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991.
O. B. Mokhodoeva G. V. Myasoedova I. V. Kubrakova 《Journal of Analytical Chemistry》2007,62(7):607-622
Combined methods for the determination of noble metals with the use of sorption preconcentration with complexing, anion-exchange, and other sorbents are reviewed. Characteristics of sorbents, techniques of sorption preconcentration, and techniques for the preparation of a concentrate for determination are considered. Features of instrumental methods for the determination of noble metals in the analysis of different materials are discussed. Examples of the use of sorption preconcentration in combined methods for the determination of noble metals are given from publications between 1996–2005. 相似文献
992.
L. V. Baikalova V. I. Sokol I. A. Zyryanova I. V. Fedyanin V. N. Khrustalev E. A. Zel’bst O. A. Tarasova V. S. Sergienko B. A. Trofimov 《Russian Journal of General Chemistry》2006,76(5):791-797
The crystal and molecular structures of bis(1-isopropenylimidazole)dichlorocobalt (C12H16Cl2·N4Co) [R 0.036 (R W 0.089) for 3229 unique reflections with I > 2σ(I)] and tetra(1-vinylimidazole)dichlorocobalt (C20H24Cl2N8Co) [R 0.031 (R W 0.072) for 1863 unique reflections with I > 2σ(I)] were determined. In these molecular complexes, the monodentate terminal 1-alkenylimidazole ligands coordinate to the metal via a “pyridine” nitrogen atom. In C12H16Cl2N4Co, the Co atom has a distorted tetrahedral 2N,2Cl coordination. The coordination polyhedron of cobalt in C20H24Cl2N8Co is a strongly elongated 4N,2Cl octahedron. The Co-N and Co-Cl bonds [Co-N 2.015(2) and 2.032(4) Å; Co-Cl 2.229(2) Å] in the tetrahedral complex C12H16Cl2N4Co are shorter than those in the octahedral complex C20H24Cl2N8Co [Co-N 2.134(2) and 2.157(2) Å; Co-Cl 2.518(1) Å]. In the structures of both complexes there are short contacts involving the Cl atoms. 相似文献
993.
994.
Ostanina T. N. Rudoi V. M. Yaroslavtseva O. V. Solov'ev A. S. Subbotina O. Yu. Dokashenko S. I. 《Russian Journal of Electrochemistry》2004,40(10):1019-1023
The impedance of zinc-rich polymer coatings on steel in a 3-% NaCl solution is studied. The electrochemical behavior of the electrode is satisfactorily described by an equivalent circuit that contains a constant-phase element, which reflects fractal properties of the zinc surface in the binder. From the results of calculations of the circuit elements for metal-rich electrodes with different zinc contents computed are fractions of the active area of the surface of the coating and its fractal dimensionality. 相似文献
995.
Gostev F. E. Petrukhin A. N. Titov A. A. Shienok A. I. Marevtsev V. S. Sarkisov O. M. 《Russian Chemical Bulletin》2003,52(3):557-561
Intramolecular processes in electronic-excited states of 2,4,5-triarylimidazole molecules were studied by femtosecond laser spectroscopy. Experiments were carried out with two types of compounds, namely, those experiencing intramolecular proton transfer and two model compounds in which it is impossible. Schemes of the processes studied were proposed and the characteristic rate constants were determined. The excited-state intramolecular proton transfer (ESIPT) in the molecules with planar structure of the reaction center is a very fast process (100 fs). If the reaction center has a nonplanar structure and, hence, the intramolecular hydrogen bond is weakened, the ESIPT time is determined by the time of conformational rearrangement of the molecule. 相似文献
996.
Fürstner A Ackermann L Gabor B Goddard R Lehmann CW Mynott R Stelzer F Thiel OR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(15):3236-3253
Exchange of one PCy3 unit of the classical Grubbs catalyst 1 by N-heterocyclic carbene (NHC) ligands leads to "second-generation" metathesis catalysts of superior reactivity and increased stability. Several complexes of this type have been prepared and fully characterized, six of them by X-ray crystallography. These include the unique chelate complexes 13 and 14 in which the NHC- and the Ru-CR entities are tethered to form a metallacycle. A particularly favorable design feature is that the reactivity of such catalysts can be easily adjusted by changing the electronic and steric properties of the NHC ligands. The catalytic activity also strongly depends on the solvent used; NMR investigations provide a tentative explanation of this effect. Applications of the "second-generation" catalysts to ring closing alkene metathesis and intramolecular enyne cycloisomerization reactions provide insights into their catalytic performance. From these comparative studies it is deduced that no single catalyst is optimal for different types of applications. The search for the most reactive catalyst for a specific transformation is facilitated by IR thermography allowing a rapid and semi-quantitative ranking among a given set of catalysts. 相似文献
997.
Analysis of changes in 35Cl NQR frequency of complexes MCl4.L and MCl4.2L for M = Si, Ge, Sn and Ti was performed. The population of the atomic orbitals was calculated by the quantum chemistry methods PM3 and INDO. The results provided an explanation of the changes in 35Cl NQR frequency and the asymmetry parameter upon complex formation. In the complexes of non-transition elements, a decrease in 35Cl NQR frequency is first of all related to increasing population of pz orbitals on Cl atoms. In the complexes of Ti, the increase in 35Cl NQR frequency depends on a decrease in the pπ to dπ electron density transfer. 相似文献
998.
N. A. Ustynyuk M. G. Peterleitner O. V. Gusev L. I. Denisovich 《Russian Chemical Bulletin》1993,42(10):1727-1730
The electrochemical behavior of rhodium sandwich complexes containing η4-pentamethylcyclopentadiene or tetramethylfulvene fragments has been studied by cyclic voltammetry. The complexes undergo
one-electron oxidation to give unstable 17-electron radical cations which are converted into rhodocenium salts as a result
of elimination or uptake of hydrogen or C-C bond cleavage.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1802–1805, October, 1993. 相似文献
999.
M. A. Pudovik S. A. Terent'eva I. A. Litvinov O. N. Kataeva V. A. Naumov A. N. Pudovik 《Russian Chemical Bulletin》1993,42(10):1706-1709
The reaction of 2-diethylamino-3-diethylaminomethyl-1,3,2-benzoxazaphospholine with functionally substituted alcohols and
phenols occurs with the cleavage of exocyclic P-N bond followed by N→P migration of the diethylaminomethyl group and formation
of imidophosphonate dimers. A similar reaction with polyhydroxy compounds (diethylene glycol, glycerol) results in symmetrical
and asymmetrical spirophosphoranes.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1781–1784, October, 1993. 相似文献
1000.
Aromatic bisorthoesters were found to be good polymer intermediates and could be condensed with aromatic tetramines under mild conditions, in DMSO at 100°C in a relatively short reaction time to give polybenzimidazoles. The hexapropyl orthoesters of terephthalic and isophthalic acid were the preferred aromatic orthoesters because they were relatively easily purified by vacuum distillation to polymer grade intermediates, since they are liquids. Higher orthoesters distill even under good vacuum near or above the decomposition temperature of the orthoester group. Hexaethyl orthooxalate was also used and is a very useful and stable derivative of oxalic acid, which can be used for condensation reactions. These three orthoesters were used for condensations with 3,3′,4,4′-tetraaminobiphenyl, 1,2,3,4-tetraaminobenzene, 3,3′,4,4′-tetraaminobiphenyl ether, and 3,3′,4,4′-tetraaminobenzophenone. All polybenzimidazoles were obtained in high to quantitative yields and with varying molecular weights (ηinh = 0.1?0.8 dl/g), which in some cases were in the fiber forming range. 相似文献