全文获取类型
收费全文 | 2805篇 |
免费 | 407篇 |
国内免费 | 488篇 |
专业分类
电工技术 | 45篇 |
综合类 | 393篇 |
化学工业 | 149篇 |
金属工艺 | 118篇 |
机械仪表 | 42篇 |
建筑科学 | 703篇 |
矿业工程 | 107篇 |
能源动力 | 5篇 |
轻工业 | 90篇 |
水利工程 | 32篇 |
石油天然气 | 55篇 |
武器工业 | 5篇 |
无线电 | 279篇 |
一般工业技术 | 45篇 |
冶金工业 | 888篇 |
原子能技术 | 4篇 |
自动化技术 | 740篇 |
出版年
2023年 | 39篇 |
2022年 | 274篇 |
2021年 | 171篇 |
2020年 | 198篇 |
2019年 | 137篇 |
2018年 | 91篇 |
2017年 | 72篇 |
2016年 | 80篇 |
2015年 | 82篇 |
2014年 | 332篇 |
2013年 | 189篇 |
2012年 | 177篇 |
2011年 | 189篇 |
2010年 | 91篇 |
2009年 | 266篇 |
2008年 | 108篇 |
2007年 | 175篇 |
2006年 | 157篇 |
2005年 | 86篇 |
2004年 | 94篇 |
2003年 | 131篇 |
2002年 | 228篇 |
2001年 | 53篇 |
2000年 | 36篇 |
1999年 | 41篇 |
1998年 | 48篇 |
1997年 | 17篇 |
1996年 | 36篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1965年 | 3篇 |
1964年 | 3篇 |
1963年 | 2篇 |
1962年 | 4篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1957年 | 3篇 |
1956年 | 2篇 |
1955年 | 5篇 |
1954年 | 1篇 |
排序方式: 共有3700条查询结果,搜索用时 15 毫秒
61.
Text mining has become a major research topic in which text classification is the important task for finding the relevant information from the new document. Accordingly, this paper presents a semantic word processing technique for text categorization that utilizes semantic keywords, instead of using independent features of the keywords in the documents. Hence, the dimensionality of the search space can be reduced. Here, the Back Propagation Lion algorithm (BP Lion algorithm) is also proposed to overcome the problem in updating the neuron weight. The proposed text classification methodology is experimented over two data sets, namely, 20 Newsgroup and Reuter. The performance of the proposed BPLion is analysed, in terms of sensitivity, specificity, and accuracy, and compared with the performance of the existing works. The result shows that the proposed BPLion algorithm and semantic processing methodology classifies the documents with less training time and more classification accuracy of 90.9%. 相似文献
62.
Blanchet-Sadri et al. have shown that Avoidability, or the problem of deciding the avoidability of a finite set of partial words over an alphabet of size k≥2, is NP-hard [F. Blanchet-Sadri, R. Jungers, J. Palumbo, Testing avoidability on sets of partial words is hard, Theoret. Comput. Sci. 410 (2009) 968-972]. Building on their work, we analyze in this paper the complexity of natural variations on the problem. While some of them are NP-hard, others are shown to be efficiently decidable. Using some combinatorial properties of de Bruijn graphs, we establish a correspondence between lengths of cycles in such graphs and periods of avoiding words, resulting in a tight bound for periods of avoiding words. We also prove that Avoidability can be solved in polynomial space, and reduces in polynomial time to the problem of deciding the avoidability of a finite set of partial words of equal length over the binary alphabet. We give a polynomial bound on the period of an infinite avoiding word, in the case of sets of full words, in terms of two parameters: the length and the number of words in the set. We give a polynomial space algorithm to decide if a finite set of partial words is avoided by a non-ultimately periodic infinite word. The same algorithm also decides if the number of words of length n avoiding a given finite set of partial words grows polynomially or exponentially with n. 相似文献
63.
64.
针对实际密文数据库的应用,在全文检索倒排索引技术的基础上,设计了一种通过密文倒排索引文件对其进行快速检索的方法。密文索引文件中主要包含有索引项、相对应的记录主键等信息。检索时,通过用检索词匹配索引文件中的索引项,找到对应的记录主键集合,再根据记录主键集合查询密文数据库,获取相应的密文数据,进行解密即可获取明文数据信息。整个检索过程中不对数据库进行解密,从而实现了在不解密的情况下对密文数据库的快速检索。 相似文献
65.
66.
基于购物网站用户搜索日志的商品词发现 总被引:1,自引:0,他引:1
商品词是电子商务领域描述商品的新词。主要介绍基于购物网站用户搜索日志的商品词发现的方法。该方法从搜索日志中提取用户查询,对查询进行分词,采用N元递增分步算法和串频统计,计算候选串的条件概率,选择候选商品词。为了降低人工审核的成本,只对产出商品词的准确率进行评价。利用该方法在手机、面霜和香水三类商品的搜索日志上进行了实验,最高准确率达到92.58%。 相似文献
67.
68.
Well-known results on the avoidance of large squares in (full) words include the following: (1) Fraenkel and Simpson showed that we can construct an infinite binary word containing at most three distinct squares; (2) Entringer, Jackson and Schatz showed that there exists an infinite binary word avoiding all squares of the form xx such that |x|≥3, and that the bound 3 is optimal; (3) Dekking showed that there exists an infinite cube-free binary word that avoids all squares xx with |x|≥4, and that the bound of 4 is best possible. In this paper, we investigate these avoidance results in the context of partial words, or sequences that may have some undefined symbols called holes. Here, a square has the form uv with u and v compatible, and consequently, such a square is compatible with a number of full words that are squares over the given alphabet. We show that (1) holds for partial words with at most two holes. We prove that (2) extends to partial words having infinitely many holes. Regarding (3), we show that there exist binary partial words with infinitely many holes that avoid cubes and have only eleven full word squares compatible with factors of it. Moreover, this number is optimal, and all such squares xx satisfy |x|≤4. 相似文献
69.
A synchronizing word for a given synchronizing DFA is called minimal if none of its proper factors is synchronizing. We characterize the class of synchronizing automata having only finitely many minimal synchronizing words (the class of such automata is denoted by FG). Using this characterization we prove that any such automaton possesses a synchronizing word of length at most 3n-5. We also prove that checking whether a given DFA A is in FG is co-NP-hard and provide an algorithm for this problem which is exponential in the number of states A. 相似文献
70.
We introduce techniques to prove lower bounds for the number of states needed by finite automata operating on nested words. We study the state complexity of Boolean operations and obtain lower bounds that are tight within an additive constant. The results for union and complementation differ from corresponding bounds for ordinary finite automata. For reversal and concatenation, we establish lower bounds that are of a different order than the worst-case bounds for ordinary finite automata. 相似文献