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   2772篇
  免费   154篇
  国内免费   17篇
林业   309篇
农学   206篇
基础科学   23篇
  331篇
综合类   1053篇
农作物   190篇
水产渔业   103篇
畜牧兽医   560篇
园艺   30篇
植物保护   138篇
  2023年   11篇
  2022年   8篇
  2021年   18篇
  2020年   23篇
  2019年   32篇
  2018年   72篇
  2017年   69篇
  2016年   75篇
  2015年   37篇
  2014年   83篇
  2013年   106篇
  2012年   123篇
  2011年   137篇
  2010年   48篇
  2009年   70篇
  2008年   54篇
  2007年   155篇
  2006年   510篇
  2005年   312篇
  2004年   169篇
  2003年   332篇
  2002年   152篇
  2001年   60篇
  2000年   50篇
  1999年   31篇
  1998年   17篇
  1997年   10篇
  1996年   6篇
  1995年   6篇
  1994年   19篇
  1993年   6篇
  1992年   4篇
  1991年   7篇
  1990年   4篇
  1989年   7篇
  1988年   6篇
  1986年   5篇
  1984年   5篇
  1983年   4篇
  1980年   5篇
  1979年   4篇
  1969年   3篇
  1968年   4篇
  1965年   3篇
  1964年   5篇
  1963年   6篇
  1960年   3篇
  1957年   3篇
  1927年   7篇
  1926年   3篇
排序方式: 共有2943条查询结果,搜索用时 187 毫秒
41.
Investment on construction projects has become an important factor in improving the development of economy in China.The non-price bottom bidding is a representation that the investment on projects is becoming standardized.During the years of trying out the non-price bottom bidding,the colluding in bidding or bidding below the cost has happened several times,which have damaged the benefits of owners.To solve theses problems,this paper firstly studies the reason of these problems-the failure in the normal relationship between principal and agent.Then,some measures have been presented as follows: building systematic and scientific system of qualification prejudication,judging behaviors of colluding in bidding and bidding below the cost with reason and providing a surety mechanism of the project.The authors hope that these measures are beneficial to non-price bottom bidding.  相似文献   
42.
In this study the influence of the low-intensity ultrasound treatment on excess sludge has been observed.The oxygen uptake rate(OUR),soluble chemical oxygen demand(SCOD),soluble total nitrogen(TN) and soluble total phosphorus(TP) were examined for three power levels of 0.03 W/mL, 0.05 W/mL and 0.1 W/mL as well as two time series of 0~5 min and 0~30 min.It showed that there were two stages of ultrasonic treatment: the first stage took place within the flocs in four minutes,in which SCOD,TN,TP were dissolved from flocs.In the second stage,the microbial activities have been strengthened,as well as OUR,TN,TP have increased greatly.  相似文献   
43.
The existence of ettringite in sulphoaluminate cement hardened paste is mainly in the form of pole-like crystal,which causes unfavorable effect on the cement.In this paper the strength and microstructure of the sulphoaluminate cement containing ultra-fine CaCO_3 weze discussed.Experimet results show that the strength of sulphoaluminate cement was obviously improved by adding 3% of ultra-fine CaCO_3.After curing for 28d,the compressive strength of cement paste and mortar is 100.6MPa and 94.1MPa respectively,and the bending strength of the mortar reached 12.5MPa.SEM study on hardened paste of sulphoaluminate cement containing ultra-fine CaCO_3 showed that its structure was dense and homogeneous,there was hardly any massive crystall detected.  相似文献   
44.
In this paper,four models are selected as the representatives and applied to nonlinear dynamic analysis program for space frames which is based on the beam-column elements using the finite element flexibility method and the fiber model.Park's test on combined axial and bending columns under cyclic loading are taken as the calibrations,comparisons to material and structural member level are drawn and the analytical results of various models are discussed.  相似文献   
45.
After the completion of the Three Gorges project,the navigation conditions of the reservoir region will be improved evidently,which has laid the foundation for straight run of the 10,000-ton-class fleet to Chongqing Port,and is the promotion of the development of shipping in Yangtze River.But according to the standard of the 10,000-ton-class fleet,there are still some reaches of the reservoir region can not meet the requirements of the waterway on smooth and safe navigation.Therefore,some regulation measures should be adopted to eliminate these obstructions.It is one of the important parts in the reservoir region waterway regulation work for the Fuling to Tongluo canyon reach blasting project.30 reef obstacle blocks of 14 reaches in this project were removed by blasting.Based on the analysis of obstruct features of various rocks,according to the standard of the 10,000-ton-class fleet,the design parameters and blasting regulation program were put forward,and the regulation effect is analyzed and forecasted.  相似文献   
46.
City is not a concretionary but a dynamic matter. It should keep close touch with the animated tradition, and we should look forward to its future too. Thus we will be facing with the problem of inheritance and development of the tradition. Because the tradition is a potential for good as wdll as for evil, it can promote the development of a thing, and also may hinder its progress, so there should be correct attitudes to the traditional inheritance. This paper studies the modem application of the traditional street, lane and courtyard, which brings new vitality to the tradition and imparts fresh life to the modem city.  相似文献   
47.
Construction industry is not only the pillar industry in national economy,but also the typical industry with intensive labors.As a major part of the construction industry,the Construction Employment System(CES) is an important factor of the market order,as well as the quality,the safety and the development of the industry.It is also an important part for building a harmonious society.It concerns the social harmony,political harmony,societal harmony,cultural harmony,urban-rural harmony,etc.However,at present,there are still many problems in CES that might influence the harmonious society building.This paper advises to speed up the reformation of CES,to establish and consummate the system of construction labor subcontract,to develop vigorously labor subcontract corporations,to improve the quality of the labors,to ensure the rights and interests of the labor.  相似文献   
48.
This paper analyzes the SOHO and the reuse of old industry building, and deeply explores the creation and application of SOHO mode in the reuse of old industry building, furthermore, it points out the four inspirations to the reuse of old industry building, at the end, a general judgment of the development logic of SOHO is given.  相似文献   
49.
Based on a cable -stayed bridge girder as an example, the structure and function, the operating principle and calculation model of the main elements of the Basket of wide - stayed bridge were described in detail. A further discussion was carried out on the Basket of Cantilever construction of the main beam in the structure.  相似文献   
50.
Geogrid reinforced soil retaining wall(GRSRW) is composed of panel,geogrid and soil,its coupled hydromechanical structural characteristics are increasingly emphasized in practice.In this paper,based on the characteristics of the reinforcement-soil interaction,the grogrid and soil around it with a definite thickness were regarded as a kind of composite material with strain-compatible condition.A saturated porous media model was introduced to simulate the soil and reinforcement-soil composite material hereby and the mathematic model for numerical analysis on structural characteristics of GRSRW was built up.The FEM equations were deduced from the standard Galerkin procedure,resolving these equations,we can gain the relevant dynamic response of saturated GRSRW.  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