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251.
Hiroshi Watanabe Tomohiro Sato Kunihiro Osaki Mutsuo Matsumoto Dobrin P. Bossev Cathy E. McNamee Masaru Nakahara 《Rheologica Acta》2000,39(2):110-121
Linear viscoelastic behavior was investigated for aqueous solutions of perfluorooctyl sulfonate (C8F17SO−
3; abbreviated as FOS) micelles having a mixture of tetraethylammonium (N+(C2H5)4; TEA) and lithium (Li+) ions as the counter-ions. The solutions had the same FOS concentration (0.1 mol l−1) and various Li+ fractions in the counter-ions, φLi = 0−0.6, and the FOS micelles in these solutions formed threads which further organized into dendritic networks. At T ≤ 15 °C,
the terminal relaxation time τ and the viscosity η, governed by thermal scission of the networks, increased with increasing
φLi up to 0.55. A further increase of φLi resulted in decreases of τ and η and in broadening of the relaxation mode distribution. These rheological changes are discussed
in relation to the role of TEA ions in thermal scission: Previous NMR studies revealed that only a fraction of TEA ions were
tightly bound to the FOS micellar surfaces and these bound ions stabilized the thread/network structures. The concentration
of non-bound TEA ions, CTEA
*, decreased and finally vanished on increasing φLi up to φLi
* ≅ 0.6, and the concentration of the bound TEA ions significantly decreased on a further increase of φLi. The non-bound TEA ions appeared to catalyze the thermal scission of the FOS threads, and the observed increases of τ and
η for φLi < 0.55 were attributed to the decrease of CTEA
*. On the other hand, the decreases of τ and η as well as the broadening of the mode distribution, found for φLi > 0.55 (where CTEA
* ≅ 0), were related to destabilization of the FOS threads/networks due to a shortage of the bound TEA ions and to the existence
of concentrated Li+ ions. Viscoelastic data of pure FOSTEA and FOSTEA/FOSLi/TEACl solutions lent support to these arguments for the role of TEA
ions in the relaxation of FOSTEA/FOSLi solutions.
Received: 12 October 1999/Accepted: 1 November 1999 相似文献
252.
253.
Tomohiro Nagasawa 《Tetrahedron letters》2010,51(5):875-877
The first synthesis of aspergillide A, a cytotoxin produced by a marine-derived fungus, has been achieved from a synthetic intermediate of aspergillide B by using a proline-mediated epimerization of a 2,6-trans-substituted tetrahydropyran-2-acetaldehyde intermediate into the corresponding cis-isomer via a retro-oxy-Michael/oxy-Michael sequence as the key transformation. 相似文献
254.
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256.
Optical coherence tomography (OCT) is a new diagnostic technology which allows visualization of a cross-sectional image of the anterior eye and the retina in vivo with a high resolution similar to a histological section by light microscopy. Although the fundus can be examined at the semihistologic level by a biomicroscope, histopathologic study has been difficult because of the rare opportunity for retinal biopsy or enucleation. OCT reveals the intraretinal structure of macular diseases on the histopathologic level. In this article, we review the research on various macular diseases using OCT at Gunma University School of Medicine. 相似文献
257.
A Structure-Preserving Numerical Method for the Fourth-Order Geometric Evolution Equations for Planar Curves 下载免费PDF全文
For fourth-order geometric evolution equations for planar curves
with the dissipation of the bending energy, including the Willmore and the
Helfrich flows, we consider a numerical approach. In this study, we construct
a structure-preserving method based on a discrete variational derivative method. Furthermore, to prevent the vertex concentration that may lead to numerical instability, we discretely introduce Deckelnick’s tangential velocity. Here,
a modification term is introduced in the process of adding tangential velocity.
This modified term enables the method to reproduce the equations’ properties
while preventing vertex concentration. Numerical experiments demonstrate
that the proposed approach captures the equations’ properties with high accuracy and avoids the concentration of vertices. 相似文献
258.
259.
Qi Wang Yaomi Itoh Tohru Tsuruoka Shintaro Ohtsuka Tomohiro Shimizu Shoso Shingubara Tsuyoshi Hasegawa Masakazu Aono 《固体物理学:研究快报》2015,9(3):166-170
ReRAMs using oxygen vacancy drift in their resistive switching are promising candidates as next generation memory devices. One remaining issue is degradation of the on/off ratio down to 102 or less with an increased number of switching cycles. Such degradation is caused by a local hard breakdown in a set process due to a very high electric field formed just before the completion of a conductive filament formation. We found that introducing an ultra‐thin SiO2 layer prevents the hard breakdown by dynamical moderation of the electric field formed in the TaOx matrix, resulting in repeated switching while retaining a higher on/off ratio of about 105. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
260.
Tomohiro Seki Taichi Ozaki Takuma Okura Kiyotaka Asakura Aya Sakon Hidehiro Uekusa Hajime Ito 《Chemical science》2015,6(4):2187-false
In this study, we report the interconvertible tetracolored solid state photoluminescence of gold(i) isocyanide complex 2 upon various external stimuli through solid state structural changes. Soaking complex 2 in acetone yields blue emission as a result of the formation of 2B. The subsequent removal of acetone yields 2G through a crystal-to-crystal phase transition, which exhibits green emission. This green-emitting solid 2G exhibits stepwise emission color changes to yellow and then to orange upon mechanical stimulation by ball-milling, which corresponds to the formation of 2Y and 2O, respectively. 2B could be recovered upon the addition of acetone to 2G, 2Y, and 2O. Thus, these four emitting solid states of 2 can be switched between repeatedly by means of acetone soaking and the application of mechanical stimulation. Importantly, single crystal and powder X-ray diffraction (PXRD) studies fully show the detailed molecular arrangements of 2B, 2G, and 2Y. This is the first mechanochromic compound to show interconvertible four color emission in the solid state. We also present the first example of using PXRD measurements and the Rietveld refinement technique for the structural analysis of a ground powder in a luminescence mechanochromism study. We obtained complete molecular-level structural information of the crystalline states of 2B, 2G, 2Y, and 2O. In comparison with a more solvophobic analogue 1, we suggest that the weak interaction of 2 with acetone in the solid state would allow a solvent inclusion/release mode, which is an important structural factor for the unprecedented multicolor mechanochromic luminescence. 相似文献