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911.
A. N. Novikov V. A. Bacherikov Yu. E. Shapiro A. I. Gren 《Journal of Structural Chemistry》2006,47(6):1003-1015
The cone conformation of C 4 symmetry is shown by the Hartree-Fock method (3-21G basis) to be the predominant conformer of calix[4]arene; the compressed cone of C 2 symmetry is the major conformer of calix[6]arene. Using quantum chemical methods we calculated hydrogen bond cleavage energies for calix[4]-(ab initio and density functional methods) and calix[6]arene (ab initio), and also for the complex of calix[4]arene with carbon disulfide. These energies along with structural data point to the cooperative effect of hydrogen bonds. The results of these studies provided an explanation to the greater conformational lability of calix[6]arene compared with calix[4]arene molecules. It is also predicted that the nucleophilic substitution reaction involving calix[6]arene in the presence of weak bases and in aprotic solvents, as well as in the gas phase, will occur via diastereomeric transition states. 相似文献
912.
R. G. Gasanov M. V. Tsikalova E. V. Martynova A. L. Chistyakov I. V. Stankevich Yu. N. Novikov 《Russian Chemical Bulletin》2007,56(7):1351-1358
The addition of ·P(O)(OPri)2 (R1), ·CMe3 (R2), and ·CCl3 (R3) radicals to metallofullerenes (η2-C60)IrH(CO)(CNBut)2(o-HCB10H9CCH2PPh2-B,P) (1), (η2-C60)IrH(CO)(DIOP) (DIOP is (4R,5R)-(+)-4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane, 2), and (η2-C60)IrH(CO)(PPh3)2 (3) was studied by EPR spectroscopy. A stability study of spin adducts (SAs) of R1 radicals with complexes 1 and 2 showed that when the reactions are initiated by illumination with 366-nm light, the EPR spectra exhibit only signals of those
isomers that are formed upon attack of the R1 radicals on the carbon atoms of the cis-1 and cis-2 bonds (i.e., carbon atoms of the fullerene hemisphere to which the metallofragment is attached). Investigations of the reactions of R2 and R3 radicals with complexes 1–3 initiated with 366-nm light made it possible to detect (i) regioisomers formed by adding these radicals to carbon atoms of
the cis-n bonds and (ii) SAs formed by adding the radicals to carbon atoms of other bonds in complexes 1–3. The hyperfine structure of the EPR spectrum essentially depends on the spatial structure of substituents at the metal atom
and allows individual regioisomers of not only phosphoryl radicals, but also carbon-centered radicals R2 and R3 with metallofullerenes 1–3 to be identified. The rate constants for addition of R2 and R3 radicals to complexes 2 and 3 were determined.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1302–1309, July, 2007. 相似文献
913.
Rong Jian SA Ke Chen WU* Ping LIU Chen Sheng LIN Chao Yong MANG State Key Laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter Chinese Academy of Sciences Fuzhou The Graduate school of the Chinese Academy of Sciences Beijing 《中国化学快报》2002,(12)
A series of tri-nuclear transition metal clusters with incomplete cubane-like configurations have been studied by TDDFT method. The calculations show that they have enormously large second-order polarizabilities () and are potential nonlinear optical materials for infrared double frequency conversion1. In this paper some tetra-nuclear transition metal clusters with cubane-like configurations, MCu3X4 (PPh3)3 (M=W, Mo; X= S, O, Cl, Se, Br), were studied by TDDFT method for a reference… 相似文献
914.
N. N. Novikov 《Russian Physics Journal》1976,19(6):765-768
The dependence of activation volume and dislocation start stress in sodium and calcium chloride crystals on-radiation dosage (in the range 104–109rad) is studied. It is established that these functions indicate that the hardening of crystals subjected to radiation is of a dislocation nature. Analysis of data from the literature leads to the conclusion that in the medium and high radiation dose region planar precipitates and surrounding dislocations formed by halogen molecules are responsible for hardening.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 99–103, June, 1976. 相似文献
915.
Geometric parameters of dimethylphenylphosphine molecule were determined by gas-phase electron diffraction using a dynamic model in which the rotation of the PMe2 group is treated as large-amplitude motion. Refinement of the structural parameters and parameters of the potential function was performed taking into account the geometry relaxation on the basis of HF/6-311++G** calculations. The internal rotation potential has a single minimum at 0° ( is the angle between the bisector of the MePMe angle and the phenyl ring plane) and may be described by the function of the form V() = 0.5V
2(1 - cos2), where V
2 = 0.38±0.36 kcal mol-
1. The data obtained are compared with those for related molecules. Steric effects affect the geometry of the phenylphosphine molecule more significantly than does p- interaction. 相似文献
916.
Yu. I. Gusev Yu. N. Novikov A. V. Popov V. I. Tikhonov 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(8):875-879
The design and expected characteristics of an experimental setup for generating a beam of singly, doubly, and triply charged ions of 229mTh isomer are considered. The scheme of ion transport, the preparation of the thin source, and the means of registering low-energy conversion electrons are described. 相似文献
917.
P. V. Enkovich V. V. Brazhkin S. G. Lyapin A. P. Novikov H. Kanda S. M. Stishov 《Journal of Experimental and Theoretical Physics》2016,123(3):443-451
The Raman scattering by isotopically pure 12C and 13C diamond single crystals and by isotopically mixed 12.5C diamond single crystals is studied at a high accuracy. The studies are performed over a wide pressure range up to 73 GPa using helium as a hydrostatic pressure-transferring medium. It is found that the quantum effects, which determine the difference between the ratio of the Raman scattering frequencies in the 12C and 13C diamonds and the classical ratio (1.0408), increase to 30 GPa and then decrease. Thus, inversion in the sign of the quantum contribution to the physical properties of diamond during compression is detected. Our data suggest that the maximum possible difference between the bulk moduli of the 12C and 13C diamonds is 0.15%. The investigation of the isotopically mixed 12.5C diamond shows that the effective mass, which determines the Raman frequency, decreases during compression from 12.38 au at normal pressure to 12.33 au at 73 GPa. 相似文献
918.
Let G be a graph with n(G) vertices and m(G) be its matching number.The nullity of G,denoted by η(G),is the multiplicity of the eigenvalue zero of adjacency matrix of G.It is well known that if G is a tree,then η(G) = n(G)-2m(G).Guo et al.[Jiming GUO,Weigen YAN,Yeongnan YEH.On the nullity and the matching number of unicyclic graphs.Linear Alg.Appl.,2009,431:1293 1301]proved that if G is a unicyclic graph,then η(G)equals n(G)-2m(G)-1,n(G)-2m(G),or n(G)-2m(G) +2.In this paper,we prove that if G is a bicyclic graph,then η(G) equals n(G)-2m(G),n(G)-2m(G)±1,n(G)-2m(G)±2or n(G)-2m(G) + 4.We also give a characterization of these six types of bicyclic graphs corresponding to each nullity. 相似文献
919.
A phenomenological theory for polarization flop in spiral multiferroic TbMnO<Subscript>3</Subscript>
A phenomenological Landau theory has been used to explain magnetic field-driven polarization flop in TbMnO 3. The Néel wall-like magnetic structure in spiral multiferroics induces a space-dependent internal magnetic field which exerts a torque on spins to rotate bc-spiral to ab-spiral. The external magnetic field is argued to be competing with easy axis anisotropy and the system stabilizes when anisotropy is minimum. With the help of Landau free energy with DM magnetoelectric coupling and a general ansatz for magnetization, the phenomenon of polarization flop has been explained. Relation between Tflop and critical magnetic field has been established and found to be in good agreement with the experiment. This could be an indication that anisotropy of the system is temperature- and magnetic field-dependent. 相似文献
920.