全文获取类型
收费全文 | 716197篇 |
免费 | 7660篇 |
国内免费 | 2997篇 |
专业分类
化学 | 387147篇 |
晶体学 | 11136篇 |
力学 | 31717篇 |
综合类 | 74篇 |
数学 | 84491篇 |
物理学 | 212289篇 |
出版年
2020年 | 5788篇 |
2019年 | 6275篇 |
2018年 | 8121篇 |
2017年 | 8228篇 |
2016年 | 12222篇 |
2015年 | 7735篇 |
2014年 | 11929篇 |
2013年 | 31153篇 |
2012年 | 23230篇 |
2011年 | 28297篇 |
2010年 | 20193篇 |
2009年 | 19838篇 |
2008年 | 25833篇 |
2007年 | 25987篇 |
2006年 | 24316篇 |
2005年 | 21935篇 |
2004年 | 19979篇 |
2003年 | 17786篇 |
2002年 | 17645篇 |
2001年 | 19975篇 |
2000年 | 15354篇 |
1999年 | 12036篇 |
1998年 | 10119篇 |
1997年 | 9974篇 |
1996年 | 9740篇 |
1995年 | 8738篇 |
1994年 | 8555篇 |
1993年 | 8244篇 |
1992年 | 9332篇 |
1991年 | 9323篇 |
1990年 | 8941篇 |
1989年 | 8912篇 |
1988年 | 8669篇 |
1987年 | 8741篇 |
1986年 | 8296篇 |
1985年 | 11033篇 |
1984年 | 11198篇 |
1983年 | 9286篇 |
1982年 | 9950篇 |
1981年 | 9380篇 |
1980年 | 9290篇 |
1979年 | 9715篇 |
1978年 | 10558篇 |
1977年 | 10278篇 |
1976年 | 9972篇 |
1975年 | 9308篇 |
1974年 | 9268篇 |
1973年 | 9528篇 |
1972年 | 6797篇 |
1967年 | 5798篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
891.
S.H Chen 《Journal of luminescence》2004,109(2):93-102
The ZnS:Cu,Al,Au (P22G) phosphor powder was bombarded by an electron beam in an O2 ambient, Ar ambient and other mixture of gases. These gases consisted of mixtures of O2 and COx, and O2, COx and Ar gas. Auger electron spectroscopy (AES) was used to monitor changes in the surface composition of the P22G phosphor during electron bombardment. When the P22G phosphor powder was exposed to the electron beam in a water-rich O2 ambient, a chemically limited ZnO layer was formed on the surface. The electron beam degradation of the P22G phosphor powder was also performed in a dry O2 ambient and a layer of ZnSO4 was formed on the surface. The ZnSO4 formation decayed exponentially with time and it is postulated that this was due to the diffusion of the charge reactants through the ZnSO4 film to the reaction interfaces. The P22G phosphor exposed to the electron beam in an Ar ambient and to the other gas mixtures degraded at a lower rate than in the case of the O2 ambient. This suggests that Ar and COx may suppress the degradation of the P22G phosphor powder. 相似文献
892.
893.
A rigorous and systematic intercomparison of codes used for the retrieval of trace gas profiles from high-resolution ground-based solar absorption FTIR measurements is presented for the first time. Spectra were analyzed with the two widely used independent, retrieval codes: SFIT2 and PROFFIT9. Vertical profiles of O3, HNO3, HDO, and N2O were derived from the same set of typical observed spectra. Analysis of O3 was improved by using updated line parameters. It is shown that profiles and total column amounts are in excellent agreement, when similar constraints are applied, and that the resolution kernel matrices are also consistent. Owing to the limited altitude resolution of ground-based observations, the impact of the constraints on the solution is not negligible. It is shown that the results are also compatible for independently chosen constraints. Perspectives for refined constraints are discussed. It can be concluded that the error budget introduced by the radiative transfer code and the retrieval algorithm on total columns deduced from high-resolution ground-based solar FTIR spectra is below 1%. 相似文献
894.
W.F. Wang 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,86(4):437-444
It is shown that by including the second term of Magnus expansion, improved convergence can be achieved for the non-perturbative pressure broadening formalism proposed by Neilson and Gordon (J. Chem. Phys. 58 (1973) 4131). The present method was applied to the line broadening calculations of CO in a bath of Ar. 相似文献
895.
A survey of recent developments concerning rigorously defined infinite dimensional integrals, mainly of the type of “Feynman path integrals,” is given. Both the theory and its applications, especially in quantum theory, are presented. As for the theory, general results are discussed including the case of polynomially growing phase functions, which are handled by exploiting the connection with probabilistic functional integrals. Also applications to continuous measurement theory and the stochastic Schrödinger equation are given. Other applications of probabilistic methods in non relativistic quantum theory and in quantum field theory, and their relations with statistical mechanics, are discussed. 相似文献
896.
An analytical approach for vibration response analysis of a beam with single passive constrained layer damping (PCLD) patch is presented. The governing equation of motion of the beam is firstly derived on the basis of an energy approach and the Lagrange equation. The noval contribution is that a third admissible function is introduced to represent the longitudinal displacements of the constraining layer in the PCLD patch when the assumed-modes method is applied for discretizing the governing equation. In conventional analytical approaches, only two admissible functions are used together with a longitudinal static equilibrium equation of a section of base beam or constraining layer. Comparison of the computational results from the proposed analytical approach and the conventional analytical approach as well as a commercial FEM code reveals that the proposed analytical approach can describe the vibration responses of the damped beam more accurately for commonly used viscoelastic material (VEM) layer in the PCLD patch while the conventional analytical approach, in general, overestimates the damping effects of the PCLD patch. The advantages and disadvantages of the proposed analytical approach and conventional analytical approach are discussed through some case studies. 相似文献
897.
The construction of non-Abelian affine Toda models is discussed in terms of its underlying Lie algebraic structure. It is shown that a subclass of such non-conformal two-dimensional integrable models naturally leads to the construction of a pair of actions, which share the same spectra and are related by canonical transformations. 相似文献
898.
L. K. Seah U. S. Dinish S. K. Ong Z. X. Chao V. M. Murukeshan 《Optics & Laser Technology》2004,36(5):371-376
Imaging of latent fingerprints using time-resolved (TR) method offers a broader platform to eliminate the unwanted background emission. In this paper, a novel TR imaging technique is demonstrated and implemented, which facilitates the detection of latent fingerprints with nanosecond resolution. Simulated experiments were carried out with two overlapping fingerprints treated with two fluorescent powders having different lifetimes in nanosecond range. The dependence of the fluorescence emission intensity in nanosecond resolution of TR imaging is also revealed. 相似文献
899.
The spectra of absorption (77–398 K) and luminescence (5 K) of poly(di-n-hexylsilane) films are studied in relation to the heating of the films above the phase transition temperature. Two new absorption bands in the region of the band of the gauche conformation are found. The position and intensity of these bands depend on the annealing temperature, annealing regime, and sample thickness. These bands are assumed to be associated with the appearance of a liquid crystalline phase in the polymer, which is determined by intermolecular interactions between neighboring polymer chains. The appearance of the liquid crystalline phase in the heat-treated polymer films is confirmed by the increase in their birefringence in comparison with the birefringence of the initial films and by the observation of a stable orientation of an E 7 nematic liquid crystal applied to the surface of an annealed sample. In addition, the absorption spectra of the films cooled after the annealing exhibit many new bands in comparison with the spectra of the initial samples. These bands are associated with the appearance in the polymer of defect states and longer segments as a result of orientation of polymer chains. The appearance of longer segments is consistent with the observation of a long-wavelength band in the luminescence spectra of the annealed samples. 相似文献
900.