首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   261篇
  免费   6篇
  国内免费   6篇
化学   130篇
力学   9篇
数学   68篇
物理学   66篇
  2022年   3篇
  2021年   4篇
  2020年   5篇
  2018年   4篇
  2017年   4篇
  2014年   5篇
  2013年   11篇
  2012年   5篇
  2011年   12篇
  2010年   10篇
  2009年   9篇
  2008年   14篇
  2007年   5篇
  2006年   9篇
  2005年   11篇
  2004年   8篇
  2003年   5篇
  2002年   11篇
  2001年   11篇
  2000年   5篇
  1999年   9篇
  1998年   8篇
  1997年   9篇
  1996年   5篇
  1995年   4篇
  1994年   3篇
  1993年   6篇
  1992年   7篇
  1991年   3篇
  1990年   8篇
  1989年   6篇
  1988年   3篇
  1987年   5篇
  1986年   5篇
  1985年   3篇
  1984年   4篇
  1983年   4篇
  1981年   3篇
  1976年   2篇
  1975年   3篇
  1973年   2篇
  1971年   1篇
  1970年   3篇
  1968年   1篇
  1967年   1篇
  1965年   2篇
  1963年   1篇
  1955年   1篇
  1954年   1篇
  1935年   2篇
排序方式: 共有273条查询结果,搜索用时 343 毫秒
11.
We study the large-time behaviors of solutions of viscous conservation laws whose inviscid part is a nonstrictly hyperbolic system. The initial data considered here is a perturbation of a constant state. It is shown that the solutions converge to single-mode diffusion waves in directions of strictly hyperbolic fields, and to multiple-mode diffusion waves in directions of nonstrictly hyperbolic fields. The multiple-mode diffusion waves, which are the new elements here, are the self-similar solutions of the viscous conservation laws projected to the nonstrictly hyperbolic fields, with the nonlinear fluxes replaced by their quadratic parts. The convergence rate to these diffusion waves isO(t –3/4+1/2p+) inL p , 1p, with >0 being arbitrarily small.This work was supported by the Applied Mathematical Sciences subprogram of the Office of Energy Research, U.S. Department of Energy, under Contract W-31-109-Eng-38  相似文献   
12.
A series of 4‐[2‐(alicyclic‐[1,2,4]oxadiazol‐3‐yl)phenoxy]‐butyric acids were synthesized from N‐hydroxy‐2‐isopropoxy benzamidine in 4 steps with good yields. These [1,2,4]oxadiazoles are novel platelet aggregation inhibitors preventing human platelet aggregation induced by thromboxane derivative U44,619 and adenosine diphosphate. A structure‐activity‐relationship study revealed that the potency for these 5‐oxadiazoles increases with the increase in the ring size of the alicylic rings. Derivative 8f may be useful as a template for the design of more potent anti‐platelet agents.  相似文献   
13.
In this paper, we consider a Liouville-type system with singularity in the plane. The existence and uniqueness of solutions to the Dirichlet problem are proved. In addition, the structure of solutions in terms of analogues of the so-called total curvature in geometry or total mass in physics will be offered as well.  相似文献   
14.
Through Haldane's construction, the fractional quantum Hall states on a two-sphere were shown to be the ground states of one-dimensional SU(2) spin Hamiltonians. In this Letter we generalize this construction to obtain a new class of SU(N) spin Hamiltonians. These Hamiltonians describe center-of-mass-position conserving pair hopping fermions in space dimension d>/=2.  相似文献   
15.
In this study, we reported the inhibition profiles of 4′-acylpyrrole–5-fluoroindolin-2-one 3 with a C-3′ side chain for VEGFR2, PDGFR-β, and FGFR-1 protein kinases. The pyrrole-fused cyclohexanone moiety provided 3 with the best potency to inhibit the three kinases, and the C-3′ side chains contributed to the different inhibition profiles of 3 . Compound 3b with a C-3′ 2-carboxylethyl side chain showed good potency for the three kinase (IC50: 25–260 nM), and compound 3g with a N,N-dialkyl-2-carbamoylethyl side chain was more active for VEGFR2 (IC50: 59 nM) and PDGFR-β (IC50: 16 nM) than FGFR-1 (IC50: 1.7 μM). The C-3′ 3-(dialkylamino)propyl side chain accomplished 3h – j as selective PDGFR-β inhibitors (IC50: 7.8–13 nM). Compound 3b was further investigated and found potent to inhibit VEGF- and FGF-dependent cell proliferation with moderate in vivo anticancer activity. Results from docking simulations revealed that the interactions of 3b with VEGFR2 and FGFR-1 which could account for the different inhibition profiles of 3 .  相似文献   
16.
Lim TS  Chern JL  Otsuka K 《Optics letters》2002,27(12):1037-1039
Relative intensity fluctuations in single-mode class B lasers, i.e., a laser diode (LD) and a microchip Nd YVO(4) solid-state laser (SSL), were examined. Experimental observations revealed significant difference in the characteristics of the LD and the SSL. A stochastic laser model and the Fokker-Planck equation approach were used, and reduced moment equations were developed. A close agreement was achieved between the theoretical and experimental results. As indicated by the theoretical analysis, the intrinsic parameter of the lasers; i.e., the time ratio between the lifetimes of the carrier density (population inversion) and the photons, is crucial to fluctuation dynamics.  相似文献   
17.
18.
We provide a simple explanation of complex magnetic patterns observed in ferromagnetic nanostructures. To this end we identify elementary topological defects in the field of magnetization: ordinary vortices in the bulk and vortices with half-integer winding numbers confined to the edge. Domain walls found in experiments and numerical simulations in strips and rings are composite objects containing two or more of the elementary defects.  相似文献   
19.
Chu SC  Chern JL 《Optics letters》2004,29(10):1045-1047
The dynamic signature of the subwavelength variation of a slit is shown to be determinable from far-field irradiance with a precision of better than 1 nm. One can increase the efficiency of measurement of the subwavelength's signature by adjusting the detection width over which the subwavelength variation is detected. The subwavelength variation of a rectangular aperture was also examined to show the general feasibility.  相似文献   
20.
1.5-mum emissions from Nd:YAG, Nd:YVO(4), and LiNdP(4) O>(12) microchip lasers pumped by laser diodes have been observed. These coherent emissions are attributed to the effect of high-energy modified lattice vibration owing to the existence of Nd ions as well as to stimulated intracavity Raman scattering enhanced by the microchip configuration. A four-wave mixing process involving two lasing fields and a Stokes field was identified as the generator of new adjacent 1.5-mu;m emission.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号