全文获取类型
收费全文 | 73956篇 |
免费 | 2132篇 |
国内免费 | 197篇 |
专业分类
化学 | 43552篇 |
晶体学 | 393篇 |
力学 | 1628篇 |
综合类 | 10篇 |
数学 | 13040篇 |
物理学 | 17662篇 |
出版年
2023年 | 439篇 |
2022年 | 477篇 |
2021年 | 1004篇 |
2020年 | 1110篇 |
2019年 | 1048篇 |
2018年 | 1403篇 |
2017年 | 1275篇 |
2016年 | 2407篇 |
2015年 | 1969篇 |
2014年 | 2050篇 |
2013年 | 4178篇 |
2012年 | 4292篇 |
2011年 | 4329篇 |
2010年 | 2770篇 |
2009年 | 2464篇 |
2008年 | 3718篇 |
2007年 | 3510篇 |
2006年 | 3219篇 |
2005年 | 3641篇 |
2004年 | 3359篇 |
2003年 | 2608篇 |
2002年 | 2070篇 |
2001年 | 1628篇 |
2000年 | 1548篇 |
1999年 | 1055篇 |
1998年 | 836篇 |
1997年 | 742篇 |
1996年 | 961篇 |
1995年 | 743篇 |
1994年 | 823篇 |
1993年 | 772篇 |
1992年 | 798篇 |
1991年 | 681篇 |
1990年 | 664篇 |
1989年 | 568篇 |
1988年 | 549篇 |
1987年 | 505篇 |
1986年 | 488篇 |
1985年 | 673篇 |
1984年 | 624篇 |
1983年 | 513篇 |
1982年 | 514篇 |
1981年 | 532篇 |
1980年 | 446篇 |
1979年 | 425篇 |
1978年 | 445篇 |
1977年 | 401篇 |
1976年 | 413篇 |
1974年 | 385篇 |
1973年 | 386篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
In this work the results of the statistical topometric analysis of fracture surfaces of soda-lime-silica glass with and without ionic exchange treatment are reported. In this case, the mechanism of substitution is K+-Na+. atomic force microscopy (AFM) was employed to record the topometric data from the fracture surface. The roughness exponent (ζ) and the correlation length (ξ) were calculated by the variable bandwidth method. The analysis for both glasses (subjected and non-subjected to ionic exchange) for ζ shows a value ∼0.8, this value agrees well with that reported in the literature for rapid crack propagation in a variety of materials. The correlation length shows different values for each condition. These results, along with those of microhardness indentations suggest that the self-affine correlation length is influenced by the complex interactions of the stress field of microcracks with that resulting from the collective behavior of the point defects introduced by the strengthening mechanism of ionic exchange. 相似文献
72.
73.
Christelle de Bellefontaine Flore Josse Martine Domurado Dominique Domurado 《Applied biochemistry and biotechnology》1994,48(2):117-123
In order to detect low levels of enzyme activity, specifically glucose oxidase, in biological samples, an immunoenzymatic assay was developed since currently available methods could not be used because of either their lack of sensitivity or the conditions prevailing in our samples: turbidity of the medium, presence of redox systems other than glucose oxidase, and high concentration of proteins. The principle of the method is to coat a polystyrene surface with a fragment Fc-specific anti-IgG, then with an antibody directed against the looked-for enzyme, which is simultaneously the antigen and the enzyme activity required for immunoenzymatic detection. We applied this concept to biological samples after glucose oxidase administration to mice. This method achieves specificity and sensitivity (20 ng/mL or 1 ng) with samples of biological origin. No marker is needed since the antigen itself possesses an enzyme activity. This method, which requires a small sample volume (50 ΜL, 20 ΜL, if necessary), can be extended easily to the many enzymes currently used as markers. It could also be applied to the native enzymes of medical interest for which antibodies and a colorimetric reaction are available. 相似文献
74.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields. 相似文献
75.
In this Note we give a necessary and sufficient condition for the spectral controllability from one simple node of a general network of strings that undergoes transversal vibrations in a sufficiently large time. This condition asserts that no eigenfunction vanishes identically on the string that contains the controlled node. The proof combines the Beurling–Malliavin's theorem and an asymptotic formula for the eigenvalues of the network. The optimal control time may be characterized as twice the sum of the lengths of all the strings of the network. To cite this article: R. Dáger, E. Zuazua, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 545–550. 相似文献
76.
We study spectral properties of discrete Schrödinger operators with potentials obtained via dimerization of a class of aperiodic sequences. It is shown that both the nature of the autocorrelation measure of a regular sequence and the presence of generic (full probability) singular continuous spectrum in the hull of primitive and palindromic (four block substitution) potentials are robust under dimerization. Generic results also hold for circle potentials. We illustrate these results with numerical studies of the quantum mean square displacement as a function of time. The numerical techniques provide a very fast algorithm for the time evolution of wave packets. 相似文献
77.
78.
79.
80.
The capability of gated saturable absorbers for single-pulse selection is studied theoretically using the classical space-time-dependent rate-equation model. The dynamics of operation is followed experimentally by the well-known pump—probe technique. Comparing the theoretical and experimental results, it is found that gated saturable absorbers can efficiently be used for pulse forming and pulse selection of pulses longer than picosecond. 相似文献