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41.
J. J. Borras-Almenar R. Jorge S. I. Klokishner E. Coronado S. M. Ostrovskii A. V. Palii B. S. Tsukerblat 《Journal of Structural Chemistry》1996,37(5):699-706
The energy states of tetrameric iron clusters with d6-d6-d6-d5 and d5-d5-d5-d6 electronic configurations, which form the metal frameworks of the [Fe4S4]+ and [Fe4S4]3+ iron-sulfur proteins, are calculated using a general approach. It is revealed that the structural distortions of these systems
significantly affect the composition of the magnetic states. The effect of the isotropic Heisenberg exchange is considered.
Valencia University, Spain. Bordeaux University, France. Moldova State University. Institute of Chemistry, Academy of Sciences,
Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 816–825, September–October, 1996.
Translated by I. Izvekova 相似文献
42.
[reaction: see text] The title reactions, in 44 wt % ethanol-water at 25.0 degrees C, exhibit slightly curved Br?nsted-type plots (log kN versus pKa of amines) with slopes beta1 = 0.1-0.44 (at high pKa) and beta2 ca. 0.7 (at low pKa). The magnitude of some of these slopes, together with the fact that the curvature center (pKa(0) = 9.5-10.8) does not change with the electronic effects of the benzoyl substituent, suggests that these reactions are not stepwise, but concerted. 相似文献
43.
Jaime De Andres Antonio Aguilar Jorge Domenech 《Journal of polymer science. Part A, Polymer chemistry》1988,26(5):1323-1334
The kinetics of the reaction between atactic polypropylene (APP) and oxygen in bulk at temperatures ranging from 170 to 210°C and oxygen partial pressures from 160 to 760 torr have been studied by thermal differential analysis. The reaction takes place in two successive steps, both giving hydroperoxide groups as product. Partial reaction orders with respect to APP and oxygen for the first step, which corresponds to the uncatalyzed attack of a C? H tertiary bond to give a hydroperoxide, are one and two, respectively. In the second step, interpreted as another attack on a tertiary C? H by oxygen, catalyzed by a neighboring hydroperoxide group, reaction orders are one and one-half for APP and oxygen, respectively. Activation parameters have been determined and a reaction sequence is proposed. Hydroperoxidated APP subsequently decomposes via a zero-order process giving methylketone groups as its main product. An interpretation of this process is also given. 相似文献
44.
Raymundo Cea-Olivares Jesús Wingartz Jorge Cárdenas Jesus Valdés-Martínez Thelma Alvarado 《Transition Metal Chemistry》1991,16(1):62-64
Summary The interaction of non-anhydrous solutions of the ligand 1,3-bis-(2-hydroxyphenyl)-1,3-propanedione (bhppH3) with hydrated rare earth chlorides resulted in the formation of anhydrous, non-solvated, complexes M(bhppH2)3 (M=Y, La, Nd, Pr, Sm or Yb). The complexes have been characterized by elemental analysis, t.g., i.r. and1H n.m.r. spectroscopy. The evidence suggests that the coordination is through the -diketone site. 相似文献
45.
46.
Jorge Bravo Jesús Castro Soledad García‐Fontn Elvira M. Lamas Pilar Rodríguez‐Seoane 《无机化学与普通化学杂志》2003,629(2):297-302
The manganese carbonyl complex [MnBr(CO)3 L ] ( 1 ), where L = Ph2POCH2CH2OPPh2, was prepared by reacting [MnBr(CO)5] with the bidentate ligand 1, 2‐Bis(diphenylphosphinite)ethane. From this compound and the appropriate phosphite, phosphinite or phosphonite ligands were synthesized the complexes [MnBr(CO)2 LL ′], where L ′ = P(OMe)3 ( 2 ) or P(OEt)3 ( 3 ) and [MnBr(CO)3 L ′2], where L ′ =PPh(OEt)2 ( 4 ) or PPh2(OEt) ( 5 ). The obtained compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR (1H, 13C and 31P) spectroscopies and X‐ray diffractometry for the complexes 1 , 4 and 5 . 相似文献
47.
Double exchange in polynuclear mixed-valence clusters. 1. General solution of the electronic problem
J. J. Borras-Almenar R. Jorge S. I. Klokishner E. Coronado S. M. Ostrovskii A. V. Palii B. S. Tsukerblat 《Journal of Structural Chemistry》1996,37(5):689-698
The problem of calculating the electronic energy spectra of mixed-valence clusters with one “extra” electron (dn-dn...dn+1) or hole (dn+1-dn+1...dn) delocalized in the paramagnetic cores of transition metals is solved. Unlike the available particular solutions, which are
restricted to small numbers of ions and electrons, the solution proposed in this work is general and is suitable for many-electron
systems of arbitrary numbers of nuclei and arbitrary symmetries. The new microscopic approach to the double exchange problem
is based on the combination of the sequential (“chain”) scheme of spin coupling and angular momentum method. In terms of this
approach, an analytical dependence of the matrix elements of the double exchange, Heisenberg exchange, and vibronic interaction
on all spin quantum numbers is obtained. The final equations contain only the 6j symbols and are free of the higher-order
nj symbols, which obstructed the solution of the double exchange problem in previous works.
Valencia University, Spain. Bordeaux University, France. Moldova State University. Institute of Chemistry, Academy of Sciences,
Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 805–815, September–October, 1996.
Translated by I. Izvekova 相似文献
48.
In this work the effect of the basis set superposition error (BSSE) is explored with the counterpoise method on the occupied and unoccupied Hartree-Fock (HF) and Kohn-Sham (KS) orbitals. Three different systems linked by hydrogen bonds, H(2)O...FH, H(2)O...H(2)O, and H(2)O...CFH(3), were studied by using the basis set families cc-pVXZ and aug-cc-pVXZ (X = D, T, Q). The basis sets were tested with the HF method and two approximations for the exchange-correlation functional of KS: a generalized gradient approximation and a hybrid approach. In addition to these methods, the second-order M?ller-Plesset perturbation theory, MP2, was considered. It was found that the presence of the "ghost" basis set affects the orbitals in two ways: (1) The occupied KS orbitals are more sensitive to the presence of this "ghost" basis set than the occupied HF orbitals. For this reason the BSSE observed in HF is less than that obtained with KS. (2) The unoccupied HF orbitals are more sensitive to the presence of the "ghost" basis set than their corresponding occupied orbitals. Because the MP2 method uses both, occupied and unoccupied HF orbitals, to compute the total energy, the contribution of the BSSE is bigger than that obtained with HF or KS methodologies. 相似文献
49.
Jorge Moreda-Pieiro Carmen Moscoso-Prez María Pieiro-Iglesias Purificacin Lpez-Mahía Soledad Muniategui-Lorenzo Esther Fernndez-Fernndez Darío Prada-Rodríguez 《Talanta》2007,71(5):1834-1841
A novel, rapid and simple method by hydride generation-electrothermal atomic absorption spectrometry (HG-ETAAS) after direct As, Bi, Sb and Sn hydrides generation from untreated filters of atmospheric particulate matter (PM10 and PM2.5) was optimised. PM10 and PM2.5 were not subjected to any pre-treatment: circular portions between 0.28 and 6.28 cm2 were directly placed into the reaction vessel of a batch mode generation system. A 28 × 3/64 Plackett–Burman design was used as a multivariate strategy for the evaluation of the effects of several variables affecting the hydride generation, trapping and atomisation efficiencies. Trapping temperature was the most statistically significant variable for As, Bi and Sn. Atomisation temperature was also statistically significant for Sb determination. Optimum values of significant variables were selected by using univariate optimisation approaches. An aqueous calibration method was used throughout. The developed method has been found to be precise with relative standard deviations of 6.2, 5.3, 9.1 and 7.5% for 11 determinations in a filter sample containing 0.7, 1.0, 1.4 and 1.7 μg l−1 for As, Bi, Sb and Sn, respectively. Results obtained by direct solid sampling-HG-ETAAS have been found statistically comparable with those obtained after conventional method based on an acid digestion followed to ICP-MS. Absolute detection limits were 37, 15, 30, and 41 ng l−1 for As, Bi, Sb and Sn, respectively. Detection limits referred to the air volume sampled (in the range of 0.020–0.050 ng m−3) were low enough for the determination of several hydride-forming elements from PM10 and PM2.5 samples collected in a non-polluted suburban area of A Coruña (NW Spain). 相似文献
50.
Antonio Fernández-Ramos Benjamin A. Ellingson Rubén Meana-Pañeda Jorge M. C. Marques Donald G. Truhlar 《Theoretical chemistry accounts》2007,118(4):813-826
This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them
to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational
symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i)
if the reaction is symmetric, (ii) if reactants and/or transition states are chiral, (iii) if the reaction has multiple conformers
for reactants and/or transition states and, (iv) if there is an internal rotation of part of the molecular system. All these
four situations are treated systematically and analyzed in detail in the present article. We also include a large number of
examples to clarify some complicated situations, and in the last section we discuss an example involving an achiral diasteroisomer. 相似文献