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881.
Marcos Salvai 《Monatshefte für Mathematik》2006,117(1):173-177
The Fréchet manifold
E/ ~ {\cal E}/_{\!\sim}
of all embeddings (up to orientation preserving reparametrizations) of the circle in S
3 has a canonical weak Riemannian metric. We use the characterization obtained by H. Gluck and F. Warner of the oriented great
circle fibrations of S
3 to prove that among all such fibrations π:S
3→B, the manifold B consisting of the oriented fibers is totally geodesic in
E/ ~ {\cal E}/_{\sim }
, or has minimum volume or diameter with the induced metric, exactly when π is a Hopf fibration. 相似文献
882.
Marcos R. S. Tavares G. -Q. Hai G. E. Marques 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):479
We calculate the interwire element of the impurity spectral function in coupled double quantum wires at finite temperatures. Simple anisotropy in the direction perpendicular to the wires gives rise to this element, which is responsible for tunneling-induced effects. We find interwire particle–hole (single-particle) excitations contributing to the total impurity spectral function for temperatures up to 20 K. 相似文献
883.
In this paper we study superlinear elliptic systems in Hamiltonian form. Using an Orlicz-space setting, we extend the notion of critical growth to superlinear nonlinearities which do not have a polynomial growth. Existence of nontrivial solutions is proved for superlinear nonlinearities which are subcritical in this generalized sense. 相似文献
884.
The Passerini reaction between glyoxals, isocyanides and acetic acid forms β-keto acyloxyamides, which are readily transformed in β-keto amides by reductive deacetoxylation with zinc. The versatility of this procedure, which allows introducing different groups both in position-3 and the amide nitrogen, makes it ideal for its use in diversity-oriented synthesis, in combination with subsequent complexity generation reactions. 相似文献
885.
José F. Sierra Marta de Pedro Susana de Marcos J. Galbán Juan R. Castillo C. Ubide 《Fresenius' Journal of Analytical Chemistry》1999,363(7):713-715
The application of the intrinsic fluorescence of alcohol dehydrogenase (ADH) for the simultaneous determination of propanol
and butanol was investigated by using only one kinetic run. An absolute calibration method (based on a mathematical model
derived from the enzymatic reaction) and a multivariate calibration method (partial least squares regression, PLSR) were tested
for this purpose. Both methods were applied to synthetic samples of both alcohols with good results.
Received: 17 September 1998 / Revised: 21 December 1998 / Accepted: 28 December 1998 相似文献
886.
S. Marcos M. López-Quelle R. Niembro L.N. Savushkin P. Bernardos 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):173-180
The reliability of the pseudospin symmetry (PSS) in atomic nuclei is analyzed in the framework of the relativistic Hartree
approach. We find that the nuclear surface strongly increases the effect of the pseudospin-orbit potential (PSOP), spoiling
the possibility of the exact realization of the PSS even in the limit of a vanishing PSOP. It is also shown that the PSS cannot
be explained by the fact that ΣS ≃ - Σ. New arguments to explain the PSS in finite nuclei are given. The important role the spin-orbit interaction plays in
the achievement of the PSS is also discussed.
Received: 22 July 2002 / Accepted: 18 February 2003 / Published online: 20 May 2003 相似文献
887.
Mass spectrometric behavior of anabolic androgenic steroids using gas chromatography coupled to atmospheric pressure chemical ionization source. Part I: Ionization 下载免费PDF全文
M. Raro T. Portolés J. V. Sancho E. Pitarch F. Hernández J. Marcos R. Ventura C. Gómez J. Segura O. J. Pozo 《Journal of mass spectrometry : JMS》2014,49(6):509-521
The detection of anabolic androgenic steroids (AAS) is one of the most important topics in doping control analysis. Gas chromatography coupled to (tandem) mass spectrometry (GC–MS(/MS)) with electron ionization and liquid chromatography coupled to tandem mass spectrometry have been traditionally applied for this purpose. However, both approaches still have important limitations, and, therefore, detection of all AAS is currently afforded by the combination of these strategies. Alternative ionization techniques can minimize these drawbacks and help in the implementation of a single method for the detection of AAS. In the present work, a new atmospheric pressure chemical ionization (APCI) source commercialized for gas chromatography coupled to a quadrupole time‐of‐flight analyzer has been tested to evaluate the ionization of 60 model AAS. Underivatized and trimethylsylil (TMS)‐derivatized compounds have been investigated. The use of GC–APCI–MS allowed for the ionization of all AAS assayed irrespective of their structure. The presence of water in the source as modifier promoted the formation of protonated molecules ([M+H]+), becoming the base peak of the spectrum for the majority of studied compounds. Under these conditions, [M+H]+, [M+H‐H2O]+ and [M+H‐2·H2O]+ for underivatized AAS and [M+H]+, [M+H‐TMSOH]+ and [M+H‐2·TMSOH]+ for TMS‐derivatized AAS were observed as main ions in the spectra. The formed ions preserve the intact steroid skeleton, and, therefore, they might be used as specific precursors in MS/MS‐based methods. Additionally, a relationship between the relative abundance of these ions and the AAS structure has been established. This relationship might be useful in the structural elucidation of unknown metabolites. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
888.
Paloma Souza Cabral Arion Zandoná Filho Fernando Augusto Pedersen Voll Marcos Lúcio Corazza 《Applied biochemistry and biotechnology》2014,173(6):1336-1348
This work reports experimental data, kinetic modeling, and simulations of enzyme-catalyzed hydrolysis of olive oil. This reaction was performed in batch system and an ordered-sequential Bi Bi model was used to model the kinetic mechanism. A fed-batch system was proposed and experimental data were obtained and compared to the simulated values. The kinetic model used was able to correlate the experimental data, in which a satisfactory agreement between the experimental data and modeling results was obtained under different enzyme concentration and initial free water content. Therefore, the modeling allowed a better understanding of the reaction kinetics and affords a fed-batch simulation for this system. From the results obtained, it was observed that the fed-batch approach showed to be more advantageous when compared to the conventional batch system. 相似文献
889.
The application in alkylation reactions of an acyclic chiral auxiliary is described. The synthesis is straightforward from a chiral primary amine and a double acylation. A characteristic of this auxiliary is its modular design formed by an achiral part (acyl) and a chiral component (primary amine) so it can be tuned for different reactions without difficulty. The alkylation proceeds with excellent diastereoselectivity because the conformational flexibility of the enolate is restricted by the formation of a chelate and the allylic 1,3-strain. 相似文献
890.
We show that, in local Calabi–Yau manifolds, the topological open string partition function transforms as a wavefunction under modular transformations. Our derivation is based on the topological recursion for matrix models, and it generalizes in a natural way the known result for the closed topological string sector. As an application, we derive results for vacuum expectation values of 1/2 BPS Wilson loops in ABJM theory at all genera in a strong coupling expansion, for various representations. 相似文献