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   136756篇
  免费   7481篇
  国内免费   84篇
林业   5218篇
农学   4042篇
基础科学   852篇
  14840篇
综合类   28410篇
农作物   5476篇
水产渔业   6279篇
畜牧兽医   69172篇
园艺   1633篇
植物保护   8399篇
  2018年   1596篇
  2017年   1822篇
  2016年   1701篇
  2015年   1477篇
  2014年   1771篇
  2013年   4888篇
  2012年   3457篇
  2011年   4121篇
  2010年   2674篇
  2009年   2622篇
  2008年   3998篇
  2007年   3878篇
  2006年   3739篇
  2005年   3593篇
  2004年   3358篇
  2003年   3505篇
  2002年   3324篇
  2001年   3930篇
  2000年   3838篇
  1999年   3134篇
  1998年   1383篇
  1997年   1309篇
  1995年   1419篇
  1994年   1334篇
  1993年   1277篇
  1992年   2773篇
  1991年   2854篇
  1990年   2855篇
  1989年   2981篇
  1988年   2679篇
  1987年   2745篇
  1986年   2832篇
  1985年   2725篇
  1984年   2231篇
  1983年   1965篇
  1982年   1438篇
  1981年   1301篇
  1979年   2010篇
  1978年   1649篇
  1977年   1464篇
  1976年   1346篇
  1975年   1522篇
  1974年   1933篇
  1973年   1915篇
  1972年   1924篇
  1971年   1842篇
  1970年   1730篇
  1969年   1549篇
  1968年   1232篇
  1967年   1388篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Ohne Zusammenfassung Hoewel dit artikel ook reeds in eenige bladen is gepubliceerd, meenen wij het, in verband met het groote belang, dat aan een ruime bekendmaking van het gebruik van Derris bij de thripsbestrijding in vlas verbonden is, ook in ons Tijdschrift te kunnen opnemen, mede als aanvulling van wat daarin over dit onderwerp reeds verschenen is. Red.  相似文献   
102.
COPYRIGHT     
  相似文献   
103.
104.
Observations on transplacental infection with bluetongue virus in sheep   总被引:1,自引:0,他引:1  
Twenty-four ewes were inoculated with 1 of 2 strains of bluetongue virus type 4 at 40, 60, or 80 days of gestation. Two ewes aborted, 2 ewes died, and 1 was killed during the experiment, but their fetuses were recovered. At term, 2 mummified fetuses, 4 dead lambs, and 17 clinically healthy lambs were produced by 12 sheep, and the remaining 7 sheep were barren. Porencephaly and cerebellar dysgenesis were found in term lambs born to sheep inoculated at 40 and 60 days of gestation. Radiographic examination of 12 fetuses showed developmental ages far less than their chronologic age; 8 fetuses had skeletal growth-retardation lines, which were also observed in the dead lambs. A systemic lymphoreticular hyperplasia was observed in the dead lambs and in all lambs at 12 weeks of age; in 4 of the latter, granulomatous reactions were present in the liver and kidney. Lungs of the full-term lambs were reduced in weight and showed poor alveolar development and mononuclear cell infiltration, which persisted in the 12-week-old lambs. It was concluded that bluetongue virus is capable of causing not only gross abnormalities of the CNS, but also generalized growth retardation and fetal lymphoreticular hyperplasia.  相似文献   
105.
106.
Antigens in the extracellular protein (ECP) complexes of Bacteroides nodosus, isolated from sheep with either benign or virulent footrot, were studied by immunoelectrophoresis (IEP). Rabbit antisera against ECP from virulent and benign strains, were used in homologous and heterologous crossed IEP. Four precipitin peaks unique to the virulent strain, and five peaks unique to the benign strain were identified. In an attempt to characterize the different antigens in ECP, rabbit antisera were raised against an outer membrane protein (OMP, mol. wt. 35 000 daltons), pili and various proteases of virulent and benign strains of B. nodosus. No precipitin band was observed when ECP from both B. nodosus strains were reacted against anti-OMP and anti-pilus antisera. However, single precipitin bands unique to one protease from the benign strain and one protease from the virulent strain were identified. The results suggest that specific antigens other than proteases or pili are important in determining whether a B. nodosus isolate is virulent or benign.  相似文献   
107.
Isolated dog neutrophils exposed to known chemotactic factors assumed a bipolar configuration in suspension. This response was initiated within 2 minutes with a gradual return to spherical shape. The rate of return to sphere was positively correlated with the dose of stimulant. Dog neutrophils exposed to N-formylmethionyl-leucyl-phenylalanine (fMLP) did not adapt to bipolar conformation and did not bind radiolabeled fMLP. These findings are consistent with other species (pig and cow) that also did not respond to fMLP.  相似文献   
108.
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   
109.
Disseminated Aspergillus terreus infection was diagnosed in ten previously healthy adult dogs--nine German shepherds and one dalmatian. The disease was characterized by the presence of multiple granulomas and infarcts in a wide range of organs. The kidney, spleen, and skeletal system were most commonly and severely affected. Fungal hyphae were demonstrated in large numbers within granulomas and thrombi, and A. terreus was readily isolated by culture. This disseminated mycosis appears unique; in this series of cases there was no apparent predisposing factor, portal of entry, or primary focus for dissemination of the infection.  相似文献   
110.
A steam-dryer, designed and manufactured in Sweden, was evaluated for destroying Bursaphelenchus xylophilus in pine chips from southern USA. In a trial, pine chips were treated at different temperature and pressure regimes for 5 or 10min. The lowest time/temperature/pressure combination was to increase the vessel temperature from 85 to 104°C in 5 min at low pressure. Samples of pine chips were assayed for nematodes in laboratories in USA, Sweden, and Finland. No nematodes of any species were recovered from any of the treated pine-chip samples. Large and heterogeneous pieces of wood in the treated samples were also nematode-free. The apparatus was a prototype capable of handling about 400 kg h-1. The final version would have to be able to process 100-200 th-1.  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