全文获取类型
收费全文 | 174167篇 |
免费 | 1946篇 |
国内免费 | 627篇 |
专业分类
化学 | 98433篇 |
晶体学 | 2510篇 |
力学 | 6700篇 |
综合类 | 4篇 |
数学 | 18903篇 |
物理学 | 50190篇 |
出版年
2021年 | 1296篇 |
2020年 | 1508篇 |
2019年 | 1548篇 |
2018年 | 1898篇 |
2017年 | 1973篇 |
2016年 | 3106篇 |
2015年 | 2152篇 |
2014年 | 2983篇 |
2013年 | 7380篇 |
2012年 | 6166篇 |
2011年 | 7557篇 |
2010年 | 5092篇 |
2009年 | 4997篇 |
2008年 | 7114篇 |
2007年 | 6905篇 |
2006年 | 6847篇 |
2005年 | 6241篇 |
2004年 | 5694篇 |
2003年 | 5161篇 |
2002年 | 5015篇 |
2001年 | 5978篇 |
2000年 | 4368篇 |
1999年 | 3451篇 |
1998年 | 2480篇 |
1997年 | 2623篇 |
1996年 | 2450篇 |
1995年 | 2250篇 |
1994年 | 2290篇 |
1993年 | 2057篇 |
1992年 | 2525篇 |
1991年 | 2603篇 |
1990年 | 2403篇 |
1989年 | 2372篇 |
1988年 | 2331篇 |
1987年 | 2299篇 |
1986年 | 2150篇 |
1985年 | 2719篇 |
1984年 | 2755篇 |
1983年 | 2217篇 |
1982年 | 2247篇 |
1981年 | 2060篇 |
1980年 | 2064篇 |
1979年 | 2290篇 |
1978年 | 2393篇 |
1977年 | 2320篇 |
1976年 | 2194篇 |
1975年 | 2048篇 |
1974年 | 2036篇 |
1973年 | 2036篇 |
1972年 | 1346篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
The study of the angular distribution of slow particles during high energy hadron-nucleus interaction indicates that emission of slow particles takes place from a thermally non-equilibrated system. This evidence has come out from the presence of intermittency - a phenomenon that reveals a fractal structure and represents a self-similarity in the particle production process. Hence, this study highlights inadequacy of cascade-evaporation model and advocates the need of its refinement. 相似文献
172.
T. M. Shneidman G. G. Adamian N. V. Antonenko S. P. Ivanova R. V. Jolos W. Scheid 《Physics of Atomic Nuclei》2003,66(2):206-217
Based on the dinuclear system concept, the role of bending vibrations in creation of the angular momentum of primary fission fragments is investigated. For 252Cf spontaneous fission, the angular momenta of the fragments are calculated as a function of the neutron multiplicity and compared with available experimental data. Different cluster compositions of the 252Cf fission modes at the scission point are considered. 相似文献
173.
174.
We prove new theorems on the justification of the averaging method for multifrequency oscillation systems with pulse influence at fixed times. 相似文献
175.
176.
177.
A solution to the phase problem in optics is considered within the context of registration and analysis of two-dimensional stationary optical fields transformed by the object under study or fields forming an image. To obtain information on amplitude and phase distributions of the light field analyzed, a method of registration of two intensity distributions is used. The first distribution corresponds directly to the amplitude distribution. The other is formed for the sum of the initial field and the field shifted along a certain direction. The intensity distributions obtained allow one to calculate the two-dimensional structure of the field under study. It is noteworthy that the method requires no iteration procedures in solving the problem. This leads to speeding up of the processing and analysis of the information. Two variants of optical schemes for the analysis of light fields are considered. The first one corresponds to registration of the image of the analyzed plane and the second to registration of the spectrum of the spatial frequencies. 相似文献
178.
Design theory crosses the boundary between mathematics and statistics, and includes a wide range of disparate types of design. In this paper we present a classification scheme which aims to include as many important types as possible, based on a balance among concept, representation and use. 相似文献
179.
For any two points p and q in the Euclidean plane, define LUNpq = { v | v ∈ R2, dpv < dpq and dqv < dpq}, where duv is the Euclidean distance between two points u and v . Given a set of points V in the plane, let LUNpq(V) = V ∩ LUNpq. Toussaint defined the relative neighborhood graph of V, denoted by RNG(V) or simply RNG, to be the undirected graph with vertices V such that for each pair p,q ∈ V, (p,q) is an edge of RNG(V) if and only if LUNpq (V) = ?. The relative neighborhood graph has several applications in pattern recognition that have been studied by Toussaint. We shall generalize the idea of RNG to define the k-relative neighborhood graph of V, denoted by kRNG(V) or simply kRNG, to be the undirected graph with vertices V such that for each pair p,q ∈ V, (p,q) is an edge of kRNG(V) if and only if | LUNpq(V) | < k, for some fixed positive number k. It can be shown that the number of edges of a kRNG is less than O(kn). Also, a kRNG can be constructed in O(kn2) time. Let Ec = {epq| p ∈ V and q ∈ V}. Then Gc = (V,Ec) is a complete graph. For any subset F of Ec, define the maximum distance of F as maxepq∈Fdpq. A Euclidean bottleneck Hamiltonian cycle is a Hamiltonian cycle in graph Gc whose maximum distance is the minimum among all Hamiltonian cycles in graph Gc. We shall prove that there exists a Euclidean bottleneck Hamiltonian cycle which is a subgraph of 20RNG(V). Hence, 20RNGs are Hamiltonian. 相似文献
180.
A conjecture of Toft [17] asserts that any 4-critical graph (or equivalently, every 4-chromatic graph) contains a fully odd subdivision ofK
4. We show that if a graphG has a degree three nodev such thatG-v is 3-colourable, then eitherG is 3-colourable or it contains a fully oddK
4. This resolves Toft's conjecture in the special case where a 4-critical graph has a degree three node, which is in turn used to prove the conjecture for line-graphs. The proof is constructive and yields a polynomial algorithm which given a 3-degenerate graph either finds a 3-colouring or exhibits a subgraph that is a fully odd subdivision ofK
4. (A graph is 3-degenerate if every subgraph has some node of degree at most three.) 相似文献