全文获取类型
收费全文 | 40871篇 |
免费 | 2288篇 |
国内免费 | 1523篇 |
专业分类
化学 | 15604篇 |
晶体学 | 360篇 |
力学 | 766篇 |
综合类 | 101篇 |
数学 | 18185篇 |
物理学 | 9666篇 |
出版年
2023年 | 406篇 |
2022年 | 370篇 |
2021年 | 359篇 |
2020年 | 631篇 |
2019年 | 1010篇 |
2018年 | 859篇 |
2017年 | 651篇 |
2016年 | 739篇 |
2015年 | 806篇 |
2014年 | 1134篇 |
2013年 | 2400篇 |
2012年 | 1309篇 |
2011年 | 2012篇 |
2010年 | 1424篇 |
2009年 | 1984篇 |
2008年 | 2223篇 |
2007年 | 2233篇 |
2006年 | 1918篇 |
2005年 | 1388篇 |
2004年 | 1656篇 |
2003年 | 1762篇 |
2002年 | 2167篇 |
2001年 | 2067篇 |
2000年 | 1918篇 |
1999年 | 2046篇 |
1998年 | 1769篇 |
1997年 | 1121篇 |
1996年 | 706篇 |
1995年 | 570篇 |
1994年 | 487篇 |
1993年 | 304篇 |
1992年 | 308篇 |
1991年 | 176篇 |
1990年 | 274篇 |
1989年 | 246篇 |
1988年 | 188篇 |
1987年 | 173篇 |
1986年 | 199篇 |
1985年 | 316篇 |
1984年 | 255篇 |
1983年 | 128篇 |
1982年 | 259篇 |
1981年 | 330篇 |
1980年 | 308篇 |
1979年 | 162篇 |
1978年 | 248篇 |
1977年 | 182篇 |
1976年 | 156篇 |
1975年 | 104篇 |
1974年 | 94篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
We consider normal ≡ Gaussian seemingly unrelated regressions (SUR) with incomplete data (ID). Imposing a natural minimal set of conditional independence constraints, we find a restricted SUR/ID model whose likelihood function and parameter space factor into the product of the likelihood functions and the parameter spaces of standard complete data multivariate analysis of variance models. Hence, the restricted model has a unimodal likelihood and permits explicit likelihood inference. In the development of our methodology, we review and extend existing results for complete data SUR models and the multivariate ID problem. 相似文献
42.
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
43.
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
44.
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
45.
A. M. Vinogradov 《Acta Appl Math》1989,15(1-2):3-21
The main notions and results which are necessary for finding higher symmetries and conservation laws for general systems of partial differential equations are given. These constitute the starting point for the subsequent papers of this volume. Some problems are also discussed. 相似文献
46.
Summary In 1980 Dahmen-DeVore-Scherer introduced a modulus of continuity which turns out to reflect invariance properties of compound cubature rules effectively. Accordingly, sharp error bounds are derived, the existence of relevant counterexamples being a consequence of a quantitative resonance principle, established previously. 相似文献
47.
Yevhen Zelenyuk 《Topology and its Applications》2006,153(14):2382-2385
We introduce the notion of a partially selective ultrafilter and prove that (a) if G is an extremally disconnected topological group and p is a converging nonprincipal ultrafilter on G containing a countable discrete subset, then p is partially selective, and (b) the existence of a nonprincipal partially selective ultrafilter on a countable set implies the existence of a P-point in ω∗. Thus it is consistent with ZFC that there is no extremally disconnected topological group containing a countable discrete nonclosed subset. 相似文献
48.
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
49.
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
50.
D. De Salvador A. Coati E. Napolitani M. Berti A.V. Drigo M.S. Carroll J.C. Sturm J. Stangl G. Bauer L. Lazzarini 《Applied Physics A: Materials Science & Processing》2002,75(6):667-672
In this work we investigate the diffusion and precipitation of supersaturated substitutional carbon in 200-nm-thick SiGeC
layers buried under a silicon cap layer of 40 nm. The samples were annealed in either inert (N2) or oxidizing (O2) ambient at 850 °C for times ranging from 2 to 10 h. The silicon self-interstitial (I) flux coming from the surface under
oxidation enhances the C diffusion with respect to the N2-annealed samples. In the early stages of the oxidation process, the loss of C from the SiGeC layer by diffusion across the
layer/cap interface dominates. This phenomenon saturates after an initial period (2–4 h), which depends on the C concentration.
This saturation is due to the formation and growth of C-containing precipitates that are promoted by the I injection and act
as a sink for mobile C atoms. The influence of carbon concentration on the competition between precipitation and diffusion
is discussed.
Received: 19 October 2001 / Accepted: 19 December 2001 / Published online: 20 March 2002 / Published online: 20 March 2002 相似文献