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1.
We present a stratification by “normal flatness” associated to an analytic mapping, analogous to Hironaka's classical result for analytic spaces. Our construction is based on a generic normal flatness theorem for mappings, proved using techniques concerning the variation of modules of meromorphically parametrized formal power series [1]. The existence of such a stratification was announced by Hironaka [13], but the other claims made in [13] are false. Counterexamples are also presented here. 相似文献
2.
Steven D. Bull Simon W. Epstein Nadeam Mujtaba Edward D. Savory Juan A. Tamayo 《Tetrahedron》2006,62(33):7911-7925
Enolates of (S)-N,N′-bis-(p-methoxybenzyl)-3-iso-propylpiperazine-2,5-dione exhibit high levels of enantiodiscrimination in alkylations with (RS)-1-aryl-1-bromoethanes and (RS)-2-bromoesters, affording substituted diketopiperazines containing two new stereogenic centres in high de. Deprotection and hydrolysis of the resultant substituted diketopiperazines provides a route to the asymmetric synthesis of homochiral methyl 2-amino-3-aryl-butanoates and 3-methyl-aspartates in high de and ee. 相似文献
3.
David S. McGuinness Edward L. Marshall Vernon C. Gibson Jonathan W. Steed 《Journal of polymer science. Part A, Polymer chemistry》2003,41(23):3798-3803
Hetero‐bimetallic Fe(II) alkoxide/aryloxides were evaluated as initiators for the ring‐opening polymerization of rac‐lactide. [(THF)NaFe(OtBu)3]2 ( 1 ) and [(THF)4Na2Fe(2,6‐diisopropylphenolate)4] ( 2 ) (THF = tetrahydrofuran) both polymerized lactide efficiently at room temperature, with complex 1 affording better control over the molecular weight parameters of the resultant polymer. At conversions below 70%, a linear increase in molecular weight with conversion was observed, indicative of a well‐controlled polymerization process. Complex 2 is the first example of a dianionic Fe(II) alkoxide and has been structurally characterized to reveal a distorted square planar FeO4 array in which both Na counterions bridge two aryloxide ligands and are further complexed by two THF ligands. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3798–3803, 2003 相似文献
4.
John L. Wood Johannes Schwarzenberg Edward F. Zganjar Dubravka Rupnik 《Hyperfine Interactions》1992,75(1-4):51-58
State-of-the-art spectroscopy of nuclei far from stability has achieved an extraordinary level of sophistication and detail
in the last ten years. In principle, if a state can be populated, it can be characterized by its energy, spin, parity, and
major decay paths. Sometimes its lifetime can be measured. In practice, one is confronted with enormous complexity. To convert
raw spectroscopic data into nuclear structure data involves a complex process of disentangling gamma rays and conversion electrons
into decay schemes. Specifically, coincidence techniques, especially coincidence intensities, play a crucial role in this
process. Recent examples and methods from work done at UNISOR are presented. 相似文献
5.
Butyltins were analyzed in waters from California river and lake marinas and were detected at the part per trillion (ppt) level in most locations. The tributyltin:dibutyltin (TBT/DBT) ratios in the fresh waters were similar to those in their saline counterparts indicating like rates of degradation in the two salinity regimes. 相似文献
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8.
Characterizations of real inner product spaces among a class of metric spaces have been obtained based on homogeneity of metric pythagorean orthogonality, a metrization of the concept of pythagorean orthogonality as defined in normed linear spaces. In the present paper a considerable weakening of this hypothesis is shown to characterize real inner product spaces among complete, convex, externally convex metric spaces, generalizing a result of Kapoor and Prasad [9], and providing a connection with the many characterizations of such spaces using euclidean four point properties. 相似文献
9.
10.
Utilizing forward recoil spectrometry (FRES), we have determined the segregation isotherm which describes the interfacial excess zi* of diblock copolymers of poly (d8-styrene-b-2-vinylpyridine) (dPS-PVP) at the interface between the homopolymers PS and PVP as a function of ?∞, the volume fraction of diblock copolymer remaining in the host homopolymer. All the samples were analyzed after annealing at temperatures and times sufficient to achieve equilibrium segregation. The effect of the degree of polymerization of both the diblock copolymers and the host homopolymers on the segregation isotherm is investigated. When the degree of polymerization of the homopolymer is much larger than that of the diblock copolymer, the normalized interfacial excess (zi*/Rg), where Rg is the radius of gyration of an isolated block copolymer chain, is a universal function of that portion of the block copolymer chemical potential due to chain stretching. The existence of such a universal function is predicted by theory and its form is in good agreement with self-consistent mean field calculations. Using these results, one can predict important aspects of the block copolymer segregation (e.g., the saturation interfacial excess) without recourse to the time-consuming numerical calculations. © 1994 John Wiley & Sons, Inc. 相似文献