全文获取类型
收费全文 | 60794篇 |
免费 | 7637篇 |
国内免费 | 5026篇 |
专业分类
电工技术 | 5646篇 |
综合类 | 5807篇 |
化学工业 | 8233篇 |
金属工艺 | 4076篇 |
机械仪表 | 3832篇 |
建筑科学 | 4627篇 |
矿业工程 | 1980篇 |
能源动力 | 1668篇 |
轻工业 | 7086篇 |
水利工程 | 1785篇 |
石油天然气 | 2047篇 |
武器工业 | 828篇 |
无线电 | 6905篇 |
一般工业技术 | 5917篇 |
冶金工业 | 2115篇 |
原子能技术 | 1114篇 |
自动化技术 | 9791篇 |
出版年
2024年 | 459篇 |
2023年 | 1318篇 |
2022年 | 2761篇 |
2021年 | 3647篇 |
2020年 | 2547篇 |
2019年 | 1973篇 |
2018年 | 1940篇 |
2017年 | 2155篇 |
2016年 | 1930篇 |
2015年 | 3053篇 |
2014年 | 3508篇 |
2013年 | 4128篇 |
2012年 | 4898篇 |
2011年 | 5188篇 |
2010年 | 4790篇 |
2009年 | 4694篇 |
2008年 | 4554篇 |
2007年 | 4264篇 |
2006年 | 3701篇 |
2005年 | 2998篇 |
2004年 | 2153篇 |
2003年 | 1475篇 |
2002年 | 1538篇 |
2001年 | 1346篇 |
2000年 | 1003篇 |
1999年 | 469篇 |
1998年 | 196篇 |
1997年 | 141篇 |
1996年 | 121篇 |
1995年 | 86篇 |
1994年 | 84篇 |
1993年 | 61篇 |
1992年 | 32篇 |
1991年 | 48篇 |
1990年 | 27篇 |
1989年 | 26篇 |
1988年 | 17篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1959年 | 12篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
抚顺石油化工研究院研制开发的新一代FC -2 6高中油型加氢裂化催化剂 ,以W -Ni为加氢组分 ,以无定型硅铝为主载体 ,并添加改性分子筛。工艺研究及工业应用结果表明 ,FC -2 6催化剂活性及中油选择性高 ,稳定性好 ,原料适应性强 ,具有广阔的应用前景。 相似文献
22.
The aim of this work is to analyse the possibility of using co-gasification technology to process coal mixed with wastes to take profit of its energy content and at the same time to minimize the environmental impact associated with the use of wastes and to diminish the costs of flue gas treatment. The addition to coal of different types of materials, like: pine based waste, petcoke and polyethylene (PE), was not found to give rise to any operational problems, regarding both the feeding system and gasification process and led to higher energy conversions, however, the gas presented higher tars and hydrocarbons content. Several catalysts were tested, such as, dolomite, olivine, nickel and magnesium oxides, zinc oxides and cobalt and molybdenum oxides. Catalyst action was analysed in tars release and also in ammonia compounds reduction. The presence of catalysts allowed increasing hydrogen release, whilst there was a decrease in hydrocarbons and tars contents. A nickel-magnesium oxide was the catalyst that led to the highest reduction in hydrocarbons and tars. This catalyst also led to the lowest NH3 content in the fuel gas produced, due to the catalyst efficiency in NH3 destruction. 相似文献
23.
Twin support vector machine (TSVM) is regarded as a milestone in the development of the powerful SVM. It finds two nonparallel planes by resolving a pair of smaller-sized quadratic programming problems rather than a single large one, which makes the learning speed of TSVM approximately four times faster than that of the standard SVM. However, the empirical risk minimization principle is implemented in the TSVM, so it easily leads to the over-fitting problem and reduces the prediction accuracy of the classifier. ν-TSVM, as a variant of TSVM, also implements the empirical risk minimization principle. To enhance the generalization ability of the classifier, we propose an improved ν-TSVM by introducing a regularization term into the objective function, so there are two parts in the objective function, one of which is to maximize the margin between the two parallel hyper-planes, and the other one is to minimize the training errors of two classes of samples. Therefore the structural risk minimization principle is implemented in our improved ν-TSVM. Numerical experiments on one artificial dataset and nine benchmark datasets show that our improved ν-TSVM yields better generalization performance than SVM, ν-SVM, and ν-TSVM. Moreover, numerical experiments with different proportions of outliers demonstrate that our improved ν-TSVM is robust and stable. Finally, we apply our improved ν-TSVM to two BCI competition datasets, and also obtain better prediction accuracy. 相似文献
24.
炭黑填充硬聚氯乙烯的改性 总被引:1,自引:0,他引:1
为使聚氯乙烯具有抗静电性能,采用加入具有导电性填料的方法,但加入大量的填料,会使硬聚氯乙烯的冲击性能降低,加工性能变差。本文是在以炭黑为填料的基础上,研究不同的改性剂和加工助剂改进硬聚氯乙烯的效果,结果表明,加入冲击改性剂和加工助剂后,大大增加了硬聚氯乙烯的冲击强度,且加工性能也得到改善,同时由于炭黑具有补强效果,其拉伸强度和弯曲强度在加入改性剂后也能满足使用要求。 相似文献
25.
26.
27.
介绍了氟化氢吸收原理、流程 ,国内外氟化氢吸收设备的选型 ,满足工艺要求的穿流栅板塔的设计计算及应用。 相似文献
28.
29.
Jianzhong Qi Rui Zhang Yanqiu Wang Andy Yuan Xue Ge Yu Lars Kulik 《World Wide Web》2014,17(6):1261-1293
We propose and study a new type of location optimization problem, the min-dist location selection problem: given a set of clients and a set of existing facilities, we select a location from a given set of potential locations for establishing a new facility, so that the average distance between a client and her nearest facility is minimized. The problem has a wide range of applications in urban development simulation, massively multiplayer online games, and decision support systems. We also investigate a variant of the problem, where we consider replacing (instead of adding) a facility while achieving the same optimization goal. We call this variant the min-dist facility replacement problem. We explore two common approaches to location optimization problems and present methods based on those approaches for solving the min-dist location selection problem. However, those methods either need to maintain an extra index or fall short in efficiency. To address their drawbacks, we propose a novel method (named MND), which has very close performance to the fastest method but does not need an extra index. We then utilize the key idea behind MND to approach the min-dist facility replacement problem, which results in two algorithms names MSND and RID. We provide a detailed comparative cost analysis and conduct extensive experiments on the various algorithms. The results show that MND and RID outperform their competitors by orders of magnitude. 相似文献
30.