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   18658篇
  免费   1426篇
  国内免费   619篇
电工技术   941篇
技术理论   5篇
综合类   1947篇
化学工业   2110篇
金属工艺   528篇
机械仪表   621篇
建筑科学   2609篇
矿业工程   1229篇
能源动力   553篇
轻工业   1836篇
水利工程   1001篇
石油天然气   1436篇
武器工业   101篇
无线电   526篇
一般工业技术   1644篇
冶金工业   1838篇
原子能技术   178篇
自动化技术   1600篇
  2025年   126篇
  2024年   342篇
  2023年   334篇
  2022年   675篇
  2021年   723篇
  2020年   662篇
  2019年   565篇
  2018年   511篇
  2017年   550篇
  2016年   698篇
  2015年   744篇
  2014年   1276篇
  2013年   1101篇
  2012年   1309篇
  2011年   1416篇
  2010年   1029篇
  2009年   1101篇
  2008年   891篇
  2007年   1062篇
  2006年   962篇
  2005年   840篇
  2004年   691篇
  2003年   599篇
  2002年   526篇
  2001年   391篇
  2000年   294篇
  1999年   240篇
  1998年   184篇
  1997年   142篇
  1996年   95篇
  1995年   92篇
  1994年   68篇
  1993年   55篇
  1992年   49篇
  1991年   33篇
  1990年   32篇
  1989年   23篇
  1988年   19篇
  1987年   15篇
  1986年   25篇
  1985年   16篇
  1984年   15篇
  1983年   17篇
  1982年   10篇
  1966年   10篇
  1964年   17篇
  1963年   12篇
  1960年   11篇
  1959年   10篇
  1957年   12篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
In 1993, the American Society for Testing and Materials carried out a field test of newly calculated tristimulus weighting factors. These weighting factors had been calculated by a method proposed by Venable. the test also included a method of correction for bandpass dependence put forth by Stearns. the purpose of the trial was to assess the possible reduction in bandpass dependence introduced by each of these sets of weights. A large number of sets of spectral data were gathered from the cooperators in the field test. Results of integration by the various sets of tristimulus weighting factors were calculated. A total of 15 120 color differences were calculated and statistics were derived to test the probable error resulting from each method of correction. Errors attributable to bandpass dependence were on the order of a few tenths to as much as one CIELAB unit when uncorrected weight sets were used. These errors could be reduced to a few hundreths of a CIELAB unit, and in some cases to a few thousandths of a unit, by employing one correcting strategy or the other. an overall mix of strategies was ultimately chosen to minimize the bandpass dependence over the entire range of weight sets. Utilizing this mixed strategy, the median error introduced into 10-nm integration by bandpass dependence was only 0.004 CIELAB units. © 1995 John Wiley & Sons, Inc.  相似文献   
2.
In order to study the influence of depth-thickness ratio on bedding slope stability, whose sliding surface is flexural concave in shape under mining conditions, this paper aims to study the characteristics of deformation and damage of bedding sliding with depth-thickness ratios of 200:1, 150:1, 120:1, 100:1 and 50:1by adopting numerical simulation analysis software combined with laboratory-made ‘‘under the influence of mining variable sliding surface slope similar simulation test bed", and to propose identification methods for slope stability under the influence of mining. The results show that mining activities under the slope reduce slope stability. With a decrease in the mining depth ratio, the influence of mining on the slope increases gradually, and the damage to the slope gradually expands, the stability of the slope gradually reduces, fracture occurs on the slope toe and the central fissure gradually develops to the surface,and reaches slide threshold when the depth-thickness ratio is 50:1.  相似文献   
3.
性伦理思想对我国当代大学生性教育具有十分重要的意义,通过对中国传统性伦理思想的研究分析,探索其对大学生性教育产生的主要影响,为进一步推进当代大学生的性教育提供合理性依据。  相似文献   
4.
Problems from plastic analysis are based on the convex, linear or linearised yield/strength condition and the linear equilibrium equation for the stress (state) vector. In practice one has to take into account stochastic variations of several model parameters. Hence, in order to get robust maximum load factors, the structural analysis problem with random parameters must be replaced by an appropriate deterministic substitute problem. A direct approach is proposed based on the primary costs for missing carrying capacity and the recourse costs (e.g. costs for repair, compensation for weakness within the structure, damage, failure, etc.). Based on the mechanical survival conditions of plasticity theory, a quadratic error/loss criterion is developed. The minimum recourse costs can be determined then by solving an optimisation problem having a quadratic objective function and linear constraints. For each vector a(·) of model parameters and each design vector x, one obtains then an explicit representation of the “best” internal load distribution F. Moreover, also the expected recourse costs can be determined explicitly. Consequently, an explicit stochastic nonlinear program results for finding a robust maximal load factor μ. The analytical properties and possible solution procedures are discussed.  相似文献   
5.
论述了泉州市金鸡拦河闸重建工程的意义,分析了重建工程对河道上下游水生态环境的影响,提出了环境保护与污染防治措施。  相似文献   
6.
《Ergonomics》2012,55(1-3):85-91
Shiftwork researchers have concentrated on the problems on the night shift, and have tended to neglect the truncation of sleep that can occur before morning, or ‘early’, shifts. We examined the sleep timing and duration between morning shifts of shiftworkers on a variety of shift systems. The extent of morning shift sleep truncation depended very largely on the time at which individuals had to leave home. Further, there was some suggestive evidence that the failure of individuals to compensate by going to sleep earlier was not simply due to social pressures to stay up. Rather it would appear to have depended, at least in part, on the biological clock determined ‘forbidden zone’ for sleep that occurs shortly before habitual sleep onset.  相似文献   
7.
在纤维缠绕压力容器设计中,纤维缠绕的方向及各方向纤维用量配比是关键问题。过去的研究中,这一问题一直没能得到很好地解决,特别是各方向纤维用量问题。本文在文献[1~4]的基础上,以加权因子和铺设角为参量给出了对称多层正交各向异性外压容器筒体失稳的最佳铺层理论值。得出了加权因子s取最佳值的范围为0<s<0.25的结论。文中算例表明,按最佳取值给出的临界压力较其它情况有较大幅度的提高。  相似文献   
8.
Extreme winds, hurricanes, and tornadoes produce significant damage to electrical transmission and distribution line structures. The damage produces loss of power to the affected communities for a variable length of time, depending on severity of damage. Most institutions whose operations would be life threatening in the event of power failure have emergency power. However, loss of power to both residences and businesses can have economic impact on the community in the form of temporary housing shortages and loss of business. Utility companies seem to cope with wind damage fairly well, following risk management procedures in designing for wind and in providing alternate routing for distribution lines. However, continuing research and developments are needed to keep abreast of the problem.  相似文献   
9.
空冷机组是解决富煤贫水地区电力工业发展问题的有效措施,近年来在国内外发展迅速。作为海勒式间接空冷系统的关键设备,喷射式凝汽器的性能与整个空冷机组的性能直接相关。介绍了国内外喷射式凝汽器的研究现状,分析了影响喷射式凝汽器传热性能的主要因素。  相似文献   
10.
对Cr-Mo系列有代表性钢种SCM822H的临界点、连续冷却曲线进行了测试,探讨了不同热处理状态对其晶粒度、组织和性能的影响,为进一步优化和完善该钢的生产工艺提供了理论依据。  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