全文获取类型
收费全文 | 43451篇 |
免费 | 2779篇 |
国内免费 | 2186篇 |
专业分类
化学 | 22989篇 |
晶体学 | 238篇 |
力学 | 4211篇 |
综合类 | 568篇 |
数学 | 9614篇 |
物理学 | 10796篇 |
出版年
2024年 | 73篇 |
2023年 | 399篇 |
2022年 | 1110篇 |
2021年 | 1098篇 |
2020年 | 1090篇 |
2019年 | 1080篇 |
2018年 | 970篇 |
2017年 | 1204篇 |
2016年 | 1599篇 |
2015年 | 1222篇 |
2014年 | 1771篇 |
2013年 | 3067篇 |
2012年 | 2441篇 |
2011年 | 2300篇 |
2010年 | 1964篇 |
2009年 | 2531篇 |
2008年 | 2494篇 |
2007年 | 2784篇 |
2006年 | 2338篇 |
2005年 | 2067篇 |
2004年 | 1986篇 |
2003年 | 1677篇 |
2002年 | 1315篇 |
2001年 | 1076篇 |
2000年 | 1038篇 |
1999年 | 915篇 |
1998年 | 873篇 |
1997年 | 791篇 |
1996年 | 707篇 |
1995年 | 665篇 |
1994年 | 590篇 |
1993年 | 488篇 |
1992年 | 442篇 |
1991年 | 381篇 |
1990年 | 348篇 |
1989年 | 230篇 |
1988年 | 251篇 |
1987年 | 153篇 |
1986年 | 128篇 |
1985年 | 156篇 |
1984年 | 119篇 |
1983年 | 63篇 |
1982年 | 101篇 |
1981年 | 66篇 |
1980年 | 49篇 |
1979年 | 75篇 |
1978年 | 34篇 |
1977年 | 15篇 |
1976年 | 25篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
Orewczyk J. Jasieńska S. Iwanczenko S. 《Journal of Thermal Analysis and Calorimetry》1998,54(1):79-84
This paper presents applications of thermal analysis to observe the course of reduction of acidic pellets, metallurgical substances
whose reducibility and strength are basic parameters of use in blast furnace processes. Both parameters depend on the mineral
composition of the samples. The investigations included determination of the chemical and phase compositions of the initial
samples and reduction products.
Research was conducted on acidic pellets from Połtawa (Poland), applied in the T. Sendzimir Steelworks (Poland), in comparison
with pellets from Brazil, Canada and Lebedyn (Russia).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
242.
Michael A. Zazanis 《Queueing Systems》1992,11(4):419-428
We examine level crossings of sample paths of queueing processes and investigate the conditions under which the limiting empirical distribution for the workload process exists and is absolutely continuous. The connection between the density of the workload distribution and the rate of downcrossings is established as a sample path result that does not depend on any stochastic assumptions. As a corollary, we obtain the sample path version of the Takács formula connecting the time and customer stationary distributions in a queue. Defective limiting empirical distributions are considered and an expression for the mass at infinity is derived.This research has been supported in part by NSF Grants ECS-8811003 and DDM-8905638. 相似文献
243.
高阶非线性波动方程的有限差分方法 总被引:2,自引:0,他引:2
本文研究一类广泛的高阶非线性波动方程组初边值问题的有限差分格式,用离散泛函分析方法和先验估计的技巧得到了有限差分格式的收敛性。 相似文献
244.
本文对四个主要麦芽品质性状—a一淀粉酶活力、麦芽汁粘度、麦芽汁色度和搪化力进行了杂种优势和相关分析.(1)相对优势结果表明,在84个组合次中,呈正向优势的46个,占54.76男,负向优势34个,占40.48男,无显性4个,占4.75男;(2)四个品质性状的中亲优势平均值分别为一6.117、一9.965 40.452和一。.545s a-淀粉酶活力和糖化力的超高亲优势分别为一14.578和一8.201,麦芽汁粘度和色度的超低亲优势分别为5.442和70.455.四个性状杂种优势的变异系数均很大.(3)麦芽汁色度的F,对MP的回归系数(B)和相关系数(r)均达显著水平,分别为。..43和0.50,麦芽汁粘度的相关系数达显著水平,为一。.45,其余均未达显著水平,(4)除麦芽汁色度性状外,另三个性状的中亲优势、超亲优势和特殊配合力的相关均达显著或极显著水平.(5)四个麦芽品质性状间的相关结果表明,仅有a-淀粉酶活力和麦芽汁粘度间呈极显著负相关(r=一0.56').最后,文章根据实验结果,就啤酒大麦麦芽品质改良的遗传育种及其杂种优势应用进行了初步讨论. 相似文献
245.
Masakazu Muramatsu 《Mathematical Programming》1998,83(1-3):393-406
In this paper, we introduce an affine scaling algorithm for semidefinite programming (SDP), and give an example of a semidefinite
program such that the affine scaling algorithm converges to a non-optimal point. Both our program and its dual have interior
feasible solutions and unique optimal solutions which satisfy strict complementarity, and they are non-degenerate everywhere. 相似文献
246.
The goal of this paper is to compute the shape Hessian for a generalized Oseen problem with nonhomogeneous Dirichlet boundary
condition by the velocity method. The incompressibility will be treated by penalty approach. The structure of the shape gradient
and shape Hessian with respect to the shape of the variable domain for a given cost functional are established by an application
of the Lagrangian method with function space embedding technique.
This work was supported by the National Natural Science Fund of China (No. 10371096) for ZM Gao and YC Ma. 相似文献
247.
Alexis C. Kaporis Lefteris M. Kirousis Yannis C. Stamatiou Malvina Vamvakari Michele Zito 《Discrete Applied Mathematics》2007,155(12):1525-1538
The problem of determining the unsatisfiability threshold for random 3-SAT formulas consists in determining the clause to variable ratio that marks the experimentally observed abrupt change from almost surely satisfiable formulas to almost surely unsatisfiable. Up to now, there have been rigorously established increasingly better lower and upper bounds to the actual threshold value. In this paper, we consider the problem of bounding the threshold value from above using methods that, we believe, are of interest on their own right. More specifically, we show how the method of local maximum satisfying truth assignments can be combined with results for the occupancy problem in schemes of random allocation of balls into bins in order to achieve an upper bound for the unsatisfiability threshold less than 4.571. In order to obtain this value, we establish a bound on the q-binomial coefficients (a generalization of the binomial coefficients). No such bound was previously known, despite the extensive literature on q-binomial coefficients. Finally, to prove our result we had to establish certain relations among the conditional probabilities of an event in various probabilistic models for random formulas. It turned out that these relations were considerably harder to prove than the corresponding ones for unconditional probabilities, which were previously known. 相似文献
248.
This article concerns the existence of global smooth solution for scalar conservation laws with degenerate viscosity in 2-dimensional space. The analysis is based on successive approximation and maximum principle. 相似文献
249.
The authors consider the exact controllability of the vibrations of a thin shallow shell, of thickness 2εwith controls imposed on the lateral surface and at the top and bottom of the shell. Apart from proving the existence of exact controls, it is shown that the solutions of the three dimensional exact controllability problems converge, as the thickness of the shell goes to zero, to the solution of an exact controllability problem in two dimensions. 相似文献
250.
Shigeki Aida 《Journal of Functional Analysis》2007,251(1):59-121
We determine the limit of the bottom of spectrum of Schrödinger operators with variable coefficients on Wiener spaces and path spaces over finite-dimensional compact Riemannian manifolds in the semi-classical limit. These are extensions of the results in [S. Aida, Semiclassical limit of the lowest eigenvalue of a Schrödinger operator on a Wiener space, J. Funct. Anal. 203 (2) (2003) 401-424]. The problem on path spaces over Riemannian manifolds is considered as a problem on Wiener spaces by using Ito's map. However the coefficient operator is not a bounded linear operator and the dependence on the path is not continuous in the uniform convergence topology if the Riemannian curvature tensor on the underling manifold is not equal to 0. The difficulties are solved by using unitary transformations of the Schrödinger operators by approximate ground state functions and estimates in the rough path analysis. 相似文献