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   116952篇
  免费   10880篇
  国内免费   5321篇
电工技术   7641篇
技术理论   10篇
综合类   7985篇
化学工业   18522篇
金属工艺   6692篇
机械仪表   7887篇
建筑科学   8739篇
矿业工程   3114篇
能源动力   3557篇
轻工业   8415篇
水利工程   2357篇
石油天然气   5466篇
武器工业   1034篇
无线电   14514篇
一般工业技术   14824篇
冶金工业   5070篇
原子能技术   1632篇
自动化技术   15694篇
  2025年   29篇
  2024年   1983篇
  2023年   2197篇
  2022年   3502篇
  2021年   4916篇
  2020年   3882篇
  2019年   3495篇
  2018年   3412篇
  2017年   3745篇
  2016年   3708篇
  2015年   4798篇
  2014年   5871篇
  2013年   6972篇
  2012年   7699篇
  2011年   8289篇
  2010年   7388篇
  2009年   6899篇
  2008年   6755篇
  2007年   6295篇
  2006年   6105篇
  2005年   5208篇
  2004年   3860篇
  2003年   3615篇
  2002年   3953篇
  2001年   3370篇
  2000年   2700篇
  1999年   2475篇
  1998年   1853篇
  1997年   1513篇
  1996年   1386篇
  1995年   1207篇
  1994年   960篇
  1993年   757篇
  1992年   562篇
  1991年   433篇
  1990年   329篇
  1989年   238篇
  1988年   234篇
  1987年   120篇
  1986年   118篇
  1985年   71篇
  1984年   55篇
  1983年   33篇
  1982年   35篇
  1981年   29篇
  1980年   22篇
  1979年   18篇
  1976年   11篇
  1975年   12篇
  1970年   7篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications.  相似文献   
3.
通过对相变增韧陶瓷及一种可切削玻璃-陶瓷动态疲劳(恒应力速率)试验中高应力速率区断裂应力下降现象的理论分析,发现这种现象与材料的阻力特性(R-curve)密切相关。确立的σ_f-σ理论关系能够很好地描述整个应力速率区间内的动态疲劳试验结果。高应力速率区σ_f-σ在双对数坐标下为负斜率直线,直线斜率为(m为阻力曲线KR=k(△a)~m的指数),断裂主要由材料阻力行为控制;低应力速率区,σ_f-σ在双对数坐标下为正斜率直线,直线斜率为 (n为应力腐蚀指数),断裂主要由材料应力腐蚀行为控制。建立了测定材料阻力特性的一种新方法,分别用这种方法及压痕/弯曲方法对一种可切削玻璃-陶瓷的阻力特性进行了实验测定,两种方法所得结果有很好的一致性。  相似文献   
4.
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models  相似文献   
5.
本文提出新型布线算法,集李氏迷宫法与线搜索法的长处为一体,以饱和带法进行动态排序,以线搜索法确定借孔位置,然后用李氏法进行单层布线,获得最佳路径,从而达到线型好,布通率高的效果。  相似文献   
6.
The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water‐cooling tower and during urea granulation in an air‐cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters.  相似文献   
7.
Biodegradable multiblock poloxamers (BMPs) with gel duration of 8 h to several weeks were prepared by varying their molecular weights from 4000 to 40 000 g mol?1. The molecular weight of the BMP was controlled by changing the poloxamer to coupling agent ratio. Assuming a micelle packing model of the BMP gel, as in the case of a poloxamer gel, the micelle properties and critical gel concentration of BMPs were investigated on the basis of the scaling concept. The findings suggest that the control of molecular weight by hydrolyzable groups can be a facile approach to optimize the gel properties for biomedical applications. Copyright © 2005 Society of Chemical Industry  相似文献   
8.
The application of the Trefftz method for calculating wave forces on offshore structures is presented. Indirect and direct formulations using complete and non-singular systems of Trefftz functions for the Helmholtz equation are posed in this paper. An effective technique using different interpolation functions for the velocity potential and wave force are suggested to improve the computational accuracy of the wave force. The numerical examples show that the present method is highly efficient and accurate.  相似文献   
9.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper.  相似文献   
10.
In this paper we design an experiment which can be depicted as a simple scenario, a very limited 'world'. In this world, there are an actor that can pursue a project and an observer that is keeping its eyes on the actor. We try to show in the experiment that the observer can to some degree understand the actor based on its knowledge and some metaphors, i.e. understand what the actor is doing and why. As the conclusion of this experiment, we try to show some features of 'understanding'. These are (1) that 'understanding' has to be based on some preliminary knowledge; (2) that 'understanding' is a process of incremental learning; (3) that, as for symbolic systems, some metaphors are necessary for mapping real entities into concepts in mind.  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