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   342522篇
  免费   5224篇
  国内免费   2221篇
电工技术   6155篇
技术理论   5篇
综合类   3452篇
化学工业   53232篇
金属工艺   15665篇
机械仪表   10726篇
建筑科学   8705篇
矿业工程   2211篇
能源动力   6705篇
轻工业   29275篇
水利工程   4122篇
石油天然气   6330篇
武器工业   243篇
无线电   36831篇
一般工业技术   64920篇
冶金工业   49751篇
原子能技术   5855篇
自动化技术   45784篇
  2021年   2587篇
  2019年   2145篇
  2018年   17552篇
  2017年   16412篇
  2016年   13474篇
  2015年   3408篇
  2014年   4830篇
  2013年   11569篇
  2012年   10762篇
  2011年   19318篇
  2010年   16160篇
  2009年   14043篇
  2008年   16021篇
  2007年   17076篇
  2006年   8555篇
  2005年   8539篇
  2004年   7741篇
  2003年   7332篇
  2002年   6725篇
  2001年   6414篇
  2000年   6078篇
  1999年   5934篇
  1998年   12902篇
  1997年   9562篇
  1996年   7317篇
  1995年   5536篇
  1994年   5092篇
  1993年   4955篇
  1992年   3954篇
  1991年   3773篇
  1990年   3823篇
  1989年   3770篇
  1988年   3536篇
  1987年   3021篇
  1986年   3050篇
  1985年   3409篇
  1984年   3321篇
  1983年   3074篇
  1982年   2698篇
  1981年   2902篇
  1980年   2644篇
  1979年   2839篇
  1978年   2736篇
  1977年   2841篇
  1976年   3694篇
  1975年   2459篇
  1974年   2291篇
  1973年   2320篇
  1972年   1981篇
  1971年   1785篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
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   
43.
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   
44.
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   
45.
Lenin Dnepropetrovsk Pipe Plant. Translated from Metallurg, No. 8, p. 39, August, 1989.  相似文献   
46.
Intense irradiation (25–40 A/cm2) at intermediate energy (400 keV) has been found to cause “metallisation” of tungsten oxide and titanium niobate crystal surfaces. The possible mechanisms and the likely consequences for high-resolution imaging of clean oxide surfaces are briefly discussed.  相似文献   
47.
48.
We consider three types of near-boundary elements: curvilinear quadrangles and families of arcs and points, and their application to a two-dimensional problem of the static theory of elasticity with boundary conditions in displacements. The comparison of the theoretical and numerical aspects of the obtained solutions is performed. It is shown that the accuracy of evaluation of the components of the vector of displacements increases in the following cases: in the case of complete quantization of the near-boundary region (but not in the case of its partial quantization or quantization with overlapping), in the case where the numbers of arcs and points increase, and in the case of simultaneous application of different types of near-boundary elements (specifically, quadrangles and families of arcs).  相似文献   
49.
Poiseuille, known for his law of fluid flow, which is the analog of Ohm's law, introduced the units (mmHg) by which we measure blood pressure by using the mercury manometer, which he described in his medical school thesis in 1828. For 50 years, mean blood pressure was all that could be measured because of the long response time of the mercury manometer. It is true that the height of the mercury column displayed pulsatile oscillations, but their amplitude was much less than that of pulse pressure. It is interesting to note that the slowly responding mercury manometer was made to display first systolic then diastolic pressure by means of an ingenious device that contained two oppositely directed check valves. It took from 1828 to 1903 for high-fidelity graphic recordings of blood pressure to appear in which systolic and diastolic pressures were believable. However, systolic and diastolic pressures were measurable since 1878 when Golz and Gaule created their ingenious valved device that permitted use of the slowly responding mercury manometer to display these pressures accurately  相似文献   
50.
巴西的一个重要电力公司COPEL最近开发了一个水电站高级控制系统,这是在电力部门经受重大变革时期,提高水电竞争力的里程碑。  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