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991.
Bernard Cathala Claude Picard Louis Cazaux Pierre Tisnès 《Journal of Molecular Structure》1996,385(3):353-174
Doubly-armed diazatetralactams constitute a new series of easily synthesized tetralactams. The structural study of the calcium complexes of their N,N′-dimethyl acetamido and (2-pyridylmethyl) derivatives was performed by IR, 1H, 13C NMR spectroscopies and molecular modeling. These complexes showed a C2 symmetry and a high number (8–9) of coordination around the calcium atom. 相似文献
992.
Bergeat A Calvo T Caralp F Fillion JH Dorthe G Loison JC 《Faraday discussions》2001,(119):67-77; discussion 121-43
The multichannel CH + O2 reaction was studied at room temperature, in a low-pressure fast-flow reactor. CH radical was obtained from the reaction of CHBr3 with potassium atoms. The overall rate constant was determined from the decay of CH with distance, O2 being introduced in excess. The result, after corrections for axial and radial diffusion, is k = (3.6 +/- 0.5) x 10(-11) cm3 molecule-1 s-1. The OH(A2 sigma +) chemiluminescence was observed, confirming the existence of the OH + CO channel. The vibrational population distribution of OH(A2 sigma +) is 32% in the v' = 1 level and 68% in the v' = 0 level (+/- 5%). The relative atomic concentrations were determined by resonance fluorescence in the vacuum ultraviolet. A ratio of 1.4 +/- 0.2 was found between the H atom density (H atoms being produced from the H + CO2 channel and from the HCO dissociation) and the O atom density (O + HCO). Ab initio calculations of the transition structures have been performed, associated with statistical estimations. The estimated branching ratios are: O + HCO, 20%; O + H + CO, 30%; H + CO2, 30%; and CO + OH, 20%. 相似文献
993.
Maryvonne Hervieu Francis Studer Bernard Raveau 《Journal of solid state chemistry》1977,22(3):273-289
Three perovskite-like phases of the CaNbO system have been isolated, , and Ca3Nb2O8?x. X-ray powder diffraction and electron microscopy and diffraction were used to obtain crystallographic data of these phases. The high temperature form of Ca(CaxNb1?x)O3 perovskites, where calcium ions occupy partially the octahedral sites, presents an orthorhombic symmetry and quasi-periodic twin bands like CaxNbO3 compounds. Two monoclinic forms (for and ) were found by heating Ca(CaxNb1?x)O3 compounds at lower temperature for long periods; ordering of calcium and niobium ions in octahedral sites is proposed for that structure. The Ca3Nb2O8?x compound presents a quadratic cell: ordering of the cations derived from (NH4)3FeF6 structure is proposed in agreement with the observed space group . A new multiple-phase family, with general formula CanNbnO3n+2, was obtained for n = 4.25, 4.5, and 5; electron microscopy shows intergrowth phenomena. 相似文献
994.
A system of general “open-ended” configuration-interaction (CI ) programs, specifically designed for the Harris Corporation Slash Four minicomputer, is described. These methods are general in the sense that an arbitrary list of configurations (linear combinations of Slater determinants) may be used, and open ended in that peripheral (i.e., disk) storage capacity determines the maximum size problem that can be solved. The largest variational calculations carried out to date using BERKELEY involve 7064 open-shell singlet configurations (31,898 Slater determinants). Detailed timing breakdowns are presented for four test cases, two of which involve the lowest ππ* singlet state of ethylene. The other two examples are the orthogonal or bisected singlet state of trimethylenemethane and the 8B1 state of the MnCH2 complex. In the latter case, it is found that the predicted Mn? CH2 dissociation energy is only slightly increased by electron correlation effects. 相似文献
995.
Evidence is presented suggesting that hydrogen-bonded base pairing and/or aryl stacking interactions between derivatives of guanine (9-[(4-aminobutyloxy)-methyl]guanine) and cytosine (1-([(2-benzyloxy)ethoxy]methyl)cytosine) lead to enhanced intracomplex chemical reaction between the corresponding amino and ester groups. On the basis of analysis of the kinetic data it is concluded that a chain length of four methylene groups (4-amino- butyloxy as compared to 2-aminoethoxy or 6-aminohexyloxy) on the guanine is necessary to achieve the appropriate geometry for intracomplex reaction. Support for the reaction scheme is provided by the absence of reaction between the guanine derivative and a corresponding ester derivative of thymine, not expected to associate. 相似文献
996.
André Leclaire Valérie Pralong Bernard Raveau 《Journal of solid state chemistry》2005,178(5):1406-1413
Two new Mo(V) and Mo(V)/Mo(VI) phosphates, β-Ba(MoO)2(P2O7)2 and Ba(MoO)2O(P2O7)PO4, with original tunnel structures have been synthesized. The first one crystallizes in the space group P21/n with , , , β=91.67°, and the second one in the space group Cc with , , , β=99.50°. β-Ba(MoO)2(P2O7)2 shows close relationships with the α-form, i.e., it consists of similar MoP2O11 units sharing their apices and forming [MoP2O10]∞ chains. It differs from the latter by the configuration of the chains, so that one chain is linked to four other identical chains, instead of six chains in the α-form. Like the α-form, the β-form exhibits intersecting tunnels running along [010] and [011] direction where the Ba2+ cations sit. The 3D-framework of the second phosphate Ba(MoO)2O(P2O7)PO4, is built up of MoO6 octahedra, P2O7 groups, and PO4 tetrahedra, can be described by the assemblage of zig-zag [Mo2P2O14]∞ chains through PO4 tetrahedra, forming large tunnels running along , occupied by Ba2+ cations. In this framework one observes that adjacent tunnels communicate through large six-sided windows, showing the opened character of this structure. The magnetic behaviour of these phosphates is discussed with respect to the results previously obtained by Canadell et al. [Chem. Mater. 9 (1997) 68]. 相似文献
997.
Cationic porphyrin derivatives such as meso-tetrakis(4-N-methylpyridinium)porphyrin, TMPyP, have been shown to interact with double-stranded DNA. The manganese derivative, Mn(III)-TMPyP, activated by an oxygen donor like potassium monopersulfate, provides an efficient DNA-cleaving system. Previous experimental work1 has shown that DNA cleavage by the Mn(III)-TMPyP/KHSO(5) system was due to an oxidative attack, within the minor groove of B-DNA, at the C5' or C1' carbons of deoxyribose units. The aim of this study was to use molecular modeling to elucidate the specificity of the interactions between the transient active species oxyl-Mn(IV)-TMPyP and the DNA target. Geometric parameters, charges, and force field constants consistent with the AMBER 98 force field were calculated by DFT methods. Molecular modeling (mechanics and dynamic simulations) were performed for oxyl-(hydroxo)-Mn(IV)-TMPyP bound in the minor groove of the dodecamer d(5'-TCGTCAAACCGC)-d(5'-GCGGTTTGACGA). Geometry, interactions, and binding energy of the metalloporphyrin located at the A.T triplet region of the dodecamer were analyzed. These studies show no significant structural change of the DNA structure upon ligand binding. Mobility of the metalloporphyrin in the minor groove was restrained by the formation of a hydrogen bond between the hydroxo ligand trans to the metal-oxyl and a DNA phosphate, restricting the access of the oxyl group to the (pro-S) H atom at C5'. 相似文献
998.
The combination of glass capillary gas chromatography--mass spectrometry is especially suitable for the recognition of compounds. The use of [3,4-13C]testosterone as internal standard, mass fragmentography and isotope ratio measurement have been applied to the quantitative determination of testosterone in plasma. This paper describes the method, using tert.-butyldimethylsilylmethoxime and di-heptafluorobutyrate derivatives. The calibration graph in isotopic dilution is examined. The results obtained are compared with the results obtained by radioimmunoassay. The sensitivity of the method is judged from the lower limit of detection: 4.5 pg. The precision, and inter- and intra-assay are calculated. 相似文献
999.
Claude Mathis Lydia Christmann-Lamande Bernard Francois 《Journal of polymer science. Part A, Polymer chemistry》1980,18(2):671-679
The self-deactivation of polystyryl-barium and polystyryl-strontium in tetrahydrofuran (THF) results essentially from protonation by the solvent. The deactivation constant kd of this reaction is independent of carbanion concentration, length, and functionality of chains. Relations of kd with temperature are: polystyryl-barium: kd = 6.25 × 107 exp(-18,900/RT) sec?1; polystyryl-strontium: kd = 4.1 × 106 exp(?16,000/RT) sec?1. The self-deactivation of α,ω-dicarbanionic oligostyryl-barium is a nonrandomlike reaction. Residual living oligomers are left dicarbanionic even if an important deactivation occurs. 相似文献
1000.
Ab initio SCF computations indicate that Mg2+ should bind essentially to the oxygen atoms of uracil, the remaining part of the base being rather repulsive towards such an interaction. The Coulombic component predominates in the interaction, the essential feature of which may thus be deduced from the study of the molecular electrostatic potential of uracil. These ab initio results contradict an earlier CNDO prediction that the binding of uracil and Mg2+ should occur preferentially at the C5=C6 double bond of the base. It is shown that the CNDO result is an artifact due to an exaggeration by this method of the charge transfer between the ligand and the cation. The small amount of available experimental data seem in favor of the ab initio results. 相似文献