全文获取类型
收费全文 | 532篇 |
免费 | 33篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 20篇 |
综合类 | 1篇 |
化学工业 | 166篇 |
金属工艺 | 16篇 |
机械仪表 | 3篇 |
建筑科学 | 9篇 |
能源动力 | 10篇 |
轻工业 | 19篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 87篇 |
一般工业技术 | 154篇 |
冶金工业 | 11篇 |
自动化技术 | 68篇 |
出版年
2024年 | 2篇 |
2023年 | 26篇 |
2022年 | 40篇 |
2021年 | 43篇 |
2020年 | 34篇 |
2019年 | 17篇 |
2018年 | 29篇 |
2017年 | 10篇 |
2016年 | 13篇 |
2015年 | 21篇 |
2014年 | 19篇 |
2013年 | 22篇 |
2012年 | 41篇 |
2011年 | 39篇 |
2010年 | 32篇 |
2009年 | 24篇 |
2008年 | 20篇 |
2007年 | 32篇 |
2006年 | 26篇 |
2005年 | 17篇 |
2004年 | 18篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有566条查询结果,搜索用时 10 毫秒
71.
前言 同步降压型开关电源具有输出电流大、效率高等优点,适合电池供电、注重效率的笔记本电脑等产品。一般笔记本电脑各部分组件,如CPU、芯片组、绘图芯片、内存、硬盘、光驱等,对电源电压/电流的要求不同。因此笔记本电脑内需要多路降压型DC/DC转换器产生不同的输出电压/电流,这些DC/DC转换器大多采用脉冲宽度调制(PWM)。 相似文献
72.
半导体技术的进展已使集成电路(IC)能够取代很多机械式继电器,但在任意极性的高电压大电流电路中,继电器仍然占据主导地位.然而,这类继电器的触点回跳会给下游电路带来麻烦.解决触点回跳的一种办法是把继电器与一个热插拔控制器结合起来. 相似文献
73.
Yurkin MA Semyanov KA Tarasov PA Chernyshev AV Hoekstra AG Maltsev VP 《Applied optics》2005,44(25):5249-5256
Elastic light scattering by mature red blood cells (RBCs) was theoretically and experimentally analyzed by use of the discrete dipole approximation (DDA) and scanning flow cytometry (SFC), respectively. SFC permits measurement of the angular dependence of the light-scattering intensity (indicatrix) of single particles. A mature RBC is modeled as a biconcave disk in DDA simulations of light scattering. We have studied the effect of RBC orientation related to the direction of the light incident upon the indicatrix. Numerical calculations of indicatrices for several axis ratios and volumes of RBC have been carried out. Comparison of the simulated indicatrices and indicatrices measured by SFC showed good agreement, validating the biconcave disk model for a mature RBC. We simulated the light-scattering output signals from the SFC with the DDA for RBCs modeled as a disk-sphere and as an oblate spheroid. The biconcave disk, the disk-sphere, and the oblate spheroid models have been compared for two orientations, i.e., face-on and rim-on incidence, relative to the direction of the incident beam. Only the oblate spheroid model for rim-on incidence gives results similar to those of the rigorous biconcave disk model. 相似文献
74.
Ferromagnetic nanowires are likely to play an important role in future spintronic devices. Magnetic domain walls, which separate regions of opposing magnetization in a nanowire, can be manipulated and used to encode information for storage or to perform logic operations. Owing to their reduced size and dimensionality, the characterization of domain-wall motion is an important problem. To compete with other technologies, high-speed operation, and hence fast wall propagation, is essential. However, the domain-wall dynamics in nanowires has only been investigated in the last five years and some results indicate a drastic slowing down of wall motion in higher magnetic fields. Here we show that the velocity-field characteristic of a domain wall in a nanowire shows two linear regimes, with the wall mobility at high fields reduced tenfold from that at low fields. The transition is marked by a region of negative differential mobility and highly irregular wall motion. These results are in accord with theoretical predictions that, above a threshold field, uniform wall movement gives way to turbulent wall motion, leading to a substantial drop in wall mobility. Our results help resolve contradictory reports of wall propagation velocities in laterally confined geometries, and underscore the importance of understanding and enhancing the breakdown field for practical applications. 相似文献
75.
Jessica Schulz Thomas Siegert Enrico Reimer Christian Labadie Julian Maclaren Michael Herbst Maxim Zaitsev Robert Turner 《Magma (New York, N.Y.)》2012,25(6):443-453
Object
Prospective motion correction using data from optical tracking systems has been previously shown to reduce motion artifacts in MR imaging of the head. We evaluate a novel optical embedded tracking system.Materials and methods
The home-built optical embedded tracking system performs image processing within a 7T scanner bore, enabling high speed tracking. Corrected and uncorrected in vivo MR volumes are acquired interleaved using a modified 3D FLASH sequence, and their image quality is assessed and compared.Results
The latency between motion and correction of the slice position was measured to be (19?±?5)?ms, and the tracking noise has a standard deviation no greater than 10???m/0.005° during conventional MR scanning. Prospective motion correction improved the edge strength by 16?% on average, even though the volunteers were asked to remain motionless during the acquisitions.Conclusion
Using a novel method for validating the effectiveness of in vivo prospective motion correction, we have demonstrated that prospective motion correction using motion data from the embedded tracking system considerably improved image quality. 相似文献76.
Dmitry A. Alentiev Elena S. Egorova Maxim V. Bermeshev Ludmila E. Starannikova Yuri P. Yampolskii Eugene Sh. Finkelshtein 《Polymer Engineering and Science》2019,59(12):2502-2507
Here, we report the synthesis and the study of gas‐transport properties of crosslinked highly permeable copolymers from Si‐containing norbornene derivatives. The initial high‐molecular‐weight copolymers were prepared via addition copolymerization of 3‐trimethylsilyltricyclo[4.2.1.02,5]non‐7‐ene (TCNSi1) with 3‐triethoxysilyltricyclo[4.2.1.02,5]non‐7‐ene (TCNSiOEt) in good or high yields using a Pd‐catalyst. The obtained copolymers included up to 10 mol% of TCNSiOEt units bearing reactive Si–O–C‐containing substituents. The crosslinking was readily realized by using simple sol–gel chemistry in the presence of Sn‐catalyst. The formed crosslinked copolymers were insoluble in common organic solvents. Permeability coefficients of various gases (He, H2, O2, N2, CO2, CH4, C2H6, C3H8, n‐C4H10) in these copolymers before and after crosslinking were determined and the influence of the incorporated TCNSiOEt units as well as the crosslinking on gas transport properties were established. As a result, it was found that only a small reduction of gas‐permeability was observed when TNCSiOEt units were incorporated into the main chains, and the copolymers were crosslinked. At the same time, the selectivity for C4H10/CH4 pair was increased. The suggested approach has allowed obtaining crosslinked polymers from Si‐containing monomers without a loss of the main membrane characteristics. POLYM. ENG. SCI., 59:2502–2507, 2019. © 2019 Society of Plastics Engineers 相似文献
77.
Maxim K. Rabchinskii Vladimir V. Shnitov Dina Yu. Stolyarova Sergei A. Ryzhkov Marina V. Baidakova Eugenia Yu. Lobanova 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(3):221-225
AbstractThe one-step method for graphene oxide (GO) simultaneous reduction and carboxylation via ultraviolet irradiation in the inert atmosphere has been reported. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) data revealed that the proposed approach allows to obtain reduced graphene oxide (rGO) films, containing up to 10 at.% of carboxyl groups. The carboxyl groups concentration can be tuned within the range of 3 to 10 at.% by controlling the oxidation degree of the irradiated GO via the preliminary low-temperature air heating. Furthermore, no carboxylation effect is observed in the case of irradiation of the completely reduced GO films. This coincides with our previous results, validating the proposed model of GO carboxylation based on photoinduced conversion of basal-plane hydroxyl groups and ketones into carboxyl ones. Despite a different degree of carboxylation, all the obtained samples demonstrate almost complete elimination of basal plane groups and restoration of the graphene flakes aromatic structure. This fact is emphasized by the sheet resistance measurements, demonstrating that the obtained C-xy graphene exhibits high electrical conductivity. As a net result, the material obtained by the presented method shows promising applications in the manufacturing of biosensor transducers owing to both its conductive nature and presence of carboxyl groups, playing the role of the anchoring points for biomolecules. 相似文献
78.
79.
Kate Higgins Matthias Lorenz Maxim Ziatdinov Rama K. Vasudevan Anton V. Ievlev Eric D. Lukosi Olga S. Ovchinnikova Sergei V. Kalinin Mahshid Ahmadi 《Advanced functional materials》2020,30(36)
The instability of hybrid organic–inorganic perovskite (HOIP) devices is one of the significant challenges preventing commercialization. Exploring these phenomena is severely limited by the complexity of the intrinsic electrochemistry of HOIPs, the presence of multiple volatile and mobile ionic species, and the possible role of environmentally induced reactions at surfaces and triple‐phase junctions. Here, in situ studies of the electrochemistry of methylammonium lead bromide perovskite with the Au electrode interface are reported via light‐ and voltage‐dependent time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) imaging of lateral perovskite heterostructures. While ToF‐SIMS allows for the visualization of the chemical composition along the surface and its evolution with light and electrical bias, the interpretation of the multidimensional data obtained is often limited due to strong correlations between chemical signatures and the need to track multiple peaks at once. Here, a machine learning workflow combining the Hough transform and non‐negative matrix factorization and non‐negative tensor decomposition is developed to avoid this limitation and extract salient features of associated chemical changes and to separate the light‐ and voltage‐dependent dynamics. Combining these in situ characterizations and the machine learning workflow provides comprehensive information on the chemical nature of moving species, ion accumulation, and interfacial electrochemical reactions in HOIP devices. 相似文献
80.
We discuss models of preventive maintenance (PM) under different assumptions on the failure/repair processes. The main emphasis is on the PM modeling under the Brown‐Proschan model for minimal/perfect repairs. We also present the generalization of this model for the failure/repair process governed by the generalized Polya process. Some comparisons with conventional PM models are discussed (Nonhomogeneous Poisson process, renewal process, and geometric process of failure/repairs). Several practical examples are considered. 相似文献