全文获取类型
收费全文 | 779篇 |
免费 | 42篇 |
专业分类
林业 | 9篇 |
农学 | 13篇 |
基础科学 | 3篇 |
81篇 | |
综合类 | 123篇 |
农作物 | 31篇 |
水产渔业 | 29篇 |
畜牧兽医 | 495篇 |
园艺 | 15篇 |
植物保护 | 22篇 |
出版年
2023年 | 8篇 |
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 35篇 |
2012年 | 25篇 |
2011年 | 21篇 |
2010年 | 30篇 |
2009年 | 14篇 |
2008年 | 33篇 |
2007年 | 35篇 |
2006年 | 24篇 |
2005年 | 20篇 |
2004年 | 32篇 |
2003年 | 33篇 |
2002年 | 39篇 |
2001年 | 24篇 |
2000年 | 27篇 |
1999年 | 20篇 |
1998年 | 7篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 21篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1979年 | 5篇 |
1974年 | 8篇 |
1972年 | 11篇 |
1971年 | 11篇 |
1970年 | 8篇 |
1968年 | 6篇 |
1967年 | 6篇 |
1966年 | 7篇 |
1965年 | 6篇 |
1963年 | 5篇 |
1961年 | 5篇 |
1946年 | 9篇 |
排序方式: 共有821条查询结果,搜索用时 15 毫秒
801.
802.
Fruchter JS Robertson DE Evans JC Olsen KB Lepel EA Laul JC Abel KH Sanders RW Jackson PO Wogman NS Perkins RW VAN Tuyl HH Beauchamp RH Shade JW Daniel JL Erikson RL Sehmel GA Lee RN Robinson AV Moss OR Briant JK Cannon WC 《Science (New York, N.Y.)》1980,209(4461):1116-1125
Samples of ash from the 18 May 1980 eruption of Mount St. Helens were collected from several locations in eastern Washington and Montana. The ash was subjected to a variety of analyses to determine its chemical, physical, mineralogical, and biological characteristics. Chemically, the ash samples were of dacitic composition. Particle size data showed bimodal distributions and differed considerably with location. However, all samples contained comparable amounts of particles less than 3.5 micrometers in diameter (respirable fraction). Mineralogically, the samples ranged from almost totally glassy to almost totally crystalline. Crystalline samples were dominated by plagioclase feldspar (andesine) and orthopyroxene (hypersthene), with smaller amounts of titanomagnetite and hornblende. All but one of the samples contained from less than 1 percent to 3 percent free crystalline silica (quartz, trydimite, or cristobalite) in both the bulk samples and 1 to 2 percent in the fractions smaller than 3.5 micrometers. The long-lived natural radionuclide content of the ash was comparable to that of crustal material; however, relatively large concentrations of short-lived radon daughters were present and polonium-210 content was inversely correlated with particle size. In vitro biological tests showed the ash to be nontoxic to alveolar macrophages, which are an important part of the lungs' natural clearance mechanism. On the basis of a substantial body of data that has shown a correlation between macrophage cytotoxicity and fibrogenicity of minerals, the ash is not predicted to be highly fibrogenic. 相似文献
803.
804.
805.
806.
Worobey M Rambaut A Pybus OG Robertson DL 《Science (New York, N.Y.)》2002,296(5566):211 discussion 211
807.
Omar G Johnson KR Hickey LJ Robertson PB Dawson MR Barnosky CW 《Science (New York, N.Y.)》1987,237(4822):1603-1605
Haughton Astrobleme is a major extraterrestrial impact structure located on Devon Island in the Canadian Arctic Archipelago, Northwest Territories. Apatite grains separated from shocked Precambrian gneiss contained in a polymict breccia from the center of the astrobleme yielded a fission-track date of 22.4 million +/- 1.4 million years before the present or early Miocene (Aquitanian). This provides a date for the impact event and an upper limit on the age of crater-filling lake sediments and a flora and vertebrate fauna occurring in them. A geologically precise date for these fossils provides an important biostratigraphic reference point for interpreting the biotic evolution of the Arctic. 相似文献
808.
Contrary to the prevailing notion that oxygen-depleting reactions in the soil zone and in the aquifer rapidly reduce the dissolved oxygen content of recharge water to detection limits, 2 to 8 milligrams per liter of dissolved oxygen is present in water from a variety of deep (100 to 1000 meters) aquifers in Nevada, Arizona, and the hot springs of the folded Appalachians and Arkansas. Most of the waters sampled are several thousand to more than 10,000 years old, and some are 80 kilometers from their point of recharge. 相似文献
809.
810.