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   318702篇
  免费   7781篇
  国内免费   3792篇
电工技术   7289篇
技术理论   6篇
综合类   6397篇
化学工业   49201篇
金属工艺   16092篇
机械仪表   11810篇
建筑科学   11166篇
矿业工程   3600篇
能源动力   7683篇
轻工业   23250篇
水利工程   3984篇
石油天然气   7966篇
武器工业   459篇
无线电   35151篇
一般工业技术   55906篇
冶金工业   38960篇
原子能技术   5247篇
自动化技术   46108篇
  2022年   2468篇
  2021年   3724篇
  2020年   2722篇
  2019年   2877篇
  2018年   17820篇
  2017年   16980篇
  2016年   13583篇
  2015年   4462篇
  2014年   5898篇
  2013年   11370篇
  2012年   11179篇
  2011年   19402篇
  2010年   16665篇
  2009年   14464篇
  2008年   15654篇
  2007年   16536篇
  2006年   8286篇
  2005年   8577篇
  2004年   7573篇
  2003年   7403篇
  2002年   7098篇
  2001年   6275篇
  2000年   5688篇
  1999年   5797篇
  1998年   11667篇
  1997年   8464篇
  1996年   6794篇
  1995年   5129篇
  1994年   4255篇
  1993年   4036篇
  1992年   2978篇
  1991年   2829篇
  1990年   2622篇
  1989年   2601篇
  1988年   2537篇
  1987年   2214篇
  1986年   2135篇
  1985年   2404篇
  1984年   2220篇
  1983年   2038篇
  1982年   1905篇
  1981年   1958篇
  1980年   1818篇
  1979年   1820篇
  1978年   1778篇
  1977年   2110篇
  1976年   2687篇
  1975年   1557篇
  1974年   1550篇
  1973年   1607篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms.  相似文献   
35.
A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current densityJ cs and the intergranular transport current densityJ cr are identical if the measurement conditions are similar. A degradation ofJ cs measured in the external field with AC ripple has been observed.  相似文献   
36.
37.
Containment structures have several regions in which the continuity of the cylindrical pressure boundary is interrupted, e.g., shell penetrations, discontinuous stiffeners, and changes in the shell thickness. Significant strain concentrations can occur in these areas of discontinuity. The Sandia National Laboratories 1:8-scale steel containment equipment hatch was analyzed as an example of an eccentricity at a stiffener intersection.A portion of the as-built 1:8-scale model was modeled with the ANSYS general purpose finite element program using triangular, thin shell finite elements. The overall size of the model was determined from Saint-Venant type considerations of the stress field around the hatch. Shell elements were used to model the ring and formed stiffeners. Geometric and material nonlinear behavior were included. The model was loaded using discrete load steps up to a pressure of 165 psig. At this pressure, the maximum strain was 19.7 percent in the formed stiffener near its intersection with the ring stiffener. The finite element solution demonstrated the very localized nature of the strain field near the ring/formed stiffener intersection.In an attempt to reduce analysis costs, a small portion of the 1:8-scale model immediately surrounding the ring/formed stiffener intersection was selected for further analysis. Two smaller models, a ring/formed stiffener intersection and a ring/circular stiffener intersection, were studied. The models were significantly smaller than the regions used previously. A comparison of the two intersection models showed that the circular stiffener is a more efficient configuration.  相似文献   
38.
39.
Lenin Dnepropetrovsk Pipe Plant. Translated from Metallurg, No. 8, p. 39, August, 1989.  相似文献   
40.
Depending on the spectal width of the source illuminating an interferometer, measurement procedures can utilize either the whole interferogram, or only the fringe envelope, or only the fringe quick oscillations. With an ultraband spectrum source, a simplified adaptation of the methods of Fourier transform spectroscopy yields the variations of the test-fiber propagation constant over the whole wavelength-interval of the source. Chromatic dispersion can then be computed from a single interferogram. With narrower spectrum sources, only the fringe envelopes are utilized and yield measurements of mode delay, with application to chromatic and polarization mode dispersion. In this case, however, interferograms at several wavelengths are necessary. With even narrower spectrum sources, the fringe quick oscillations provide measurements of phase shifts, related to changes in the mode propagation constant, when outside perturbations are applied to the test fiber. A direct method for measuring the third-order nonlinear susceptibilities is discussed. In this case the outside perturbation is an intense pump laser field  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