全文获取类型
收费全文 | 3683篇 |
免费 | 98篇 |
国内免费 | 13篇 |
专业分类
化学 | 2334篇 |
晶体学 | 26篇 |
力学 | 113篇 |
数学 | 412篇 |
物理学 | 909篇 |
出版年
2022年 | 51篇 |
2021年 | 97篇 |
2020年 | 79篇 |
2019年 | 110篇 |
2018年 | 115篇 |
2017年 | 109篇 |
2016年 | 168篇 |
2015年 | 100篇 |
2014年 | 105篇 |
2013年 | 194篇 |
2012年 | 186篇 |
2011年 | 261篇 |
2010年 | 160篇 |
2009年 | 152篇 |
2008年 | 196篇 |
2007年 | 207篇 |
2006年 | 245篇 |
2005年 | 197篇 |
2004年 | 133篇 |
2003年 | 113篇 |
2002年 | 112篇 |
2001年 | 60篇 |
2000年 | 65篇 |
1999年 | 42篇 |
1998年 | 40篇 |
1997年 | 38篇 |
1996年 | 32篇 |
1995年 | 22篇 |
1994年 | 20篇 |
1993年 | 17篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1987年 | 9篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1976年 | 18篇 |
1975年 | 15篇 |
1974年 | 15篇 |
1973年 | 12篇 |
1972年 | 18篇 |
1971年 | 12篇 |
1970年 | 10篇 |
1965年 | 11篇 |
排序方式: 共有3794条查询结果,搜索用时 156 毫秒
11.
D. Hugh Powell Andr E. Merbach Gabriel Gonzlez Ern Brücher Kroly Micskei M. Francesca Ottaviani Klaus Khler Alex Von Zelewsky Oleg Ya. Grinberg Yakob S. Lebedev 《Helvetica chimica acta》1993,76(5):2129-2146
EPR Spectra have been measured for aqueous solutions of a series of Gd3+ complexes at variable temperature and a range of magnetic fields; S-band (0.14 T), X-band (0.34 T), Q-band (1.2 T), and 2-mm-band (5.0 T). The major contribution to the observed line widths is magnetic-field-dependent and is interpreted as being due to the modulation of the zero-field splitting produced by distortion of the complexes from perfect symmetry. The transverse and longitudinal relaxation matrices for an 8S ion with such an interaction have been calculated using Redfield theory with vector-coupling methods, and diagonalised numerically to obtain relaxation rates and intensities for the degenerate transitions which contribute to the multiplet. The observed line width, which is inversely proportional to the magnetic field at low temperatures, is best described by the intensity-weighted mean transverse relaxation time for the four transitions with non-zero intensity. A least-squares fit of the data yields the square of the zero-field splitting tensor, Δ2, and a correlation time, τv, with activation energy, Ev. The physical significance of these parameters and the extent of validity of the theoretical approach are considered. The parameters are used to predict the magnetic-field dependence of the longitudinal and transverse electronic relaxation times, which are discussed in the context of their relevance to 1H-NMR relaxivity. 相似文献
12.
Arthur Greenberg Oleg P. Charkin Ralph H. Bartram István Hargittai Gyula Beke 《Structural chemistry》1992,3(3):221-224
Unsigned book reviews are by the Book Review Editor. 相似文献
13.
The mechanism of X-ray waveguide-resonance propagation or the radiation superstream model, which can become the ground of X-ray nanophotonics, is discussed briefly. Some attention is devoted to features consideration of the simplest devices characterized by the waveguide-resonance transportation of X-ray beams. The experimental data showing the user possibilities of a simplest waveguide-resonators application for diffractometry are presented. We discuss the main reasons to improve the metrological characteristics for total reflection X-ray fluorescence (TXRF) analytical method in case when the target exciting beam is formed by a waveguide-resonator. Some problems appearing during the waveguide-resonator application are formulated. 相似文献
14.
Sergio Guerrero Oleg Yurievich Imanuvilov Jean-Pierre Puel 《Comptes Rendus Mathematique》2006,343(9):573-577
This Note deals with the two-dimensional Navier–Stokes system. In this context, we prove a result concerning its global approximate controllability by means of boundary controls. To cite this article: S. Guerrero et al., C. R. Acad. Sci. Paris, Ser. I 343 (2006). 相似文献
15.
Oleg S. Ugolnikov Igor A. Maslov 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,102(3):499-512
The work is devoted to the analysis of the surface photometric observations of two total lunar eclipses in 2004. The lunar surface relative brightness distribution inside the umbra was used to retrieve the vertical distribution of aerosol extinction of the solar radiation expanding by a tangent path and its dependence on the location at the limb of the Earth. The upper altitude of troposphere aerosol layer was estimated for different latitude zones. The correlation between additional aerosol extinction in the upper troposphere and cyclones was investigated. 相似文献
16.
V. A. Egorov 《Journal of Mathematical Sciences》1987,36(4):476-481
One finds conditions for the relation
are the absolute order statistics for a repeated sample from a symmetric distribution.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 142, pp. 59–67, 1985. 相似文献
17.
Oleg Safronov 《Arkiv f?r Matematik》2004,42(2):363-377
We study the spectral properties of Jacobi matrices. By combining Killip's technique [12] with the technique of Killip and
Simon [13] we obtain a result relating the properties of the elements of Jacobi matrices and the corresponding spectral measures.
This theorem is a natural extension of a recent result of Laptev-Naboko-Safronov [17].
The author thanks Sergei Naboko for useful discussions and Barry Simon for pointing out the conjecture. 相似文献
18.
The reactions of bis(trimethylstannyl)ethyne, Me3Sn–C?C–SnMe3 ( 4 ), with trimethylsilyl‐ or dimethylsilyl‐dialkylboryl‐substituted alkenes 1 – 3 afford organometallic‐substituted allenes 5 , 6 and 8 , 9 in high yield. In the case of (E)‐2‐trimethylsilyl‐3‐diethylboryl‐2‐pentene ( 1) , a butadiene derivative 7 could be detected as an intermediate prior to rearrangement into the allene. All reactions were monitored by 29Si and 119Sn NMR, and the products were characterized by an extensive NMR data set (1H, 11B, 13C, 29Si, 119Sn NMR). Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
19.
Victor N. Khrustalev Eugene A. Komissarov Oleg V. Kulikov 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(7):o374-o377
The macrocyclic title compound crystallizes as a dioxane solvate, C30H22Cl2N4O4·C4H8O2, with two independent formula units in the unit cell. The observed syn conformation is controlled by both intramolecular N—H...O hydrogen bonds and intermolecular C—H...π interactions. The relative macrocyclic inner bore is estimated to be 4.19 Å. In the crystal structure, molecules form dimers via intermolecular C—H...π interactions, and these dimers are, in turn, linked to form columns along the a axis by intermolecular C—H...O hydrogen bonds. Both X‐ray diffraction analysis and density functional theory (DFT) calculations reveal that the macrocycle possesses very high flexibility. This property, as well as the presence of six donor atoms accessible for coordination, makes the title macrocycle a very promising ligand for complexation with the majority of transition metals. 相似文献
20.
The effect of diatomite on the inflammability, combustibility, and smoke-forming ability of poly(vinyl chloride)-based plastisols has been studied. A substantial decrease in these characteristics takes place upon the introduction of 2–3% diatomite as compared with 10–15% for vermiculite and phlogopite fillers. This phenomenon is associated with a high viscosity of the plastisol melt filled with diatomite and its better foaming and carbonization, along with the formation of a high-porosity coke demonstrating heat-shielding behavior. The use of diatomite also improves the mechanical properties of the tested material. 相似文献