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991.
Argelio González Rosa M. Linares Juan H. Ayala Ana M. Afonso Venerando González 《Mikrochimica acta》1995,118(3-4):153-162
The effect of cationic micelles of benzyldimethylhexadecylammonium chloride and hexadecyltrimethylammonium bromide on the fluorescence spectra of indole and its carboxylic derivatives were determined. The larger solute-micelle binding constants were provided by benzyldimethylhexadecylammonium chloride, ranging from 0.10·105 and 2.15·105
M
–1 for indole-5-carboxylic and indole-2-carboxylic acid, respectively. The determination of indole-4-carboxylic acid with a detection limit of 1.0 ng ml–1, in the presence of the 3-and 5-substituted derivatives, shows the analytical potential of the synchronous spectrofluorimetry combined with the enhancement effects caused by micellar media. 相似文献
992.
Margarita R. Marín‐Yaseli Dr. Elena González‐Toril Cristina Mompeán Dr. Marta Ruiz‐Bermejo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(36):12785-12799
The origin of life is one of the fundamental questions in science. Eschenmoser proposed the “glyoxylate scenario”, in which plausible abiotic synthesis pathways were suggested to be compatible with the constraints of prebiotic chemistry. In this proposal, the stem compound is HCN. In this work, we explore the “glyoxylate scenario” through several syntheses of HCN polymers, paying particular attention to the role of the aqueous aerosols, together with statistical methods, as a step to elucidate the synthetic problem of the origin of life. The soluble and insoluble HCN polymers synthetized were analyzed by GC‐MS. We identified, for the first time, glyoxylic acid in these polymers, together with some constituents of the reductive tricarboxylic acid cycle, amino acids and several N‐heterocycles. The findings presented herein, as the first global approach to the “glyoxylate scenario”, give full effect to this hypothesis and prove that aqueous aerosols could play an important role in this plausible scene of the origin of life. 相似文献
993.
994.
A near-Heyting algebra is a join-semilattice with a top element such that every principal upset is a Heyting algebra. We establish a one-to-one correspondence between the lattices of filters and congruences of a near-Heyting algebra. To attain this aim, we first show an embedding from the lattice of filters to the lattice of congruences of a distributive nearlattice. Then, we describe the subdirectly irreducible and simple near-Heyting algebras. Finally, we fully characterize the principal congruences of distributive nearlattices and near-Heyting algebras. We conclude that the varieties of distributive nearlattices and near-Heyting algebras have equationally definable principal congruences. 相似文献
995.
996.
Design and Synthesis of Aviram–Ratner‐Type Dyads and Rectification Studies in Langmuir–Blodgett (LB) Films 下载免费PDF全文
Dr. Govindasamy Jayamurugan Dr. Vijayendran Gowri David Hernández Prof. Dr. Santiago Martin Dr. Alejandro González‐Orive Dr. Cagatay Dengiz Dr. Oliver Dumele Prof. Dr. Francesc Pérez‐Murano Dr. Jean‐Paul Gisselbrecht Prof. Dr. Corinne Boudon Dr. W. Bernd Schweizer Dr. Benjamin Breiten Dr. Aaron D. Finke Prof. Dr. Gunnar Jeschke Dr. Bruno Bernet Prof. Dr. Laurent Ruhlmann Prof. Dr. Pilar Cea Prof. Dr. François Diederich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10539-10547
The design and synthesis of Aviram–Ratner‐type molecular rectifiers, featuring an anilino‐substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ‐spacer bicyclo[2.2.2]octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X‐ray analysis. The photophysical properties of the TTF‐BCO‐exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir–Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current–voltage (I–V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I–V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor. 相似文献
997.
998.
Edgar Ocando-mavarez Merlin Rosales Ninoska Silva 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract Addition of four equivalents of tButyldiallylphosphine to a solution of one equivalent of [(COE)2Cl]2 in CHCl3 at low temperature produced two isomers of the metallated complex 2, formed by C-H activation. 2 evolve at 40°C to 3, by a hydride transfer from iridium to the cyclooctene (COE) ligand. 相似文献
999.
Edgar Pereira Jacques A.L. da Silva 《Mathematical Methods in the Applied Sciences》2013,36(3):275-289
A nonautonomous SIRVS model with time‐dependent parameters is considered. The global dynamics is investigated, and conditions for the permanence, extinction, and disease‐free equilibrium are studied. Substitute quantities that replace the basic reproduction number are presented. Numerical simulations illustrate the dynamic behavior of the proposed model. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
1000.
Julia Ramos González 《Linear and Multilinear Algebra》2013,61(4):548-552
The aim of this note is to solve a problem proposed by J. Tate in 1968 by offering a counter-example of the linearity of the trace for the sum of two finite potent operators on an infinite-dimensional vector space. 相似文献