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   34383篇
  免费   1269篇
  国内免费   1137篇
电工技术   1043篇
技术理论   1篇
综合类   778篇
化学工业   4427篇
金属工艺   3027篇
机械仪表   1672篇
建筑科学   1234篇
矿业工程   304篇
能源动力   1172篇
轻工业   1698篇
水利工程   347篇
石油天然气   1174篇
武器工业   88篇
无线电   3849篇
一般工业技术   7965篇
冶金工业   4543篇
原子能技术   421篇
自动化技术   3046篇
  2024年   58篇
  2023年   215篇
  2022年   384篇
  2021年   556篇
  2020年   428篇
  2019年   517篇
  2018年   720篇
  2017年   717篇
  2016年   760篇
  2015年   745篇
  2014年   1045篇
  2013年   2174篇
  2012年   1506篇
  2011年   2117篇
  2010年   1729篇
  2009年   1899篇
  2008年   1937篇
  2007年   1930篇
  2006年   1707篇
  2005年   1579篇
  2004年   1199篇
  2003年   1075篇
  2002年   1087篇
  2001年   1023篇
  2000年   995篇
  1999年   1073篇
  1998年   1740篇
  1997年   1285篇
  1996年   1098篇
  1995年   729篇
  1994年   576篇
  1993年   485篇
  1992年   317篇
  1991年   304篇
  1990年   204篇
  1989年   218篇
  1988年   145篇
  1987年   104篇
  1986年   76篇
  1985年   64篇
  1984年   44篇
  1983年   35篇
  1982年   32篇
  1981年   31篇
  1980年   19篇
  1979年   10篇
  1978年   9篇
  1976年   20篇
  1975年   11篇
  1973年   10篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
31.
32.
Clinical manifestations and peripheral blood lymphocyte subset changes were studied in patients with myasthenia gravis (MG) to elucidate the mechanism of clinical improvement following treatment, with thymectomy (Tx) or glucocorticoid (GC) therapy. The changes found were: 1. There was a significant increase in percentages of CD3+, CD29+ CD4+ cells and CD4/CD8 ratio and a significant decrease in percentages of CD8+ and CD16,56+ cells in patients who had never been treated with any immune therapy. 2. After Tx or GC therapy, CD3+ and CD4+, CD29+ cells were decreased, but the number CD19+ and CD16, CD56 cells did not change. 3. Tx had a special effect on CD8+ cells. In most of the patients who showed clinical improvement after Tx, CD8+ cells were increased and CD4/CD8 ratio wad decreased. 4. Anti-acetylcholine receptor (AChRAb) titers were markedly decreased after GC therapy. These results indicate that there were obvious abnormalities in cell-mediated immunity in addition to those in humoral immunity in myasthenia gravis. These abnormalities tended to be normalized after Tx or GC therapy.  相似文献   
33.
The influence of the specimen thickness B and the ligament length b on the J R -curves is numerically investigated for CT specimens. The thickness effect is taken into account with 2-D analyses by dividing a plain sided specimen into a plane stress part and a plane strain part. The fracture process is controlled by experimentally determined critical values of the crack tip opening displacement for crack growth initiation (CTODi) and the crack tip opening angle for stable crack growth (CTOAC). It is shown that for the global behaviour of a plain sided specimen, the B/b ratio is essential. The difference between the geometry dependence of the initiation value of the J-integral and the geometry dependence of the slope of the J R -curves is also shown.  相似文献   
34.
35.
The binomial single g-pulses — dopant segregation in a generic virtual µg Bridgman growth arrangement is discussed here with the help of a time dependent two-dimensional scheme. To attain this objective, the so-called solid composition drop distribution has been previously defined enabling a global two-dimensional information of the segregation impact in each virtually grown crystal. Based on this parameter it has been concluded that, at equal g-dose, solid segregation is independent on the shape of the single external pulse and that, for single g-pulses of equal g-dose, compositional variations are practically independent on the activity time but depend on the crystal growth rate. Finally, taking into account all these set of results, the pertinence of the g-dose as the only self-consistent parameter to describe the segregation impact has been discussed.  相似文献   
36.
37.
38.
This paper presents a finite element method with high spatial order for solving the Maxwell equations in the time domain. In the first part, we provide the mathematical background of the method. Then, we discuss the advantages of the new scheme compared to a classical finite-difference time-domain (FDTD) method. Several examples show the advantages of using the new method for different kinds of problems. Comparisons in terms of accuracy and CPU time between this method, the FDTD and the finite-volume time-domain methods are given as well.  相似文献   
39.
An improved coupled-mode equation for nonlinear directional couplers (NLDC) with Kerr-like nonlinear media is proposed. The method is based on the generalized reciprocity relation in which two sets of field solutions satisfying Maxwell's equations are for the NLDC and for the isolated nonlinear waveguide. That leads to a reasonable result that all the coefficients in the coupled-mode equations, including the coupling coefficient, become power dependent. For the NLDC with a self-focusing or self-defocusing nonlinear material, the authors examine how the coupling coefficient, the coupling length, and the guided power depend on the input power in the range of coupling stronger than in previous reports. It is found that the critical power at which the coupling length becomes infinity does not increase as much with the two guides for the case of self-focusing media  相似文献   
40.
Brambilla  G. Xu  F. Feng  X. 《Electronics letters》2006,42(9):517-519
It is demonstrated for the first time that long nanowires with radii as small as 30 nm can be manufactured with a conventional coupler fabrication rig. The temporal deterioration of nanowire optical properties has been studied and correlated with its mechanical behaviour. The original transmission properties have been restored by a post-fabrication treatment.  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