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   13951篇
  免费   768篇
  国内免费   1511篇
林业   1456篇
农学   1797篇
基础科学   963篇
  2138篇
综合类   4986篇
农作物   892篇
水产渔业   677篇
畜牧兽医   1889篇
园艺   601篇
植物保护   831篇
  2024年   47篇
  2023年   134篇
  2022年   422篇
  2021年   545篇
  2020年   513篇
  2019年   510篇
  2018年   361篇
  2017年   498篇
  2016年   455篇
  2015年   635篇
  2014年   611篇
  2013年   806篇
  2012年   1011篇
  2011年   991篇
  2010年   945篇
  2009年   925篇
  2008年   828篇
  2007年   803篇
  2006年   798篇
  2005年   714篇
  2004年   427篇
  2003年   324篇
  2002年   369篇
  2001年   345篇
  2000年   314篇
  1999年   295篇
  1998年   221篇
  1997年   206篇
  1996年   171篇
  1995年   156篇
  1994年   135篇
  1993年   139篇
  1992年   121篇
  1991年   81篇
  1990年   93篇
  1989年   85篇
  1988年   63篇
  1987年   41篇
  1986年   28篇
  1985年   16篇
  1984年   12篇
  1983年   5篇
  1982年   13篇
  1981年   6篇
  1980年   4篇
  1979年   3篇
  1976年   1篇
  1965年   1篇
  1962年   3篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
盾叶薯蓣良种离体快繁关键技术研究   总被引:7,自引:0,他引:7  
以盾叶薯蓣的单节茎段为外植体,培养基 MS 2.0mg/L BA 0.6mg/L NAA对腋芽诱导效果最好,诱导率达 77.4%; MS 0.5mg/L BA 0.5~ 1.0mg/L 2,4- D为诱导愈伤组织的培养基;在 MS 1.0mg/L BA 0.2mg/L NAA或 MS 2.0mg/L BA 0.5mg/L IBA培养基上能有效地诱导多芽; BA与 NAA的组合较 BA与 IBA组合更有利于多芽的诱导; MS 2.5mg/L BA 0.5mg/L NAA可作为愈伤组织及多芽组织的继代培养.  相似文献   
152.
Earning report is a main accounting report that transmits earning information to users. It is the core of financial reports system. Earning information is significant to users' decision making. This paper studies the respond of stock trading volume to earning report and draws the curve of trading volume before and after earning report. This paper further does a regression analysis of accidental earning and abnormal return rate, and draws the relation curve of them on the earning report date to prove stock trading volume does have remarkable respond to earning report. This research is significant to either lessen small investors blindness investment and help them make reasonable forecast to markets and regulate the disclosure of listed companies.  相似文献   
153.
The paper studies a drug deliversy system for protein and find the optimum preparation condition.Cross-linked alginate(Alg) microcapsule was used to prepare microcapsule for protein,using bovine serum album(BSA) as a model drug.Effect of different cations and content of protein on configuration,size and enveloped rate of microcapsule were investigated.It is shown that Ba-Alg microcapsule has steady configuration,homogeneous size and high-enveloped rate.Also electrophoresis of native BSA before microencapsulation and after microencapsulation is measured by(SDS-PAGE),it is found that no significant change is observed BSA integrity.Release of BSA from microcapsule in vitro presents sustained release in some extent,and initial burst effect is significantly obvious.Microenpsulation drug in alginate will be a wishful drug delivery system.  相似文献   
154.
The holographic three wavefront interferometer is used to measure large optical path difference. This method is proved to be practical through the measurement of the deformation -Voltage Curve of piezocrystal.  相似文献   
155.
Based on [l].this paper presents a new spline-BEM for calculating 3-D electrostatic fields,in which bi-cubic B-splines are used as basis functions. The corner problem in BEM and the extreme conditions for splines are circumvented. The numerical results presented show that the global approximation .convergence and stability of the method are satisfactory.  相似文献   
156.
The dynamic characteristic of active isolation atuator on flexible foundations was studied under the installation of parallel structure and foundation cancellation.The influencing relationships between active isolation force of the different installation ways and passive isolation system and flexible foundation were analyzed and compared.Scientific basis for selecting installation ways of active isolator is provided in this paper.  相似文献   
157.
The electrochromism of polyaniline films, which is prepared by electropolymer-ization from aniline in acidic aqueous solution onto platinum,is investigated in 330-700nm through in-situ ellipsometric technique. The results indicate that the ellipsometric peak of the reduced state(-0. 2V) of the film appears at 390-400nm and the oxidized state(0. 55V) at 500-530nm. The elec-trochromic reaction from the reduced "yellow" state to the oxidized "green" state is suggested via intermediate state whose ellipsometric peak appears at 466-470nm.  相似文献   
158.
With the strengthening of constitutional protection that legal private property is not to be encroached upon and the land usufructs paid regime are further clear, the regime of urban housing dismantling and moving is facing a vigorous test. This paper analyzes three problems: the justice of the withdrawal of land use right, the legality of the alteration of the land use right and the rationality of the compensation of the land use right during the urban housing dismantling and moving. Finally, this paper tries to find some effective measures to solve the chain problems.  相似文献   
159.
160.
Electromagnetic potentials and gauge transformation are derived for non-cloSedexterior differential forms with the help of relevant homology.Since de Rham ccahomology is sure-ly a relavant homology. potentials for both closed and non-closed forms and the gauge transforma-tion ean be unified in terms of relavent homology.  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