全文获取类型
收费全文 | 2640篇 |
免费 | 67篇 |
国内免费 | 22篇 |
专业分类
化学 | 1615篇 |
晶体学 | 17篇 |
力学 | 75篇 |
数学 | 399篇 |
物理学 | 623篇 |
出版年
2022年 | 18篇 |
2021年 | 36篇 |
2020年 | 30篇 |
2019年 | 23篇 |
2018年 | 30篇 |
2017年 | 29篇 |
2016年 | 34篇 |
2015年 | 43篇 |
2014年 | 58篇 |
2013年 | 146篇 |
2012年 | 116篇 |
2011年 | 149篇 |
2010年 | 76篇 |
2009年 | 55篇 |
2008年 | 124篇 |
2007年 | 140篇 |
2006年 | 111篇 |
2005年 | 110篇 |
2004年 | 109篇 |
2003年 | 102篇 |
2002年 | 88篇 |
2001年 | 52篇 |
2000年 | 49篇 |
1999年 | 28篇 |
1998年 | 21篇 |
1997年 | 35篇 |
1996年 | 50篇 |
1995年 | 45篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 48篇 |
1991年 | 36篇 |
1990年 | 26篇 |
1989年 | 22篇 |
1988年 | 31篇 |
1987年 | 24篇 |
1985年 | 34篇 |
1984年 | 32篇 |
1983年 | 21篇 |
1982年 | 28篇 |
1981年 | 27篇 |
1980年 | 39篇 |
1979年 | 31篇 |
1978年 | 35篇 |
1977年 | 27篇 |
1976年 | 36篇 |
1975年 | 32篇 |
1974年 | 24篇 |
1973年 | 35篇 |
1972年 | 19篇 |
排序方式: 共有2729条查询结果,搜索用时 171 毫秒
1.
2.
3.
A two-dimensional framework (G,p) is
a graph G = (V,E) together with a map p: V → ℝ2. We view (G,p) as a straight line realization of G in ℝ2. Two realizations of G are equivalent if the corresponding edges in the two frameworks have the same length.
A pair of vertices {u,v} is globally linked in G if %and for all equivalent frameworks (G,q), the distance between the points
corresponding to u and v is the same
in all pairs of equivalent generic realizations of G. The graph G is globally rigid
if all of its pairs of vertices are globally linked. We extend the characterization of globally rigid graphs given by the
first two authors [13] by characterizing globally linked pairs in M-connected graphs, an important family of rigid graphs.
As a byproduct we simplify the proof of a result of Connelly [6] which is a key step in the characterization of globally rigid
graphs. We also determine the number of distinct realizations of an M-connected graph, each of which is equivalent to a given
generic realization. Bounds on this number for minimally rigid graphs were obtained by Borcea and Streinu in [3]. 相似文献
4.
C. Uranga C. Connell G.M. Borstad L.R. Zink M. Jackson 《Applied physics. B, Lasers and optics》2007,88(4):503-505
A three-laser heterodyne system was used to measure the frequencies of twelve previously observed far-infrared laser emissions
from the partially deuterated methanol isotopologues 13CD3OH and CHD2OH. Two laser emissions, a 53.773 μm line from 13CD3OH and a 74.939 μm line from CHD2OH, have also been discovered and frequency measured. The CO2 pump laser offset frequency was measured with respect to its center frequency for twenty-four FIR laser emissions from CH3OH, 13CD3OH and CHD2OH.
PACS 07.57.Hm; 42.55.Lt; 42.62.Eh 相似文献
5.
6.
7.
Let G = (V,E) be a graph or digraph and r : V → Z+. An r‐detachment of G is a graph H obtained by ‘splitting’ each vertex ν ∈ V into r(ν) vertices. The vertices ν1,…,νr(ν) obtained by splitting ν are called the pieces of ν in H. Every edge uν ∈ E corresponds to an edge of H connecting some piece of u to some piece of ν. Crispin Nash‐Williams 9 gave necessary and sufficient conditions for a graph to have a k‐edge‐connected r‐detachment. He also solved the version where the degrees of all the pieces are specified. In this paper, we solve the same problems for directed graphs. We also give a simple and self‐contained new proof for the undirected result. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 67–77, 2003 相似文献
8.
9.
S. David Morley Raymond J. Abraham Ian S. Haworth David E. Jackson Martin R. Saunders Jeremy G. Vinter 《Journal of computer-aided molecular design》1991,5(5):475-496
Summary Four modifications to the COSMIC molecular mechanics force field are described, which greatly increase both its versatility and the accuracy of calculated conformational energies. The Hill non-bonded van der Waals potential function has been replaced by a two-parameter Morse curve and a new H-H potential, similar to that in MM3, incorporated. Hydrocarbon energies in particular are much improved.A simple iterative Hückel pi-electron molecular orbital calculation allows modelling of conjugated systems. Calculated bond lengths and rotational barriers for a series of conjugated hydrocarbons and nitrogen heterocycles are shown to be as accurate as those determined by the MM2 SCF method.Explicit hydrogen-bonding potentials for H-bond acceptor-donor atom pairs have been included to give better hydrogen bond energies and lengths. The van der Waals radii of protonic hydrogens are reduced to 0.5 Å and the energy well depth is increased to 1.0 kcal mol-1.Two new general atom types, N+
sp
2
and O-
sp
3
, have been introduced which allow a wide variety of charged conjugated systems to be studied. A minimum of parameterisation is required, as the new types are easily included in the Hückel scheme which automatically adjusts bond and torsional parameters according to the defined bond-order relationships. 相似文献
10.
Ge segregation during the growth of Si1 − xGex alloys (x = 5, 10, 20, and 40%) was studied using X-ray photoelectron spectroscopy. The alloys were grown in thicknesses up to 20.0 nm at 500°C to measure quantitatively the amount of segregated surface Ge. The length of alloy needed to reach steady-state growth edge was found to decrease with increasing alloy concentration (4.8, 2.8, 2.4, and 2.0 nm, respectively). It was found that each alloy had a complete monolayer of Ge on the surface and an increasing amount of segregated Ge in the second layer (20, 55, 80, and 95%, respectively) during steady-state growth. An increase in the temperature of alloy growth (400–750°C) resulted in an increase in the leading edge of alloy growth but did not change the amount of segregated Ge during steady-state growth. We propose that film stress is responsible for the amount of Ge segregation. 相似文献