全文获取类型
收费全文 | 6274篇 |
免费 | 1101篇 |
国内免费 | 474篇 |
专业分类
化学 | 1000篇 |
晶体学 | 22篇 |
力学 | 720篇 |
综合类 | 50篇 |
数学 | 290篇 |
物理学 | 5767篇 |
出版年
2024年 | 8篇 |
2023年 | 46篇 |
2022年 | 135篇 |
2021年 | 128篇 |
2020年 | 125篇 |
2019年 | 102篇 |
2018年 | 126篇 |
2017年 | 260篇 |
2016年 | 273篇 |
2015年 | 262篇 |
2014年 | 402篇 |
2013年 | 425篇 |
2012年 | 405篇 |
2011年 | 442篇 |
2010年 | 319篇 |
2009年 | 387篇 |
2008年 | 442篇 |
2007年 | 452篇 |
2006年 | 382篇 |
2005年 | 324篇 |
2004年 | 300篇 |
2003年 | 271篇 |
2002年 | 244篇 |
2001年 | 246篇 |
2000年 | 213篇 |
1999年 | 176篇 |
1998年 | 149篇 |
1997年 | 150篇 |
1996年 | 113篇 |
1995年 | 90篇 |
1994年 | 61篇 |
1993年 | 69篇 |
1992年 | 48篇 |
1991年 | 47篇 |
1990年 | 39篇 |
1989年 | 33篇 |
1988年 | 30篇 |
1987年 | 24篇 |
1986年 | 12篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有7849条查询结果,搜索用时 15 毫秒
171.
Experiment on relationship between the magnetic gradient of low-carbon steel and its stress 总被引:1,自引:0,他引:1
Xingliang Jian Xingchao Jian Guoyong Deng 《Journal of magnetism and magnetic materials》2009,321(21):3600-3606
In geomagnetic field, a series of tensile experiments on the low-carbon steel sticks were carried out. A special homemade detector was used to measure the magnetic gradient on the material surface. The results showed that the relationship between the magnetic gradient and the stress varied with different conditions of measurement. There was no obvious correlation between the magnetic gradient and the tensile stress if the sample remained on the material test machine. If the sample was taken off from the machine, the measured magnetic gradient was linear with the prior maximum stress. In Nanjing, PR China, a place of 32°N latitude, the slope of the linear relationship was about 67 (uT/m)/MPa. This offered a new method of non-destructive stress testing by measuring the magnetic gradient on the ferromagnetic component surface. The prior maximum applied stress of the sample could be tested by measuring the present surface magnetic gradient. Actually this phenomenon was the metal magnetic memory (MMM). The magnetic gradient near the stress concentration zone of the sample, the necking point, was much larger than other area. Thus, the hidden damage in the ferromagnetic component could be detected early by measuring the magnetic gradient distribution on its surface. In addition, the magnetic memory signal gradually weakened as the sample was taken off and laid aside. Therefore, it was effective for a given period of time to detect the stress or stress concentration based on the MMM testing. 相似文献
172.
Long distance atomic teleportation (LDAT) is of prime importance in long distance quantum communication. Scheme proposed by Bose et al. (1999) in principle enables us to have LDAT using cavity decay. However it gives message state dependent fidelity and success rate. Here, using interaction of entangled coherent states with atom–cavity systems and a two-step measurement, we show how, LDAT can be achieved with unit fidelity and as good success as desired under ideal conditions. The scheme is unique in that, the first measurement predicts success or failure. If success is predicted then second measurement gives perfect teleportation. If failure is predicted the message-qubit remains conserved therefore a second attempt may be started. We found that even in presence of decoherence due to dissipation of energy our scheme gives message state independent success rate and almost perfect teleportation in single attempt with mean fidelity of teleportation equal to 0.9 at long distances. However if first attempt fails, unlike ideal case where message-qubit remains conserved with unit fidelity, in presence of decoherence the message-qubit remains conserved to some degree, therefore mean fidelity of teleportation can be increased beyond 0.9 by repeating the process. 相似文献
173.
We show that the semiclassical approach to chaotic quantum transport in the presence of time-reversal symmetry can be described by a matrix model. In other words, we construct a matrix integral whose perturbative expansion satisfies the semiclassical diagrammatic rules for the calculation of transport statistics. One of the virtues of this approach is that it leads very naturally to the semiclassical derivation of universal predictions from random matrix theory. 相似文献
174.
A novel optical extensometer is developed to estimate the local uniform strain on planar surface accurately. The proposed system consists of a shared large format lens and two image sensors, which acquire pairs of images of two isolated small regions on the object surface simultaneously. Digital image correlation (DIC) algorithm is applied to determine the relative displacement between gauge points designated on recorded pairs of images. Then local strain can be extracted after dividing the relative displacement by the scale distance. Moreover, a special experimental setup called “correction sheet” is used to eliminate the virtual strain induced by out-of-plane motions. Uni-axial tensile experiments are performed to validate the reliability and resolution of the optical extensometer, and the measurement results demonstrate that the resolution of the optical extensometer achieves 2–3 με. 相似文献
175.
Simple and readily available chiral N‐(sulfinyl)allylamines have been developed as efficient novel ligands for the rhodium‐catalyzed enantioselective 1,2‐addition of arylboronic acids to challenging aliphatic α‐ketoesters. By employing the linear or branched sulfinamide‐olefin ligands, interesting enantioselectivity as well as regioselectivity reversal in the related asymmetric additions were observed. 相似文献
176.
177.
You Wei 《Journal of Dispersion Science and Technology》2013,34(12):1785-1794
178.
《Journal of Dispersion Science and Technology》2013,34(3-4):517-525
Abstract Sorption of ions may lead to variations in interparticle forces and, thus, changes in the stability of colloidal particles. Chemical interactions between metal ions and colloidal particles modify the molecular structure of the surface, the surface charge, and the electrical potential between colloidal particles. These modifications to the surface and to the electrical double layer due to metal ion sorption are reflected in the interaction force between a particle and another surface, which is measured in this study by atomic force microscopy (AFM). Specifically, AFM is used to investigate the sorption of copper ions from aqueous solutions by silica particles. The influence of metal ion concentration and solution ionic strength on surface forces is studied under transient conditions. Results show that as the metal ion concentration is decreased, charge reversal occurs and a longer period of time is required for the system to reach equilibrium. The ionic strength has no significant effect on sorption kinetics. Furthermore, neither metal concentration nor ionic strength exhibits any effect on sorption equilibria, indicating that for the experimental conditions used in this study, the surface sites of the silica particle are fully occupied by copper ions. 相似文献
179.
Qidong Wang Zenghui Peng Lishuang Yao Yonggang Liu Lifa Hu Zhaoliang Cao 《Liquid crystals》2013,40(11):1569-1574
It has been a crucial technique to improve the dynamic response characteristics of a liquid crystal wavefront corrector (LCWFC) with optimal cell gap since the LCWFC needs at least 2π (or π) phase modulation in adaptive optics systems (AOSs). We have given a complete process for obtaining the optimal cell gap accurately from a single photoelectric measurement, which can be conducted with a liquid crystal (LC) cell of any known thickness. This method has been analysed theoretically and confirmed experimentally by using a wedge-shaped cell; the experimental results match very well with the theoretical analysis. The response time of an optimal gap cell can be a novel evaluation method of response performance of LC materials. 相似文献
180.
A. K. Prajapati 《Liquid crystals》2013,40(8):1017-1020
Two mesogenic homologous series, 2-[4-(4-n-alkoxybenzoyloxy)-2-methylphenylazo]-naphthalenes (I) and 2-[4-(4-n-alkoxybenzoyloxy)-3-methylphenylazo]naphthalenes (II) with a lateral methyl group have been synthesized. Both series are purely nematogenic. The mesomorphic properties of both series are compared with each other and also with the properties of other structurally related series to evaluate the effect of the lateral methyl group on mesomorphism. The chiral nematic (N*) mesophase was induced in the system by doping with a derivative of naturally occurring chiral menthol. 相似文献