全文获取类型
收费全文 | 5501篇 |
免费 | 73篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 48篇 |
综合类 | 6篇 |
化学工业 | 808篇 |
金属工艺 | 95篇 |
机械仪表 | 57篇 |
建筑科学 | 272篇 |
矿业工程 | 55篇 |
能源动力 | 122篇 |
轻工业 | 407篇 |
水利工程 | 61篇 |
石油天然气 | 27篇 |
武器工业 | 1篇 |
无线电 | 286篇 |
一般工业技术 | 649篇 |
冶金工业 | 2159篇 |
原子能技术 | 36篇 |
自动化技术 | 493篇 |
出版年
2022年 | 30篇 |
2021年 | 49篇 |
2020年 | 34篇 |
2019年 | 45篇 |
2018年 | 53篇 |
2017年 | 39篇 |
2016年 | 51篇 |
2015年 | 26篇 |
2014年 | 71篇 |
2013年 | 275篇 |
2012年 | 142篇 |
2011年 | 223篇 |
2010年 | 181篇 |
2009年 | 146篇 |
2008年 | 217篇 |
2007年 | 196篇 |
2006年 | 210篇 |
2005年 | 209篇 |
2004年 | 170篇 |
2003年 | 141篇 |
2002年 | 109篇 |
2001年 | 83篇 |
2000年 | 90篇 |
1999年 | 132篇 |
1998年 | 437篇 |
1997年 | 263篇 |
1996年 | 196篇 |
1995年 | 151篇 |
1994年 | 131篇 |
1993年 | 129篇 |
1992年 | 76篇 |
1991年 | 65篇 |
1990年 | 81篇 |
1989年 | 84篇 |
1988年 | 66篇 |
1987年 | 69篇 |
1986年 | 57篇 |
1985年 | 66篇 |
1984年 | 80篇 |
1983年 | 52篇 |
1982年 | 73篇 |
1981年 | 73篇 |
1980年 | 53篇 |
1979年 | 44篇 |
1978年 | 40篇 |
1977年 | 68篇 |
1976年 | 96篇 |
1975年 | 30篇 |
1974年 | 28篇 |
1973年 | 27篇 |
排序方式: 共有5582条查询结果,搜索用时 15 毫秒
51.
Bruce P. Johnston John M. Sullivan Andrew Kwasnik 《International journal for numerical methods in engineering》1991,31(1):67-84
A method is presented for the fully automatic conversion of a general finite element mesh containing triangular elements into a mesh composed of exclusively quadrilateral elements. The initial mesh may be constructed of entirely triangular elements or may consist of a mixture of triangular and quadrilateral elements. The technique used employs heuristic procedures and criteria to selectively combine adjacent triangular elements into quadrilaterals based on preestablished criteria for element quality. Additional procedures are included to eliminate isolated triangles. The methods operates completely without user intervention once the nodal co-ordinates and element connectivity of the original mesh are supplied. 相似文献
52.
53.
Judge Timothy A.; Jackson Christine L.; Shaw John C.; Scott Brent A.; Rich Bruce L. 《Canadian Metallurgical Quarterly》2007,92(1):107
The present study estimated the unique contribution of self-efficacy to work-related performance controlling for personality (the Big 5 traits), intelligence or general mental ability, and job or task experience. Results, based on a meta-analysis of the relevant literatures, revealed that overall, across all studies and moderator conditions, the contribution of self-efficacy relative to purportedly more distal variables is relatively small. Within moderator categories, there were several cases in which self-efficacy made unique contributions to work-related performance. For example, self-efficacy predicted performance in jobs or tasks of low complexity but not those of medium or high complexity, and self-efficacy predicted performance for task but not job performance. Overall, results suggest that the predictive validity of self-efficacy is attenuated in the presence of individual differences, though this attenuation does depend on the context. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
54.
55.
非洲油气勘探区战略选择建议 总被引:8,自引:5,他引:3
非洲不同类型的沉积盆地主要可归纳为:古、中生代挠曲盆地,中、新生代大陆边缘断陷盆地,板内裂谷盆地和大陆边缘进积三角洲盆地。通过盆地油气成藏条件地质综合评价、不同勘探阶段的类比和最终勘探潜力分析,对非洲的沉积盆地进行了划分,在此基础上,总结出非洲油气勘探区选择应遵循的原则。对于油气勘探长期战略选区,原则上,优选低成本油气远景区,即使存在高风险,但亦可获得高回报;对于油气勘探中期发展策略选区,应该寻找地质条件好的油气资源区,投资中短期高利润项目;对于油气勘探中短期发展策略选区,一般应优选中低成本、低风险、低利润且短期能获得油气发现和勘探突破的有利油气勘探区。图1表3参5 相似文献
56.
Braver Sanford L.; Wolchik Sharlene A.; Sandler Irwin N.; Sheets Virgil L.; Fogas Bruce; Bay R. Curtis 《Canadian Metallurgical Quarterly》1993,7(1):9
Reports the results of a 3-wave longitudinal study of a sizable, regionally representative sample of both noncustodial and custodial parents interviewed initially before their divorce was final. A model was tested that predicted the noncustodial parent's postdivorce contact with the child and the payment of child support from a series of factors related to a social exchange orientation. This orientation highlights the noncustodial parent's implicit calculation of the rewards vs the costs of continuing involvement and support of the child. It was found that noninvolvement was, in general, well-predicted, both cross-sectionally and longitudinally, by the model. The most powerful factor in the model was the noncustodial parent's perception that he or she had some control over the child's upbringing. Among fully employed noncustodial parents who reported high perceived control, there was an excellent record of involvement and child support payment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
57.
M.R.X. de Barros G. Nykolak D.J. DiGiovanni A. Bruce W.H. Grodkiewicz P.C. Becker 《Photonics Technology Letters, IEEE》1996,8(6):761-763
We report the gain, noise figure, output saturation power, and conversion efficiency of a highly concentrated Er/sup 3+/-doped alumino silicate fiber amplifier. We obtain a gain per unit length of 1.0 dB/cm, which corresponds to the highest gain per unit length obtained in an Er/sup 3+/-doped fiber amplifier. The pump power threshold ranges from 2 to 5 mW, depending on the fiber length. 相似文献
58.
DM Foreman S Jones NM McKechnie G Williams ME Boulton 《Canadian Metallurgical Quarterly》1996,28(5):296-302
We describe a simple method for combining in situ hybridisation and immunohistochemistry on the same retinal section. The technique was developed using a radiolabelled cDNA probe for opsin and an antibody (ROS1F4) against rhodopsin. This method retains the antigenic sites if immunocytochemistry is performed prior to in situ hybridisation. Opsin mRNA was found in the photoreceptor inner segment with rhodopsin immunolocalised to the photoreceptor outer segments. The technique should be applicable to numerous situations including analysis of the sequence of events in the expression and synthesis of the various opsins during retinal development and degeneration. 相似文献
59.
PR Bennett R Warwick J Vaughan H Chana A Lubenko NM Fisk 《Canadian Metallurgical Quarterly》1994,101(3):246-249
OBJECTIVE: To assess the effectiveness of a newly developed individualised birthweight ratio (IBR), which corrects for physiological birthweight determinants, in identifying infants at risk from the complications of macrosomia. DESIGN: Prospective observational study. SETTING: Obstetric unit, Nottingham City Hospital. SUBJECTS: 2835 women delivered between December 1991 and July 1992 and the infants of 624 of these, selected by virtue of their birthweight for gestation and IBR centile positions. MAIN OUTCOME MEASURES: Skinfold thickness and ponderal index measurements, operative delivery, shoulder dystocia, fetal trauma, impaired glucose tolerance. RESULTS: Using an IBR above the 90th centile as a cut off results in 2.4% of infants being reclassified as normally grown and 3.1% are reclassified as large. The IBR does not result in the identification of any more infants with abnormal ponderal indices or skinfold thicknesses than birthweight for gestation. It does, however, identify more of the infants at risk of operative delivery, shoulder dystocia, fetal trauma and impaired glucose tolerance. CONCLUSION: The IBR significantly improves upon birthweight for gestation in identifying infants who suffer from the complications of relative macrosomia. 相似文献
60.
J Desaki M Kinutani K Tan-Takeuchi NM Le Douarin 《Canadian Metallurgical Quarterly》1996,45(5):448-452
The migration of leucocytes through the walls of venules was examined in detail in the posterior latissimus dorsi muscle of quail-chick spinal cord chimeras, in which flaccid paralysis of the wings was observed. Examinations were made from the 70th to 80th day after hatching. Muscle fibers were degenerated and intramuscular nerve bundles destroyed. Massive leucocytes (almost lymphocytes) were found around the venules, depending on the passage of wandering leucocytes through the endothelium. Lymphocytes penetrated and were encased in the cytoplasm of the venular endothelial cell, and did not pass through the interendothelial junction. These findings suggest that, in the venules of the atrophied chimeric muscle, wandering leucocytes in the blood may pass through the endothelial cell body and migrate into the inflamed extravascular space. 相似文献