全文获取类型
收费全文 | 2853篇 |
免费 | 85篇 |
国内免费 | 25篇 |
专业分类
化学 | 1852篇 |
晶体学 | 42篇 |
力学 | 52篇 |
数学 | 547篇 |
物理学 | 470篇 |
出版年
2023年 | 18篇 |
2022年 | 50篇 |
2021年 | 58篇 |
2020年 | 42篇 |
2019年 | 47篇 |
2018年 | 62篇 |
2017年 | 58篇 |
2016年 | 105篇 |
2015年 | 77篇 |
2014年 | 118篇 |
2013年 | 213篇 |
2012年 | 167篇 |
2011年 | 182篇 |
2010年 | 127篇 |
2009年 | 139篇 |
2008年 | 155篇 |
2007年 | 160篇 |
2006年 | 151篇 |
2005年 | 119篇 |
2004年 | 112篇 |
2003年 | 72篇 |
2002年 | 84篇 |
2001年 | 42篇 |
2000年 | 46篇 |
1999年 | 38篇 |
1998年 | 42篇 |
1997年 | 19篇 |
1996年 | 33篇 |
1995年 | 41篇 |
1994年 | 16篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 29篇 |
1989年 | 20篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 18篇 |
1985年 | 25篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1973年 | 9篇 |
1969年 | 5篇 |
排序方式: 共有2963条查询结果,搜索用时 15 毫秒
1.
A Continuation Method of Parameter Inversion for Non-Equilibrium Convection-Dispersion Equation 总被引:1,自引:0,他引:1 下载免费PDF全文
Based on the homotopy mapping, a globally convergent method of parameter inversion for non-equilibrium convection-dispersion equations (CDEs) is developed. Moreover, in order to further improve the computational efficiency of the algorithm, a properly smooth function, which is derived from the sigmoid function, is employed to update the homotopy parameter during iteration. Numerical results show the feature of global convergence and high performance of this method. In addition, even the measurement quantities are heavily contaminated by noises, and a good solution can be found. 相似文献
2.
Adam Kiersnowski Jochen S. Gutmann Jacek Pigłowski 《Journal of Polymer Science.Polymer Physics》2007,45(17):2350-2367
ε‐caprolactone was polymerized in the presence of neat montmorillonite or organomontmorillonites to obtain a variety of poly(ε‐caprolactone) (PCL)‐based systems loaded with 10 wt % of the silicates. The materials were thoroughly investigated by different X‐ray scattering techniques to determine factors affecting structure of the systems. For one of the nanocomposites it was found that varying the temperature in the range corresponding to crystallization of PCL causes reversible changes in the interlayer distance of the organoclay. Extensive experimental and literature studies on this phenomenon provided clues indicating that this effect might be a result of two‐dimensional ordering of PCL chains inside the galleries of the silicate. Small angle X‐ray scattering and wide angle X‐ray scattering investigation of filaments oriented above melting point of PCL revealed that polymer lamellae were oriented perpendicularly to particles of unmodified silicate, while in PCL/organoclay systems they were found parallel to clay tactoids. Calorimetric and microscopic studies shown that clay particles are effective nucleating agents. In the nanocomposites, PCL crystallized 20‐fold faster than in the neat polymer. The crystallization rate in nanocomposites was also significantly higher than in microcomposite. Further research provided an insight how the presence of the filler affects crystalline fraction and spherulitic structure of the polymer matrix in the investigated systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2350–2367, 2007 相似文献
3.
We construct polynomial orthonormal bases in various function spaces. Our bases have linear order of growth of degrees of
polynomials. We show that this order is optimal. 相似文献
4.
A proper edge colouring of a graph G is neighbour-distinguishing provided that it distinguishes adjacent vertices by sets of colours of their incident edges.
It is proved that for any planar bipartite graph G with Δ(G)≥12 there is a neighbour-distinguishing edge colouring of G using at most Δ(G)+1 colours. Colourings distinguishing pairs of vertices that satisfy other requirements are also considered. 相似文献
5.
6.
Wojciech Bocian Jarosław Jaźwínski Lech Stefaniak Graham A. Webb 《Chemistry of Heterocyclic Compounds》1995,31(9):1103-1107
1H,13C,14N and15N NMR measurements are reported for four mesoionic 1-oxa-2, 3, 4-triazoles containing exocyclic nitrogenous groups. The NMR signal assignments are discussed and compared with those previously published for some corresponding oxatriazoles. The results obtained support the proposed cyclic mesoionic structures for the compounds studied. The questions of possible charge delocalization and valence tautomerism are addressed. Compound with N– H as a exocyclic group (Fig. 1) is found to be relatively unstable, this is attributed to proton migration in the corresponding non-cyclic form of this molecule.Published in Khimiya Geterotsikiicheskikh Soedinenii, No. 9, pp. 1260–1263, September, 1995. 相似文献
7.
A paraxial ray-optics formalism proposed for designing radially symmetric variable-index lenses is extended to the case of lenses of elliptical symmetry of the index profile. 相似文献
8.
9.
It is shown how the energy-positivity criterion enables us to localize the energy in various field theories. For this purpose the role of surface integrals in a canonical formalism is investigated. The same techniques are applied to linearized gravity, where the mixed Cauchy-boundary value problem in a finite volume is analyzed. Unconstrained degrees of freedom and boundary data which have to be controlled are found. This paper is part of a program to analyze the possibility of localization of gravitational energy in complete General Relativity. 相似文献
10.
Jacek Polewczak 《Journal of statistical physics》1989,56(1-2):159-173
A global existence theorem with large initial data inL
1 is given for the modified Enskog equation in 3. The method, which is based on the existence of a Liapunov functional (analog of theH-Boltzmann theorem), utilizes a weak compactness argument inL
1 in a similar way to the DiPerna-Lions proof for the Boltzmann equation. The existence theorem is obtained under certain condition on the behavior of the geometric factorY. The condition onY amounts to the fact that theL
1 norm of the collision term grows linearly when the local density tends to infinity. 相似文献