全文获取类型
收费全文 | 120088篇 |
免费 | 9384篇 |
国内免费 | 12787篇 |
专业分类
化学 | 70628篇 |
晶体学 | 1159篇 |
力学 | 2402篇 |
综合类 | 938篇 |
数学 | 12858篇 |
物理学 | 19960篇 |
无线电 | 34314篇 |
出版年
2024年 | 249篇 |
2023年 | 1096篇 |
2022年 | 2117篇 |
2021年 | 2337篇 |
2020年 | 2836篇 |
2019年 | 2676篇 |
2018年 | 2533篇 |
2017年 | 3746篇 |
2016年 | 3834篇 |
2015年 | 3826篇 |
2014年 | 4979篇 |
2013年 | 8318篇 |
2012年 | 8282篇 |
2011年 | 7451篇 |
2010年 | 5972篇 |
2009年 | 7524篇 |
2008年 | 7944篇 |
2007年 | 8468篇 |
2006年 | 7847篇 |
2005年 | 6677篇 |
2004年 | 6088篇 |
2003年 | 5039篇 |
2002年 | 5928篇 |
2001年 | 3631篇 |
2000年 | 3217篇 |
1999年 | 2916篇 |
1998年 | 2577篇 |
1997年 | 2046篇 |
1996年 | 1777篇 |
1995年 | 1687篇 |
1994年 | 1449篇 |
1993年 | 1159篇 |
1992年 | 1076篇 |
1991年 | 761篇 |
1990年 | 606篇 |
1989年 | 557篇 |
1988年 | 410篇 |
1987年 | 307篇 |
1986年 | 287篇 |
1985年 | 232篇 |
1984年 | 248篇 |
1983年 | 144篇 |
1982年 | 211篇 |
1981年 | 176篇 |
1980年 | 196篇 |
1979年 | 184篇 |
1978年 | 169篇 |
1977年 | 122篇 |
1976年 | 110篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
981.
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
982.
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
983.
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
984.
985.
Y. Huang D.J.H. Cockayne C. Marsh J.M. Titchmarsh A.K. Petford-Long 《Applied Surface Science》2005,252(5):1954-1958
A method using a focused ion beam (FIB) to prepare a silicon amorphous material is presented. The method involves the redeposition of sputtered material generated during the interaction of the Ga+ ion beam with a silicon substrate material. The shape and dimensions of this amorphous material are self-organized and reproducible. The stability of this amorphous material under electron irradiation was investigated in the transmission electron microscopy (TEM). Electron irradiation can induce recrystallization of the amorphous material, resulting in the lateral and vertical growth, starting at an amorphous-crystalline interface, of polysilicon containing defects. 相似文献
986.
Richard Arratia Bla Bollobs Gregory B. Sorkin 《Journal of Combinatorial Theory, Series B》2004,92(2):199-233
Motivated by circle graphs, and the enumeration of Euler circuits, we define a one-variable “interlace polynomial” for any graph. The polynomial satisfies a beautiful and unexpected reduction relation, quite different from the cut and fuse reduction characterizing the Tutte polynomial.It emerges that the interlace graph polynomial may be viewed as a special case of the Martin polynomial of an isotropic system, which underlies its connections with the circuit partition polynomial and the Kauffman brackets of a link diagram. The graph polynomial, in addition to being perhaps more broadly accessible than the Martin polynomial for isotropic systems, also has a two-variable generalization that is unknown for the Martin polynomial. We consider extremal properties of the interlace polynomial, its values for various special graphs, and evaluations which relate to basic graph properties such as the component and independence numbers. 相似文献
987.
《Magnetic resonance in chemistry : MRC》2003,41(8):626-628
15N isotopic enrichment was necessary for the unequivocal assignment of the 1H NMR lines to the protons in the NH–OH fragment of benzohydroxamic acid, BHXA, C6H5CONHOH, in dry dimethyl sulfoxide solutions. The assignment [δ(NH) = 11.21, δ(OH) = 9.01, 1J(15N,1H) = 102.2 Hz, 2J(15N,1H) <1.5 Hz], which is opposite to that used by other authors, confirms the assignment extended to BHXA by Brown and co‐workers from the spectra of acetohydroxamic acid. The enrichment allowed also assignment of the 29Si lines in the spectra of disilylated benzohydroxamic acid, (Z)‐tert‐butyldimethylsilyl N‐tert‐butyldimethylsilyloxybenzoimidate (2) and (Z)‐tert‐butyldiphenylsilyl N‐tert‐butyldiphenylsilyloxybenzoimidate (3), and confirmed structure of the monosilylated products, N‐tert‐butyldiphenylsilyloxybenzamide (4) and N‐tert‐butyldiphenylsilyloxy benzoimidic acid (5). Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
988.
Dmitry V. Moiseev Vera A. Morugova Andrey S. Shavirin Victor A. Dodonov 《Journal of organometallic chemistry》2004,689(4):731-737
Tetraphenylantimony(V) carboxylates have been used in the palladium-catalyzed C-phenylation reaction of methyl acrylate in the presence of (PhCO2)2 or t-BuOOH under mild conditions (50 °C). The peroxides promote a cascade participation of the organoantimony compound and result in the transfer of three phenyl groups. Organoantimony intermediates have been isolated from the reaction. 相似文献
989.
Ya.G. Groda P. Argyrakis G.S. Bokun V.S. Vikhrenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):527-535
The selfconsistent diagram approximation (SCDA) is generalized for three-dimensional lattice gases with nearest neighbor repulsive
interactions. The free energy is represented in a closed form through elementary functions. Thermodynamical (phase diagrams,
chemical potential and mean square fluctuations), structural (order parameter, distribution functions) as well as diffusional
characteristics are investigated. The calculation results are compared with the Monte Carlo simulation data to demonstrate
high precision of the SCDA in reproducing the equilibrium lattice gas characteristics. It is shown that similarly to two-dimensional
systems the specific statistical memory effects strongly influence the lattice gas diffusion in the ordered states.
Received 7 August 2002 / Received in final form 22 January 2003 Published online 24 April 2003 相似文献
990.
Richard P. Kent IV 《Geometriae Dedicata》2004,106(1):145-159
We answer a question of J. Anderson's by producing infinitely many commensurability classes of fibered hyperbolic 3-manifolds whose fundamental groups contain subgroups that are locally free and not free. These manifolds are obtained by performing 0–surgery on a collection of knots with the same properties. 相似文献