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   309830篇
  免费   3719篇
  国内免费   714篇
电工技术   6193篇
综合类   560篇
化学工业   46738篇
金属工艺   10323篇
机械仪表   8820篇
建筑科学   7898篇
矿业工程   862篇
能源动力   8568篇
轻工业   31078篇
水利工程   2532篇
石油天然气   3669篇
武器工业   8篇
无线电   39749篇
一般工业技术   58442篇
冶金工业   56632篇
原子能技术   5458篇
自动化技术   26733篇
  2021年   2276篇
  2019年   2138篇
  2018年   3608篇
  2017年   3448篇
  2016年   3538篇
  2015年   2540篇
  2014年   4439篇
  2013年   14271篇
  2012年   7364篇
  2011年   10112篇
  2010年   7902篇
  2009年   9136篇
  2008年   9599篇
  2007年   9582篇
  2006年   8506篇
  2005年   7888篇
  2004年   7761篇
  2003年   7499篇
  2002年   7344篇
  2001年   7545篇
  2000年   7209篇
  1999年   7547篇
  1998年   17660篇
  1997年   12835篇
  1996年   10100篇
  1995年   7877篇
  1994年   7207篇
  1993年   6905篇
  1992年   5288篇
  1991年   5068篇
  1990年   4938篇
  1989年   4783篇
  1988年   4675篇
  1987年   3887篇
  1986年   4008篇
  1985年   4719篇
  1984年   4277篇
  1983年   4022篇
  1982年   3601篇
  1981年   3762篇
  1980年   3457篇
  1979年   3420篇
  1978年   3225篇
  1977年   3814篇
  1976年   4847篇
  1975年   2780篇
  1974年   2660篇
  1973年   2675篇
  1972年   2215篇
  1971年   1963篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
The evolution of RFID security   总被引:11,自引:0,他引:11  
As RFID technology progresses, security and privacy threats also evolve. By examining RFID's history, we can learn from past mistakes, rediscover successful solutions, and inspire future research.  相似文献   
132.
We examine the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two-dimensional (2-D) systems under a plane-strain condition with the principal misfit strain components ε* xx and ε* yy . For systems with cubic elastic moduli, we first show all the shape transitions associated with different values of t=ε* yy /ε* xx . We also characterize each of these transitions, by studying its dependence on elastic anisotropy and inhomogeneity. For systems with dilatational misfit (t=1) and those with pure shear misfit (t=−1), the transition is from an equiaxed shape to an elongated shape, resulting in a break in rotational symmetry. For systems with nondilatational misfit (−1<t<1; t ≠ 0), the transition involves a break in mirror symmetries normal to the x- and y-axes. The transition is continuous in all cases, except when 0<t<1. For systems which allow an invariant line (−1≤t<0), the critical size increases with an increase in the particle stiffness. However, for systems which do not allow an invariant line (0<t≤1), the critical size first decreases, reaches a minimum, and then starts increasing with increasing particle stiffness; moreover, the transition is also forbidden when the particle stiffness is greater than a critical value.  相似文献   
133.
The results of finite element calculations for a hollow sphere micromodel are used to examine the underlying assumptions and the specific yield functions in the dilatant plasticity theories of Gurson (1977) and Mear and Hutchinson  相似文献   
134.
135.
136.
Depending on the spectal width of the source illuminating an interferometer, measurement procedures can utilize either the whole interferogram, or only the fringe envelope, or only the fringe quick oscillations. With an ultraband spectrum source, a simplified adaptation of the methods of Fourier transform spectroscopy yields the variations of the test-fiber propagation constant over the whole wavelength-interval of the source. Chromatic dispersion can then be computed from a single interferogram. With narrower spectrum sources, only the fringe envelopes are utilized and yield measurements of mode delay, with application to chromatic and polarization mode dispersion. In this case, however, interferograms at several wavelengths are necessary. With even narrower spectrum sources, the fringe quick oscillations provide measurements of phase shifts, related to changes in the mode propagation constant, when outside perturbations are applied to the test fiber. A direct method for measuring the third-order nonlinear susceptibilities is discussed. In this case the outside perturbation is an intense pump laser field  相似文献   
137.
A continuous phase quadrature phase shift keyed (CPQPSK) modulation technique is presented. This method utilizes a conventional QPSK modulator and a phase trajectory converter to approximate M=4, h=1/4 continuous phase signal and allows low cost, low complexity, and high rate (>1 Gbit/s) CPM modem implementation for bandwidth efficient transmission through nonlinear satellite channels. Using a communications analysis computer program it has been found that CPQPSK has 99 percent out-of-band power of 0.8R (MSK has 99 percent out-of-band power of 1.2 R where R is defined as bit rate), continuous phase trajectories, and nearly constant envelope amplitude. Simulation of realistic hardware designs indicate that the CPQPSK will require an Eb/No of 14 dB to achieve a bit error rate (BER) of 10-6. Forward error correcting techniques using block codes with an overhead of 10 percent indicate that the Eb/No requirements can be reduced to 11.2 dB for 10-6 BER  相似文献   
138.
139.
Determined the specific type of sexual functioning deficits and the relationship between global sexual satisfaction and adjustment in 2 related life areas (marital relationship and body image) for 2 groups of cancer patients at high risk for sexual difficulties. The 2 groups included 16 27–67 yr old females with Stage 2 breast cancer and 16 31–65 yr old females with gynecologic cancer. These Ss were compared to 16 healthy female outpatients (controls). Measures included the Sexual Activities scale from the Derogatis Sexual Functioning Inventory, a modified version of the Dyadic Assessment Scale (marital adjustment), a global sexual evaluation, and a body-image scale. Analyses revealed that the aspects of sexual functioning for breast-cancer and gynecologic-cancer Ss that differed from those of controls were the frequency of sexual behaviors and the level of sexual arousal. Whereas Ss' evaluations of their current sexual life had no relationship to their marital-adjustment ratings, analyses suggested that body-image disruption may be a prevalent problem for gynecologic cancer patients. Data suggest that cancer diagnosis and treatment are instrumental in producing reductions in sexual activity and arousability. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
140.
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