全文获取类型
收费全文 | 20786篇 |
免费 | 498篇 |
国内免费 | 553篇 |
专业分类
化学 | 2934篇 |
晶体学 | 130篇 |
力学 | 186篇 |
综合类 | 29篇 |
数学 | 16260篇 |
物理学 | 2298篇 |
出版年
2023年 | 58篇 |
2022年 | 104篇 |
2021年 | 149篇 |
2020年 | 140篇 |
2019年 | 445篇 |
2018年 | 435篇 |
2017年 | 282篇 |
2016年 | 197篇 |
2015年 | 244篇 |
2014年 | 471篇 |
2013年 | 1551篇 |
2012年 | 624篇 |
2011年 | 1252篇 |
2010年 | 1034篇 |
2009年 | 1300篇 |
2008年 | 1597篇 |
2007年 | 1653篇 |
2006年 | 1310篇 |
2005年 | 923篇 |
2004年 | 771篇 |
2003年 | 600篇 |
2002年 | 500篇 |
2001年 | 472篇 |
2000年 | 478篇 |
1999年 | 497篇 |
1998年 | 427篇 |
1997年 | 365篇 |
1996年 | 391篇 |
1995年 | 431篇 |
1994年 | 413篇 |
1993年 | 314篇 |
1992年 | 271篇 |
1991年 | 172篇 |
1990年 | 166篇 |
1989年 | 150篇 |
1988年 | 112篇 |
1987年 | 135篇 |
1986年 | 130篇 |
1985年 | 174篇 |
1984年 | 135篇 |
1983年 | 98篇 |
1982年 | 156篇 |
1981年 | 127篇 |
1980年 | 130篇 |
1979年 | 82篇 |
1978年 | 109篇 |
1977年 | 92篇 |
1976年 | 86篇 |
1975年 | 23篇 |
1974年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
The moduli space of torus sextics with the configuration of singularities {A2+A5+2E6} has two connected components. We compute the fundamental groups π1(CP2−C) for sextics C in both components and study their differences. 相似文献
22.
More than 250 rotationally resolved vibrational bands of the A2B2-X2A1 electronic transition of 15NO2 have been observed in the 14 300-18 000 cm−1 range. The bands have been recorded in a recently constructed setup designed for high resolution spectroscopy of jet cooled molecules by combining time gated fluorescence spectroscopy and molecular beam techniques. The majority of the observed bands has been rotationally assigned and can be identified as transitions starting from the vibrational ground state or from vibrationally excited (hot band) states. An exceptionally strong band is located at 14 851 cm−1 and studied in more detail as a typical benchmark transition to monitor 15NO2 in atmospheric remote sensing experiments. Standard rotational fit routines provide band origins, rotational and spin rotation constants. A subset of 177 vibronic levels of 2B2 vibronic symmetry has been analyzed in the energy range between 14 300 and 17 250 cm−1, in terms of integrated density and using Next Neighbor Distribution. It is found that the overall statistical properties and polyad structure of 15NO2 are comparable to those of 14NO2 but that the internal structures of the polyads are completely different. This is a direct consequence of the X2A1-A2B2 vibronic mixing. 相似文献
23.
Let T and S be invertible measure preserving transformations of a probability measure space (X, ℬ, μ). We prove that if the group generated by T and S is nilpotent, then exists in L
2-norm for any u, v∈L
∞(X, ℬ, μ). We also show that for A∈ℬ with μ(A)>0 one has . By the way of contrast, we bring examples showing that if measure preserving transformations T, S generate a solvable group, then (i) the above limits do not have to exist; (ii) the double recurrence property fails, that
is, for some A∈ℬ, μ(A)>0, one may have μ(A∩T
-n
A∩S
-
n
A)=0 for all n∈ℕ. Finally, we show that when T and S generate a nilpotent group of class ≤c, in L
2(X) for all u, v∈L
∞(X) if and only if T×S is ergodic on X×X and the group generated by T
-1
S, T
-2
S
2,..., T
-c
S
c
acts ergodically on X.
Oblatum 19-V-2000 & 5-VII-2001?Published online: 12 October 2001 相似文献
24.
Balázs Szendröi 《Mathematische Zeitschrift》2002,240(2):233-241
This note shows that a certain toric quotient of the quintic Calabi-Yau threefold in provides a counterexample to a recent conjecture of Cox and Katz concerning nef cones of toric hypersurfaces.
Received: 8 February 2001; in final form: 17 September 2001 / Published online: 1 February 2002 相似文献
25.
Michael Carr 《Topology and its Applications》2006,153(12):2155-2168
Given a graph Γ, we construct a simple, convex polytope, dubbed graph-associahedra, whose face poset is based on the connected subgraphs of Γ. This provides a natural generalization of the Stasheff associahedron and the Bott-Taubes cyclohedron. Moreover, we show that for any simplicial Coxeter system, the minimal blow-ups of its associated Coxeter complex has a tiling by graph-associahedra. The geometric and combinatorial properties of the complex as well as of the polyhedra are given. These spaces are natural generalizations of the Deligne-Knudsen-Mumford compactification of the real moduli space of curves. 相似文献
26.
A Volterra type integral equation in a Hilbert space with an additional linear operator L and a spectral parameter depending
on time is considered. If the parameter does not belong to the spectrum of L unconditional solvability of the considered problem
is proved. In the case where the initial value of the parameter coincides with some isolated point of the spectrum of the
operator L sufficient conditions for solvability are established. The obtained results are applied to the partial integral
equations associated with a contact problem of the theory of elasticity. 相似文献
27.
Saida Sultanic 《Integral Equations and Operator Theory》2006,55(4):573-595
The central question of this paper is the one of finding the right analogue of the Commutant Lifting Theorem for the Bergman
space La2. We also analyze the analogous problem for weighted Bergman spaces La,α2, − 1 < α < ∞. 相似文献
28.
M.F. Al-Kuhaili 《Journal of luminescence》2006,117(2):209-216
Thin films of sodium salicylate were deposited by spin coating from a solution prepared by dissolving sodium salicylate in methanol. The films were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, UV-visible spectroscopy and spectrofluorometry. The films were crystalline with a strong blue fluorescence peak at an emission wavelength of 419.3 nm. The influence of solution concentration, spin speed and annealing temperature on the fluorescence intensity was studied. Optimum results were obtained with a solution whose concentration was 2.5 M. It was found that lower spin speed resulted in higher fluorescence intensity. Moreover, the fluorescence intensity decreased as the annealing temperature was increased. The durability of the films over a period of 30 days was also investigated, and films annealed at higher temperatures were found to be less degraded with time. 相似文献
29.
Michel Hébert 《Archive for Mathematical Logic》1991,31(2):133-143
Summary We give a syntactic characterization of (finitary) theories whose categories of models are closed under the formation of connected limits (respectively the formation of pullbacks and substructures) in the category of all structures. They are also those theories whose consistent extensions by new atomic facts admit in each component an initial structure (respectively an initial term structure), and also thoseT for whichM(T) is locally finitely multi-presentable in a canonical way. We also show that these two properties of theories are nonuniform. 相似文献
30.