全文获取类型
收费全文 | 13533篇 |
免费 | 1203篇 |
国内免费 | 1028篇 |
专业分类
化学 | 2232篇 |
晶体学 | 163篇 |
力学 | 920篇 |
综合类 | 269篇 |
数学 | 9689篇 |
物理学 | 2491篇 |
出版年
2024年 | 24篇 |
2023年 | 104篇 |
2022年 | 173篇 |
2021年 | 227篇 |
2020年 | 360篇 |
2019年 | 341篇 |
2018年 | 351篇 |
2017年 | 378篇 |
2016年 | 415篇 |
2015年 | 316篇 |
2014年 | 570篇 |
2013年 | 1226篇 |
2012年 | 514篇 |
2011年 | 743篇 |
2010年 | 721篇 |
2009年 | 854篇 |
2008年 | 952篇 |
2007年 | 854篇 |
2006年 | 761篇 |
2005年 | 700篇 |
2004年 | 643篇 |
2003年 | 591篇 |
2002年 | 545篇 |
2001年 | 432篇 |
2000年 | 364篇 |
1999年 | 354篇 |
1998年 | 283篇 |
1997年 | 278篇 |
1996年 | 220篇 |
1995年 | 160篇 |
1994年 | 151篇 |
1993年 | 124篇 |
1992年 | 110篇 |
1991年 | 87篇 |
1990年 | 78篇 |
1989年 | 62篇 |
1988年 | 62篇 |
1987年 | 41篇 |
1986年 | 61篇 |
1985年 | 61篇 |
1984年 | 73篇 |
1983年 | 49篇 |
1982年 | 63篇 |
1981年 | 54篇 |
1980年 | 44篇 |
1979年 | 56篇 |
1978年 | 37篇 |
1977年 | 21篇 |
1976年 | 25篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
变系数(2+1)维Broer-Kaup方程的精确解 总被引:19,自引:4,他引:15
利用齐次平衡原则,导出了变系数(2+1)维Broer-Kaup方程的B?cklund变换(BT),并由该BT,求出了(2+1)维Broer-Kaup方程的各种形式的精确解. 相似文献
52.
Influence of the Type of a Ligand on the Intensity of Luminescence of Ln3+ Ions in Aqueous Solutions
I. V. Barsukov E. N. Kabaeva V. V. Syt'ko S. D. Umreiko 《Journal of Applied Spectroscopy》2003,70(3):470-473
The luminescence characteristics of hydrated Ln3+ ions and their complexes with some acidic ligands have been investigated. The possibility of determining the stability of the complexes of lanthanides in solutions from the intensity of luminescence bands is shown. The influence of the characteristic features of the f-electron shell of Ln3+ on the formation of the spectrochemical series is discussed. 相似文献
53.
一类含有P-Laplacian算子的奇异边值问题解的确切个数 总被引:2,自引:0,他引:2
讨论了一类p-L ap lac ian算子型的奇异边值问题正解的确切个数以及解的性质. 相似文献
54.
研究了Banach空间中非线性混合型微分-积分方程初值问题u′=f(t,u,Tu,Su),u(0)=x0的整体解,完全没有要求f的任何增性,利用Mnch不动点定理和比较结果得到了初值问题整体解的存在性和唯一解,并且给出了一致收敛于唯一解的迭代序列,改进推广和统一了已有的许多结果. 相似文献
55.
研究了m-维离散Lotka-Volterra竞争系统,并获得了该系统周期解的存在性及其全局吸引性. 相似文献
56.
John A. Ekaterinaris 《国际流体数值方法杂志》2004,45(11):1187-1207
A high‐order accurate, finite‐difference method for the numerical solution of incompressible flows is presented. This method is based on the artificial compressibility formulation of the incompressible Navier–Stokes equations. Fourth‐ or sixth‐order accurate discretizations of the metric terms and the convective fluxes are obtained using compact, centred schemes. The viscous terms are also discretized using fourth‐order accurate, centred finite differences. Implicit time marching is performed for both steady‐state and time‐accurate numerical solutions. High‐order, spectral‐type, low‐pass, compact filters are used to regularize the numerical solution and remove spurious modes arising from unresolved scales, non‐linearities, and inaccuracies in the application of boundary conditions. The accuracy and efficiency of the proposed method is demonstrated for test problems. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
57.
A new approach to the robust handling of non‐linear constraints for GAs (genetic algorithms) optimization is proposed. A specific feature of the approach consists of the change in the conventional search strategy by employing search paths which pass through both feasible and infeasible points (contrary to the traditional approach where only feasible points may be included in a path). The method (driven by full Navier–Stokes computations) was applied to the problem of multiobjective optimization of aerodynamic shapes subject to various geometrical and aerodynamic constraints. The results demonstrated that the method retains high robustness of conventional GAs while keeping CFD computational volume to an acceptable level, which allowed the algorithm to be used in a demanding engineering environment. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
58.
Fukuji Higashi Kanako Sugishita 《Journal of polymer science. Part A, Polymer chemistry》2004,42(1):44-51
A two‐stage co‐oligomerization of the oligomers initially formed from an equimolar mixture of isophthalic acid (IPA) and terephthalic acid (TPA) and 2,2‐bis(4‐hydroxyphenyl)propane (BPA, 50 mol %) with bisphenols (BPs, 20 mol %) was carried out using a tosyl chloride/dimethylformamide/pyridine condensing agent. The distributions of the resulting oligomers (nx‐mers), which were quenched with methanol, were determined by a combination of gel permeation chromatography (GPC) and NMR. These distributions (presented by molar percentage) were conveniently calculated with the equation nx (mol %) = nx (% mol by GPC) × n0 (mol % by NMR)/n0 (% mol by GPC), where nx (% mol) = nx (wt % by GPC)/its molecular weight. The results showed the distributions of the preformed IPA/TPA‐BPA oligomers to be in fairly good accord with those obtained directly from GPC and to be supported by the NMR results. The calculation was applied to the co‐oligomers prepared up to a reaction of 0.7, at which there was an increase in the number of higher oligomers indivisible by GPC and the distributions could no longer be determined by molar percentage. The calculated distributions are discussed in relation to the results of copolycondensation. The sequence distributions in the resulting co‐oligomers, which were also examined by NMR, are compared with those in the copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 44–51, 2004 相似文献
59.
60.
V.B. Fainerman V.N. Kazakov S.V. Lylyk A.V. Makievski R. Miller 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):97-102
One of the essential differences in the design of bubble pressure tensiometers consists in the geometry of the measuring capillaries. To reach extremely short adsorption times of milliseconds and below, the so-called deadtime of the capillaries must be of the order of some 10 ms. In particular, for concentrated surfactant solutions, such as micellar solutions, short deadtimes are needed to minimize the initial surfactant load of the generated bubbles. A theoretical model is derived and confirmed by experiments performed for a wide range of experimental conditions, mainly in respect to variations in deadtime and bubble volume. 相似文献