全文获取类型
收费全文 | 1686728篇 |
免费 | 25545篇 |
国内免费 | 7237篇 |
专业分类
电工技术 | 35770篇 |
综合类 | 6813篇 |
化学工业 | 281759篇 |
金属工艺 | 67555篇 |
机械仪表 | 49415篇 |
建筑科学 | 50330篇 |
矿业工程 | 12094篇 |
能源动力 | 50756篇 |
轻工业 | 134700篇 |
水利工程 | 17323篇 |
石油天然气 | 38510篇 |
武器工业 | 210篇 |
无线电 | 202906篇 |
一般工业技术 | 315619篇 |
冶金工业 | 241020篇 |
原子能技术 | 34809篇 |
自动化技术 | 179921篇 |
出版年
2021年 | 15904篇 |
2020年 | 12184篇 |
2019年 | 14971篇 |
2018年 | 20078篇 |
2017年 | 19927篇 |
2016年 | 23825篇 |
2015年 | 18011篇 |
2014年 | 29188篇 |
2013年 | 88837篇 |
2012年 | 40839篇 |
2011年 | 57312篇 |
2010年 | 47687篇 |
2009年 | 54935篇 |
2008年 | 52063篇 |
2007年 | 50575篇 |
2006年 | 49082篇 |
2005年 | 45003篇 |
2004年 | 46078篇 |
2003年 | 45500篇 |
2002年 | 43860篇 |
2001年 | 40998篇 |
2000年 | 38829篇 |
1999年 | 39048篇 |
1998年 | 68322篇 |
1997年 | 53574篇 |
1996年 | 44847篇 |
1995年 | 36555篇 |
1994年 | 33505篇 |
1993年 | 33140篇 |
1992年 | 27773篇 |
1991年 | 25178篇 |
1990年 | 25295篇 |
1989年 | 24407篇 |
1988年 | 22948篇 |
1987年 | 21106篇 |
1986年 | 20575篇 |
1985年 | 23942篇 |
1984年 | 23362篇 |
1983年 | 21269篇 |
1982年 | 19953篇 |
1981年 | 20071篇 |
1980年 | 18739篇 |
1979年 | 19191篇 |
1978年 | 18369篇 |
1977年 | 19487篇 |
1976年 | 22674篇 |
1975年 | 16487篇 |
1974年 | 15959篇 |
1973年 | 16086篇 |
1972年 | 13505篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Kawai S. Iwatsuki K. Suzuki K. Nishi S. Saruwatari M. Sato K. Wakita K. 《Electronics letters》1994,30(3):251-252
The authors demonstrate 10 Gbit/s optical soliton transmission in a recirculating loop through the use of a monolithically integrated MQW-DFB-LD/MQW-EA modulator light source. The timing jitter due to the Gordon-Haus effect is successfully reduced by the optical bandpass filters conventionally used in the cascaded EDFAs to avoid the accumulation of amplified spontaneous emission. The transmission distance of 7200 km is achieved at a bit error rate of 10-9 相似文献
992.
K. Nomoto H. Saitoh A. Chida H. Sannomiya M. Itoh Y. Yamamoto 《Solar Energy Materials & Solar Cells》1994,34(1-4)
a-Si alloy three-stacked solar cells have been studied to improve the stabilized efficiency of a-Si: H based solar cells. Based on the analysis by the individual characterization method of the component cells in stacked type cells, the a-Si :H middle cell was replaced with an a-SiGe :H cell. Furthermore, the optical confinement technology was improved to obtain a high-output current with thin i-layer thickness in the a-SiGe :H bottom cell. By this device design, the initial conversion efficiency was improved up to 12.4% and more than a 10% stabilized efficiency was obtained in a-SiC :H/a-SiGe :H/a-SiGe :H three-stacked cells. These cell characteristics were confirmed by measurements at the JQA Organization (the former JMI Institute). 相似文献
993.
Marginal costs of electricity vary by time and location. In the past, researchers attributed the variations to factors related to electricity generation and transmission. These authors, however, have not analyzed possible variations in marginal distribution capacity costs (MDCC). The objectives of this paper are:
- 1. (i) to show that large MDCC variations are due to the dispersion in distribution capital expenditures by time and space,
- 2. (ii) to propose a method for quantifying the area- and time-specific MDCC in the presence of lumpy investments, and
- 3. (iii) to compare our MDCC estimates to those commonly used in the electric utility industry.
994.
995.
Several simple 3D experiments are used to provide J correlations between methionine C epsilon methyl carbons and either the C gamma H2 protons or C beta and C gamma. The intensity of the J correlations provides information on the size of the three-bond J couplings and thereby on the chi 3 torsion angle. In addition, a simple 3D version of the HMBC experiment provides a sensitive link between the C epsilon H3 methyl protons and C gamma. The methods are demonstrated for a 20 kDa complex between calmodulin and a 26-residue peptide fragment of skeletal muscle myosin light chain kinase. 相似文献
996.
997.
A Gopal G Li Mandri DL King C Marboe S Homma 《Canadian Metallurgical Quarterly》1994,105(6):1885-1887
Cardiac papillary fibroelastomas are unusual, frond-like growths typically found on cardiac valves, diagnosed incidentally on autopsy or cardiac surgery, but rarely during life. We report a rare case of an aortic valve papillary fibroelastoma detected by transthoracic echocardiography and confirmed by histologic study. 相似文献
998.
R Herruzo-Cabrera L Malo-González ME Calle Purón MJ Vizcaíno-Alcaide J Del Rey-Calero 《Canadian Metallurgical Quarterly》1993,9(4):442-446
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program. 相似文献
999.
1000.
Several methodological and ethical issues are addressed in the context of 3 related school-based studies of the primary and targeted prevention of depressive symptoms and disorder in high school adolescents. These issues include obtaining S consent and the protection of confidentiality, minimizing attrition over long-term follow-up periods, the "unit of assignment" issue common to most school-based research, and ensuring therapist fidelity to the intervention protocol. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献