全文获取类型
收费全文 | 3259篇 |
免费 | 78篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 187篇 |
综合类 | 5篇 |
化学工业 | 1054篇 |
金属工艺 | 109篇 |
机械仪表 | 107篇 |
建筑科学 | 93篇 |
能源动力 | 142篇 |
轻工业 | 198篇 |
水利工程 | 7篇 |
石油天然气 | 3篇 |
无线电 | 184篇 |
一般工业技术 | 728篇 |
冶金工业 | 174篇 |
原子能技术 | 121篇 |
自动化技术 | 244篇 |
出版年
2023年 | 17篇 |
2022年 | 47篇 |
2021年 | 54篇 |
2020年 | 24篇 |
2019年 | 36篇 |
2018年 | 56篇 |
2017年 | 50篇 |
2016年 | 64篇 |
2015年 | 53篇 |
2014年 | 71篇 |
2013年 | 167篇 |
2012年 | 109篇 |
2011年 | 200篇 |
2010年 | 142篇 |
2009年 | 148篇 |
2008年 | 174篇 |
2007年 | 118篇 |
2006年 | 139篇 |
2005年 | 123篇 |
2004年 | 89篇 |
2003年 | 119篇 |
2002年 | 84篇 |
2001年 | 62篇 |
2000年 | 67篇 |
1999年 | 62篇 |
1998年 | 106篇 |
1997年 | 100篇 |
1996年 | 81篇 |
1995年 | 52篇 |
1994年 | 41篇 |
1993年 | 50篇 |
1992年 | 37篇 |
1991年 | 34篇 |
1990年 | 35篇 |
1989年 | 50篇 |
1988年 | 31篇 |
1987年 | 35篇 |
1986年 | 56篇 |
1985年 | 47篇 |
1984年 | 58篇 |
1983年 | 51篇 |
1982年 | 33篇 |
1981年 | 27篇 |
1980年 | 22篇 |
1979年 | 27篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 12篇 |
1974年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有3356条查询结果,搜索用时 10 毫秒
131.
In this study, the effect of temperature on the stereoselectivity of phospholipase D (PLD) toward the two primary hydroxyl
groups of glycerol in the transphosphatidylation reaction of phosphatidylcholine to phosphatidylglycerol (PtdGro) was investigated.
For this purpose, PLD from bacteria (Streptomyces septatus TH-2, S. halstedii subsp. scabies K6, and Actinomadura sp.) and cabbage were tested. At the reaction temperatures employed (0–60°C), the proportions of the two PtdGro diastereomers,
namely, 1,2-dioleoyl-sn-glycero-3-phospho-3′-sn-glycerol (R,R configuration) and 1,2-dioleoyl-sn-glycero-3-phosphol-1′-sn-glycerol (R,S configuration), which were produced with PLD from Streptomyces TH-2 and Actinomadura sp., changed gradually from 50% R,R and 50% R,S at 50–60°C to 70% R,R and 30% R,S at O°C. These alterations suggested that the stereoselectivity of the bacterial PLD toward the two primary hydroxyl groups
of prochiral glycerol was significantly influenced by reaction temperature. PLD from Streptomyces K6 showed relatively little effect of temperature on stereoselectivity, giving 65–69% R,R in the temperature range of 60–10°C examined. The plots of In ([R,R]/[R,S]) vs. 1/T gave good linear fits for these three bacterial PLD. No temperature effect was observed for cabbage PLD, which gave an almost
equimolar mixture of the R,R and R,S diastereomers in the range from 0 to 40°C. The temperature-dependent change in enantiomeric selectivity of the bacterial
PLD promises potentially profitable commercial exploitation. 相似文献
132.
Yamaguchi A Uejo F Yoda T Uchida T Tanamura Y Yamashita T Teramae N 《Nature materials》2004,3(5):337-341
A mesoporous membrane composed of nanochannels with a uniform diameter has a potential use for precise size-exclusive separation of molecules. Here, we report a novel method to form a hybrid membrane composed of silica-surfactant nanocomposite and a porous alumina membrane, by which size-selective transport of molecules across the membrane becomes possible. The nanocomposite formed inside each columnar alumina pore was an assembly of surfactant-templated silica-nanochannels with a channel diameter of 3.4 nm; the channel direction being predominantly oriented along the wall of the columnar alumina pore. Molecules could be transported across the membrane including the silica-surfactant nanocomposite with a capability of nanometre-order size-exclusive separation. Our proposed membrane system has a potential use not only for separation science, but also catalysis and chip technologies. 相似文献
133.
A principal research area in biomolecular computing is the development of analytical methods for evaluating computational fidelity and efficiency. In this work, the equilibrium theory of the DNA helix-coil transition is reviewed and expanded, as applied to the analysis and design of oligonucleotide-based computers. After a review of the equilibrium apparatus for modeling the helix-coil transition for single dsDNA species, application to complex hybridizing systems is discussed, via decomposition into component equilibria, which are presumed to proceed independently. The alternative approach, which involves estimation of a mean error probability per hybridized structure, or computational incoherence, is then presented, along with a discussion of a special-case exact solution (directed dimer formation), and an approximate general solution, applicable to conditions of uniform fractional-saturation. In order to clarify the opposing nature of the predictions of these two models, simulations are presented for the uniform saturation solution for , as applied to a small Tag–Antitag (TAT) system, along with the behavior expected via isolated melting curves. By a comparison with the predictions of a recent, TAT-specific solution for , the views provided by these generalized approximate models are shown to define the opposing limits of a more general error-response. 相似文献
134.
Profile structure of magnetic flux lines in type-II superconductor from a rectangular electron hologram 总被引:1,自引:0,他引:1
Harada K Beleggia M Endo J Kasai H Togawa Y Matsuda T Tonomura A 《Journal of electron microscopy》2003,52(4):369-373
Profile magnetic configuration of a quantized flux line and flux-line lattice penetrating a type-II superconductor thin foil, niobium, was observed by electron holography and Lorentz microscopy using a 300 kV field-emission electron microscope. Each single flux line was distributed periodically as lattice structure in the mixed state just below its critical temperature of 8.5 K, while at low temperature of 5 K the flux lines were weakly bound as bundles. In order to observe the flux-line distribution over a wide area, discrete Fourier transform reconstruction in the holography was extended for a rectangular area without loss of information and data precision. 相似文献
135.
Akira Yamaguchi Hirofumi Nema Yuichi Tanaka Hidehiko Ishimoto 《Journal of Low Temperature Physics》2007,148(5-6):755-759
Two-dimensional anti-ferromagnetic solid 3He on graphite, so called 4/7 phase, is a highly frustrated magnetic system and its ground state is considered to be a gapless spin liquid. Then how is the behavior in high magnetic fields? We tried to observe the magnetization curve at around 1 mK in high magnetic fields up to 10 T, using a Faraday-type magnetometer. To eliminate a large background signal from graphite as a substrate and copper as a thermal link, a double gradient coil system is employed to produce opposite field gradients in two regions equidistant from the field center. Preliminary results of the 4/7 phase on graphite show no saturated magnetization even at 1 mK and 10 T, suggesting the existence of magnetization plateau. 相似文献
136.
Takuya Otani Kenji Hashimoto Takaya Isomichi Akira Natsuhara Masanori Sakaguchi Yasuo Kawakami 《Advanced Robotics》2013,27(22):1197-1206
In previous studies, various stabilizing control methods for humanoids during the stance phase while hopping and running were proposed. Although these methods contribute to stability while hopping and running, it is possibility that the control during the flight phase could also affect the stability. In this study, we investigated whether the control during the flight phase can affect the stability of a humanoid while running. To achieve stable hopping, we developed a control system that accounts for the angular momentum of the whole body during the flight phase. In this system, the angular momentum generated by the motion of the lower body in each time interval is calculated during the flight phase, and the trunk joints are controlled to generate the angular momentum necessary to compensate for the deviation of the waist posture, which is used as the reference point for the motion coordinate system of the robot. Once the proposed control system was developed and simulated, we found that the hopping duration in the unconstrained state was extended. 相似文献
137.
Mingcong Deng Changan Jiang Akira Inoue Chun-Yi Su 《International journal of systems science》2013,44(4):643-652
This article presents an operator-based robust control method for nonlinear systems with Prandtl–Ishlinskii (PI) hysteresis. On the existence of the hysteresis, the system usually exhibits undesirable oscillations and even instability. While addressing the hysteresis, PI model is adopted to describe it. Especially, the PI model is decomposed into two terms: an invertible part and a disturbance part. In this way, the invertible part could be considered as a part of the nonlinear system. Based on the concept of Lipschitz's operator and the robust right coprime factorisation condition, a robust control design scheme is given to guarantee the bounded input bounded output stability of the obtained system. Further, a tracking operator design method is given to ensure the control system output-tracking performance under the existence of the disturbance part. Numerical simulation results are presented to validate the effectiveness of the proposed method. 相似文献
138.
Akira Kojima Sugio Ōtani Terushi Iwata Sadakatsu Yanagisawa EikŌ Sairenji Kunio Niijima 《Carbon》1984,22(1):47-52
Blade- and tooth-root-form carbon dental implants were prepared by fixing fine Rahmen surface (FRS) layers of carbon fabric on a carbon fiber-reinforced carbon (CFRC) core. The fixing was successfully performed through the low-temperature deposition of pyrolytic carbon using cis-1,2-dichloroethylene as the raw material. The resultant implants showed flexural and compressive strength more than 150 and 100 MPa, respectively. The outer part of this FRS layer contained many pores ranging from 30 to 300 μm in diameter and 40–75% in volume fraction.New bone was generated in the open pores after being embedded in the femur of a monkey for 6 months. The shear strength of the embedded implant vs bone interface was 15 MPa. On the other hand, the blade-form FRS implant in the mandible of a monkey gave a locking system consisting of “bone-collagen fiber-calcified layer” after two years under a masticating pressure. The latter is very similar to the natural tooth system. 相似文献
139.
Tamada Tsutomu Ueda Yu Kido Ayumu Yoneyama Masami Takeuchi Mitsuru Sanai Hiroyasu Ono Kentaro Yamamoto Akira Sone Teruki 《Magma (New York, N.Y.)》2022,35(4):549-556
Magnetic Resonance Materials in Physics, Biology and Medicine - Image quality (IQ) of diffusion-weighted imaging (DWI) with single-shot echo-planar imaging (ssEPI) suffers from low signal-to-noise... 相似文献
140.
Scintillation properties of Tm-doped Lu3Al5O12 single crystals 总被引:1,自引:0,他引:1
Makoto Sugiyama Yutaka Fujimoto Takayuki Yanagida Daisuke Totsuka Yuui Yokota Akira Yoshikawa 《Optical Materials》2011,34(2):439-443
Using the micro-pulling-down (μ-PD) method, Tm-doped Lu3Al5O12 (Tm:LuAG) single crystals were grown to examine their scintillation properties. In transmittance spectra, they exhibited about 80% transparency in the wavelengths longer than 320 nm and five absorption lines due to Tm3+ 4f–4f transitions were observed. 241Am α-ray excited radioluminescence spectra were measured and intense 4f–4f emission peaks were observed with the host emission. When excited by 137Cs γ-Ray to obtain pulse height spectra, Tm 1% doped LuAG showed the highest light yield coupled with a photomultiplier (PMT) or a silicon avalanche photodiode (Si-APD). The light yield was estimated to be 5800 and 7300 photons/MeV for PMT and Si-APD, respectively. Decay time profiles consist of two exponential components and the fast and slow components are considered to be attributed to the host and the combination of the host and Tm3+ 4f–4f emission, respectively. 相似文献