全文获取类型
收费全文 | 24233篇 |
免费 | 47篇 |
国内免费 | 32篇 |
专业分类
化学 | 10264篇 |
晶体学 | 413篇 |
力学 | 942篇 |
综合类 | 11篇 |
数学 | 3527篇 |
物理学 | 9155篇 |
出版年
2023年 | 12篇 |
2022年 | 186篇 |
2021年 | 365篇 |
2020年 | 373篇 |
2019年 | 554篇 |
2018年 | 1012篇 |
2017年 | 1111篇 |
2016年 | 1324篇 |
2015年 | 539篇 |
2014年 | 1104篇 |
2013年 | 1669篇 |
2012年 | 1488篇 |
2011年 | 1578篇 |
2010年 | 1780篇 |
2009年 | 1740篇 |
2008年 | 1698篇 |
2007年 | 1620篇 |
2006年 | 1424篇 |
2005年 | 882篇 |
2004年 | 627篇 |
2003年 | 334篇 |
2002年 | 322篇 |
2001年 | 322篇 |
2000年 | 612篇 |
1999年 | 348篇 |
1998年 | 452篇 |
1997年 | 429篇 |
1996年 | 109篇 |
1995年 | 34篇 |
1994年 | 29篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 13篇 |
1982年 | 6篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1972年 | 5篇 |
1971年 | 7篇 |
1968年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
201.
V. F. Tret’yakov A. G. Zakirova V. A. Matyshak T. N. Burdeinaya V. N. Korchak L. S. Glebov V. V. Lunin 《Kinetics and Catalysis》2006,47(6):873-880
According to X-ray diffraction analysis data, the test catalyst was a Ni-Cr spinel with an impurity of NiO. With the use of in situ IR spectroscopy, it was found that nitrite, nitrate, and acetate surface complexes occurred under the reaction conditions of the selective catalytic reduction of nitrogen oxides by propane in the presence of oxygen on the nickel-chromium catalyst. As the temperature was increased, the nitrite complexes were converted into nitrate species. The molar absorption coefficient of surface nitrate complexes was determined. According to IR-spectroscopic and TPD data, the nitrate complexes were bound relatively weakly to the surface. The temperature region of their existence was 50–200°C. The temperature region of existence of the surface acetate complexes was 200–400°C. The individual adsorption of oxygen was not observed; however, oxygen-containing surface sites (Cr5+=O) participated in the formation of the surface complexes of reactants. 相似文献
202.
V. I. Voronkova I. N. Leont’eva N. I. Sorokina T. I. Ovsetsina I. A. Verin 《Crystallography Reports》2006,51(6):977-981
A series of iron-doped KTiOPO4 (KTP: Fe) single crystals in which iron substitutes for 0.1–0.3% titanium was grown. The structure of the KTP: Fe crystals was determined, and their dielectric and conducting properties were studied. An X-ray diffraction analysis failed to reveal such asmall amount of Fe+3 ions in titanium octahedral positions of the structure. It was found that an increase in the iron concentration results in a lowering of the symmetry of Ti(1)O6 and Ti(2)O6 octahedra. The splitting of the dielectric anomaly due to the ferroelectric phase transition was explained by the mechanism of incorporation of an impurity into different growth pyramids of the crystals. It was established that the aging of the KTP: Fe crystals leads to changes in the permittivity and electrical conductivity during long storage. 相似文献
203.
Yu. F. Popov A. M. Kadomtseva G. P. Vorob’ev S. S. Krotov K. I. Kamilov M. M. Lukina 《Physics of the Solid State》2003,45(11):2155-2159
Complex studies of the magnetic, magnetoelectric, and magnetoelastic properties of GdMn2O5 single crystals in strong pulsed magnetic fields are carried out in order to obtain additional indirect information on the character of the rare-earth and manganese spin ordering. It is shown that magnetic ordering of Gd3+ spins affects the manganese sublattice spin orientation and initiates new magnetic phase transitions. The observed magnetoelectric properties of the GdMn2O5 system are interpreted in terms of the theory of phase transitions. 相似文献
204.
S. K. Gorbatsevich I. A. Kaputskaya S. A. Maskevich S. Yu. Mikhnevich N. D. Strekal’ 《Optics and Spectroscopy》2004,97(2):238-243
The fluorescence of solid solutions of CdSe/ZnS quantum dots and the organic dye DODCI is investigated. It is shown that nonradiative transfer of electronic excitation energy to dye molecules, which with some probability lose their acceptor properties as a result of photoisomerization or photodegradation, is responsible for a significant increase in the fluorescence intensity of a donor. The degree of polarization of the donor fluorescence attains values exceeding 0.5, which is due to the difference in the fluorescence quantum yields of donors with different orientations of the oscillator with respect to the electric vector of an excitation light wave. A numerical simulation of the experimentally observed dependences is performed. 相似文献
205.
T. O. Denisova E. V. Amel’chenkova I. V. Pruss Zh. V. Dobrokhotova O. P. Fialkovskii S. E. Nefedov 《Russian Journal of Inorganic Chemistry》2006,51(7):1020-1064
Specific features of the chemical behavior and structure of copper(II) trimethylacetate complexes with 3,5-dimethylpyrazole have been considered based on X-ray crystallographic data. 相似文献
206.
The pseudopotential augmented-plane-wave method was used to study the surface structure of thin copper films with monolayers of Co, Ni, and Cs. Local densities of electron states, distributions of charge densities in the layers, and electron energy spectra are analyzed. The effect of adsorbates on the electronic properties of the Cu(001) surface and work function are discussed. Satisfactory agreement with available experimental data has been obtained. 相似文献
207.
In this paper we prove that all positive eigenvalues of the Laplacian of an arbitrary simple graph have some positive lower bounds. For a fixed integer k 1 we call a graph without isolated vertices k-minimal if its kth greatest Laplacian eigenvalue reaches this lower bound. We describe all 1-minimal and 2-minimal graphs and we prove that for every k 3 the path Pk+1 on k + 1 vertices is the unique k-minimal graph. 相似文献
208.
V. V. Pakal’nis I. V. Zerova S. I. Yakimovich 《Russian Journal of General Chemistry》2007,77(10):1732-1741
Acylhydrazines react with 1,3-diketones of the general formula CF3COCH2COR (where R is an aryl or hetaryl group) at both carbonyl groups. The reaction at the trifluoroacetyl group is favored by donor substituents in the aromatic ring of the 1,3-diketone or by the 2-furyl and, especially, 2-thienyl group as a hetaryl substituent, as well as by elevated temperature. The condensation products at the carbonyl group contiguous to the aryl or hetaryl ring have the structure of 5-hydroxy-4,5-dihydropyrazoles and do not undergo tautomeric transformations in solution. The condensation products at the trifluoroacetyl group have either 5-hydroxy-4,5-dihydropyrazole or hydrazone structure and give rise to ring-chain tautomeric equilibrium in solution. Electron-withdrawing substituents in the aromatic ring of the 1,3-dicarbonyl fragment and CDCl3 as solvent favor formation of the cyclic tautomer. The state of the tautomeric equilibrium is weakly sensitive to structural variations in the hydrazine component. 相似文献
209.
210.