全文获取类型
收费全文 | 18308篇 |
免费 | 1289篇 |
国内免费 | 607篇 |
专业分类
电工技术 | 392篇 |
综合类 | 966篇 |
化学工业 | 3387篇 |
金属工艺 | 1530篇 |
机械仪表 | 746篇 |
建筑科学 | 2417篇 |
矿业工程 | 157篇 |
能源动力 | 683篇 |
轻工业 | 289篇 |
水利工程 | 235篇 |
石油天然气 | 272篇 |
武器工业 | 35篇 |
无线电 | 2017篇 |
一般工业技术 | 3944篇 |
冶金工业 | 830篇 |
原子能技术 | 162篇 |
自动化技术 | 2142篇 |
出版年
2024年 | 29篇 |
2023年 | 509篇 |
2022年 | 340篇 |
2021年 | 530篇 |
2020年 | 561篇 |
2019年 | 552篇 |
2018年 | 517篇 |
2017年 | 530篇 |
2016年 | 590篇 |
2015年 | 642篇 |
2014年 | 956篇 |
2013年 | 1120篇 |
2012年 | 948篇 |
2011年 | 1402篇 |
2010年 | 936篇 |
2009年 | 1051篇 |
2008年 | 1007篇 |
2007年 | 981篇 |
2006年 | 909篇 |
2005年 | 816篇 |
2004年 | 732篇 |
2003年 | 660篇 |
2002年 | 595篇 |
2001年 | 397篇 |
2000年 | 368篇 |
1999年 | 358篇 |
1998年 | 338篇 |
1997年 | 272篇 |
1996年 | 239篇 |
1995年 | 216篇 |
1994年 | 184篇 |
1993年 | 142篇 |
1992年 | 145篇 |
1991年 | 107篇 |
1990年 | 101篇 |
1989年 | 63篇 |
1988年 | 64篇 |
1987年 | 38篇 |
1986年 | 33篇 |
1985年 | 42篇 |
1984年 | 27篇 |
1983年 | 35篇 |
1982年 | 23篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 15篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1974年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 416 毫秒
101.
A. S. S. R. Reddy 《Canadian Metallurgical Quarterly》1992,5(1):70-78
The dynamic analysis and control system design of large space structures involve the solution of the large‐dimensional generalized matrix eigenvalue problem. The computational effort involved is proportional to the third power of the dimension of the matrices involved. To minimize the computational time a graph‐theory approach to reduce a matrix to lower‐ordered submatrices is proposed. The matrix‐reduction algorithm uses the Boolean matrices corresponding to the original numerical matrices and, thus, the computational effort to reduce the original matrix is nominal. The computational savings directly depend upon the number of submatrices into which the original matrix is reduced. A free‐free square plate is considered as an example to illustrate the technique. In this example a matrix of 16th order is reduced to three scalars corresponding to three rigid‐body modes, and three matrices of order three and one matrix of order four. 相似文献
102.
上海市电话局用户接入网建设经历了调研、网络规划、启动实施和进一步完善、规范四个怅阶段、现已基本形成了覆盖政府机关、大专院校、医院、商务大楼及高层建筑、新建住宅小区、区级以上图书馆等范围的用户光纤网络,为加快经济建设步伐、满足多层次用户需求、拓展电信新业务打下了坚实基础。 相似文献
103.
添加剂及硫元素对ZL108合金中铁相形态的影响 总被引:7,自引:1,他引:6
在含铁为12%的ZL108合金中,加入5%的以锰、铬、稀土为基本成分的添加剂时,合金中针状、片状的铁相变为团球状、块状及梅花状。单独加硫时,铁相呈短杆状。先加入3%的添加剂再加硫,则铁相变为非常细小的团球状、块状,根据GB3508-83的规定,铁相形态可达一级 相似文献
104.
在BSO晶体中同时掺入Ce和Eu离子,生长了Ce:Eu:BSO晶体,对晶体的二波耦合和四波混频性能了测试。结果表明,Ce和Eu离子对晶体的光折变效应起到了增强的作用。 相似文献
105.
The expert process of engineering involves application of knowledge fundamental to the engineering process at one end, and of compiled knowledge in the form of heuristics gained through many years of experience at the other. Developments in Artificial Intelligence have made the process of computer aided engineering richer by enabling the simulation of this human process of engineering, which until now has been difficult to capture. Knowledge Based Expert Systems (KBES) in engineering developed so far have addressed only narrow domains of the entire process of engineering. This paper discusses a KBES shell (IES) that integrates various AI technologies, which makes it possible to implement new problem-solving strategies required for efficient handling of the entire engineering process. Issues in the integrated process of engineering are discussed first, in order to evolve a specification for the shell. The blackboard architecture is shown to be the ideal backbone for such a shell. The details of inference techniques, the knowledge based backtracking mechanism and the DBMS used in the IES are presented. The application of the IES is demonstrated using the domain of integrated engineering of steel industrial structures as an example. This application encompasses the engineering activities of conceptual design, detailed design, documentation and construction planning. 相似文献
106.
107.
病险水工建筑物可靠性评估方法初探 总被引:4,自引:0,他引:4
水工建筑物可靠性评估是水利工程管理中急需解决的问题,将水工建筑物分解为由分部工程组成的层次结构,引入子系统概率重要性系数,用层次分析法导出水工建筑物系统可靠度指标的实用计算方法。 相似文献
108.
单元系T—p相图的数学结构 总被引:1,自引:0,他引:1
作者以化学元素的稳定单质为基准,推演出了任意物质M_i(相态Ω)的热力学生成活度{相态Ω)的函数形式:?D_Ω数值的大小体现着相态Ω的热力学相对稳定性.根据集合论原理沿D(稳定性)座标取极大值的方法把物理性质互不连续的各个异相态连结在一起,建立了单元系在T-p面上的优势分布方程(PSDE):■作者以H_2O为实例,计算了T-p相图,与实验相图基本一致. 相似文献
109.
Elias G. Abu‐Saba William M. McGinley Raymond C. Montgomery 《Canadian Metallurgical Quarterly》1991,4(4):347-354
As the manned exploration of space continues, many complex structural components are being developed to construct the orbital platforms that will be used to house communication hardware, personnel, and manufacturing complexes. These components are extremely flexible and complex in their behavior. There is a need for a simple method for determining the dynamic characteristics of these space structures with a minimum of effort. A mathematical model of one of these structural elements, an articulating truss beam, has been developed to predict its dynamic response. Assumptions of the force interaction between the beam elements and the joints have been made for using this model. Algorithms are provided to determine the flexibility matrix of the truss beam for use in the equation of motion. The natural frequencies obtained from using this method are compared with those obtained by the finite element method. An experimental procedure is planned to validate the results from the theoretical method. 相似文献
110.