全文获取类型
收费全文 | 13015篇 |
免费 | 1252篇 |
国内免费 | 956篇 |
专业分类
化学 | 6847篇 |
晶体学 | 125篇 |
力学 | 540篇 |
综合类 | 57篇 |
数学 | 856篇 |
物理学 | 3281篇 |
综合类 | 3517篇 |
出版年
2024年 | 57篇 |
2023年 | 239篇 |
2022年 | 390篇 |
2021年 | 501篇 |
2020年 | 418篇 |
2019年 | 404篇 |
2018年 | 336篇 |
2017年 | 345篇 |
2016年 | 494篇 |
2015年 | 514篇 |
2014年 | 626篇 |
2013年 | 838篇 |
2012年 | 997篇 |
2011年 | 988篇 |
2010年 | 729篇 |
2009年 | 677篇 |
2008年 | 798篇 |
2007年 | 706篇 |
2006年 | 637篇 |
2005年 | 594篇 |
2004年 | 472篇 |
2003年 | 414篇 |
2002年 | 418篇 |
2001年 | 269篇 |
2000年 | 266篇 |
1999年 | 307篇 |
1998年 | 278篇 |
1997年 | 228篇 |
1996年 | 231篇 |
1995年 | 168篇 |
1994年 | 154篇 |
1993年 | 137篇 |
1992年 | 134篇 |
1991年 | 111篇 |
1990年 | 62篇 |
1989年 | 56篇 |
1988年 | 59篇 |
1987年 | 40篇 |
1986年 | 23篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1977年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1970年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We consider a stowage-planning problem of arranging containers on a container ship in the maritime transportation system. Since containers are accessible only from the top of the stack, temporary unloading and reloading of containers, called shifting, is unavoidable if a container required to be unloaded at the current port is stacked under containers to be unloaded at later ports on the route of the ship. The objective of the stowage planning problem is to minimize the time required for shifting and crane movements on a tour of a container ship while maintaining the stability of the ship. For the problem, we develop a heuristic solution method in which the problem is divided into two subproblems, one for assigning container groups into the holds and one for determining a loading pattern of containers assigned to each hold. The former subproblem is solved by a greedy heuristic based on the transportation simplex method, while the latter is solved by a tree search method. These two subproblems are solved iteratively using information obtained from solutions of each other. To see the performance of the suggested algorithm, computational tests are performed on problem instances generated based on information obtained from an ocean container liner. Results show that the suggested algorithm works better than existing algorithms. 相似文献
42.
In this paper, we give a recursive construction from an LTTS(v + 2) to an LTTS(16v + 2) for v 3. Furthermore, the existence of LTTS(2n + 2) is proved. Thereby, we completely solve the existence problem of LTTS)(v) (large set of pairwise disjoint transitive triple systems of order v). 相似文献
43.
44.
45.
对加速管的放电或击穿与绝缘环,电极材料,极间距离和真空度等因素的关系进行了分析,为加速管的设计提供了依据。以此研制的加速算运行正常。 相似文献
46.
HL-1装置中LHCD和等离子体参数的关系 总被引:1,自引:1,他引:0
本文研究了在HL-1托卡马克的不同放电阶段的低混杂波驱动特性。给出了驱动电流及驱动效率和等离子体参数,如电子平均密度ne、等离子体电流Ip及纵向磁场的关系。也给出和分析了波驱动和入射波功率的关系。在放电平段,对正反向驱动效率进行了研究和比较。 相似文献
47.
beta-Glucosidase and beta-glucuronidase of human and rat fecal bacteria were induced by cultivation in alkaline media although their growths were not affected. When a bacterium isolated from human feces producing each enzyme was cultured in a medium at pH 5 for 12-15 h and then adjusted to pH 8, beta-glucosidase and beta-glucuronidase were induced 9.2-fold and 11.5-fold, respectively. 相似文献
48.
Existing home devices in home network provides only independent services limited on a homogeneous protocol and/or do not fully support an intelligent service provided by cooperating among heterogeneous protocol devices. This paper proposes an intelligent and integrated service binding architecture which allow the users to figure out the status of devices and to cooperate among home network devices regardless of supported protocols or operational characteristics. 相似文献
49.
Suoyuan Lian Lei Gao Zhenhui Kang Di Wu Yang Lan Lin Xu 《Solid State Communications》2004,132(6):375-378
Single-crystal magnetite nanowires with average diameter of ca. 20 nm and length of up to several micrometers were prepared by a simple alkaline surfactant-free hydrothermal process. The crystallinity, purity, morphology, and structural features of the as-prepared magnetite nanowires were investigated by powder X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction. The composition and length of nanowires depends on the pH, with higher pH favoring longer nanowires composed entirely of Fe3O4. A mechanism for nanowire growth is proposed. 相似文献
50.
对一类遗传程序设计问题,提出了简单等长的分布式染色体,取代复杂变长的树结构染色体,使演化算子操作更方便,个体复杂度得到有效控制.用该染色体形式解决割草问题,分析了分布式染色体带来的一些性质,并给出了很好的计算结果. 相似文献