全文获取类型
收费全文 | 3438篇 |
免费 | 241篇 |
国内免费 | 384篇 |
专业分类
林业 | 210篇 |
农学 | 253篇 |
基础科学 | 410篇 |
1682篇 | |
综合类 | 977篇 |
农作物 | 35篇 |
水产渔业 | 289篇 |
畜牧兽医 | 84篇 |
园艺 | 38篇 |
植物保护 | 85篇 |
出版年
2024年 | 28篇 |
2023年 | 91篇 |
2022年 | 133篇 |
2021年 | 126篇 |
2020年 | 147篇 |
2019年 | 154篇 |
2018年 | 117篇 |
2017年 | 210篇 |
2016年 | 218篇 |
2015年 | 133篇 |
2014年 | 166篇 |
2013年 | 193篇 |
2012年 | 267篇 |
2011年 | 254篇 |
2010年 | 199篇 |
2009年 | 161篇 |
2008年 | 145篇 |
2007年 | 219篇 |
2006年 | 167篇 |
2005年 | 140篇 |
2004年 | 117篇 |
2003年 | 89篇 |
2002年 | 97篇 |
2001年 | 71篇 |
2000年 | 41篇 |
1999年 | 39篇 |
1998年 | 51篇 |
1997年 | 40篇 |
1996年 | 42篇 |
1995年 | 38篇 |
1994年 | 54篇 |
1993年 | 32篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有4063条查询结果,搜索用时 15 毫秒
31.
Jinshajiang River, which has a drainage area of 485,100 Km 2, average flux of 142.9 billion m 3, and soil conveyance of 247 million t/a, is the largest branch of Changjiang river. It is also the largest soil resource of the Three Gorges reservoir and upper reach of Changjiang River. To research the development and trend of Jinshajiang sediment not only has a relation to Jinshajiang water resource strategy, but also has important meaning to control the silt in Three Gorges reservoir and the Changjiang water resource development. The paper statistically analyses the flux and sediment conveyance of the Pingshan station, which is the primary hydrological station in the Jinshajiang River Drainage Area. Through several non-parameter statistical methods such as Spearman order correlativity check, Kendell order correlativity check, and linear regression check, the paper concludes that the sediment evolvement trend of Pingshan station is not distinct. 相似文献
32.
This paper uses the method of mixed-type series to derive the analyticsolution of cylindrical shell roof,being simply supported transversely,arbitra-rily restrained longitudinally and subjected to gereral transverse local loads.This paper also presents the analytic expressions of the solutions for somekinds of local load.Some examples of this kind of shell roof subjected to ainlined single force near the middle of it with free lorgitudinal edges aregiven.The computation shows that the convergence of the solution is woll 相似文献
33.
34.
Spatial load forecasting is a process distributing the total forecasted load to all partitioned area, and involving more spatial information and more factor influencing application of the future small area, which need a great deal of memory space and longer operation time. Rough set is new method of data analysis. It need not be provided with any advanced information except data set. But attribute reduct is its main algorithms. Division matrix approach on rough set used to reduce the attribute related to land - use decision in order to remove redundancy attribute and then the rules of small area land - use decision is distilled. The method obtained better effect and enhanced the total load forecasting efficiency. 相似文献
35.
Some thoroughly research on the basic method for load state detection in MIN is introduced. Load sources of SCP and SSP in MIN are analyzed in detail after investigating the relationship between inter resource and load state in the system. And load detection parameters and model are presented. Moreover, a novel strategy to detect system load state based on fusion of multi detection data is presented. By some test, the theory and method are proved most feasible. Our research show that load state of MIN can be recognized by detecting utility of internal resource utilizing of single node in MIN, and multi redundant detecting data fusion is effective approach to improve the reliability and trust degree of the result. 相似文献
36.
37.
Some conclusions were drawn from two groups of in-site tests on concrete pile composite foundations. In the tests, it was found that the pressure under the rigid loading slab is different, in which the pressure under the center of the slab is the less and under the edge of the slab is the biggest. The pile-soil stress ratio is not a constant; it increases with the adding of the load. Most of the pile-soil ratio vary from 9 to 13 in these tests and the load that the piles share can be more than seventy percent of the whole load. It was proved that the bearing capacity of the concrete pile composite foundation is high with a little settlement, so it will be used more and more in the future. 相似文献
38.
39.
Ren Yuanzhi 《保鲜与加工》1994,(1)
The condition when forces are applied to load mechnical mornent limiter of tow-er cranes is analysed and disctissed in this paper.A lifting performance curve adapted for the me-chanical load moment limiter is also obtained.And finally,the curve drawing method is explainedthrough the practical example. 相似文献
40.