全文获取类型
收费全文 | 9007篇 |
免费 | 317篇 |
国内免费 | 40篇 |
专业分类
电工技术 | 121篇 |
综合类 | 22篇 |
化学工业 | 2101篇 |
金属工艺 | 167篇 |
机械仪表 | 231篇 |
建筑科学 | 573篇 |
矿业工程 | 31篇 |
能源动力 | 171篇 |
轻工业 | 772篇 |
水利工程 | 54篇 |
石油天然气 | 11篇 |
武器工业 | 1篇 |
无线电 | 591篇 |
一般工业技术 | 1451篇 |
冶金工业 | 1522篇 |
原子能技术 | 70篇 |
自动化技术 | 1475篇 |
出版年
2023年 | 58篇 |
2022年 | 120篇 |
2021年 | 144篇 |
2020年 | 105篇 |
2019年 | 119篇 |
2018年 | 168篇 |
2017年 | 110篇 |
2016年 | 191篇 |
2015年 | 191篇 |
2014年 | 249篇 |
2013年 | 563篇 |
2012年 | 398篇 |
2011年 | 546篇 |
2010年 | 410篇 |
2009年 | 391篇 |
2008年 | 432篇 |
2007年 | 420篇 |
2006年 | 366篇 |
2005年 | 313篇 |
2004年 | 291篇 |
2003年 | 221篇 |
2002年 | 227篇 |
2001年 | 173篇 |
2000年 | 165篇 |
1999年 | 157篇 |
1998年 | 258篇 |
1997年 | 194篇 |
1996年 | 159篇 |
1995年 | 141篇 |
1994年 | 122篇 |
1993年 | 136篇 |
1992年 | 130篇 |
1991年 | 76篇 |
1990年 | 93篇 |
1989年 | 79篇 |
1988年 | 94篇 |
1987年 | 66篇 |
1986年 | 54篇 |
1985年 | 79篇 |
1984年 | 94篇 |
1983年 | 60篇 |
1982年 | 66篇 |
1981年 | 83篇 |
1980年 | 68篇 |
1979年 | 85篇 |
1978年 | 68篇 |
1977年 | 67篇 |
1976年 | 56篇 |
1975年 | 58篇 |
1973年 | 47篇 |
排序方式: 共有9364条查询结果,搜索用时 9 毫秒
991.
992.
Some existing work on optimizing the operational cost of the primary end of an integrated steel plant containing two blast furnaces utilizing both pellets and sinters, an electric furnace and a basic oxygen furnace was further advanced using a multi‐objective genetic algorithm, along with a Nash equilibrium analysis. The new formulation was able to improve the earlier results very significantly, suggesting the efficacy of the multi‐objective approach over the more conventional single objective genetic algorithms. 相似文献
993.
Fincham Frank D.; Beach Steven R. H.; Arias Ileana; Brody Gene H. 《Canadian Metallurgical Quarterly》1998,12(4):481
This study assessed children's attributions in parent–child relationships, examined their association with relationship positivity and behavior displayed toward the parent, determined whether depressive symptoms account for these associations, and investigated whether parent and child attributions are linked. Ten- to 12-year-old children (116 girls, 116 boys) completed several questionnaires and were observed during parent–child interactions. Children's attributions for parent behavior were related to positivity of the parent–child relationship and to self- and parent-reported conflict and observed behavior with the father. These associations were not due to children's depressive symptoms but potentially augment our understanding of the effect of depression on parent–child relationships. Finally, gender moderated the parent attribution–child attribution association. The results underscore the importance of children's perceptions of family processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
994.
Effects of salicylic acid on plant-water relationships 总被引:8,自引:0,他引:8
Soybean seedlings [Glycine max (L.) Merr.] were used as the test species to study the allelopathic influence of salicylic acid (SA) on short- and long-term plant water status. Plants were grown in greenhouse conditions in nutrient culture medium amended with SA. Treatments were initiated 10 days after germination and continued for either 14 or 28 days. The threshold for inhibition of seedling growth over a 28-day treatment was 0.15 mM SA. Seedlings grown with 0.3 mM SA consistently had higher leaf diffusive resistance and lower transpiration and water potentials than control plants. The stable carbon isotope ratio (13C:12C) in tissue from both the 0.15 and 0.30 mM SA-treated plants was significantly higher than control seedlings, indicating SA caused a chronic water stress during the 28-day treatment. These data show that an interference with plant-water relationships is one mechanism whereby this allelochemical inhibits plant growth.This study was supported by National Science Foundation grant STI-8902066. 相似文献
995.
Self-report estimates of frequency and duration of computer use are used extensively in research related to computer and information systems acceptance. Despite concerns that self-report estimates are inferior to computer log data there is a paucity of research investigating the relationship between self-report and log data measures of computer use. The present study compared self-report estimates and six months of electronic log data for 62 health care workers using a new Community Services Information System. There were moderate to strong correlations between the self-report and electronic log estimates of frequency and duration of system use. Self-report estimates were relatively accurate in that they were quite similar in magnitude to log data values. The merits of combinations of frequency and duration data (composites) were also assessed. 相似文献
996.
J Frank DK Kelleher A Pompella O Thews HK Biesalski P Vaupel 《Canadian Metallurgical Quarterly》1998,58(13):2693-2698
Polymerase chain reaction (PCR) assays were designed to amplify 56- and 99-base regions of the pmoA gene from Methylosinus trichosporium OB3b and Methylomicrobium albus BG8, two species of methanotrophic bacteria that are of interest for monitoring bioremediation activity. The PCR product sizes are in a mass range that is accessible to analysis by MALDI-TOF mass spectrometry. A rapid purification procedure using commercially available reversed-phase cartridges was applied prior to MALDI-TOF analysis. A small aliquot (1.5%, 1.5 microL) from a single 100-microL PCR reaction was sufficient for reliable detection. No cross-amplification products were observed when primers designed for one bacterial species were used with genomic DNA of the other species. The methodology described here has potential to allow less expensive and faster characterization of the ability of microbial populations to destroy pollutants in groundwater and soil at contaminated industrial sites. 相似文献
997.
Research reported here addresses the issue of the reliability of retrospective reports of children's perceptions of maternal acceptance-rejection as measured by the Parental Acceptance-Rejection Questionnaire. A sample of 49 middle-class Caucasian 7- to 11-yr.-old children were asked to respond to the questionnaire reflecting on their mothers' current accepting-rejecting behaviors. Seven years later the same children--now adolescents--responded to the same questionnaire with the instruction to reflect back on their mothers' behavior when the youth were about 7 to 11 years of age. None of these youth recalled having been tested seven years earlier. A simple zero-order correlation between scores in childhood and adolescence was 62, indicating that adolescents' retrospective recollections were in moderate agreement with their reports during childhood. Thus, it seems clear that, at least with respect to perceptions of maternal acceptance-rejection as measured by the Parental Acceptance-Rejection Questionnaire, researchers can have reasonable confidence that adolescents' current recollections about their experiences of maternal acceptance-rejection are likely to be in moderate agreement with what they would have reported had they been tested during childhood. 相似文献
998.
Prof. Dr. med. Dipl. Psych. Frank Erbguth 《Ethik in der Medizin》2006,18(2):182-185
Ohne Zusammenfassung 相似文献
999.
Precise determination of the dielectric constant of microelectronic packaging materials is critical for the performance optimization of high frequency devices. Accurate empirical data, however, is difficult to obtain and often not available for these complex composite materials. In order to provide a basis for predictive model verification, dielectric analysis of a series of model microelectronic packaging materials was conducted. Physical characteristics of the composite constituents, including the morphology of the dispersed phase as well as the dielectric constant of the dispersed and host phases, were used to define the indeterminate variables. The results of these analyses provide a systematic verification of a newly developed physical model for predicting the effective dielectric constant of complex composite systems. The model considers an interphase zone surrounding each dispersed particle having unique physical and electrical characteristics. A physical interpretation is presented to explain the indeterminate variables incorporated in this model. 相似文献
1000.