全文获取类型
收费全文 | 8570篇 |
免费 | 596篇 |
国内免费 | 7篇 |
专业分类
林业 | 345篇 |
农学 | 192篇 |
基础科学 | 72篇 |
1105篇 | |
综合类 | 2143篇 |
农作物 | 253篇 |
水产渔业 | 456篇 |
畜牧兽医 | 4061篇 |
园艺 | 149篇 |
植物保护 | 397篇 |
出版年
2021年 | 104篇 |
2020年 | 124篇 |
2019年 | 138篇 |
2018年 | 148篇 |
2017年 | 139篇 |
2016年 | 164篇 |
2015年 | 123篇 |
2014年 | 163篇 |
2013年 | 333篇 |
2012年 | 349篇 |
2011年 | 396篇 |
2010年 | 248篇 |
2009年 | 195篇 |
2008年 | 418篇 |
2007年 | 402篇 |
2006年 | 393篇 |
2005年 | 364篇 |
2004年 | 370篇 |
2003年 | 368篇 |
2002年 | 332篇 |
2001年 | 172篇 |
2000年 | 190篇 |
1999年 | 170篇 |
1998年 | 70篇 |
1997年 | 58篇 |
1996年 | 58篇 |
1995年 | 62篇 |
1992年 | 126篇 |
1991年 | 134篇 |
1990年 | 125篇 |
1989年 | 124篇 |
1988年 | 103篇 |
1987年 | 104篇 |
1986年 | 142篇 |
1985年 | 159篇 |
1984年 | 123篇 |
1983年 | 115篇 |
1982年 | 75篇 |
1981年 | 86篇 |
1980年 | 71篇 |
1979年 | 110篇 |
1978年 | 100篇 |
1977年 | 61篇 |
1974年 | 65篇 |
1973年 | 80篇 |
1972年 | 77篇 |
1971年 | 68篇 |
1970年 | 58篇 |
1969年 | 62篇 |
1968年 | 63篇 |
排序方式: 共有9173条查询结果,搜索用时 15 毫秒
71.
72.
Freeman RG Grabar KC Allison KJ Bright RM Davis JA Guthrie AP Hommer MB Jackson MA Smith PC Walter DG Natan MJ 《Science (New York, N.Y.)》1995,267(5204):1629-1632
The self-assembly of monodisperse gold and silver colloid particles into monolayers on polymer-coated substrates yields macroscopic surfaces that are highly active for surface-enhanced Raman scattering (SERS). Particles are bound to the substrate through multiple bonds between the colloidal metal and functional groups on the polymer such as cyanide (CN), amine (NH(2)), and thiol (SH). Surface evolution, which can be followed in real time by ultraviolet-visible spectroscopy and SERS, can be controlled to yield high reproducibility on both the nanometer and the centimeter scales. On conducting substrates, colloid monolayers are electrochemically addressable and behave like a collection of closely spaced microelectrodes. These favorable properties and the ease of monolayer construction suggest a widespread use for metal colloid-based substrates. 相似文献
73.
Land cover data for landscape ecological studies are frequently obtained by field survey. In the United Kingdom, temporally separated field surveys have been used to identify the locations and magnitudes of recent changes in land cover. However, such map data contain errors which may seriously hinder the identification of land cover change and the extent and locations of rare landscape features. This paper investigates the extent of the differences between two sets of maps derived from field surveys within the Northumberland National Park in 1991 and 1992. The method used in each survey was the Phase 1 approach of the Nature Conservancy Council of Great Britain. Differences between maps were greatest for the land cover types with the smallest areas. Overall spatial correspondence between maps was found to be only 44.4%. A maximum of 14.4% of the total area surveyed was found to have undergone genuine land cover change. The remaining discrepancies, equivalent to 41.2% of the total survey area, were attributed primarily to differences of land cover interpretation between surveyors (classification error). Differences in boundary locations (positional error) were also noted, but were found to be a relatively minor source of error. The implications for the detection of land cover change and habitat mapping are discussed. 相似文献
74.
75.
76.
77.
78.
79.
Smith RJ 《Science (New York, N.Y.)》1982,216(4553):1391
80.