全文获取类型
收费全文 | 7546篇 |
免费 | 224篇 |
国内免费 | 11篇 |
专业分类
化学 | 4836篇 |
晶体学 | 28篇 |
力学 | 272篇 |
数学 | 1045篇 |
物理学 | 1600篇 |
出版年
2023年 | 43篇 |
2022年 | 77篇 |
2021年 | 89篇 |
2020年 | 102篇 |
2019年 | 106篇 |
2018年 | 125篇 |
2017年 | 85篇 |
2016年 | 205篇 |
2015年 | 230篇 |
2014年 | 225篇 |
2013年 | 428篇 |
2012年 | 498篇 |
2011年 | 502篇 |
2010年 | 328篇 |
2009年 | 206篇 |
2008年 | 472篇 |
2007年 | 438篇 |
2006年 | 414篇 |
2005年 | 401篇 |
2004年 | 336篇 |
2003年 | 312篇 |
2002年 | 247篇 |
2001年 | 144篇 |
2000年 | 149篇 |
1999年 | 75篇 |
1998年 | 95篇 |
1997年 | 71篇 |
1996年 | 102篇 |
1995年 | 54篇 |
1994年 | 59篇 |
1993年 | 54篇 |
1992年 | 56篇 |
1991年 | 36篇 |
1990年 | 44篇 |
1989年 | 39篇 |
1988年 | 48篇 |
1986年 | 27篇 |
1985年 | 52篇 |
1984年 | 67篇 |
1983年 | 36篇 |
1982年 | 44篇 |
1981年 | 50篇 |
1980年 | 43篇 |
1979年 | 36篇 |
1978年 | 48篇 |
1977年 | 44篇 |
1976年 | 55篇 |
1975年 | 37篇 |
1974年 | 27篇 |
1973年 | 32篇 |
排序方式: 共有7781条查询结果,搜索用时 15 毫秒
41.
Indentation tests were performed at a high temperature on GaAs(011). This orientation allowed the activation of normal and inclined slip systems. Samples with two different thicknesses were prepared and a large range of loads was used. Observations on decreasing scales were carried out using different microscopies and more particularly transmission electron microscopy on thin foils prepared by the focused-ion-beam technique. The back side of the thinnest samples could be deformed using the highest loads. The deformation was observed to be anisotropic on the back side as well as at the indented surface. On one side of the indentation, an anisotropic climb of matter was revealed and associated with microtwinning development. Convergent-beam electron diffraction as well as chemical etching allowed us to determine rigorously the polarity of the samples and the character of dislocations ( for g) generated by the indenter. The dislocations extending deeper into the samples were determined to be fdislocations. This result was discussed in view of the difference between the core reconstructions and mobilities of fand gdislocations. 相似文献
42.
The role of Al5Ti3 and h-Al2Ti long-period superstructures on the plastic properties of TiAl at room temperature is investigated on five single crystals with aluminium content comprised between 54.7 at.%, and 62.5 at.%. After annealing at 1200°C for 1?h, the Al5Ti3 superstructure develops in the L10 (γ) matrix upon increasing Al concentration except for Ti–62.5 at.%Al where h-Al2Ti substitutes for Al5Ti3. The CRSS for <110]{111} first increases abruptly with the development of the Al5Ti3-type ordering. Then, the CRSS reaches a plateau at which dislocations assemble in groups of four to prevent extra anti-phase boundary (APB) from being engendered during glide throughout the Al5Ti3 phase. In Ti–62.5 at.%Al, the CRSS for ordinary slip further increases upon the precipitation of h-Al2Ti in the L10 phase, whereas it decreases when the crystal is fully transformed into single-phased Al5Ti3. <101] superlattice dislocations are primarily activated under both the [210] and [1?1?8.6] load orientations irrespective of the Al concentration, but the dislocation microstructure strongly depends on orientation as well as on the degree of Al5Ti3 ordering. In the [210] orientation, the frequency of the decomposition of <101] dislocations into 1/2<110] and 1/2<112] dislocations decreases abruptly with the development of Al5Ti3. This is interpreted in terms of the increased difficulty to move ordinary dislocations. Under the [1?1?8.6] orientation, the density of faulted dipoles diminishes remarkably with the development of Al5Ti3. This is consistent with the transformation of the low energy extrinsic stacking fault of the L10 phase into a higher energy complex extrinsic stacking fault. 相似文献
43.
Clément Barrière Virginie Latour Pierre Fau Anne-Marie Caminade Cédric-Olivier Turrin 《Tetrahedron letters》2012,53(15):1908-1911
We present a simple strategy to obtain non-symmetrical polyethylene glycols equipped with telechelic phosphorus-containing dendrimeric moieties having adhesive phosphonate surface functions. The dendronized PEG tails were characterized by means of multi-nucleus NMR. The grafting abilities of model symmetrical PEG compounds equipped with telechelic amino-bis(methylene-dimethylphosphonates) and amino-bis(methylenephosphonic acids) were rapidly screened on plasma treated silicon wafers and activated silica. 相似文献
44.
Pierrick Nun Violaine Pérez Monique Calmès Jean Martinez Frédéric Lamaty 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(12):3773-3779
The asymmetric alkylation of Schiff bases under basic conditions in a ball mill was performed. The starting Schiff bases of glycine were prepared beforehand by milling protected glycine hydrochloride and benzophenone imine, in the absence of solvent. The Schiff base was then reacted with a halogenated derivative in a ball mill in the presence of KOH. By adding a chiral ammonium salt derived from cinchonidine, the reaction proceeded asymmetrically under phase‐transfer catalysis conditions, giving excellent yields and enantiomeric excesses up to 75 %. Because an equimolar amount of starting material was used, purification was greatly simplified. 相似文献
45.
Giovanni Di Nicola Cristiano Di Nicola Matteo Moglie Marco Pacetti 《Journal of Thermal Analysis and Calorimetry》2012,108(2):621-625
This study presents a new formula for the surface tension prediction of alkenes. As a first step, an analysis of the available data of the experimental surface tension data for alkenes was performed. The experimental data were collected, after a careful literature survey, for the following pure fluids: propene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, and 1-pentadecene. Then, the experimental data were regressed with the most reliable semi-empirical correlating methods based on the corresponding state theory existing in the literature. As a final step, an analysis of the available data of the experimental surface tension data for alkenes was performed starting from the two recently proposed equations for the prediction of the surface tension of refrigerants based on the corresponding states principle. To minimize the deviation between the predicted data and the experimental data and to find the optimal equation coefficients for experimental data regression, a (μ + λ)-evolution strategy was adopted. The analysis showed that the equation that gave the best results for the prediction of the surface tension of alkenes was the one with a very limited number of parameters. The finally proposed equation is very simple and gives a noticeable improvement with respect to the existing equations. It is based on the corresponding state principle, containing the acentric factor, the critical temperature, and pressure. 相似文献
46.
47.
Núria Alegret Marc Mulet-Gas Xavier Aparicio-Anglès Antonio Rodríguez-Fortea Josep M. Poblet 《Comptes Rendus Chimie》2012,15(2-3):152-158
The electronic structure of endohedral metallofullerenes is rationalized by connecting the apparently independent orbital and topological rules that explain the stability of this family of fullerenes. The separation of the 12 pentagons of the fullerene, which is maximized in order to minimize the Coulomb repulsion, is found to be correlated with the orbital energies of the cage that accepts the electron transfer from the internal cluster. An explanation for the absence of non-IPR cages in large-size EMFs is also provided. 相似文献
48.
In this paper, it is considered the inverse kinematics problem, which is faced from a differential point of view. In particular, it is shown that an asymptotic inverse kinematics can be interpreted as a Lie symmetry of the direct kinematics. A parameterization of all Lie symmetries of the direct kinematics is proposed, and the classical Newton and gradient method are obtained as particular cases. 相似文献
49.
50.