全文获取类型
收费全文 | 291489篇 |
免费 | 9061篇 |
国内免费 | 4599篇 |
专业分类
电工技术 | 9592篇 |
技术理论 | 1篇 |
综合类 | 4047篇 |
化学工业 | 42420篇 |
金属工艺 | 13636篇 |
机械仪表 | 10184篇 |
建筑科学 | 10135篇 |
矿业工程 | 2151篇 |
能源动力 | 7693篇 |
轻工业 | 27752篇 |
水利工程 | 3131篇 |
石油天然气 | 3667篇 |
武器工业 | 646篇 |
无线电 | 37122篇 |
一般工业技术 | 50197篇 |
冶金工业 | 51892篇 |
原子能技术 | 4321篇 |
自动化技术 | 26562篇 |
出版年
2022年 | 3381篇 |
2021年 | 5051篇 |
2020年 | 3474篇 |
2019年 | 3220篇 |
2018年 | 4140篇 |
2017年 | 4231篇 |
2016年 | 4231篇 |
2015年 | 4330篇 |
2014年 | 6039篇 |
2013年 | 14047篇 |
2012年 | 9198篇 |
2011年 | 11592篇 |
2010年 | 9569篇 |
2009年 | 10050篇 |
2008年 | 10541篇 |
2007年 | 10335篇 |
2006年 | 9419篇 |
2005年 | 8629篇 |
2004年 | 7563篇 |
2003年 | 7257篇 |
2002年 | 7145篇 |
2001年 | 7142篇 |
2000年 | 6494篇 |
1999年 | 7006篇 |
1998年 | 16942篇 |
1997年 | 11927篇 |
1996年 | 9247篇 |
1995年 | 6926篇 |
1994年 | 6108篇 |
1993年 | 5844篇 |
1992年 | 4151篇 |
1991年 | 4071篇 |
1990年 | 3634篇 |
1989年 | 3543篇 |
1988年 | 3473篇 |
1987年 | 2931篇 |
1986年 | 2874篇 |
1985年 | 3424篇 |
1984年 | 3059篇 |
1983年 | 2745篇 |
1982年 | 2558篇 |
1981年 | 2574篇 |
1980年 | 2439篇 |
1979年 | 2282篇 |
1978年 | 2235篇 |
1977年 | 2809篇 |
1976年 | 4171篇 |
1975年 | 1900篇 |
1974年 | 1795篇 |
1973年 | 1784篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
995.
Nascent high-molecular-weight (UHMW) polyethylene (PE) samples of different origins show a rather high crystallinity of about 70–75% and contain both a major portion of orthorhombic extended chain crystallites and a minor portion of triclinic crystallites. The triclinic content is greater the higher the molecular weight of the sample and the higher the activity of the used catalyser. A melting / recooling treatment results in a reduction of crystallinity by about 15–25% and disappearance of the triclinic phase. Further, an irreversible conversion of nascent orthorhombic extended chain crystallites to orthorhombic folded chain crystallites of increased lateral dimensions and crystalline perfections takes place during the melting / recooling treatment. The results are compared to those obtained for lower-molecular-weight PE samples and for high-strength / modulus PE fibers of different origins. 相似文献
996.
Modified Imidazoles: Degradation Inhibitors and Adhesion Promoters for Polyimide Films on Copper Substrates 总被引:1,自引:0,他引:1
Polyimide films on copper substrates that are exposed to elevated temperatures and an oxidizing environment will be subject to degradation. In order to halt this degradation without changing the properties of the system, a polymeric agent could be placed between the polyimide and the copper. This paper will investigate three such materials that will not only slow down the degradation of the polyimide and the oxidation of the copper, but will also improve adhesion within the system. Fourier transform infrared reflection-absorption spectroscopy (FTIR-RAS) will be used to investigate the polyimide/polymeric agent/copper system. 相似文献
997.
A system has been developed for tracking the motion of objects in two dimensions in real-time. The system consists of a conventional CCD camera linked to a transputer-based frame grabber and an array of nine transputers. A parallel moments algorithm is used to extract the co-ordinates of the object's centre of gravity and orientation at field rate, i.e. 60 Hz. Since the position data are made available in real-time—with a small time delay—the system has the potential for inclusion in a feedback loop. Results are presented for tracking the trajectory of a chocolate bar diverted by an air jet. The potential of the system for higher sampling rates—up to 200 Hz—is discussed. 相似文献
998.
A multilevel soliton communication system is proposed and assessed. In this system, at the transmitter end each channel transmits its data via fundamental solitons with a pre-specified amplitude (i.e., soliton width). At the receiver end we take advantage of the sensitive relationship between the amount or fundamental soliton self-wavelength shift and the width of the soliton in the subpicosecond region. We first compress the incoming soliton noises to the subpicosecond level and pass them through a short length of fiber at the end of which the pulses have become separated in the wavelength domain since each soliton, corresponding to a data channel, has experienced a different Raman self-wavelength shift. The channels are then easily separated by optical filters. We have derived the design constraint relations for such a system. We have then heuristically designed a 40 Gbs (four channels) system for a 1000 km propagation distance (total data-rate distance product of 40 Tb/km). Numerical simulations and noise analyses have verified the feasibility and practicality of the proposed system with very good design margins. The wavelength jitter is found to be much smaller than the desired filter spacing, and thus its contribution to the bit error rate is negligible. We also argue that the system is more tolerant to Gordon-Haus timing jitter than conventional TDM soliton systems. The system is all fiber and is, therefore very cost effective as it does not require sophisticated electro-optic and microwave circuits for demultiplexing. The system can potentially operate at much higher speeds than those achievable in conventional soliton systems and it can be used in parallel with WDM soliton system 相似文献
999.
W Samuel M Dryden M Sampson A Page H Shepherd 《Canadian Metallurgical Quarterly》1997,22(23):2763-2765
STUDY DESIGN: A case of paraspinal abscess formation from Haemophilus paraphrophilus is presented. OBJECTIVES: To describe a case of paraspinal abscess formation from H. paraphrophilus, a fastidious commensal organism of the mouth and pharynx. A precise bacteriologic identification can be difficult; techniques for such identification are discussed. SUMMARY OF BACKGROUND DATA: Spinal abscess caused by H. paraphrophilus is unusual and can be very difficult to diagnose. METHODS: The etiology, clinical presentation, technical examinations, and treatment are reviewed. RESULTS: Prolonged antibiotic treatment was curative, although surgery was considered. CONCLUSIONS: Bacteriologic diagnoses in these rare infections are difficult. Antibiotic therapy was curative in the patient described. 相似文献
1000.
Ernst L.J. Hinman W.L. Quam D.H. Thorp J.S. 《Power Delivery, IEEE Transactions on》1992,7(4):1834-1852
The authors describe the relaying concepts of charge comparison. Charge comparison is a new transmission line protection system. It is a form of current differential relaying. Charge comparison largely resolves the traditional problems of current differential relaying of transmission lines, which are that protection is lost if a channel fails, a large channel capacity is required, and precise channel delay compensation is required. This technique is suitable for the protection of two- or three-terminal AC transmission lines, of all lengths and voltage levels, with or without series of shunt compensation, with three-hole or single-pole tripping 相似文献