全文获取类型
收费全文 | 3868篇 |
免费 | 253篇 |
国内免费 | 50篇 |
专业分类
化学 | 1182篇 |
晶体学 | 55篇 |
力学 | 81篇 |
数学 | 99篇 |
物理学 | 2754篇 |
出版年
2023年 | 13篇 |
2022年 | 30篇 |
2021年 | 39篇 |
2020年 | 76篇 |
2019年 | 65篇 |
2018年 | 49篇 |
2017年 | 47篇 |
2016年 | 108篇 |
2015年 | 105篇 |
2014年 | 92篇 |
2013年 | 394篇 |
2012年 | 108篇 |
2011年 | 183篇 |
2010年 | 121篇 |
2009年 | 181篇 |
2008年 | 241篇 |
2007年 | 275篇 |
2006年 | 246篇 |
2005年 | 182篇 |
2004年 | 146篇 |
2003年 | 147篇 |
2002年 | 217篇 |
2001年 | 144篇 |
2000年 | 195篇 |
1999年 | 138篇 |
1998年 | 135篇 |
1997年 | 56篇 |
1996年 | 38篇 |
1995年 | 49篇 |
1994年 | 42篇 |
1993年 | 32篇 |
1992年 | 33篇 |
1991年 | 17篇 |
1990年 | 20篇 |
1989年 | 24篇 |
1988年 | 18篇 |
1987年 | 23篇 |
1986年 | 20篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 19篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1973年 | 6篇 |
1972年 | 2篇 |
排序方式: 共有4171条查询结果,搜索用时 31 毫秒
51.
A model is considered in which the bonds of a lattice are covered by rodlike molecules. Neighboring molecular ends interact with orientation-dependent interactions. The model exhibits closed -loop phase diagrams and double critical points. Exact coexistence surfaces are calculated for the model on the Bethe, honeycomb, and square lattices. The nature of the doubling of the critical exponent near a double critical point is calculated. The behavior of the critical line in the neighborhood of a double critical point is calculated exactly. 相似文献
52.
A
DSC investigation has been performed on a Mg–RE–Y–Zr (RE=rare earth) technical alloy WE43. Hardness trend
during isothermal treatments has been correlated to the calorimetric traces
evolution and to the forming β phases with its precursors. Oversaturation
of solute elements occurs at temperatures higher than 150±C, on cooling
at room temperature after the anneals. Activation energies, found under non-isothermal
conditions on artificially aged samples, suggest a slow transformation velocity,
while the hardness response is relatively fast. 相似文献
53.
Suzdalev I. P. Buravtsev V. N. Maksimov Yu. V. Zharov A. A. Imshennik V. K. Novichikhin S. V. Matveev V. V. 《Russian Chemical Bulletin》2003,52(9):1950-1958
Magnetic phase transitions of the first and second order were revealed by Mössbauer spectroscopy in nanosystems of - and -ferric oxides and metallic europium subjected to shear stress (240°) under high pressure (20 kbar). For - and -ferric oxide nanoclusters, the Curie (Neel) points decreased to 300 K, whereas for nanostructured europium the Neel point increased from 90 to 100 K. The thermodynamic model of magnetic phase transitions predicting a change in the character of magnetic phase transitions and a decrease (increase) in the critical Neel (Curie) points in nanoclusters was developed. The type of magnetic phase transitions and the change in the critical points were caused by defects in nanoclusters, whose maximum concentration was observed for the clusters with the 20—50 nm size range. 相似文献
54.
The lattice model for equilibrium polymerization in a solvent proposed by Wheeler and Pfeuty is solved exactly on a Bethe lattice (core of a Caylay tree) with general coordination numberq. Earlier mean-field results are reobtained in the limitq, but the phase diagrams show deviations from them for finiteq. Whenq=2, our results turn into the solution of the one-dimensional problem. Although the model is solved directly, without the use of the correspondence between the equilibrium polymerization model and the diluten0 model, we verified that the latter model may also be solved on the Bethe lattice, its solution being identical to the direct solution in all parameter space. As observed in earlier studies of the puren0 vector model, the free energy is not always convex. We obtain the region of negative susceptibility for our solution and compare this result with mean field and renormalization group (-expansion) calculations. 相似文献
55.
The gas-phase electronic absorption spectra of (6-C6R6)2Cr (R = Me (1) and Et (2)) reveal Rydberg structures, which disappear on going to the condensed phase. Each spectrum shows a Rydberg series converging to the ionization threshold. The first ionization potential determined as the series convergence limit is 4.662±0.008 eV for 1 and 4.667±0.019 eV for 2. The Rydberg bands are due to the transitions from the non-bonding MO 3dz2 to the R4s and Rnp (n = 4—10) levels. The influence of methyl and ethyl substituents on the term values of the Rydberg transitions depends on the principal quantum number of the Rydberg MO. 相似文献
56.
Cooperative conformational transitions of proteins and nucleic acids are of decisive importance to many processes of molecular biology, and particularly to their regulation. They proceed via numerous interdependent elementary processes, and their kinetics are therefore often complicated. They are frequently also very fast. However, kinetic analyses can be carried out by chemical relaxation methods. The theoretical interpretation is comparatively simple in the case of linear biopolymers. When the linear Ising model extended for kinetics was applied to model peptides and polynucleotides, it provided an insight into the fundamental principles of cooperative transformations. 相似文献
57.
S. N. Shkerin D. I. Bronin S. A. Kovyazina V. P. Gorelov A. V. Kuz'min Z. S. Martem'yanova S. M. Beresnev 《Journal of Structural Chemistry》2003,44(2):216-221
Electric conductivity, Raman spectra, and thermal expansion of La0.88Sr0.12Ga0.82Mg0.18O2.85 solid solution (LSGM1218) based on lanthanum gallate were studied at various temperatures, and Xray phase analysis was performed at room temperature. Dilatometric measurements showed that secondorder phase transitions occur at 775±10$ and 880± 20 K. The transition around 880 K is confirmed by Raman spectra and by a change in the conductivity activation energy in this temperature range. This transition is associated with a symmetry change in the oxygen sublattice. 相似文献
58.
Molecular mobility in thermotropic polyesters and side-chain polymers with different struc-ture of mesogens and spacers has been studied by dielectrical method in dilutesolutions. The results made it possible to establish the multiplicity of dielectric relaxationtransitions which reflects the small- and large-scale types of molecular motion. It was shownthat dielectric relaxation processes occurring in accordance with local mechanism (relaxationtimes 10~(-9)--10~(-7)s. and the activation energy 10--50kJ/mol) are due to the mobility of kineticchain elements of different length within a monomer units. It was found that the dielectricrelaxation process connected with a large-scale form of molecular motion (relaxation times10~(-5)--10~(-6)s. and the activation energy 100kJ/mol) did not depend on the molecular massbut was infiuenced by factors changing the conformational state of the macromolecule. It isestablished tha the cooperative reorientation mobility of associated mesogenic fragments isthe source of the large-scale process. 相似文献
59.
J. M. Igartua G. Aguirre-Zamalloa I. Ruiz-Larrea M. Couzi A. López-Echarri T. Breczewski 《Journal of Thermal Analysis and Calorimetry》1994,41(6):1211-1215
The specific heat of N(CH3)4CdBr3 from 50 to 300 K has been measured by adiabatic calorimetry, using both static and dynamic methods. The obtained results have permitted a careful study of the ferro-paraelectric phase transition the crystal shows at 160 K. The available spectroscopic data have been used to generate a reliable baseline which accounts for the normal lattice contribution to the specific heat. These results allow for an accurate estimation of the phase transition thermodynamic functions: ΔH=2620 J·mol?1 and ΔS=18.04 J·(mol°C)?1. These high values are in agreement with the predictions of the 6 well potential Frenkel model. 相似文献
60.
Haponiuk J. T. Strankowski M. Łazarewicz T. 《Journal of Thermal Analysis and Calorimetry》2003,74(2):609-613
The melting and crystallization of a series of polyurethanes derived from poly(1,6-hexylene adipate)diol (PHA), 4,4'-dicyclohexylomethane
diisocyanate (HMDI) and 4,4'-bis(10-hydroxydecaoxy)biphenyl (BHDBP) as a chain extender were investigated by using DSC. Thermal
properties of the polyurethanes were found to be strongly influenced by the hard segment content.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献