全文获取类型
收费全文 | 975篇 |
免费 | 104篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 22篇 |
综合类 | 4篇 |
化学工业 | 193篇 |
金属工艺 | 9篇 |
机械仪表 | 27篇 |
建筑科学 | 33篇 |
矿业工程 | 1篇 |
能源动力 | 30篇 |
轻工业 | 41篇 |
水利工程 | 12篇 |
石油天然气 | 1篇 |
无线电 | 209篇 |
一般工业技术 | 197篇 |
冶金工业 | 106篇 |
原子能技术 | 17篇 |
自动化技术 | 182篇 |
出版年
2023年 | 9篇 |
2022年 | 16篇 |
2021年 | 28篇 |
2020年 | 14篇 |
2019年 | 21篇 |
2018年 | 28篇 |
2017年 | 41篇 |
2016年 | 44篇 |
2015年 | 26篇 |
2014年 | 34篇 |
2013年 | 55篇 |
2012年 | 60篇 |
2011年 | 73篇 |
2010年 | 47篇 |
2009年 | 46篇 |
2008年 | 50篇 |
2007年 | 39篇 |
2006年 | 40篇 |
2005年 | 32篇 |
2004年 | 32篇 |
2003年 | 31篇 |
2002年 | 28篇 |
2001年 | 24篇 |
2000年 | 26篇 |
1999年 | 32篇 |
1998年 | 40篇 |
1997年 | 33篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 8篇 |
1993年 | 16篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有1084条查询结果,搜索用时 30 毫秒
101.
Kam A.C. Kai-Yeung Siu Barry R.A. Swanson E.A. 《Selected Areas in Communications, IEEE Journal on》1998,16(7):1024-1039
Most existing wavelength-division multiplexed (WDM) networks employ circuit switching, typically with one session having exclusive use of one entire wavelength. Consequently, they are not suitable for data applications involving bursty traffic patterns. The All-Optical Network (AON) Consortium has developed an all-optical LAN/MAN test bed which provides time-slotted WDM service. We explore extensions of this service to achieve fine-grained statistical multiplexing with different virtual circuits time sharing the wavelengths in a fair manner. We develop a very fast, best effort time-slotted WDM network protocol with very good fairness and throughput characteristics. As an additional design feature, our protocol supports the assignment of guaranteed bandwidths (GBW) to selected sessions. This feature acts as a first step toward supporting integrated services at the optical layer in WDM networks 相似文献
102.
L Siegfried M Kmetová V Janigová M Sasinka V Takácová 《Canadian Metallurgical Quarterly》1995,63(11):4543-4545
A total of 109 alpha-hemolytic and 104 nonhemolytic Escherichia coli isolates from children with dyspepsia and urinary tract infections were investigated for resistance to the bactericidal activity of human serum. A significantly higher proportion of serum resistance was found in alpha-hemolytic E. coli isolates than in nonhemolytic isolates (P < 0.01). An association between the titer of alpha-hemolysin produced and serum resistance was found. 相似文献
103.
Based on a single-stage isolated power-factor-corrected power supply (SSIPP or S2IP2) employing a boost power-factor-correction (PFC) cell, the relationship between the input line voltage and line current of such switching regulators is studied. The conditions for unity power factor are derived. A control scheme to reduce the switch voltage stress while maintaining unity power factor is proposed. Practical implementation of the proposed control scheme is discussed. It is found that, by adding a simple input voltage feedforward to a conventional PWM controller, the switch voltage stress can be much reduced, while keeping the power factor very close to unity. Analysis and experimental results indicate that such a scheme is effective and feasible 相似文献
104.
Two genes from Corynebacterium equii, a Gram-positive bacterium producing the CeqI restriction-modification enzymes were cloned and sequenced. In vivo restriction experiments, DNA and amino acid sequence data suggest that the two genes code for the endonuclease and the methyltransferase enzymes. However, when the two genes are expressed in E. coli, practically no enzyme activity can be detected in the supernatants of sonicated cells. Based on the DNA sequence data CeqI restriction endonuclease (an EcoRV izoschizomer) consists of 270 amino acid residues with a predicted molecular mass of 31.6 kDa, in good agreement with the previously measured 32 +/- 2 kDa. The methyltransferase is 517 residues long (approx. 60 kDa). The two genes are in opposite orientation and overlap by 37 base pairs on the chromosome. The deduced amino acid sequence of the putative endonuclease gene revealed long stretches of hydrophobic amino acids, that may form the structural basis of the unusual aggregation properties of the restriction endonuclease. The amino acid sequence of the methylase shows homologies with other type II methyltransferases. 相似文献
105.
Ki Hwan Kim Chong Tak LeeChan Bock Lee R.S. FieldingJ.R. Kennedy 《Thin solid films》2011,519(20):6969-6973
Candidate coating materials for re-usable metallic nuclear fuel crucibles, HfN, TiC, ZrC, and Y2O3, were plasma-sprayed onto niobium substrates. The coating microstructure and the thermal cycling behavior were characterized, and U-Zr melt interaction studies carried out. The Y2O3 coating layer had a uniform thickness and was well consolidated with a few small pores scattered throughout. While the HfN coating was not well consolidated with a considerable amount of porosity, but showed somewhat uniform thickness. Thermal cycling tests on the HfN, TiC, ZrC, and Y2O3 coatings showed good cycling characteristics with no interconnected cracks forming even after 20 cycles. Interaction studies done on the coated samples by dipping into a U-20wt.%Zr melt indicated that HfN and Y2O3 did not form significant reaction layers between the melt and the coating while the TiC and the ZrC coatings were significantly degraded. Y2O3 exhibited the most promising performance among HfN, TiC, ZrC, and Y2O3 coatings. 相似文献
106.
Silicon nanowire field effect transistor sensors with SiO(2)/HfO(2) as the gate dielectric sensing surface are fabricated using a top down approach. These sensors are optimized for pH sensing with two key characteristics. First, the pH sensitivity is shown to be independent of buffer concentration. Second, the observed pH sensitivity is enhanced and is equal to the Nernst maximum sensitivity limit of 59 mV/pH with a corresponding subthreshold drain current change of ~ 650%/pH. These two enhanced pH sensing characteristics are attributed to the use of HfO(2) as the sensing surface and an optimized fabrication process compatible with silicon processing technology. 相似文献
107.
Jiaming?Li Feifei?WangEmail author Chung?Ming?Leung Siu?Wing?Or Yanxue?Tang Xinman?Chen Tao?Wang Xiaomei?Qin Wangzhou?Shi 《Journal of Materials Science》2011,46(17):5702-5708
Effects of Fe and La addition on the dielectric, ferroelectric, and piezoelectric properties of Bi0.5Na0.5TiO3–Bi0.5Li0.5TiO3–BaTiO3–Mn ceramics were investigated. Similar to the doping effect in lead-based piezoelectric materials, here the Fe-doped ceramic
created a hard effect with an improved mechanical quality factor (Q
m) ~ 160, coercive field (E
c) ~ 2.9 kV/mm, decreased dielectric constant ( e33T /e0 ) ~ 80 3, \left( {\varepsilon_{33}^{T} /\varepsilon_{0} } \right)\sim 80 3, and loss (tanδ) ~ 0.024 while the La-doped one indicated a soft feature with improved piezoelectric constant (d
33) ~ 184 pC/N, e33T /e0 ~ 983, \varepsilon_{33}^{T} /\varepsilon_{0} \,\sim { 983}, tanδ ~ 0.033, and decreased E
c ~ 2.46 kV/mm. In addition, the temperature dependence of the ferroelectric hysteresis loops and strain response under unipolar
electric field was also studied. Around the depolarization temperature T
d, large strain value was obtained with the normalized d33* d_{33}^{*} up to ~1,000 pC/N, which was suggested originated from the development of the short-range order or non-polar phases in the
ferroelectric matrix. All these would provide a new way to realize high piezoelectric response for practical application in
different temperature scale. 相似文献
108.
Can Bayram John A. Ott Kuen‐Ting Shiu Cheng‐Wei Cheng Yu Zhu Jeehwan Kim Manijeh Razeghi Devendra K. Sadana 《Advanced functional materials》2014,24(28):4492-4496
A method of forming cubic phase (zinc blende) GaN (referred as c‐GaN) on a CMOS‐compatible on‐axis Si (100) substrate is reported. Conventional GaN materials are hexagonal phase (wurtzite) (referred as h‐GaN) and possess very high polarization fields (~MV/cm) along the common growth direction of <0001>. Such large polarization fields lead to undesired shifts (e.g., wavelength and current) in the performance of photonic and vertical transport electronic devices. The cubic phase of GaN materials is polarization‐free along the common growth direction of <001>, however, this phase is thermodynamically unstable, requiring low‐temperature deposition conditions and unconventional substrates (e.g., GaAs). Here, novel nano‐groove patterning and maskless selective area epitaxy processes are employed to integrate thermodynamically stable, stress‐free, and low‐defectivity c‐GaN on CMOS‐compatible on‐axis Si. These results suggest that epitaxial growth conditions and nano‐groove pattern parameters are critical to obtain such high quality c‐GaN. InGaN/GaN multi‐quantum‐well structures grown on c‐GaN/Si (100) show strong room temperature luminescence in the visible spectrum, promising visible emitter applications for this technology. 相似文献
109.
110.
By restricting weight functions to satisfy the quadrangle inequality or the inverse quadrangle inequality, significant progress has been made in developing efficient sequential algorithms for the least-weight subsequence problem [10], [9], [12], [16]. However, not much is known on the improvement of the naive parallel algorithm for the problem, which is fast but demands too many processors (i.e., it takesO(log2
n) time on a CREW PRAM with n3/logn processors). In this paper we show that if the weight function satisfies the inverse quadrangle inequality, the problem can be solved on a CREW PRAM in O(log2
n log logn) time withn/log logn processors, or in O(log2
n) time withn logn processors. Notice that the processor-time complexity of our algorithm is much closer to the almost linear-time complexity of the best-known sequential algorithm [12]. 相似文献