全文获取类型
收费全文 | 5697篇 |
免费 | 81篇 |
国内免费 | 13篇 |
专业分类
化学 | 3900篇 |
晶体学 | 27篇 |
力学 | 150篇 |
数学 | 1048篇 |
物理学 | 666篇 |
出版年
2020年 | 52篇 |
2019年 | 51篇 |
2016年 | 103篇 |
2015年 | 71篇 |
2014年 | 50篇 |
2013年 | 157篇 |
2012年 | 146篇 |
2011年 | 212篇 |
2010年 | 136篇 |
2009年 | 154篇 |
2008年 | 202篇 |
2007年 | 197篇 |
2006年 | 194篇 |
2005年 | 176篇 |
2004年 | 151篇 |
2003年 | 133篇 |
2002年 | 127篇 |
2001年 | 75篇 |
2000年 | 96篇 |
1999年 | 77篇 |
1998年 | 70篇 |
1997年 | 67篇 |
1996年 | 97篇 |
1995年 | 94篇 |
1994年 | 73篇 |
1993年 | 89篇 |
1992年 | 115篇 |
1991年 | 135篇 |
1990年 | 97篇 |
1989年 | 93篇 |
1988年 | 81篇 |
1987年 | 80篇 |
1986年 | 79篇 |
1985年 | 106篇 |
1984年 | 116篇 |
1983年 | 109篇 |
1982年 | 102篇 |
1981年 | 120篇 |
1980年 | 82篇 |
1979年 | 90篇 |
1978年 | 98篇 |
1977年 | 103篇 |
1976年 | 81篇 |
1975年 | 92篇 |
1974年 | 91篇 |
1973年 | 70篇 |
1972年 | 63篇 |
1971年 | 53篇 |
1970年 | 44篇 |
1967年 | 37篇 |
排序方式: 共有5791条查询结果,搜索用时 0 毫秒
1.
2.
Helmut Schmidhammer Eva Scherb-Bukowiecki Thomas A. Mayer Peter Schnholzer 《Helvetica chimica acta》1994,77(6):1590-1594
The synthesis of benzazepine analogues of the opium alkaloid noscapine ( 1 ) is described. The benzazepines 2 and 3 were prepared starting from nornarceine ethyl ester ( 4 ; readily available from 1 ) in several steps. X-Ray analysis of compound 2 revealed that it is not a diastereosisomer mixture but a racemate of the threo-form and thus has the same configuration as 1 . 相似文献
3.
Aspects of Generic Entanglement 总被引:4,自引:4,他引:0
Patrick Hayden Debbie W. Leung Andreas Winter 《Communications in Mathematical Physics》2006,265(1):95-117
We study entanglement and other correlation properties of random states in high-dimensional bipartite systems. These correlations
are quantified by parameters that are subject to the ``concentration of measure' phenomenon, meaning that on a large-probability
set these parameters are close to their expectation. For the entropy of entanglement, this has the counterintuitive consequence
that there exist large subspaces in which all pure states are close to maximally entangled. This, in turn, implies the existence
of mixed states with entanglement of formation near that of a maximally entangled state, but with negligible quantum mutual
information and, therefore, negligible distillable entanglement, secret key, and common randomness. It also implies a very
strong locking effect for the entanglement of formation: its value can jump from maximal to near zero by tracing over a number
of qubits negligible compared to the size of the total system. Furthermore, such properties are generic. Similar phenomena
are observed for random multiparty states, leading us to speculate on the possibility that the theory of entanglement is much
simplified when restricted to asymptotically generic states. Further consequences of our results include a complete derandomization
of the protocol for universal superdense coding of quantum states. 相似文献
4.
Peter Karduck Norbert Ammann Hans Günter Esser Jörg Winter 《Fresenius' Journal of Analytical Chemistry》1991,341(5-6):315-319
Summary The first wall of the fusion device TEXTOR at the Forschungszentrum Jülich has been coated in situ with an amorphous hydrogen rich carbon/boron film (a-C/B:H) which reduces plasma impurities caused by the plasma surface interaction. The results of the coating process of the 35 m2 large inner wall surface have been controlled by a recently developed modification of the quantitative electron probe microanalysis, which has been applied to 12 samples from specified positions inside the tokamak. The quantification itself is based on a Monte Carlo simulation of electron trajectories providing very accurate results for X-ray intensities emitted by elements present in the electron bombarded sample. The Monte Carlo results are used in the present work to calibrate the measured X-ray intensities emitted by boron and carbon from the a-C/B:H layers deposited on pure silicon substrates. As a result the total deposited mass of the layer per area unit as well as the composition of the layers (except hydrogen) could be determined very accurately. The relative errors were less than 7%. The limit of detectability were found to be in the range of one monolayer for boron as well as for carbon. 相似文献
5.
6.
7.
Simply generated families of trees are described by the equation T(z) = ϕ(T(z)) for their generating function. If a tree has n nodes, we say that it is increasing if each node has a label ∈ { 1,…,n}, no label occurs twice, and whenever we proceed from the root to a leaf, the labels are increasing. This leads to the concept of simple families of increasing trees. Three such families are especially important: recursive trees, heap ordered trees, and binary increasing trees. They belong to the subclass of very simple families of increasing trees, which can be characterized in 3 different ways. This paper contains results about these families as well as about polynomial families (the function ϕ(u) is just a polynomial). The random variable of interest is the level of the node (labelled) j, in random trees of size n ≥ j. For very simple families, this is independent of n, and the limiting distribution is Gaussian. For polynomial families, we can prove this as well for j,n → ∞ such that n − j is fixed. Additional results are also given. These results follow from the study of certain trivariate generating functions and Hwang's quasi power theorem. They unify and extend earlier results by Devroye, Mahmoud, and others. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2007 相似文献
8.
9.
10.
This paper presents an analytic approach to the construction cost of fringe-balanced binary search trees. In [7], Mahmoud used a bottom-up approach and an urn model of Pólya. The present method is top-down and uses differential equations and Hwang's quasi-power theorem to derive the asymptotic normality of the number of rotations needed to construct such afringe balanced search tree. We also obtain the exact expectation and variance with this method. Although Pólya's urn model is no longer needed, we also present an elegant analysis of it based on an operator calculus as in [4].This research was supported by the Austrian Research Society (FWF) under the project number P12599-MAT. 相似文献