全文获取类型
收费全文 | 12540篇 |
免费 | 1212篇 |
国内免费 | 25篇 |
专业分类
电工技术 | 173篇 |
综合类 | 17篇 |
化学工业 | 3266篇 |
金属工艺 | 509篇 |
机械仪表 | 626篇 |
建筑科学 | 200篇 |
矿业工程 | 4篇 |
能源动力 | 540篇 |
轻工业 | 1286篇 |
水利工程 | 38篇 |
石油天然气 | 12篇 |
武器工业 | 1篇 |
无线电 | 2117篇 |
一般工业技术 | 2933篇 |
冶金工业 | 673篇 |
原子能技术 | 149篇 |
自动化技术 | 1233篇 |
出版年
2024年 | 14篇 |
2023年 | 175篇 |
2022年 | 269篇 |
2021年 | 453篇 |
2020年 | 312篇 |
2019年 | 331篇 |
2018年 | 454篇 |
2017年 | 483篇 |
2016年 | 568篇 |
2015年 | 514篇 |
2014年 | 657篇 |
2013年 | 870篇 |
2012年 | 950篇 |
2011年 | 1205篇 |
2010年 | 826篇 |
2009年 | 797篇 |
2008年 | 621篇 |
2007年 | 550篇 |
2006年 | 482篇 |
2005年 | 412篇 |
2004年 | 366篇 |
2003年 | 346篇 |
2002年 | 252篇 |
2001年 | 221篇 |
2000年 | 228篇 |
1999年 | 205篇 |
1998年 | 290篇 |
1997年 | 172篇 |
1996年 | 147篇 |
1995年 | 91篇 |
1994年 | 87篇 |
1993年 | 61篇 |
1992年 | 50篇 |
1991年 | 34篇 |
1990年 | 34篇 |
1989年 | 35篇 |
1988年 | 24篇 |
1987年 | 14篇 |
1986年 | 23篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1974年 | 9篇 |
1971年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Jong Whan Lee Dong Hee Kwon Jeong Suk Kim Duck Whan Kim Myung Chang Kang Bok Kyu Lim 《Journal of Mechanical Science and Technology》2007,21(2):244-250
This paper presents an investigation on the characteristics of damaged layer in micro-machining by using the ultrahigh-speed
air spindle. The damaged layer in metal cutting is derived from plastic deformation and transformation of metal structure.
In this study, micro-cutting force, surface roughness, and plastic deformation layer according to the variation of machining
conditions were investigated by experiments. The damaged layer was measured using optical microscope for the samples prepared
by metallographic techniques. Its scale was dependent on cutting process parameters, especially feed per tooth. According
to experimental results, it was verified that the thickness of damaged layer was increased with increasing of feed per tooth
and cutting depth, also thickness of damaged layer was reduced in down-milling compared to upmilling during micro-endmilling
operation. 相似文献
52.
53.
Onishi K. Rino Choi Chang Seok Kang Hag-Ju Cho Young Hee Kim Nieh R.E. Jeong Han Krishnan S.A. Akbar M.S. Lee J.C. 《Electron Devices, IEEE Transactions on》2003,50(6):1517-1524
Bias-temperature instabilities (BTI) of HfO/sub 2/ metal oxide semiconductor field effect transistors (MOSFETs) have been systematically studied for the first time. NMOS positive BTI (PBTI) exhibited a more significant V/sub t/ instability than that of PMOS negative BTI (NBTI), and limited the lifetime of HfO/sub 2/ MOSFETs. Although high-temperature forming gas annealing (HT-FGA) improved the interface quality by passivating the interfacial states with hydrogen, BTI behaviors were not strongly affected by the technique. Charge pumping measurements were extensively used to investigate the nature of the BTI degradation, and it was found that V/sub t/ degradation of NMOS PBTI was primarily caused by charge trapping in bulk HfO/sub 2/ rather than interfacial degradation. Deuterium (D/sub 2/) annealing was found to be an excellent technique to improve BTI immunity as well as to enhance the mobility of HfO/sub 2/ MOSFETs. 相似文献
54.
Stanley C. Ahalt Prakoon Chen Cheng-Taou Chou Tzyy-Ping Jung 《The Journal of supercomputing》1992,5(4):307-330
We describe an implementation of a vector quantization codebook design algorithm based on the frequencysensitive competitive learning artificial neural network. The implementation, designed for use on high-performance computers, employs both multitasking and vectorization techniques. A C version of the algorithm tested on a CRAY Y-MP8/864 is discussed. We show how the implementation can be used to perform vector quantization, and demonstrate its use in compressing digital video image data. Two images are used, with various size codebooks, to test the performance of the implementation. The results show that the supercomputer techniques employed have significantly decreased the total execution time without affecting vector quantization performance.This work was supported by a Cray University Research Award and by NASA Lewis research grant number NAG3-1164. 相似文献
55.
根据球铁件凝固原理,对常用湿砂铸型中制造球铁件,用计算机完成控制压力冒口的设计,流程框图适于各工厂和车间之用。 相似文献
56.
G Stoll S Müller B Schmidt P van der Meide S Jung KV Toyka HP Hartung 《Canadian Metallurgical Quarterly》1993,142(6):1866-1875
This study reports the cellular localization of interferon-gamma (IFN-gamma) and MHC class II antigen (Ia) in the spinal cord of rats with experimental autoimmune encephalomyelitis induced by adoptive transfer of myelin basic protein-specific T cells. Numerous IFN-gamma-positive cells, stained with two different monoclonal antibodies against IFN-gamma, were present from days 3 to 7 after cell transfer. Their number was greatly reduced on day 10. A subpopulation of T cells was IFN-gamma positive. Moreover, a large number of ED1-positive macrophages contained IFN-gamma immunoreactivity. The transient presence of immune cells containing IFN-gamma immunoreactivity in experimental autoimmune encephalomyelitis suggests a pathogenic role of this cytokine in immune-mediated demyelination of the central nervous system. 相似文献
57.
A study on the prediction of heat transfer coefficient (HTC) and pressure drop of refrigerant mixtures is reported. HTCs and pressure drops of prospective mixtures to replace R12 and R22 are predicted on the same cooling capacity basis. Results indicate that nucleate boiling is suppressed at qualities greater than 20.0% for all mixtures and evaporation becomes the main heat transfer mechanism. For the same capacity, some mixtures containing R32 and R152a show 8.0–10.0% increase in HTCs. Some mixtures with large volatility difference exhibit as much as 55.0% reduction compared with R12 and R22, caused by mass transfer resistance and property degradation due to mixing (32.0%) and reduced mass flow rates (23.0%). Other mixtures with moderate volatility difference exhibit 20.0–30.0% degradation due mainly to reduced mass flow rates. The overall impact of heat transfer degradation, however, is insignificant if major heat transfer resistance exists in the heat transfer fluid side (air system). If the resistance in the heat transfer fluid side is of the same order of magnitude as that on the refrigerant side (water system), considerable reduction in overall HTC of up to 20% is expected. A study of the effect of uncertainties in transport properties on heat transfer shows that transport properties of liquid affect heat transfer more than other properties. Uncertainty of 10.0% in transport properties causes a change of less than 6% in heat transfer prediction. 相似文献
58.
In Europe, the challenge of the design of third-generation cellular mobile radio systems has been taken numerous research and development activities in this field have been started. The authors try to give an overview of the European activities in this field. The article is organized in two parts. In the first part, the requirements for third-generation cellular mobile radio systems such as Universal Mobile Telecommunications System (UMTS) and Future Public Land Mobile Telecommunications System (FPLMTS), which has been named International Mobile Telecommunications after the year 2000 (IMT-2000) are presented concisely. Also, the importance and challenge of the multiple access design for such third-generation cellular mobile radio systems is explained. In the second part, numerous European research activities with focus on the multiple access design for third-generation cellular mobile radio systems are reviewed 相似文献
59.
Disagreement exists in the literature concerting the activity of NiO in (Ni,Mg)O solid solutions. Ideal behavior, as well as strong positive deviations and strong negative deviations from ideality, has been reported. In the present study, the activity of NiO was determined by electromotive force measurements using the solid-state cell Pt/Ni-NiO/0.92ZrO2 -0.08Y2 O3 /Ni-(Ni,Mg)O/Pt. The compositions studied had NiO mole fractions of 0.1,0.3,0.5,0.7, and 0.9. In agreement with theoretical expectations, the solid solutions exhibited ideal behavior at 882° and 982°C. Possible reasons for the conflicting results in the literature arc presented. 相似文献
60.
The energy release rate, which is the total derivative of the energy with respect to crack length, is recognized as corresponding to the shape sensitivity analysis with the crack length change represented by the tangential component of design velocity. In this paper the sensitivity formula recently developed for a changing boundary condition has been further extended to cover crack kinking under mixed mode loading. Due to difficulty in defining the velocity field at the corner, the energy release rate at the onset of crack kinking is obtained by extrapolating the energy release rates for finite length kinked cracks. A rectangular plate with a single edge slant crack under uniform tension is taken as a numerical example. The multi-region technique in the numerical implementation of the boundary integral equation is adopted to consider the asymmetry of the problem. Excellent accuracy is observed as compared with reference analytic solutions. 相似文献