全文获取类型
收费全文 | 5903篇 |
免费 | 544篇 |
国内免费 | 307篇 |
专业分类
电工技术 | 478篇 |
综合类 | 474篇 |
化学工业 | 1080篇 |
金属工艺 | 130篇 |
机械仪表 | 376篇 |
建筑科学 | 188篇 |
矿业工程 | 60篇 |
能源动力 | 532篇 |
轻工业 | 93篇 |
水利工程 | 47篇 |
石油天然气 | 178篇 |
武器工业 | 66篇 |
无线电 | 1279篇 |
一般工业技术 | 552篇 |
冶金工业 | 132篇 |
原子能技术 | 89篇 |
自动化技术 | 1000篇 |
出版年
2024年 | 9篇 |
2023年 | 76篇 |
2022年 | 89篇 |
2021年 | 134篇 |
2020年 | 143篇 |
2019年 | 123篇 |
2018年 | 122篇 |
2017年 | 146篇 |
2016年 | 195篇 |
2015年 | 233篇 |
2014年 | 366篇 |
2013年 | 386篇 |
2012年 | 431篇 |
2011年 | 502篇 |
2010年 | 383篇 |
2009年 | 390篇 |
2008年 | 342篇 |
2007年 | 421篇 |
2006年 | 353篇 |
2005年 | 287篇 |
2004年 | 205篇 |
2003年 | 226篇 |
2002年 | 183篇 |
2001年 | 172篇 |
2000年 | 155篇 |
1999年 | 132篇 |
1998年 | 106篇 |
1997年 | 80篇 |
1996年 | 73篇 |
1995年 | 62篇 |
1994年 | 42篇 |
1993年 | 52篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有6754条查询结果,搜索用时 31 毫秒
1.
针对现有基于视频监控的人流量统计方案成本高、算法复杂且不利于个人隐私保护的局限性,利用毫米波雷达体积小、成本低、分辨率高的特点,提出了一种基于双时间点检测的人流量监测方法。该方法先获取人体目标散射点位置和多普勒频移信息来构成点云数据,然后根据多普勒频移正负来判断人体的运动方向,并筛选具有高多普勒频移值的点云数据以降低干扰点对聚类结果的影响;在双时间点对特定区域内人员数量进行统计,并根据双时间点之间所获取的点云数据聚类结果对所统计人员数据进行修正。实验结果表明,该方法能够用匿名的方式以较高的正确率统计人员进出。 相似文献
2.
Dongdong Ji Zheng Liu Bailing Jiang Xiaofei Luo 《International Journal of Hydrogen Energy》2021,46(27):13960-13970
The evaluation of cell's weatherability is of practical interest. To further improve the soluble lead flow battery's weatherability, physiochemical properties of electrolytes containing fluoborate, perchlorate, methanesulfonate and trifluoromethanesulfonate are investigated from ?60 to 50 °C. Activities of CF3SO3H and HClO4 are poor in trifluoromethanesulfonate and perchlorate solutions due to common anion effect. The solubility of lead salt can be improved by increasing temperature, but worsened by increasing acid's content. With the temperature increasing, the conductivity is enhanced, and the viscosity is lowered for four solutions. The same results have been found by increasing acid's content except for CF3SO3H. The high energy efficiency can be achieved for cells over ?40–0 °C using fluoborate and perchlorate solutions, 73.2% at ?40 °C and 78.1% at ?30 °C respectively. Over the temperature range of 20–50 °C, the cells with methanesulfonate and trifluoromethanesulfonate solutions have good performance, 77.4% and 73.7% at 50 °C respectively. 相似文献
3.
《Journal of the European Ceramic Society》2020,40(13):4647-4654
The in vitro lifetime assessment of dental zirconia has been the focus of researchers. This work mainly studied the cyclic fatigue lifetime in saliva and aging lifetime of three commercial zirconia dental materials: two kinds of 3 mol%-yttria stabilized zirconia ST(super-translucence) and MT(medium-translucence), in which MT contains a small amount of alumina; a 5 mol%-yttria stabilized zirconia TT(tooth-translucency). ST and MT materials have higher initial mechanical strength (flexural strength) and initial crack propagation threshold than TT materials, thus they have longer cycle fatigue lifetime, but TT has best aging resistance(no aging) in existing aging procedures. MT has a higher initial mechanical strength and better aging resistance than ST samples due to the influence of alumina at grain boundary, but has lower strength reliability. Finally the service lifetime of the three materials was evaluated, and some guidance for their use is provided. 相似文献
4.
Robert Creutznacher Eric Schulze Georg Wallmann Prof. Dr. Thomas Peters Dr. Matthias Stein Dr. Alvaro Mallagaray 《Chembiochem : a European journal of chemical biology》2020,21(7):1007-1021
Bile acids have been reported as important cofactors promoting human and murine norovirus (NoV) infections in cell culture. The underlying mechanisms are not resolved. Through the use of chemical shift perturbation (CSP) NMR experiments, we identified a low-affinity bile acid binding site of a human GII.4 NoV strain. Long-timescale MD simulations reveal the formation of a ligand-accessible binding pocket of flexible shape, allowing the formation of stable viral coat protein–bile acid complexes in agreement with experimental CSP data. CSP NMR experiments also show that this mode of bile acid binding has a minor influence on the binding of histo-blood group antigens and vice versa. STD NMR experiments probing the binding of bile acids to virus-like particles of seven different strains suggest that low-affinity bile acid binding is a common feature of human NoV and should therefore be important for understanding the role of bile acids as cofactors in NoV infection. 相似文献
5.
Naoki Yokokawa Yutaro Masuda Eri Amasawa Hirokazu Sugiyama Masahiko Hirao 《Packaging Technology and Science》2020,33(11):445-459
This study presents systematic packaging design tools integrating functional and environmental consequences on product life cycle. To design packaging for sustainability, the trade-offs between functional and environmental aspects of packaging throughout the product life cycle should be considered. However, it is difficult for packaging designers to understand the overall trade-offs because the extent of the design consequences on the entire life cycle of packaging and its contents is unclear. We developed two tools for packaging design: the Life Cycle Association Matrix (LCAM) and the Function Network Diagram (FND). The following three steps, based on literature reviews and interviews with industrial experts, were applied. Firstly, we listed the product functions and design variables related to the functions as the attributes allocated to the product life cycle. Secondly, the attributes were connected appropriately based on causal relationships. Lastly, we identified the factors to support decision making in the packaging design procedure. As a result, the LCAM depicts the design consequences on the life cycle, and the FND determines the stakeholders affected by the design consequences. Two case studies were demonstrated to analyze the trade-offs by using our tools. In the case studies, a liquid laundry detergent bottle and a milk carton were redesigned. The tools identified the design consequences and stakeholders affected by the redesign of the usability and protective function for the detergent and milk cases, respectively. The results showed the significance of understanding the design consequences on the product life cycle by integrating the functional and environmental aspects. 相似文献
6.
Reliability based criteria are quite popular for optimal sensor network design. We present a modified definition of system reliability for sensor network design for two applications: reliable estimation of variables in a steady state linear flow process, and reliable fault detection and diagnosis for any process. Unlike the weakest-link based definition of system reliability in the literature, the proposed definition considers the entire system and is consistent with the reliability concept used in classical reliability literature. For each application, dual approaches for defining system reliability are proposed, and their analogy with the reliability problem in the classical reliability literature is established. Using examples and stochastic simulations, the advantage of using the proposed system reliability in contrast to the existing definition is illustrated. Part II of this series of articles presents methods for efficient generation of the system reliability function and its use in optimization-based approaches for designing optimal sensor networks. 相似文献
7.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention. 相似文献
8.
The phase shift characteristics reflect the state change of electromagnetic wave in plasma sheath and can be used to reveal deeply the action mechanism between electromagnetic wave and plasma sheath. In this paper, the phase shift characteristics of electromagnetic wave propagation in plasma were investigated. Firstly, the impact factors of phase shift including electron density,collision frequency and incident frequency were discussed. Then, the plasma with different electron density distribution profiles were employed to investigate the influence on the phase shift characteristics. In a real case, the plasma sheath around the hypersonic vehicle will affect and even break down the communication. Based on the hypersonic vehicle model, we studied the electromagnetic wave phase shift under different flight altitude, speed, and attack angle. The results indicate that the phase shift is inversely proportional to the flight altitude and positively proportional to the flight speed and attack angle. Our work provides a theoretical guidance for the further research of phase shift characteristics and parameters inversion in plasma. 相似文献
9.
《International Journal of Hydrogen Energy》2021,46(66):33186-33196
Additive doping is one of the effective methods to overcome the shortcomings of MgH2 on the aspect of relatively high operating temperatures and slow desorption kinetics. In this paper, hollow g-C3N4 (TCN) tubes with a diameter of 2 μm are synthesized through the hydrothermal and high-temperature pyrolysis methods, and then nickel is chemically reduced onto TCN to form Ni/TCN composite at 278 K. Ni/TCN is then introduced into the MgH2/Mg system by means of hydriding combustion and ball milling. The MgH2–Ni/TCN composite starts to release hydrogen at 535 K, which is 116 K lower than the as-milled MgH2 (651 K). The MgH2–Ni/TCN composite absorbs 5.24 wt% H2 within 3500 s at 423 K, and takes up 3.56 wt% H2 within 3500 s, even at a temperature as low as 373 K. The apparent activation energy (Ea) of the MgH2 decreases from 161.1 to 82.6 kJ/mol by the addition of Ni/TCN. Moreover, the MgH2–Ni/TCN sample shows excellent cycle stability, with a dehydrogenation capacity retention rate of 98.0% after 10 cycles. The carbon material enhances sorption kinetics by dispersing and stabilizating MgH2. Otherwise, the phase transformation between Mg2NiH4 and Mg2NiH0.3 accelerates the re/dehydrogenation reaction of the composite. 相似文献
10.
This paper proposes a thermoelectric-assisted vapor compression cycle (TVCC) for applications in air-source heat pump systems which could enhance the heating capacity of the system. Performances of TVCC are calculated and then compared with that of basic vapor compression cycle (BVCC). The simulation results show that when coefficients of performance (COPs) of the two cycles are almost equal, the TVCC under maximum COP condition of the thermoelectric modules still performs better than BVCC by 13.0% in heating capacity through selecting the appropriate intermediate temperature. In addition, the TVCC can also achieve an improvement of 16.4%–21.7% in both the heating COP and capacity when compared with the BVCC with an assistant electric heater that is provided with the equivalent power input of thermoelectric heat exchanger. Thus, the TVCC could be beneficial to the applications in small heat pumps if there is always need for auxiliary electric heat. 相似文献