全文获取类型
收费全文 | 2538篇 |
免费 | 35篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 17篇 |
化学工业 | 462篇 |
金属工艺 | 52篇 |
机械仪表 | 36篇 |
建筑科学 | 87篇 |
矿业工程 | 5篇 |
能源动力 | 45篇 |
轻工业 | 201篇 |
水利工程 | 8篇 |
石油天然气 | 28篇 |
无线电 | 111篇 |
一般工业技术 | 341篇 |
冶金工业 | 826篇 |
原子能技术 | 31篇 |
自动化技术 | 326篇 |
出版年
2021年 | 17篇 |
2020年 | 16篇 |
2019年 | 15篇 |
2018年 | 21篇 |
2017年 | 23篇 |
2016年 | 32篇 |
2014年 | 24篇 |
2013年 | 164篇 |
2012年 | 47篇 |
2011年 | 72篇 |
2010年 | 65篇 |
2009年 | 70篇 |
2008年 | 65篇 |
2007年 | 77篇 |
2006年 | 77篇 |
2005年 | 75篇 |
2004年 | 60篇 |
2003年 | 52篇 |
2002年 | 62篇 |
2001年 | 60篇 |
2000年 | 50篇 |
1999年 | 40篇 |
1998年 | 78篇 |
1997年 | 76篇 |
1996年 | 67篇 |
1995年 | 53篇 |
1994年 | 43篇 |
1993年 | 56篇 |
1992年 | 47篇 |
1991年 | 31篇 |
1990年 | 46篇 |
1989年 | 43篇 |
1988年 | 36篇 |
1987年 | 36篇 |
1986年 | 48篇 |
1985年 | 49篇 |
1984年 | 35篇 |
1983年 | 48篇 |
1982年 | 47篇 |
1981年 | 30篇 |
1980年 | 24篇 |
1979年 | 50篇 |
1978年 | 46篇 |
1977年 | 45篇 |
1976年 | 54篇 |
1975年 | 19篇 |
1974年 | 30篇 |
1973年 | 37篇 |
1972年 | 30篇 |
1969年 | 19篇 |
排序方式: 共有2576条查询结果,搜索用时 15 毫秒
81.
Increasingly, application developers are looking for ways to provide users with higher levels of personalization that capture different elements of a user’s operating context, such as her location, the task that she is currently engaged in, who her colleagues are, etc. While there are many sources of contextual information, they tend to vary from one user to another and also over time. Different users may rely on different location tracking functionality provided by different cell phone operators; they may use different calendar systems, etc. In this article, we describe work on a Semantic e-Wallet aimed at supporting automated identification and access of personal resources, each represented as a Semantic Web Service. A key objective is to provide a Semantic Web environment for open access to a user’s contextual resources, thereby reducing the costs associated with the development and maintenance of context-aware applications. A second objective is, through Semantic Web technologies, to empower users to selectively control who has access to their contextual information and under which conditions. This work has been carried out in the context of myCampus, a context-aware environment aimed at enhancing everyday campus life. Empirical results obtained on Carnegie Mellon’s campus are discussed. 相似文献
82.
This paper presents a formulation of the facilities block layout problem which explicitly considers uncertainty in material handling costs on a continuous scale by use of expected values and standard deviations of product forecasts. This formulation is solved using a genetic algorithm meta-heuristic with a flexible bay construct of the departments and total facility area. It is shown that depending on the attitude of the decision-maker towards uncertainty, the optimal design can change significantly. Furthermore, designs can be optimized directly for robustness over a range of uncertainty that is pre-specified by the user. This formulation offers a computationally tractable and intuitively appealing alternative to previous stochastic layout formulations that are based on discrete scenario probabilities. 相似文献
83.
Rats were exposed to shock-paired cues immediately after training on an appetitive preference task. Elevated levels of freezing in and active avoidance of the shock-paired compartment were observed, and memory for the appetitive task was improved when tested 24 hr later. Intra-amygdala muscimol injected before the posttraining exposure eliminated freezing, avoidance, and memory modulation. The blockade of both freezing and active avoidance, which involve competing behavioral tendencies, makes it unlikely that the amygdala itself generates either behavior. The elimination of conditioned memory modulation suggests that conditioned neurohormonal responses were blocked. These conditioned internal responses may comprise the intervening variable of "conditioned fear" and may promote observable behaviors, the form of which is determined by the environment in which they occur. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
Lambert Sharon F.; McCreary Beth T.; Joiner Thomas E.; Schmidt Norman B.; Ialongo Nicolas S. 《Canadian Metallurgical Quarterly》2004,72(5):904
In this study, the authors examined the validity of the tripartite model of anxiety and depression (L. A. Clark & D. Watson, 1991) in a community epidemiological sample of 467 urban African American youth. Participants completed the Baltimore How I Feel (N. S. Ialongo, S. G. Kellam, & J. Poduska, 1999), a measure of anxiety and depressive symptoms, in Grades 6 and 9. Confirmatory factor analyses indicated that a 3-factor model representing the tripartite model fit the data well and better than competing models. Longitudinal confirmatory factor analysis revealed configural invariance of the tripartite factor structure. However, a predicted divergence among dimensions over time was not evidenced. High correlations among the tripartite dimensions suggest that anxiety and mood symptoms may not differentiate in urban youth. Results are discussed in terms of the ethnicity and urban context of this community sample. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
85.
A. Norman A. Ahmed J. Chou A. Dalal K. Fortson M. Jindal C. Kurz H. Lee K. Payne R. Rando K. Sheppard E. Sublett J. Sussman I. White 《Computational Economics》2004,23(2):173-192
A consumer entering a new bookstore can face more than 250,000alternatives. The efficiency of compensatory and noncompensatory decisionrulesfor finding a preferred item depends on the efficiency of their associatedinformation operators. At best, item-by-item information operators lead tolinear computational complexity; set information operators, on the other hand,can lead to constant complexity. We perform an experiment demonstrating thatsubjects are approximately rational in selecting between sublinear and linearrules. Many markets are organized by attributes that enable consumers toemploya set-selection-by-aspect rule using set information operations. In cyberspacedecision rules are encoded as decision aids. 相似文献
86.
A randomisation procedure is given for making tests on the coefficients of regression equations developed from data which arise from a general multivariate distribution, not necessarily Normal. The procedure makes use of a six card computer subroutine which randomly permutes an array of numbers. This subroutine is extremely useful and can be employed in many other types of problems. 相似文献
87.
Within immunization programs supported by the World Health Organization, current practice is to use a vial as the basic unit for managing vaccine inventories at the clinic level. In addition to being inconvenient, this has the potential to induce errors in the ordering process. We propose alternative ordering policies based on using inner pack quantities corresponding to secondary vaccine packaging and draw upon visual management, simplified inventory tracking, better housekeeping, and other lean related concepts that have been used in the manufacturing sector to simplify and improve the vaccine inventory management system. We present analyses that show that the proposed polices only require very modest increases in fixed storage and transport requirements. 相似文献
88.
Ixent Galpin Alvaro A. A. Fernandes Norman W. Paton 《The VLDB Journal The International Journal on Very Large Data Bases》2013,22(4):495-517
The resource-constrained nature of mote-level wireless sensor networks (WSNs) poses challenges for the design of a general-purpose sensor network query processors (SNQPs). Existing SNQPs tend to generate query execution plans (QEPs) that are selected on the basis of a fixed, implicit expectation, for example, that energy consumption should be kept as small as possible. However, in WSN applications, the same query may be subject to several, possibly conflicting, quality-of-service (QoS) expectations concomitantly (for example maximizing data acquisition rates subject to keeping energy consumption low). It is also not uncommon for the QoS expectations to change over the lifetime of a deployment (for example from low to high data acquisition rates). This paper describes optimization algorithms that respond to stated QoS expectations (about acquisition rate, delivery time, energy consumption and lifetime) when making routing, placement, and timing decisions for in-WSN query processing. The paper shows experimentally that QoS-awareness offers significant benefits in responding to, and reconciling, diverse QoS expectations, thereby enabling QoS-aware SNQPs to generate efficient QEPs for a broader range WSN applications than has hitherto been possible. 相似文献
89.
The routines of information work are commonplace yet difficult to characterize. Although cognitive models have successfully characterized routine tasks within which there is little variation, a large body of ethnomethodological research has identified the inherent nonroutineness of routines in information work. We argue that work does not fall into discrete classes of routine versus nonroutine; rather, task performance lies on a continuum of routineness, and routineness metrics are important to the understanding of workplace multitasking. In a study of 10 information workers shadowed for 3 whole working days each, we utilize the construct of working sphere to model projects/tasks as a network of humans and artifacts. Employing a statistical technique called T-pattern analysis, we derive measures of routineness from these real-world data. In terms of routineness, we show that information workers experience archetypes of working spheres. The results indicate that T-patterns of interactions with information and computational media are important indicators of facets of routineness and that these measures are correlated with workers' affective states. Our results are some of the first to demonstrate how regular temporal patterns of media interaction in tasks are related to stress. These results suggest that designs of systems to facilitate so-called routine work should consider the degrees to which a person's working spheres fall along varying facets of routineness. 相似文献
90.
Ivan Rodero David Villegas Norman Bobroff Yanbin Liu Liana Fong S. Masoud Sadjadi 《Journal of Grid Computing》2013,11(2):311-336
The goal of Grid computing is to integrate the usage of computer resources from cooperating partners in the form of Virtual Organizations (VO). One of its key functions is to match jobs to execution resources efficiently. For interoperability between VOs, this matching operation occurs in resource brokering middleware, commonly referred to as the meta-scheduler or meta-broker. In this paper, we present an approach to a meta-scheduler architecture, combining hierarchical and peer-to-peer models for flexibility and extensibility. Interoperability is further promoted through the introduction of a set of protocols, allowing meta-schedulers to maintain sessions and exchange job and resource state using Web Services. Our architecture also incorporates a resource model that enables an efficient resource matching across multiple Virtual Organizations, especially where the compute resources and state are dynamic. Experiments demonstrate these new functional features across three distributed organizations (BSC, FIU, and IBM), that internally use different job scheduling technologies, computing infrastructure and security mechanisms. Performance evaluations through actual system measurements and simulations provide the insights on the architecture’s effectiveness and scalability. 相似文献