全文获取类型
收费全文 | 226376篇 |
免费 | 1989篇 |
国内免费 | 521篇 |
专业分类
化学 | 117972篇 |
晶体学 | 3532篇 |
力学 | 10998篇 |
综合类 | 19篇 |
数学 | 25226篇 |
物理学 | 71139篇 |
出版年
2021年 | 2347篇 |
2020年 | 2361篇 |
2019年 | 2874篇 |
2018年 | 4045篇 |
2017年 | 4026篇 |
2016年 | 5417篇 |
2015年 | 2843篇 |
2014年 | 4876篇 |
2013年 | 9514篇 |
2012年 | 8015篇 |
2011年 | 9379篇 |
2010年 | 7213篇 |
2009年 | 7350篇 |
2008年 | 8759篇 |
2007年 | 8691篇 |
2006年 | 7695篇 |
2005年 | 7340篇 |
2004年 | 7079篇 |
2003年 | 6169篇 |
2002年 | 5817篇 |
2001年 | 6123篇 |
2000年 | 4657篇 |
1999年 | 3445篇 |
1998年 | 2971篇 |
1997年 | 3036篇 |
1996年 | 2889篇 |
1995年 | 2519篇 |
1994年 | 2618篇 |
1993年 | 2544篇 |
1992年 | 2836篇 |
1991年 | 2898篇 |
1990年 | 2758篇 |
1989年 | 2819篇 |
1988年 | 2703篇 |
1987年 | 2714篇 |
1986年 | 2572篇 |
1985年 | 3241篇 |
1984年 | 3312篇 |
1983年 | 2771篇 |
1982年 | 2739篇 |
1981年 | 2696篇 |
1980年 | 2496篇 |
1979年 | 2847篇 |
1978年 | 2836篇 |
1977年 | 2996篇 |
1976年 | 2995篇 |
1975年 | 2769篇 |
1974年 | 2726篇 |
1973年 | 2827篇 |
1972年 | 2134篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
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
143.
A. N. Grishkov 《Algebra and Logic》1998,37(5):294-306
Ordinary cohomologies in an algebra most often exhibit themselves either as objects that describe extensions (of algebras,
groups, or modules) or as subjects hindering the existence of algebraic constructions. We introduce the notion of nonlinear
cohomologies at a level of cochain complexes, furnish particular examples for Lie algebras, and give an interpretation of
first nonlinear cohomologies in terms of “quasiextensions” of orthogonal modules.
Translated fromAlgebra i Logika, Vol. 37, No. 5, pp. 522–541, September–October, 1998. 相似文献
144.
We investigate theoretically the effects of optical absorption and saturation of the non-linear index of refraction on the
bistability of non-linear distributed feedback structures (NLDFBs). By assuming that the Kerr non-linearity saturates in an
exponential fashion, we obtain for the first time closed-form expressions for the so-called self-phase and cross-phase modulation
terms. Our investigation shows that both absorption and, in particular, saturation significantly affect the bistable properties
of this structure and in many cases eliminate this response completely. In some cases, however, saturation alters the NLDFB's
transfer characteristics in a potentially useful manner. We find that weak levels of saturation may increase the contrast
ratio between the intensities of the high and low bistable states. At increasing levels of saturation, where bistability is
no longer observed, we find regimes where the NLDFB structure could possibly be used for optical amplification.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
145.
E. Jackiewicz M. Lukasiak M. Kopcewicz K. Szpila N. Bakun-Czubarow 《Hyperfine Interactions》1992,70(1-4):993-996
Terrestrial basalt rocks considered to be a good analogues of the Martian regolith were studied by using the Mössbauer spectroscopy and X-ray diffraction. The weathering of basalts was followed by the changes of the Fe2+/Fe3+ ratio. The basalt rock undergoes alteration from primary mineral composition (olivine+pyroxene+plagioclase) through smectite to kaolinite clay with oxides and hydroxides with the increase of the Fe2+/Fe3+ ratio. 相似文献
146.
The dependence of distribution functions of quarks, antiquarks, diquarks and their fragmentation into hadrons on the transverse momentumk t is discussed in the frame of the quark-gluon string model. We then discuss the division ofk t between 2n-quark-antiquark chains, orn-pomeron showers. Hadron and hadron-nuclear processesp?p,p?A,K +?p,K +?A are analysed. A strong dependence of the observed values on the numbern is derived by this method, which is of special importance for the analysis of hadron-nucleus collisions. Our method is compared with the regulark t division method. 相似文献
147.
148.
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
149.
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
150.
The three-band two-dimensional repulsive Hubbard model in the formalism of the temperature Green function is investigated.
The applicability of the weak coupling approach at the values of the dimensionless coupling constant U/t≈10–11 is justified.
The normal state, the antiferromagnetic state with Neel magnetic ordering on the “copper” sublattice, and the superconducting
state with nontrivial Cooper pairing in channels with odd angular momenta are studied. The possibility of other magnetic states
in the model is discussed. Bibliography: 20 titles.
Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 209, 1994, pp. 194–228.
Translated by K. Malyshev. 相似文献