全文获取类型
收费全文 | 190244篇 |
免费 | 10930篇 |
国内免费 | 836篇 |
专业分类
林业 | 7947篇 |
农学 | 6309篇 |
基础科学 | 1418篇 |
24090篇 | |
综合类 | 31831篇 |
农作物 | 7176篇 |
水产渔业 | 9428篇 |
畜牧兽医 | 98930篇 |
园艺 | 2669篇 |
植物保护 | 12212篇 |
出版年
2020年 | 1708篇 |
2019年 | 2069篇 |
2018年 | 3022篇 |
2017年 | 3412篇 |
2016年 | 3098篇 |
2015年 | 2811篇 |
2014年 | 3349篇 |
2013年 | 7601篇 |
2012年 | 6128篇 |
2011年 | 7357篇 |
2010年 | 5039篇 |
2009年 | 4945篇 |
2008年 | 7020篇 |
2007年 | 6799篇 |
2006年 | 6290篇 |
2005年 | 5808篇 |
2004年 | 5464篇 |
2003年 | 5557篇 |
2002年 | 5141篇 |
2001年 | 6123篇 |
2000年 | 6047篇 |
1999年 | 4880篇 |
1998年 | 1960篇 |
1997年 | 1907篇 |
1996年 | 1779篇 |
1995年 | 2058篇 |
1994年 | 1782篇 |
1993年 | 1804篇 |
1992年 | 3715篇 |
1991年 | 4010篇 |
1990年 | 3929篇 |
1989年 | 3920篇 |
1988年 | 3606篇 |
1987年 | 3635篇 |
1986年 | 3633篇 |
1985年 | 3368篇 |
1984年 | 2804篇 |
1983年 | 2437篇 |
1982年 | 1641篇 |
1979年 | 2429篇 |
1978年 | 1921篇 |
1977年 | 1653篇 |
1976年 | 1658篇 |
1975年 | 1721篇 |
1974年 | 2120篇 |
1973年 | 2181篇 |
1972年 | 2118篇 |
1971年 | 1883篇 |
1970年 | 1916篇 |
1969年 | 1773篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
Concentrations of DDT, TDE, DDE, and sigma DDT were determined in homogenized whole fish samples of 129 northern pike (Esox lucius). These fish were netted between June 1974 and June 1975 in the first 10 km of the Richelieu River flowing in Canadian territory. Two years after the banning of DDT, sigma DDT levels ranged from 0.2 ppm fresh body weight in two-year-old specimens to 1.5 ppm in a six-year-old pike. Residues increased greatly with age, and significant seasonal variations in the sigma DDT levels were found in five- and six-year-old pike. 相似文献
962.
Exposure of Israeli agricultural spray pilots and ground crews to parathion was studied. Measurements were made with personal samplers contianing wet midget impingers; samples were analyzed by gas chromatography. Cockpit air exposure levels during 11-21-minute sampling periods for 12 flights ranged from nearly 0 to 430 microgram/m3. During sampling periods of 30 minutes to 4 hours the threshold limit value (TLV) of 100 microgram/m3 was exceeded in 2 of 19 instances. In seven measurements of ground crew exposures, TLV was not exceeded. Air washing with parathion resulted in airborne contamination of the ground level area at more than three times the TLV. Skin exposure data suggested that this route of exposure was significant for ground crew workers but not for pilots. Calculations based on the present data and standard absorption formula suggested that total daily intake for ground crew, but not for pilots, exceeded the Accepted Daily Intake (ADI) of 5 microgram/kg body weight. Sources of exposure and contamination for ground crew and pilots were identified. Recommended environmental control measures for parathion exposure should include cockpit air filtration, modification in flight patterns, paving landing areas, installation of hosing and drainage, NaOH neutralization point, and separate loading and unloading sites. Personal control measures were suggested as a supplement. 相似文献
963.
964.
965.
Continuous estimates were obtained of zooplankton abundance, chlorophyll fluorescence, and water temperature along 10-to 100-kilometer transects of the North Sea. Spectral analysis methods were applied to the data. The "patchiness" of the plankton was distributed over all the length scales resolved with no indication of a characteristic patch size. The relative intensity of the zooplankton patchiness was greater than that of the phytoplankton at all spatial scales, with this difference becoming progressively greater for finer-scale features. In the North Sea data, the concentrations of phytoplankton and zooplankton consistently showed negative spatial correlations. 相似文献
966.
967.
Magnitude of shear stress on the san andreas fault: implications of a stress measurement profile at shallow depth 总被引:1,自引:0,他引:1
A profile of measurements of shear stress perpendicular to the San Andreas fault near Palmdale, California, shows a marked increase in stress with distance from the fault. The pattern suggests that shear stress on the fault increases slowly with depth and reaches a value on the order of the average stress released during earthquakes. This result has important implications for both long- and shortterm prediction of large earthquakes. 相似文献
968.
Carter LJ 《Science (New York, N.Y.)》1979,203(4384):983-984
969.
970.
Carter LJ 《Science (New York, N.Y.)》1979,206(4424):1287