首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3969篇
  免费   264篇
  国内免费   226篇
林业   382篇
农学   266篇
基础科学   129篇
  357篇
综合类   2015篇
农作物   292篇
水产渔业   100篇
畜牧兽医   561篇
园艺   252篇
植物保护   105篇
  2024年   15篇
  2023年   61篇
  2022年   181篇
  2021年   175篇
  2020年   176篇
  2019年   197篇
  2018年   113篇
  2017年   200篇
  2016年   118篇
  2015年   194篇
  2014年   154篇
  2013年   264篇
  2012年   338篇
  2011年   311篇
  2010年   308篇
  2009年   283篇
  2008年   263篇
  2007年   294篇
  2006年   212篇
  2005年   201篇
  2004年   113篇
  2003年   53篇
  2002年   70篇
  2001年   59篇
  2000年   60篇
  1999年   17篇
  1998年   2篇
  1997年   1篇
  1996年   1篇
  1993年   1篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1987年   1篇
  1986年   3篇
  1984年   1篇
  1983年   3篇
  1980年   1篇
  1978年   3篇
  1976年   1篇
  1975年   1篇
  1967年   1篇
  1960年   1篇
  1959年   1篇
  1955年   1篇
  1948年   1篇
  1946年   1篇
排序方式: 共有4459条查询结果,搜索用时 31 毫秒
991.
玉米马铃薯间作对根际微生物群落结构和多样性的影响   总被引:6,自引:0,他引:6  
覃潇敏  郑毅  汤利  龙光强 《作物学报》2015,41(6):919-928
设置3个种植处理(玉米单作、马铃薯单作和玉米马铃薯间作),通过田间试验和盆栽试验,采用Biolog技术分析了玉米马铃薯根际微生物的群落结构和功能多样性的变化情况。结果表明,与单作相比,间作处理使玉米和马铃薯根际微生物对31种碳源的平均利用率(AWCD)分别增加17.36%、7.38%和3.76%、32.21%,其中间作马铃薯的AWCD值最高,单作玉米最低。间作玉米和间作马铃薯根际微生物群落的Shannon指数(H)、Simpson指数(D)、均匀度指数(E)、丰富度指数(S)均高于单作,但在间作和单作之间差异不显著。根际微生物对6类碳源的利用强度以糖类、羧酸类和氨基酸最高,并存在一定的差异。主成分和聚类分析表明,玉米与马铃薯间作改变了根际微生物的群落组成,糖类、羧酸类和氨基酸类碳源是区分单间作处理差异的敏感碳源。说明玉米马铃薯间作改变了根际微生物群落结构组成,提高了根际微生物群落功能多样性。  相似文献   
992.
993.
When light spreads in gravitational wave, its frequency is changed. Usually considering frequency gravitational shift, the rest mass of the photon is neglected. According to Proca equations of weight electromagnetic wave the authors investigate the Frequency shift of Proca light. The results of numerical estimation show that frequency shift of the photon has a small change when considering the rest mass of the photon and it is not detected at present experimental condition.  相似文献   
994.
Based on the contrast experiment, the condition of air-cooled heat pump operating indoors is analyzed in this paper.The operating performance corresponding to such conditions is gained.The ventilation condition of stable operation for air-cooled heat pump is found.At the same time, the experimental results based on actual work are proved. indoors; air-cooled heat pump; ventilation   相似文献   
995.
The tremendous seasonal variation of rainfall and the relative little dispose capacity of sewage are the main reason of the lack of water quantity and the contaminate of water quality in low water season in LIJIANG. Adjusting water quantity is an important measure to resolve the problem. So, the author does an investigation on water resource of LIJIANG, calculates upper-water supply and requires equation. As a result, in the condition of no water adjust, and if in the extraordinary year of the lack of water quantity, the water flow will fade in 2010, and the demand of water quantity of 30 m~3/s in the season of the lack of water will not be satisfied. Based on the actuality of water resource, the thesis introduces the project of mending water reservoir to LIJIANG,analyzes its feasibility in the respect of technique and financial condition,brings forward major problem of the project. The result proves the benefit of the project in the field of environment,economy society is very prominent, and the project is an engineering to realize water resource of LIJIANG reasonable utilize; for the reason to guarantee this project to bring into play its function,it is time to carry out integrate management to water resource and water environment in LIJIANG valley.  相似文献   
996.
The wall thickness and strengthen muscle of motorcycle crankcase box influences its structure intensity directly. The static model of crankcase box of a magnesium alloy material is established by finite element method. The structure is analyzed with I-DEAS, the reason the crankcase box is crazed is pointed out. The structure is rebuilt, the intensity is increased remarkablely, the cost of manufacture is reduced largely. And the capability of a originally material, i.e. aluminium alloy is validated.  相似文献   
997.
The residential area studied in this paper is situated on the special borderland between Beibei town and Jinyun Mountain,which is a national beauty spot and natural conservation region.In order to conserve the ecological environment of JinYun Mountain,prevent the excessive development,and promote sustainable progress of the residential area,it is suggested in this article that an ecological sustainable residential area should be designed for this area. Then this paper puts emphasis on the design strategies in following three parts:(i) protecting ecological environment,(ii) providing healthy building environment,and(iii) enhancing building energy efficiency.  相似文献   
998.
999.
1000.
The conception of virtual logistics and virtual logistics enterprise are introduced,and the importance of information technology in virtual logistics organization is indicated.Then the four layer structure of the support system of virtual logistics enterprise is propaed,which are information collection technical,information share technical,information disposal technical and the theory and methods of information management.The five-layer construction of information system of virtual logistics enterprises is built.This paper can be of instructive significance to the building of the virtual logistics enterprise's information platform.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号