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   13702篇
  免费   726篇
  国内免费   1625篇
林业   1554篇
农学   1986篇
基础科学   1309篇
  2578篇
综合类   4121篇
农作物   775篇
水产渔业   535篇
畜牧兽医   1793篇
园艺   423篇
植物保护   979篇
  2024年   62篇
  2023年   186篇
  2022年   434篇
  2021年   600篇
  2020年   533篇
  2019年   557篇
  2018年   329篇
  2017年   543篇
  2016年   460篇
  2015年   669篇
  2014年   598篇
  2013年   738篇
  2012年   884篇
  2011年   902篇
  2010年   861篇
  2009年   810篇
  2008年   756篇
  2007年   822篇
  2006年   765篇
  2005年   701篇
  2004年   332篇
  2003年   231篇
  2002年   235篇
  2001年   239篇
  2000年   260篇
  1999年   368篇
  1998年   301篇
  1997年   271篇
  1996年   235篇
  1995年   252篇
  1994年   179篇
  1993年   206篇
  1992年   172篇
  1991年   134篇
  1990年   123篇
  1989年   84篇
  1988年   68篇
  1987年   57篇
  1986年   34篇
  1985年   9篇
  1984年   7篇
  1983年   11篇
  1982年   12篇
  1981年   5篇
  1980年   6篇
  1973年   2篇
  1964年   2篇
  1963年   3篇
  1935年   1篇
  1934年   2篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
161.
本试验旨在研究苏氨酸和异亮氨酸对皖西白鹅屠宰性能、器官指数及肠道形态结构、消化酶活性、抗氧化和免疫指标的影响。选取30日龄体重相近的皖西白鹅180只,随机分为3组,每组3个重复,每个重复20只。对照组饲喂基础饲粮,苏氨酸组在基础饲粮中添加2.0 g/kg的L-苏氨酸,异亮氨酸组在基础饲粮中添加2.5 g/kg的L-异亮氨酸。试验期60 d。结果表明:1)各组之间90日龄屠宰性能和器官指数无显著差异(P>0.05)。2)异亮氨酸组60日龄十二指肠和空肠绒毛高度、隐窝深度显著或极显著高于对照组(P<0.05或P<0.01),苏氨酸组60日龄十二指肠、空肠和回肠隐窝深度及90日龄十二指肠和回肠绒毛高度显著或极显著高于对照组(P<0.05或P<0.01)。3)苏氨酸组和异亮氨酸组60、90日龄十二指肠胰蛋白酶活性极显著高于对照组(P<0.01),苏氨酸组60、90日龄十二指肠麦芽糖酶活性及90日龄空肠淀粉酶、乳糖酶活性显著或极显著高于对照组(P<0.05或P<0.01)。4)异亮氨酸组60日龄空肠总抗氧化能力显著高于对照组和苏氨酸组(P<0...  相似文献   
162.
杂交水稻品种鉴定技术研究   总被引:1,自引:1,他引:1  
李稳香  胡少奇 《种子》1995,(6):18-19
该试验用幼苗形态鉴定法对杂交裟品种进行鉴定。结果表明,通过特定的温度、光照和药剂处理,杂交一代F1的茎基部呈深红色,而不育系A和保持系B的茎基部无色或仅呈微红色。故可鉴定出F1的纯度,但不能将A与B区分出来。  相似文献   
163.
Magnetorheological materials are a class of smart materials whose reological properties may be rapidly varied by application of magnetic field. By a simple mechanical mold, a visco-plastic model for the materials is developed. It is shown that the model can describe the variation of the mechanical properties for the Magnetorheological materials in the different magnetic field. The result is shown that the model can characterize the mechanical properties of Magnetorheological Materials in plastic and viscous variation.  相似文献   
164.
To construct data warehouse with heterogeneous, self-governing and distributed database system is a challenge. Two problems have to be solved: one is how to collect data from heterogeneous data sources by an effective method, the other is how to clear up and change the format of the data collected from data sources. The opening and the interact-operation property of Web Services is Analyzed. A Data Collection System based on Web Services, which communicates with heterogeneous data sources with SOAP and HTTP, has been designed. A Data Collector is introduced to clear up and to transform data with composition technology. The pivotal XML technology of transforming and loading up the data are discussed.  相似文献   
165.
In this paper,a new algorithm for solving large-scale finite element system is presented, which utilizes the architecture of parallel processing. Firstly, the structure is partitioned into sub-regions. Then multi-fronts are used to assemble and eliminate concurrently in every sub-region. Thus the condensed interface stiffness matrices and load vectors are obtained. By serially assembling and solving global equation to get interface displacements and backing to every sub-region, the inter-nodal displacements and element stresses can be solved. The results of computation show that it can not only increase the speed of computation,but also save the memory space of computer effectively. This algorithm is an effective method for solving large-scale structural finite element systems.  相似文献   
166.
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   
167.
168.
The development circumstance about Handhold Computer technology and products at home and abroad are described in details, resumes the development of the technology and elaborates the difference between our country's technology and the advanced foreign technology. Besides, it also introduces the relationship of Windows CE and Handhold Computer.  相似文献   
169.
Employing the standpoint of irrational investors in the behavior finance, the authors study the relation on the irrational behavior of medium and small Investors and underpricing of IPO in our country. The paper premises that a revenue-maximizing issuer will be regarded as the target function, and the rational institutional investors can be delegated the task of holding the stocks in the after-market for resale to the irrational medium and small investors--thereby extracting surplus from them, finally the issuer can maximize their expected revenue. We model the process mentioned above and find that the high underpricing of IPO in our country has the direct relation with numerous the irrational medium and small investors existing in our country who cause the underpricing.  相似文献   
170.
After researching the function requirements of the planning and scheduling in manufacturing cells, the paper advanced a control structure with three phases, i. e. planning , scheduling and dispatching. The paper represented in detail the main purposes, requirements and scheduling actions in each phase. It suits to general machining FMSs.  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