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   322882篇
  免费   17516篇
  国内免费   693篇
林业   24600篇
农学   14269篇
基础科学   3010篇
  46792篇
综合类   45492篇
农作物   17495篇
水产渔业   18368篇
畜牧兽医   138617篇
园艺   6558篇
植物保护   25890篇
  2019年   3752篇
  2018年   4346篇
  2017年   4715篇
  2016年   5049篇
  2015年   4516篇
  2014年   5918篇
  2013年   16625篇
  2012年   7914篇
  2011年   10243篇
  2010年   7995篇
  2009年   8436篇
  2008年   9561篇
  2007年   8753篇
  2006年   9262篇
  2005年   8432篇
  2004年   8254篇
  2003年   8010篇
  2002年   7443篇
  2001年   8518篇
  2000年   8188篇
  1999年   7244篇
  1998年   4411篇
  1997年   4456篇
  1996年   4146篇
  1995年   4813篇
  1994年   4279篇
  1993年   3961篇
  1992年   5928篇
  1991年   6222篇
  1990年   6060篇
  1989年   6028篇
  1988年   5489篇
  1987年   5564篇
  1986年   5596篇
  1985年   5667篇
  1984年   5033篇
  1983年   4626篇
  1982年   3574篇
  1981年   3384篇
  1980年   3318篇
  1979年   4518篇
  1978年   3881篇
  1977年   3508篇
  1976年   3196篇
  1975年   3208篇
  1974年   3915篇
  1973年   3949篇
  1972年   3729篇
  1971年   3535篇
  1970年   3353篇
排序方式: 共有10000条查询结果,搜索用时 317 毫秒
221.
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   
222.
Des informations sur la biologie et la diffusion des principaux insectes nuisibles aux eucalyptus en Italie sont données, ainsi que sur l'importance de leurs dégats et sur les méthodes de lutte les plus couramment employées. En plus des quelques espèces polyphages, qui peuvent causer des dégats sporadiques, les phytophages vivant exclusivement aux dépens d'Eucalyptus spp. en Italie sont Phoracantha semipunctata, Gonipterus scutellatus et Ctenarytaina eucalypti. La première espèce est nuisible aux eucalyptus cultivès pour la production du bois et est répandue en Italie centrale et méridionale, en Sicile et en Sardaigne, alors que les deux autres espèces endommagent surtout les eucalyptus destinés aux marchés de fleurs (fleurs et rameaux) et ne sont prèsentes qu'en Ligurie occidentale. La lutte contre P. semipunctata est conduite par des interventions d'ordre sylvicultural, consistant essentiellement è recéper des peuplements sérieusement attaqués; le parasite oophage Patasson nitens, importé d'Afrique du Sud, permet de controler G. scutellatus alors que les larves de plusieurs syrphes prédatrices agissent efficacement contre C. eucalypti.  相似文献   
223.
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   
224.
Twenty stifles (10 dogs) were studied for a period of 1 year after various lesions of the cranial cruciate ligament and medial meniscus were produced surgicaoy. Through serial arthroscopic evaluations, degenerative processes In stifles with a "torn" cranial cruciate ligament were documented. Intra-articular changes were minimal after partial meniscectomy and were severe after total meniscectomy. Multiple arthroscopies caused no demonstrable changes.  相似文献   
225.
226.
陈向新 《油气储运》1994,13(5):32-34
随着输气管道建设的发展,管道自身及其周围建筑物的安全保证问题,已引起人们高度重视,关于管道安全保证有两种指导思想:①距离安全保证模式,其设防原则是对管道自身强度有一定要求,主要通过控制不同压力,不同管径的管距建筑物的相应距离来保证管道及附近建筑物的安全;②强度安全保证模式,其设防原则是在管道设计,材料及设备选用,施工,检验,生产到更新改造的全过程中,对管道的强度和严密性有严格的要求,为管道系统及周  相似文献   
227.
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   
228.
Antiserum to a partially purified neuraminidase fromPasteurella multocida, type A:3, was adsorbed with protease-digestedP. multocida type 3 lipopolysaccharide (LPS) to remove LPS immunoreactivity. The LPS-adsorbed antineuraminidase caused a 77% reduction in the neuraminidase activity of homologousP. multocida in anin vitro enzyme neutralization test. All 14 mice passively immunized with the adsorbed antineuraminidase were protected against challenge infection with homologousP. multocida in a mouse protection test. Ten out of 14 mice in one group that received antisera containing antibodies to both neuraminidase and LPS were protected. In contrast, only 1 out of 14 mice that were immunized with pre-immune serum survived the challenge. These results suggest that antiserum toP. multocida neuraminidase was, at least partly, responsible for the protection observed in this study. Neuraminidase may be one of the immunogenic protective proteins present in aqueous extracts ofPasteurella multocida.  相似文献   
229.
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   
230.
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