全文获取类型
收费全文 | 7970篇 |
免费 | 255篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 72篇 |
综合类 | 5篇 |
化学工业 | 1424篇 |
金属工艺 | 158篇 |
机械仪表 | 166篇 |
建筑科学 | 419篇 |
矿业工程 | 13篇 |
能源动力 | 231篇 |
轻工业 | 717篇 |
水利工程 | 114篇 |
石油天然气 | 38篇 |
无线电 | 630篇 |
一般工业技术 | 1331篇 |
冶金工业 | 1712篇 |
原子能技术 | 64篇 |
自动化技术 | 1138篇 |
出版年
2023年 | 37篇 |
2022年 | 87篇 |
2021年 | 111篇 |
2020年 | 100篇 |
2019年 | 104篇 |
2018年 | 117篇 |
2017年 | 133篇 |
2016年 | 125篇 |
2015年 | 149篇 |
2014年 | 200篇 |
2013年 | 442篇 |
2012年 | 364篇 |
2011年 | 454篇 |
2010年 | 317篇 |
2009年 | 373篇 |
2008年 | 467篇 |
2007年 | 390篇 |
2006年 | 339篇 |
2005年 | 352篇 |
2004年 | 283篇 |
2003年 | 258篇 |
2002年 | 236篇 |
2001年 | 136篇 |
2000年 | 115篇 |
1999年 | 152篇 |
1998年 | 300篇 |
1997年 | 195篇 |
1996年 | 192篇 |
1995年 | 143篇 |
1994年 | 123篇 |
1993年 | 123篇 |
1992年 | 96篇 |
1991年 | 72篇 |
1990年 | 79篇 |
1989年 | 103篇 |
1988年 | 57篇 |
1987年 | 68篇 |
1986年 | 63篇 |
1985年 | 84篇 |
1984年 | 79篇 |
1983年 | 70篇 |
1982年 | 60篇 |
1981年 | 72篇 |
1980年 | 45篇 |
1979年 | 49篇 |
1978年 | 38篇 |
1977年 | 45篇 |
1976年 | 59篇 |
1975年 | 37篇 |
1973年 | 26篇 |
排序方式: 共有8232条查询结果,搜索用时 15 毫秒
31.
Brian J. Ross 《Formal Aspects of Computing》1997,9(3):331-348
Imperative programs can be inverted directly from their forward-directed program code with the use of logical inference. The relational semantics of imperative computations treats programs as logical relations over the observable state of the environment, which is taken to be the state of the variables in memory. Program relations denote both forward and backward computations, and the direction of the computation depends upon the instantiation pattern of arguments in the relation. This view of inversion has practical applications when the relational semantics is treated as a logic program. Depending on the logic programming inference scheme used, execution of this relational program can compute the inverse of the imperative program. A number of nontrivial imperative computations can be inverted with minimal logic programming tools. 相似文献
32.
33.
Francis E. Powell Brian W. Brooks 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1993,57(1):65-71
Dimensionless material balance equations describing an uninhibited enzyme hydrolysis process in a semi-batch reactor (i.e. fed-batch reactor) are formulated; numerical solution of these equations provided concentration profiles of the enzyme-substrate complex by using published kinetic parameters. The unrestricted values obtained are compared with estimates based separately on the reaction steady state and stationary state assumptions. Results are discussed in terms of the enzyme/substrate inventory used and it is found that the reaction steady state is a satisfactory approximation only when this ratio is sufficiently small. The stationary state may be a better approximation at other values, particularly when enzyme is added to substrate or when an empty tank is being filled. Reaction yields from semi-batch and batch operations are compared. Processing takes longer in the semi-batch operations and complete conversions are only practical in this mode when enzyme is added to substrate. 相似文献
34.
35.
Developing competency-based methods for near-real-time air combat problem solving assessment 总被引:1,自引:0,他引:1
Air combat scenarios present unique problems where the solution is not obvious. An advanced networked simulation environment can be used to train high-level cognitive air combat skills such as problem solving. A problem in the development of principled and construct oriented assessment is related to determining the level of specificity of the assessment. We present a detailed discussion of the definition of critical competencies associated with combat mission problem solving performance, and we describe our approach to develop and implement an embedded performance assessment system that maps outcomes to these competencies. Finally, we discuss the implications for our approach for comprehensive assessment and discuss our goals for an evaluation of the competency-based approach to assessment. 相似文献
36.
37.
A one–dimensional, transient thermal degradation heat transfer model for the response of composite materials when exposed to fire is presented. The model can handle layers of different materials. Material properties are functions of temperature. The reaction can be specified using Arrhenius‐type parameters or by inputting a density–temperature relationship determined by any experimental technique such as thermogravimetric analysis. The model is validated against the experimental data presented in Boyer's 1984 dissertation. Overall, the model provides excellent agreement with the experimental data. It is shown that very little difference is found between results arrived at by Arrhenius kinetics and results obtained by specifying the easier to measure density–temperature relationship. From this it is concluded that this technique is a viable alternative to Arrhenius‐type models. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
38.
On 25 June 2003, a new mass-mailing worm, Sobig.E, emerged. The worm was highly successful at infecting computer systems. It is the fifth revision of a worm that first raised its ugly head in January 2003. There is strong evidence that spammers use infected computers to relay unsolicited commercial e-mail. 相似文献
39.
Abstract. Certification is one criterion that employers seek when hiring network professionals. Many employers assume a certified network professional is better able to manage networked resources than is a non-certified counterpart. Therefore, employers often offer a monetary premium to attract certified network professionals. By measuring end-user perceptions, the current study empirically assesses the popular industry assumption that certified network professionals are more adept managers of network resources than those individuals who are not certified network professionals. Analyses of a data derived from 299 end-users of 11 separate local area networks indicate no statistically significant difference exists between the capabilities of certified network professionals and non-certified network professionals. 相似文献
40.
Trust for Ubiquitous,Transparent Collaboration 总被引:1,自引:0,他引:1
In this paper, trust-based recommendations control the exchange of personal information between handheld computers. Combined with explicit risk analysis, this enables unobtrusive information exchange, while limiting access to confidential information. The same model can be applied to a wide range of mobile computing tasks, such as managing personal address books and electronic diaries, to automatically provide an appropriate level of security. Recommendations add structure to the information, by associating categories with data and with each other, with degrees of trust belief and disbelief. Since categories also in turn confer privileges and restrict actions, they are analogous to rôles in a Rôle-Based Access Control system, while principals represent their trust policies in recommendations. Participants first compute their trust in information, by combining their own trust assumptions with others' policies. Recommendations are thus linked together to compute a considered, local trust assessment. Actions are then moderated by a risk assessment, which weighs up costs and benefits, including the cost of the user's time, before deciding whether to allow or forbid the information exchange, or ask for help. By unifying trust assessments and access control, participants can take calculated risks to automatically yet safely share their personal information. 相似文献