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   12772篇
  免费   120篇
  国内免费   9篇
电工技术   99篇
综合类   2篇
化学工业   1027篇
金属工艺   101篇
机械仪表   300篇
建筑科学   218篇
矿业工程   28篇
能源动力   129篇
轻工业   875篇
水利工程   108篇
石油天然气   15篇
无线电   865篇
一般工业技术   1023篇
冶金工业   7255篇
原子能技术   108篇
自动化技术   748篇
  2021年   68篇
  2020年   51篇
  2019年   62篇
  2018年   60篇
  2017年   82篇
  2016年   65篇
  2015年   47篇
  2014年   104篇
  2013年   315篇
  2012年   160篇
  2011年   238篇
  2010年   211篇
  2009年   232篇
  2008年   261篇
  2007年   240篇
  2006年   246篇
  2005年   220篇
  2004年   180篇
  2003年   203篇
  2002年   201篇
  2001年   163篇
  2000年   160篇
  1999年   332篇
  1998年   2135篇
  1997年   1249篇
  1996年   916篇
  1995年   549篇
  1994年   477篇
  1993年   499篇
  1992年   143篇
  1991年   167篇
  1990年   171篇
  1989年   180篇
  1988年   182篇
  1987年   162篇
  1986年   132篇
  1985年   150篇
  1984年   97篇
  1983年   110篇
  1982年   81篇
  1981年   105篇
  1980年   105篇
  1979年   79篇
  1978年   74篇
  1977年   194篇
  1976年   387篇
  1975年   78篇
  1974年   71篇
  1973年   63篇
  1972年   54篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Wastewater treatment technologies suitable for serving large populations are generally reliable and reasonably cost-effective, yet they are almost always financially inappropriate for small communities (< 2,000 p.e.). Comparative cost data suggests that waste stabilization ponds should be an attractive option for small communities, yet perceptions relating to land costs, climate and effluent quality have limited their application in the UK. This paper details typical UK land costs, climate and winter performance data for a pilot-scale waste stabilization pond with various upgrading technologies: system A, two tertiary maturation ponds in series; B, two tertiary maturation ponds in series followed by a reed bed channel; C, a control rock filter; D, an aerated rock filter; and E, a constructed wetland. System D was found to perform best, closely followed by system B.  相似文献   
72.
The results of Stan ton and Bairstow (1908) have been reanalyzed to yield information on the composition dependence of the low cycle impact fatigue properties of pearlitic plain carbon steels. It has been found that the energy absorbed per impact, Ei, and the number of impacts are failure, Nf, are related by the equation: In this equation q is determined by the carbon, manganese and silicon contents of the steel; Eo is the impact endurance limit; and C and D are constants. The curve represented by this equation intersects that representing the Johnson-Keller high cycle impact fatigue equation at a value of logeNf equal to 1/C. Thus, the transition from low to high cycle impact fatigue occurs at this value of logeNf.  相似文献   
73.
纽约州立大学Buffalo分校电子封装实验室正在为美国海军开发新型的功率电子封装,在一些极端苛刻的工作条件下(比如在军舰和战机上).它们能够解决大电流密度、高温和大的温度梯度所引起的种种问题。这类功率电子封装还有可能很快进入民用产品。  相似文献   
74.
Evaluative responses appear to involve 2 seemingly distinct sets of processes: those that are automatically activated and others that are more consciously controlled. Using functional magnetic resonance imaging, the authors investigated the brain systems associated with automatic and controlled evaluative processing. Participants made either evaluative (good-bad) or nonevaluative (past-present) judgments about famous names. Greater amygdala activity was observed for names rated as "bad" relative to those rated as "good," regardless of whether the task directly involved an evaluative judgment (good-bad) or not (past-present). Good-bad judgments resulted in greater medial and ventrolateral prefrontal cortex (PFC) activity than past-present judgments. Furthermore, there was greater ventrolateral PFC activity in good-bad judgments marked by greater ambivalence. Together, these findings indicate a neural distinction between processes engaged for automatic and controlled evaluation. Whereas automatic processes are sensitive to simple valence, controlled processes are sensitive to attitudinal complexity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
76.
Over the past seven years, Columbia-Presbyterian Medical Center has been planning and implementing an integrated academic information management system. Accomplishments to date include establishing an institutional information architecture, installing a campus-wide network of workstations, recruiting the staff needed to develop and implement the system, and developing various applications. This paper presents the rationale and steps involved in these accomplishments, as well as data on use of the system so far.  相似文献   
77.
78.
79.
80.
OBJECTIVE: To evaluate the diagnostic accuracy and clinical usefulness of high-resolution transvaginal duplex Doppler ultrasound in postpartum and post-abortion patients with excessive hemorrhage who are suspected of having residual trophoblast. METHODS: Forty-eight women with excessive hemorrhage referred for possible residual trophoblastic tissue were evaluated by transvaginal duplex Doppler ultrasonography. Based on two-dimensional imaging, the patients were divided prospectively into groups: women who had an empty uterus with a normal uterine cavity, those with a pure endometrial fluid collection and no echogenic foci, those who had a mixed endometrial fluid collection with foci of echogenicity, and those with intracavitary heterogeneous material with mixed echo patterns of fluid and solid components. In each group, Doppler studies were performed and the resistance index (RI) was calculated. The two-dimensional patterns and Doppler results were correlated with clinical and pathologic follow-up. RESULTS: Twenty-eight subjects had a normal uterine cavity and seven had a pure endometrial fluid collection; all were treated conservatively and none showed later clinical evidence of residual trophoblastic tissue. In 13 women, residual trophoblast was strongly suggested from the images of two-dimensional ultrasonography: Five showed an endometrial fluid collection with some echogenic foci, and eight exhibited intracavitary mixed echogenic material. All underwent curettage, and residual trophoblastic tissue was found in ten of the 13. The mean (+/- standard deviation) RI to flow in the myometrial arteries was 0.54 +/- 0.15 in women without residual trophoblast and 0.35 +/- 0.1 in those with residual trophoblastic tissue (P < .01). CONCLUSION: Our experience suggests that transvaginal duplex Doppler ultrasonography is an effective noninvasive method for evaluating patients with excessive postpartum and post-abortion hemorrhage who are suspected of having residual trophoblastic tissue. Its use enhances the positive preoperative diagnosis of residual trophoblastic tissue and may reduce unnecessary curettage procedures.  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