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   16805篇
  免费   2328篇
  国内免费   988篇
电工技术   778篇
综合类   1659篇
化学工业   1077篇
金属工艺   1708篇
机械仪表   1801篇
建筑科学   1251篇
矿业工程   333篇
能源动力   297篇
轻工业   440篇
水利工程   310篇
石油天然气   381篇
武器工业   249篇
无线电   1241篇
一般工业技术   2774篇
冶金工业   845篇
原子能技术   115篇
自动化技术   4862篇
  2025年   160篇
  2024年   383篇
  2023年   432篇
  2022年   442篇
  2021年   564篇
  2020年   676篇
  2019年   616篇
  2018年   573篇
  2017年   593篇
  2016年   669篇
  2015年   628篇
  2014年   887篇
  2013年   1024篇
  2012年   1024篇
  2011年   1116篇
  2010年   881篇
  2009年   932篇
  2008年   895篇
  2007年   1118篇
  2006年   932篇
  2005年   834篇
  2004年   767篇
  2003年   612篇
  2002年   572篇
  2001年   454篇
  2000年   435篇
  1999年   354篇
  1998年   281篇
  1997年   267篇
  1996年   206篇
  1995年   168篇
  1994年   137篇
  1993年   96篇
  1992年   83篇
  1991年   61篇
  1990年   58篇
  1989年   58篇
  1988年   26篇
  1987年   17篇
  1986年   11篇
  1985年   14篇
  1984年   13篇
  1983年   11篇
  1982年   10篇
  1981年   6篇
  1980年   8篇
  1979年   7篇
  1978年   2篇
  1964年   2篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
There is no good method to measure the shape and the strain distributions of a structure changing with time. We have previously proposed the Fourier transform grid method (FTGM) to measure the three-dimensional shape and surface strain distributions of stationary objects by analysing the two-dimensional grating images recorded with two cameras. In the stereoscopic method, it is very important to determine the accurate geometric parameters of the camera system. In this paper, the positions and the directions of cameras are accurately determined using the FTGM applied to images of a reference object on which a two-dimensional grating is drawn. Applications for analysing shape and strain distributions of vibrating rubber plates and a moving human skin are shown.  相似文献   
2.
Although brushless resolvers have been used widely as angular position transducers, they are expensive due to their intricate construction, involving a rotary transformer to supply the exciting coils wound on the rotor poles with the current. It is shown theoretically in this paper that the resolver without rotary transformer or brushes can be realized by simple construction, which consists of the stator core with both 4-poles exciting windings and 2-poles output ones and the rotor core carrying no windings. In this resolver the rotor core has minimum gap at one side and a maximum gap at another side of the diameter. It is characterized by an outer surface form that makes the fluctuation part of gap permeance very in proportion to cos θ, where θ represents the angular position of a point in the air gap with respect to the origin on the rotor, the point of minimum air gap. The method determining the rotor form to embody the aforementioned gap permeance variation is also shown. It has been confirmed not only by simulation but also experiment that the 2-phase output voltages of a model designed based on the theory have sinusoidal waveforms with very small harmonic contents. Moreover, the rotor position detected by processing the output voltages through the conventional resolver/digital converter was within acceptable engineering accuracy.  相似文献   
3.
In shape memory materials,that have been trained to have a two way shape memory effect(TWSM),themartensitic variants are classified into two groups,i.e.,preferentially oriented variants and self-accommodatingvariants.Applied stress may promote or constrain the transition of preferentially oriented variants and so changetransformation temperatures but has no essential effect on self-accommodating variants.According to the pointof view mentioned above,some experimental phenomena during thermocycling of a TWSM device may be ex-plained,such as the absence of synchronization between the plot of resistance change.temperature and the plotof memory strain vs.temperature.  相似文献   
4.
Robert Rodošek 《Constraints》2001,6(2-3):257-269
This paper presents an hybrid algorithm for deriving 3-D structures of cyclic polypeptides. The algorithm combines constraint-based techniques with the most widely used methods for non-cyclic polypeptides. The empirical results demonstrate that the proposed hybrid algorithm outperforms traditional methods especially with respect to running times.  相似文献   
5.
We consider discrete event systems (DES) involving tasks with real-time constraints and seek to control processing times so as to minimize a cost function subject to each task meeting its own constraint. When tasks are processed over a single stage, it has been shown that there are structural properties of the optimal sample path that lead to very efficient solutions of such problems. When tasks are processed over multiple stages and are subject to end-to-end real-time constraints, these properties no longer hold and no obvious extensions are known. We consider a two-stage problem with homogeneous cost functions over all tasks at each stage and derive several new optimality properties. These properties lead to the idea of introducing “virtual” deadlines at the first stage, thus partially decoupling the stages so that the known efficient solutions for single-stage problems can be used. We prove that the solution obtained by an iterative virtual deadline algorithm (VDA) converges to the global optimal solution of the two-stage problem and illustrate the efficiency of the VDA through numerical examples.
Christos G. CassandrasEmail:
  相似文献   
6.
讨论了16QAM调制时应用不同类型和参数的滤波器对系统性能的影响.针对16QAM的特点,采用了存储波形累加求和法来代替一般的滤波成形,提高了调制速度.并利用其相位对称的特点将波形存储表压缩为原容量的1/4,有效地节约了存储空间.  相似文献   
7.
连铸钢包使用的滑动激光器是控制连铸生产过程的关键设备之一。为了确定501滑板使用中产生裂纹的原因,抑制裂纹形成,提高滑板使用寿命,本文应用有限元法进行了滑板热应力分析,并与生产中使用的滑板比较,有限元分析显示:在滑板材质一定的情况下,滑板形状以及滑板的预紧能力和固定方式是影响滑板使用寿命的基本因素。  相似文献   
8.
简要地讨论了惯性、刚性振动出矿机在三个自由度下运动的解答;并根据实际使用情况,提出了振动出矿机合理振动形态的概念及条件。从理论上导出了求得合理振动形态的设计方法及计算公式。  相似文献   
9.
Martensitic stabilization caused by deformation in a TiNi shape memory alloy was studied.Special attention was paid to the deformed microstructures to identify the cause of martensitic stabilization.Martensitic stabilization was demonstrated by differential scanning calorimetry for the tensioned TiNi shape memory alloy.Transmission electron microscopy revealed that antiphase boundaries were formed because of the fourfold dissociation of[110]B19'super lattice dislocations and were preserved after reverse transformation due to the lattice correspondence.Martensitic stabilization was attributed to dislocations induced by deformation,which reduced the ordering degree of the microstructure,spoiled the reverse path from martensite to parent phase compared with thermoelastic transformation,and imposed resistance on phase transformation through the stress field.  相似文献   
10.
陈瑛 《宽厚板》1999,5(5):1-6
本文综述了中厚钢板板形控制内容,纵向板形控制,横向板形控制,平面板形控制以及板形检测技术,并对其技术提出今后的展望。  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