全文获取类型
收费全文 | 17615篇 |
免费 | 2963篇 |
国内免费 | 1676篇 |
专业分类
化学 | 8649篇 |
晶体学 | 72篇 |
力学 | 2052篇 |
综合类 | 164篇 |
数学 | 1453篇 |
物理学 | 5576篇 |
无线电 | 4288篇 |
出版年
2024年 | 48篇 |
2023年 | 239篇 |
2022年 | 389篇 |
2021年 | 461篇 |
2020年 | 558篇 |
2019年 | 587篇 |
2018年 | 588篇 |
2017年 | 640篇 |
2016年 | 731篇 |
2015年 | 846篇 |
2014年 | 1156篇 |
2013年 | 1417篇 |
2012年 | 1241篇 |
2011年 | 1343篇 |
2010年 | 1052篇 |
2009年 | 1152篇 |
2008年 | 1156篇 |
2007年 | 1083篇 |
2006年 | 1113篇 |
2005年 | 933篇 |
2004年 | 872篇 |
2003年 | 740篇 |
2002年 | 592篇 |
2001年 | 477篇 |
2000年 | 412篇 |
1999年 | 356篇 |
1998年 | 302篇 |
1997年 | 277篇 |
1996年 | 242篇 |
1995年 | 240篇 |
1994年 | 177篇 |
1993年 | 143篇 |
1992年 | 115篇 |
1991年 | 71篇 |
1990年 | 98篇 |
1989年 | 72篇 |
1988年 | 45篇 |
1987年 | 53篇 |
1986年 | 39篇 |
1985年 | 26篇 |
1984年 | 34篇 |
1983年 | 13篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1980年 | 9篇 |
1979年 | 20篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1971年 | 5篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The influence of the parameter of amplitude-phase coupling for nonlinear amplification on the phase-frequency characteristics of an injection laser in the regime of pumping current modulation has been investigated theoretically. The parameter is defined as the coefficient of proportionality between changes in the real and imaginary parts of the refractive index during variation of the density of photons in the cavity. The substantial dependence of the coefficient of phase modulation on the parameter of the amplitude-phase coupling for nonlinear amplification at small modulation frequencies is shown. A technique to determine the indicated parameter based on the frequency dependence of the ratio between the coefficients of phase and amplitude modulation is suggested. 相似文献
22.
23.
提出种基于TEMIC射频卡Manchester编码的速率自适应读卡算法,并对该算法进行了说明和示例。 相似文献
24.
Francisco‐Javier Sayas 《Numerical Methods for Partial Differential Equations》2003,19(5):555-570
This article presents and analyzes a simple method for the exterior Laplace equation through the coupling of finite and boundary element methods. The main novelty is the use of a smooth parametric artificial boundary where boundary elements fit without effort together with a straight approximate triangulation in the bounded area, with the coupling done only in nodes. A numerically integrated version of the algorithm is also analyzed. Finally, an isoparametric variant with higher order is proposed. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 555–570, 2003 相似文献
25.
Bai-suo JIN~ 《中国科学A辑(英文版)》2007,50(9):1303-1315
In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted. 相似文献
26.
27.
DIELECTRIC EFFECT ON THE RADIO-FREQUENCY CHARACTERISTICS OF A RECTANGULAR WAVEGUIDE GRATING TRAVELING WAVE TUBE 总被引:2,自引:0,他引:2
Zhigang Lu Yubin Gong Yanyu Wei Wenxiang Wang 《International Journal of Infrared and Millimeter Waves》2006,27(8):1095-1108
A new type of partial-dielectric-loaded rectangular waveguide grating slow-wave structure (SWS) for millimeter wave traveling
wave tube (TWT) is presented in this paper. The radio-frequency characteristics including the dispersion properties, the longitudinal
electric field distribution and the beam-wave coupling impedance of this structure are analyzed. The results show that the
dispersion of the rectangular waveguide grating circuit is weakened, the phase velocity is reduced and the position of the
maximum E
z
is basically invariant after partially filling the dielectric materials in the rectangular waveguide grating SWS. Although
the coupling impedance decreases a little, it still keeps above 40 Ω. 相似文献
28.
H. Barentzen 《Annalen der Physik》2006,15(9):684-698
The eigenvalues of the weakly coupled T ? t Jahn‐Teller problem are known for several decades, and the same holds also true for the eigenstates. These, however, are only given in the traditional position representation, which proves inconvenient if one attempts to extend the weak‐coupling treatment into the region of stronger coupling. Here the solution of the T ? t eigenvalue problem at weak coupling is derived in terms of creation and annihilation operators. This reformulation of the problem is nontrivial, since the algebraic form of the oscillator eigenvectors, being simultaneous angular‐momentum eigenstates, has been worked out only recently and is probably still widely unknown. The electronic and oscillator eigenstates are then coupled to form eigenvectors of the total angular momentum. Finally, in preparation for an extension of the weak‐coupling treatment, the action of the boson creation and annihilation operators on the oscillator eigenvectors is calculated, thus completing the algebraic approach to the weakly coupled T ? t system. 相似文献
29.
The quantum action (dynamical) principle is exploited to investigate the nature and origin of the Faddeev–Popov (FP) factor in gauge theories without recourse to path integrals. Gauge invariant as well as gauge non-invariant interactions are considered to show that the FP factor needs to be modified in more general cases and expressions for these modifications are derived. In particular we show that a gauge invariant theory does not necessarily imply the familiar FP factor for proper quantization.
PACS numbers: 11.15.-q; 12.10.-g; 12.15.-y; 12.38.-t 相似文献
30.
实验获得了Ar+激光514.5nm线诱导23Na39K分子产生的D1∏→X1∑+跃迁荧光谱.通过测量激光感生荧光光谱强度随泵浦功率、热管炉温度及缓冲气压变化规律,详细研究了其跃迁机制.用最小二乘法拟合获得23Na39K分于X1∑+态振动常数.理论计算了各跃迁谱支波长值及Franck-Condon因子和光谱强度值,与实验观测值符合得相当好,充分表明本文对激光感生荧光光谱的归属以及对各支谱线振、转量子数的赋值是合理的. 相似文献