全文获取类型
收费全文 | 8043篇 |
免费 | 222篇 |
国内免费 | 1575篇 |
专业分类
化学 | 6451篇 |
晶体学 | 131篇 |
力学 | 174篇 |
综合类 | 7篇 |
数学 | 642篇 |
物理学 | 2435篇 |
出版年
2024年 | 11篇 |
2023年 | 335篇 |
2022年 | 249篇 |
2021年 | 218篇 |
2020年 | 233篇 |
2019年 | 290篇 |
2018年 | 203篇 |
2017年 | 231篇 |
2016年 | 255篇 |
2015年 | 219篇 |
2014年 | 275篇 |
2013年 | 572篇 |
2012年 | 407篇 |
2011年 | 467篇 |
2010年 | 401篇 |
2009年 | 594篇 |
2008年 | 561篇 |
2007年 | 562篇 |
2006年 | 511篇 |
2005年 | 420篇 |
2004年 | 366篇 |
2003年 | 270篇 |
2002年 | 232篇 |
2001年 | 210篇 |
2000年 | 216篇 |
1999年 | 179篇 |
1998年 | 209篇 |
1997年 | 145篇 |
1996年 | 142篇 |
1995年 | 118篇 |
1994年 | 102篇 |
1993年 | 89篇 |
1992年 | 84篇 |
1991年 | 76篇 |
1990年 | 63篇 |
1989年 | 47篇 |
1988年 | 54篇 |
1987年 | 37篇 |
1986年 | 19篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 20篇 |
1981年 | 22篇 |
1980年 | 19篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 7篇 |
排序方式: 共有9840条查询结果,搜索用时 0 毫秒
11.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献
12.
Nanograins are characterized by a typical grain size from lto 100 nm.Mclecular dynamics aimubations have been carried out for the nanograin sphere with the diameters from 1.45 to 10.12 nm.We study the influence of grain size on structure and diffusion properties of the nanograins.The results reveal that as the grain size is reduced,the fraction of grain surface increases significantly,and the surface width is approximately constant;the diffusicn coefficlent is increased sharply,and the relation of the diffusion coefficient and the grain size is close to exponential relation below 10nm. 相似文献
13.
Jumiarti Agus Hideki Abe Yoshiharu Doi Takeharu Tsuge 《Polymer Degradation and Stability》2006,91(8):1645-1650
Polyhydroxyalkanoate (PHA) synthase (PhaC) from Wautersia eutropha was expressed in a wide range of production level in Escherichia coli XL1-Blue cells and its effects on PhaC activity, poly[(R)-3-hydroxybutyrate] [P(3HB)] production and its molecular weights were investigated. The production level of PhaC was controlled both by the amount of chemical inducer (isopropyl-β-d-thiogalactopyranoside, IPTG) added into the medium and the use of different copy number of plasmids. In a flask experiment, as PhaC production level in the cells increased, the PhaC activity also increased in the range of low PhaC concentration. However, PhaC activity did not further increase in the range of high PhaC concentration, probably due to the formation of inclusion body in the cells. The molecular weight of P(3HB) was found to decrease with increasing PhaC activity. This trend was also verified in high cell density cultivation using 10-l jar fermentor. Furthermore, we demonstrated that the use of low copy number plasmid and appropriate induction of PhaC expression were effective in achieving both high productivity and high molecular weight of P(3HB). 相似文献
14.
S. Koh K. Konishi Y. Shiraki 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):440
Self-assembled GeSiC dots stacked on a Ge hut-cluster layer buried in Si have been investigated. The critical thickness for formation of GeSiC dots is reduced owing to the strain fields from the buried hut-clusters. By utilizing the stacked structure, the dot size is decreased and the uniformity is improved. The highest density of the GeSiC dots with stacked structures is 7.4×1010 cm−2, which is six times larger than that of single GeSiC dots. The formation of the self-assembled GeSiC dots is strongly influenced by being stacked with buried Ge dots as well as C incorporation. 相似文献
15.
XiWenHE HongShengGUO YuMeiJIA 《中国化学快报》2003,14(9):979-982
In order to obtain mechanically stable membrane for practical application, the imprinted polymer was synthesized in the pores of polyfluoromembrane, the binding and transport ability of the membrane were studied. 相似文献
16.
We show that an electron confined to a single finite parabolic quantum well in crossed electric and magnetic fields can behave as a double quantum well system. The magnetic field is parallel to the heterostructure layers and the electric field is perpendicular to those. For a suitable choice of both fields and quantum well width, the electron can be confined to a double quantum well effective potential that is very similar to the electronic potential model for diatomic molecules. The double quantum well spectrum is calculated using a numerical algorithm based on semiclassical methods. A physical interpretation of this quantum system is given based on the analogy to the electrons bound to diatomic molecules. 相似文献
17.
Xu Tianzhou 《东北数学》1997,(1)
ModulesoverOperatorAlgebrasandItsModuleMapsXuTianzhou(许天周)(DepartmentofMathematics,NanjingUniersity,Nanjing,210093)AbstractLe... 相似文献
18.
A Note on Topological Entropy of Maps 总被引:1,自引:0,他引:1
For a given collection of subsets of a compact metric space X which cover X,the entropies,hm(f)and hi(f),are introduced for a continuous map f of X to itseif. Also the concept of shadowing property with same end point (SPSEP for short) is introduced. The main results are,(1)H(f)≤hi(f)+hm(f)and,(2)h(f)=hm(f)whenever f has SPSEP,where h(f) is the topological entropy of f. Moreover,several corollaries are obtained. 相似文献
19.
We show that the LF-algebra considered by Akkar and Nacir in [1] is topologically simple. 相似文献
20.
Semi-empirical molecular orbital calculations were carried out for the compounds (C2H5)3As, (C2H5)3Ga and RAsH2 (R = C2H5, i-C3H7, i-C4H9, and t-C4H9) by using the CNDO/2-U program, and their capability of β-elimination reaction is compared on the basis of the torsion energy to the transition state, electrostatic interactions and orbital overlapping between the central atom and the β-hydrogen, and bond order of the metal-carbon, and carbon-hydrogen bond. In the comparison of (C2H5)3As with (C2H5)3Ga, we found that the β-elimination of (C2H5)3As could hardly be expected to take place in the thermal decomposition. The capability of β-elimination would be smaller in C2H5AsH2 than that in (C2H5)3As. Moreover when the ethyl group is replaced by a t-butyl group in RAsH2, the β-elimination reaction appears to become more difficult and a large possibility for a radical process is suggested. 相似文献