全文获取类型
收费全文 | 672203篇 |
免费 | 6525篇 |
国内免费 | 2197篇 |
专业分类
化学 | 336924篇 |
晶体学 | 9715篇 |
力学 | 33528篇 |
综合类 | 74篇 |
数学 | 94485篇 |
物理学 | 206199篇 |
出版年
2021年 | 6096篇 |
2020年 | 6665篇 |
2019年 | 7475篇 |
2018年 | 11269篇 |
2017年 | 11430篇 |
2016年 | 15072篇 |
2015年 | 8705篇 |
2014年 | 13907篇 |
2013年 | 29574篇 |
2012年 | 25508篇 |
2011年 | 29554篇 |
2010年 | 21885篇 |
2009年 | 21768篇 |
2008年 | 26421篇 |
2007年 | 26018篇 |
2006年 | 23880篇 |
2005年 | 24557篇 |
2004年 | 22751篇 |
2003年 | 19301篇 |
2002年 | 17817篇 |
2001年 | 18790篇 |
2000年 | 14509篇 |
1999年 | 11245篇 |
1998年 | 9724篇 |
1997年 | 9333篇 |
1996年 | 8832篇 |
1995年 | 7977篇 |
1994年 | 7923篇 |
1993年 | 7697篇 |
1992年 | 8373篇 |
1991年 | 8707篇 |
1990年 | 8419篇 |
1989年 | 8233篇 |
1988年 | 8013篇 |
1987年 | 7953篇 |
1986年 | 7453篇 |
1985年 | 9344篇 |
1984年 | 9563篇 |
1983年 | 7805篇 |
1982年 | 8039篇 |
1981年 | 7736篇 |
1980年 | 7251篇 |
1979年 | 7951篇 |
1978年 | 8157篇 |
1977年 | 8149篇 |
1976年 | 8178篇 |
1975年 | 7545篇 |
1974年 | 7402篇 |
1973年 | 7508篇 |
1972年 | 5760篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
13.
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
14.
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
15.
Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as
hydroxyl (OH−) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as
provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place.
In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested
hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development
of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
16.
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
17.
18.
We prove a character formula for any finite-dimensional irreducible representationV of the “queer” Lie superalgebra g=q(n). It expresses chV in terms of the multiplicities of the irreducible g-subquotients of the cohomology groups of certain dominant g-bundles on
the Π-symmetric projective spaces (i.e., on the homogeneous superspacesG/P whose reduced space is a projective space, whereG=Q(n)). We also establish recurrent relations for the above multiplicities, and this enables us to compute explicitly chV for any givenV. This provides a complete solution to the Kac character problem for the Lie superalgebraq(n). Finally, we consider the particular cases ofq(2), q(3), andq(4) in which we compare the new character formula with the generic character formula of [12].
Translated from Itogi Nauki i Tekhniki, Seriya Sovremennaya Matematika i Ee Prilozheniya. Tematicheskie Obzory. Vol. 41, Algebraic
Geometry-7, 1997. 相似文献
19.
A. M. Nikitin 《Journal of Mathematical Sciences》1997,87(6):4138-4146
An explicit way for producing invariants for 6-valent graphs with rigid vertices within the framework of Kauffman's approach
to graph invariants is presented. These invariants can be used to detect the chirality of a 6-valent graph with rigid vertices.
A relevant example is considered. Bibliography: 19 titles.
Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 223, 1995, pp. 251–262.
Translated by A. M. Nikitin 相似文献
20.