全文获取类型
收费全文 | 14124篇 |
免费 | 2283篇 |
国内免费 | 1874篇 |
专业分类
电工技术 | 1150篇 |
综合类 | 1762篇 |
化学工业 | 385篇 |
金属工艺 | 124篇 |
机械仪表 | 651篇 |
建筑科学 | 501篇 |
矿业工程 | 163篇 |
能源动力 | 254篇 |
轻工业 | 219篇 |
水利工程 | 203篇 |
石油天然气 | 151篇 |
武器工业 | 172篇 |
无线电 | 1659篇 |
一般工业技术 | 1219篇 |
冶金工业 | 466篇 |
原子能技术 | 47篇 |
自动化技术 | 9155篇 |
出版年
2024年 | 130篇 |
2023年 | 268篇 |
2022年 | 482篇 |
2021年 | 453篇 |
2020年 | 542篇 |
2019年 | 527篇 |
2018年 | 492篇 |
2017年 | 680篇 |
2016年 | 681篇 |
2015年 | 808篇 |
2014年 | 968篇 |
2013年 | 1204篇 |
2012年 | 1170篇 |
2011年 | 1230篇 |
2010年 | 915篇 |
2009年 | 960篇 |
2008年 | 1032篇 |
2007年 | 1018篇 |
2006年 | 841篇 |
2005年 | 706篇 |
2004年 | 590篇 |
2003年 | 430篇 |
2002年 | 395篇 |
2001年 | 353篇 |
2000年 | 282篇 |
1999年 | 168篇 |
1998年 | 159篇 |
1997年 | 147篇 |
1996年 | 109篇 |
1995年 | 96篇 |
1994年 | 75篇 |
1993年 | 67篇 |
1992年 | 47篇 |
1991年 | 42篇 |
1990年 | 25篇 |
1989年 | 31篇 |
1988年 | 20篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
In this paper we develop and compare several heuristic methods for solving the general two-dimensional cutting stock problem.
We follow the Gilmore-Gomory column generation scheme in which at each iteration a new cutting pattern is obtained as the
solution of a subproblem on one stock sheet. For solving this subproblem, in addition to classical dynamic programming, we
have developed three heuristic procedures of increasing complexity, based on GRASP and Tabu Search techniques, producing solutions
differing in quality and in time requirements. In order to obtain integer solutions from the fractional solutions of the Gilmore-Gomory
process, we compare three rounding procedures, rounding up, truncated branch and bound and the solution of a residual problem.
We have coded and tested all the combinations of algorithms and rounding procedures. The computational results obtained on
a set of randomly generated test problems show their relative efficiency and allow the potential user to choose from among
them, according to the available computing time.
Rceived: January 9, 2001 / Accepted: December 10, 2001 相似文献
52.
浅析中央空调系统替代制冷剂的选择 总被引:1,自引:0,他引:1
田国庆 《制冷空调与电力机械》2002,23(2):25-27
根据大气臭氧层耗损和温室气体对全球气候变化的影响,分析了中央空调系统几种替代制冷剂的特性,探讨了在实际使用中如何进行替代制冷剂的选择。 相似文献
53.
郑国忠 《中国非金属矿工业导刊》1994,(4)
本文首先讨论GPS星座组成及美国的用政策,阐述了AS措施及其对GPS测量的影响。然后,对抗AS的若干方案进行介绍,分别对平方法、互相关法、码相关干法及P-W技术(Ashtech法)进行叙述和评论,指出它们的优缺点,评述它们在GPS技术发展过程所起的作用。最后,对GPS星座建成后的形势作了小结,并对当前我国GPS事业的有关问题提出四点建议。 相似文献
54.
将汉白玉废料通过高温煅烧分解得到氧化钙,再用氯化铵循环液溶解氧化钙制得碱性氯化钙溶液,除去其中的Mg、Fe等杂质得到氯化钙精制溶液,利用化学方法合成得到碳酸钙粉体.用X射线衍射(XRD)、扫描电镜(SEM)及激光粒度分析仪、白度仪对碳酸钙产品的晶相组成、形貌、粒度分布、白度及化学组成进行了分析,所得产品为纯度达98.5%以上、白度达97%以上、平均粒度为80nm左右的球形纳米级碳酸钙.并对碳化反应速率及合成球形纳米碳酸钙的影响因素进行了分析.实验中循环使用NH4Cl,氨的排放量小,减少了环境污染. 相似文献
55.
硅酸盐矿物和碳酸盐矿物是构成地壳的主要造岩矿物,论述了两类矿物溶解动力学的研究现状与展望,指出两类矿物的溶解和沉积过程中CO2吸收和释放,对全球环境有重要影响。 相似文献
56.
57.
本详细描述了移动IP的工作过程,并介绍了移动IP的隧道技术和IPSec,最后对移动IP技术中存在几个热点问题进行了讨论。 相似文献
58.
The search for good lineal, or depth-first, spanning trees is an important aspect in the implementation of a wide assortment of graph algorithms. We consider the complexity of findingoptimal lineal spanning trees under various notions of optimality. In particular, we show that several natural problems, such as constructing a shortest or a tallest lineal tree, are NP-hard. We also address the issue of polynomial-time, near-optimization strategies for these difficult problems, showing that efficient absolute approximation algorithms cannot exist unlessP = NP.This author's research was supported in part by the Sandia University Research Program and by the National Science Foundation under Grant M IP-8603879.This author's research was supported in part by the National Science Foundation under Grants ECS-8403859 and MIP-8603879. 相似文献
59.
Matthew Huntbach 《International journal of parallel programming》1991,20(4):299-314
The concurrent logic languages, of which Parlog is one, have been promoted as a new generation of software languages specifically designed for parallel programming. This paper investigates their application to a search problem commonly used as an illustration of artificial intelligence techniques, the 8-puzzle. It notes that programs written in the concurrent logic languages which do not pay attention to the parallelism can fall into two possible traps: either there is little real parallelism in them due to data dependencies, or there is too much parallelism and any practical architecture will be overwhelmed. A solution which controls the parallelism using user-defined priorities is proposed. This solution has the advantage of being architecture-independent. 相似文献
60.
Multiple forms of a symbol-digit substitution task were used to provide a componential analysis of age differences in coding task performance. The results demonstrated age differences in feature encoding, memory, and visual search. A 2nd experiment was conducted with young adults to investigate a sensory deficit as a locus of age differences. The spatial contrast sensitivity deficit of older adults was simulated on forms by applying a digital filter. Persons in the age-simulated contrast condition performed worse than those in the normal contrast condition. The stimulus degradation effect was linked to visual search speed. The study illustrates the utility of componential analysis and offers direct support for the hypothesis that sensory deficits affect performance on tasks used to assess intelligence (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献