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991.
Spectral projected gradient and variable metric methods for optimization with linear inequalities 总被引:2,自引:0,他引:2
Andreani Roberto; Birgin Ernesto G.; Martinez Jose Mario; Yuan Jinyun 《IMA Journal of Numerical Analysis》2005,25(2):221-252
A family of variable metric methods for convex constrained optimizationwas introduced recently by Birgin, Martínez and Raydan.One of the members of this family is the inexact spectral projectedgradient (ISPG) method for minimization with convex constraints.At each iteration of these methods a strictly convex quadraticfunction with convex constraints must be (inexactly) minimized.In the case of the ISPG method it was shown that, in some importantapplications, iterative projection methods can be used for thisminimization. In this paper the particular case in which theconvex domain is a polytope described by a finite set of linearinequalities is considered. For solving the linearly constrainedconvex quadratic subproblem a dual approach is adopted, by meansof which subproblems become (not necessarily strictly) convexquadratic minimization problems with box constraints. Thesesubproblems are solved by means of an active-set box-constraintquadratic optimizer with a proximal-point type unconstrainedalgorithm for minimization within the current faces. Convergenceresults and numerical experiments are presented. 相似文献
992.
Ernesto Schulz Lang Gelson Manzoni de Oliveira Gabriela Nanci Ledesma 《无机化学与普通化学杂志》2005,631(8):1524-1527
[PhTe]2 and [(β‐naphthyl)Te]2 react with iodine and tetraethylammonium iodide in toluene/methanol to give (Et4N)[PhTeI4] and (Et4N)[(β‐Naphthyl)TeI4]. The complexes were analysed by single crystal X‐ray diffraction affording the centrosymmetric monoclinic space group P21/c. In the novel compounds only anionic interactions of the types Te···I and I···I take place, cation‐anion effective contacts do not occur. Both anions [PhTeI4] and [(β‐naphthyl)TeI4] exhibit square pyramidal coordination at tellurium, with the iodine atoms in the basal positions and the organic groups apical. The tellurium centers achieve an octahedral coordination in the whole lattices through Te···I secondary bonds with the adjacent ionic species. Only the Te–I‐ and I–I‐secondary bonds behave as structure‐forming interactions in the self‐organization of the supramolecular anionic gatherings. New evidences show that for organyltellurates (Q)[PhTeX4] (Q = protonated amines, amides or amino acids; X = Cl, Br, I), NH···X hydrogen bondings are able to hinder the anionic halogen‐halogen secondary interactions. In case of the more frequent I···I interactions, they have been observed only in the absence of NH···I hydrogen bonds. 相似文献
993.
Let Mn be the set of n×n matrices and r a nonnegative integer with r ≤ n. It is known,from Lie groups, that the rank r idempotent matrices in Mn form an arcwise connected 2n (n-r)-dimensional analytic manifold. This paper provides an elementary proof of this result making it accessible to a larger audience. 相似文献
994.
We characterize the minimal and maximal operator ideals associated, in the sense of Defant and Floret, to a wide class of tensor norms derived from a Banach sequence space. Our results are extensions of classical ones about tensor norms of Saphar [Studia Math. 38 (1972) 71-100] and show the key role played by the structure of finite-dimensional subspaces in this kind of problems. 相似文献
995.
996.
Flow
microcalorimetry and thermokinetics of liquid mixtures 总被引:1,自引:0,他引:1
The identification of the calorimetric curves corresponding to liquid
mixtures for different injection flows, given by a flow microcalorimeter,
permits to classify in a kinetic way the studied mixtures. For this purpose,
it is determined the establishment time constant of the mixture (τmix)
that allows us to estimate the length occupied by the dissipation (through
the parameter λmix) and thus to justify the
sensitivity variation obtained in different chemical calibrations. 相似文献
997.
Ferran Gonzàlez de Rivera Dr. Inmaculada Angurell Dr. Marta D. Rossell Dr. Rolf Erni Dr. Jordi Llorca Núria J. Divins Prof. Guillermo Muller Dr. Miquel Seco Prof. Oriol Rossell 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(36):11963-11974
A facile strategy has been explored for loading noble metals onto the surface of ferrite nanoparticles with the assistance of phosphine‐functionalized linkers. Palladium loading is shown to occur with participation of both the phosphine function and the surface hydroxyl groups. Hybrid nanoparticles containing simultaneously Pd and Au (or Rh) are obtained by successive loading of metals. Similarly, ferrite nanoparticles decorated with Pd, Au, and Rh have also been formed by using the same strategy. The catalytic properties of the new nanoparticles are evidenced in processes such as reduction of 4‐nitrophenol or hydrogenation of styrene. Besides, the sequential process involving a cross‐coupling reaction followed by reduction of 1‐nitrobiphenyl has been successfully achieved by employing Pd/Au decorated nanoferrite particles. 相似文献
998.
Manuel G. Ricardo Celia G. Moya Carlos S. Prez Andrea Porzel Ludger A. Wessjohann Daniel G. Rivera 《Angewandte Chemie (International ed. in English)》2020,59(1):259-263
In contrast to the myriad of methods available to produce α‐helices and antiparallel β‐sheets in synthetic peptides, just a few are known for the construction of stable, non‐cyclic parallel β‐sheets. Herein, we report an efficient on‐resin approach for the assembly of parallel β‐sheet peptides in which the N‐alkylated turn moiety enhances the stability and gives access to a variety of functionalizations without modifying the parallel strands. The key synthetic step of this strategy is the multicomponent construction of an N‐alkylated turn using the Ugi reaction on varied isocyano‐resins. This four‐component process assembles the orthogonally protected turn fragment and incorporates handles serving for labeling/conjugation purposes or for reducing peptide aggregation. NMR and circular dichroism analyses confirm the better‐structured and more stable parallel β‐sheets in the N‐alkylated peptides compared to the non‐functionalized variants. 相似文献
999.
Ernesto Suárez Natalia Díaz Jefferson Méndez Dimas Suárez 《Journal of computational chemistry》2013,34(23):2041-2054
We present the CENCALC software that has been designed to estimate the conformational entropy of single molecules from extended Molecular Dynamics (MD) simulations in the gas‐phase or in solution. CENCALC uses both trajectory coordinates and topology information in order to characterize the conformational states of the molecule of interest by discretizing the time evolution of internal rotations. The implemented entropy methods are based on the mutual information expansion, which is built upon the converged probability density functions of the individual torsion angles, pairs of torsions, triads, and so on. Particularly, the correlation‐corrected multibody local approximation selects an optimum cutoff in order to retrieve the maximum amount of genuine correlation from a given MD trajectory. We illustrate these capabilities by carrying out conformational entropy calculations for a decapeptide molecule either in its unbound form or in complex with a metalloprotease enzyme. CENCALC is distributed under the GNU public license at http://sourceforge.net/projects/cencalc/ . 相似文献
1000.
Ruud J. B. Peters Zahira Herrera Rivera Greet van Bemmel Hans J. P. Marvin Stefan Weigel Hans Bouwmeester 《Analytical and bioanalytical chemistry》2014,406(16):3875-3885
The application of nanomaterials is leading to innovative developments in industry, agriculture, consumer products, and food and related sectors. However, due to the special properties of these materials there are concerns about their safety, especially because of our limited knowledge of human health effects and the fact that constantly new nanomaterials and applications thereof are being produced. The development of analytical techniques is a key element to understand the benefits as well as the risks of the application of such materials. In this study, a method is developed and validated for sizing and quantifying nano-silver in chicken meat using single particle inductive coupled plasma mass spectrometry (ICP-MS). Samples are processed using an enzymatic digestion followed by dilution of the digest and instrumental analysis of the diluted digest using single particle ICP-MS. Validation of the method in the concentration of 5–25 mg/kg 60-nm silver nanoparticles showed good performance with respect to trueness (98–99 % for size, 91–101 % for concentration), repeatability (<2 % for size, <11 % for concentration), and reproducibility (<6 % for size, <16 % for concentration). The response of the method is linear, and a detection limit as low as 0.1 mg/kg can be obtained. Additional experiments showed that the method is robust and that digests are stable for 3 weeks at 4 °C. Once diluted for single particle ICP-MS analysis, the stability is limited. Finally, it was shown that nano-silver in chicken meat is not stable. Silver nanoparticles dissolved and were transformed into silver sulfide. While this has implications for the form in which nano-silver will be present in real-life meat samples, the developed method will be able to determine the presence and quantity of nanoparticle silver in such samples. 相似文献