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   243558篇
  免费   2952篇
  国内免费   1243篇
电工技术   4829篇
综合类   264篇
化学工业   35430篇
金属工艺   10861篇
机械仪表   7068篇
建筑科学   6243篇
矿业工程   481篇
能源动力   6275篇
轻工业   24158篇
水利工程   1836篇
石油天然气   1335篇
武器工业   3篇
无线电   31063篇
一般工业技术   44894篇
冶金工业   50108篇
原子能技术   3860篇
自动化技术   19045篇
  2021年   1571篇
  2019年   1424篇
  2018年   2323篇
  2017年   2223篇
  2016年   2447篇
  2015年   1908篇
  2014年   3160篇
  2013年   10797篇
  2012年   5450篇
  2011年   7793篇
  2010年   6289篇
  2009年   6965篇
  2008年   7562篇
  2007年   7665篇
  2006年   7034篇
  2005年   6524篇
  2004年   6245篇
  2003年   6262篇
  2002年   6241篇
  2001年   6371篇
  2000年   5801篇
  1999年   6418篇
  1998年   16559篇
  1997年   11597篇
  1996年   8950篇
  1995年   6689篇
  1994年   5907篇
  1993年   5729篇
  1992年   4052篇
  1991年   3997篇
  1990年   3583篇
  1989年   3505篇
  1988年   3441篇
  1987年   2909篇
  1986年   2843篇
  1985年   3414篇
  1984年   3052篇
  1983年   2744篇
  1982年   2553篇
  1981年   2570篇
  1980年   2432篇
  1979年   2271篇
  1978年   2235篇
  1977年   2808篇
  1976年   4171篇
  1975年   1899篇
  1974年   1795篇
  1973年   1783篇
  1972年   1460篇
  1971年   1317篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
71.
72.
In the development of a novel freeze-drying technique in a fluidized bed at atmospheric pressure, a parallel study was undertaken using a conventional vacuum equipment. Two kinetically distinct phases were observed during freeze drying of representative Pood samples:

(1) a period during which the rate of drying was constant and (2) a second period during which the drying rate sufferedcontinual reduction. This paper focused attention on the primary drying period which corresponded with the kinetics of sublimation of pure  相似文献   
73.
74.
The effect of secondary scattering that is produced by the induced current in an infinitely long, finitely conducting wire over a plane, finitely conducting earth from an incident electromagnetic pulse is investigated. This is accomplished by finding the field of a Hertzian dipole over the earth and identifying the part that is due to secondary scattering. Frequency-domain results for the overall induced current require that certain infinite integrals be numerically evaluated. Fourier inversion to the time domain in turn requires the numerical evaluation of another infinite integral. When the results are compared to those obtained when secondary scattering is ignored, it is found that secondary scattering slightly increases the current for the case of broadside incidence and reduces it for the case of grazing incidence by as much as two orders of magnitude. Peak currents are much smaller than previously thought. These general results hold for all of the earth parameters that were used in the study  相似文献   
75.
Reduced glutenin is separated by gel permeation high-performance liquid chromatography into three major and five minor fractions, which significantly differ in their amino acid compositions. By reversed-phase high performance liquid chromatography, about 20 glutenin components are obtained. These can be classified into three groups according to their amino acid compositions: a hydrophilic group with relatively high values of Glx and Phe, a more hydrophobic group with a high content of Gly, and a strongly hydrophobic group with higher values of Val and Leu. Groups 1, 2 and 3 contain middle-, high- and low-molecular-weight (MMW-, HMW-, LMW-) subunits respectively.  相似文献   
76.
77.
78.
This letter further discusses the difference between different definitions of voltage unbalance. Contrary to an earlier letter (see P. Pillay et al., ibid., vol.5, p.50-1, 2001), it is concluded that different definitions may give significantly different results. The two IEEE definitions that were not discussed in the earlier letter give different results and both deviate significantly from the true value (ratio of negative, and positive-sequence voltage) when a zero-sequence component is present.  相似文献   
79.
80.
I have experimentally studied the influence of the buoyancy force and inlet flow conditions on the laminar-turbulent transition process of fully developed air flow in a heated horizontal tube with uniform wall heat flux at modified Rayleigh number 3.1×106. Eight time-series of the air temperature were simultaneously obtained using eight thermocouples positioned within the tube along a vertical line passing through the tube's axis. I have studied the time and space dependence of the transition behavior by analyzing these instantaneous time-series. By calculating a set of Lyapunov exponents and the correlation dimension of the time-series of a single thermocouple, these transitional flows are found to be chaotic.  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