全文获取类型
收费全文 | 132354篇 |
免费 | 7396篇 |
国内免费 | 90篇 |
专业分类
林业 | 5381篇 |
农学 | 4270篇 |
基础科学 | 831篇 |
17044篇 | |
综合类 | 21482篇 |
农作物 | 5373篇 |
水产渔业 | 6686篇 |
畜牧兽医 | 67987篇 |
园艺 | 1801篇 |
植物保护 | 8985篇 |
出版年
2020年 | 1180篇 |
2019年 | 1375篇 |
2018年 | 2031篇 |
2017年 | 2333篇 |
2016年 | 2095篇 |
2015年 | 1745篇 |
2014年 | 2225篇 |
2013年 | 5293篇 |
2012年 | 4114篇 |
2011年 | 5094篇 |
2010年 | 3245篇 |
2009年 | 3392篇 |
2008年 | 4971篇 |
2007年 | 4666篇 |
2006年 | 4353篇 |
2005年 | 4090篇 |
2004年 | 3852篇 |
2003年 | 3973篇 |
2002年 | 3546篇 |
2001年 | 4151篇 |
2000年 | 4253篇 |
1999年 | 3372篇 |
1998年 | 1475篇 |
1997年 | 1387篇 |
1996年 | 1288篇 |
1995年 | 1531篇 |
1994年 | 1358篇 |
1993年 | 1231篇 |
1992年 | 2585篇 |
1991年 | 2704篇 |
1990年 | 2596篇 |
1989年 | 2615篇 |
1988年 | 2369篇 |
1987年 | 2350篇 |
1986年 | 2432篇 |
1985年 | 2341篇 |
1984年 | 1882篇 |
1983年 | 1677篇 |
1982年 | 1149篇 |
1979年 | 1749篇 |
1978年 | 1397篇 |
1977年 | 1151篇 |
1976年 | 1212篇 |
1975年 | 1294篇 |
1974年 | 1501篇 |
1973年 | 1514篇 |
1972年 | 1405篇 |
1971年 | 1305篇 |
1970年 | 1253篇 |
1969年 | 1284篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
621.
Fifty different mineral samples were tested as potential heterogeneous or epitaxial nucleants for four commonly crystallized proteins. It was found, by conventional protein crystallization techniques, that for each protein there was a set of mineral substrates that promoted nucleation of crystals at lower critical levels of supersaturation than required for spontaneous growth. Numerous examples, involving all four proteins, were observed of modification of crystal habit and, in some cases, unit cell properties promoted by the presence of the mineral nucleants. In at least one case, the growth of lysozyme on the mineral apophyllite, it was shown by lattice analysis and x-ray diffraction that the nucleation and growth of the protein crystal on the mineral was likely to involve a direct lattice match. 相似文献
622.
623.
Gas-phase clusters, which are weakly bound aggregates comprised of either atoms or molecules, often display properties that lie between those of the gaseous and condensed states. Interesting questions arise concerning how large a cluster must be before it will display bulk properties. Currently there is extensive research activity directed toward studies of their formation and varying properties and reactivity as a function of the degree of aggregation. Results serve to elucidate at the molecular level the course of change of a system to be followed from the gas to the condensed state, thereby enabling a spanning of the states of matter. 相似文献
624.
625.
626.
627.
628.
629.
An experimental technique is described for simultaneously measuring the static and dynamic interactions of very thin liquid films between two surfaces as they are moved normally or laterally relative to each other. Film thickness can be measured and controlled to 1 angstrom. Initial results are presented of the transition in the physical properties of liquid films only one molecular layer thick to thicker films whose properties are practically indistinguishable from the bulk. In particular, the results show that two molecularly smooth surfaces, when close together in simple liquids, slide (shear) past each other while separated by a discrete number of molecular layers, and that the frictional force is "quantized" with the number of layers. 相似文献
630.