全文获取类型
收费全文 | 8940篇 |
免费 | 202篇 |
国内免费 | 156篇 |
专业分类
电工技术 | 421篇 |
综合类 | 314篇 |
化学工业 | 1477篇 |
金属工艺 | 760篇 |
机械仪表 | 1075篇 |
建筑科学 | 512篇 |
矿业工程 | 108篇 |
能源动力 | 729篇 |
轻工业 | 560篇 |
水利工程 | 74篇 |
石油天然气 | 274篇 |
武器工业 | 57篇 |
无线电 | 739篇 |
一般工业技术 | 815篇 |
冶金工业 | 488篇 |
原子能技术 | 164篇 |
自动化技术 | 731篇 |
出版年
2024年 | 4篇 |
2023年 | 94篇 |
2022年 | 127篇 |
2021年 | 160篇 |
2020年 | 165篇 |
2019年 | 126篇 |
2018年 | 119篇 |
2017年 | 173篇 |
2016年 | 205篇 |
2015年 | 221篇 |
2014年 | 435篇 |
2013年 | 489篇 |
2012年 | 436篇 |
2011年 | 704篇 |
2010年 | 492篇 |
2009年 | 511篇 |
2008年 | 434篇 |
2007年 | 587篇 |
2006年 | 500篇 |
2005年 | 494篇 |
2004年 | 416篇 |
2003年 | 394篇 |
2002年 | 313篇 |
2001年 | 224篇 |
2000年 | 203篇 |
1999年 | 236篇 |
1998年 | 215篇 |
1997年 | 176篇 |
1996年 | 150篇 |
1995年 | 117篇 |
1994年 | 83篇 |
1993年 | 72篇 |
1992年 | 52篇 |
1991年 | 44篇 |
1990年 | 32篇 |
1989年 | 20篇 |
1988年 | 27篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有9298条查询结果,搜索用时 128 毫秒
101.
采用超音速火焰喷涂(HVOF)制备了WC-WB-CoCr涂层,研究了温度对WC-WB-CoCr涂层高温摩擦磨损性能的影响。通过SEM、XRD和显微硬度仪对涂层的微观组织、相结构和力学性能进行表征。通过摩擦磨损试验机和拉曼光谱仪研究了WC-WB-CoCr涂层的高温摩擦学性能和氧化产物,采用台阶仪扫描磨痕形貌并计算WC-WB-CoCr涂层的磨损率。结果表明:WC-WB-Co-Cr涂层主要由WC和CoW2B2组成,涂层结构致密,与基体结合紧密;随着磨损试验温度升高,涂层的摩擦系数从0.66降低到0.57,涂层的磨损率随着温度的升高而升高,但是其磨损率增长程度随着温度的升高而降低。在高温磨损过程中,磨痕表面的氧化膜主要由WO3和CoWO4组成,且CoWO4比WO3表现出更好的耐高温磨损性能。涂层的主要磨损机制为氧化磨损、疲劳磨损和粘着磨损。 相似文献
102.
《Journal of the European Ceramic Society》2014,34(7):1727-1732
The dielectric and ferroelectric properties of the ceramic system, (1 − x)Ba0.8Ca0.2TiO3–xBi(Zn0.5Ti0.5)O3, were investigated for compositions 0 ≤ x ≤ 0.4. X-ray powder diffraction patterns indicated tetragonal symmetry at x ≤ 0.05, switching to pseudocubic at x ≥ 0.1, with a single-phase solid solution limit at 0.2 < x < 0.3. The x = 0 and 0.05 samples were ferroelectric; a change to relaxor behaviour occurred at x ≥ 0.1, with broad frequency dependent peaks in plots of relative permittivity versus temperature. A significant reduction in the temperature dependence of relative permittivity occurred at x = 0.3, with ɛr = 1030 ± 15% over the temperature range ∼25–425 °C, and loss tangent, tan δ ≤ 0.01 from 110 °C to 420 °C. The dc resistivity values for x = 0.3 were ∼109 Ω m at 300 °C and ∼106 Ω m at 450 °C. 相似文献
103.
《Food and Bioproducts Processing》2014,92(2):208-225
Ion exchange processes are widely used in the food, bioprocessing and related industries for the isolation of proteins and other ionic species. Traditional ion exchange resins require salts, acids or bases for releasing adsorbed molecules creating a strong saline waste stream with negative environmental and economic impact. Stimuli responsive polymers (SRPs) with ion exchange functional groups can be used to selectively capture and release charged molecules from a complex mixture using physical stimuli to trigger conformational transitions in the polymer. The structural change of the polymers in response to a stimulus may lead to reduced ligand–target molecule interaction resulting in the release of the captured molecule without the use of chemical reagents, thereby reducing the environmental burden associated with ion exchange processes. The use of temperature responsive polymers has already been demonstrated for such applications at analytical scale. However, little progress has been made to extend these discoveries to the development of materials and methods amenable to industrial scale processing. So far, other SRPs such as, electric, magnetic and light responsive polymers remain largely unexplored for such application. This article discusses the potential of temperature responsive and other SRPs for developing sustainable ion exchange processes. It also highlights the material science and engineering challenges that need to be overcome to bring such processes to industrial application. 相似文献
104.
105.
F. Erchiqui 《Drying Technology》2014,32(8):946-959
This article analyzes the influence of frequency, temperature, moisture content, and structural orientation on the applicability of the Beer-Lambert law for various wood species using radio frequency and microwave radiation. To achieve this objective, the study compares the power dissipation computed from Maxwell's equation and Lambert's power law. The wood species considered are white oak (Quercus alba), Douglas fir (Pseudotsuga menziesii), trembling aspen (Populus tremuloides), white birch (Betula paperyfera), yellow birch (Betula alleghaniensis), sugar maple (Acer saccharum), and four commercial hardboards. The dielectric constant and dielectric loss factor are examined as a function of moisture conditions, temperature, frequencies, and the three principal structural orientations. The study involved 3,000 complex dielectric constants. It was found that the radial critical thickness is somewhat smaller than the tangential critical thickness (0.95 times smaller) and the longitudinal critical thickness is significantly smaller than the radial (0.52 times). It was demonstrated that the critical thickness L crit above which the Beer-Lambert law is valid for all of the wood species studied under various conditions obeys the following conditions: log10(L crt) = 0.999 log10(β?1) + 0.4122, where β?1 is the penetration depth (cm). In the case of microwave radiation, the critical thickness can be estimated from L crt = 2.615 β?1 ? 0.0626. Finally, a model is proposed to take into consideration the effect of moisture content with frequency (or with attenuation constant). 相似文献
106.
107.
108.
渤海湾盆地冀中坳陷霸县地区是地热资源富集区,其以"雄县模式"为示范引领,成功打造了中国第一个"无烟城"。为指导下一步地热能的勘探开发,基于大量油田钻井实测温度和压力数据,对该区现今地温梯度及温度、压力平面分布特征进行了系统研究,探讨了温压场与地热资源的关系。结果表明:(1)该区现今地温梯度介于21.8~73.5℃/km,平均值为33.5℃/km;(2)霸县地区地层温度随着深度的增加而逐渐升高,其平面变化特征与地温梯度展布特征相似,两者都与基底起伏形态具有很好的对应关系——对于同一深度,牛驼镇凸起温度最高,而廊固凹陷和霸县凹陷则较低,牛驼镇凸起北部、霸县凹陷中部及廊固凹陷中东部普遍存在高异常温度区,是潜在的地热资源有利开发区;(3)霸县地区现今地层压力以常压、弱超压为主,其平面分布规律随深度变化而存在着一定的差异,廊固凹陷南部和霸县凹陷南部在深度4 000 m处普遍发育中—强超压带,在开展下一步的地热能开发时需要格外注意。 相似文献
109.
《Journal of the European Ceramic Society》2022,42(9):3913-3919
Artificially tilted multilayer thermoelectric devices (ATMTDs) have attracted growing attention due to their ease in miniaturization and high flexibility in device design. However, most of these devices are inefficient due to the lack of effective strategy to optimize their material matching and geometrical configurations. Herein, a high-throughput optimization approach is employed to screen high-performance Bi2Te2.7Se0.3-based ATMTDs from a material genome database covering 230 kinds of candidates. 14 kinds of ATMTDs are found to have ZTzx,max values exceeding 0.3 and tilt angles greater than 15°. Bi0.1Sb1.9Te3/Bi2Te2.7Se0.3 ATMTD is screened out and fabricated because of its excellent transverse figure of merit, large tilt angle, and good interface compatibility. Consequently, transverse figure of merit over 0.3, thermal sensitivity greater than 0.11 mV·K?1, and power density up to 1.1 kW·m?2 are recorded in Bi0.1Sb1.9Te3/Bi2Te2.7Se0.3 ATMTD. This indicates that ATMTDs have great potential for application in the fields of temperature detection and power generation. 相似文献
110.
光环境作为菜市场物理环境的重要部
分,对农产品的颜色呈现具有较大影响,决定了
购买者对农产品的品质评价。当前,针对LED光
源相关色温对农产品颜色感知的影响研究较少,
存在着不同类型农产品外观展示的适用光源无
法明确的问题。为了探究中国人对菜市场展示光
源的视觉偏好,改善菜市场照明环境质量,提高
购买者的体验感和满意度,本研究基于菜市场
光环境现状调研结果,以蔬菜、水果和鲜肉三
类典型农产品为观察样本,选择不同相关色温
的LED(2 500 K、3 000 K、4 000 K、5 000 K、
6 500 K)作为测试光源,通过心理物理实验,从
人因工学角度探讨LED光源相关色温对农产品
颜色感知的影响。研究表明:当测试光源相关色
温增加,农产品更加接近标准光源下的颜色,显
色指数不能很好地反映光源的颜色还原性;不同类型的农产品在色彩偏好度上具有差异,水果的偏好度在相关色温4 000~5 000 K时最高,蔬菜
类的偏好度在相关色温5 000~6 500 K时最高;测试光源下,人们对鲜肉的色彩偏好度总体低于水
果和蔬菜。本研究探讨了菜市场光源相关色温对农产品颜色感知的影响,为中国人色彩感知研究
和LED光源在菜市场中科学合理的应用提供参考与依据。 相似文献