全文获取类型
收费全文 | 781篇 |
免费 | 3篇 |
专业分类
化学 | 259篇 |
晶体学 | 19篇 |
力学 | 33篇 |
数学 | 120篇 |
物理学 | 353篇 |
出版年
2022年 | 8篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 18篇 |
2017年 | 18篇 |
2016年 | 34篇 |
2015年 | 11篇 |
2014年 | 30篇 |
2013年 | 35篇 |
2012年 | 24篇 |
2011年 | 34篇 |
2010年 | 30篇 |
2009年 | 33篇 |
2008年 | 21篇 |
2007年 | 30篇 |
2006年 | 17篇 |
2005年 | 12篇 |
2004年 | 27篇 |
2003年 | 26篇 |
2002年 | 23篇 |
2001年 | 24篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1982年 | 8篇 |
1980年 | 7篇 |
1978年 | 8篇 |
1976年 | 8篇 |
1974年 | 10篇 |
1973年 | 9篇 |
1972年 | 7篇 |
1971年 | 9篇 |
1970年 | 13篇 |
1969年 | 9篇 |
1967年 | 16篇 |
1966年 | 5篇 |
1965年 | 7篇 |
排序方式: 共有784条查询结果,搜索用时 31 毫秒
21.
A model of multicharge centers is proposed. Multicharge local centers are due to negatively charged As atoms in a twin coordination and positively charged Se atoms in a triple coordination. The change in the charge state of these centers because of capture of the light-generated non-equilibrium charge carriers depends on the temperature. Within the framework of this model, three reversing components of the permanent optical memory and the behavior of the low-temperature components at temperatures above the erasure temperature are discussed. The model agrees with experiments on the partial erasure by laser radiation during a change in its intensity or in the specimen temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 48–52, December, 1978. 相似文献
22.
V.M. Bondareva T.V. Andrushkevich O.B. Lapina A.A. Vlasov L.S. Dovlitova 《Reaction Kinetics and Catalysis Letters》2003,79(1):165-173
Vanadium-titanium catalysts modified with phosphorus additives (1-15 wt.% of P2O5) have been studied in methylpyrazine ammoxidation. Introduction of high amounts of the additive (≥ 10 wt.% of P2O5) results in a decrease in activity and selectivity of the catalysts due to formation of low active phase - a ternary compound
with the component ratio V : P : Ti ≈ 1 : 1 : 1 with only one type of slightly distorted tetrahedral vanadium (5+) bound via
oxygen to phosphorus (5+). The nature of the active sites of the samples modified with 1-5 wt.% of P2O5, similarly to that in the V-Ti-O catalyst, was found to include the V5+ cations strongly bound with TiO2 and located in the significantly distorted octahedral oxygen environment.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
23.
Bondareva V. M. Andrushkevich T. V. Lapina O. B. Khabibulin D. F. Vlasov A. A. Dovlitova L. S. Burgina E. B. 《Kinetics and Catalysis》2004,45(1):104-113
Oxide vanadium–titanium catalysts modified by phosphorus additives (20V2O5–(80 –n)TiO2–nP2O5, n = 1, 3, 5, 10, and 15 wt %) are studied in methylpyrazine ammoxidation. Two regions of compositions are found corresponding to radically different catalytic properties, namely, catalysts with a low (5 wt % P2O5) and high (10 wt % P2O5) concentration of the additive. In the first case, the introduction of phosphorus is accompanied by a gradual increase in the activity. In the second case, an increase in the additive concentration results in a decrease in the activity and selectivity to the target product, pyrazineamide, and a simultaneous increase in the selectivities to by-products, pyrazine and carbon oxides. The catalysts are characterized by X-ray diffraction analysis, differential dissolution, IR, and NMR spectroscopic data. As in the binary system, the active sites of the samples with a low concentration of phosphorus contain V5+ cations in a strongly distorted octahedral oxygen environment, which are strongly bound to a support due to the formation of V–O–Ti bonds. The catalytic properties of the samples containing 10 wt % P2O5 are due to the presence of the phase of a triple V–P–Ti compound with an atomic ratio V : P : Ti approximately equal to 1 : 1 : 1. The V5+ cations in this compound occur in a weakly distorted tetrahedral oxygen environment and are bound to the tetrahedral P5+ cations. 相似文献
24.
The effect of the substituent in the benzoyl group on the relative rate and activation parameters of transesterification of substituted 4-nitrophenyl benzoates with 4-chlorophenol in dimethylformamide in the presence of potassium carbonate was studied by the competing reaction technique. The whole series of benzoates showed the enthalpy-entropy compensation effect. 4-Nitrophenyl benzoates having electronacceptor substituents give rise to isokinetic relationship with an isokinetic temperature β of 382 K. The mechanism of the transesterification process is discussed. 相似文献
25.
A very large diversity space of synthetically accessible compounds for use with drug design programs
Nikitin S Zaitseva N Demina O Solovieva V Mazin E Mikhalev S Smolov M Rubinov A Vlasov P Lepikhin D Khachko D Fokin V Queen C Zosimov V 《Journal of computer-aided molecular design》2005,19(1):47-63
We have constructed a very large virtual diversity space containing more than 1013 chemical compounds. The diversity space is built from about 400 combinatorial libraries, which have been expanded by choosing sizeable collections of suitable R-groups that can be attached to each link point of their scaffolds. These R-group collections have been created by selecting reagents that have drug-like properties from catalogs of available chemicals. As members of known combinatorial libraries, the compounds in the diversity space are in general synthetically accessible and useful as potential drug leads. Hence, the diversity space can be used as a vast source of compounds by a de novo drug design program. For example, we have used such a program to generate inhibitors of HIV integrase enzyme that exhibited activity in the micromolar range. 相似文献
26.
The relative mobility of the nitro group and fluorine atom in 3,5-dinitro- and 3-fluoro-5-nitrobenzofluorides was estimated by the competing reaction technique using phenols in the presence of potassium carbonate (DMF, 65-95°C). Correlation analysis of the relative rate constants k(NO2)/k(F) and of the differences in the activation parameters (H
and S
) of competing reactions showed the existence of two reaction series for the examined phenols. The higher mobility of the nitro group was found to result from the entropy control of the reactivity of arenes. The mechanism of these reactions is discussed. 相似文献
27.
G. M. Beladidze S. I. Bityukov G. V. Borisov Yu. P. Gouz R. I. Dzhelyadin Yu. M. Ivanyushenkov A. N. Karyukhin I. A. Kachaev G. A. Klyuchnikov V. F. Konstantinov M. E. Kostrikov V. V. Kostyukhin A. A. Kriushin Yu. A. Khoklov V. V. Lapin T. A. Lomtadze V. D. Matveyev V. A. Medovikov V. F. Obraztsov A. P. Ostankov D. I. Ryabchikov V. K. Semenov E. A. Starchenko N. A. Shalanda E. G. Tskhadadze N. K. Vishnevsky E. V. Vlasov V. I. Yakimschuk A. M. Zaitsev S. A. Zimin 《Zeitschrift fur Physik C Particles and Fields》1992,54(2):235-238
The reaction
–
C
–
C has been studied at 36 GeV/c. A clear signal for the decaya
2
–
(1320)
–
· is observed in the
–
mass spectrum. The measured ratio of branchings is BR (a
2
–
–
)/BR(a
2
–
–
);(3.4±0.8±0.5)·10–2. 相似文献
28.
C. T. Simmons S. L. Molodtsov S. I. Fedoseenko J. C. Allman C. Laubschat G. Kaindl S. V. Moshikin M. A. Kuzmina M. U. Vlasov O. F. Vyvenko 《Zeitschrift für Physik B Condensed Matter》1992,87(3):271-273
The results of a high-resolution photoemission study using synchrotron radiation of two single crystals of Bi2Sr2CaCu2O8+, with different critical temperaturesT
c
due to a variation in oxygen stoichiometry are reported. Within experimental accuracy, the energy gap 2 is found to scale withT
c
, amounting to a reduced gap parameter of 2/k
BTc7.4. Employing resonant photoemission at the O–2s and Cu–3p thresholds, two spectral peaks at binding energies of 180 meV and 320 meV were identified as predominantly O–2p-and Cu–3d 4s-derived states, respectively. 相似文献
29.
M. A. Vlasov A. A. Korolev Yu. D. Nosach V. V. Popovich A. V. Rykhlov V. A. Safonov 《Radiophysics and Quantum Electronics》1991,34(2):162-167
Results obtained from experimental studies of the interaction between a quasistationary electron beam (300 keV, 20 A, 500 sec, 0.3 cm) and a dense gas are presented. These investigations were carried out in air at atmospheric pressure and, for the purpose of modeling the propagation of a magnetostricted REB, at reduced pressure (3–300 torr). The rarefaction dynamics of a channel heated by the beam are studied and its maximum propagation distances in a dense gas are determined. The results obtained are compared with the theoretical model examined earlier.V. I. Lenin All-Union Institute of Electrical Engineering. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 2, pp. 190–197, February, 1991. 相似文献
30.
A. A. Vlasov 《Theoretical and Mathematical Physics》1982,53(1):998-1003
Conclusions Proceeding from the equations of motion of two bodies and using the wave solution of the equations of the field theory, we have obtained in the post-Newtonian approximation for a binary system of relatively extended bodies expressions for the power L (8) of the gravitational radiation, the radiated gravitational energy E
e
(10) during a period of elliptic motion, and the angular momentum J (19)–(22) carried away by the gravitational waves. On their basis, we have obtained relations for the change in the parameters T and p of a binary system of compact bodies with the passage of time [the expressions (25)–(26)], and also the additional advance of the periastron (27) due to the fact that the bodies are not points. These results make it possible to verify the correspondence between the predictions of the field theory of gravitation and the results of observations of a large class of binary systems and determine the value of the parameter combination b2+2b4 of the theory.It is a pleasant duty to thank Academician A. A. Logunov and V. I. Denisov for valuable discussions of the work, and also A. Ya. Rodionov for assistance in checking the results of calculations on an EC 1040 computer (at the Scientific Research Institute of Nuclear Physics at the Moscow State University) using the program REDUCE for algebraic computations.Moscow State University. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 53, No. 1, pp. 83–92, October, 1982. 相似文献