter their appearance. Definitive identification is dependent on physical methods such as optical crystallography, x-ray diffraction, and electron microscopic analysis.  相似文献   
79.
The association of tumor-associated antigen (TAA) on the proliferation of BLV-infected lymphoblastoid B-cell lines (BL2M3 and BL312) was investigated. Flow cytometric analysis of the expression of TAA with monoclonal antibody (mAb) c143 showed high expression of TAA on the surfaces of BL2M3 and BL312 cells. A large amount of TAA was found in the culture supernatant of BL2M3 and BL312 cells as well as in the lysates of BL2M3 and BL312 cells. Culture supernatant but not lysates of BL2M3 and BL312 cells promoted the growth of either BL2M3 cells or BL312 cells. Furthermore, this growth promoting activity in culture supernatants of BL2M3 and BL312 cells was inhibited in a dose-dependent manner when cultured with mAb c143. These results suggested that TAA may be involved in the growth factor-mediated cell growth of bovine B-lymphoblastoid cell lines expressing TAA on their cell surface.  相似文献   
80.
Hyperchylomicronaemia was identified in a four-week-old Siamese kitten with lethargy, in-appetence, hindlimb ataxia and profound anaemia. The kitten was euthanased and at necropsy a thrombus was found occluding the caudal aorta. Two littermates later presented with lethargy, inappetence and hypertriglyceri-daemia which resolved after being weaned on to a low fat diet. A similar condition was subsequently diagnosed in a kitten born to the same sire but a different queen. The expression of hyperchylomicronaemia in two related litters was suggestive of an inherited, familial defect in the function of lipoprotein lipase (LPL). The activity of this enzyme was reduced in all three parents, the two recovered cases and two related, but apparently unaffected kittens, compared with a control group of unrelated cats belonging to the breeder. This reduction in activity was not attributable to defective activation of LPL by its serum cofactor apolipoprotein C-II or the presence in plasma of a factor that inhibited LPL. The gene that codes for LPL was examined by restriction fragment length polymorphism analysis using a human LPL cDNA probe. The results showed that the cat has a similar, but not identical, LPL gene to man. However, there were no differences in the restriction fragment patterns obtained from affected, unaffected and control animals.  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