全文获取类型
收费全文 | 200995篇 |
免费 | 2273篇 |
国内免费 | 503篇 |
专业分类
化学 | 110378篇 |
晶体学 | 2704篇 |
力学 | 7998篇 |
综合类 | 11篇 |
数学 | 19240篇 |
物理学 | 63440篇 |
出版年
2020年 | 1735篇 |
2019年 | 1935篇 |
2018年 | 2245篇 |
2017年 | 2364篇 |
2016年 | 3532篇 |
2015年 | 2201篇 |
2014年 | 3583篇 |
2013年 | 9125篇 |
2012年 | 6557篇 |
2011年 | 8067篇 |
2010年 | 5729篇 |
2009年 | 5689篇 |
2008年 | 7202篇 |
2007年 | 7116篇 |
2006年 | 6730篇 |
2005年 | 6095篇 |
2004年 | 5555篇 |
2003年 | 5135篇 |
2002年 | 4892篇 |
2001年 | 6156篇 |
2000年 | 4640篇 |
1999年 | 3525篇 |
1998年 | 2754篇 |
1997年 | 2712篇 |
1996年 | 2602篇 |
1995年 | 2370篇 |
1994年 | 2280篇 |
1993年 | 2126篇 |
1992年 | 2764篇 |
1991年 | 2657篇 |
1990年 | 2618篇 |
1989年 | 2614篇 |
1988年 | 2645篇 |
1987年 | 2654篇 |
1986年 | 2503篇 |
1985年 | 3239篇 |
1984年 | 3243篇 |
1983年 | 2527篇 |
1982年 | 2644篇 |
1981年 | 2706篇 |
1980年 | 2478篇 |
1979年 | 2829篇 |
1978年 | 2828篇 |
1977年 | 2955篇 |
1976年 | 2792篇 |
1975年 | 2532篇 |
1974年 | 2478篇 |
1973年 | 2440篇 |
1972年 | 1677篇 |
1968年 | 1702篇 |
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
961.
Feng S.-W. Tsai C.-Y. Cheng Y.-C. Liao C.-C. Yang C.C. Lin Y.-S. Ma K.-J. Chyi J.-I. 《Optical and Quantum Electronics》2002,34(12):1213-1219
A side-bump feature in a photoluminescence (PL) spectrum of an InGaN compound was widely observed. With reasonable fitting to PL spectra with three Gaussian distributions, the temperature variations of the peak positions, integrated PL intensities, and peak widths of the main and first side peaks of three InGaN/GaN multiple quantum well samples with different nominal indium contents are shown and interpreted. The existence of the side peaks is attributed to phonon–replica transitions. The variations of the peak position separations and the decreasing trends of the first side peak widths beyond certain temperatures in those samples were explained with the requirement of phonon momentum condition for phonon–replica transitions. In the sample with 25% nominal indium content, the phonon–replica transition could become stronger than the direct transition of localized states. 相似文献
962.
We calculate s-wave and p-wave absorptive pion-nucleus optical potentials assuming that a pion is absorbed by a pair of nucleons. Employing a model which takes into account both a single nucleon absorption with nucleon-nucleon correlations and rescattering, we obtain simple analytic expressions for Im B0 sid Im C0 of the pion-nucleus optical potential. The off-shell effect on the s-wave pion absorption is examined and shown to be strongly modified by short range correlations. The result for the p-wave absorptive part Im C0 clearly shows the importance of the tensor correlations. The enhanced nn emission after π? absorption is shown to be related with a large p-wave πN scattering length a33 via the tensor correlations. 相似文献
963.
964.
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
965.
966.
Let R be a prime ring of char R≠2, d a non-zero derivation of R and ρ a non-zero right ideal of R such that [[d(x),d(y)]n [y,x]m] = 0 for all x,y ∈ ρ or [[d(x),d(y)]n d[y,x]m] = 0 for all x,y ∈ ρ, n, m ≥ 0 are fixed integers. If [ρ,ρ]ρ ≠ 0, then d(ρ)ρ = 0. 相似文献
967.
968.
Laser Doppler vibrometer (LVD) has been the most favorite instrument for precision dynamics measurement due to its non-contact, high accuracy and high resolution. However, LDV can only give the dynamic data of a particular location on the entire feature. In order to get the whole field data, a laser beam-scanning mechanism has to be implemented. Currently, motor-driven scanning mirror is used to move the measurement probe from one point to another. The mechanical vibrations of the scanning mirror will reduce the measurement accuracy. This paper introduces a novel scanning LDV optical system embodied in an acousto-optic deflector scanning mechanism. It can improve the measurement accuracy since there is no mechanical motion involved. One main advantage of this system is that it generates a laser scanning beam in parallel that is different from the beam scanning in the conventional scanning laser Doppler vibrometer (SLDV). The new system has a board scanning range. The measurement target size ranges from few tens of millimeters down to 10 μm. We have demonstrated the capability of the novel system on scanning measurements of features as big as ultra-precision cutting tool to features as tiny as AFM cantilever. We believe that the novel SLDV will find profound potential applications in the precision engineering field. 相似文献
969.
970.
This paper is based on the M. Sc. thesis written by the third author under the supervision of the first two authors. It was submitted to the University of Baghdad in 1986. 相似文献