全文获取类型
收费全文 | 140524篇 |
免费 | 8259篇 |
国内免费 | 73篇 |
专业分类
林业 | 5950篇 |
农学 | 4793篇 |
基础科学 | 899篇 |
18534篇 | |
综合类 | 19710篇 |
农作物 | 5288篇 |
水产渔业 | 7524篇 |
畜牧兽医 | 74845篇 |
园艺 | 1931篇 |
植物保护 | 9382篇 |
出版年
2020年 | 1257篇 |
2019年 | 1496篇 |
2018年 | 2362篇 |
2017年 | 2606篇 |
2016年 | 2426篇 |
2015年 | 2094篇 |
2014年 | 2590篇 |
2013年 | 6026篇 |
2012年 | 4598篇 |
2011年 | 5492篇 |
2010年 | 3695篇 |
2009年 | 3711篇 |
2008年 | 5438篇 |
2007年 | 5243篇 |
2006年 | 4917篇 |
2005年 | 4515篇 |
2004年 | 4323篇 |
2003年 | 4410篇 |
2002年 | 4013篇 |
2001年 | 4863篇 |
2000年 | 4735篇 |
1999年 | 3835篇 |
1998年 | 1521篇 |
1997年 | 1498篇 |
1996年 | 1388篇 |
1995年 | 1639篇 |
1994年 | 1357篇 |
1993年 | 1394篇 |
1992年 | 2795篇 |
1991年 | 2953篇 |
1990年 | 2902篇 |
1989年 | 2941篇 |
1988年 | 2639篇 |
1987年 | 2631篇 |
1986年 | 2571篇 |
1985年 | 2448篇 |
1984年 | 1992篇 |
1983年 | 1758篇 |
1982年 | 1178篇 |
1979年 | 1687篇 |
1978年 | 1313篇 |
1977年 | 1159篇 |
1976年 | 1130篇 |
1975年 | 1185篇 |
1974年 | 1389篇 |
1973年 | 1474篇 |
1972年 | 1403篇 |
1971年 | 1208篇 |
1970年 | 1269篇 |
1969年 | 1171篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Grossman CM 《Science (New York, N.Y.)》1995,269(5231):1653-1655
992.
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
993.
994.
Hodge IM 《Science (New York, N.Y.)》1995,267(5206):1945-1947
Physical aging refers to structural relaxation of the glassy state toward the metastable equilibrium amorphous state, and it is accompanied by changes in almost all physical properties. These changes, which must be taken into account in the design, manufacture, and use of glassy polymer materials and devices, present a daunting challenge to theorists. 相似文献
995.
E. Adipala J. P. Takan M. W. Ogenga-Latigo 《European journal of plant pathology / European Foundation for Plant Pathology》1995,101(1):25-33
Effect of plant density (37,037, 44,444 and 55,555 plants/ha) on the increase of northern leaf blight in time and space on two maize cultivars planted at spacings of 90, 75 and 60 between rows and 30 cm within rows was investigated.Exserohilum turcicum infested maize residue was used as an inoculum source. Maize density did not significantly affect the disease indices, but significantly influenced the grain yield of the two cultivars. In contrast, the two cultivars differed significantly (P0.01) in disease severity, but not grain yield. Higher disease severities and grain yields were associated with higher plant densities, whereas the apparent infection rate was lower in higher plant density. Distance from the maize residue (inoculum source) significantly influenced disease severity. The percentage leaf area blighted, area under disease progress curve and disease progress curve intercept decreased with distance from the maize residue area, but the apparent infection rate on EV8429-SR appeared to increase with distance. Disease gradients (b) were higher in closely planted maize and flattened with time in one location only. 相似文献
996.
The relationship between fine-scale spatial patterns of forage abundance and the feeding patterns of large ungulates is not well known. We compared these patterns for areas grazed in winter by elk and bison in a sagebrush-grassland landscape in northern Yellowstone National Park. At a fine scale, the spatial distribution of mapped feeding stations in 30 m × 30 m sites was found to be random where there were no large patches devoid of vegetation. In areas similar to the mapped sites, the underlying spatial distribution pattern of biomass was also determined to be random. At a broad scale, forage biomass differed among communities across the northern range but forage quality did not. These results suggest that ungulates are feeding randomly within forage patches (fine scale) but may select feeding sites based upon forage abundance at broader, landscape scales. Contrary to what has been suggested in other systems, ungulates were not overmatching at finer scales. 相似文献
997.
Balter M 《Science (New York, N.Y.)》1995,268(5214):1132-1133
998.
999.
1000.
Three groups of eight Friesian calves, reared parasite-free, were experimentally infected with 1000 infective larvae of Dictyocaulus viviparus. Two groups were injected subcutaneously with 1% doramectin at 0.2 mg/kg body weight, one group 5 days after infection and the other 25 days after infection. A third group served as untreated controls. Faecal samples were examined for lungworm larvae on days 28, 32, 33, 34 and 35 after infection; the calves were killed and necropsied 39 or 40 days after infection and any lungworms present recovered and counted. Doramectin proved 100% effective against both 5-day-old and mature D. viviparus infections. 相似文献