全文获取类型
收费全文 | 6021篇 |
免费 | 366篇 |
国内免费 | 222篇 |
专业分类
电工技术 | 179篇 |
技术理论 | 1篇 |
综合类 | 241篇 |
化学工业 | 361篇 |
金属工艺 | 225篇 |
机械仪表 | 913篇 |
建筑科学 | 210篇 |
矿业工程 | 68篇 |
能源动力 | 454篇 |
轻工业 | 55篇 |
水利工程 | 45篇 |
石油天然气 | 150篇 |
武器工业 | 118篇 |
无线电 | 638篇 |
一般工业技术 | 458篇 |
冶金工业 | 236篇 |
原子能技术 | 62篇 |
自动化技术 | 2195篇 |
出版年
2024年 | 10篇 |
2023年 | 55篇 |
2022年 | 104篇 |
2021年 | 165篇 |
2020年 | 143篇 |
2019年 | 102篇 |
2018年 | 102篇 |
2017年 | 157篇 |
2016年 | 169篇 |
2015年 | 270篇 |
2014年 | 362篇 |
2013年 | 397篇 |
2012年 | 385篇 |
2011年 | 497篇 |
2010年 | 346篇 |
2009年 | 362篇 |
2008年 | 346篇 |
2007年 | 426篇 |
2006年 | 368篇 |
2005年 | 314篇 |
2004年 | 253篇 |
2003年 | 235篇 |
2002年 | 182篇 |
2001年 | 98篇 |
2000年 | 99篇 |
1999年 | 108篇 |
1998年 | 92篇 |
1997年 | 89篇 |
1996年 | 59篇 |
1995年 | 61篇 |
1994年 | 49篇 |
1993年 | 32篇 |
1992年 | 31篇 |
1991年 | 34篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 8篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有6609条查询结果,搜索用时 15 毫秒
11.
Environmental contaminants such as trace elements may be present in all foods. Foods, raw materials and ingredients for food production are to an increasing extent traded across borders. Hence, there is a need for international legislation on trace elements as contaminants in food. In 1961, the FAO and WHO established the Codex Alimentarius to elaborate international food legislation. Contaminants in food are handled by the Codex Committee for Food Additives and Contaminants (CCFAC). The Codex Alimentarius system for developing legislation concerning trace elements as contaminants in food is based upon the Codex General Standard for Contaminants and Toxins in Food (GSCTF). By October 2001, the principles for setting maximum limits (MLs) for contaminants in food are agreed, and work is in progress on MLs for trace elements such as lead and cadmium in the various food categories. The status for the proposals is presented and discussed. The EU Regulation 466/2001 of 8 March 2001 sets MLs for lead and cadmium in various foods. This regulation will apply from 5 April 2002. The EU regulation is more detailed but similar to the Codex draft standards for lead and cadmium in food. In future, legislators and administrators in the Codex and EU and analytical chemists will discuss how to use more and better analytical data as risk-management tools to protect public health. Trace elements' speciation is an important aspect of this discussion. 相似文献
12.
用仿真工具优化车辆动力系统(一) 总被引:1,自引:0,他引:1
在本文的第一部分,介绍了一种理想的车辆动力系统的计算机辅助开发过程。它显示了现代仿真技术在产品持续发展过程中的作用,该技术采用硬件回路作非在线的仿真,并通过现代化的试验手段对车辆进行匹配。特别重要的是提供了将电控变速器和发动机控制单元综合的可能性。接着是在线仿真在诸如发动机和变速器模式方面的应用和发展,它是上述开发过程的基础。根据上述的方法论,本文论述了仿真技术已取得的成绩和将来的应用可能性。 相似文献
13.
灰度图像的子块压缩方法 总被引:2,自引:0,他引:2
从灰度图像的局部几何特性出发,把图像中像素灰度相近或相同的区域当作一个整体处理,从而达到图像压缩的目的。计算机仿真实验表明,该方法可以获得产高的压缩比和峰值信噪比,有效地消除方块效应,很好地保持目标细节,具有较高的实用价值。 相似文献
14.
Doratha E Drake 《Information Processing Letters》2003,85(4):211-213
We present a linear time approximation algorithm with a performance ratio of 1/2 for finding a maximum weight matching in an arbitrary graph. Such a result is already known and is due to Preis [STACS'99, Lecture Notes in Comput. Sci., Vol. 1563, 1999, pp. 259-269]. Our algorithm uses a new approach which is much simpler than the one given by Preis and needs no amortized analysis for its running time. 相似文献
15.
神经网络系统学习过程初探 总被引:10,自引:1,他引:9
本文给出了神经网络系统学习过程的一个随机模型--马尔柯夫模型,从最大熵原理的
观点讨论神经网络系统的学习过程,提出将神经网络系统的学习过程分为两个阶段的想法并
给出学习过程的算法. 相似文献
16.
Catherine J. Harrison Yann A. Le Gouellec Robert C. Cheng Amy E. Childress 《Canadian Metallurgical Quarterly》2007,133(11):1004-1014
A dual-staged nanofiltration process is being evaluated as an alternative to reverse osmosis for seawater desalination. The primary goal of this system is to reduce energy consumption while producing potable water at an acceptable recovery rate. Investigation of this system at the bench-scale level focused on membrane surface characterization, ion rejection (including boron, bromide, and iodide rejection), and flux decline. Results from this study showed that two commercially available nanofiltration membranes can effectively desalinate seawater. Although fouling was apparent—and resulted in approximately 20% flux decline over 3 days—a critical flux was not identifiable. Operation of the system at different cross-flow velocities revealed the significance of hydrodynamic conditions on the polarization modulus, and hence on membrane performance. 相似文献
17.
利用多普勒信息的波达方向最大似然估计方法 总被引:11,自引:3,他引:8
为了充分利用信号的时域特性来改善信号波达方向(DOA)的估计性能,本文从最大似然估计出发,推导出了有限快拍,低信噪比情况下多普勒信号波达方向的迭代估计计算法,为进一步减小运算量,本文还推导了一种简化算法,本文提出的两种算法对低信噪比,少快拍数下多普勒信号的DOA估计性能比不利用时域特性的ML方法有明显改善,Monte-Carlo实验验证了本文方法的有效性。 相似文献
18.
19.
20.
The three-parameter and two-parameter Weibull distributions are compared using 26 mechanical property data sets of fiber-reinforced polymeric (FRP) composite materials manufactured by the pultrusion process. Both strength and stiffness properties were examined. The probability distributions were compared on the basis of goodness of fit, nominal design values, and allowable load to achieve uniform reliability. It is recommended that the two-parameter Weibull distribution be used to characterize FRP composite material properties. The primary basis for this recommendation is small differences in nominal design values and small differences in allowable loads between the two-parameter and three-parameter Weibull distributions. Other supporting reasons for the recommendation are similar observed significance levels in distribution fitting, computational efficiency, and the fact that the location parameter of the three-parameter Weibull distribution is near the first order statistic. 相似文献