全文获取类型
收费全文 | 70664篇 |
免费 | 2326篇 |
国内免费 | 216篇 |
专业分类
化学 | 43847篇 |
晶体学 | 423篇 |
力学 | 1465篇 |
综合类 | 3篇 |
数学 | 11940篇 |
物理学 | 15528篇 |
出版年
2022年 | 440篇 |
2021年 | 816篇 |
2020年 | 1053篇 |
2019年 | 859篇 |
2018年 | 1233篇 |
2017年 | 1010篇 |
2016年 | 1811篇 |
2015年 | 1515篇 |
2014年 | 1759篇 |
2013年 | 3707篇 |
2012年 | 3361篇 |
2011年 | 4067篇 |
2010年 | 2165篇 |
2009年 | 1902篇 |
2008年 | 3625篇 |
2007年 | 3661篇 |
2006年 | 3372篇 |
2005年 | 3094篇 |
2004年 | 2493篇 |
2003年 | 2170篇 |
2002年 | 2029篇 |
2001年 | 1237篇 |
2000年 | 1212篇 |
1999年 | 858篇 |
1998年 | 768篇 |
1997年 | 805篇 |
1996年 | 951篇 |
1995年 | 792篇 |
1994年 | 802篇 |
1993年 | 908篇 |
1992年 | 752篇 |
1991年 | 619篇 |
1990年 | 634篇 |
1989年 | 532篇 |
1988年 | 530篇 |
1987年 | 553篇 |
1986年 | 492篇 |
1985年 | 742篇 |
1984年 | 802篇 |
1983年 | 667篇 |
1982年 | 731篇 |
1981年 | 749篇 |
1980年 | 637篇 |
1979年 | 582篇 |
1978年 | 664篇 |
1977年 | 586篇 |
1976年 | 538篇 |
1975年 | 510篇 |
1974年 | 488篇 |
1973年 | 474篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
Csilla Bujtás 《Discrete Applied Mathematics》2007,155(11):1395-1407
For a mixed hypergraph H=(X,C,D), where C and D are set systems over the vertex set X, a coloring is a partition of X into ‘color classes’ such that every C∈C meets some class in more than one vertex, and every D∈D has a nonempty intersection with at least two classes. A vertex-orderx1,x2,…,xn on X (n=|X|) is uniquely colorable if the subhypergraph induced by {xj:1?j?i} has precisely one coloring, for each i (1?i?n). We prove that it is NP-complete to decide whether a mixed hypergraph admits a uniquely colorable vertex-order, even if the input is restricted to have just one coloring. On the other hand, via a characterization theorem it can be decided in linear time whether a given color-sequence belongs to a mixed hypergraph in which the uniquely colorable vertex-order is unique. 相似文献
143.
144.
A. Ferreira da Silva I. Pepe S.A. Tomás W.M. de Azevedo R. Ahuja 《Applied Surface Science》2006,252(15):5365-5367
In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO2) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO2 thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO2 absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO2 are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO2 films prepared for undoped sol-gels and by sputtering is performed. 相似文献
145.
von Eynatten G. Ritter T. Bömmel H. E. Dransfeld K. 《Zeitschrift für Physik B Condensed Matter》1987,65(3):341-345
A new model is presented which explains well the dramatic decrease of the Mössbauer line intensities with raising temperatures for freely dispersed iron microscrystals. In contrast to other theories which consider mainly vibration to be responsible we discuss here the decrease in terms of large amplitude diffusive rotational or translational jumps of the particles. Such diffusive jumps lead — in agreement with the observation — to a strong reduction of the Mössbauer-intensity without broadening the line width in a noticeable way. The typical potential well for a diffusing particle in an equilibrium position is derived quantitatively to be 13 meV. The model might be important also for a new understanding of the dynamics of catalytic clusters either in contact with each other or with larger solid surfaces.Part of this work was supported by the DFG Sonderforschungsbereich 306, Konstanz 相似文献
146.
The hyperfine fields for the systems140CeLa and140CeLu have been determined by time differential perturbed angular correlations (TDPAC) in the temperature range 4.2 K≤T≤330 K. Magnitude and temperature dependence of the paramagnetic enhancement factor β indicate that cerium in either system
is of intermediate valence. This behaviour is discussed in terms of a theory proposed by Ramakrishnan et al. [1–3]. 相似文献
147.
148.
Twelve-membered ring pseudopeptidic cyclic disulfides have been prepared by iodine oxidation of the parent dithiols. However, oxidation of N,N′-(1,2-phenylene)bis(2-mercapto-2-methylpropanamide) afforded a 25/75 mixture of cyclic mono- and bis-disulfides that were separated by selective precipitation in CHCl3. The cyclic bis-disulfide was selectively prepared by iodine oxidation of the Ni complex of this dithiol and crystallized. Its crystal structure was solved by X-ray diffraction. All these cyclic mono- or bis-disulfides were selectively converted to cyclic mono- and bis-thiosulfinates upon stoichiometric oxidation with dimethyldioxirane at low temperature. 1H NMR of the cyclic bis-thiosulfinate revealed the presence of four isomers, two couples of stereoisomers, as expected from the insertion of two oxygen atoms in this compound, one on each disulfide bond. The two couples of cis/trans isomers were separated by preparative TLC and identified after alkaline cleavage of the two S(O)-S bonds and metalation with Ni(II). As HO− attack is selective for the sulfinyl sulfur, the nature of the Ni complexes obtained is a signature of each couple of stereoisomers. 相似文献
149.
Paul Fabel 《Topology and its Applications》2007,154(3):635-638
With a certain natural topology, the fundamental group of a locally path connected metric space X becomes discrete if and only if X is semilocally simply connected. We include some related material and offer a counterexample to a similar result. 相似文献
150.