全文获取类型
收费全文 | 352210篇 |
免费 | 3603篇 |
国内免费 | 1252篇 |
专业分类
化学 | 162529篇 |
晶体学 | 4485篇 |
力学 | 12855篇 |
综合类 | 10篇 |
数学 | 30210篇 |
物理学 | 91263篇 |
无线电 | 55713篇 |
出版年
2021年 | 2130篇 |
2020年 | 2393篇 |
2019年 | 2463篇 |
2018年 | 2937篇 |
2017年 | 2958篇 |
2016年 | 5057篇 |
2015年 | 3491篇 |
2014年 | 4994篇 |
2013年 | 13899篇 |
2012年 | 10913篇 |
2011年 | 13527篇 |
2010年 | 9303篇 |
2009年 | 10153篇 |
2008年 | 13917篇 |
2007年 | 14338篇 |
2006年 | 13945篇 |
2005年 | 13086篇 |
2004年 | 11847篇 |
2003年 | 10759篇 |
2002年 | 10436篇 |
2001年 | 12765篇 |
2000年 | 9949篇 |
1999年 | 7958篇 |
1998年 | 6316篇 |
1997年 | 6275篇 |
1996年 | 6075篇 |
1995年 | 5637篇 |
1994年 | 5523篇 |
1993年 | 5257篇 |
1992年 | 5984篇 |
1991年 | 5967篇 |
1990年 | 5488篇 |
1989年 | 5293篇 |
1988年 | 5069篇 |
1987年 | 4402篇 |
1986年 | 4144篇 |
1985年 | 5473篇 |
1984年 | 5407篇 |
1983年 | 4421篇 |
1982年 | 4558篇 |
1981年 | 4286篇 |
1980年 | 4201篇 |
1979年 | 4323篇 |
1978年 | 4479篇 |
1977年 | 4358篇 |
1976年 | 4221篇 |
1975年 | 4046篇 |
1974年 | 3928篇 |
1973年 | 4068篇 |
1972年 | 2584篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We investigated that the effect of the number of segregated Li atoms on the rate of oxidation on a LiAl alloy surface. Oxygen molecules adsorbed on the LiAl alloy react with the surface atoms to form stable oxides. The segregated Li atoms at reconstructed surfaces (c(2×2) and (2×1)) enhance the oxidation rate and form stable LiAlOx and Li2O. The degree of enhancement of oxidation by segregated Li atoms varies as a function of O2 exposure and annealing temperature, where the latter is directly related to the mode of surface reconstruction by Li segregation. 相似文献
992.
Wang K.C. Asbeck P.M. Chang M.F. Sullivan G.J. Miller D.L. Basit H.F. 《Electronics letters》1989,25(17):1111-1112
The authors report a novel noninterfering and simple approach for evaluation of circuits implemented with AlGaAs/GaAs heterojunction bipolar transistors (HBTs). This method makes use of radiative recombination in the base region of current-carrying HBTs. The infrared radiation emitted is 'visible' to the closed-circuit TV (CCTV) cameras. Therefore, one can view the operation of the HBT circuit under test at normal biases with a TV monitor. This method can be used to determine logic states of gates, as well as collector current of individual HBTs within integrated circuits.<> 相似文献
993.
A measurement technique is presented which uses narrow, fast-rise-time pulses applied to both the gate and the drain of a GaAs MESFET to obtain the drain characteristics of the device. This allows the characteristics of the device to be obtained which correspond to frequencies above those at which surface and substrate traps can respond. The resulting characteristics show significant departures from those obtained using conventional long pulse and DC measurement techniques. 相似文献
994.
L. Bernal-Gonzalez A. Bonilla M.C. Calderon-Moreno J.A. Prado-Bassas 《Constructive Approximation》2007,25(2):211-219
Let Ώ be a domain in the N-dimensional real space, let L be an elliptic differential operator, and let (Tn) be a sequence whose members belong to a certain class of operators defined on the space of L-analytic functions on Ώ. This
paper establishes the existence of a dense linear manifold of L-analytic functions all of whose nonzero members have maximal
cluster sets under the action of every Tn along any curve ending at the boundary of Ώ such that its closure does not contain any component of the boundary. The above
class contains all partial differentiation operators ∂α, hence the statement extends earlier results due to Boivin, Gauthier, and Paramonov, and due to the first, third, and fourth
authors. 相似文献
995.
Nanometer scale Al/AlN multilayers have been prepared by dc magnetron sputtering technique with a columnar target. A set of Al/AlN multilayers with the Al layer thickness of 2.9 nm and the AlN layer thickness variation from 1.13 to 6.81 nm were determined. Low angle X-ray diffraction (LAXRD) was used to analyze the layered structure of multilayers. The phase structure of the coatings was investigated with grazing angle XRD (GAXRD). Mechanical properties of these multilayers were thoroughly studied using a nanoindentation and ball-on-disk micro-tribometer. It was found that the multilayer hardness and reduced modulus showed no strong dependence on the AlN layer thickness. Al2.9 nm/AlN1.13 nm multilayer had more excellent tribological properties than single layers and other proportion multilayers with a lowest friction coefficient of 0.15. And the tribological properties of all the multilayers are superior to the AlN single layer. 相似文献
996.
The behavior of a spatially smoothing adaptive array is examined. An expression for the weight vector is first derived. Using the array gain on the desired signal and the coherent interference is obtained. Then the expression for output signal-to-noise (SNR) is derived. It shows that the performance of the spatially smoothing array depends on the number of the subarrays, the angle separation, relative power and initial phase difference between the desired signal and the coherent interference. For good interference suppression it is found that the magnitude of the phase difference of the incident and interference signals must be greater than the beamwidths of both the subarray and the equivalent array. There is also a tradeoff between increasing the groups of subarrays and decreasing the number of elements in the subarrays. Computer simulation results are given that validate the analysis 相似文献
997.
998.
H. D. Dahmen P. Manakos T. Mannel T. Ohl 《Zeitschrift fur Physik C Particles and Fields》1989,44(1):139-147
The photon two-point function is calculated using the exponential representation for the time-evolution operator taking into account terms up to second order ine in the exponent. The limiting case of vanishing electron mass is examined and it is shown that mass singularities cancel by means of unitarity. Near mass shell the causal Green function exhibits in the limit of vanishing electron mass the expected cut behaviour, off mass shell we recover the result of the usual perturbation theory. 相似文献
999.
Presented is an eigen filter to remove autogenic electrical stimulation artefacts and M-waves while preserving the volitional electromyographic signal. The optimality of the eigen filter is shown, along with simulated and measured data to indicate its superior performance over conventional prediction error filters. 相似文献
1000.
The present paper is aimed to display the performance of the Fourier-Galerkin technique developed earlier by the authors for numerical treatment of localized solutions in
2(-∞, ∞) for higher-order equations. The solitary-wave solution of the Kortweg-de Vries fifth order equation is obtained numerically and compared with approximate results of other authors. 相似文献