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991.
A handoff scheme with the combination of channel reservation and preemptive priority in integrated voice/data cellular mobile systems is proposed. In the scheme, calls are divided into three different classes: handoff voice calls, originating voice calls, and data calls. An access strategy with the combination of channel reservation and preemptive priority is provided to a handoff voice call. Furthermore, in order to improve the system capacity for the total voice traffic, preemptive priority is also given to partial originating voice calls. The system is modeled by a two-dimensional Markov chain. Both the iteration method and the approximate method are used to calculate and analyze some of the most important performance measures of the system. It is shown that our scheme can provide better quality of services for mobile subscribers. 相似文献
992.
制备工艺对热压烧结SiC/SiC复合材料结构与性能的影响 总被引:3,自引:0,他引:3
采用纳米SiC和亚微米SiC粉料作为基体形成原料,通过热压烧结技术制备了SiC/SiC 复合材料.研究了粉料颗粒、烧结温度、烧结压力对复合材料显微结构和各种性能的影响.结果显示,采用纳米碳化硅粉体可有效降低烧结温度,促进复合材料的致密化过程,在1780℃、20MPa条件下可获得性能优良的复合材料.而采用亚微米SiC粉体,复合材料的致密化过程需要较高的温度,但随着密度的增加,基体与纤维之间的作用力增强,不利于性能的提高. 相似文献
993.
994.
Akira Taniike Yasutomo KidaYuichi Furuyama Akira Kitamura 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(24):3237-3241
The graft polymerization method is one of the most effective techniques to produce a new polymer with unique function. To produce the polymer, we conducted experiments on radiation graft polymerization using ion beams of several hundred keV energy. A high density polyethylene (PE) film was irradiated with H+ beams, then, graft polymerization with monomer solution such as acrylic acid or acrylonitrile was conducted. Radicals generated by the interaction between the beam ions and the PE molecules become the starting point of the graft polymerization. Since the range in PE depends on ion energy, the density distribution of the graft chain can be controlled by the ion energy. Using a mask which restricts the ion beam incidence, PE sheets containing graft chains only in the unmasked area were obtained. Multiple ion beam graft polymerization can produce a polymer which has some functional bases at specified position. We have demonstrated the production of a polymer film with a three-dimensional structure. 相似文献
995.
Kentaro Fukuda Sumito IshizuNoriaki Kawaguchi Toshihisa SuyamaTakayuki Yanagida Yuui YokotaMartin Nikl Akira Yoshikawa 《Optical Materials》2011,33(8):1143-1146
Thirty millimeter diameter single crystal of Nd3+ doped LuF3 was grown using LiF as solvent. The single phase crystallization was confirmed by the powder X-ray diffraction, and high structural perfection was demonstrated by X-ray rocking curve (XRC) measurements. FWHM of XRC for 220 reflection was 32 arcsec. No remarkable absorption due to unfavorable impurities was observed from optical absorption measurements in the VUV spectral region. The crystal showed the VUV luminescence peaking around 178 nm that is consistent with the 4f25d-4f3 transition of Nd3+ ion. The luminescence intensity of Nd:LuF3 under X-ray irradiation was significantly higher than that of reported VUV scintillators such as Nd:LaF3 or Nd:LiLuF4. 相似文献
996.
Akira Mochizuki Tatsuhisa OgawaKeishi Okamoto Tatsuyuki NakataniYuki Nitta 《Materials science & engineering. C, Materials for biological applications》2011,31(3):567-573
From the knowledge that zwitterion-type polymers show good blood compatibility, the introduction of both cationic and anionic functional groups onto diamond-like carbon (DLC) surface is expected to improve blood compatibility. Thus, DLC films were treated with oxygen and ammonia gas plasmas. The surfaces were characterized in terms of chemical composition by XPS, contact angle, and zeta potential. XPS analysis showed the introductions of a carboxyl group by oxygen plasma treatment and nitrogen atoms by ammonia plasma treatment. The evaluation of blood compatibility for the DLC surfaces was carried out in terms of platelets and the coagulation system. Excellent improvement of platelet compatibility was observed by the treatment with the gas plasmas, regardless of the plasma species. As for the compatibility with the coagulation system, DLC surfaces with a high concentration of carboxyl groups (COOH) markedly activated the system via the intrinsic pathway. However, the surfaces treated with ammonia plasma did not activate the system even though they had high COOH concentration. Measurement of the zeta potential revealed that the ammonia plasma treatment raised the potential from a negative value to a positive one. Though the introduction of amino groups to the surface was not detected directly, the treatment of ammonia plasma changed the electrical state of the DLC surface having COOH group, causing a difference in blood compatibility among the DLCs obtained by various plasma conditions. 相似文献
997.
Masahiko Yagi Akira Kitamura Nobutaka Shimizu Yoshinori Yasuta Minoru Kubota 《Journal of Low Temperature Physics》2011,162(5-6):754-761
We describe a highly stable, rotating cryostat designed for torsional oscillator experiments under DC rotation, where vortex lines penetration has been studied for 3D superfluids made of monolayer He films as well as for the supersolid state in hcp solid 4He. Especially, torsional oscillator experiments on hcp solid 4He are known to be quite sensitive to small vibrations or linear velocities on the order of 10 ??m/s or less. Thus, vibrations of the apparatus may destroy the measurements if they are not smaller than or equal to those of the building or the ground itself. The torsional oscillator performance described here often gives better data under steady rotation at moderate speeds than under stationary conditions. The article describes briefly a design idea shared by the two rotating cryostats at ISSP, the University of Tokyo, and discusses the torsional oscillator (TO) experiments under DC rotation. This is truly a high speed rotating cryostat with maximum rotational speed of at least 6 revolutions per second for TO experiments. It gives also much higher stability at reasonably low rotational speed because of the well-planned structure of the double frame construction with a lot of mass for the upper drive frame for rotation and the almost mechanically isolated, except for the drive mode motion, rotating cryostat with much higher stability of the inner frame for the cryostat mount. Phenomena of quantized vortex lines penetration through a macroscopic superfluid give unique information about the superfluidity itself. A method for detection of vortex lines penetration events using TO technology is also briefly reviewed. 相似文献
998.
Masahiko Yagi Akira Kitamura Nobutaka Shimizu Yoshinori Yasuta Minoru Kubota 《Journal of Low Temperature Physics》2011,162(5-6):492-499
We report how one can detect quantized vortices in superfluids contained in cylindrical vessels in well-designed torsional oscillator (TO) experiments under DC rotation. We show the case of an artificial 3D superfluid (Fukuda et al. in Phys. Rev. B 71:212502, 2005) which is made of Kosterlits-Thouless 2D He film condensed on a porous glass substrate with a 3D connected surface of well-controlled pore size. We understand the TO experimental results with an extra energy dissipation peak under DC rotation by considering the circular quantized superflow around each of the vortex lines and interaction with thermally excited 2D vortices as discussed in Fukuda et al. (Phys. Rev. B 71:212502, 2005) and in Nemirovskii and Sonin (Phys. Rev. B 76: 224507, 2007). We discuss here the case of hcp solid 4He (see for ex. Balibar and Caupin in J. Phys., Condens. Matter 20:173201-1-19, 2008) and show the evidence of observation of the vortex lines penetration below a supersolid transition temperature (Kubota et al. in J. Low Temp. Phys. 158:572, 2010), T c , where macroscopic phase coherence is realized. It is found at exactly the same temperature T c , below which the hysteresis occurrs (Shimizu et ail. in arXiv:0903.1326, 2009). For hcp solid 4He we have reported the vortex fluid (VF) state onset temperature (Penzev et al. in Phys. Rev. Lett. 101:065301, 2008) T o =??500 mK, by detailed drive velocity, V ac dependence study using TO technique. The TO response of the hcp 4He is characterized by the energy dissipation peaked at T p near 100 mK similar to the behavior in a KT transition. The real supersolid (SS) state occurs at T c below T p and much lower than T o . Our observation of the evidence of vortex lines penetration just below T c together with the VF state properties gives support for the idea that hcp 4He shares some features with the ??new type of superconductors??, where the vortex state, involving the VF as well as various vortex solid states, has been commonly discussed (Fisher et al. in Phys. Rev. B 43(1):130, 1991; Leggett in Quantum Liquids, Oxford University Press, London, 2006). 相似文献
999.
The radiation dose to workers at nuclear power stations (NPSs) in Japan was drastically reduced between the late-1970s and the early-1990s by continuous dose-reduction programmes. The total collective dose of radiation workers in FY 2008 was 84.04 person Sv, while the average collective dose was 1.5 person Sv per reactor. The average annual individual dose was 1.1 mSv and the maximum annual individual dose was 19.5 mSv. These values are sufficiently lower than the regulatory dose limits. Radioactive effluent released from NPSs is already so trivial that additional protective measures will not be necessary. Experience in radiation protection at NPSs has been accumulated over 40 y and will be very useful in establishing a rational radiation control system in the future. 相似文献
1000.
Basic study of single crystal fibers of Pr:Lu3Al5O12 scintillator for gamma-ray imaging applications
Takayuki Yanagida Kei KamadaNoriaki Kawaguchi Yutaka FujimotoKentaro Fukuda Yuui YokotaValery Chani Akira Yoshikawa 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,652(1):256-259
Single-crystalline fibers were grown from 0.25, 0.70, and 1.50 mol% Pr-doped Lu3Al5O12 (LuAG) melts by the micro-pulling down (μ-PD) method with a diameter of 0.3-0.5 mm and a length of about 200 mm. They were cut to 10 mm long specimens, and their scintillation properties, including light yield and decay time profile, were examined. These results were compared with corresponding properties of the specimens (0.8×0.8×10 mm3) cut from the bulk crystals produced by conventional Czochralski (CZ) growth. The μ-PD-grown fibers demonstrated relatively low light yield and had the same decay time constant when compared with those of the samples cut from the CZ-grown crystals. The fiber crystals were used to assemble scintillating arrays with dimensions of Ø 0.5×10 mm2×20 pixels and Ø 0.3×10 mm2×30 pixels coated by a BaSO4 reflector. After optical coupling with a position sensitive photomultiplier tube, the fiber-based arrays demonstrated acceptable imaging capability with a spatial resolution of about 0.5 mm. 相似文献