全文获取类型
收费全文 | 26698篇 |
免费 | 773篇 |
国内免费 | 33篇 |
专业分类
电工技术 | 329篇 |
综合类 | 14篇 |
化学工业 | 5923篇 |
金属工艺 | 521篇 |
机械仪表 | 464篇 |
建筑科学 | 1159篇 |
矿业工程 | 332篇 |
能源动力 | 650篇 |
轻工业 | 1725篇 |
水利工程 | 226篇 |
石油天然气 | 245篇 |
无线电 | 1711篇 |
一般工业技术 | 4081篇 |
冶金工业 | 6150篇 |
原子能技术 | 265篇 |
自动化技术 | 3709篇 |
出版年
2022年 | 246篇 |
2021年 | 411篇 |
2020年 | 266篇 |
2019年 | 346篇 |
2018年 | 423篇 |
2017年 | 369篇 |
2016年 | 485篇 |
2015年 | 391篇 |
2014年 | 614篇 |
2013年 | 1652篇 |
2012年 | 937篇 |
2011年 | 1201篇 |
2010年 | 923篇 |
2009年 | 972篇 |
2008年 | 1149篇 |
2007年 | 1063篇 |
2006年 | 974篇 |
2005年 | 881篇 |
2004年 | 743篇 |
2003年 | 712篇 |
2002年 | 705篇 |
2001年 | 486篇 |
2000年 | 390篇 |
1999年 | 447篇 |
1998年 | 441篇 |
1997年 | 427篇 |
1996年 | 474篇 |
1995年 | 443篇 |
1994年 | 451篇 |
1993年 | 436篇 |
1992年 | 431篇 |
1991年 | 271篇 |
1990年 | 410篇 |
1989年 | 388篇 |
1988年 | 337篇 |
1987年 | 404篇 |
1986年 | 348篇 |
1985年 | 441篇 |
1984年 | 463篇 |
1983年 | 398篇 |
1982年 | 375篇 |
1981年 | 297篇 |
1980年 | 298篇 |
1979年 | 357篇 |
1978年 | 299篇 |
1977年 | 238篇 |
1976年 | 217篇 |
1975年 | 245篇 |
1974年 | 217篇 |
1973年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
61.
Prevention and Mitigation Strategies to Address Recent Brittle Fractures in Steel Bridges 总被引:1,自引:0,他引:1
Robert J. Connor Eric J. Kaufmann John W. Fisher William J. Wright 《Canadian Metallurgical Quarterly》2007,12(2):164-173
Brittle fracture results in unplanned loss of service, very costly repairs, concern regarding the future safety of the structure, and potential loss of life. These types of failures are most critical when there is no evidence of fatigue cracking leading up to the fracture and the fracture origin is concealed from view. Hence, the failure occurs without warning and the details are, essentially, noninspectable. In these cases, it appears desirable to take a proactive approach and introduce preventative retrofits to reduce the potential for future crack development. These efforts will help ensure that the likelihood of unexpected fractures is minimized. This paper examines the behavior of two bridge structures in which brittle fractures have developed in recent times, discusses the causes of the failures, and offers suggested design strategies for prevention and retrofit mitigation techniques. In situations where considerable uncertainty exists in the prediction of accumulated damage or in the ability to reliably inspect critical details, preemptive retrofit strategies appear to be highly desirable. 相似文献
62.
63.
Emergency department status boards: user-evolved artefacts for inter- and intra-group coordination 总被引:1,自引:1,他引:0
Robert L. Wears Shawna J. Perry Stephanie Wilson Julia Galliers James Fone 《Cognition, Technology & Work》2007,9(3):163-170
Large, easily viewed status boards are commonly used in some healthcare settings such as emergency departments, operating
theaters, intensive care units, and inpatient wards. Because these artefacts were developed by front-line users, and have
little to no supervisory or regulatory control, they offer valuable insights into the theories of work and hazard held by
those users. Although the status boards case were locally developed over many years for within-group coordination, they have
also become useful for between-group coordination across organizational boundaries. In this paper, we compare and contrast
the use of such status boards in two disparate settings: a US emergency department, and a UK pediatric ward, and note striking
similarities in their form and usage, despite the large differences in setting. 相似文献
64.
Ronald R. Delyser Sheila S. Thompson Jerry Edelstein Corinne Lengsfeld Albert J. Rosa Paul J. Rullkoetter Robert Whitman Margaret Whitt 《工程教育杂志》2003,92(3):269-273
A team of faculty members at the University of Denver changed the learning environment in key courses in the Department of Engineering from predominately teacher centered to student centered. Through this funded project new grading methods were implemented, classrooms were renovated and wired with studio layouts to facilitate learning, the Engineering Circuits Laboratory was rewired and instrumented for automated data acquisition and reporting, and two new pedagogical approaches were developed. At the onset of the project, six goals were established related to student learning. The introduction of industry standard hardware and software provided students with unprecedented hands‐on experience and project related activities stimulated faculty innovations in other current and future courses. Assessment results indicate that the new grading system improved the clarity of expectations for students before assignments were given resulting in increased reported motivation for learning in many courses. Even though course GPAs did not always reflect higher achievement on graded work, faculty members firmly believe that deeper understanding was achieved because more complex material was assimilated. 相似文献
65.
Robert R. Gillies Jayne Brim Box Jürgen Symanzik Eli J. Rodemaker 《Remote sensing of environment》2003,86(3):411-422
Impervious surface area (ISA) was derived for a period from 1979 to 1997 from Landsat MSS and TM data for the Line Creek watershed that lies to the south of the city of Atlanta, GA. The change in ISA is presented as an ecological indicator to examine the cumulative water resource impacts on mussel population in three sub-watersheds of Line Creek—namely, Line, Flat, and Whitewater creeks. The satellite analysis shows that ISA expansion occurred substantially from 1987 to 1997 and is predominantly in industrial, commercial, and shopping center (ICS) complexes but also in smaller lot-size residential development. Evidence of mussel habitat degradation is indicated and loss of species (in the region of 50 to 70%) is present in areas where ISA expansion is observed—specifically in ICS complex development in and around Peachtree City that drains directly into the Line and Flat creeks. This is in marked contrast to Whitewater Creek where overall development of ISA is less and no major loss of mussel species is observed. 相似文献
66.
The goal of the PMS project is to produce an environment in which the intelligent online assessment of the design for large-scale ADA programming projects is provided. The focus is on the representation of knowledge about the design process for an individual module. Changes in pseudocode complexity are measured in terms of partial metrics. These metrics can take the designers inferences about the pseudocode program structure into account when assessing module complexity. Next, a model of the stepwise refinement process is given which demonstrates how pseudocode elaboration decisions can be modelled in partial metric terms. Finally, the decisions associated with each refinement step for 17 example refinements taken from the computer science literature are described using partial metrics. 相似文献
67.
Robert Kass 《User Modeling and User-Adapted Interaction》1991,1(3):203-258
This paper reviews existing methods for building user models to support adaptive, interactive systems, identifies sigificant problems with these approaches, and describes a new method for implicitly acquiring user models from an ongoing user-system dialog. Existing explicit user model acquisition methods, such as user edited models or model building dialogs put additional burden on the user and introduce artificial model acquisition dialogs. Hand coding stereotypes, another explicit acquisition method, is a tedious and error-prone process. On the other hand, implicit acquisition techniques such as computing presuppositions or entailments either draw too few inferences to be generally useful, or too many to be trusted.In contrast, this paper describes GUMAC, a General User Model Acquisition Component that uses heuristic rules to make default inferences about users' beliefs from their interaction with an advisory expert system. These rules are based on features of human action and conversation that constrain people's behavior and establish expectations about their knowledge. The application of these rules is illustrated with two examples of extended dialogs between users and an investment advisory system. During the course of these conversations, GUMAC is able to acquire an extensive model of the users' beliefs about the aspects of the domain considered in the dialog. These models, in turn, provide the sort of information needed by an explanation generator to tailor explanations the advisory system gives to its users. 相似文献
68.
Joos F. Miguel Snaddon Robert W. L. Johnson Neil A. 《Industry Applications, IEEE Transactions on》1985,(6):1366-1372
Droplet growth is examined in a water-in-oil type emulsion where the droplets are subjected exclusively to viscous and dielectrophoretic forces. The latter are produced by the interaction of the droplets with an otherwise uniformly imposed electric field. Theoretical considerations are presented as a basis for understanding and interpreting the experiments. An emulsion consisting of deionized water droplets in a silicone oil of specific gravity I is subjected to a uniform 60 Hz, ac electrostatic field. Initially, the droplets are fairly monodisperse with mean diameters of approximately 25 , sm. The changes in droplet size distributions with time are examined with a laser diffraction system for water volume fractions ranging from 0.001 to 0.1 and applied fields ranging from 52 to 520 kVm-1. The average droplet size increases exponentially with time; we examine the exponent's dependence on average field strength and droplet volume fraction. 相似文献
69.
Robert Schifreen 《Network Security》1994,1994(10):17-19
We have no wish to frighten our readers, but here's a simple guide to some of the things hackers can do to access your system or network. Bet you didn't know there were so many ways to get in! 相似文献
70.
Robert Hieb R. Kent Dybvig Claude W. Anderson III 《Higher-Order and Symbolic Computation》1994,7(1):83-109
Continuations have proven to be useful for implementing a variety of control structures, including exception handling facilities and breadth-first searching algorithms. However, traditional continuations are not useful in the presence of concurrency, because the notion of the rest of the computation represented by a continuation does not in general make sense. Traditional continuations can also be difficult to use in nonconcurrent settings, since their global nature is sometimes problematic. This article presents a new type of continuation, called asubcontinuation. Just as a traditional continuation represents the rest of a computation ¿from a given point in the computation, a subcontinuation represents the rest of asubcomputation ¿from a given point in the subcomputation. Subcontinuations may be used to control tree-structured concurrency by allowing nonlocal exits to arbitrary points in a process tree and allowing the capture of a subtree of a computation as a composable continuation for later use. In the absence of concurrency the localized control achievable with subcontinuations makes them more useful than traditional continuations. 相似文献