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Manuel Bodirsky David Evans Michael Kompatscher Michael Pinsker 《Israel Journal of Mathematics》2018,224(1):57-82
We present an example of two countable ω-categorical structures, one of which has a finite relational language, whose endomorphism monoids are isomorphic as abstract monoids, but not as topological monoids—in other words, no isomorphism between these monoids is a homeomorphism. For the same two structures, the automorphism groups and polymorphism clones are isomorphic, but not topologically isomorphic. In particular, there exists a countable ω-categorical structure in a finite relational language which can neither be reconstructed up to first-order biinterpretations from its automorphism group, nor up to existential positive bi-interpretations from its endomorphism monoid, nor up to primitive positive bi-interpretations from its polymorphism clone. 相似文献
955.
Gwyndaf Evans 《Synchrotron Radiation News》2015,28(6):31-36
It is a very exciting time in the field of macromolecular crystallography for those of us who are fortunate enough to be involved in the development of instrumentation and software methods. The driver for much of this change has been the remarkable developments in synchrotron light sources and beamline instrumentation over the last two decades. In the 1990s, the ESRF, APS, and SPring-8 set the tone for many of these developments and the 2000s capitalized on them by seeding a host of medium-energy national light sources around the world. 相似文献
956.
Kimberly Geoghegan Dr. Paul Evans Prof. Isabel Rozas Prof. Ibon Alkorta 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(42):13379-13387
Regioselectivity in the intramolecular Heck reaction of a series of N‐sulfonyl‐2,5‐dihydro‐3‐substituted pyrroles was studied. These substrates are unbiased in terms of the formed ring size of the new heterocycle. Results indicate that high levels of regioselectivity are observed under a range of conditions, and that there is an underlying propensity for carbon–carbon bond formation at the most hindered end of the alkene. For two examples (3‐Me and 3‐tBu), DFT calculations were performed and indicate that in both cases, the modelled transition state for carbopalladation is energetically lower for the experimentally preferred isomer. 相似文献
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Expanding the Chemistry of Molecular U2+ Complexes: Synthesis,Characterization, and Reactivity of the {[C5H3(SiMe3)2]3U}− Anion 下载免费PDF全文
Cory J. Windorff Dr. Matthew R. MacDonald Dr. Katie R. Meihaus Dr. Joseph W. Ziller Prof. Jeffrey R. Long Prof. William J. Evans 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(2):772-782
The synthesis of new molecular complexes of U2+ has been pursued to make comparisons in structure, physical properties, and reactivity with the first U2+ complex, [K(2.2.2‐cryptand)][Cp′3U], 1 (Cp′=C5H4SiMe3). Reduction of Cp′′3U [Cp′′=C5H3(SiMe3)2] with KC8 in the presence of 2.2.2‐cryptand or 18‐crown‐6 generates [K(2.2.2‐cryptand)][Cp′′3U], 2‐K(crypt) , or [K(18‐crown‐6)(THF)2][Cp′′3U], 2‐K(18c6) , respectively. The UV/Vis spectra of 2‐K and 1 are similar, and they are much more intense than those of U3+ analogues. Variable temperature magnetic susceptibility data for 1 and 2‐K(crypt) reveal lower room temperature χMT values relative to the experimental values for the 5f3 U3+ precursors. Stability studies monitored by UV/Vis spectroscopy show that 2‐K(crypt) and 2‐K(18c6) have t1/2 values of 20 and 15 h at room temperature, respectively, vs. 1.5 h for 1 . Complex 2‐K(18c6) reacts with H2 or PhSiH3 to form the uranium hydride, [K(18‐crown‐6)(THF)2][Cp′′3UH], 3 . Complexes 1 and 2‐K(18c6) both reduce cyclooctatetraene to form uranocene, (C8H8)2U, as well as the U3+ byproducts [K(2.2.2‐cryptand)][Cp′4U], 4 , and Cp′′3U, respectively. 相似文献
959.
Patricia A. Evans 《Journal of Discrete Algorithms》2011,9(4):335-343
This paper presents the first polynomial time algorithm for finding common RNA substructures that include pseudoknots and similar structures. While a more general problem is known to be NP-hard, this algorithm exploits special features of RNA structures to match RNA bonds correctly in polynomial time. Although the theoretical upper bound on the algorithm?s time and space usage is high, the data-driven nature of its computation enables it to avoid computing unnecessary cases, dramatically reducing the actual running time. The algorithm works well in practice, and has been tested on sample RNA structures that include pseudoknots and pseudoknot-like tertiary structures. 相似文献
960.
J.T. Evans 《Journal of the mechanics and physics of solids》1980,28(2):95-112
Experiments were performed using grain-orientated per cent silicon-iron. Plane-strain deformation can be obtained in thin plates of this material and, also, the plastic deformation that occurs can be revealed by etching. In some experiments the slot was extended while the specimen was under load and the plastic deformation was then observed. The distribution and density of the resulting slip-lines agrees qualitatively with J. R. Rice's (1968) model of the deformation at the tip of a crack growing in a continuum. In Rice's model, irreversible plastic deformation prevents complete focusing of the slip-lines at a crack tip; and in the present work an analogous effect was observed, the major difference being that in the present experiments the slip-lines are fixed by the crystal structure of the material. A qualitative explanation of the observations is given in terms of the interaction that exists between dislocations and a crack. 相似文献