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71.
K. Rózga-Wijas U. Mizerska W. Fortuniak J. Chojnowski R. Hałasa W. Werel 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(4):605-613
Three types of silica particles modified with vinyl groups were obtained: (i) xerogel formed by hydrolytic polycondensation
of the mixture of tetramethoxysilane (TMOS) and 1,1,1,7−tetramethoxy-3,5,7-trimethyl-3,5,7-trivinyltetrasiloxane, (ii) mesoporous
silica obtained from the same precursors in the presence of the cetyltrimethylammonium bromide (CTAB), and (iii) commercial
Fluka silica gel 60A with a vinyltriethoxysilane-treated surface. Vinyl groups on these silica materials were transformed
into silyl chloride by hydrosilylation with HMe2SiCl. These groups were used to graft living polysiloxane that was synthesized by anionic ring-opening polymerization of 2,4,6-tri(3-chloropropyl)-2,4,6-trimethylcyclotrisiloxane
and initiated by BuLi. Chloropropyl groups on the grafted polymer were used to quaternize N,N-dimethyl-n-octylamine. Silica particles with grafted polysiloxane having quaternary ammonium salt (QAS) groups pendant to polymer chains
were obtained. Silica material with QAS groups directly attached to the surface were generated by the action of N,N-dimethyl-n-octylamine on particles obtained by the sol–gel process involving tetraethoxysilane (TEOS) with 3-chloropropyltriethoxysilane.
The bacteriocidal properties of all these materials were tested in water suspension against five representative strains for
Gram-positive and Gram-negative bacteria. Some of the silica–polysiloxane hybrid materials have good antibacterial properties
against Gram-positive strains, but not as good as the non-tethered QAS-substituted polysiloxane in water solution. The QAS
groups that are directly bonded to the silica material surface are inactive. 相似文献
72.
Harukazu Yoshino Zeynel Bayindir Joydeep Roy Ben Shaw Heon-ick Ha Andrei Lebed Michael J. Naughton 《Journal of Low Temperature Physics》2006,142(3-4):323-326
A new TTP donor, Me-DH-TTP (2-methyl-5-(1,3-dithiolan-2-yliden)-1,3,4,6-tetrathiapentalene), was designed to realize a system
with large on-site Coulomb repulsion as compared with the previously known bis-fused type TTP donors. Probably as a consequence,
(Me-DH-TTP)2AsF6 exhibits semiconducting behavior from room temperature to liquid helium temperature. By increasing pressure, metallic behavior
appears below 300 K, and with distinct metal-insulator (M-I) transition up to 2.2 GPa. This M-I transition suddenly disappears
beyond 2.5 GPa, and metallic state is stabilized down to 2.6 K. We discuss the possibility of quantum critical point around
2.4 GPa. 相似文献
73.
Jung-Hyuk Koh Mun-Su Ha Soon-Jong Jeong Jae-Sung Song Tae-geun Kim Sang-Mo Koo Jae-geun Ha 《Journal of Electroceramics》2006,16(4):403-406
The solid solution of Pb(Mg,Nb)O3-Pb(Zr,TiO) O3 materials have high piezoelectric constant of 600 ∼650 pC/N and electromechanical coupling coefficient k
p of 0.65. Due to such high piezoelectric constant and electromechanical coupling coefficient, Pb(Mg,Nb)O3-Pb(Zr,TiO)O3 materials have been attracted attentions for the applications of multilayer ceramic actuators. Actuators can be produced
by staking piezoelectric ceramic materials and inner electrodes, alternatively. However, it is difficult to fabricate huge
ceramic actuators without any serious problems during the process conditions. Because ceramic are easily cracked during the
sintering process, due to strikingly different shrinkage rate between the ceramic materials and metal electrodes. In this
research, new jointing methods will be proposed for huge ceramic actuators, and then their electrical properties were investigated.
Time dependent leakage current and impedance spectroscopy were employed to expect device performances. 相似文献
74.
利用压实热拌沥青混合料的空隙率和矿料间隙率等体积特性,考虑集料吸收沥青的情况,提出了“有效油石体积比”的概念,依据最佳有效油石体积比,分析研究了同类级配矿料的最佳油石比之间的关系,建立了具有普遍意义的关系式,并与新的公路沥青路面施工技术规范提供的预估公式作了比较. 相似文献
75.
Seok-In Na Ga-Young Ha Dae-Seob Han Seok-Soon Kim Ja-Yeon Kim Jae-Hong Lim Dong-Joon Kim Kyeong-Ik Min Seong-Ju Park 《Photonics Technology Letters, IEEE》2006,18(14):1512-1514
The selective wet etching of a p-GaN layer by using a solution of KOH in ethylene glycol (KE) was studied to enhance the optical and electrical performance of the GaN-based light-emitting diodes (LEDs). The surface of the p-GaN, which was selectively etched in the KE solution, showed hexagonal-shaped etch pits. The light-output power of etched LEDs was improved by 29.4% compared to that of the nonetched LED. This improvement was attributed to the increase in the probability of photons to escape due to the increased surface area of textured surface and the reduction in contact resistance of the ohmic layer resulting from the increased contact area and hole concentration on the textured p-GaN. The reverse leakage current of the LED was also greatly decreased due to the surface passivation and the removal of defective regions from the p-GaN. 相似文献
76.
Operation, system architectures, and physical Layer design considerations of distributed MAC protocols for UWB 总被引:2,自引:0,他引:2
Impulse-based ultra wideband (I-UWB) is an attractive radio technology for large ad hoc and sensor networks due to its robustness to harmful multipath effects, sub-centimeter ranging ability, simple hardware, and low radiated power. To scale to large sizes, networks often implement distributed medium access control (MAC) protocols. However, most MAC protocols for I-UWB are centralized, and they target small wireless personal area networks and cellular networks. We propose three distributed MAC protocols suitable for I-UWB. Two multichannel protocols, called multichannel pulse sense multiple access (M-PSMA) and multichannel ALOHA achieve high aggregate throughput. A busy-signal protocol, called busy-signal multiple access (BSMA), reduces the energy wasted from re-transmitted packets. This paper describes the three protocols in terms of the protocol's operation, the supporting system architecture, and the I-UWB physical layer. Physical layer simulations confirm the feasibility of implementing the proposed systems and also provide parameters for network simulations. Network simulations show that the throughput of M-PSMA exceeds that of a centralized time-division multiple-access protocol and that the energy efficiency of BSMA far surpasses that of other distributed protocols. 相似文献
77.
Recrystallization and grain growth of a cold-rolled gold sheet with 98 pct reduction in area (RA) were investigated with electron
backscatter diffraction (EBSD) and X-ray diffraction (XRD). Gold with some dopants (Be, Ca, and La) was used in this research
and its recrystallization temperature was 320 °C. Isothermal annealing experiments at 400 °C, 500 °C, and 600 °C were carried
out for the cold-rolled gold sheet, and recrystallization texture was examined. In the cold-rolled gold sheet, α- and β-fibers were measured mainly and some shear texture components were found on the surface. Shear texture components remained
on the surface for 2 hours at 400 °C and were consumed by other recrystallized grains after 24 hours at 400 °C. Microstructure
and texture evolution during in-situ annealing at 400 °C were investigated from the cold-rolled state to the fully recrystallized state using EBSD. Most of the
newly, recrystallized grains came from the deformed β-fiber regions and consisted of β-fiber, cube, and other random orientations. 相似文献
78.
Jong-Yoon Ha Ji-Won Choi Chong-Yun Kang Doo Jin Choi Hyun-Jai Kim Seok-Jin Yoon 《Materials Chemistry and Physics》2005,90(2-3):396-400
The microstructure and piezoelectric properties of the 0.01Pb(Mg1/2W1/2)O3–0.41Pb(Ni1/3Nb2/3)O3–0.35PbTiO3–0.23PbZrO3 + 0.1 and 0.3 wt.% Y2O3 + x ZnO ceramics were investigated. The crystal structure changed from psudocubic to tetragonal when ZnO added. The average grain size increased from 4 μm to 8 μm with the addition of ZnO by oxygen diffusion, even if the growth rate was low. When ZnO added until 0.5 wt.%, the , kp and d33 values of specimens were slightly increased regardless Y2O3 contents. The curie point of PMW–PNN–PT–PZ ceramics were increased from 162 °C to 232 °C, as increasing the ZnO contents. When ZnO added, the kp of specimens slightly was increased regardless Y2O3 contents. The mechanical quality factors were abruptly decreased regardless Y2O3 contents, when ZnO added until 0.75 wt.%. The optimized piezoelectric properties were obtained; d33 = 730 (pC/N), kp = 60, Qm = 50, and = 4750, when PMW–PNN–PT–PZ + 0.3 wt.% Y2O3 + 0.5 wt.% ZnO sintered at 1200 °C for 1 h. 相似文献
79.
Fuzzy Web ad selector based on Web usage mining 总被引:1,自引:0,他引:1
Sung Min Bae Sang Chan Park Sung Ho Ha 《Intelligent Systems, IEEE》2003,18(6):62-69
Internet and Web technologies are widely available, making it easier for companies to conduct business and transfer information to customers. Moreover, they speed up financial transactions efficiently, reducing the transaction costs of commercial activities that businesses would normally incur. So, Internet business has created a competitive environment, a successful company wanting to survive and gain a competitive advantage must provide an acceptable bundle of customized services that satisfy customers' needs. Despite the Internet's obvious benefits as a new communication medium its advertising gives the same advertising messages to all customers and so has suffered from poor responses. To raise a Web ad's effectiveness, we propose a Web ad selector that personalizes advertising messages for customers based on their preferences and interests. The Web ad selection system divides Web site customers with similar preferences into several segments through Web usage mining. It uses fuzzy rules that express customer segments' surfing patterns on the basis of expert advice, and recommends appropriate ads by fuzzy inference. 相似文献
80.
Off-line, handwritten numeral recognition by perturbation method 总被引:4,自引:0,他引:4
This paper presents a new approach to off-line, handwritten numeral recognition. From the concept of perturbation due to writing habits and instruments, we propose a recognition method which is able to account for a variety of distortions due to eccentric handwriting. We tested our method on two worldwide standard databases of isolated numerals, namely CEDAR and NIST, and obtained 99.09 percent and 99.54 percent correct recognition rates at no-rejection level respectively. The latter result was obtained by testing on more than 170000 numerals 相似文献