全文获取类型
收费全文 | 4224篇 |
免费 | 206篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 79篇 |
综合类 | 32篇 |
化学工业 | 1376篇 |
金属工艺 | 106篇 |
机械仪表 | 70篇 |
建筑科学 | 315篇 |
矿业工程 | 22篇 |
能源动力 | 108篇 |
轻工业 | 369篇 |
水利工程 | 10篇 |
石油天然气 | 2篇 |
无线电 | 239篇 |
一般工业技术 | 774篇 |
冶金工业 | 299篇 |
原子能技术 | 22篇 |
自动化技术 | 614篇 |
出版年
2023年 | 38篇 |
2022年 | 56篇 |
2021年 | 81篇 |
2020年 | 51篇 |
2019年 | 79篇 |
2018年 | 96篇 |
2017年 | 80篇 |
2016年 | 119篇 |
2015年 | 122篇 |
2014年 | 155篇 |
2013年 | 196篇 |
2012年 | 213篇 |
2011年 | 273篇 |
2010年 | 177篇 |
2009年 | 199篇 |
2008年 | 199篇 |
2007年 | 213篇 |
2006年 | 162篇 |
2005年 | 144篇 |
2004年 | 118篇 |
2003年 | 118篇 |
2002年 | 103篇 |
2001年 | 71篇 |
2000年 | 67篇 |
1999年 | 70篇 |
1998年 | 109篇 |
1997年 | 70篇 |
1996年 | 56篇 |
1995年 | 56篇 |
1994年 | 56篇 |
1993年 | 55篇 |
1992年 | 49篇 |
1991年 | 60篇 |
1990年 | 42篇 |
1989年 | 27篇 |
1988年 | 32篇 |
1987年 | 39篇 |
1986年 | 33篇 |
1985年 | 54篇 |
1984年 | 45篇 |
1983年 | 43篇 |
1982年 | 30篇 |
1981年 | 40篇 |
1980年 | 39篇 |
1979年 | 32篇 |
1978年 | 35篇 |
1977年 | 28篇 |
1976年 | 25篇 |
1975年 | 33篇 |
1973年 | 21篇 |
排序方式: 共有4437条查询结果,搜索用时 15 毫秒
891.
Monitoring Measures and the Reliability of Structures – Connections and Effects The quality of structures is reflected by its reliability. In case of quality control during the production process lower variations of enclosed parameters like the tolerances of dimensions or material strength will occur. Different variations of these random variables are considered in reliability analysis depending on different intensities of inspection. Hence the intensity of inspection ca be judged with respect to failure probability and resulting safety elements. 相似文献
892.
893.
Empirical nonlinear analysis of combined piled‐raft foundation (CPRF). Depending on load‐settlement curve obtained from field measurements or empirical relations, a nonlinear analysis of combined piled‐raft is presented to take into account the actual response of subsoil behavior. In the analysis, each pile is treated as two units, shaft and base, having a uniform settlement along the pile shaft and in the pile base. This assumption enables modeling the nonlinear behavior of combined piled‐raft. The nonlinear response of the pile is based on the DIN 4014 empirical relation of load‐settlement curve. Connecting between empirical and theoretical procedures, a method termed NPRD for nonlinear analysis of combined piled‐raft using DIN 4014 is developed. The procedure meets the requrements of the KPP‐guideline, section 6, to a computation model. The efficiency of NPRD is demonstrated in a comparison computation of Frankfurt Messeturm with the results of different authors. The proposed method was implemented in the program ELPLA. The special cases “single pile/pile group” and “raft” are contained in. 相似文献
894.
Jürgen Schnell Robert Kautsch Piotr Noakowski Martin Breddermann 《Beton- und Stahlbetonbau》2005,100(5):406-415
Behaviour of Building Floors with Imposed Longitudinal Forces Imposed longitudinal forces are frequently activated in building floors fixed to neighbouring components (stability cores, utility cores, walls), which restrain temperature and shrinkage controlled deformation. This leads to increased crack formation with positive consequences such as reduction of the imposed force and of moment peaks. At the same time wide cracks may occur which endanger the tightness, the shear force capacity and the supported components following excessive deflection. In this connection the behavior of a typical floor is analyzed in this study under variation of its most important design features. The determined sensitivity of the floor towards the design features has allowed to formulate the corresponding laws. The results represent the first step for working out proper recommendations regarding activation and effects of the imposed tension forces in building floors. 相似文献
895.
Siegfried Skirl Ralph Krause Sheldon M. Wiederhorn Jürgen Rödel 《Journal of the American Ceramic Society》2001,84(9):2034-2040
Composites with microstructures of interpenetrating networks were manufactured by gas pressure infiltration of Ni3 Al into porous preforms of aluminum oxide. Composites with Ni3 Al contents of between 15% and 30% by volume were made and evaluated mechanically at temperatures between room temperature and 1000°C. The fracture strength, the fracture toughness, Young's modulus, and the thermal expansion coefficient were measured for each composite and test condition and were correlated with the microstructures of the composites. Composites with low Ni3 Al contents had strengths below 400 MPa, presumably due to microcracking along the interface between the Ni3 Al and the Al2 O3 . The composite with the highest content of Ni3 Al, 30 vol%, had a mean fracture strength of 675 ± 16 MPa, a Weibull modulus of 23.9, and a room-temperature toughness of 9.2 ± 0.5 MPa·m1/2 . 相似文献
896.
Robert Dittmer Wook Jo Jürgen Rödel Sergei Kalinin Nina Balke 《Advanced functional materials》2012,22(20):4208-4215
Piezoresponse force microscopy (PFM) is used to afford insight into the nanoscale electromechanical behavior of lead‐free piezoceramics. Materials based on Bi1/2Na1/2TiO3 exhibit high strains mediated by a field‐induced phase transition. Using the band excitation technique the initial domain morphology, the poling behavior, the switching behavior, and the time‐dependent phase stability in the pseudo‐ternary system (1–x)(0.94Bi1/2Na1/2TiO3‐0.06BaTiO3)‐xK0.5Na0.5NbO3 (0 <= x <= 18 mol%) are revealed. In the base material (x = 0 mol%), macroscopic domains and ferroelectric switching can be induced from the initial relaxor state with sufficiently high electric field, yielding large macroscopic remanent strain and polarization. The addition of KNN increases the threshold field required to induce long range order and decreases the stability thereof. For x = 3 mol% the field‐induced domains relax completely, which is also reflected in zero macroscopic remanence. Eventually, no long range order can be induced for x >= 3 mol%. This PFM study provides a novel perspective on the interplay between macroscopic and nanoscopic material properties in bulk lead‐free piezoceramics. 相似文献
897.
Beza?Negash?GetuEmail author J?rgen?Bach?Andersen 《Wireless Personal Communications》2004,30(1):27-61
The paper discusses the BER and spectral efficiency of different MIMO systems in random uncorrelated, correlated and deterministic environments, and more specifically uncorrelated and correlated Rayleigh and Ricean fading channels. It is known that the so-called MIMO eigenmode transmission assumes channel knowledge at the transmitter for pre-coding, whereas V-BLAST and STC do not assume the channel knowledge at the transmitter, instead they use it at the receiver for recovering the transmitted information. It is shown that for the same spectral efficiency, the BER performance of the MIMO eigenmode transmission outperforms MIMO systems like V-BLAST and STBC. In fully correlated random environment, transmitting through the largest eigenmode exploits the full transmitter-receiver array gain and diversity order, giving the maximal possible performance in terms of reducing the BER. In any of the scenarios, transmitting through the largest eigenmode gives better performance in terms of reducing the BER compared with STBC systems. Spatial multiplexing through the so-called eigensets (sets which consist of transmission modes with significant channel gain) outperforms systems like V-BLAST. In this context, adaptive modulation has been used to minimize the overall BER for a given spectral efficiency. 相似文献
898.
Dynamic Control Over Electronic Transport in 3D Bulk Nanographene via Interfacial Charging 下载免费PDF全文
Subho Dasgupta Di Wang Christian Kübel Horst Hahn Theodore F. Baumann Jürgen Biener 《Advanced functional materials》2014,24(23):3494-3500
Electrochemical surface charge‐induced variation of physical properties in interface‐dominated bulk materials is a rapidly emerging field in material science. The recently developed three‐dimensional bulk nanographene (3D‐BNG) macro‐assemblies with ultra‐high surface area and chemical inertness offer new opportunities in this area. Here, the electronic transport in centimeter‐sized 3D‐BNG monoliths can be dynamically controlled via electrochemically induced surface charge density. Specifically, a fully reversible variation in macroscopic conductance up to several hundred percent is observed with ≤1 V applied gate potential. The observed conductivity change can be explained in the light of the electrochemically‐induced accumulation or depletion of charge carriers in combination with a large variation in the carrier mobility; the latter, being highly affected by the defect density modulations resulting from the interfacial charge injection, sharply decreases with an increase in defect concentrations. The phenomenon presented in this study is believed to open the door to novel applications of bulk graphene materials such as, for example, low voltage and high power tunable resistors. 相似文献
899.
Analysis of Optical Losses in a Photoelectrochemical Cell: A Tool for Precise Absorptance Estimation 下载免费PDF全文
Peter Cendula Ludmilla Steier Paolo A. Losio Michael Grätzel Jürgen O. Schumacher 《Advanced functional materials》2018,28(1)
Optical losses in a photoelectrochemical (PEC) cell account for a substantial part of solar‐to‐hydrogen conversion losses, but limited attention is paid to the detailed investigation of optical losses in PEC cells. In this work, an optical model of combined coherent and incoherent light propagation in all layers of the PEC cell based on spectroscopic measurements is presented. Specifically, photoelectrodes using transparent conductive substrates such as F:SnO2 coated with thin absorber films are focused. The optical model is verified for hematite photoanodes fabricated by atomic layer deposition and successfully used to determine wavelength‐dependent reflection, transmission, layer absorptances, and charge generation rates. Furthermore, the calculated absorptances enable 20–30% more accurate calculations of the absorbed photon‐to‐current efficiency of PEC cells. Our optical model is a powerful tool for the optimization of the optical performance of PEC cells focusing on single absorber or tandem configurations and represents a cornerstone of a complete (optical and electrical) model for PEC water splitting cells. 相似文献
900.
Jana Dulle Silke Nemeth Ekaterina V. Skorb Torsten Irrgang Jürgen Senker Rhett Kempe Andreas Fery Daria V. Andreeva 《Advanced functional materials》2012,22(15):3128-3135
This paper proposes a sonochemical approach to the nanostructuring of Al/Ni catalyst with high content of accessible Ni centers and a high reusability. The surface and bulk composition as well as pore size distribution of this catalyst are controlled synergistically by adjusting the ultrasound intensity in aqueous solution. Sonochemical activation of Al/Ni alloy leads to formation of mesoporous Al/Ni metallic based frameworks with surface area up to 125 m2 g?1, and regular distribution of nickel active center in the porous matrix. One of the opportunities of porous Al/Ni catalyst is that due to a time‐resolved controllable formation of protective oxide layer it can be stored and handled under air in comparison to traditional Raney catalysts which need inert conditions. The Al/Ni catalyst is characterized by scanning electron microscopy (SEM), electron diffraction spectroscopy (EDS), X‐ray photoelectron spectroscopy (XPS), confocal scanning fluorescence microscopy (CSFM), solid‐state NMR experiments, and powder X‐ray diffraction analysis (PXRD). The catalytic activity was investigated for the hydrogenation of acetophenone. 相似文献