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   206222篇
  免费   2210篇
  国内免费   567篇
电工技术   3515篇
综合类   141篇
化学工业   31861篇
金属工艺   10266篇
机械仪表   7014篇
建筑科学   3996篇
矿业工程   2162篇
能源动力   4633篇
轻工业   12888篇
水利工程   2922篇
石油天然气   7727篇
武器工业   22篇
无线电   21514篇
一般工业技术   45175篇
冶金工业   34406篇
原子能技术   6624篇
自动化技术   14133篇
  2021年   2053篇
  2019年   1998篇
  2018年   3680篇
  2017年   3717篇
  2016年   4000篇
  2015年   2234篇
  2014年   3785篇
  2013年   8742篇
  2012年   5680篇
  2011年   7224篇
  2010年   5856篇
  2009年   6487篇
  2008年   6618篇
  2007年   6494篇
  2006年   5573篇
  2005年   5119篇
  2004年   4636篇
  2003年   4557篇
  2002年   4373篇
  2001年   4477篇
  2000年   4188篇
  1999年   4205篇
  1998年   10187篇
  1997年   7187篇
  1996年   5508篇
  1995年   4132篇
  1994年   3598篇
  1993年   3839篇
  1992年   2985篇
  1991年   2996篇
  1990年   2891篇
  1989年   2853篇
  1988年   2867篇
  1987年   2509篇
  1986年   2569篇
  1985年   2854篇
  1984年   2688篇
  1983年   2556篇
  1982年   2301篇
  1981年   2270篇
  1980年   2346篇
  1979年   2359篇
  1978年   2382篇
  1977年   2490篇
  1976年   2878篇
  1975年   2188篇
  1974年   2068篇
  1973年   2166篇
  1972年   1940篇
  1971年   1755篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Levels of benzaldehyde recovered from virginPseudaletia unipuncta (Haw.) males were not influenced by (1) the time hairpencils remained in the solvent (1-72 hr), (2) anesthetization or agitation of males prior to excision of hairpencils, or (3) the time (photophase or scotophase) that hairpencils were excised. Thus the interindividual variability observed is not a methodological artifact. Most males had similar concentrations in both hairpencils, although in some cases only one hairpencil contained pheromone. In one case, a male with partially extruded hairpencils had no benzaldehyde at all. Neither pupal weight nor hairpencil length proved to be reliable indicators of pheromone content.Contribution No. 373, Département de biologie, Université Laval.  相似文献   
992.
Problems associated with different calibration techniques and some instrumental effects that can determine instrumental accuracy are discussed. It is shown how transmission effects can be observed and used to generate a correction curve for refracted near-field instruments. High-quality fiber slices needed for axial interferometry were used to obtain refractive index differences on suitable fibers to ±1% with the measurements traceable to national standards. Interferometry was used to calibrate a multiple-step fiber which is available in 10-m lengths with a certificate of calibration. The limitations of the technique are discussed, and preliminary results of a study on the effects of residual stress and stress relief on measurements are given. Comparisons are made between measurements made by axial interferometry and refracted near field on a range of fibers. It is shown that commercial profilers can produce reliable measurements of refractive index difference, absolute refractive index, profile shape, and numerical aperture that agree well with measurements by other techniques  相似文献   
993.
The martensitic transformation temperatures and the types of martensitic phases have been determined in a wide concentration range of technological interest for Cu-Al-Ni shape-memory alloys (SMAs) A stability diagram of martensitic phases as a function of alloy concentration has been determined. It is found that when the aluminum content increases, the transformation changes from β 3β3 to β 3γ3, with an intermediate concentration range where both martensites coexist due to a β 3γ3+β3 transformation. On the other hand, an increase of nickel content stabilizes the martensite β3, changing from a mixed β 3γ3 + β3 to a single β 3β3 transformation. Furthermore, linear relationships between M s and Al and Ni concentrations have been obtained for all types of martensitic phases.  相似文献   
994.
995.
996.
997.
A quasi-TEM approach based on conformal transformation is used for the determination of the characteristic impedance of a rectangular coaxial line (TEM cell) having a symmetrically located inner conductor (septum) supported on a dielectric slab of equal width. The method of determination of the capacitance of the dielectric-filled portion is discussed. The results on characteristic impedance for two values of dielectric constant are presented.  相似文献   
998.
Precipitation of nickel ammonium sulphate achieved by mixing solutions of nickel sulphate and ammonium sulphate in a 5 1 MSMPR crystallizer is used to investigate both crystallization and agglomeration kinetics from the steady-state crystal size distribution. An iterative non-linear parameter estimation procedure is used to deduce the kinetic rate parameters in the solution of the agglomeration model suggested by Liao and Hulburt from the data-set obtained by size analysis of the product crystals. The results obtained are correlated in terms of conventional power law kinetic expressions.  相似文献   
999.
A mathematical model for the drying rate of granular particles in a multistage inclined fluidized bed(IFB) is presented from the standpoint of simultaneous heat and mass transfer, with taking the effect of mechanical vibration added vertically into consideration.

Steady-state distributions for the temperatures and concentrations of the particles and the heating gas, and for the moisture content of the particles are numerically calculated based on the present model. The calculated results show fairly good agreement with the experimental data, which were obtained from the drying experiments of brick particles in a three-stage IFB using comparatively low temperature air(40-60°C) as the heating gas.

It has been found within the range of the experimental conditions employed that, the mechanical vibration added vertically enhances the over-all drying rate of the particles and its effect can be considered equivalent to an increase in the air velocity.  相似文献   
1000.
The bubble eater is a device which can sense, capture, and recycle bubble gas in a bubbling fluidized bed. The theory describing the enhancement of reactant gas conversion are presented and illustrated by means of a numerical example.  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