全文获取类型
收费全文 | 99258篇 |
免费 | 5656篇 |
国内免费 | 7443篇 |
专业分类
林业 | 9743篇 |
农学 | 8146篇 |
基础科学 | 5661篇 |
14475篇 | |
综合类 | 46053篇 |
农作物 | 5677篇 |
水产渔业 | 3543篇 |
畜牧兽医 | 12141篇 |
园艺 | 3475篇 |
植物保护 | 3443篇 |
出版年
2024年 | 762篇 |
2023年 | 1998篇 |
2022年 | 3303篇 |
2021年 | 3809篇 |
2020年 | 3677篇 |
2019年 | 4119篇 |
2018年 | 2263篇 |
2017年 | 3875篇 |
2016年 | 4745篇 |
2015年 | 3946篇 |
2014年 | 5643篇 |
2013年 | 5618篇 |
2012年 | 7854篇 |
2011年 | 7851篇 |
2010年 | 6064篇 |
2009年 | 6108篇 |
2008年 | 5348篇 |
2007年 | 6016篇 |
2006年 | 5147篇 |
2005年 | 4162篇 |
2004年 | 3378篇 |
2003年 | 2784篇 |
2002年 | 2057篇 |
2001年 | 1848篇 |
2000年 | 1629篇 |
1999年 | 1279篇 |
1998年 | 1044篇 |
1997年 | 934篇 |
1996年 | 807篇 |
1995年 | 845篇 |
1994年 | 737篇 |
1993年 | 579篇 |
1992年 | 460篇 |
1991年 | 411篇 |
1990年 | 320篇 |
1989年 | 275篇 |
1988年 | 202篇 |
1987年 | 147篇 |
1986年 | 76篇 |
1985年 | 47篇 |
1984年 | 41篇 |
1983年 | 18篇 |
1982年 | 28篇 |
1981年 | 27篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1963年 | 6篇 |
1962年 | 6篇 |
1956年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
911.
According to the graphics characteristics of metallic doors & windows design and based on the research of graphics dimension restriction problems. This paper provides a new method for parameterized design of metallic doors & windows in virtue of expression solution. In this method, the restrictions of graphic elements have been changed into the parameter expressions of sizes and positions of graphic elements. Through the calculation of such expressions, the parameter driven method has been reached. Thus the parameterization of graphics can be easier and quicker than before. It can be used to setup the open parameterized graphics libraries. 相似文献
912.
In this paper, the authors adopt a method of structural analysis and stereography in combination with acoustic emission Kaiser Effect test in laboratory to find out the main direction of initial stresses. For overcoming the shortcomings of Kaiser effect by comparing it with traditional methods of measuring in-situ stresses, it is shown that this method is simpler, more economical and convenient for a large number of measurements and for studying the law of changes of regional in-situ stresses. 相似文献
913.
The 'Design and Build' contract mode is a new contract and managerial approach, to which more and more attention has been paid. Now it becomes the contracting tendency in the international construction market. In this paper, the basic theories and method of the 'Design and Build' mode are widely and systematically studied. It specifies the intention of the 'Design and Build'contract mode, existing problems and corresponding countermeasures as well as its developing direction. 相似文献
914.
This paper takes "how to estimate the complex security of Large Convention and Exhibition Centre effectively" as the research goal.Based on analyzing the difficulties,target system,technical constitution,probing into the architecture,safety science,and using for reference the mathematics,operational research,statistics and modern system theory and method,trying to explore establishing an evaluation methodological system,which is provided with integrated characters on subject.Based on these ways,it exerts "quality to quantity" fuzzy analytical hierarchy process(FAHP) and aims at discussing the safety grade assessment of the Chongqing International Conference Exhibition Center focusing on designing theories.The aim is to enhance the integration of design practice and safe consciousness,strengthen the building safety management,and perfect city public security system.In practice,it is also an efficient tool for favoring values of architectural environmental safety. 相似文献
915.
Valuation based on the bill of quantifies will change the existing valuation mode of tender and bidding. For the standardized management of tender and bidding for power projects and the inteUigentized information management of power enterprises, it is an inevitable trend of reform to apply the valuation mode based on the bill of quantifies. According to the characteristics of power projects, this paper expounds the working process of the valuation mode based on the bill of quantities and analyzes the goal and function need of the tender and bidding management system. Considering the calculation procedure of the valuation and the quote strategy of quantities bill, the composition of fees for the valuation is settled and the calculation method is designed. To establish the management system of tender and bidding with a valuation based on the bill of quantities is beneficial for the costing reform of power projects and the perfection of the tender and bidding market. Therefore it is of great significance to spread the new management mode of project costing with a valuation based on the bill of quantities. 相似文献
916.
Voltage fluctuation and flicker is one of the main causation that imperils reliability of power supply. Steelmaking EAF with large load of distribution network produces large impact and interference on the public electric network in operation. So it is very important to control reactive power for voltage fluctuation and flicker mitigation. STATCOM possessing high response speed is an effective measure to mitigate voltage fluctuation and flicker of distribution network. Here, comparing to static var compensation, many advantages of STATCOM are analyzed. Operation principles COM mitigating voltage fluctuation and flicker, general control strategies and control method are introduced cussed. The researching pivot and trend in the future are also discussed. of STAT- and discussed. The researching pivot and trend in the future are also discussed. 相似文献
917.
为了验证用CO2替代部分O2进行转炉氧化提钒的可行性,在实验室进行了CO2-O2混合喷吹提钒模拟实验。结果显示C的氧化量与C的氧化速率随CO2含量的增加而升高;V的氧化量随CO2含量的增加而降低,其中CO2含量为20%与纯O2对C、V的氧化量接近;纯O2喷吹时C的氧化量为34.56%,V的氧化量为96.85%;CO2含量为20%混合气体喷吹时C的氧化量为36.83%,V的氧化量为93.29%;以V的相对氧化量与C的相对氧化量的比值(ΔV/ΔC)来衡量提钒保碳能力,CO2含量为20%的最终ΔV/ΔC为5.96,CO2含量,40%、60%、80%的最终ΔV/ΔC均小于3.8;反应前期,V的氧化速率随CO2含量的增加而升高,反应后期V的氧化速率随CO2含量的增加而降低。 相似文献
918.
Dai Dayu Xu Mingxi Peng Qingchu 《保鲜与加工》1993,(3):99-103
The status quo of heauy-metals pollution in water phase of course of Long-Tan hydropower statian was eualuated by water Quality Standand Level Method. With this special method,mone objectiue and definite results were obtained. 相似文献
919.
920.
Lin Yan Gu Hengyue Sun Yang 《保鲜与加工》1997,(1):38-42
A new method for assessment of ambient air quality is proposed by using matter element analysis.This model is simple and reasonable in assessment.The practical example is given,and compared with other methods. 相似文献