全文获取类型
收费全文 | 705474篇 |
免费 | 7733篇 |
国内免费 | 1541篇 |
专业分类
电工技术 | 13379篇 |
综合类 | 558篇 |
化学工业 | 107551篇 |
金属工艺 | 28244篇 |
机械仪表 | 22100篇 |
建筑科学 | 15473篇 |
矿业工程 | 4731篇 |
能源动力 | 17785篇 |
轻工业 | 55155篇 |
水利工程 | 8051篇 |
石油天然气 | 16188篇 |
武器工业 | 45篇 |
无线电 | 79722篇 |
一般工业技术 | 141942篇 |
冶金工业 | 130258篇 |
原子能技术 | 16747篇 |
自动化技术 | 56819篇 |
出版年
2021年 | 6240篇 |
2019年 | 6030篇 |
2018年 | 10422篇 |
2017年 | 10598篇 |
2016年 | 11109篇 |
2015年 | 6978篇 |
2014年 | 11879篇 |
2013年 | 31708篇 |
2012年 | 18499篇 |
2011年 | 25090篇 |
2010年 | 20175篇 |
2009年 | 22716篇 |
2008年 | 23219篇 |
2007年 | 22971篇 |
2006年 | 20113篇 |
2005年 | 18367篇 |
2004年 | 17669篇 |
2003年 | 17249篇 |
2002年 | 16715篇 |
2001年 | 16561篇 |
2000年 | 15748篇 |
1999年 | 15990篇 |
1998年 | 39482篇 |
1997年 | 27875篇 |
1996年 | 21525篇 |
1995年 | 16368篇 |
1994年 | 14607篇 |
1993年 | 14391篇 |
1992年 | 10714篇 |
1991年 | 10424篇 |
1990年 | 10235篇 |
1989年 | 9946篇 |
1988年 | 9410篇 |
1987年 | 8321篇 |
1986年 | 8207篇 |
1985年 | 9303篇 |
1984年 | 8355篇 |
1983年 | 7882篇 |
1982年 | 7143篇 |
1981年 | 7378篇 |
1980年 | 6910篇 |
1979年 | 6917篇 |
1978年 | 6811篇 |
1977年 | 7664篇 |
1976年 | 9743篇 |
1975年 | 6069篇 |
1974年 | 5846篇 |
1973年 | 5858篇 |
1972年 | 5062篇 |
1971年 | 4661篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
The purpose of this study is to evaluate the effect of one abrasive cleaner, one non-abrasive cleaner and one non-abrasive alcohol-based cleaner on the lens parameter stability of the NOVALENS. Twenty-four lenses, all NOVALENS material of identical design, were cleaned 100 times each. Eight lenses were cleaned with MiraFlow (CIBA Vision), eight lenses with Optic-Free Daily Cleaner and eight lenses with the Gas Permeable Daily Cleaner (PBH). The base curve radius, center thickness and power were verified immediately before, immediately after and (per manufacturer's recommendation) 4 hours after cleaning at baseline, 25, 50, 75 and 100 cleanings. Lens toricity of approximately 0.50D was found with all three cleaners after 100 cleanings. No change in lens power or center thickness was found. It was concluded that extreme care must be taken in handling the NOVALENS due to the potential of induced warpage. 相似文献
994.
995.
233 undergraduates (162 women and 71 men) completed a demographics questionnaire and measures of career-decision-making (CDM) self-efficacy (K. M. Taylor and N. E. Betz, 1983), CDM attitudes (J. O. Crites, 1978), and CDM skills (D. E. Super et al, 1981). Results revealed that CDM self-efficacy was moderately and positively related to CDM attitudes and age of participants (p? 相似文献
996.
Durhuus T. Mikkelsen B. Joergensen C. Lykke Danielsen S. Stubkjaer K.E. 《Lightwave Technology, Journal of》1996,14(6):942-954
Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber 相似文献
997.
BACKGROUND: In the outpatient use of tuberculin skin testing (purified protein derivative [PPD]), it is at times inconvenient to have a patient revisit for interpretation. Therefore, we assessed patients' ability to self-interpret these test results. METHODS: In keeping with prior custom, patients were seen by an experienced nurse, who performed skin testing with PPD intermediate strength as well as mumps and Candida anergy control tests in some cases, and explained the procedure. The patients were asked to return 48 to 72 h later, at which time one of the researchers recorded their test interpretations before they were again evaluated by the nurse. RESULTS: Sixty-eight patients were studied, of whom 59 returned at appropriate interval. Eighteen patients had a positive PPD test reaction of 10 to 20 mm induration, which only one patient correctly identified as a positive test result. However, positive anergy control tests were correctly interpreted in 10 of 27 cases. CONCLUSION: The small number of positive PPD test result recognition by these patients may be partially attributed to their lack of education, as well as foreign birth and denial of illness. PPD results should be checked by an experienced professional. 相似文献
998.
999.
1000.
The performance of two distributed channel assignment algorithms which use coexistence etiquettes for point to point links are considered by the authors. It has been found that selecting channels prior to transmission at the transmitter as opposed to the receiver, supports greater offered traffic with the additional advantage of a less complex protocol 相似文献