全文获取类型
收费全文 | 122881篇 |
免费 | 6096篇 |
国内免费 | 12379篇 |
专业分类
化学 | 76925篇 |
晶体学 | 1425篇 |
力学 | 3184篇 |
综合类 | 913篇 |
数学 | 31038篇 |
物理学 | 27871篇 |
出版年
2023年 | 796篇 |
2022年 | 2090篇 |
2021年 | 1961篇 |
2020年 | 2411篇 |
2019年 | 3035篇 |
2018年 | 2726篇 |
2017年 | 3265篇 |
2016年 | 3171篇 |
2015年 | 2720篇 |
2014年 | 4077篇 |
2013年 | 8395篇 |
2012年 | 7138篇 |
2011年 | 6632篇 |
2010年 | 5424篇 |
2009年 | 7305篇 |
2008年 | 7758篇 |
2007年 | 8035篇 |
2006年 | 7299篇 |
2005年 | 5849篇 |
2004年 | 5861篇 |
2003年 | 5108篇 |
2002年 | 6504篇 |
2001年 | 4334篇 |
2000年 | 4015篇 |
1999年 | 3945篇 |
1998年 | 3405篇 |
1997年 | 2551篇 |
1996年 | 2063篇 |
1995年 | 1871篇 |
1994年 | 1671篇 |
1993年 | 1359篇 |
1992年 | 1224篇 |
1991年 | 788篇 |
1990年 | 661篇 |
1989年 | 624篇 |
1988年 | 463篇 |
1987年 | 366篇 |
1986年 | 356篇 |
1985年 | 445篇 |
1984年 | 438篇 |
1983年 | 270篇 |
1982年 | 385篇 |
1981年 | 465篇 |
1980年 | 411篇 |
1979年 | 291篇 |
1978年 | 309篇 |
1977年 | 244篇 |
1976年 | 213篇 |
1975年 | 131篇 |
1974年 | 138篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Let
be an open set. We consider on Ω the competitors (U,K) for the reduced Mumford–Shah functional, that is to say the Mumford–Shah functional in which the
-norm of U term is removed, where K is a closed subset of Ω and U is a function on ΩK with gradient in
. The main result of this paper is the following: there exists a constant c for which, whenever (U,K) is a quasi-minimizer for the reduced Mumford–Shah functional and B(x,r) is a ball centered on K and contained in Ω with bounded radius, the
-measure of
is bounded above by crN−1 and bounded below by c−1rN−1. 相似文献
993.
Padma Gopalan Xuefa Li Mingqi Li Christopher K. Ober Chad P. Gonzales Craig J. Hawker 《Journal of polymer science. Part A, Polymer chemistry》2003,41(22):3640-3656
A modular approach has been developed for the synthesis of rod–coil block copolymers involving the initial preparation of a macroinitiator based on the rod block followed by the growth of the coil segment with living free-radical procedures. The key feature of this strategy is the utilization of an alkoxyamine group from the beginning of the synthesis, which serves as a solubilizing group and ensures that each rod block contains a single initiating fragment. Using this approach permits block copolymers based on insoluble biphenyl ester oligomers to be conveniently prepared with coil segments that range from styrenes to acrylates to 1,3-dienes. The tendency of the rod segments to crystallize is strongly dependent on the weight fraction of the rod segment and the chemical nature of the coil segment. Rod–coil molecules containing at least 25–35 wt % polystyrene or poly(n-butyl acrylate) coil segments show a two-dimensional hexagonal arrangement of rod aggregates, as characterized by transmission electron microscopy and small-angle X-ray scattering. Polyisoprene block copolymers exhibit a lamellar microstructure with short rigid domains in which the rod units lie in an interdigitated smectic C arrangement. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3640–3656, 2003 相似文献
994.
Xiaohua He Hailiang Zhang Deyue Yan Xiayu Wang 《Journal of polymer science. Part A, Polymer chemistry》2003,41(18):2854-2864
A series of side‐chain liquid‐crystalline (LC) homopolymers of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with different degrees of polymerization were synthesized by atom transfer radical polymerization (ATRP), which were prepared with a wide range of number‐average molecular weights from 5.1 × 103 to 20.6 × 103 with narrow polydispersities of around 1.17. Thermal investigation showed that the homopolymers exhibit two mesophases, a smectic phase, and a nematic phase, and the phase‐transition temperatures of the homopolymers increase clearly with increasing molecular weights. A series of novel LC coil triblock copolymers with narrow polydispersities was synthesized by ATRP, and their thermotropic phase behavior was investigated with differential scanning calorimetry and polarized optical microscopy. The LC coil triblocks were designed to have an LC conformation of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with a wide range of molecular weights from 3.5 × 103 to 1.7 × 104 and the coil conformation of poly(ethylene glycol) (PEG) (number‐average molecular weight: 6000 or 12,000) segment. Their characterization was investigated with 1H NMR, Fourier transform infrared spectra, and gel permeation chromatography. Triblock copolymers exhibited a crystalline phase, a smectic phase, and a nematic phase. The phase‐transition temperatures from the smectic to nematic phase and from the nematic to isotropic phase increased, and the crystallization of PEG depressed with increasing molecular weight of the LC block. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2854–2864, 2003 相似文献
995.
In this paper,the authors obtain the Backlund transformation on time-like surfaces with constant mean curvature in R2,1.Using this transformation,families of surfaces with constant mean curvature from known ones can be constructed. 相似文献
996.
An alternative discretization of pressure‐correction equations within pressure‐correction schemes for the solution of the incompressible Navier–Stokes equations is introduced, which improves the convergence and robustness properties of such schemes for non‐orthogonal grids. As against standard approaches, where the non‐orthogonal terms usually are just neglected, the approach allows for a simplification of the pressure‐correction equation to correspond to 5‐point or 7‐point computational molecules in two or three dimensions, respectively, but still incorporates the effects of non‐orthogonality. As a result a wide range (including rather high values) of underrelaxation factors can be used, resulting in an increased overall performance of the underlying pressure‐correction schemes. Within this context, a second issue of the paper is the investigation of the accuracy to which the pressure‐correction equation should be solved in each pressure‐correction iteration. The scheme is investigated for standard test cases and, in order to show its applicability to practical flow problems, for a more complex configuration of a micro heat exchanger. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
997.
Chau O. Shillor M. Sofonea M. 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2004,55(1):32-47
A model for the dynamic, adhesive, frictionless contact
between a viscoelastic body and a deformable foundation is
described. The adhesion process is modeled by a bonding field on
the contact surface. The contact is described by a modified normal
compliance condition. The tangential shear due to the bonding
field is included. The problem is formulated as a coupled system
of a variational equality for the displacements and a differential
equation for the bonding field. The existence of a unique weak
solution for the problem is established, together with a partial
regularity result. The existence proof proceeds by construction of
an appropriate mapping which is shown to be a contraction on a
Hilbert space. 相似文献
998.
Hang-Chin Lai 《Journal of Mathematical Analysis and Applications》2004,294(2):644-654
Consider a two-person zero-sum game constructed by a dynamic fractional form. We establish the upper value as well as the lower value of a dynamic fractional game, and prove that the dual gap is equal to zero under certain conditions. It is also established that the saddle point function exists in the fractional game system under certain conditions so that the equilibrium point exists in this game system. 相似文献
999.
We provide a proof of Connes’ formula for a representative of the Hochschild class of the Chern character for (p,∞)-summable spectral triples. Our proof is valid for all semifinite von Neumann algebras, and all integral p?1. We employ the minimum possible hypotheses on the spectral triples. 相似文献
1000.