全文获取类型
收费全文 | 148232篇 |
免费 | 8235篇 |
国内免费 | 133篇 |
专业分类
林业 | 5698篇 |
农学 | 4345篇 |
基础科学 | 901篇 |
16856篇 | |
综合类 | 28552篇 |
农作物 | 5970篇 |
水产渔业 | 6904篇 |
畜牧兽医 | 76557篇 |
园艺 | 1783篇 |
植物保护 | 9034篇 |
出版年
2019年 | 1352篇 |
2018年 | 1992篇 |
2017年 | 2279篇 |
2016年 | 2034篇 |
2015年 | 1787篇 |
2014年 | 2239篇 |
2013年 | 5442篇 |
2012年 | 4086篇 |
2011年 | 4960篇 |
2010年 | 3203篇 |
2009年 | 3271篇 |
2008年 | 4850篇 |
2007年 | 4604篇 |
2006年 | 4412篇 |
2005年 | 4111篇 |
2004年 | 3953篇 |
2003年 | 4012篇 |
2002年 | 3753篇 |
2001年 | 4569篇 |
2000年 | 4547篇 |
1999年 | 3642篇 |
1998年 | 1499篇 |
1997年 | 1442篇 |
1996年 | 1351篇 |
1995年 | 1570篇 |
1994年 | 1407篇 |
1993年 | 1441篇 |
1992年 | 2974篇 |
1991年 | 3163篇 |
1990年 | 3026篇 |
1989年 | 3066篇 |
1988年 | 2703篇 |
1987年 | 2837篇 |
1986年 | 2944篇 |
1985年 | 2848篇 |
1984年 | 2249篇 |
1983年 | 2035篇 |
1982年 | 1433篇 |
1979年 | 2071篇 |
1978年 | 1639篇 |
1977年 | 1408篇 |
1975年 | 1438篇 |
1974年 | 1831篇 |
1973年 | 1861篇 |
1972年 | 1843篇 |
1971年 | 1766篇 |
1970年 | 1701篇 |
1969年 | 1553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