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   3822篇
  免费   54篇
  国内免费   1篇
电工技术   82篇
综合类   1篇
化学工业   398篇
金属工艺   20篇
机械仪表   37篇
建筑科学   48篇
矿业工程   2篇
能源动力   25篇
轻工业   110篇
水利工程   9篇
石油天然气   5篇
无线电   325篇
一般工业技术   390篇
冶金工业   1825篇
原子能技术   29篇
自动化技术   571篇
  2021年   28篇
  2020年   17篇
  2019年   28篇
  2018年   26篇
  2017年   31篇
  2016年   19篇
  2015年   27篇
  2014年   24篇
  2013年   135篇
  2012年   64篇
  2011年   80篇
  2010年   84篇
  2009年   87篇
  2008年   95篇
  2007年   72篇
  2006年   81篇
  2005年   72篇
  2004年   49篇
  2003年   75篇
  2002年   76篇
  2001年   69篇
  2000年   55篇
  1999年   106篇
  1998年   433篇
  1997年   267篇
  1996年   193篇
  1995年   153篇
  1994年   134篇
  1993年   136篇
  1992年   66篇
  1991年   54篇
  1990年   76篇
  1989年   62篇
  1988年   64篇
  1987年   49篇
  1986年   64篇
  1985年   66篇
  1984年   41篇
  1983年   49篇
  1982年   45篇
  1981年   47篇
  1980年   37篇
  1979年   27篇
  1978年   38篇
  1977年   56篇
  1976年   103篇
  1975年   24篇
  1974年   30篇
  1972年   20篇
  1970年   17篇
排序方式: 共有3877条查询结果,搜索用时 31 毫秒
41.
Add-drop filters are demonstrated using silica-on-silicon optical waveguide technology. This device consists of a full directional coupler subdivided by Mach-Zehnder sections. Tapering of the coupling coefficients is experimentally shown to dramatically reduce the filters' sidelobes. Only one photolithographic step is required using the silica planar waveguide technology, yielding accurate wavelength control of the filters. Excellent agreement between measurement and design was achieved  相似文献   
42.
This paper presents a finite element method with high spatial order for solving the Maxwell equations in the time domain. In the first part, we provide the mathematical background of the method. Then, we discuss the advantages of the new scheme compared to a classical finite-difference time-domain (FDTD) method. Several examples show the advantages of using the new method for different kinds of problems. Comparisons in terms of accuracy and CPU time between this method, the FDTD and the finite-volume time-domain methods are given as well.  相似文献   
43.
The synthesis and characterization of a novel silicon–silica nanocomposite material are reported. A self‐assembly method allows the encapsulation of silicon nanoclusters within the channels of a periodic mesoporous silica thin film. The result is the formation of a silicon–silica nanocomposite film with bright, room‐temperature photoluminescence in the visible range, and a nanosecond luminescence lifetime. The properties of the nanocomposite material have been studied by several analytical techniques, which collectively show the existence within the channels of non‐diamondoid‐structure‐type silicon nanoclusters with various hydrogenated silicon sites. It is estimated that the silicon nanoclusters in the silica mesoporous films occupy up to 39 % of the accessible pore volume. The nanocomposite film shows improved resistance to air oxidation compared to crystalline silicon. The high loading and chemical stability to oxidation under ambient conditions are important advantages in terms of the development of silicon‐based light‐emitting diodes from this class of materials.  相似文献   
44.
A longitudinal design was used to test the effects of life events experienced by young adolescents and their parents. The criteria were the adolescents' depression, anxiety, and self-esteem. The longitudinal analysis revealed a significant effect for the adolescents' controllable, but not uncontrollable, negative events. However, causal analyses revealed that this effect was the result of the significant relation between initial adjustment and the subsequent occurrence of controllable life stress (e.g., school suspension). The longitudinal analysis also revealed the stress-protective role of positive events, but only with respect to girls' self-esteem. There was no longitudinal support for the role of the parents' negative life events. These findings do not support the etiological importance of an accumulation of relatively discrete negative events experienced by early adolescents and their parents, but they do suggest the need (a) to conceptualize (controllable) life stress as a dependent variable in future research on developmental psychopathology; (b) to examine gender differences in early adolescent life stress; and (c) to develop more sophisticated measures of family life stress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
45.
46.
Two studies explored how domestic violence may be implicitly or explicitly sanctioned and reinforced in cultures where honor is a salient organizing theme. Three general predictions were supported: (a) female infidelity damages a man's reputation, particularly in honor cultures; (b) this reputation can be partially restored through the use of violence; and (c) women in honor cultures are expected to remain loyal in the face of jealousy-related violence. Study 1 involved participants from Brazil (an honor culture) and the United States responding to written vignettes involving infidelity and violence in response to infidelity. Study 2 involved southern Anglo, Latino, and northern Anglo participants witnessing a "live" incident of aggression against a woman (actually a confederate) and subsequently interacting with her. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
47.
Parents (N?=?124) who had lost an infant to sudden infant death syndrome were interviewed 3 wks and 18 mo postloss. Two components of religion (religious participation and religious importance) were assessed, and their relations with 3 coping-process variables (perceived social support, cognitive processing of the loss, and finding meaning in the death) were examined. Greater religious participation was related to increased perception of social support and greater meaning found in the loss. Importance of religion was positively related to cognitive processing and finding meaning in the death. Furthermore, through these coping-process variables, religious participation and importance were indirectly related to greater well-being and less distress among parents 18 mo after their infants' deaths. Results suggest that further study of the social and cognitive aspects of religion would be profitable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
48.
49.
50.
Tripe palms is a cutaneous paraneoplastic syndrome. We report a case of tripe palms in a 71-year-old man with non-small cell lung cancer. Approximately 90% of patients with tripe palms have an associated cancer, most commonly involving the lung or the stomach. Any patient with tripe palms must have a complete cancer workup, especially for lung and stomach cancer.  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