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   2977篇
  免费   45篇
  国内免费   10篇
化学   1927篇
晶体学   18篇
力学   82篇
数学   304篇
物理学   701篇
  2021年   19篇
  2020年   26篇
  2019年   27篇
  2018年   22篇
  2017年   20篇
  2016年   38篇
  2015年   35篇
  2014年   34篇
  2013年   92篇
  2012年   129篇
  2011年   159篇
  2010年   77篇
  2009年   46篇
  2008年   128篇
  2007年   133篇
  2006年   158篇
  2005年   139篇
  2004年   136篇
  2003年   94篇
  2002年   112篇
  2001年   76篇
  2000年   86篇
  1999年   44篇
  1998年   45篇
  1997年   31篇
  1996年   68篇
  1995年   38篇
  1994年   54篇
  1993年   76篇
  1992年   54篇
  1991年   33篇
  1990年   35篇
  1989年   37篇
  1988年   30篇
  1987年   39篇
  1986年   28篇
  1985年   48篇
  1984年   30篇
  1983年   23篇
  1982年   49篇
  1981年   31篇
  1980年   45篇
  1979年   29篇
  1978年   44篇
  1977年   36篇
  1976年   27篇
  1975年   43篇
  1974年   29篇
  1973年   35篇
  1972年   19篇
排序方式: 共有3032条查询结果,搜索用时 15 毫秒
101.
This paper describes the first general large-signal dynamic multiple-mode laser model that incorporates all the main mechanisms known to influence the dynamic behaviour of DFB laser structures with the exception of thermal effects: longitudinal mode spatial hole burning, carrier transport effects, nonlinear gain, and laser and submount parasitics. The time evolution of the output power and wavelength of all modes is predicted, and full spectra can be plotted as a function of time. The model has been extended to include an approximation to the effects of propagation down dispersive fibre, thereby allowing the simulation of filtered received eye diagrams. Detailed comparison of the model with the experimental performance of 2×/8 DFB lasers has shown good agreement, allowing the performance to be optimized, particularly with respect to longitudinal hole burning and carrier transport. The model is also applied to gain-switched operation of 2×/8 DFB structures, fast pulsing of three-section /4 DFB lasers, and the dynamic behaviour of complex coupling coefficient DFB laser structures.  相似文献   
102.
We exploit the quantum coherence between pair-produced D0 and D[over]0 in psi(3770) decays to study charm mixing, which is characterized by the parameters x and y, and to make a first determination of the relative strong phase delta between D0-->K+pi- and D[over]0-->K+pi-. Using 281 pb(-1) of e+e- collision data collected with the CLEO-c detector at Ecm=3.77 GeV, as well as branching fraction input and time-integrated measurements of RM identical with (x2 + y2)/2 and RWS identical with Gamma(D0-->K+pi-)/Gamma(D[over]0-->K+pi-) from other experiments, we find cosdelta=1.03(-0.17)(+0.31)+/-0.06, where the uncertainties are statistical and systematic, respectively. By further including other mixing parameter measurements, we obtain an alternate measurement of cosdelta=1.10+/-0.35+/-0.07, as well as x sindelta=(4.4(-1.8)(+2.7)+/-2.9)x10(-3) and delta=(22(-12-11)(+11+9)) degrees .  相似文献   
103.
Core electron-temperature fluctuations [0.5%< or =T[over ]_(e)/T_(e)< or =2%, k_(theta)rho_(s)< or =0.3 in neutral-beam-heated low confinement-mode (L-mode) plasmas] are observed to decrease by at least a factor of 4 in standard and quiescent high-confinement-mode (H-mode and QH-mode) regimes in the DIII-D tokamak (r/a=0.7). These fluctuations are attributed to ion temperature gradient (ITG) modes stabilized by rotational shear at the H-mode transition. The simultaneous reduction in electron heat diffusivity (chi_(e)(QH)/chi_(e)(L)<0.25) suggests that T[over ]_(e) fluctuations can contribute significantly to L-mode electron heat transport.  相似文献   
104.
Terahertz Time Domain Imaging has been used in the last few years for the investigation of cultural heritage. In this article, the authors demonstrate the possibility to apply it for the investigation of clay artifacts. Tomographic images were obtained of a model in reflection, and an Egyptian vessel in transmission.  相似文献   
105.
Rigorous numerical modeling of optical systems has attracted interest in diverse research areas ranging from biophotonics to photolithography. We report the full-vector electromagnetic numerical simulation of a broadband optical imaging system with partially coherent and unpolarized illumination. The scattering of light from the sample is calculated using the finite-difference time-domain (FDTD) numerical method. Geometrical optics principles are applied to the scattered light to obtain the intensity distribution at the image plane. Multilayered object spaces are also supported by our algorithm. For the first time, numerical FDTD calculations are directly compared to and shown to agree well with broadband experimental microscopy results.  相似文献   
106.
Tests such as Bell's inequality and Hardy's paradox show that joint probabilities and correlations between distant particles in quantum mechanics are inconsistent with local realistic theories. Here we experimentally demonstrate these concepts in the time domain, using a photonic entangling gate to perform nondestructive measurements on a single photon at different times. We show that Hardy's paradox is much stronger in time and demonstrate the violation of a temporal Bell inequality independent of the quantum state, including for fully mixed states.  相似文献   
107.
The non-linear vibration of a clamped-clamped beam at large displacement amplitudes is examined in this work. Complementary theoretical and experimental studies have been carried out to examine the amplitude dependence of the fundamental mode shape and its derivatives and the spatially-dependent harmonic distortion of the transverse displacement which occurs at large deflections.  相似文献   
108.
109.
110.
An optical backplane based on a meshed polymer waveguide architecture enabling high-speed board-to-board optical interconnection is presented. This planar array of multimode polymer waveguides can provide passive strictly non-blocking links between server line cards fitted with optical transmitter and receiver arrays. This architecture offers a scalable and low-cost solution to the bandwidth limitations faced by electrical backplanes and is suitable for PCB integration. The reported backplane demonstrator uses a matrix of 100 waveguides each capable of 10 Gb/s operation to interconnect 10 cards for a total capacity of a terabit per second aggregate data rate in multicast mode. Characterisation of the backplane demonstrator reveals low link losses of 2 to 8 dB for a multimode fibre input and crosstalk values below −35 dB. Error free data transmission at 10 Gb/s is achieved with a power penalty of only 0.2 dB at a bit-error-rate of 10−9. Additionally, lossless operation of a Gigabit Ethernet link over the backplane is achieved even when using the worst-case highest loss links.  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