全文获取类型
收费全文 | 4318篇 |
免费 | 107篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 44篇 |
综合类 | 1篇 |
化学工业 | 820篇 |
金属工艺 | 79篇 |
机械仪表 | 75篇 |
建筑科学 | 186篇 |
矿业工程 | 23篇 |
能源动力 | 85篇 |
轻工业 | 390篇 |
水利工程 | 25篇 |
石油天然气 | 16篇 |
无线电 | 259篇 |
一般工业技术 | 650篇 |
冶金工业 | 1093篇 |
原子能技术 | 53篇 |
自动化技术 | 631篇 |
出版年
2021年 | 41篇 |
2020年 | 31篇 |
2019年 | 37篇 |
2018年 | 37篇 |
2017年 | 40篇 |
2016年 | 57篇 |
2015年 | 51篇 |
2014年 | 76篇 |
2013年 | 245篇 |
2012年 | 141篇 |
2011年 | 170篇 |
2010年 | 149篇 |
2009年 | 167篇 |
2008年 | 197篇 |
2007年 | 194篇 |
2006年 | 178篇 |
2005年 | 133篇 |
2004年 | 124篇 |
2003年 | 109篇 |
2002年 | 123篇 |
2001年 | 92篇 |
2000年 | 85篇 |
1999年 | 77篇 |
1998年 | 65篇 |
1997年 | 77篇 |
1996年 | 74篇 |
1995年 | 80篇 |
1994年 | 74篇 |
1993年 | 75篇 |
1992年 | 90篇 |
1991年 | 29篇 |
1990年 | 67篇 |
1989年 | 56篇 |
1988年 | 59篇 |
1987年 | 67篇 |
1986年 | 66篇 |
1985年 | 88篇 |
1984年 | 86篇 |
1983年 | 81篇 |
1982年 | 83篇 |
1981年 | 74篇 |
1980年 | 45篇 |
1979年 | 61篇 |
1978年 | 60篇 |
1977年 | 54篇 |
1976年 | 52篇 |
1975年 | 64篇 |
1974年 | 38篇 |
1973年 | 39篇 |
1972年 | 32篇 |
排序方式: 共有4430条查询结果,搜索用时 78 毫秒
11.
This article discusses the phenomenon of youth violence from a psychology of gender perspective. Although other factors are discussed--including gun availability, violence-related media influence, family and caretaker factors, and effects of teasing and bullying--the intention is to highlight new thinking on the potential relationship between boys' traditional masculine socialization experiences and violence. In this new perspective, traditional masculine socialization estranges and isolates many boys from their genuine inner lives and vital connections to others, which is theorized to heighten their risk of engaging in acts of violence. The authors identify school and community programs that may be helpful in counteracting damaging socialization experiences and supporting boys' healthier emotional and psychological development. Finally, the article discusses approaches that psychologists and other mental health professionals can use to help address this vital issue. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
12.
Ronald Szypura 《百年建筑》2006,(8):21-22
住宅概念会随着时间而变动,我们需要考虑的是如何利用住宅形式的改变去迎合住宅概念的改变。[编者按] 相似文献
13.
Our fundamental premise is that energy consumption at the household level is a key indicator of standard of living. We employ state-of-the-art panel cointegration techniques to evaluate the nature of the relationship between income measures and energy consumption measures for seven East Indian Ocean countries. The general finding is that income and household electricity consumption are not cointegrated. Given this finding, we conclude that standard of living measures that rely on income measures and do not include household-level energy consumption information will necessarily miss important indications of both levels and changes of standard of living. 相似文献
14.
Boesch Ronald D. Magin Richard L. Franke Stevenb J. 《IEEE transactions on bio-medical engineering》1987,(11):904-907
This paper describes a design for an analog phase shifter operating at 915 MHz and suitable for use in a phased array microwave hyperthermia system. Here, the major operating constraint was minimization of amplitude variation over a 1800 phase shift, whereas previous phase shifters were designed to obtain a linear relationship between phase and control voltage. The result is a simple, inexpensive hybrid coupler phase shifter that operates over a narrow bandwidth and provides 180°of continuous phase shift with input powers up to 1 W. 相似文献
15.
16.
Ronald Smith 《Canadian Metallurgical Quarterly》2004,130(2):165-169
For longitudinally uniform stretches of waterways there is a mixing center for the across-channel location of a steady point source in steady flow, such that complete mixing is achieved as soon as possible and there is no concentration overshoot at either of the two shorelines. A mathematical definition of the mixing center is the zero of the first oscillatory cross-channel diffusion mode. With the shorelines plus four interior data points across the channel, the starting estimate for the mixing center suffices to keep peak shoreline concentrations to within 6% of optimal. For comparison, a source at mid flow gives 18% shoreline concentration overshoot in the test case. Should very high precision be required, the Appendix gives an iterative construction that converges to the first oscillatory diffusion mode. 相似文献
17.
This study investigated the relationship between self-appraisals of performance, symptom severity and post-event rumination in social phobia, and evaluated the effect of treatment on these variables. A socially phobic group and a nonanxious control group performed an impromptu speech and were told that their performance would be evaluated. Participants appraised their performance immediately after the speech and 1 week later, and the frequency of post-event rumination during the week following the speech was assessed. The socially phobic group maintained the negative appraisals of their speech over the week, whereas the nonclinical group showed increased positivity about their performance The socially phobic group also engaged in more negative rumination than controls. Treatment improved perceptions of performance and reduced negative rumination. These results are discussed in the light of cognitive models of social phobia. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
18.
Various ways of quantifying damages have been applied to productivity loss claims in construction. All of the ways attempt to be as objective as possible based on the extent of information available in a particular case. The measured mile, a widely accepted method, is employed when an unimpacted baseline period of production can be identified. Although that approach is considered to be the most objective method available in such cases, the method is limited and does not directly account for variation in individual productivity values about a normal or natural level of productivity. A gap exists between the use of existing methods and the availability of an appropriate methodology that specifically addresses variation in productivity. The key lies in the way baseline productivity is measured, which is inherently statistical, yet no truly statistical methods are used to establish such a baseline. Using the measured mile as a backdrop, this article provides an objective, measurement-based approach that can be used to establish a productivity baseline applied to construction productivity loss claims, based on the application of statistical methods aided by a process control chart. The focus is on providing the basic principles and concepts underlying the approach presented. 相似文献
19.
A greedy algorithm to determine the number of transporters in a cyclic electroplating process 总被引:3,自引:0,他引:3
This paper presents a local optimization algorithm for minimizing the number of transporters required for material handling in a cyclic processing line. Within a cycle, a given set of transportation operations must be performed. Each operation consists of picking up a work-in-process job at a stage and delivering it to the next stage. The length of time that a job can remain at a particular stage is restricted by a time window. The transporters that perform the operations move on a shared track, and traffic collisions must be avoided during their movements. To avoid traffic collisions, the operations are partitioned into groups, where each group is served by a single transporter. A local optimal solution is obtained when the group sizes are maximized. We show that the duals of the linear programming subproblems formulated in the process of maximizing the group sizes are specially structured shortest-path problems. This leads to an effective search method for the maximization problem. Conditions when die proposed algorithm achieves die global optimal solution are discussed. The algorithm's performance is evaluated on both randomly generated test problems and benchmark problems. 相似文献
20.
This communication describes the application and extension of a method for calculating the helical parameters with which to describe molecular conformations. The method, which was originally developed by Shimanouchi and others, is applied to a polyimide of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and 2,2-dimethyl-1,3-(4-aminophenoxy)propane (DMDA) which has eight torsional bonds in the chemical repeat unit. Discrete low energy states for these torsions were determined by Ramanchandran energy maps of sequential dihedral pairs or single bond torsional energy diagrams. The total number of possible low energy conformations for these states is 1152 including conformationally related isoenantiomorphs. The method conveniently generates the conformations for subsequent crystal structure packing and refinement. Consideration of these together with the X-ray data of Cheng and co-workers reduces the number to about 15 with about a 2/1 conformation and a c axis of approximately 49.2 Å. Of these, about half appear to be good candidates for crystal packing. 相似文献