全文获取类型
收费全文 | 39618篇 |
免费 | 4172篇 |
国内免费 | 2524篇 |
专业分类
电工技术 | 2855篇 |
技术理论 | 6篇 |
综合类 | 5125篇 |
化学工业 | 5955篇 |
金属工艺 | 1587篇 |
机械仪表 | 1514篇 |
建筑科学 | 3542篇 |
矿业工程 | 1389篇 |
能源动力 | 1572篇 |
轻工业 | 3768篇 |
水利工程 | 1144篇 |
石油天然气 | 2096篇 |
武器工业 | 444篇 |
无线电 | 3207篇 |
一般工业技术 | 4658篇 |
冶金工业 | 1371篇 |
原子能技术 | 806篇 |
自动化技术 | 5275篇 |
出版年
2024年 | 93篇 |
2023年 | 696篇 |
2022年 | 991篇 |
2021年 | 1231篇 |
2020年 | 1407篇 |
2019年 | 1198篇 |
2018年 | 1174篇 |
2017年 | 1351篇 |
2016年 | 1528篇 |
2015年 | 1594篇 |
2014年 | 2360篇 |
2013年 | 2581篇 |
2012年 | 2885篇 |
2011年 | 3070篇 |
2010年 | 2318篇 |
2009年 | 2246篇 |
2008年 | 2261篇 |
2007年 | 2647篇 |
2006年 | 2389篇 |
2005年 | 1974篇 |
2004年 | 1659篇 |
2003年 | 1418篇 |
2002年 | 1146篇 |
2001年 | 937篇 |
2000年 | 777篇 |
1999年 | 651篇 |
1998年 | 581篇 |
1997年 | 506篇 |
1996年 | 462篇 |
1995年 | 377篇 |
1994年 | 360篇 |
1993年 | 237篇 |
1992年 | 246篇 |
1991年 | 201篇 |
1990年 | 159篇 |
1989年 | 146篇 |
1988年 | 106篇 |
1987年 | 68篇 |
1986年 | 56篇 |
1985年 | 49篇 |
1984年 | 39篇 |
1983年 | 24篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1964年 | 6篇 |
1960年 | 6篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
《岩石力学与岩土工程学报(英文版)》2020,12(6):1214-1225
With rapid development of infrastructures like tunnels and open excavations in Shanghai, investigations on deeper soils have become critically important. Most of the existing laboratory works were focused on the clayey strata up to Layer 6 in Shanghai, i.e. at depth of up to 40 m. In this paper, Layers 7, 9, and 11, which were mostly formed of sandy soils at depth of up to 150 m, were experimentally investigated with respect to physico-mechanical behaviors. The stress–strain behaviors were analyzed by the consolidated drained/undrained (CD/CU) triaxial tests under monotonic loading. One-dimensional (1D) oedometer tests were performed to investigate the consolidation properties of the sandy soils. Specimens were prepared at three different relative densities for each layer. Also, the micro-images and particle size analyzers were used to analyze the shape and size of the sand grains. The influences of grain size, density, and angularity on the stress–strain behaviors and compressibility were also studied. Compared to the other layers, Layer 11 had the smallest mean grain size (D50), highest compressibility, and lowest shear strength. In contrast, Layer 9 had the largest mean grain size, lowest compressibility, and highest shear strength. Layer 7 was of intermediate mean grain size, exhibiting more compressibility and less shear strength than that of Layer 9. Also, the critical state parameters and maximum dilatancy rate of different layers were discussed. 相似文献
82.
83.
Naveed Mushtaq Chen Xia Wenjing Dong G. Abbas Rizwan Raza Amjad Ali Sajid Rauf Baoyuan Wang Jung-Sik Kim Bin Zhu 《Ceramics International》2018,44(9):10266-10272
Stable and compatible cathode materials are a key factor for realizing the low-temperature (LT, ≤600?°C) operation and practical implementations of solid oxide fuel cells (SOFCs). In this study, perovskite oxides SrFe1-xTixO3-δ (x?< = 0.1), with various ratios of Ti doping, are prepared by a sol-gel method for cathode material for LT-SOFCs. The structure, morphology and thermo-gravimetric characteristics of the resultant SFT powders are investigated. It is found that the Ti is successfully doped into SrFeO3-δ to form a single phase cubic perovskite structure and crystal structure of SFT shows better stability than SrFeO3-δ. The dc electrical conductivity and electrochemical properties of SFT are measured and analysed by four-probe and electrochemical impedance spectra (EIS) measurements, respectively. The obtained SFT exhibits a very low polarization resistance (Rp), .01 Ωcm2 at 600?C. The SFT powders using as cathode in fuel cell devices, exhibit maximum power density of 551?mW?cm?2 with open circuit voltage (OCV) of 1.15?V at 600?C. The good performance of the SFT cathode indicates a high rate of oxygen diffusion through the material at cathode. By enabling operation at low temperatures, SFT cathodes may result in a practical implementation of SOFCs. 相似文献
84.
Ruipeng Zhao Yinchang Ma Qing Liu Fei Zhang Yudong Xia Hao Tang Yuming Lu Chuanbing Cai Bowan Tao Yanrong Li 《Ceramics International》2018,44(11):12125-12131
The metal organic chemical vapor deposition (MOCVD) method was used to prepare GdYBCO films on LaMnO3/ homo epitaxial-MgO/ ion-beam-assisted-deposition-MgO/ solution-deposition-planarization-Y2O3 buffered Hastelloy tapes. By adopting a simple self-heating technique, the substrates were heated by the joule effect after applying a heating current (Ih) through Hastelloy metal tapes. The effects of substrate temperature and (Gd, Y)/Ba ratio (rc) in the precursor on the biaxial texture, surface morphology and superconducting performance of GdYBCO films were systematically investigated by varying the values of Ih and rc. Needle-like outgrowths formed on the substrate surface were characterized using a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction system. The results show that a high Ih or rc leads to the formation of needle-like outgrowths. Therefore, Ih and rc are crucial process parameters that control the growth of needle-like outgrowths on the surface of GdYBCO films. Three hundred nanometer thick GdYBCO films were prepared at different Ih and rc by the MOCVD process. At an Ih of 27.0?A and an rc of 0.6, the surface of the GdYBCO film was very smooth and dense, which can provide a good template for multiple depositions of GdYBCO films. The critical current density of the deposited 300?nm-thick GdYBCO film was 4.4 MA/cm2 (77?K, 0?T), which is attributed to good biaxial texture and appropriate film composition. Furthermore, the microwave surface resistance (77?K, 10?GHz) of the GdYBCO film was merely 0.581?mΩ. 相似文献
85.
Carmen Camarero Izquierdo Javier Rodríguez Pinto Rebeca San José-Cabezudo 《Telematics and Informatics》2018,35(5):1176-1189
This research explores how digital publications may be turned into something more than just a meeting point for people who are seeking information and may become a latent community. The paper proposes that the network of editors, followers, and advertisers of digital publications determine the user sense of community towards the publication. While the pattern of connections among editors and followers reinforces the sense of community, advertisers act as intruders who weaken the feasibility of building a community. Data were collected from followers of digital publications. The dynamics of the sense of community is described as a process in which informational value and identification are essential to nurturing readers’ soft or hard commitment. Findings indicate that the strong ties between editors and followers as well as the diversity positively impacts on informational value and identification, whereas advertising intrusiveness diminishes the informational value. 相似文献
86.
通过对磷酸二铵生产造粒特性分析,高压中速磨粉机原理分析,结合实践生产中的工艺需求,利用高压中速磨粉系统将颗粒状不合格品磨成细粉后添加进系统重新喷浆造粒,提高返料添加量,减少不合格品的产生,腾空仓库有限货位,以获取更大的经济价值。 相似文献
87.
Serge Nyallang Nyamsi Mykhaylo Lototskyy Ivan Tolj 《International Journal of Hydrogen Energy》2018,43(50):22568-22583
Thermo-chemical energy storage based on metal hydrides has gained tremendous interest in solar heat storage applications such as concentrated solar power systems (CSP) and parabolic troughs. In such systems, two metal hydride beds are connected and operating in an alternative way as energy storage or hydrogen storage. However, the selection of metal hydrides is essential for a smooth operation of these CSP systems in terms of energy storage efficiency and density. In this study, thermal energy storage systems using metal hydrides are modeled and analyzed in detail using first law of thermodynamics. For these purpose, four conventional metal hydrides are selected namely LaNi5, Mg, Mg2Ni and Mg2FeH6. The comparison of performance is made in terms of volumetric energy storage and energy storage efficiency. The effects of operating conditions (temperature, hydrogen pressure and heat transfer fluid mass flow rates) and reactor design on the aforementioned performance metrics are studied and discussed in detail. The preliminary results showed that Mg-based hydrides store energy ranging from 1.3 to 2.4 GJ m?3 while the energy storage can be as low as 30% due to their slow intrinsic kinetics. On the other hand, coupling Mg-based hydrides with LaNi5 allow us to recover heat at a useful temperature above 330 K with low energy density ca.500 MJ m?3 provided suitable operating conditions are selected. The results of this study will be helpful to screen out all potentially viable hydrides materials for heat storage applications. 相似文献
88.
Rizwan Ahmed Malik Ali Hussain Matias Acosta John Daniels Hyoung-Su Han Myong-Ho Kim Jae-Shin Lee 《Journal of the European Ceramic Society》2018,38(6):2511-2519
In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi0.5Na0.84K0.16TiO3)–0.04SrTiO3 (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x?=?0.0175, a large-signal piezoelectric coefficient (Smax/Emax?=?d33*) of 735 pm?V?1 at 6?kV mm?1 was observed at room temperature. Interestingly, at a higher temperature of 110?°C, the sample still showed a large d33* of 570 pm V?1. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285?m4?C?2 over the temperature range of 25–170?°C. Moreover, the energy density for x?=?0.030 sample was ~1.0?J?cm?3 with an energy storage efficiency of ?70% in the temperature range of 25–135?°C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications. 相似文献
89.
In past research, mechanical recycling of automotive shredder residue (ASR) has led to serious deterioration of material performance, and real‐scale application in this way still remains a challenge. Here, we report a sustainable approach called solid‐state shear milling (SSSM) for the production of high‐performance polypropylene (PP)/ASR composites with robust mechanical performance on a commercial scale. After the SSSM process, the obtained 50/50 wt% PP/ASR composite exhibited a 41.3% increase in tensile strength, 32.9% increase in flexural strength and 55.0% increase in impact toughness when compared with corresponding composites made by traditional direct melt blending. In particular, the toughness of the material can be improved by further addition of PP grafted with maleic anhydride with toughness comparable to that of recycled PP, and a 325% increase in toughness can be obtained with addition of styrene–butadiene–styrene block copolymer grafted with maleic anhydride. This PP/ASR composite shows good processability and high thermal stability, and meets the requirements of many applications for nonstructural products. The approach presented in this paper highlights a novel technique for ASR recycling. © 2018 Society of Chemical Industry 相似文献
90.
Thanh Bao Nguyen Erwin van der Krabben Clément Musil Duc Anh Le 《International Planning Studies》2018,23(3):310-326
This paper explores how land-based financing mechanisms are currently used in Ho Chi Minh City as a public-private funding strategy. The Land-for-Infrastructure (LFI) mechanism appears as a solution to produce infrastructures. We found that the implementation of the LFI mechanism remains difficult, but eventually can lead to success. By ‘trial-error-transcend,’ the City managed to build two essential roads while the developers received attractive investment opportunities in urban development. This mechanism cannot, however, be seen as a panacea for the local authorities due to constraints to replicate it and potential undesired ‘side effects.’ 相似文献