全文获取类型
收费全文 | 2299篇 |
免费 | 386篇 |
国内免费 | 165篇 |
专业分类
电工技术 | 62篇 |
技术理论 | 1篇 |
综合类 | 220篇 |
化学工业 | 288篇 |
金属工艺 | 105篇 |
机械仪表 | 121篇 |
建筑科学 | 46篇 |
矿业工程 | 23篇 |
能源动力 | 173篇 |
轻工业 | 19篇 |
水利工程 | 9篇 |
石油天然气 | 15篇 |
武器工业 | 45篇 |
无线电 | 700篇 |
一般工业技术 | 415篇 |
冶金工业 | 26篇 |
原子能技术 | 31篇 |
自动化技术 | 551篇 |
出版年
2024年 | 15篇 |
2023年 | 182篇 |
2022年 | 116篇 |
2021年 | 150篇 |
2020年 | 161篇 |
2019年 | 121篇 |
2018年 | 139篇 |
2017年 | 165篇 |
2016年 | 163篇 |
2015年 | 130篇 |
2014年 | 176篇 |
2013年 | 155篇 |
2012年 | 192篇 |
2011年 | 144篇 |
2010年 | 129篇 |
2009年 | 118篇 |
2008年 | 54篇 |
2007年 | 74篇 |
2006年 | 73篇 |
2005年 | 38篇 |
2004年 | 22篇 |
2003年 | 27篇 |
2002年 | 45篇 |
2001年 | 23篇 |
2000年 | 19篇 |
1999年 | 28篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 24篇 |
1987年 | 31篇 |
1986年 | 35篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有2850条查询结果,搜索用时 78 毫秒
81.
In contrast to pure ammonia, some additives into it may provide better solubility of the mineral oils, higher refrigeration capacity and lower discharge temperature of the compressor. In this paper, the vapor liquid phase equilibrium for the ammonia + 1,1-difluoroethane system at temperatures ranging from 253.150 K to 293.150 K were studied. The Peng–Robinson equation of state with the Huron–Vidal mixing rule involving the non-random two-liquid activity coefficient model was employed to describe the VLE behavior of the system concerned. The maximum average absolute relative deviation of pressure and average absolute deviation of vapor phase are 0.31% and 0.009, respectively. A positive azeotropic behavior was exhibited at the experimental temperature range. 相似文献
82.
《Optical Fiber Technology》2013,19(1):40-46
It is proposed and demonstrated a design of 2-to-1 photonic data selector based on the cross-phase modulation in a highly nonlinear fiber. By using bidirectional configuration, this scheme has potentially advantages of cost effective and simple structure. The correct output logic function is obtained at 40 Gbit/s without using any additional input light beams. In addition, the output signals have a single spectrum component by reasonable selecting input signals wavelength, which is important for transmission and scalability. The dependences of performances on signal wavelength, pump power, the temporal relative position of pulses, as well as the OSNR and chirp of input signals are calculated and discussed respectively, showing impressive operation performance. This scheme could be a promising candidate for future ultrafast all-optical signal processing applications. 相似文献
83.
《Microelectronics Journal》2014,45(8):1093-1102
This paper aims to present in detail the design, fabrication and the various characterization techniques adopted in realizing a novel miniature-size switched capacitor based phase shifter. The work strives to provide an all-round development of a DMTL (Distributed MEMS Transmission Line) based phase shifting unit yielding an overall phase shift of 15° at a frequency of 15 GHz. The RF MEMS (Radio Frequency Micro Electro Mechanical Systems) Switched Capacitor based phase shifter has highly miniaturized dimensions, and is capable of solving many limitations to which the conventional Switched Capacitors are mostly susceptible. This miniature RF MEMS switched capacitor actuates at a low actuation voltage of 12 V, exhibits a fundamental frequency of vibration as high as 1.468 MHz and a switching time of 1.4 µs which is an improvement over the other reported designs. Various characterization results seem to validate the simulations. 相似文献
84.
O. Kirichek A.J. Church M.G. Thomas D. Cowdery S.D. Higgins M.P. Dudman Z.A. Bowden 《低温学》2012,52(7-9):325-330
Adhesion and plasticity of polycrystalline solid methane have been studied in the temperature range 10–90 K. It was shown that adhesion is very strong in the 50–90 K temperature range where the solid methane is soft and sticky. Closer to the melting point (at 90.6 K) the solid methane behaves as extremely viscous non-Newtonian liquid. Below 30 K solid methane loses its stickiness and ductility and acts like ordinary glass. Methane adhesion remains similar for very different materials. We have also made some video observations which reveal unexpected and mostly inexplicable properties of solid methane which could be of some interest for designing new methane moderators for neutron sources and planetary physics particularly the study of the environment of Titan. 相似文献
85.
To fast remove the surface damage layer from single-crystal-diamond, we have developed a chemical etching process using molten KCl and KOH solution at high temperature around 1100 °C. High removal rate about R{001} = 2.0 μm/h, R{101} = 20 μm/h and R{111} = 26 μm/h was achieved for the {001} sample surfaces, {101} and {111} sample edges, respectively. Laser microscope observation has confirmed that the {001} surface flatness has been greatly improved after etching and surface roughness formed during previous lift-off process has been effectively removed. 相似文献
86.
C. Niu D. Z. Liu X. H. Li Y. H. Sun Y. H. Li S. F. Qi X. N. Zeng 《Journal of Low Temperature Physics》2013,170(5-6):322-327
A new method for the prediction of the geomagnetic variation time series based on multiple geomagnetic components is presented in this paper. The method used the data of multiple geomagnetic components (H, D, Z) with different kinds of combination (H, Z; H, D; H, D, Z) from a series of geomagnetic stations to predict the Z component (both in single-step prediction and multi-steps prediction). The comparison and analysis between the new method and the method based on single Z component are done in the paper. The results indicate that the new prediction method based on components (Z, H) has a higher precision than the model based on single Z component. 相似文献
87.
《Ceramics International》2017,43(3):3346-3355
The structural, mechanical, and thermodynamic properties of cubic Y2O3 crystals at different hydrostatic pressures and temperatures are systematically investigated based on density functional theory within the generalized gradient approximation. The calculated ground state properties, such as equilibrium lattice parameter a0, the bulk modulus B0, and its pressure derivative B0′ are in favorable agreement with the experimental and available theoretical values. The pressure dependence of a/a0 and V/V0 are also investigated. Furthermore, the elastic constants Cij, bulk modulus B, shear modulus G, Young's modulus E, the ductile or brittle (B/G), Vickers hardness Hv, isotropic wave velocities and sound velocities are calculated in detail in a pressure range from 0 to 14 GPa. It was found that the Debye temperature decreases monotonically with an increase in pressure, the calculated elastic anisotropic factors indicate that Y2O3 has low anisotropy at zero pressure, and that its elastic anisotropy increases as the pressure increases. Finally, the thermodynamic properties of Y2O3, such as the dependence of the heat capacities CV and CP, the thermal expansion coefficient α, the isothermal bulk modulus, and the Grüneisen parameter γ on temperature and pressure, are discussed from 0 to 2000 K and from 0 to 14 GPa, respectively, applying the non-empirical Debye model in the quasi-harmonic approximation. 相似文献
88.
Based on learning neighborhood patches a new single face hallucination method is proposed in this paper. In the proposed method, each input low-resolution (LR) position-patch and all patches in a local window centered at the same position of training images are used to hallucinate a high-resolution (HR) face patch, meanwhile two local similarity measurements between each input LR patch and all local LR and HR neighborhood patches of training images are computed to constrain the hallucination. Additionally, a residue image is estimated for the further improvement of the reconstructed result. Experimental results show that the proposed method can obtain superior or competitive results. 相似文献
89.
《低温学》2018
The linear compressor works as an important driver for high frequency regenerative cryocoolers. The acoustic power output of the compressor is a critical parameter in the design and the optimization of a linear compressor. To measure this parameter, several approaches based on different theories have been developed. In this paper, the RC load approach and the back chamber approach have been applied to a linear compressor to measure the acoustic power output. The results measured by the approaches indicate a good consistency with the theoretical calculation and reveal the connections between different approaches.The difference between the acoustic power at the piston surface and the exit of a linear compressor has been analyzed based on the experimental results from the RC load approach and the back chamber approach. The volume flow rate difference which accounts for the acoustic power difference is studied theoretically. Furthermore, based on the RC load approach, the optimum impedance together with the impedance cloudy map for the linear compressor to reach its highest efficiency has been obtained by analyzing the experimental and the theoretical results. 相似文献
90.
《International Journal of Hydrogen Energy》2020,45(7):5055-5066
In this paper, a novel Ag NPs-PANI/MnO2 tag was synthesized for the first time, and the electrochemical immunoassay for carcinoembryonic antigen (CEA) was achieved. In this experiment, gold nanoparticles (Au NPs) were used as an electrochemical sensing platform to increase conductivity and improve electrode surface capture antibody (Ab1). We use PANI as a green sacrificial agent reduces Ag NPs and MnO2, while improving the conductivity and electrochemical stability of the immunosensor. MnO2 and Ag NPs effectively raise the sensitivity of the sensor by catalytically reducing hydrogen peroxide (H2O2) into water and oxygen to achieve a double amplified sensing signal. It is found that the surface plasmon resonance of Ag NPs has an interesting SERS characteristic structure, and the equivalent circuit simulation of the electrode assembly process results in an error of less than 10%, indicating that the electrochemical immunosensor is successfully prepared. Under optimal conditions, the electrochemical immunosensor has a linear range of 0.0005–80 ng/mL and a detection limit of 0.17 pg/mL (S/N = 3). The immunosensor is expected to be used in clinical laboratories to detect CEA and other tumor markers in human plasma for precancerous screening or surveillance. 相似文献