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   8395篇
  免费   537篇
  国内免费   827篇
林业   652篇
农学   795篇
基础科学   720篇
  1097篇
综合类   3418篇
农作物   513篇
水产渔业   478篇
畜牧兽医   1169篇
园艺   506篇
植物保护   411篇
  2024年   51篇
  2023年   184篇
  2022年   443篇
  2021年   477篇
  2020年   461篇
  2019年   480篇
  2018年   342篇
  2017年   510篇
  2016年   411篇
  2015年   561篇
  2014年   552篇
  2013年   628篇
  2012年   768篇
  2011年   700篇
  2010年   651篇
  2009年   503篇
  2008年   475篇
  2007年   349篇
  2006年   249篇
  2005年   174篇
  2004年   123篇
  2003年   83篇
  2002年   119篇
  2001年   90篇
  2000年   91篇
  1999年   41篇
  1998年   26篇
  1997年   22篇
  1996年   16篇
  1995年   20篇
  1994年   30篇
  1993年   16篇
  1992年   17篇
  1991年   19篇
  1990年   8篇
  1989年   8篇
  1988年   15篇
  1987年   9篇
  1986年   2篇
  1985年   2篇
  1981年   3篇
  1979年   2篇
  1978年   2篇
  1966年   1篇
  1965年   3篇
  1964年   3篇
  1963年   3篇
  1960年   1篇
  1956年   5篇
  1955年   1篇
排序方式: 共有9759条查询结果,搜索用时 171 毫秒
81.
The high-precision displacement measuring technology of optic-measuring mechanics is, for the first time,successfully applied on the similar model of the model land-layer with a new-type variable modulus of elasticity. The angle of movement and the distributed displacement of upper and lower rock-layers are measured. The technology is a combination of laser's technology and the modern chemical sticker-it is called the sticking moire interferometry. Compared with the measured values, the result is very satisfactory.  相似文献   
82.
Critical information system in Interact is in face of increasingly security problems. More attention has been focused on the survivability of information system, which is the capability of system to continue its mission even in the presence of damage to the system. The authors first introduce the definition of survivability. According to four function properties of survivability, which are Resistance, Recognition, Recovery, and Adaption, the authors design a model of survivable system structure and then explain survivability requirement, survivability strategy in this model. Additionally, they provide possible technical solutions for the survivability of systems, categorized by different aspects of our survivability strategy.  相似文献   
83.
The green is as a symbol of no pollution,no public harm and environmental protection. The green automobile is the inevitable results that the automobile technique continuously developes. A new style vehicle--the green automobile is the urgent solicit of environmental protection is developed. The automobile industry can develop continuously. This article mainly discusses the importance of the green auto_mobile's research and development,the development status in quo and prospect of the green auto_mobile technique in the world,and states the relationship between the green automobile technique and environmental protection from green technical system theoretically clarify the study of green automobile,including its design and the system,the manufacture and its technology,the energy,the rebuild engineering and a series of subjects. How to evaluate the cycle and the evaluable mark of the green automobile,the prospect of green automobile are pointed out.  相似文献   
84.
The process of actin polymerization and depolymerization have some relation with its function,the activation of such process is compatible to its functions. The polymerization progress is divided into four steps: The first step is the activation of the monomer actin. The nucleation of actin nucleus forms in the second step which limits the polymerization speed. The elongation of the F-actin filaments happens in the following step. In the last step, a steady-state is attained, the length of the filament does not change because the polymerizing rate in the barbed end is the same with the depolymerizing rate in the pointed end. Some factors which affect the polymerizing process, such as nucleotide, actin related proteins are discussed. The aim is to know more about how to assemble the complicated system with biomacromolecule and what to function.  相似文献   
85.
Melt flow in the course of laser alloying is considered on the basis of mechanics. The findings show that the melt flow in laser alloying pool is mainly controlled by two action forces,i. e. the surface tension force on alloying pool.surface,caused by the temperature difference on the pool surface and the buoyancy force in alloying pool caused by the temperature difference in the horizontal direction in the melt pool. These two forces differ in their acting areas. The analysis of the Bond dimensionless number used for laser alloying shows that the two force actions are in the same order,and almost equal under the certain condition.  相似文献   
86.
87.
88.
The damage of bridge cable directly hazards the normal use of bridge and the safety of people. The paper discussed the signal acquisition and detection system which takes embedded DSP processor as core technology, combined with CCD, video decode chip, SDRAM, FLASH ROM, and established the fast measuring algorithm of the surface corrosion and damage, which includes deteminating the processing region, improving medium filter, sobel edge detection and dynamic threshold segment, close operation of morphology, computing defect area and saving. The experimental resuits show that this method implemented the real-time, non-contact and intelligence detecting of cable surface defect and gives the specifications of the system.  相似文献   
89.
为降低建筑能耗影响因素间复杂相关性对模型性能的影响,建立了一种基于KPCA-WLSSVM的建筑能耗预测模型。利用核主元分析(KPCA)对输入变量进行数据压缩,消除变量之间的相关性,简化模型结构;进一步采用加权最小二乘支持向量机(WLSSVM)方法建立建筑能耗预测模型,同时结合一种新型混沌粒子群-模拟退火混合优化(CPSO-SA)算法对模型参数进行优化,以提高模型的预测性能及泛化能力。通过将KPCA-WLSSVM模型方法应用于某办公建筑能耗的预测中,并与WLSSVM、LSSVM及RBFNN模型相比,实验结果表明,KPCA-WLSSVM模型方法能有效提高建筑能耗预测精度。  相似文献   
90.
In order to support flexibility and reusability of application composition based on Internet,with business rule and Aspect-Oriented Programming(AOP) which divides a business process into a control business process and a core business process,the authorsgive composition mechanism.A technique of implementation is analyzed.At last,the primary application of the above work in Chongqing of China is introduced,as well as some effects acquired.  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