全文获取类型
收费全文 | 9523篇 |
免费 | 258篇 |
国内免费 | 10篇 |
学科分类
工业技术 | 9791篇 |
出版年
2021年 | 122篇 |
2020年 | 100篇 |
2019年 | 99篇 |
2018年 | 117篇 |
2017年 | 113篇 |
2016年 | 144篇 |
2015年 | 114篇 |
2014年 | 179篇 |
2013年 | 475篇 |
2012年 | 308篇 |
2011年 | 391篇 |
2010年 | 305篇 |
2009年 | 331篇 |
2008年 | 400篇 |
2007年 | 374篇 |
2006年 | 338篇 |
2005年 | 279篇 |
2004年 | 249篇 |
2003年 | 261篇 |
2002年 | 235篇 |
2001年 | 175篇 |
2000年 | 161篇 |
1999年 | 165篇 |
1998年 | 241篇 |
1997年 | 196篇 |
1996年 | 174篇 |
1995年 | 182篇 |
1994年 | 170篇 |
1993年 | 161篇 |
1992年 | 168篇 |
1991年 | 118篇 |
1990年 | 130篇 |
1989年 | 145篇 |
1988年 | 128篇 |
1987年 | 134篇 |
1986年 | 127篇 |
1985年 | 172篇 |
1984年 | 154篇 |
1983年 | 132篇 |
1982年 | 149篇 |
1981年 | 144篇 |
1980年 | 100篇 |
1979年 | 133篇 |
1978年 | 130篇 |
1977年 | 118篇 |
1976年 | 117篇 |
1975年 | 97篇 |
1974年 | 96篇 |
1973年 | 102篇 |
1972年 | 66篇 |
排序方式: 共有9791条查询结果,搜索用时 31 毫秒
31.
Prediction of Undrained Sinkhole Collapse 总被引:2,自引:0,他引:2
Charles E. Augarde Andrei V. Lyamin Scott W. Sloan 《Canadian Metallurgical Quarterly》2003,129(3):197-205
Sinkholes are surface depressions or shafts resulting from the collapse of a submerged cavity in soil. The cavities that lead to sinkholes form as a result of underlying geology in limestone areas, or as a result of human activity such as mining or leakage from a sewer. The formation of sinkholes is often sudden and can lead to extensive damage and loss of life, especially in urban areas. Much of the literature on the subject of sinkhole formation is empirical in nature, often being associated with specific locations. This paper presents the results of a study, using numerical modeling, of the undrained stability of the submerged cavities that lead to sinkhole formation. Finite-element limit analysis techniques (using programs developed at the University of Newcastle) are used to obtain upper and lower bound values of a suitable load parameter, which bracket the exact solution. The results are compared to analytical solutions, both from literature and derived independently. 相似文献
32.
Richard F. D.; Bond Charles F. Jr.; Stokes-Zoota Juli J. 《Canadian Metallurgical Quarterly》2003,7(4):331
This article compiles results from a century of social psychological research, more than 25,000 studies of 8 million people. A large number of social psychological conclusions are listed alongside meta-analytic information about the magnitude and variability of the corresponding effects. References to 322 meta-analyses of social psychological phenomena are presented, as well as statistical effect-size summaries. Analyses reveal that social psychological effects typically yield a value of r equal to .21 and that, in the typical research literature, effects vary from study to study in ways that produce a standard deviation in r of .15. Uses, limitations, and implications of this large-scale compilation are noted. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
33.
Fellers Gloria; McInnis Charles; Cappelli Mario; Cragg Susan; Vaillancourt Raymond 《Canadian Metallurgical Quarterly》1987,19(1):108
The WAIS-R Information subtest was combined with 21 potential substitute Canadian content items and group-administered to 119 high school students ranging in age from 16 to 19 years. Seven acceptable substitute items were identified. Mean scores on the American items for the 16-17 and 18-19 age groups suggested that Canadians of these ages are not penalized by American content with respect to either Verbal or Full Scale IQ. Nevertheless, the research identified eight Information items, four easier and four more difficult than the standard WAIS-R implies. Similar results were noted in two previous studies of the WAIS-R, and indicate the extreme caution required for the clinical interpretation of intra test scatter. There is also evidence that item difficulty within the Information subtest may vary with the age of the subject. These results were considered indicative of the necessity for Canadian content Information items and the development of Canadian norms for an adapted WAIS-R Information subtest. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
34.
35.
Robbins Michael S.; Turner Charles W.; Alexander James F.; Perez Gonzalo A. 《Canadian Metallurgical Quarterly》2003,17(4):534
This study examined the relationship between alliance and retention in family therapy. Alliance was examined at the individual (parent and adolescent) and family levels (within-family differences). Participants were 34 families who received functional family therapy for the treatment of adolescent (aged 12-18 years) behavior problems. Families were classified as treatment dropouts (n=14) or completers (n=20). Videotapes of the first sessions were rated to identify parent and adolescent alliances with the therapist. Results demonstrated that individual parent and adolescent alliances did not predict retention. However, as hypothesized, dropout cases had significantly higher unbalanced alliances (parent minus adolescent) than did completer cases. These findings highlight the importance of alliances in functional family therapy and suggest that how the alliance operates in conjoint family therapy may be a function of systemic rather than of individual processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
36.
J. J. Poznanski and J. McLennan's (see record 1996-07039-001) article helpfully integrates research on a topic of considerable importance. Their derivation of two second-order "factors" (analytic-experiential and objective-subjective), as well as five more specific factors, in theoretical orientation is particularly helpful. In this comment, I seek to clarify how therapists' preferences for certain techniques relate to theoretical orientation. Reasons for the slow pace of research on multi-item self-report measures of theoretical orientation are suggested, as is an alternative measurement approach to that recommended by Poznanski and McLennan. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
37.
This article reviews the steps necessary to configure and implement a complex router internetwork. This article will specifically concentrate on Cisco routers, and since they support Transmission Control Protocol/Internet Protocol (TCP/IP) natively, it will concentrate on a backbone network employing that protocol. 相似文献
38.
Many combinatorial optimization problems are solved by a sequence of network flow computations on a network whose edge capacities are given as a function of a parameter λ. Recently Galloet al. [7] made a major advance in solving such parametric flow problems. They showed that for an important class of networks, calledmonotone parametric flow networks, a sequence ofO(n) flow computations could be solved in the same worst-case time bound as a single flow. However, these results require one of two special assumptions: either that the λ values are presented in increasing or decreasing order; or that the edge capacity functions are affine functions of λ. In this paper we show how to remove both of these assumptions while obtaining the same running times as in [7]. This observation generalizes and unifies the two major results of [7], and allows its ideas to be applied to many new combinatorial problems. Of greatest importance, it allows the efficient application of binary search and successive binary search to a sequence of network flow problems. 相似文献
39.
40.
Vinayak P. Dravid V. Ravikumar Michael R. Notis Charles E. Lyman Guy Dhalenne Alexandre Revcolevschi 《Journal of the American Ceramic Society》1994,77(10):2758-2762
A directionally solidified eutectic (DSE) of MnO-ZrO2 has been investigated using a variety of electron optical techniques. It is found that considerable MnO goes into ZrO2 to form a substitutional solid solution. About 14 wt% of MnO is soluble in ZrO2 close to the eutectic temperature. The solubility of ZrO2 in MnO, however, is quite low, less than 0.50 wt%. Electron diffraction experiments indicate that ZrO2 (MnO) has the cubic fluorite structure. Diffuse scattering, similar to other cubic zirconias (e.g., CaO, MgO stabilized zirconia), is also observed in manganese-stabilized zirconia. Diffuse scattering indicates the presence of oxygen vacancies and thus confirms the defect nature of the fluorite structure. Electron energy loss spectrometry (EELS) fine structure analysis of the Mn L23 edge provided clear evidence that Mn is present as Mn2+ in Mn-stabilized cubic ZrO2 . 相似文献