全文获取类型
收费全文 | 78319篇 |
免费 | 353篇 |
国内免费 | 378篇 |
专业分类
化学 | 24363篇 |
晶体学 | 792篇 |
力学 | 6736篇 |
数学 | 32066篇 |
物理学 | 15093篇 |
出版年
2019年 | 30篇 |
2018年 | 10445篇 |
2017年 | 10262篇 |
2016年 | 6077篇 |
2015年 | 854篇 |
2014年 | 305篇 |
2013年 | 332篇 |
2012年 | 3791篇 |
2011年 | 10512篇 |
2010年 | 5633篇 |
2009年 | 6044篇 |
2008年 | 6596篇 |
2007年 | 8746篇 |
2006年 | 220篇 |
2005年 | 1300篇 |
2004年 | 1525篇 |
2003年 | 1977篇 |
2002年 | 1012篇 |
2001年 | 251篇 |
2000年 | 293篇 |
1999年 | 158篇 |
1998年 | 195篇 |
1997年 | 146篇 |
1996年 | 198篇 |
1995年 | 121篇 |
1994年 | 77篇 |
1993年 | 96篇 |
1992年 | 63篇 |
1991年 | 66篇 |
1990年 | 51篇 |
1989年 | 61篇 |
1988年 | 61篇 |
1987年 | 60篇 |
1986年 | 59篇 |
1985年 | 53篇 |
1984年 | 51篇 |
1983年 | 45篇 |
1982年 | 46篇 |
1981年 | 40篇 |
1980年 | 54篇 |
1979年 | 50篇 |
1978年 | 45篇 |
1973年 | 32篇 |
1914年 | 47篇 |
1913年 | 43篇 |
1912年 | 43篇 |
1910年 | 29篇 |
1909年 | 43篇 |
1908年 | 41篇 |
1907年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
871.
Let p be a prime and let b be a positive integer. If a (v, k, λ, n) difference set D of order n = p b exists in an abelian group with cyclic Sylow p-subgroup S, then \({p\in\{2,3\}}\) and |S| = p. Furthermore, either p = 2 and v ≡ λ ≡ 2 (mod 4) or the parameters of D belong to one of four families explicitly determined in our main theorem. 相似文献
872.
Wei-Shih Du 《Journal of Global Optimization》2010,47(1):119-132
In this paper, we first establish the existence theorems of the solution of hybrid inclusion and disclusion systems, from
which we study mixed types of systems of generalized quasivariational inclusion and disclusion problems and systems of generalized
vector quasiequilibrium problems. Some applications of existence theorems to feasible points for various mathematical programs
with variational constraints or equilibrium constraints, system of vector saddle point and system of minimax theorem are also
given. 相似文献
873.
Anyue Chen Phil Pollett Junping Li Hanjun Zhang 《Methodology and Computing in Applied Probability》2010,12(3):511-531
We examine basic properties regarding uniqueness, extinction, and explosivity for the generalised Markov branching processes
with pairwise interaction. First we establish uniqueness criteria, proving that in the essentially-explosive case the process
is honest if and only if the mean death rate is greater than or equal to the mean birth rate, while in the sub-explosive case
the process is dishonest only in exceptional circumstances. Explicit expressions are then obtained for the extinction probabilities,
the mean extinction times and the conditional mean extinction times. Explosivity is also investigated and an explicit expression
for mean explosion time is established. 相似文献
874.
Denote by γ the Gauss measure on ℝ
n
and by ${\mathcal{L}}${\mathcal{L}} the Ornstein–Uhlenbeck operator. In this paper we introduce a Hardy space
\mathfrakh1g{{\mathfrak{h}}^1}{{\rm \gamma}} of Goldberg type and show that for each u in ℝ ∖ {0} and r > 0 the operator (rI+L)iu(r{\mathcal{I}}+{\mathcal{L}})^{iu} is unbounded from
\mathfrakh1g{{\mathfrak{h}}^1}{{\rm \gamma}} to L
1γ. This result is in sharp contrast both with the fact that (rI+L)iu(r{\mathcal{I}}+{\mathcal{L}})^{iu} is bounded from H
1γ to L
1γ, where H
1γ denotes the Hardy type space introduced in Mauceri and Meda (J Funct Anal 252:278–313, 2007), and with the fact that in the Euclidean case (rI-D)iu(r{\mathcal{I}}-\Delta)^{iu} is bounded from the Goldberg space
\mathfrakh1\mathbbRn{{\mathfrak{h}}^1}{{\mathbb{R}}^n} to L
1ℝ
n
. We consider also the case of Riemannian manifolds M with Riemannian measure μ. We prove that, under certain geometric assumptions on M, an operator T{\mathcal{T}}, bounded on L
2
μ, and with a kernel satisfying certain analytic assumptions, is bounded from H
1
μ to L
1
μ if and only if it is bounded from
\mathfrakh1m{{\mathfrak{h}}^1}{\mu} to L
1
μ. Here H
1
μ denotes the Hardy space introduced in Carbonaro et al. (Ann Sc Norm Super Pisa, 2009), and
\mathfrakh1m{{\mathfrak{h}}^1}{\mu} is defined in Section 4, and is equivalent to a space recently introduced by M. Taylor (J Geom Anal 19(1):137–190, 2009). The case of translation invariant operators on homogeneous trees is also considered. 相似文献
875.
Federico Poloni 《Numerical Algorithms》2010,55(1):115-139
We propose a new O(n)-space implementation of the GKO-Cauchy algorithm for the solution of linear systems where the coefficient matrix is Cauchy-like.
Moreover, this new algorithm makes a more efficient use of the processor cache memory; for matrices of size larger than n ≈ 500–1,000, it outperforms the customary GKO algorithm. We present an applicative case of Cauchy-like matrices with non-reconstructible
main diagonal. In this special instance, the O(n) space algorithms can be adapted nicely to provide an efficient implementation of basic linear algebra operations in terms
of the low displacement-rank generators. 相似文献
876.
Yong Fang 《Geometriae Dedicata》2010,145(1):139-150
Let g be a negatively curved Riemannian metric of a closed C
∞ manifold M of dimension at least three. Let L
λ be a C
∞ one-parameter convex superlinear Lagrangian on TM such that
L0(v) = \frac12 g(v, v){L_0(v)= \frac{1}{2} g(v, v)} for any v ∈ TM. We denote by jl{\varphi^\lambda} the restriction of the Euler-Lagrange flow of L
λ on the
\frac12{\frac{1}{2}} -energy level. If λ is small enough then the flow jl{\varphi^\lambda} is Anosov. In this paper we study the geometric consequences of different assumptions about the regularity of the Anosov
distributions of jl{\varphi^\lambda} . For example, in the case that the initial Riemannian metric g is real hyperbolic, we prove that for λ small, jl{\varphi^\lambda} has C
3 weak stable and weak unstable distributions if and only if jl{\varphi^\lambda} is C
∞ orbit equivalent to the geodesic flow of g. 相似文献
877.
Lin-Feng Wang 《Annals of Global Analysis and Geometry》2010,37(4):393-402
Let M be an n-dimensional complete non-compact Riemannian manifold, dμ = e
h
(x)dV(x) be the weighted measure and
\trianglem{\triangle_{\mu}} be the weighted Laplacian. In this article, we prove that when the m-dimensional Bakry–émery curvature is bounded from below by Ric
m
≥ −(m − 1)K, K ≥ 0, then the bottom of the Lm2{{\rm L}_{\mu}^2} spectrum λ1(M) is bounded by
l1(M) £ \frac(m-1)2K4,\lambda_1(M) \le \frac{(m-1)^2K}{4}, 相似文献
878.
Stewart Baldwin 《Journal of Fixed Point Theory and Applications》2010,7(1):201-222
We construct abstract Julia sets homeomorphic to Julia sets for complex polynomials of the form f
c
(z) = z
2 + c, having an associated periodic kneading sequence of the form [`(a*)]{\overline{\alpha\ast}} which is not a period n-tupling. We show that there is a single simply-defined space of “itineraries” which contains homeomorphic copies of all such
Julia sets in a natural combinatorial way, with dynamical properties which are derivable directly from the combinatorics.
This also leads to a natural definition of abstract Julia sets even for those kneading sequences which are not realized by
any polynomial f
c
, with similar dynamical properties. 相似文献
879.
880.
It is shown that a cost function subject to internal costs of adjustment induces a stochastic discount factor (pricing kernel)
that is a function of random output, input and output prices, existing capital stock, and investment. The only assumption
on firm preferences is that they are increasing in current period consumption and future stochastic consumption. This ensures
that the firm will always act to minimize current period cost of providing future consumption, and it is the first-order conditions
for this cost minimization problem that generate the stochastic discount factor, which itself can be interpreted as the marginal
variable cost of varying stochastic output. A cost-based pricing kernel is estimated using annual time-series data on macroeconomic
variables and returns data for the S&P 500 and commercial paper. 相似文献
|