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681.
682.
Relaxation spectra of polymers and phenomena of electrical and hydrophobic recovery: Interplay between bulk and surface properties of polymers 下载免费PDF全文
Roman Pogreb Ron Loew Edward Bormashenko Gene Whyman Victor Multanen Evgeny Shulzinger Amir Abramovich Daniel Rozban Alexander Shulzinger Eyal Zussman Arkadii Arinstein Gleb Vasilyev Alexander Ya. Malkin 《Journal of Polymer Science.Polymer Physics》2017,55(2):198-205
Low‐density polyethylene, polypropylene, and polycarbonate were exposed to cold air plasma treatment. The decay of electret response, hydrophobic recovery, and mechanical relaxation of polymers were studied experimentally. The three‐exponential decay kinetic model was used for the treatment of mechanical and electret responses. The characteristic time scales of mechanical and electret responses turned out to be very close. The “longest” relaxation time, extracted from the experimental study of the hydrophobic recovery, was also close to the corresponding characteristic time spans of electret and mechanical responses. The kinetics of surface processes taking place in polymers is controlled by the mobility of their functional groups, represented by the bulk relaxation spectra. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 198–205 相似文献
683.
Rationalising the Geometric Variation between the A and B Monomers in the 1.9 Å Crystal Structure of Photosystem II 下载免费PDF全文
Simon Petrie Prof. Robert Stranger Ron J. Pace 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(18):6780-6792
Density functional theory calculations are reported on a set of models of the water‐oxidising complex (WOC) of photosystem II (PSII), exploring structural features revealed in the most recent (1.9 Å resolution) X‐ray crystallographic studies of PSII. Crucially, we find that the variation in the Mn–Mn distances seen between the A and B monomers of this crystal structure can be entirely accounted for, in the low oxidation state (LOS) paradigm, by consideration of the interplay between two hydrogen‐bonding interactions involving proximate amino acid residues with the oxo bridges of the WOC, that is, His337 with O3 (which leads to a general elongation in the Mn–Mn distances between Mn1, Mn2 and Mn3) and Arg357 with O2 (which results in a specific elongation of the Mn2?Mn3 distance). 相似文献
684.
Dr. Martin R. L. Paine Dr. Berwyck L. J. Poad Gert B. Eijkel Dr. David L. Marshall Prof. Stephen J. Blanksby Prof. Dr. Ron M. A. Heeren Dr. Shane R. Ellis 《Angewandte Chemie (International ed. in English)》2018,57(33):10530-10534
Mass spectrometry imaging (MSI) enables the spatial distributions of molecules possessing different mass‐to‐charge ratios to be mapped within complex environments revealing regional changes at the molecular level. Even at high mass resolving power, however, these images often reflect the summed distribution of multiple isomeric molecules, each potentially possessing a unique distribution coinciding with distinct biological function(s) and metabolic origin. Herein, this chemical ambiguity is addressed through an innovative combination of ozone‐induced dissociation reactions with MSI, enabling the differential imaging of isomeric lipid molecules directly from biological tissues. For the first time, we demonstrate both double bond‐ and sn‐positional isomeric lipids exhibit distinct spatial locations within tissue. This MSI approach enables researchers to unravel local lipid molecular complexity based on both exact elemental composition and isomeric structure directly from tissues. 相似文献
685.
[reaction: see text] 1,2-Cyclic sulfamidates undergo regiospecific nucleophilic displacement with either methyl thioglycolate or alpha-amino esters, followed by lactamization (thermal, base-mediated, or cyanide-catalyzed), to give thiomorpholin-3-ones and piperazin-2-ones. 相似文献
686.
The reactions of (CO2)2 and (SO2)2 with Ba have been investigated using a crossed beam arrangement and the laser-induced fluorescence technique. Internal energy in the BaO product was probed in order to study differences between monomeric and dimeric reactions. The reaction cross section for the dimers of CO2 was found to be between four and eightfold larger than that of the monomers. This can be explained by the change in the reaction mechanism due to the positive electron affinity of the dimers versus the negative electron affinity of the monomers. The product BaO from the dimeric reactions is much colder rotationally than in the monomeric case. This phenomenon can be explained based on the kinematics. 相似文献
687.
Nasioudis A Heeren RM van Doormalen I de Wijs-Rot N van den Brink OF 《Journal of the American Society for Mass Spectrometry》2011,22(5):837-844
Quaternary ammonium salts (Quats) and amines are known to facilitate the MS analysis of high molar mass polyethers by forming
low charge state adduct ions. The formation, stability, and behavior upon collision-induced dissociation (CID) of adduct ions
of polyethers with a variety of Quats and amines were studied by electrospray ionization quadrupole time-of-flight, quadrupole
ion trap, and linear ion trap tandem mass spectrometry (MS/MS). The linear ion trap instrument was part of an Orbitrap hybrid
mass spectrometer that allowed accurate mass MS/MS measurements. The Quats and amines studied were of different degree of
substitution, structure, and size. The stability of the adduct ions was related to the structure of the cation, especially
the amine’s degree of substitution. CID of singly/doubly charged primary and tertiary ammonium cationized polymers resulted
in the neutral loss of the amine followed by fragmentation of the protonated product ions. The latter reveals information
about the monomer unit, polymer sequence, and endgroup structure. In addition, the detection of product ions retaining the
ammonium ion was observed. The predominant process in the CID of singly charged quaternary ammonium cationized polymers was
cation detachment, whereas their doubly charged adduct ions provided the same information as the primary and tertiary ammonium
cationized adduct ions. This study shows the potential of specific amines as tools for the structural elucidation of high
molar mass polyethers. 相似文献
688.
Koster S Duursma MC Boon JJ Heeren RM 《Journal of the American Society for Mass Spectrometry》2000,11(6):536-543
Electrospray ionization (ESI) was performed on a Fourier transform ion cyclotron resonance mass spectrometer for the endgroup
and monomer mass determination of three poly(oxyalkylene)s in the mass range of 400–8000 Da. A combined use of the multiple
charge states observed with ESI, leads to a threefold increase in accuracy of the endgroup and monomer determination. The
improvement is attributed to the increased number of datapoints used for the regression procedure, yielding more accurate
results. Endgroup masses are determined with a mass error better than 5 and 75 millimass units for the molecular weight range
of 400–4200 and 6200–8000 Da, respectively. A mass error of better than 1 millimass unit was observed for all monomer mass
determinations. With ESI, endgroup and monomer masses have been determined for poly(ethylene glycol) oligomers with a mass
higher than 8000 Da. This is almost two times higher than observed with matrix-assisted laser desorption/ ionization on the
same instrument. 相似文献
689.
d , and the testing algorithm can perform queries of the form: ``who is the ith neighbor of vertex v'. The tester should determine with high probability whether the graph is bipartite or ε-far from bipartite for any given
distance parameter ε. Distance between graphs is defined to be the fraction of entries on which the graphs differ in their
incidence-lists representation. Our testing algorithm has query complexity and running time where N is the number of graph vertices. It was shown before that queries are necessary (for constant ε), and hence the performance of our algorithm is tight (in its dependence on N), up to polylogarithmic factors.
In our analysis we use techniques that were previously applied to prove fast convergence of random walks on expander graphs.
Here we use the contrapositive statement by which slow convergence implies small cuts in the graph, and further show that
these cuts have certain additional properties. This implication is applied in showing that for any graph, the graph vertices
can be divided into disjoint subsets such that: (1) the total number of edges between the different subsets is small; and
(2) each subset itself exhibits a certain mixing property that is useful in our analysis.
Received: February 6, 1998 相似文献
690.
Energy transfer from benzophenone to biacetyl in the gas phase was studied by measuring the intensity and decay time of phosphorescence and fluorescence of both compounds as a function of pressure and composition of the mixture. We have established that benzophenone transfers energy along two parallel channels: singlet→singlet with high efficiency, kSS? 2 ×108 torr?1s?1, and triplet→triplet with lower efficiency, kTT?8 × 105 torr?1s?1. 相似文献