全文获取类型
收费全文 | 33292篇 |
免费 | 281篇 |
国内免费 | 303篇 |
专业分类
化学 | 13664篇 |
晶体学 | 276篇 |
力学 | 1488篇 |
综合类 | 12篇 |
数学 | 9752篇 |
物理学 | 8684篇 |
出版年
2023年 | 44篇 |
2022年 | 58篇 |
2021年 | 112篇 |
2020年 | 131篇 |
2019年 | 119篇 |
2018年 | 1248篇 |
2017年 | 1495篇 |
2016年 | 845篇 |
2015年 | 676篇 |
2014年 | 628篇 |
2013年 | 896篇 |
2012年 | 3384篇 |
2011年 | 2617篇 |
2010年 | 2020篇 |
2009年 | 1710篇 |
2008年 | 831篇 |
2007年 | 883篇 |
2006年 | 864篇 |
2005年 | 4691篇 |
2004年 | 4107篇 |
2003年 | 2478篇 |
2002年 | 676篇 |
2001年 | 360篇 |
2000年 | 154篇 |
1999年 | 235篇 |
1998年 | 165篇 |
1997年 | 129篇 |
1996年 | 110篇 |
1995年 | 83篇 |
1994年 | 79篇 |
1993年 | 43篇 |
1992年 | 187篇 |
1991年 | 183篇 |
1990年 | 153篇 |
1989年 | 136篇 |
1988年 | 116篇 |
1987年 | 65篇 |
1986年 | 60篇 |
1985年 | 64篇 |
1984年 | 58篇 |
1983年 | 53篇 |
1982年 | 51篇 |
1981年 | 41篇 |
1979年 | 47篇 |
1978年 | 57篇 |
1976年 | 94篇 |
1975年 | 49篇 |
1974年 | 58篇 |
1973年 | 58篇 |
1972年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
In this paper the performance of a fiber-optic LAN with spread spectrum multiplexing is discussed from the viewpoint of transmission parameters. Two architectures are considered. The first concerns a structure with cascade-connected Y-type fiber-optic couplers. The second concerns an architecture with cascade-connected active optoelectronic repeater-coupler (ORCA) devices. 相似文献
42.
Summary A hypermedia environment was designed to set up a collection of reference data, reference spectra and computational tools. The system may serve as an aid for the combined interpretation of molecular spectra. This paper describes the context dependent presentation of the pieces of information. 相似文献
43.
In vitro and in vivo proton T1 data are reported that demonstrate that the paramagnetic copper-D-penicillamine complex can be applied as a potential contrast agent to magnetic resonance imaging. 相似文献
44.
T Christensen E B Jensen F Junker H Dalb?ge F Abildgaard J J Led 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1992,46(1):97-99
Biosynthetic human growth hormone specifically 13C-labelled in the carbonyl positions of all 26 leucine residues has been obtained by recombinant DNA techniques using 13C-labelled leucine and an E. coli strain that requires leucine. It is shown that, on the whole, the labelling is specific with no significant mislabelling as would have been the case had the 13C-labelled leucine been metabolized. 相似文献
45.
L Jirovetz G Buchbauer W J?ger A Woidich A Nikiforov 《Biomedical chromatography : BMC》1992,6(3):133-134
After inhalation experiments with sandalwood oil and the pure fragrance compounds coumarin and alpha-terpineol, substances were detected and measured in the blood samples of test animals (mice) using gas chromatography/mass spectrometry (GC/MS) (MID) in connection with GC/FTIR (SWC), GC/AES (carbon and oxygen trace) and flame ionization detection/gas chromatography. Using tiglinic acid benzyl ester as the internal standard the following concentrations in serum could be found: alpha-santalol 6.1 ng/mL, beta-santalol 5.3 ng/mL and alpha-santalene 0.5 ng/mL. In separate inhalation experiments with coumarin and with alpha-terpineol the corresponding concentrations were 7.7 ng/mL and 6.9 ng/mL, respectively. 相似文献
46.
Gravimetric measurements of thermodesorption of n-hexane and n-heptane were performed under quasi-equilibrium conditions. Differential thermodesorption profiles for ZSM-5 and ZSM-11 showed two peaks, but for Y zeolites, only one thermodesorption peak was observed. A model function, derived from the Langmiur adsorption model, was fitted to the experimental data, and the model parameters (the adsorption entropy and enthalpy) were estimated. The two-step desorption profiles observed for ZSM-5 and ZSM-11 were attributed to the commensurate freezing effect, i.e. a transition in the adsorbed phase resulting in ordering of the adsorbed molecules in the zeolite channels. The results observed for ZSM-11 indicate that the zigzag channels typical for ZSM-5 micropore system are not necessary for this transition to occur. 相似文献
47.
R. Ochoa-Land?&#x;n M. Flores-Acosta R. Ram?&#x;rez-Bon H. Arizpe-Chávez F.F. Castillón-Barraza 《Journal of Physics and Chemistry of Solids》2003,64(11):2245-2251
CdS clusters were synthesized in A type zeolite by reaction in alkaline aqueous solution at temperatures from 30 to 70 °C. The optical properties of the samples were studied by diffuse reflectance and photoluminescence spectroscopy. Their crystalline structure and morphology were studied by X-ray diffraction and by transmission and scanning electron microscopy. We found that at lower temperatures the CdS clusters are encapsulated in the zeolite cages. We compared the properties of these clusters with those encapsulated in the cages of zeolites X and Y, prepared by similar methods. CdS clusters smaller than the CdS exciton diameter are also formed outside the cages in the zeolite matrix. The size of these clusters increases with temperature producing a red-shift of the absorption edge in the optical absorption spectra. 相似文献
48.
Mihai Tib?r 《Topology》2003,42(3):629-639
We show that the complex link of a large class of space germs (X,x0) is characterized by its “simplicity”, among the Milnor fibres of functions with isolated singularity on X. This amounts to the minimality of the Milnor number, whenever this number is defined. Such a phenomenon has been first pointed out in case (X,x0) is an isolated hypersurface singularity, by Teissier (Cycles évanescents, sections planes et conditions de Whitney, in: Singularités à Cargèse 1972, Asterisque, Nos. 7 et 8, Soc. Math. France, Paris, 1973, pp. 285-362). 相似文献
49.
The determination of the sensitivity of the acoustical characteristics of vibrating systems with respect to the variation of the design parameters predicting these characteristics is a necessary and important step of the acoustic design and optimization process. Acoustic design sensitivity analysis includes the computation and evaluation of the sensitivity information required for this procedure. In this study, a boundary element code performing the sensitivity analysis of the acoustic pressure by using the matrix sensitivities with respect to different design variables has been developed. The effect of the precision of boundary element discretization on the acoustic pressure sensitivity is examined via this code. The formulation is applied to a multi-source system and the dimension sensitivity analysis of near field pressures of two-dilating-spherical source is performed. The last application is devoted to a real sound source: a washing machine sitting on the floor. Sensitivity of the field pressures to the machine’s dimensions (size), surface velocity and frequency is examined on the bases of the boundary element model of the machine and half-space condition. The impacts of these variables are compared; and a limiting speed for the machine responding both the acoustical and operational requirements is determined. 相似文献
50.
Marc Bonnet 《International Journal of Solids and Structures》2008,45(2):705-707
The aim of this discussion is to expose incorrect results in a previous IJSS article. 相似文献