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   7285篇
  免费   39篇
  国内免费   11篇
电工技术   34篇
综合类   1篇
化学工业   611篇
金属工艺   71篇
机械仪表   58篇
建筑科学   129篇
矿业工程   11篇
能源动力   47篇
轻工业   241篇
水利工程   15篇
石油天然气   28篇
无线电   204篇
一般工业技术   492篇
冶金工业   4830篇
原子能技术   43篇
自动化技术   520篇
  2022年   22篇
  2021年   28篇
  2019年   32篇
  2018年   27篇
  2017年   44篇
  2016年   39篇
  2015年   27篇
  2014年   39篇
  2013年   196篇
  2012年   102篇
  2011年   124篇
  2010年   81篇
  2009年   104篇
  2008年   127篇
  2007年   114篇
  2006年   122篇
  2005年   122篇
  2004年   115篇
  2003年   105篇
  2002年   76篇
  2001年   81篇
  2000年   61篇
  1999年   224篇
  1998年   1403篇
  1997年   860篇
  1996年   546篇
  1995年   317篇
  1994年   281篇
  1993年   294篇
  1992年   61篇
  1991年   64篇
  1990年   90篇
  1989年   99篇
  1988年   77篇
  1987年   85篇
  1986年   70篇
  1985年   85篇
  1984年   54篇
  1983年   57篇
  1982年   56篇
  1981年   81篇
  1980年   66篇
  1979年   61篇
  1978年   58篇
  1977年   106篇
  1976年   171篇
  1975年   40篇
  1974年   43篇
  1973年   27篇
  1972年   20篇
排序方式: 共有7335条查询结果,搜索用时 15 毫秒
951.
952.
953.
An approach to studying the critical forcing parameters of an oscillator with a softening spring characteristic is developed. The harmonic response of the system is limited within a region of the phase plane, the boundary of which corresponds to a level of constant total energy for the underlying conservative system. This approach may be a useful conceptual aid in the understanding of the difficult problem of roll motion leading to capsize of a floating vessel.  相似文献   
954.
955.
956.
957.
The paper describes an aggressive marketing campaign directed by Newcastle City Libraries to promote the value of patent information to companies in the North East of England. It records how the project is staffed and funded, the strategy employed in making contact with key executives in each firm and the benefits derived by those companies using patent information.  相似文献   
958.
BACKGROUND: Doppler echocardiography is current tool for hemodynamic evaluation of mitral prosthetic heart valves. It's accepted that the area and the gradients by Doppler echocardiography are not influenced at rest by valvular type and valvular size. We evaluated the influence of valvular type, mechanical-biological, and size on exercise hemodynamic of normally-functioning mitral prosthesis. Thirty-seven patients with mitral prosthesis, mean age 56 +/- 10 years, underwent exercise Doppler echocardiography. Peak and mean prosthetic gradient were obtained at rest, during and at maximal exercise with a nonimaging transducer. Mechanical prosthesis were 23 and biological valves 14. Valvular size was less than 26 mm in 7 patients and more than 28 mm in 20 patients. Exercise increased the heart rate from 80 +/- 14 to 143 +/- 22 (p < 0.001), peak gradient from 11.4 +/- 4 to 26.1 +/- 7 mm Hg (p < 0.001) and mean gradient from 4.8 +/- 1 to 13.7 +/- 5 mm Hg (p < 0.001). We found similar peak (11.4 +/- 3 & 11.3 +/- 4) and mean gradient (3.4 +/- 1 & 2.9 +/- 0.7) at rest between mechanical and biological valves; at maximum exercise, peak (26 +/- 7 & 26 +/- 6) and mean gradient (13.9 +/- 6 & 13.2 +/- 4) were also similar. Prosthesis with > 28-mm-size compared with prosthesis < 26-mm-size showed minor peak gradient at second step (21.3 +/- 4 & 26.4 +/- 6, p < 0.05) and at peak exercise (25.4 +/- 7 & 29.8 +/- 8, ns). Hemodynamics on exercise using Doppler echocardiography was not influenced by valvular type (mechanical-biological) in normal mitral prosthesis. However, mitral prosthesis of small size showed worse on hemodynamics exercise than bigger ones.  相似文献   
959.
Nutrition plays a significant role in preventing the incidence and prevalence of disease and more importantly, promoting health. Nutrition screening is an important tool used by nurses and dietitians to identify and assess clients at risk for nutritional compromise.  相似文献   
960.
Solutions and parametric studies are presented for the buckling of rectangular plates whose axes of material orthotropy coincide with the axes of the plate. The results presented apply to homogeneous orthotropic plates, stiffened orthotropic plates, and laminated composite material plates having flexural orthotropy (i.e. single ply and multiply unidirectional, and symmetric cross-ply composite plates). The plates considered are subjected to uniform uniaxial compression and simply supported on the loaded edges. The boundary conditions are different on the two unloaded edges; one edge being free and the other edge being elastically restrained against rotation. Parametric studies showing the effect of the orthotropic properties of the plate materials, the plate aspect ratio, the rotational restraint of the one unloaded edge and the buckle half-wavelength are discussed. Results in the form of nondimensional buckling curves are given in terms of orthotropy ratios and in terms of properties of common unidirectionally reinforced composite material. The use of the solution in conjunction with experimental data to predict the edge rotational restraint coefficient for thin-walled composite material beams is described.  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