全文获取类型
收费全文 | 925769篇 |
免费 | 12008篇 |
国内免费 | 2221篇 |
专业分类
电工技术 | 16873篇 |
综合类 | 1009篇 |
化学工业 | 142333篇 |
金属工艺 | 35744篇 |
机械仪表 | 27911篇 |
建筑科学 | 22114篇 |
矿业工程 | 5667篇 |
能源动力 | 24043篇 |
轻工业 | 78203篇 |
水利工程 | 10255篇 |
石油天然气 | 19231篇 |
武器工业 | 74篇 |
无线电 | 100518篇 |
一般工业技术 | 181810篇 |
冶金工业 | 174324篇 |
原子能技术 | 20091篇 |
自动化技术 | 79798篇 |
出版年
2021年 | 8814篇 |
2020年 | 6520篇 |
2019年 | 8182篇 |
2018年 | 14037篇 |
2017年 | 14006篇 |
2016年 | 14812篇 |
2015年 | 9935篇 |
2014年 | 16228篇 |
2013年 | 42659篇 |
2012年 | 25233篇 |
2011年 | 34232篇 |
2010年 | 27379篇 |
2009年 | 30453篇 |
2008年 | 31142篇 |
2007年 | 30712篇 |
2006年 | 26600篇 |
2005年 | 24199篇 |
2004年 | 23035篇 |
2003年 | 22659篇 |
2002年 | 21710篇 |
2001年 | 21301篇 |
2000年 | 20128篇 |
1999年 | 20761篇 |
1998年 | 51891篇 |
1997年 | 36936篇 |
1996年 | 28523篇 |
1995年 | 21527篇 |
1994年 | 19054篇 |
1993年 | 18663篇 |
1992年 | 13785篇 |
1991年 | 13068篇 |
1990年 | 12931篇 |
1989年 | 12532篇 |
1988年 | 11905篇 |
1987年 | 10704篇 |
1986年 | 10454篇 |
1985年 | 11804篇 |
1984年 | 10801篇 |
1983年 | 10016篇 |
1982年 | 9212篇 |
1981年 | 9383篇 |
1980年 | 8942篇 |
1979年 | 8855篇 |
1978年 | 8650篇 |
1977年 | 10027篇 |
1976年 | 13114篇 |
1975年 | 7635篇 |
1974年 | 7266篇 |
1973年 | 7434篇 |
1972年 | 6190篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
931.
Phylogenetic scanning: a computer-assisted algorithm for mapping gene conversions and other recombinational events 总被引:1,自引:0,他引:1
An algorithm, 'phylogenetic scanning', is described for mapping gene conversion events where comparative DNA sequence data are available from different species. In this algorithm, sets of hypothetical phylogenetic trees are constructed that describe possible sequence relationships due to gene conversions in different species lineages; these trees are then evaluated by the principle of parsimony at intervals in the sequence alignment. When used to map gene conversion events that occurred between the pair of gamma-globin genes of higher primates, the algorithm gives results nearly identical to those obtained using a tedious manual approach. Suggestions are also provided for adaptation of this procedure to the analysis of other recombination events. 相似文献
932.
Arun K. Nanda Honda Shing Ten-Hwan Tzen Lionel M. Ni 《Journal of Parallel and Distributed Computing》1991,12(4)
A standard metric conventionally employed to compare the performance of different multiprocessor systems is speedup. Although providing a measure of the improvement in execution speed achievable on a system, this metric does not yield any insight into the factors responsible for limiting the potential improvement in speed. This paper studies the performance degradation in shared-memory multiprocessors as a result of contention for shared-memory resources. A replicate workload framework with a flexible mechanism for workload specification is proposed for measuring performance. Two normalized performance metrics—efficiency and overhead factor—are introduced to quantify the factors limiting performance and facilitate comparison across architectures. Finally, the proposed model is employed to measure and compare the performance of three contemporary shared-memory systems, with special emphasis on the newly released BBN Butterfly-II (TC2000), currently undergoing Beta test. 相似文献
933.
A proof system for communicating processes with value-passing 总被引:1,自引:0,他引:1
M. Hennessy 《Formal Aspects of Computing》1991,3(4):346-366
A proof system for a version of CCS with value-passing is proposed in which the reasoning about data is factored out from that about the structure of processes. The system is shown to be sound and complete for finite terms with respect to a denotational semantics based on Acceptance Trees. 相似文献
934.
935.
936.
We formulate a class of difference schemes for stiff initial-value problems, with a small parameter ε multiplying the first derivative. We derive necessary conditions for uniform convergence with respect to the small parameter ε, that is the solution of the difference scheme uih satisfies |uih−u(xi)| Ch, where C is independent of h and ε. We also derive sufficient conditions for uniform convergence and show that a subclass of schemes is also optimal in the sense that |uih−u(xi)| C min (h, ε). Finally, we show that this class contains higher-order schemes. 相似文献
937.
938.
939.
A survey of the state of SQA in Japan finds that the situation is much like, but slightly different than, that in the US. 相似文献
940.