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   71710篇
  免费   2736篇
  国内免费   35篇
林业   2464篇
农学   2141篇
基础科学   431篇
  8004篇
综合类   13030篇
农作物   2894篇
水产渔业   3488篇
畜牧兽医   36661篇
园艺   867篇
植物保护   4501篇
  2019年   659篇
  2018年   971篇
  2017年   1121篇
  2016年   1074篇
  2015年   920篇
  2014年   1093篇
  2013年   2760篇
  2012年   2060篇
  2011年   2452篇
  2010年   1572篇
  2009年   1547篇
  2008年   2385篇
  2007年   2279篇
  2006年   2137篇
  2005年   2065篇
  2004年   1900篇
  2003年   1949篇
  2002年   1827篇
  2001年   2358篇
  2000年   2211篇
  1999年   1829篇
  1998年   776篇
  1997年   674篇
  1996年   635篇
  1995年   775篇
  1994年   690篇
  1993年   692篇
  1992年   1453篇
  1991年   1439篇
  1990年   1398篇
  1989年   1446篇
  1988年   1258篇
  1987年   1336篇
  1986年   1399篇
  1985年   1328篇
  1984年   1079篇
  1983年   918篇
  1982年   683篇
  1981年   578篇
  1979年   859篇
  1978年   725篇
  1977年   622篇
  1976年   582篇
  1975年   613篇
  1974年   826篇
  1973年   831篇
  1972年   804篇
  1971年   785篇
  1970年   698篇
  1969年   645篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Holm  P.E.  Christensen  T.H.  Lorenz  S.E.  Hamon  R.E.  Domingues  H.C.  Sequeira  E.M.  McGrath  S.P. 《Water, air, and soil pollution》1998,102(1-2):105-115
Soil water concentrations of cadmium and zinc were measured in plant pots with 15 contaminated soils which differed in origin, texture, pH (5.1 – 7.8) and concentrations of cadmium (0.2 – 17 mg Cd kg-1) and zinc (36 – 1300 mg Zn kg-1). The soil waters contained total concentrations of 0.5 to 17 µg Cd L-1 and 9 to 3600 µg Zn L-1, which were dominated by free metal ions as measured by an ion exchange-resin method. Annual leaching outflows were estimated from soil water concentrations to be 0.5 – 17 g Cd ha-1 y-1 and 9 – 3600 g Zn ha-1 y-1 per 100 mm of net percolation, corresponding to 0.1% per year of the total soil content of cadmium and zinc. The measured soil water concentrations of cadmium and zinc did not correlate linearly with the corresponding soil concentrations but correlated fairly well with concentrations measured in Ca(NO3)2 extracts of the soils and with soil water concentrations estimated from soil concentrations and pH. Such concentration estimates may be useful for estimating amounts of cadmium and zinc being leached from soils.  相似文献   
92.
Malignant lymphoma involving bone and heart was diagnosed in a 4-year-old Whippet, using radiography, histologic examination, nuclear scintigraphy of the skeleton and heart, and cardiac ultrasonography.  相似文献   
93.
94.
E. C. Roumen 《Euphytica》1992,64(3):173-182
Summary Neck nodes of eight rice genotypes were inoculated with a virulent isolate of the blast pathogen at four slightly different, increasingly older stages of panicle development shortly after flowering. Resistance to infection as well as resistance to growth of the pathogen after infection was assessed. Significant differences between genotypes were found for both components of resistance. Resistance to growth of the pathogen sharply increased with aging of the neck node as was indicated by a large reduction of the length of the lesions on the culm, but resistance to infection did not change much. The lesion length was closely related to yield loss. A small delay in time of infection can lead to a large decrease in yield reduction. Meaningful comparison of partial resistance to neck blast between genotypes therefore requires infection at an identical stage of panicle development. In the field, where panicles are in different stages of development, selection of genotypes that do show the symptoms of neck blast together with relatively little yield loss in infected panicles is recommended.  相似文献   
95.
In a survey of fungi causing seedling diseases of sugar beet using a soil bioassay, Aphanomyces cochlioides and Pythium spp. were found to occur in 39% and 31%, respectively, of 341 sugar-beet fields selected in a stratified random sample in England, The frequency of A. cochlioides-infested soils varied widely in the different sugar-beet growing areas of the country. Soil pH was the single factor most strongly associated with the distribution of the pathogen, but regression models applied to combinations of factors indicated that soil texture and the interval between sugar-beet crops were also relevant to its frequency. It was detected less often in soils of high pH (≥ 75). heavy texture and where the interval between sugar-beet crops exceeded 5 years. No significant associations were found between the proportion of soils with Pythium spp. and soil or cropping factors.  相似文献   
96.
97.
98.
99.
100.
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