全文获取类型
收费全文 | 69547篇 |
免费 | 2530篇 |
国内免费 | 1686篇 |
专业分类
化学 | 34895篇 |
晶体学 | 1045篇 |
力学 | 4019篇 |
综合类 | 103篇 |
数学 | 6056篇 |
物理学 | 27645篇 |
出版年
2022年 | 603篇 |
2021年 | 753篇 |
2020年 | 831篇 |
2019年 | 765篇 |
2018年 | 872篇 |
2017年 | 784篇 |
2016年 | 1334篇 |
2015年 | 1047篇 |
2014年 | 1541篇 |
2013年 | 3263篇 |
2012年 | 3178篇 |
2011年 | 3937篇 |
2010年 | 2743篇 |
2009年 | 2851篇 |
2008年 | 3466篇 |
2007年 | 3259篇 |
2006年 | 3095篇 |
2005年 | 2762篇 |
2004年 | 2448篇 |
2003年 | 2120篇 |
2002年 | 1972篇 |
2001年 | 3300篇 |
2000年 | 2411篇 |
1999年 | 1848篇 |
1998年 | 1383篇 |
1997年 | 1274篇 |
1996年 | 1056篇 |
1995年 | 982篇 |
1994年 | 925篇 |
1993年 | 755篇 |
1992年 | 1083篇 |
1991年 | 1052篇 |
1990年 | 965篇 |
1989年 | 816篇 |
1988年 | 802篇 |
1987年 | 870篇 |
1986年 | 728篇 |
1985年 | 937篇 |
1984年 | 865篇 |
1983年 | 592篇 |
1982年 | 585篇 |
1981年 | 554篇 |
1980年 | 513篇 |
1979年 | 631篇 |
1978年 | 651篇 |
1977年 | 664篇 |
1976年 | 575篇 |
1975年 | 485篇 |
1974年 | 522篇 |
1973年 | 452篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
61.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
62.
The interaction between azathioprine (AZ) and bovine serum albumin (BSA) is mainly due to hydrophobic binding according to the dependence of the binding constant on the ionic strength obtained by equilibrium dialysis. The binding constant and partition coefficient of AZ were smaller than those of warfarin, phenylbutazone and ibuprofen. Little variation in the proton chemical shift of AZ was observed whether there was an absence or presence of BSA (7.25 x 10(-5) M). The spin-lattice relaxation time (T1) of AZ decreased in the presence of BSA to 6-22%. The spin-spin relaxation rate (1/T2) of AZ increased 16-24 times for the methyl group and the imidazole ring and 8-13 times for the purine ring in the presence of BSA. The ratio of the spin-spin relaxation rate of the free AZ to the bound AZ ((1/T2)b/(1/T2)f) of the methyl group and the imidazole ring was 2-3 times larger than that of the purine ring. The binding of AZ to BSA was concluded to be mainly at the methyl group on the imidazole ring of AZ. 相似文献
63.
加肋圆柱壳在轴压作用下的屈曲和后屈曲 总被引:2,自引:2,他引:0
本文讨论完善和非完善的,纵向加肋和正交加肋圆柱壳在轴压作用下的屈曲和后屈曲性态.依据文[1]提供的圆柱薄壳屈曲的边界层理论及其分析方法,给出了加肋圆柱壳在轴压作用下的屈曲和后屈曲理论分析.本文同时讨论肋骨与壳板材料不同时对加肋圆柱壳屈曲和后屈曲性态的影响. 相似文献
64.
Xuechu Shen 《量子光学学报》2006,12(B08):55-56
The single and a few coupled quantum dots are important for future quantum information sciences and their investigation is also a big challenge in physics. We investigate here the electronic and exciton states and their interaction with each other via micro photoluminescence. The luminescence for single and a few dots as well as a dot molecule of CdSe/ZnSe are measured with very high resolution, under liquid He temperature and magnetic fields and with different polarization of excitation laser. The observed sharp spectral lines are attributed to the atomlike transitions of exciton, trion, biexciton… in the investigated single QD or QD molecule. Band filling, Zeeman splitting, spin transition and their relaxation are observed and investigated'from the spectra and compared with those of same material in different dimensions, and compared with the primary calculation as well. In addition, quite a few new phenomena, which can not be understood based on our present model and knowledge, are also observed; and some very interesting problems are left for further investigation. 相似文献
65.
A three-dimensional molecular dynamics (MD) model is utilized to investigate the effect of tool geometry on the deformation process of the workpiece and the nature of deformation process at the atomic-scale. Results show that different states exist between the atomic force microscope (AFM) pin tool and the workpiece surface, i.e. the non-wear state, the ploughing state, the state in which ploughing is dominant and the state in which cutting plays a key role. A relationship between the deformation process of the workpiece and the potential energy variation is presented. The potential energy variation of atoms in different deformed regions in the workpiece such as plastically deformed region, elastically deformed region and the mixed deformation region is different. The features of variations of potential energy are discussed. 相似文献
66.
A.Y. El-Etre 《Applied Surface Science》2006,252(24):8521-8525
The inhibitive effect of the extract of khillah (Ammi visnaga) seeds, on the corrosion of SX 316 steel in HCl solution was determined using weight loss measurements as well as potentiostatic technique. It was found that the presence of the extract reduces markedly the corrosion rate of steel in the acid solution. The inhibition efficiency increases as the extract concentration is increased. The inhibitive effect of khillah extract was discussed on the basis of adsorption of its components on the metal surface. Negative values were calculated for the energy of adsorption indicating the spontaneity of the adsorption process. The formation of insoluble complexes as a result of interaction between iron cations and khellin, which present in the extract, was also discussed. 相似文献
67.
带干扰的多险种风险模型 总被引:2,自引:0,他引:2
由于保险公司风险经营规模不断扩大,用单一险种的模型来描述风险过程存在局限性,本文讨论了带干扰多险种风险模型,应用鞅论方法,得出伦德伯格不等式和最终破产概率公式。 相似文献
68.
A novel technique to overcome the long-term drift and hysteresis of a scanning Fabry–Perot filter was developed and applied to wavelength and power monitoring of DWDM system. By using the comb peaks generated by a temperature-stabilized, near threshold-biased Fabry–Perot diode laser as wavelength reference for the scanning Fabry–Perot filter, wavelength and power measurement accuracy of better than ±10 pm and 0.2 dB, respectively, were achieved. 相似文献
69.
70.
The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method. 相似文献