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   14225篇
  免费   649篇
  国内免费   874篇
林业   1712篇
农学   1238篇
基础科学   1638篇
  1023篇
综合类   7780篇
农作物   628篇
水产渔业   262篇
畜牧兽医   879篇
园艺   397篇
植物保护   191篇
  2024年   89篇
  2023年   219篇
  2022年   399篇
  2021年   490篇
  2020年   405篇
  2019年   516篇
  2018年   204篇
  2017年   398篇
  2016年   623篇
  2015年   500篇
  2014年   996篇
  2013年   885篇
  2012年   1509篇
  2011年   1271篇
  2010年   967篇
  2009年   968篇
  2008年   823篇
  2007年   883篇
  2006年   777篇
  2005年   649篇
  2004年   470篇
  2003年   422篇
  2002年   258篇
  2001年   203篇
  2000年   202篇
  1999年   138篇
  1998年   98篇
  1997年   86篇
  1996年   66篇
  1995年   51篇
  1994年   54篇
  1993年   34篇
  1992年   24篇
  1991年   18篇
  1990年   24篇
  1989年   9篇
  1988年   10篇
  1987年   3篇
  1986年   2篇
  1983年   1篇
  1956年   3篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
151.
The engineering design of sewage treatment plant for the Chongqing city, P. R. China is analyzed in this paper. Considering the situation of China and other projects, the characteristics of falling water reactor for the environment protection project and economy of investment is introduced ; the application and foreground of falling water aeration in the process of sewage treatment is discussed, such as Oxidation - ditch, SBR, and so on. The conclusion indicated that the falling water aeration can be designed and used as an independent aeration, and, it is an upgraded technology of sewage treatment which is adaptive for city water environment control in middle and small towns in China. The falling water aeration may reduce running cost of the sewage treatment plant, is adaptive for foothill and the mountainous areas, and reduces project investment and environments damage.  相似文献   
152.
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   
153.
154.
According to the needs of setting up a professional system based on motorcycle design,the CBR(case based reasoning) and RBR(rule based reasoning) methods are introduced.After discussing the difference between the two kinds of reasoning,a method of integrating them into the motorcycle design flow is put forward to realize the design reusable technology and improve the design efficiency,by using the CBR in the step of selecting the similar motorcycle and the RBR in project's modification according to correlative rules.  相似文献   
155.
According to the requirements of communication power supply, such as high reliability, wide application and high availability, the authors raise a new remote control design for a multi-output power supply for communication equipment based on TCPIP protocol and embedded technology. Then the hardware design is given for the system is discussed based on Ethernet professional chip PRTL8019AS and related circuits. The firmware software design for the salve-computer based TCPIP technology, and the soft design of communieation and control for the master-computer are proposed based on Winsoek and MFC technology in detail A test machine is built to do the testing, the test results prove that the test machine works stably and well, satisfies the design rules and also provides a feasible method for the remote supervise in communication power supplier whose requirement includes remote supervise, no-people on duty and so on.  相似文献   
156.
In TT&C system,unified spread spectrum framework and adaptive antenna digital beamforming technologies are used to track, telemetry and command objects. Constant modulus array (CMA) and adaptive signal canceller estimate the direction of arrival (DOA) of every signal and use the optimum weighted vector to form the beams. The phase weighted vectors estimated from DOA improve the processing gain as well as being utilized in the transmitting of tele command signal to form the beam of specified object. Its processing performance is researched and simulated in this paper.  相似文献   
157.
A new type of inorganic anchoring material is developed as a substitution for anchoring adhesive to overcome some imperfections in the process of planting reinforcing steel bar.The mix proportion of the anchoring material is determined by experiments.The compressive strength,adhesive force to concrete,volume stability and anchoring force with steel bar are studied.The early strength of the anchoring inorganic material is quite high: for 1d up to 38.5MPa and 3d up to 60MPa.It is a good adhesive to concrete and the adhesive strength of 28d is about 2MPa.The anchoring material will have tiny volume expansion with the age,which is beneficial to enhancing the anchoring force.The essential component of the inorganic anchoring material is cement-based material,so some defects of the organic macromolecular material can be avoided,such as poor stability and requirement for vigorous construction conditions.Its characteristics in early strength,adhesive force to concrete and volume expansion can satisfy the requirement of the construction to the planting reinforcing steel bar and the loading force,thus it can be used as a substituting material for anchoring adhesive.  相似文献   
158.
Product design is a procedure that enterprises meet the needs of consumers; conceptive design is one of the steps in product design and it directly considers requirements of consumers. So how to supply consumers with satisfying function is the essential point. On the basis of function analysis of Value Engineering, the paper puts forward a new method to exercise function definition and function analysis, implements conceptual product design procedure with database techniques.A new way is gotten to convert requirements to conceptual product.  相似文献   
159.
160.
Due to the sharp contradiction between rapidly developing housing construction in small-size town and quite low technological level, in this paper, the significance of setting up integrally technological system is emphasized and the suggestion that the technology should be integrated with the sustainable development, regional context and industrialization is put forward.  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