全文获取类型
收费全文 | 1645篇 |
免费 | 82篇 |
国内免费 | 2篇 |
专业分类
林业 | 129篇 |
农学 | 27篇 |
基础科学 | 4篇 |
274篇 | |
综合类 | 177篇 |
农作物 | 87篇 |
水产渔业 | 86篇 |
畜牧兽医 | 801篇 |
园艺 | 33篇 |
植物保护 | 111篇 |
出版年
2023年 | 17篇 |
2022年 | 6篇 |
2021年 | 26篇 |
2020年 | 39篇 |
2019年 | 46篇 |
2018年 | 37篇 |
2017年 | 39篇 |
2016年 | 46篇 |
2015年 | 41篇 |
2014年 | 47篇 |
2013年 | 81篇 |
2012年 | 105篇 |
2011年 | 139篇 |
2010年 | 42篇 |
2009年 | 71篇 |
2008年 | 108篇 |
2007年 | 114篇 |
2006年 | 90篇 |
2005年 | 96篇 |
2004年 | 86篇 |
2003年 | 87篇 |
2002年 | 65篇 |
2001年 | 18篇 |
2000年 | 21篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 19篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 18篇 |
1974年 | 4篇 |
1970年 | 4篇 |
排序方式: 共有1729条查询结果,搜索用时 31 毫秒
91.
Gary E. Glass John A. Sorensen Barbara W. Liukkonen George R. Rapp Jr. Orie L. Loucks 《Water, air, and soil pollution》1986,31(1-2):1-15
Present acid forming emissions to the atmosphere have the potential to alter significantly the chemistry of rain, snow, and surface water of weakly buffered lakes in the Upper Midwest. Average precipitation pH from field measurements during 1979–1983 declined from west to east from 4.8, 4.6, and 4.3 along a cross-section of sites in Minnesota, Wisconsin, and Michigan respectively where 990 lake and stream sampling sites were studied. Measurements of weakly buffered lakes show a parallel decline in lake water pH with the lowest values measured, 5.1, 4.6 and 4.4, respectively in the same regions. Correspondingly, the percentage of lakes sampled with little or no acid neutralizing capacity (ANC) was found to increase from 0 to 4 and 13%, respectively. The geographic patterns in ionic composition of airborne acids and bases, and the resultant surface water concentrations are compared. The acid forming capacity (AFC) from airborne inputs is calculated using mass balance and in-lake processes. Stoichiometric acid-base reactions are used to balance the observed chemical differences between airborne inputs and surface water composition considering nitrification, denitrification, other oxidation-reduction reactions, and the evaporation concentration process. Microbial activity in surface water can result in a net decrease in ionic strength from the conversion of most of the ammonium and nitrate to neutral compounds and biomass, but only a partial reduction of about 20% of the sulfate inputs to weakly buffered lakes. The resulting AFC of airborne inputs are calculated to range from 30 to 60, 50 to 90, and 80 to 130 μeq H+L-l, respectively, in northeastern Minnesota-Ontario, northcentral Wisconsin and northern Michigan-Ontario. The differences in AFC of airborne inputs from west to east, and differences in in-lake processes explain the observed acidity of weakly buffered lakes across the region. 相似文献
92.
Schrader Gritta Hauser Barbara Bahadir Müfit Larink Otto 《Water, air, and soil pollution》2001,128(3-4):401-406
Water, Air, &; Soil Pollution - A filter dust of a waste incineration plant provided for underground disposal was elutriated with three different elutriation media possibly be found in... 相似文献
93.
Effect of arbuscular mycorrhizal fungi (AMF) on heavy metal tolerance of alfalfa (Medicago sativa L.) and oat (Avena sativa L.) on a sewage-sludge treated soil In pot experiments with a sewage sludge treated soil, the influence of two arbuscular mycorrhizal fungi (AMF) isolates of Glomus sp. (T6 and D13) on plant growth and on the uptake of heavy metals by alfalfa (Medicago sativa L.) and oat (Avena sativa L.) was investigated. Alfalfa showed an increase of biomass with mycorrhizal infection only to a small extent. In oat AMF inoculation increased the growth of both root and shoot by up to 70% and 55% respectively. Mycorrhization raised the P-content and -uptake in alfalfa, but not in oat, in both roots and shoots. Mycorrhizal alfalfa showed lower Zn-, Cd- and Ni-contents and uptake in roots and shoots. The root length was significantly decreased in mycorrhizal alfalfa plants (up to 38%). The translocation of heavy metals into the shoot of mycorrhizal alfalfa was slightly increased. Mycorrhizal infection of oat led to higher concentrations of Zn, Cd and Ni in the root but to less Zn in the shoot. The translocation of heavy metals to the oat shoot was clearely decreased by mycorrhizal colonisation. This may be based on the ability of fungal tissues to complex heavy metals at the cell walls, thus excluding metals from the shoot. This conclusion is supported by the enhanced root length (up to 78%) of mycorrhizal oat plants in this experiment. The mycorrhizal infection seemed to protect plants against heavy metal pollution in soils. It was obvious that different host plants reacted in different ways. 相似文献
94.
K. Palanisami Ruth Meinzen-Dick Mark Giordano Barbara Van Koppen C. R. Ranganathan 《Irrigation and Drainage Systems》2011,25(3):121-134
Irrigation tanks in India are common property resources. Tanks provide not only for irrigation, but also forestry, fishing,
domestic water supply, livestock, and other uses. Using empirical results from a study of tank performance from 80 tanks in
Tamil Nadu, South India in two time period: 1996-97 and 2009-10, this paper evaluates tank irrigation system performance in
terms of economic output and revenue generation forirrigation and other uses. The results indicate that irrigation and other
productive uses put together raised the total value of output at tank level by 12 % in 1996-97 and just 6 % in 2009-10. This
may suggest that tank multiple use values are small and getting smaller, and therefore not worth consideration. However, it
was also found that, while declining in absolute terms, non-irrigation uses provided the majority of tax revenues and still
more than cover government's operation and maintenance expenditure (O&M) budget. This finding provides another reason to consider
multiple use values and their linkage with overall system viability. 相似文献
95.
Culliton BJ 《Science (New York, N.Y.)》1983,220(4601):1029
The National Institutes of Health plans to follow up on an Emory University review of John Darsee's research with an investigation of its own. Darsee, caught fabricating data in dog experiments as a Harvard cardiology fellow in 1981, engaged in research on patients while in training at Emory. NIH investigators will try to determine why Darsee's experiments, which allegedly took place at an NIH-funded center, did not come under scrutiny by Emory's institutional review board. 相似文献
96.
97.
Culliton BJ 《Science (New York, N.Y.)》1976,193(4250):300-301
98.
99.
Casassus B 《Science (New York, N.Y.)》2003,299(5614):1823-1824
100.