全文获取类型
收费全文 | 82903篇 |
免费 | 481篇 |
国内免费 | 404篇 |
专业分类
化学 | 28084篇 |
晶体学 | 816篇 |
力学 | 6825篇 |
数学 | 32492篇 |
物理学 | 15571篇 |
出版年
2021年 | 53篇 |
2020年 | 73篇 |
2019年 | 100篇 |
2018年 | 10469篇 |
2017年 | 10287篇 |
2016年 | 6147篇 |
2015年 | 935篇 |
2014年 | 387篇 |
2013年 | 513篇 |
2012年 | 4040篇 |
2011年 | 10829篇 |
2010年 | 5781篇 |
2009年 | 6180篇 |
2008年 | 6896篇 |
2007年 | 9053篇 |
2006年 | 544篇 |
2005年 | 1634篇 |
2004年 | 1816篇 |
2003年 | 2190篇 |
2002年 | 1253篇 |
2001年 | 322篇 |
2000年 | 371篇 |
1999年 | 213篇 |
1998年 | 253篇 |
1997年 | 214篇 |
1996年 | 315篇 |
1995年 | 175篇 |
1994年 | 133篇 |
1993年 | 151篇 |
1992年 | 116篇 |
1991年 | 114篇 |
1990年 | 85篇 |
1989年 | 91篇 |
1988年 | 95篇 |
1987年 | 94篇 |
1986年 | 82篇 |
1985年 | 97篇 |
1984年 | 101篇 |
1983年 | 67篇 |
1982年 | 84篇 |
1981年 | 82篇 |
1980年 | 90篇 |
1979年 | 76篇 |
1978年 | 82篇 |
1977年 | 43篇 |
1976年 | 45篇 |
1975年 | 46篇 |
1914年 | 45篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
A self-avoiding polygon (SAP) on a graph is an elementary cycle. Counting SAPs on the hypercubic lattice ℤ
d
withd≥2, is a well-known unsolved problem, which is studied both for its combinatorial and probabilistic interest and its connections
with statistical mechanics. Of course, polygons on ℤ
d
are defined up to a translation, and the relevant statistic is their perimeter.
A SAP on ℤ
d
is said to beconvex if its perimeter is “minimal”, that is, is exactly twice the sum of the side lengths of the smallest hyper-rectangle containing
it. In 1984, Delest and Viennot enumerated convex SAPs on the square lattice [6], but no result was available in a higher
dimension.
We present an elementar approach to enumerate convex SAPs in any dimension. We first obtain a new proof of Delest and Viennot's
result, which explains combinatorially the form of the generating function. We then compute the generating function for convex
SAPs on the cubic lattice. In a dimension larger than 3, the details of the calculations become very cumbersome. However,
our method suggests that the generating function for convex SAPs on ℤ
d
is always a quotient ofdifferentiably finite power series. 相似文献
142.
Christian Prins 《The Journal of the Operational Research Society》1994,45(6):611-623
Satellite communications, like batches of work in a job shop, need to be scheduled in order to use their resources as efficiently as possible. The most common satellite communications system in use today is known as Time Division Multiple Access (TDMA), in which data from earth stations is buffered before being transmitted to the appropriate receiver on a satellite. Cycles of transmission are fixed for all stations. Since the same satellite will be used for routeing data in several different ways, a schedule must be devised to use the receivers, repeaters and transmitters on board to minimize the time needed for completion of a batch of work. This paper is a survey of current scheduling algorithms used for optimizing satellite communications resources. Apart from telecommunications, the methods presented here could be applied to more general scheduling problems with renewable resources but without precedence constraints. 相似文献
143.
144.
145.
Vasily L. Morgunov 《Pramana》2007,69(6):1097-1100
A new calorimeter energy calibration method was developed for the proposed ILC detectors. The method uses the center-of-mass
energy of the accelerator as the reference. It has been shown that using the energy conservation law it is possible to make
ECAL and HCAL cross calibration to reach a good energy resolution for the simple calorimeter energy sum.
相似文献
146.
147.
Yong Nam Choi Shin Ae Kim Sung Kyu Kim Sung Baek Kim Chang-Hee Lee Pavel Mikula 《Pramana》2004,63(1):175-181
In a conventional diffractometer having single monochromator, only one position, parallel position, is used for the diffraction
experiment (i.e. detection) because the resolution property of the other one, anti-parallel position, is very poor. However,
a bent perfect crystal (BPC) monochromator at monochromatic focusing condition can provide a quite flat and equal resolution
property at both parallel and anti-parallel positions and thus one can have a chance to use both sides for the diffraction
experiment. From the data of the FWHM and the Δd/d measured on three diffraction geometries (symmetric, asymmetric compression and asymmetric expansion), we can conclude that
the simultaneous diffraction measurement in both parallel and anti-parallel positions can be achieved. 相似文献
148.
Anthony B. Evans 《Designs, Codes and Cryptography》2006,40(1):121-130
In 1779 Euler proved that for every even n there exists a latin square of order n that has no orthogonal mate, and in 1944 Mann proved that for every n of the form 4k + 1, k ≥ 1, there exists a latin square of order n that has no orthogonal mate. Except for the two smallest cases, n = 3 and n = 7, it is not known whether a latin square of order n = 4k + 3 with no orthogonal mate exists or not. We complete the determination of all n for which there exists a mate-less latin square of order n by proving that, with the exception of n = 3, for all n = 4k + 3 there exists a latin square of order n with no orthogonal mate. We will also show how the methods used in this paper can be applied more generally by deriving several
earlier non-orthogonality results. 相似文献
149.
Forecasting electricity prices in presentday competitive electricity markets is a must for both producers and consumers because both need price estimates to develop their respective market bidding strategies. This paper proposes a transfer function model to predict electricity prices based on both past electricity prices and demands, and discuss the rationale to build it. The importance of electricity demand information is assessed. Appropriate metrics to appraise prediction quality are identified and used. Realistic and extensive simulations based on data from the PJM Interconnection for year 2003 are conducted. The proposed model is compared with naïve and other techniques. 相似文献
150.
In this paper we generalize to coisotropic actions of compact Lie groups a theorem of Guillemin on deformations of Hamiltonian
structures on compact symplectic manifolds. We show how one can reconstruct from the moment polytope the symplectic form on
the manifold.
Received: 21 March 2006 相似文献