全文获取类型
收费全文 | 78163篇 |
免费 | 328篇 |
国内免费 | 379篇 |
专业分类
化学 | 24312篇 |
晶体学 | 793篇 |
力学 | 6721篇 |
数学 | 31951篇 |
物理学 | 15093篇 |
出版年
2018年 | 10434篇 |
2017年 | 10261篇 |
2016年 | 6052篇 |
2015年 | 843篇 |
2014年 | 295篇 |
2013年 | 323篇 |
2012年 | 3780篇 |
2011年 | 10492篇 |
2010年 | 5625篇 |
2009年 | 6040篇 |
2008年 | 6594篇 |
2007年 | 8767篇 |
2006年 | 219篇 |
2005年 | 1311篇 |
2004年 | 1539篇 |
2003年 | 1986篇 |
2002年 | 1036篇 |
2001年 | 245篇 |
2000年 | 296篇 |
1999年 | 157篇 |
1998年 | 195篇 |
1997年 | 151篇 |
1996年 | 195篇 |
1995年 | 120篇 |
1994年 | 78篇 |
1993年 | 98篇 |
1992年 | 58篇 |
1991年 | 67篇 |
1990年 | 57篇 |
1989年 | 64篇 |
1988年 | 65篇 |
1987年 | 59篇 |
1986年 | 60篇 |
1985年 | 52篇 |
1984年 | 51篇 |
1983年 | 40篇 |
1982年 | 45篇 |
1981年 | 42篇 |
1980年 | 47篇 |
1979年 | 51篇 |
1978年 | 43篇 |
1973年 | 27篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1910年 | 24篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32篇 |
1904年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Using variational method and lower and upper solutions, we get a generalized quasilinearization method which construct an
iterative scheme converging uniformly to a solution of a nonlinear second-order impulsive differential equations involving
the p-Laplacian, and converging quadratically when p=2. 相似文献
902.
James Mc Laughlin 《Central European Journal of Mathematics》2010,8(3):474-487
We derive several new transformations relating WP-Bailey pairs. We also consider the corresponding transformations relating
standard Bailey pairs, and as a consequence, derive some quite general expansions for products of theta functions which can
also be expressed as certain types of Lambert series. 相似文献
903.
Classification is concerned with the development of rules for the allocation of observations to groups, and is a fundamental
problem in machine learning. Much of previous work on classification models investigates two-group discrimination. Multi-category
classification is less-often considered due to the tendency of generalizations of two-group models to produce misclassification
rates that are higher than desirable. Indeed, producing “good” two-group classification rules is a challenging task for some
applications, and producing good multi-category rules is generally more difficult. Additionally, even when the “optimal” classification
rule is known, inter-group misclassification rates may be higher than tolerable for a given classification model. We investigate
properties of a mixed-integer programming based multi-category classification model that allows for the pre-specification
of limits on inter-group misclassification rates. The mechanism by which the limits are satisfied is the use of a reserved
judgment region, an artificial category into which observations are placed whose attributes do not sufficiently indicate membership
to any particular group. The method is shown to be a consistent estimator of a classification rule with misclassification
limits, and performance on simulated and real-world data is demonstrated. 相似文献
904.
Tamás Erdélyi 《Journal d'Analyse Mathématique》2010,112(1):369-381
A function Q is called absolutely monotone of order k on an interval I if Q(x) ≥ 0, Q′(x) ≥ 0, …, Q(k)(x) ≥ 0, for all x ε I. An essentially sharp (up to a multiplicative absolute constant) Markov inequality for absolutely monotone polynomials of
order k in L
p
[−1, 1], p > 0, is established. One may guess that the right Markov factor is cn
2/k, and this indeed turns out to be the case. Similarly sharp results hold in the case of higher derivatives and Markov-Nikolskii
type inequalities. There is also a remarkable connection between the right Markov inequality for absolutely monotone polynomials
of order k in the supremum norm and essentially sharp bounds for the largest and smallest zeros of Jacobi polynomials. This is discussed
in the last section of the paper. 相似文献
905.
Mario Abundo 《Methodology and Computing in Applied Probability》2010,12(3):473-490
It is studied the first-passage time (FPT) of a time homogeneous one-dimensional diffusion, driven by the stochastic differential
equation dX(t) = μ(X(t))dt + σ(X(t)) dB
t
, X(0) = x
0, through b + Y(t), where b > x
0 and Y(t) is a compound Poisson process with rate λ > 0 starting at 0, which is independent of the Brownian motion B
t
. In particular, the FPT density is investigated, generalizing a previous result, already known in the case when X(t) = μt + B
t
, for which the FPT density is the solution of a certain integral equation. A numerical method is shown to calculate approximately
the FPT density; some examples and numerical results are also reported. 相似文献
906.
Alicia Cordero José L. Hueso Eulalia Martínez Juan R. Torregrosa 《Numerical Algorithms》2010,53(4):485-495
In this paper, we present two new three-step iterative methods for solving nonlinear equations with sixth convergence order.
The new methods are obtained by composing known methods of third order of convergence with Newton’s method and using an adequate
approximation for the derivative, that provides high order of convergence and reduces the required number of functional evaluations
per step. The first method is obtained from Potra-Pták’s method and the second one, from Homeier’s method, both reaching an
efficiency index of 1.5651. Our methods are comparable with the method of Parhi and Gupta (Appl Math Comput 203:50–55, 2008). Methods proposed by Kou and Li (Appl Math Comput 189:1816–1821, 2007), Wang et al. (Appl Math Comput 204:14–19, 2008) and Chun (Appl Math Comput 190:1432–1437, 2007) reach the same efficiency index, although they start from a fourth order method while we use third order methods and simpler
arithmetics. We prove the convergence results and check them with several numerical tests that allow us to compare the convergence
order, the computational cost and the efficiency order of our methods with those of the original methods. 相似文献
907.
Daniela di Serafino Susana Gomez Leopoldo Milano Filippo Riccio Gerardo Toraldo 《Journal of Global Optimization》2010,48(1):41-55
The detection of gravitational waves is a long-awaited event in modern physics and, to achieve this challenging goal, detectors
with high sensitivity are being used or are under development. In order to extract gravitational signals emitted by coalescing
binary systems of compact objects (neutron stars and/or black holes), from noisy data obtained by interferometric detectors,
the matched filter technique is generally used. Its computational kernel is a box-constrained global optimization problem
with many local solutions and a highly nonlinear and expensive objective function, whose derivatives are not available. To
tackle this problem, we designed a real-coded genetic algorithm that exploits characteristic features of the problem itself;
special attention was devoted to the choice of the initial population and of the recombination operator. Computational experiments
showed that our algorithm is able to compute a reasonably accurate solution of the optimization problem, requiring a much
smaller number of function evaluations than the grid search, which is generally used to solve this problem. Furthermore, the
genetic algorithm largely outperforms other global optimization algorithms on significant instances of the problem. 相似文献
908.
Tohru Nakashima 《Designs, Codes and Cryptography》2010,57(1):107-115
We discuss the properties of algebraic-geometric codes defined by a vector bundle on a curve X over a finite field. We investigate the correction capacities of the codes defined from vector bundles constructed by means
of finite coverings of X. 相似文献
909.
Osamu Hatori Takeshi Miura Rumi Shindo Hiroyuki Takagi 《Rendiconti del Circolo Matematico di Palermo》2010,59(2):161-183
Let $
A
$
A
and ℬ be unital semisimple commutative Banach algebras. It is shown that if surjections S,T: $
A
$
A
→ ℬ with S(1)=T(1)= 1 and α ∈ ℂ \ {0} satisfy r(S(a)T(b) − α)= r(ab− α) for all a,b ∈ $
A
$
A
, then S=T and S is a real algebra isomorphism, where r(a) is the spectral radius of a. Let I be a nonempty set, A and B be uniform algebras. Let ρ, τ: I → A and S,T: I → B be maps satisfying σ
π
(S(p)T(q)) ⊂ σ
π
(ρ(p) τ(q)) for all p,q ∈ I, where σ
π
(f) is the peripheral spectrum of f. Suppose that the ranges ρ(I), τ(I) ⊂ A and S(I),T(I) ⊂ B are closed under multiplication in a sense, and contain peaking functions “enough”. There exists a homeomorphism ϕ: Ch(B)→Ch(A) such that S(p)(y)= ρ(p)(ϕ(y)) and T(p)(y)= τ(p)(ϕ(y)) for every p ∈ I and y ∈ Ch(B), where Ch(A) is the Choquet boundary of A. 相似文献
910.
Quadratic assignment problems (QAPs) are known to be among the hardest discrete optimization problems. Recent study shows
that even obtaining a strong lower bound for QAPs is a computational challenge. In this paper, we first discuss how to construct
new simple convex relaxations of QAPs based on various matrix splitting schemes. Then we introduce the so-called symmetric
mappings that can be used to derive strong cuts for the proposed relaxation model. We show that the bounds based on the new
models are comparable to some strong bounds in the literature. Promising experimental results based on the new relaxations
are reported. 相似文献