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   148095篇
  免费   8207篇
  国内免费   133篇
林业   5694篇
农学   4342篇
基础科学   901篇
  16852篇
综合类   28538篇
农作物   5969篇
水产渔业   6900篇
畜牧兽医   76431篇
园艺   1778篇
植物保护   9030篇
  2019年   1349篇
  2018年   1990篇
  2017年   2271篇
  2016年   2030篇
  2015年   1785篇
  2014年   2237篇
  2013年   5437篇
  2012年   4080篇
  2011年   4951篇
  2010年   3197篇
  2009年   3267篇
  2008年   4838篇
  2007年   4601篇
  2006年   4403篇
  2005年   4104篇
  2004年   3945篇
  2003年   4008篇
  2002年   3749篇
  2001年   4567篇
  2000年   4540篇
  1999年   3635篇
  1998年   1499篇
  1997年   1440篇
  1996年   1350篇
  1995年   1570篇
  1994年   1407篇
  1993年   1440篇
  1992年   2974篇
  1991年   3162篇
  1990年   3024篇
  1989年   3061篇
  1988年   2701篇
  1987年   2835篇
  1986年   2942篇
  1985年   2848篇
  1984年   2246篇
  1983年   2031篇
  1982年   1431篇
  1979年   2070篇
  1978年   1639篇
  1977年   1407篇
  1975年   1437篇
  1974年   1831篇
  1973年   1861篇
  1972年   1843篇
  1971年   1766篇
  1970年   1700篇
  1969年   1552篇
  1968年   1299篇
  1967年   1348篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
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   
15.
16.
17.
Soil pH declined from 5.9 to 5.0 in 8 years beneath plantations of Eucalyptus saligna (Sm.) in Hawaii. In stands of Albizia falcataria, (L.) Fosberg, the soil pH change was more dramatic, declining from 5.9 to 4.6. We measured several components of soil acidity beneath four mixtures of the two tree species to gain insight on the processes responsible for the decline in soil pH. These components were studied using an empirical method of comparing acid quantity, degree of neutralization (depletion of base cations), and acid strength. The decline in soil pH differed between species as a result of differences in the degree of neutralization of the soil exchange complex; the larger decrease in soil pH under Albizia was produced by greater acidification of the exchange complex. Empirical titration curves suggested that differences in acid strength moderated the divergence in soil pH beneath the species. Had the acids accumulating in the soil under Albizia been as strong as those in the Eucalyptus soil, the difference in soil pH would have been greater. Though the two species had contrasting effects on soil pH, the differences in degree of neutralization, responsible for the pH decline, were small compared with differences in the amount of cations stored in tree biomass. Continued supply of nutrient cations (from weathering or fertilization) will ultimately control both the extent of soil pH decline and the level of productivity sustained by the forest.  相似文献   
18.
Abstract. A two year field experiment was carried out in a semiarid Mediterranean area in order to evaluate, the effect on soil erosion of adding different urban organic wastes: a stabilized municipal waste (compost), an unstabilized municipal waste, and an aerobic sewage sludge. All the treatments significantly reduced soil erosion, compared to the control soil. The soil amended with compost was the most effective treatment, reducing soil loss by 94% and runoff by 54%.  相似文献   
19.
Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.  相似文献   
20.
Nephrogenic diabetes insipidus is characterized by polyuria, hyposthenuria and compensatory polydipsia. With conventional clinical and laboratory examinations the diagnosis can be established and the differential diagnostic diseases excluded. In order to verify the diagnosis, differentiate the condition from central and nephrogenic diabetes insipidus and rule out psychogenic polydipsia, additional laboratory studies are required: of these, the concentration test, modified Carter-Robbins test and AVP stimulation test are described.  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