全文获取类型
收费全文 | 299篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 143篇 |
晶体学 | 1篇 |
力学 | 8篇 |
数学 | 97篇 |
物理学 | 59篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 12篇 |
2014年 | 8篇 |
2013年 | 17篇 |
2012年 | 18篇 |
2011年 | 23篇 |
2010年 | 9篇 |
2009年 | 15篇 |
2008年 | 22篇 |
2007年 | 13篇 |
2006年 | 21篇 |
2005年 | 16篇 |
2004年 | 12篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1976年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有308条查询结果,搜索用时 250 毫秒
31.
Balance equations are derived from Enskog’s kinetic equation for a two-dimensional system of hard disks using Grad’s moment
expansion method. This set of equations constitute an extended hydrodynamics for moderately dense bi-dimensional fluids. The
set of independent hydrodynamic fields in the present formulations are: density, velocity, temperature and also—following Grad’s original idea—the symmetric and traceless pressure tensor p
ij
and the heat flux vector q
k
. An approximation scheme similar in spirit to one made by Grad in his original work is made. Once the hydrodynamics is derived
it is used to discuss the nature of a simple one-dimensional heat conduction problem. It is shown that, not too far from equilibrium,
the nonequilibrium pressure in this case only depends on the density, temperature and heat flux vector.
PACS: 51.10.+y, 05.20.Jj, 44.10.+i, 05.70.Ln 相似文献
32.
33.
Patricio Jara 《Journal of Mathematical Analysis and Applications》2008,344(2):956-968
This paper extends the Hille-Phillips functional calculus and rational approximations results due to R. Hersh, T. Kato, P. Brenner, and V. Thomée to generators of bi-continuous semigroups. The method yields error estimates for rational time-discretization schemes for such semigroups, in particular for dual semigroups, Feller semigroups such as the Ornstein-Uhlenbeck semigroup, the heat semigroup, semigroups induced by nonlinear flows, implemented semigroups, and evolution semigroups. Furthermore, the results provide error estimates for a new class of inversion formulas for the Laplace transform. 相似文献
34.
We introduce the notion ofsearchability as a property of an in place merging algorithm. We show that a pair of sorted arrays can be merged in place in linear time, so that a search can be performed in logarithmic time at any point during the merging process. We apply this method to devise an implicit data structure which can support searches inO(log2
n) time in the worst case, andO(logn) on the average, and insertions inO(logn) time, in the worst case.This research was partly supported by NSERC under grant A8237 and presented in preliminary form at the 10th International Colloquium on Automata, Languages and Programming.On leave from the University of Chile. 相似文献
35.
Learning to teach is difficult for prospective teachers because of the complex nature of the work of teaching. Practicing (Lampert in J Teach Educ 61(1–2):21–34, 2010), interacting with the practice of teaching from a first-person perspective, may give them a unique experience in learning to teach. Computer-based simulators in which the apprentice teacher can interact with virtual students may be used to create that kind of experience. In this paper, we show how to apply techniques in artificial intelligence to design an intelligent learning environment. We show how to model the apprentice’s decision making and resources that can help him or her improve the practice of teaching. 相似文献
36.
In this paper, we prove a Hadamard property and Liouville type theorems for viscosity solutions of fully nonlinear elliptic partial differential equations with a gradient term, both in the whole space and in an exterior domain. 相似文献
37.
On the Role of the Electronic Structure of the Heteronuclear Oxide Cluster [Ga2Mg2O5].+ in the Thermal Activation of Methane and Ethane: An Unusual Doping Effect 下载免费PDF全文
Dr. Jilai Li Dr. Xiao‐Nan Wu Dr. Maria Schlangen Dr. Shaodong Zhou Dr. Patricio González‐Navarrete Dr. Shiya Tang Prof. Dr. Helmut Schwarz 《Angewandte Chemie (International ed. in English)》2015,54(17):5074-5078
The reactivity of the heteronuclear oxide cluster [Ga2Mg2O5].+, bearing an unpaired electron at a bridging oxygen atom (Ob.?), towards methane and ethane has been studied using Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS). Hydrogen‐atom transfer (HAT) from both methane and ethane to the cluster ion is identified experimentally. The reaction mechanisms of these reactions are elucidated by state‐of‐the‐art quantum chemical calculations. The roles of spin density and charge distributions in HAT processes, as revealed by theory, not only deepen our mechanistic understanding of C? H bond activation but also provide important guidance for the rational design of catalysts by pointing to the particular role of doping effects. 相似文献
38.
Carmen Cortázar Manuel Elgueta Patricio Felmer 《Archive for Rational Mechanics and Analysis》1998,142(2):127-141
We study the uniqueness of radial ground states for the semilinear elliptic partial differential equation in ℝ
N
. We assume that the function f has two zeros, the origin and u
0>0. Above u
0 the function f is positive, is locally Lipschitz continuous and satisfies convexity and growth conditions of a superlinear nature. Below
u
0, f is assumed to be non-positive, non-identically zero and merely continuous. Our results are obtained through a careful analysis
of the solutions of an associated initial‐value problem, and the use of a monotone separation theorem. It is known that, for
a large class of functions f, the ground states of (*) are radially symmetric. In these cases our result implies that (*) possesses at most one ground
state.
(Accepted July 3, 1996) 相似文献
39.
Cárdenas C Tiznado W Ayers PW Fuentealba P 《The journal of physical chemistry. A》2011,115(11):2325-2331
In the course of a reaction it is the shape of the Fukui potential that guides a distant reagent toward the site where an electrophile/nucleophile is willing to accept/donate charge. In this paper we explore the mathematical characteristics of the Fukui potential and demonstrate its relationship to the hardness and the ability of an atom in a molecule to change its charge. The Fukui potential not only determines the active site for electron transfer, but it also approximates the distribution of hardness of a molecule: it is the Coulomb contribution to the frontier local hardness. The Fukui potential at the position of the nuclei is equal to the variation of the chemical potential with the nuclear charge and therefore measures the sensitivity of the system to changes in atom type. In the specific case of atoms and slightly charged ions, the Fukui potential at the nucleus measures the hardness. The strong correlation between the hardness and the Fukui potential at the nucleus suggests that the Fukui potential at the nucleus is an alternative definition for the chemical hardness. 相似文献
40.
2,9-Dimethoxymethylboldine (2), 2,9-dimethoxymethyl-3-bromoboldine (3) and 2,9-dimethoxymethyl-3-diphenylphosphinylboldine (4) have been synthesized in an effort to find compounds with potential pharmacological applications. The cytotoxic activities of the natural precursor 1 and these three derivatives have been measured as IC?? inhibitory growth. The diphenylphosphinyl derivative 4 showed a significant cytotoxic activity on two breast cancer cell lines, namely MCF-7 and MDA-MB-231, with IC?? values of 55.5 and 62.7 [μM], respectively. These results suggest that the kind of structural modifications introduced to synthesize compound 4 represent a promising way to enhance the cytotoxic activity of boldine derivatives. 相似文献