全文获取类型
收费全文 | 10241篇 |
免费 | 644篇 |
国内免费 | 557篇 |
专业分类
化学 | 765篇 |
晶体学 | 24篇 |
力学 | 328篇 |
综合类 | 132篇 |
数学 | 1832篇 |
物理学 | 1403篇 |
综合类 | 6958篇 |
出版年
2024年 | 25篇 |
2023年 | 71篇 |
2022年 | 181篇 |
2021年 | 205篇 |
2020年 | 173篇 |
2019年 | 147篇 |
2018年 | 155篇 |
2017年 | 218篇 |
2016年 | 255篇 |
2015年 | 297篇 |
2014年 | 457篇 |
2013年 | 486篇 |
2012年 | 496篇 |
2011年 | 664篇 |
2010年 | 488篇 |
2009年 | 595篇 |
2008年 | 630篇 |
2007年 | 851篇 |
2006年 | 701篇 |
2005年 | 657篇 |
2004年 | 549篇 |
2003年 | 431篇 |
2002年 | 421篇 |
2001年 | 349篇 |
2000年 | 309篇 |
1999年 | 235篇 |
1998年 | 199篇 |
1997年 | 182篇 |
1996年 | 168篇 |
1995年 | 121篇 |
1994年 | 125篇 |
1993年 | 100篇 |
1992年 | 90篇 |
1991年 | 98篇 |
1990年 | 69篇 |
1989年 | 65篇 |
1988年 | 54篇 |
1987年 | 29篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1977年 | 9篇 |
1976年 | 3篇 |
1969年 | 1篇 |
1959年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
对膜结构裁剪分析中目前应用较广的裁剪线的生成方法进行了比较研究,提出修正二次测地线法。确定了采用测地线作为裁剪线及展开图形的基准线。之后对已有图形展开方法——二次测地线法做了适当改进,提出修正二次测地线法。 相似文献
102.
In this paper we face the problem of stowing a containership, referred to as the Master Bay Plan Problem (MBPP); this problem
is difficult to solve due to its combinatorial nature and the constraints related to both the ship and the containers. We
present a decomposition approach that allows us to assign a priori the bays of a containership to the set of containers to
be loaded according to their final destination, such that different portions of the ship are independently considered for
the stowage. Then, we find the optimal solution of each subset of bays by using a 0/1 Linear Programming model. Finally, we
check the global ship stability of the overall stowage plan and look for its feasibility by using an exchange algorithm which
is based on local search techniques. The validation of the proposed approach is performed with some real life test cases.
This work has been developed within the research area: “The harbour as a logistic node” of the Italian Centre of Excellence
on Integrated Logistics (CIELI) of the University of Genoa, Italy 相似文献
103.
This paper presents a fringe pattern normalization and noise-reduction algorithm. Locally the background noise is suppressed, the modulation normalized and the noise smoothed. An expression to calculate the cosine-only term is formulated. It is related to the directional derivatives of the intensity fringes. Two-dimensional Fourier series are used to calculate the parameters needed for the algorithm. Experimental work is presented using diffraction and ESPI images. The programming is relatively simple and involves mainly local convolutions. The processing time using a 2 GHz computer to normalize an image of 256 × 256 pixels is approximately one second. 相似文献
104.
This paper describes the k-means range algorithm, a combination of the partitional k-means clustering algorithm with a well known spatial data structure, namely the range tree, which allows fast range searches. It offers a real-time solution for the development of distributed interactive decision aids in e-commerce since it allows the consumer to model his preferences along multiple dimensions, search for product information, and then produce the data clusters of the products retrieved to enhance his purchase decisions. This paper also discusses the implications and advantages of this approach in the development of on-line shopping environments and consumer decision aids in traditional and mobile e-commerce applications. 相似文献
105.
106.
COSEARCH: A Parallel Cooperative Metaheuristic 总被引:1,自引:0,他引:1
In order to design a well-balanced metaheuristic for robustness, we propose the COSEARCH approach which manages the cooperation
of complementary heuristic methods via an adaptive memory which contains a history of the search already done. In this paper,
we present the idiosyncrasies of the COSEARCH approach and its application for solving large scale instances of the quadratic
assignment problem (QAP). We propose an original design of the adaptive memory in order to focus on high quality regions of
the search and avoid attractive but deceptive areas. For the QAP, we have hybridized three heuristic agents of complementary
behaviours: a Tabu Search is used as the main search algorithm, a Genetic Algorithm is in charge of the diversification and
a Kick Operator is applied to intensify the search. The evaluations have been executed on large scale network of workstations
via a parallel environment which supports fault tolerance and adaptive dynamic scheduling of tasks. 相似文献
107.
提出了一种非刚性点匹配的算法并把其运用于医学图像配准.该算法采用信号滤波的方法来获得点集间的匹配信息,并运用松弛标记法将各点邻域关系对模糊的匹配信息进行迭代获得明确的匹配关系.在此基础上,利用高斯径向基函数来描述点模式间的弹性形变,在基本的迭代框架下实现问题的求解.实验结果显示在形变程度为5%、出格点比率50%和噪声标准差为5%的情况下该算法的匹配误差能控制在0.13以下,表明了该算法的鲁棒性和有效性,较好地解决了医学非刚性形变的点匹配问题. 相似文献
108.
We examine a sequential selection problem in which a single option must be selected. Each option's value is a function of its attributes, whose precise values can be ascertained at a given cost. We prove the optimality of a threshold stopping rule for a general class of objective functions. 相似文献
109.
In this article, local optimality in multiobjective combinatorial optimization is used as a baseline for the design and analysis
of two iterative improvement algorithms. Both algorithms search in a neighborhood that is defined on a collection of sets
of feasible solutions and their acceptance criterion is based on outperformance relations. Proofs of the soundness and completeness
of these algorithms are given. 相似文献
110.
语音是学任何一门语言的基础。语音的规范化直接影响学习者语言的学习效果,因此对英语专业师范生的语音模式要进行严格规范。 相似文献