全文获取类型
收费全文 | 670篇 |
免费 | 10篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 48篇 |
机械仪表 | 2篇 |
建筑科学 | 45篇 |
能源动力 | 5篇 |
轻工业 | 45篇 |
水利工程 | 4篇 |
无线电 | 19篇 |
一般工业技术 | 183篇 |
冶金工业 | 261篇 |
原子能技术 | 3篇 |
自动化技术 | 64篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 27篇 |
2017年 | 33篇 |
2016年 | 4篇 |
2015年 | 10篇 |
2014年 | 5篇 |
2013年 | 67篇 |
2012年 | 39篇 |
2011年 | 30篇 |
2010年 | 50篇 |
2009年 | 30篇 |
2008年 | 26篇 |
2007年 | 21篇 |
2006年 | 18篇 |
2005年 | 29篇 |
2004年 | 24篇 |
2003年 | 14篇 |
2002年 | 31篇 |
2001年 | 15篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1975年 | 4篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1890年 | 1篇 |
排序方式: 共有680条查询结果,搜索用时 187 毫秒
631.
Trocki Karen F.; Drabble Laurie A.; Midanik Lorraine T. 《Canadian Metallurgical Quarterly》2009,23(4):620
This study examined patterns of smoked substances (cigarettes and marijuana) among heterosexuals, gays, lesbians, and bisexuals based on data from the 2000 National Alcohol Survey, a population-based telephone survey of adults in the United States. We also examined the effect of bar patronage and sensation seeking/impulsivity (SSImp) on tobacco and marijuana use. Sexual orientation was defined as lesbian or gay self-identified, bisexual self-identified, heterosexual self-identified with same-sex partners in the past 5 years, and exclusively heterosexual (heterosexual self-identified, reporting no same-sex partners). Findings indicate that bisexual women and heterosexual women reporting same-sex partners had higher rates of cigarette smoking than exclusively heterosexual women. Bisexual women, lesbians, and heterosexual women with same-sex partners also used marijuana at significantly higher rates than exclusively heterosexual women. Marijuana use was significantly greater and tobacco use was elevated among gay men compared with heterosexual men. SSImp was associated with greater use of both of these substances across nearly all groups. Bar patronage and SSImp did not buffer the relationship between sexual identity and smoking either cigarettes or marijuana. These findings suggest that marijuana and tobacco use differ by sexual identity, particularly among women, and underscore the importance of developing prevention and treatment services that are appropriate for sexual minorities. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
632.
Staskal DF Scott LL Haws LC Luksemburg WJ Birnbaum LS Urban JD Williams ES Paustenbach DJ Harris MA 《Environmental science & technology》2008,42(17):6755-6761
Despite the growing public interest in polybrominated diphenyl ethers (PBDEs), there are relatively few studies in the published literature which characterize and quantify human intake of these compounds. In this study, PBDE concentrations were measured in southern Mississippi catfish to determine background levels, daily intake, and risk associated with the consumption of these chemicals from a primary food source for residents in this region of the United States. A total of 33 wild catfish samples were collected from five sites, and 28 farm-raised catfish samples were purchased, all of which were from locations in southern Mississippi. All samples were analyzed for 43 PBDEs (mono- through deca-congeners) using high-resolution gas chromatography-mass spectrometry. Both PBDE concentrations (sigmaPBDE ranged from 0.3 to 23.3 ng/g wet weight) and congener profiles varied by fish type and location; however, BDE congeners 47, 99, 100, 153, and 154 were the dominant contributors in all samples. The estimated daily intake of PBDEs associated with consumption of the catfish ranged from 0.03 to 1.80 ng/kg-day. Evaluation of the cancer risk for BDE 209 and the noncancer hazard for BDE congeners 47, 99, 153, and 209 indicated that health risks/hazards due to fish consumption in adults are substantially lower than risk levels generally considered to be at the U.S. EPA minimum concern level. 相似文献
633.
Validation and Application of Empirical Liquefaction Models 总被引:3,自引:0,他引:3
Thomas Oommen Laurie G. Baise Richard Vogel 《Canadian Metallurgical Quarterly》2010,136(12):1618-1633
Empirical liquefaction models (ELMs) are the standard approach for predicting the occurrence of soil liquefaction. These models are typically based on in situ index tests, such as the standard penetration test (SPT) and cone penetration test (CPT), and are broadly classified as deterministic and probabilistic models. No objective and quantitative comparison of these models have been published. Similarly, no rigorous procedure has been published for choosing the threshold required for probabilistic models. This paper provides (1) a quantitative comparison of the predictive performance of ELMs; (2) a reproducible method for choosing the threshold that is needed to apply the probabilistic ELMs; and (3) an alternative deterministic and probabilistic ELM based on the machine learning algorithm, known as support vector machine (SVM). Deterministic and probabilistic ELMs have been developed for SPT and CPT data. For deterministic ELMs, we compare the “simplified procedure,” the Bayesian updating method, and the SVM models for both SPT and CPT data. For probabilistic ELMs, we compare the Bayesian updating method with the SVM models. We compare these different approaches within a quantitative validation framework. This framework includes validation metrics developed within the statistics and artificial intelligence fields that are not common in the geotechnical literature. We incorporate estimated costs associated with risk as well as with risk mitigation. We conclude that (1) the best performing ELM depends on the associated costs; (2) the unique costs associated with an individual project directly determine the optimal threshold for the probabilistic ELMs; and (3) the more recent ELMs only marginally improve prediction accuracy; thus, efforts should focus on improving data collection. 相似文献
634.
Porous pavements allow precipitation to infiltrate through the pavement to the soil, reducing the volume of stormwater runoff produced at a site. However, porous pavements are not widely used on fine-grained soils due to concerns about their performance. Our objective was to investigate the efficacy of porous pavements in controlling stormwater runoff on clay soils. We compared the performance of an asphalt parking lot and a porous pavement parking lot of grass pavers in Athens, Georgia, USA, over relatively small and low-intensity rain events. The porous lot produced 93% less runoff than the asphalt lot. The total volume of runoff at the porous lot was significantly less than the asphalt lot (t = 2.96, p = 0.009). Turbidity was significantly greater at the asphalt lot (t = 6.18, p < 0.001) whereas conductivity was significantly higher at the porous lot (t = 2.31, p = 0.03). Metal and nutrient concentrations were below detection limits at both lots during seven of nine small storm events. During events in which we could detect pollutants, calcium, zinc, silica, and total phosphorus concentrations were higher at the asphalt lot whereas total nitrogen concentrations were greater at the porous lot. Our results suggest porous pavements are a viable option for reducing stormwater runoff and some pollutants from small storms or the first flush from large storms on clay soils. 相似文献
635.
Although the importance of religion in the lives of older African Americans is well documented, this is the 1st study to examine the relations between religious involvement and psychological well-being among a sample comprised exclusively of older African Americans. Eighty-six participants completed multidimensional measures of religious involvement (J. S. Levin, R. J. Taylor & L. M. Chatters, 1995) and well-being (C. D. Ryff & M. J. Essex, 1992). Results indicated that several dimensions of religious involvement (Organizational, Nonorganizational, and Subjective) were associated with several dimensions of psychological well-being (Positive Relations with Others, Self-Acceptance, Environmental Mastery, Purpose in Life, and Personal Growth). Recommendations for future research and implications for counseling are presented. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
636.
Rose Jennifer S.; Chassin Laurie; Presson Clark C.; Sherman Steven J. 《Canadian Metallurgical Quarterly》1996,10(1):28
In the current study mediators and moderators of demographic factors in smoking behavior were examined. Those with low education levels were more likely to smoke, believed less in the negative health effects of smoking, believed more in the positive psychological benefits of smoking, had lower value on a healthy lifestyle, and had more friends who smoked. Although all of these factors significantly mediated education effects on smoking, number of friends who smoke was the most powerful of these mediators. There were no gender differences in smoking rates. However, compared with men, smoking among women was more strongly related to perceived psychological benefits of smoking, number of friends who smoke, and health beliefs about smoking. Implications for targeting intervention at less educated individuals and women are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
637.
Rather Bruce C.; Goldman Mark S.; Roehrich Laurie; Brannick Michael 《Canadian Metallurgical Quarterly》1992,101(1):174
Risk-related antecedent variables can be linked to later alcohol consumption by memory processes, and alcohol expectancies may be one relevant memory content. To advance research in this area, it would be useful to apply current memory models such as semantic network theory to explain drinking decision processes. Multidimensional scaling (MDS) was used to empirically model a preliminary alcohol expectancy semantic network, from which a theoretical account of drinking decision making was generated. Subanalyses showed how individuals with differing alcohol consumption histories may have had different association pathways within the expectancy network. These pathways may have in turn influenced future drinking levels and behaviors while the person was under the influence of alcohol. All individuals associated positive/prosocial effects with drinking, but heavier drinkers indicated arousing effects as their highest probability associates, whereas light drinkers expected sedation. An important early step in this MDS modeling process is the determination of iso-meaning expectancy adjective groups, which correspond to theoretical network nodes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
638.
Tested a model asserting that goal difficulty and task component complexity influence group performance by affecting the effort exerted by group members, the amount and quality of their planning, and the timing of their planning (preplanning vs in-process planning). Hypotheses derived from this model were tested in a 2?×?2 experimental design. 56 groups of 4 students each worked for 15 min building Tinkertoy structures. Results show that group-goal difficulty influenced group performance through effort; task component complexity influenced performance through the amount of planning performed by group members and the level of effort invested in their work; and the quality of the group's planning process also influenced group performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
639.
Parks JL McNeill L Frey M Eaton AD Haghani A Ramirez L Edwards M 《Water research》2004,38(12):2827-2838
It is often desirable to quantify both dissolved Cr(VI) and total Cr in samples accurately. Various protocols are now being utilized to quantify the amount of total chromium in natural waters and each of these has possible interferences. This study describes the shortcomings of each method when particulate iron is present in a water sample, and a more rigorous digestion protocol is tested. Data from bench studies as well as a field survey of 21 water utilities are presented. Additionally, field data from several hundred water utility samples are presented to illustrate the potential for incomplete recovery of total chromium using accepted protocols. 相似文献
640.
Detailed analyses of the phospholipid compositions of cultured human endothelial cells are reported here. No significant differences
were found between the phospholipid compositions of cells from human artery, saphenous and umbilical vein. However, due to
the small sample sizes, relatively large standard deviations for some of the phospholipid classes were observed. A representative
composition of endothelial cells is: phosphatidylcholine 36.6%, choline plasmalogen 3.7%, phosphatidylethanolamine 10.2%,
ethanolamine plasmalogen 7.6%, sphingomyelin 10.8%, phosphatidylserine 7.1%, lysophosphatidylcholine 7.5%, phosphatidylinositol
3.1%, lysophosphatidylethanolamine 3.6%, phosphatidylinositol 4,5-bisphosphate 1.8%, phosphatidic acid 1.9%, phosphatidylinositol
4-phosphate 1.5%, and cardiolipin 1.9%. The cells possess high choline plasmalogen and lysophosphatidylethanolamine contents.
The other phospholipids are within the normal biological ranges expected. Phospholipids were separated by high-performance
liquid chromatography and quantified by lipid phosphorus assay. 相似文献