全文获取类型
收费全文 | 2243篇 |
免费 | 356篇 |
国内免费 | 73篇 |
专业分类
电工技术 | 11篇 |
综合类 | 236篇 |
化学工业 | 778篇 |
金属工艺 | 24篇 |
机械仪表 | 45篇 |
建筑科学 | 141篇 |
矿业工程 | 29篇 |
能源动力 | 16篇 |
轻工业 | 36篇 |
水利工程 | 30篇 |
石油天然气 | 24篇 |
武器工业 | 5篇 |
无线电 | 49篇 |
一般工业技术 | 143篇 |
冶金工业 | 568篇 |
原子能技术 | 9篇 |
自动化技术 | 528篇 |
出版年
2023年 | 16篇 |
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 31篇 |
2019年 | 29篇 |
2018年 | 43篇 |
2017年 | 58篇 |
2016年 | 115篇 |
2015年 | 128篇 |
2014年 | 149篇 |
2013年 | 182篇 |
2012年 | 102篇 |
2011年 | 157篇 |
2010年 | 142篇 |
2009年 | 158篇 |
2008年 | 156篇 |
2007年 | 143篇 |
2006年 | 166篇 |
2005年 | 134篇 |
2004年 | 135篇 |
2003年 | 116篇 |
2002年 | 74篇 |
2001年 | 68篇 |
2000年 | 34篇 |
1999年 | 23篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 19篇 |
1994年 | 11篇 |
1993年 | 18篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1966年 | 3篇 |
1962年 | 4篇 |
1959年 | 8篇 |
1958年 | 6篇 |
1957年 | 8篇 |
1956年 | 7篇 |
1955年 | 5篇 |
1954年 | 5篇 |
排序方式: 共有2672条查询结果,搜索用时 390 毫秒
101.
Stress Dilatancy and Fabric Dependencies on Sand Behavior 总被引:2,自引:0,他引:2
A stress dilatancy model with embedded microstructural information, originally developed by the writers, is used to illustrate the pivotal importance of dilatancy and fabric on the behavior of sand. Fabric, as a second-order tensor, enters into the stress dilatancy equation obtained from a microscopic analysis of an ensemble of rigid particles. Model simulations of sand behavior are carried out in triaxial stress conditions along strain paths with varying degrees of controlled dilation (or compaction) including isochoric deformations as a particular case. Under particular strain paths and fabric conditions, it is shown that a relatively dense sand can succumb to instability or liquefaction under other than isochoric (undrained) conditions. This phenomenon is in accord with laboratory experiments in which dilation or compaction is controlled by modulating the amount of water flowing in or out of a sand specimen during shearing. Mixed drained–undrained loading paths are also simulated with particular reference to fabric dependence at a fixed void ratio. Model simulations capture most of the observed characteristics of sand response, such as instability and asymptotic behavior under various conditions. 相似文献
102.
103.
It is believed that by adulthood, independent attachments to the mother and the father coalesce into a single state of mind with respect to attachment. If true, states of mind with respect to mothers and fathers should be concordant. Fifty-six young adults were administered two versions of the Adult Attachment Interview, each of which asked about their relationship with one parent. State of mind with respect to the father was significantly related to state of mind with respect to the mother, as were attachment styles regarding the two parents. Perceptions of attachment styles were not very related to corresponding states of mind but were related to inferred loving from a parent. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
104.
Hate crimes are those in which the victim is selected because of his or her actual or perceived race, color, religion, disability, sexual orientation, or national origin. Hate crime laws have frequently been met with objections. Whereas some objections are based in constitutional law, other objections invoke a variety of psychological constructs, including attitude, motivation, behavior, emotion, and intergroup relations. These objections can be illuminated by relevant psychological theory and research. Topics addressed include the measurement of motivation and intent, and distinctions among attitudes, emotions, and behavior. Hate crimes and other crimes are compared in terms of perpetrators, type and degree of violence, psychological and physical trauma suffered by victims, and community impact. Psychologically based defense strategies used by perpetrators of hate crimes are critiqued. Hate crime laws are also discussed in terms of the political and social values they reflect. Finally, research and policy implications are outlined, including implications for prevention and intervention at the individual, community, and law enforcement levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
105.
Smith J. David; Minda John Paul; Washburn David A. 《Canadian Metallurgical Quarterly》2004,133(3):398
In influential research, R. N. Shepard, C. I. Hovland, and H. M. Jenkins (1961) surveyed humans' categorization abilities using tasks based in rules, exclusive-or (XOR) relations, and exemplar memorization. Humans' performance was poorly predicted by cue-conditioning or stimulus-generalization theories, causing Shepard et al. to describe it in terms of hypothesis selection and rule application that were possibly supported by verbal mediation. The authors of the current article surveyed monkeys' categorization abilities similarly. Monkeys, like humans, found category tasks with a single relevant dimension the easiest and perceptually chaotic tasks requiring exemplar memorization the most difficult. Monkeys, unlike humans, found tasks based in XOR relations very difficult. The authors discuss the character and basis of the species difference in categorization and consider whether monkeys are the generalization-based cognitive system that humans are not. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
106.
Nitin K. Lautre Alakesh Manna 《The International Journal of Advanced Manufacturing Technology》2006,29(5-6):490-498
The paper presents a binary relational analysis and expert system base module for maintenance and fault diagnosis of CNC wire
EDM. The module proposes a framework of integrated maintenance and fault diagnosis system. The study explores the binary coded
matrix system, which plays an important role in prediction and diagnosis of wire electrical discharge machining (WEDM) faults
on the spot by expert guidance. In this study, 15 inputs were considered to observe eight probable causes with the help of
the forward and backward propagation algorithms. Inputs and output matrices were considered in the form of a square matrix.
To explain the fault diagnosis and to realize the importance of maintenance through advice, the detection of faults is investigated
through forward and back propagation of matrix transformation on the spot. It is an integrated backup that can be individually
focused when input and output parameter do not match. It is a time saving, knowledge acquisition, easy to maintain, and capable
of self-learning system. To verify the developed framework, 120 data sets were generated for proper analyzing of acquired
output through graphical representation. The paper also presents some of the important features of maintenance schedule and
probable causes of wire breakage with remedial actions in tabular form. The developed system can help the operators, trainees,
and manufacturing engineers in achieving trouble free machining through quick detection of faults and proper maintenance of
machines in actual practice. 相似文献
107.
The purpose of this study was to investigate the relation between internet dependence in university students in late adolescence and self-image. The research group consisted of first year university students studying in various departments of the Karadeniz Technical University Fatih Faculty of Education. The study was performed with 623 students, 454 female and 169 male. The Internet Dependence Questionnaire, the Offer Self-Image Questionnaire and a Personal Data Form were used for data collection. Pearson product moment coefficient and multiple linear regression analysis results showed that students' internet dependence was significantly negatively correlated with the self-image subdimensions intrafamilial and social relations, impulse control, coping ability and body image. Multiple linear regression analysis showed that the self-image subdimensions of intrafamilial and social relations and impulse control subdimensions significantly predict internet dependence. 相似文献
108.
The paper aims to develop an adjustment index based on OWA operators to enrich the results of diagnostic fuzzy models of business failure. A proposal to verify the diseases prediction accuracy of the models is also added. This allows a reduction of the map of causes or diseases detected in strategic defined areas. At the same time, these key areas can be disaggregated when an alert indicator is identified, and shows which of the causes need special attention. This application of OWA can encourage the development of suitable computer systems for monitoring companies’ problems, warn of failures and facilitate decision-making. In addition, taking Vigier and Terceño’s 2008 model as a benchmark, causes aggregation operators are introduced to evaluate alternative groupings, and the adjustment measure using approximate solutions is proposed to test the model’s prediction.The empirical estimation and the verification of the improvement proposals in a set of small and medium- sized enterprises (SMEs) in the construction industry are also presented. The functionality and the prediction capacity are thus measured and detected by monitoring key areas that warn about insolvency situations in the firm. 相似文献
109.
Nikolaj Petersen 《Centaurus; international magazine of the history of science and medicine》2013,55(3):294-318
The focus of this article is US military research in Greenland and its role in Danish‐American political relations in the early Cold War period 1945–1968. This was a period of intense US research activity that aimed to overcome the hostile Greenlandic environment and harness it for military purposes. In the US‐Danish defense agreement on Greenland of 1951 the USA got a free hand to develop three so‐called defense areas for military purposes, while it had to seek Danish permission for research and other activities outside these areas. The two partners had differing, but mainly compatible, interests in this process. The US interest was freedom to do research on the gigantic Greenland Icecap, while the Danish authorities emphasized the protection of its sovereignty over Greenland. The article follows the US research programs in the 1950s and 1960s and Danish responses in some detail, including the intriguing and still mysterious Camp Century project and its relationship with the US Army's Iceworm plan to deploy strategic missiles beneath the surface of the Greenland Icecap. 相似文献
110.
Qualitative locations describe the locations of spatial objects by relating them to a reference frame with qualitative relations. Existing models concerned with regional partitions are mainly topology-based and do not consider the effects of scale changes on locations. This study develops a direction-based multi-scale qualitative location (DMQL) model to fill this gap. First, a cell partition is defined by extending the borders of the minimum bounding rectangles of the regions in a regional partition. Relating spatial objects to all regions by a set of directions is equal to representing the objects as a set of cells in a cell partition. Second, due to the multiple cell representations of spatial objects and the changes in direction relations across scales, some approaches are presented to derive the direction changes between regions in different frames, between spatial objects and regions, and between spatial objects at different scales. Third, the location and relation consistencies of qualitative locations are evaluated based on the cell representations of spatial objects at multiple scales through a case study. The results indicate that the DMQL model can locate objects more precisely than the topology-based models. 相似文献