全文获取类型
收费全文 | 23283篇 |
免费 | 2448篇 |
国内免费 | 1561篇 |
专业分类
电工技术 | 1780篇 |
技术理论 | 1篇 |
综合类 | 2640篇 |
化学工业 | 2690篇 |
金属工艺 | 992篇 |
机械仪表 | 1717篇 |
建筑科学 | 2554篇 |
矿业工程 | 751篇 |
能源动力 | 977篇 |
轻工业 | 2998篇 |
水利工程 | 796篇 |
石油天然气 | 1301篇 |
武器工业 | 246篇 |
无线电 | 2472篇 |
一般工业技术 | 2034篇 |
冶金工业 | 1006篇 |
原子能技术 | 383篇 |
自动化技术 | 1954篇 |
出版年
2024年 | 33篇 |
2023年 | 280篇 |
2022年 | 591篇 |
2021年 | 702篇 |
2020年 | 805篇 |
2019年 | 614篇 |
2018年 | 601篇 |
2017年 | 724篇 |
2016年 | 788篇 |
2015年 | 905篇 |
2014年 | 1476篇 |
2013年 | 1530篇 |
2012年 | 1854篇 |
2011年 | 2002篇 |
2010年 | 1351篇 |
2009年 | 1415篇 |
2008年 | 1262篇 |
2007年 | 1584篇 |
2006年 | 1441篇 |
2005年 | 1191篇 |
2004年 | 1012篇 |
2003年 | 791篇 |
2002年 | 726篇 |
2001年 | 634篇 |
2000年 | 478篇 |
1999年 | 442篇 |
1998年 | 339篇 |
1997年 | 296篇 |
1996年 | 273篇 |
1995年 | 250篇 |
1994年 | 164篇 |
1993年 | 137篇 |
1992年 | 127篇 |
1991年 | 107篇 |
1990年 | 76篇 |
1989年 | 58篇 |
1988年 | 58篇 |
1987年 | 32篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
1.
The slight-alkalization of generator internal cooling water (GICW) is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator. CO2 inleakage is increasingly identified as a potential security risk for GICW system. In this paper, the influence of CO2 inleakage on the slight-alkalization of GICW was theoretically discussed. Based on the equilibriums of the CO2-NaOH-H2O system, CO2 inleakage saturation was derived to quantify the amount of the dissolved CO2 in GICW. This parameter can be directly calculated with the measured conductivity and the [Na+] of GICW. The influence of CO2 inleakage on the slight-alkalization conditioning of GICW and the measurement of its water quality parameters were then analyzed. The more severe the inleakage, the narrower the water quality operation ranges of GICW, resulting in the more difficult the slight-alkalization conditioning of GICW. The temperature calibrations of the conductivity and the pH value of GICW show non-linear correlations with the amount of CO2 inleakage and the NaOH dosage. This study provides insights into the influence of CO2 inleakage on the slight-alkalization of GICW, which can serve as the theoretical basis for the actual slight-alkalization when CO2 inleakage occurs. 相似文献
2.
Adebowale Martins Obalalu Lawal Lanre Adebayo Ilhami Colak Adebayo Olusegun Ajala Fatai Adisa Wahaab 《亚洲传热研究》2022,51(5):3951-3978
Minimizing entropy generation is a technique that helps improve the effectiveness of real processes by studying the associated irreversibility of system performance of nanofluid. This study examines the entropy generation analysis of electromagnetohydrodynamic radiative Casson flow induced by a stretching Riga plate in a non-Darcian porous medium under the influence of internal energy change, Arrhenius activation energy, chemical reaction, and melting heat transfer. The thermophysical features of the fluid are assumed constant in most of the literature. However, this current research bridges this gap by considering viscosity, conductivity, and diffusivity as temperature-dependent variables. Also, the exponential decaying Grinberg term is used as a resistive force in this investigation due to the electromagnetic properties of the Riga plate in the momentum conservation equation. Some suitable dimensionless variables are introduced to remodel the transport equations into unitless ones and then solved numerically by employing Galerkin Weighted Residual Method. Analyses reveal that the Casson parameter declines the fluid velocity, while the existence of the melting parameter has the opposite effect. Also, this article includes some future recommendations. 相似文献
3.
Pengfei Liang Jie Zhu Di Wu Hui Peng Xiaolian Chao Zupei Yang 《Journal of the American Ceramic Society》2021,104(6):2702-2710
Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO2-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag+/Nb5+ co-doped (Ag1/4Nb3/4)xTi1−xO2 (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 103 and 1.6 × 104 at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics. 相似文献
4.
Ohjin Kwon Xiaoqian Cai Wentao Qu Feng Liu Jadwiga Szydłowska Ewa Gorecka Moon Jong Han Dong Ki Yoon Silvio Poppe Carsten Tschierske 《Advanced functional materials》2021,31(28):2102271
First examples of multichain (polycatenar) compounds, based on the π-conjugated [1]benzothieno[3,2-b]benzothiophene unit are designed, synthesized, and their soft self-assembly and charge carrier mobility are investigated. These compounds, terminated by the new fan-shaped 2-brominated 3,4,5-trialkoxybenzoate moiety, form bicontinuous cubic liquid crystalline (LC) phases with helical network structure over extremely wide temperature ranges (>200 K), including ambient temperature. Compounds with short chains show an achiral cubic phase with the double network, which upon increasing the chain length, is at first replaced by a tetragonal 3D phase and then by a mirror symmetry is broken triple network cubic phase. In the networks, the capability of bypassing defects provides enhanced charge carrier mobility compared to imperfectly aligned columnar phases, and the charge transportation is non-dispersive, as only rarely observed for LC materials. At the transition to a semicrystalline helical network phase, the conductivity is further enhanced by almost one order of magnitude. In addition, a mirror symmetry broken isotropic liquid phase is formed beside the 3D phases, which upon chain elongation is removed and replaced by a hexagonal columnar LC phase. 相似文献
5.
The numerical solutions of the upper-convected Maxwell (UCM) nanofluid flow under the magnetic field effects over an inclined stretching sheet has been worked out. This model has the tendency to elaborate on the characteristics of “relaxation time” for the fluid flow. Special consideration has been given to the impact of nonlinear velocity slip, thermal radiation and heat generation. To study the heat transfer, the modified Fourier and Fick's laws are incorporated in the modeling process. The mass transfer phenomenon is investigated under the effects of chemical reaction, Brownian motion and thermophoresis. With the aid of the similarity transformations, the governing equations in the ordinary differential form are determined and then solved through the MATLAB's package “bvp4c” numerically. This study also brings into the spotlight such crucial physical parameters, which are inevitable for describing the flow and heat transfer behavior. This has been done through graphs and tables with as much precision and exactitude as is possible. The ascending values of the magnetic parameter, the Maxwell parameter and the angle of the inclined stretching sheet cause decay in the dimensionless velocity while an assisting behavior of the thermal and concentration buoyancy parameters is noticed. 相似文献
6.
根据水泥烧成热耗的组成,降低高温设备表面散热是降低水泥烧成热耗的重要途径之一,而减少高温窑炉墙壁的热传导可有效降低设备的表面散热。本文在介绍无机内保温涂层隔热原理的基础上,对保温涂层的应用效果进行了对比研究,通过在传统耐火隔热材料的基础上增加新型无机内保温涂层,可有效降低高温设备外表面温度,减少水泥生产中的散热损失,达到节能降耗的目的。 相似文献
7.
8.
针对常见泥石流防治结构被冲击破坏的问题,基于“柔性消能”理念,结合张弦梁结构和竖向预应力锚杆技术,提出一种既能改善结构受力性能、增加结构整体抗冲击能力、保证结构安全可靠,又能减小结构构件截面尺寸、节约成本、便于现场施工组装和后期运营维护的新型地锚张弦梁式泥石流格栅坝,并阐述其技术原理。根据泥石流荷载分布和新型地锚张弦梁式泥石流格栅坝的受力特征,给出其简化的内力计算方法;并利用SAP2000建立新结构有限元模型,分析了结构的整体受力,验证了构件简化计算方法的合理性;结合Python语言和Qt De? signer软件开发了相应的设计计算软件,对新型地锚张弦梁式泥石流格栅坝的内力进行求解。结果表明:提出的新结构抗冲击性能好,构件受力均匀;以后设计中应关注竖杆的剪切脆性破坏和立柱偏心受力情况,保证结构安全;变形协调仅使底层张弦梁与竖杆内力偏大,实际工程应用时,应着重验算底层构件,防止其破坏;文中提出的简化计算方法能较准确的反映结构的受力特性,具有一定的合理性,研究可为新型地锚张弦梁式泥石流格栅坝的设计计算和推广应用提供理论依据和技术支持。 相似文献
9.
Rita Głowacka Agata Górska Magdalena Wirkowska-Wojdyła Rafał Wołosiak Ewa Majewska Dorota Derewiaka 《International Journal of Food Science & Technology》2019,54(11):3008-3014
The content of bioactive compounds in spent coffee grounds (SGC) was studied. SGC were obtained from Coffea arabica beans of different roasting degrees (light and dark) and different geographical origins (Nicaragua, Columbia and Mexico) processed using four brewing methods (mocha, filtered, drip and infusion). The highest caffeine and chlorogenic acid contents were determined in filtered spent coffee extracts. All extracts of light roasted spent coffee grounds showed lower browning index levels in comparison to that from dark roasted spent coffee grounds. Generally, the highest content of total polyphenolic compounds and highest antioxidant capacity were determined in extracts prepared in drip. In conclusion, the results obtained in this study indicate that the spent coffee grounds produced of domestic levels, especially those obtained from filter coffeemaker, could be considered as a good source of natural antioxidants. 相似文献
10.
Ammar Chiter 《应用聚合物科学杂志》2021,138(12):50066
In vibratory protection and insulation systems, the major problem consist to choose suitable passive elements (spring, damper, others), which are inserted between the resonator and the exciter which have the role of preventing or reducing the transmission of dynamic forces. This work consists of characterizing a synthetic rubber (SR) sample of hollow circular shape (design requirement) by determining the coefficient of energy dissipation at an average ambient temperature of 20°C with a humidity of 25%. The mechanical load and discharge tests make it possible to draw hysteresis curves through which the dissipation coefficient will be determined, the load values is between 500 and 1000 N, with 30, 60, and 90 mm/min loading speeds and a number of cycles 2, 3, and 5, these values have been chosen so as not to cause the effect of cyclic hardening and softening and also to take into consideration, that the vibration limits movement at 3 cycles, which makes this test different from other tests such as fatigue. The processing of different curves, allows to determine energy dissipation coefficient of rubber specimen and also to examine its variation as a function of load, loading speed, and number of cycles; it is possible to determine other characteristics from this coefficient, such as, damping ratio, dynamic amplification factor, and so on, necessary to study efficiency of protection systems, design, and manufacture, based on the curve of transmissibility of dynamic forces to evaluate performance rubber conditions use. 相似文献