全文获取类型
收费全文 | 780953篇 |
免费 | 23535篇 |
国内免费 | 9665篇 |
专业分类
电工技术 | 21639篇 |
技术理论 | 14篇 |
综合类 | 11720篇 |
化学工业 | 121760篇 |
金属工艺 | 29449篇 |
机械仪表 | 28224篇 |
建筑科学 | 32427篇 |
矿业工程 | 6211篇 |
能源动力 | 21758篇 |
轻工业 | 74234篇 |
水利工程 | 7794篇 |
石油天然气 | 14347篇 |
武器工业 | 1361篇 |
无线电 | 99725篇 |
一般工业技术 | 130111篇 |
冶金工业 | 121230篇 |
原子能技术 | 9715篇 |
自动化技术 | 82434篇 |
出版年
2023年 | 4349篇 |
2022年 | 8003篇 |
2021年 | 11798篇 |
2020年 | 8544篇 |
2019年 | 8497篇 |
2018年 | 10857篇 |
2017年 | 11747篇 |
2016年 | 11710篇 |
2015年 | 12051篇 |
2014年 | 17491篇 |
2013年 | 39351篇 |
2012年 | 26504篇 |
2011年 | 34478篇 |
2010年 | 27522篇 |
2009年 | 29527篇 |
2008年 | 30139篇 |
2007年 | 29989篇 |
2006年 | 28634篇 |
2005年 | 25999篇 |
2004年 | 22408篇 |
2003年 | 21386篇 |
2002年 | 20150篇 |
2001年 | 19979篇 |
2000年 | 18910篇 |
1999年 | 20658篇 |
1998年 | 40941篇 |
1997年 | 29866篇 |
1996年 | 23608篇 |
1995年 | 18567篇 |
1994年 | 16236篇 |
1993年 | 15283篇 |
1992年 | 11253篇 |
1991年 | 10385篇 |
1990年 | 9632篇 |
1989年 | 9135篇 |
1988年 | 8667篇 |
1987年 | 7147篇 |
1986年 | 6900篇 |
1985年 | 8357篇 |
1984年 | 7654篇 |
1983年 | 6779篇 |
1982年 | 6237篇 |
1981年 | 6276篇 |
1980年 | 5837篇 |
1979年 | 5523篇 |
1978年 | 5105篇 |
1977年 | 6191篇 |
1976年 | 8182篇 |
1975年 | 4287篇 |
1974年 | 4063篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
Many activities in today's organizations are becoming ever more dependent on communications and computer networks, and network managers are faced with the enormous challenge of increasing the availability and efficiency of their infrastructures, which grow both in size and complexity. This makes it crucial to plan network operation systematically, to define and implement appropriate procedures for regular monitoring and performance assessment, and to set up proper tools for maintenance and troubleshooting purposes. Furthermore, proactive network testing must be pursued; it is vital to gather some ideas of normal network operation documented in order to have a comparison term when problems occur. The article has dealt with the measurement instruments and procedures currently adopted for network testing and advances in the field for the I&M research community. 相似文献
882.
Six synthesized magnesium aluminate spinel-based refractory compositions used in steel and cement applications, were prepared using a two stage sintering process at 1760 °C, starting with approximately 1:1 wt% ratio of pure magnesia and alumina with additions of zirconium silicate (0.5, 1.0 and 2.0 wt%) and chromite (2.0, 3.0 and 5.0 wt%). These compositions were investigated for effects on densification, chemical and mineralogical phases formed. 相似文献
883.
Heidi Bernas Arie J. Plomp Johannes H. Bitter Dmitry Yu. Murzin 《Catalysis Letters》2008,120(1-2):8-13
The density functional theory (DFT/B3LYP) calculations were applied to investigate the interaction of a Pt6 particle with the ZSM-5 zeolite framework. The electronic structure of the metal particle is strongly affected by the interaction with basic framework oxygens and acid sites of the zeolite support. Adsorption on basic sites (Eads = 6 kcal/mol) favors the formation of the electron enriched metal cluster. Interaction of the platinum cluster with the acid site characterized by stabilization energy of 47 kcal/mol results in oxidation of the metal particle and suppression of Brønsted acidity of the support. The hypothesis is put forward that the oxidized platinum particle can function as an active site for the alkane isomerisation on platinum supported high silica zeolites. 相似文献
884.
885.
886.
Rosenberg Florian Curbera Francisco Duftler Matthew J. Khalaf Rania 《Internet Computing, IEEE》2008,12(5):24-31
The use of RESTful Web services has gained momentum in the development of distributed applications based on traditional Web standards such as HTTP. In particular, these services can integrate easily into various applications, such as mashups. Composing RESTful services into Web-scale workflows requires a lightweight composition language that's capable of describing both the control and data flow that constitute a workflow. The authors address these issues with Bite, a lightweight and extensible composition language that enables the creation of Web-scale workflows and uses RESTful services as its main composable entities. 相似文献
887.
888.
Carlos Fernandes Agostinho C. Rosa 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2008,12(10):955-979
Mate selection plays a crucial role in both natural and artificial systems. While traditional Evolutionary Algorithms (EA)
usually engage in random mating strategies, that is, mating chance is independent of genotypic or phenotypic distance between
individuals, in natural systems non-random mating is common, which means that somehow this mechanism has been favored during
the evolutionary process. In non-random mating, the individuals mate according to their parenthood or likeness. Previous studies
indicate that negative assortative mating (AM)—also known as dissortative mating—, which is a specific type of non-random mating, may improve EAs performance by maintaining the genetic diversity of the
population at a higher level during the search process. In this paper we present the Variable Dissortative Mating Genetic Algorithm (VDMGA). The algorithm holds a mechanism that varies the GA’s mating restrictions during the run by means of simple rule
based on the number of chromosomes created in each generation and indirectly influenced by the genetic diversity of the population.
We compare VDMGA not only with traditional Genetic Algorithms (GA) but also with two preceding non-random mating EAs: the
CHC algorithm and the negative Assortative Mating Genetic Algorithm (nAMGA). We intend to study the effects of the different methods in the performance of GAs and verify the reliability of
the proposed algorithm when facing an heterogeneous set of landscapes. In addition, we include the positive Assortative Mating Genetic Algorithm (pAMGA) in the experiments in order test both negative and positive AM mechanisms, and try to understand if and when negative
AM (or DM) speeds up the search process or enables the GAs to escape local optima traps. For these purposes, an extensive
set of optimization test problems was chosen to cover a variety of search landscapes with different characteristics. Our results
confirm that negative AM is effective in leading EAs out of local optima traps, and show that the proposed VDMGA is at least
as efficient as nAMGA when applied to the range of our problems, being more efficient in very hard functions were traditional
GAs usually fail to escape local optima. Also, scalability tests have been made that show VDMGA ability to decrease optimal
population size, thus reducing the amount of evaluations needed to attain global optima. We like to stress that only two parameters
need to be hand-tuned in VDMGA, thus reducing the tuning effort present in traditional GAs and nAMGA. 相似文献
889.
890.