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   54310篇
  免费   4743篇
  国内免费   2321篇
电工技术   3142篇
技术理论   7篇
综合类   3465篇
化学工业   9167篇
金属工艺   3157篇
机械仪表   3449篇
建筑科学   3930篇
矿业工程   1727篇
能源动力   1647篇
轻工业   3450篇
水利工程   910篇
石油天然气   3439篇
武器工业   559篇
无线电   6281篇
一般工业技术   6700篇
冶金工业   2625篇
原子能技术   748篇
自动化技术   6971篇
  2024年   285篇
  2023年   1024篇
  2022年   1768篇
  2021年   2460篇
  2020年   1852篇
  2019年   1498篇
  2018年   1698篇
  2017年   1936篇
  2016年   1729篇
  2015年   2280篇
  2014年   2870篇
  2013年   3439篇
  2012年   3617篇
  2011年   3896篇
  2010年   3267篇
  2009年   3094篇
  2008年   3050篇
  2007年   2891篇
  2006年   2785篇
  2005年   2363篇
  2004年   1680篇
  2003年   1424篇
  2002年   1418篇
  2001年   1229篇
  2000年   1222篇
  1999年   1235篇
  1998年   1010篇
  1997年   860篇
  1996年   807篇
  1995年   615篇
  1994年   516篇
  1993年   346篇
  1992年   275篇
  1991年   211篇
  1990年   180篇
  1989年   139篇
  1988年   115篇
  1987年   61篇
  1986年   64篇
  1985年   35篇
  1984年   28篇
  1983年   27篇
  1982年   24篇
  1981年   15篇
  1980年   10篇
  1979年   7篇
  1976年   6篇
  1970年   2篇
  1959年   3篇
  1951年   2篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
71.
72.
Lim TK  Jeong MY  Song C  Kim DC 《Applied optics》1998,37(13):2723-2728
The effect of light absorption by sample in the analysis of Makerfringe data for estimating a second-order nonlinear coefficient hasbeen studied experimentally. Two theories, one by Jerphagnon andKurtz that neglects the absorption effect and one by Herman and Haydenthat takes into account the absorption effect, were compared with theexperimental results. It was found that Jerphagnon and Kurtz'sformula was unable to predict correctly not only the magnitude but alsothe incident angle dependence or the sample thickness dependence of thesecond harmonic signal generated by the sample with strong absorption, whereas the theory by Herman and Hayden was able to make thosepredictions fairly well. It was also found that the error in theestimated nonlinear coefficient when one uses Jerphagnon and Kurtz'sformula could be as large as 2-4 times the true value, depending onsample thickness.  相似文献   
73.
In an underwater environment, measurements regarding true targets and false targets (clutter) can be made. Therefore, a suitable data association method to exactly detect and track a target and an efficient track initiation method for judging tracks formed by the target should be selected in this environment. This paper attempts to propose a new data association method and track initiation method to detect and track targets more effectively. Also, the performance of the new method is tested in a series of Monte Carlo simulation runs and is compared with the existing data association and track initiation methods in a cluttered environment.  相似文献   
74.
为了提高RSA密码算法在密码芯片上的实现性能,基于SOPC技术设计了一款RSA密码芯片,完成了NIOS Ⅱ的软硬件协同设计.该硬件系统由处理器、存储模块和自定义指令3部分组成,其关键的模乘模块采用改进的模乘算法和交叉存取设计方案设计实现,显著提高了系统性能.整体设计在ALTERA的CYCLONEⅡ器件上进行了验证与测试,并进行了逻辑综合及布局布线.与传统的RSA密码芯片设计相比,该芯片系统灵活性高,资源占用少.  相似文献   
75.
An electro-optically modulated intensity interrogation method based on tunable waveguide coupled surface plasmon resonance sensors has been proposed. It has been theoretically and experimentally demonstrated that the proposed scheme can enable sensitive measurement of measurand variations. By modulating the refractive index in the waveguide layer, this interrogation method yields modulated signal whose amplitude is related to measurand's refractive index. This amplitude modulated signal offers a higher signal to noise ratio and eliminates additive noise in the sensor system. A preliminary investigation using saline buffers with different NaCl concentrations shows a resolution of 2.3 × 10?6 refractive index unit by our approach. Resolution can be controlled by the amplitude of the applied modulation voltage and can be further enhanced by optimizing the device structure or improving the electro-optical (E-O) coefficient of the E-O material. This approach is simple, stable, and promising for low-cost or multi-channel SPR biosensor applications.  相似文献   
76.
Abstract— Even though dyes have a fine resolution and good chromaticities, they are not widely used as coloring materials for color filters (CFs) due to their low thermal stability and chemical resistance. A series of azo‐dye derivatives, which consist of two cross‐linkable acrylate or methacrylate groups to improve thermal and chemical properties, have been synthesized and used to fabricate color filters. The spectral properties and chemical/thermal stabilities of the fabricated CFs were investigated by comparing dye‐based CFs, without a complicated dispersion process, but with pigment‐based CFs using dispersed pigment. Also, more properties including the development test and surface morphologies lithographic properties were studied. The synthesized azo dyes were characterized by elemental analysis, UV‐visible spectra, IR, mass, and 1H‐NMR spectra.  相似文献   
77.
78.
79.
80.
Surrogate models are used to dramatically improve the design efficiency of numerical aerodynamic shape optimization, where high-fidelity, expensive computational fluid dynamics (CFD) is often employed. Traditionally, in adaptation, only one single sample point is chosen to update the surrogate model during each updating cycle, after the initial surrogate model is built. To enable the selection of multiple new samples at each updating cycle, a few parallel infilling strategies have been developed in recent years, in order to reduce the optimization wall clock time. In this article, an alternative parallel infilling strategy for surrogate-based constrained optimization is presented and demonstrated by the aerodynamic shape optimization of transonic wings. Different from existing methods in which multiple sample points are chosen by a single infill criterion, this article uses a combination of multiple infill criteria, with each criterion choosing a different sample point. Constrained drag minimizations of the ONERA-M6 and DLR-F4 wings are exercised to demonstrate the proposed method, including low-dimensional (6 design variables) and higher-dimensional problems (up to 48 design variables). The results show that, for surrogate-based optimization of transonic wings, the proposed method is more effective than the existing parallel infilling strategies, when the number of initial sample points are in the range from N v to 8N v (N v here denotes the number of design variables). Each case is repeated 50 times to eliminate the effect of randomness in our results.  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