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951.
Communication networks and mobile devices integrate an increasing number of access technologies. At the same time, new business
roles emerge, which lead to new cooperation schemes between access providers providing different types of access connectivity.
As a result, a variety of access technologies will be available for users at the same time. In this article we present an
architecture and a framework capable of integrating different access systems into a multi-access system and selecting the
best suited access for users. A utility-based approach is proposed for the evaluation of different access allocation choices,
which is based on user and network policies, the performance of access bearers, and the availability of access resources.
We present a general multi-access management framework, which integrates the different multi-access related functions: access
detection, access evaluation and access selection, which can then lead to an access handover.
相似文献
Jens GebertEmail: |
952.
为了更好地分析现代数字无线通讯中的脉冲骚扰,在CISPR 16-1-1中新发布了两种加权方式:均方根值-平均值(CRMS)检波器和幅度概率分布(APD)测量方式.介绍了新的检波器和测量方式的目的、定义和特性评估,以及在标准中的应用. 相似文献
953.
Pierre Chevillat Jens Jelitto Hong Linh Truong 《International Journal of Wireless Information Networks》2005,12(3):123-145
In this paper a novel link adaptation algorithm is proposed that is capable of adjusting the transmit power level and the data rate jointly to the radio channel conditions. The proposed method relies solely on link quality information available at the transmitter by employing the reception or non-reception of the acknowledgment frames as a measure of the channel quality with respect to the power level and data rate. The method is fully compatible with the 802.11 wireless LAN standard. In contrast to many other proposals, it neither relies on the RTS/CTS protocol nor requires a feedback channel to transmit link-quality estimates from the receiver to the transmitter. Different strategies for optimizing the data rate and power level are given. These depend on the scenarios considered, the number of active stations, and the service requirements. The two main strategies are either to drive the system towards the highest possible data rate and adjust the rate and power levels accordingly (“high-performance” mode) or to focus on power saving, possibly trading this for other performance criteria such as throughput or delay performance (“low-power” mode). Other special cases, such as power or rate only adaptation, are also discussed. It can be shown that in most cases the best choice for achieving low transfer times, maximizing throughput, and alleviating the hidden terminal problem is to transmit at the highest possible rates and with high power levels. This “high-performance” mode of operation also minimizes the transmission times, which in turn maximizes the time for putting idling components into a sleep mode, thereby minimizing the overall power consumption. 相似文献
954.
Aerosol lidar intercomparison in the framework of the EARLINET project. 2. Aerosol backscatter algorithms 总被引:1,自引:0,他引:1
Böckmann C Wandinger U Ansmann A Bösenberg J Amiridis V Boselli A Delaval A De Tomasi F Frioud M Grigorov IV Hågård A Horvat M Iarlori M Komguem L Kreipl S Larchevêque G Matthias V Papayannis A Pappalardo G Rocadenbosch F Rodrigues JA Schneider J Shcherbakov V Wiegner M 《Applied optics》2004,43(4):977-989
An intercomparison of aerosol backscatter lidar algorithms was performed in 2001 within the framework of the European Aerosol Research Lidar Network to Establish an Aerosol Climatology (EARLINET). The objective of this research was to test the correctness of the algorithms and the influence of the lidar ratio used by the various lidar teams involved in the EARLINET for calculation of backscatter-coefficient profiles from the lidar signals. The exercise consisted of processing synthetic lidar signals of various degrees of difficulty. One of these profiles contained height-dependent lidar ratios to test the vertical influence of those profiles on the various retrieval algorithms. Furthermore, a realistic incomplete overlap of laser beam and receiver field of view was introduced to remind the teams to take great care in the nearest range to the lidar. The intercomparison was performed in three stages with increasing knowledge on the input parameters. First, only the lidar signals were distributed; this is the most realistic stage. Afterward the lidar ratio profiles and the reference values at calibration height were provided. The unknown height-dependent lidar ratio had the largest influence on the retrieval, whereas the unknown reference value was of minor importance. These results show the necessity of making additional independent measurements, which can provide us with a suitable approximation of the lidar ratio. The final stage proves in general, that the data evaluation schemes of the different groups of lidar systems work well. 相似文献
955.
Mahima Goel Marie Siegert Gert Krauss John Mohanraj Adrian Hochgesang David C. Heinrich Martina Fried Jens Pflaum Mukundan Thelakkat 《Advanced materials (Deerfield Beach, Fla.)》2020,32(43):2003596
Unlike the conventional p-doping of organic semiconductors (OSCs) using acceptors, here, an efficient doping concept for diketopyrrolopyrrole-based polymer PDPP[T]2-EDOT (OSC-1) is presented using an oxidized p-type semiconductor, Spiro-OMeTAD(TFSI)2 (OSC-2), exploiting electron transfer from HOMOOSC-1 to HOMOOSC-2. A shift of work function toward the HOMOOSC-1 upon doping is confirmed by ultraviolet photoelectron spectroscopy (UPS). Detailed X-ray photoelectron spectroscopy (XPS) and UV–vis–NIR absorption studies confirm HOMOOSC-1 to HOMOOSC-2 electron transfer. The reduction products of Spiro-OMeTAD(TFSI)2 to Spiro-OMeTAD(TFSI) and Spiro-OMeTAD is also confirmed and their relative amounts in doped samples is determined. Mott–Schottky analysis shows two orders of magnitude increase in free charge carrier density and one order of magnitude increase in the charge carrier mobility. The conductivity increases considerably by four orders of magnitude to a maximum of 10 S m−1 for a very low doping ratio of 8 mol%. The doped polymer films exhibit high thermal and ambient stability resulting in a maximum power factor of 0.07 µ W m−1 K−2 at a Seebeck coefficient of 140 µ V K−1 for a very low doping ratio of 4 mol%. Also, the concept of HOMOOSC-1 to HOMOOSC-2 electron transfer is a highly efficient, stable and generic way to p-dope other conjugated polymers. 相似文献
956.
John W. F. To Jia Wei Desmond Ng Samira Siahrostami Ai Leen Koh Yangjin Lee Zhihua Chen Kara D. Fong Shucheng Chen Jiajun He Won-Gyu Bae Jennifer Wilcox Hu Young Jeong Kwanpyo Kim Felix Studt Jens K. Nørskov Thomas F. Jaramillo Zhenan Bao 《Nano Research》2017,10(4):1163-1177
The development of high-performance and low-cost oxygen reduction and evolution catalysts that can be easily integrated into existing devices is crucial for the wide deployment of energy storage systems that utilize O2-H2O chemistries,such as regenerative fuel cells and metal-air batteries.Herein,we report an NH3-activated N-doped hierarchical carbon (NHC) catalyst synthesized via a scalable route,and demonstrate its device integration.The NHC catalyst exhibited good performance for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER),as demonstrated by means of electrochemical studies and evaluation when integrated into the oxygen electrode of a regenerative fuel cell.The activities observed for both the ORR and the OER were comparable to those achieved by state-of-the-art Pt and Ir catalysts in alkaline environments.We have further identified the critical role of carbon defects as active sites for electrochemical activity through density functional theory calculations and high-resolution TEM visualization.This work highlights the potential of NHC to replace commercial precious metals in regenerative fuel cells and possibly metal-air batteries for cost-effective storage of intermittent renewable energy. 相似文献
957.
Worarin Meesorn Cline Calvino Jens C. Natterodt Justin O. Zoppe Christoph Weder 《Advanced materials (Deerfield Beach, Fla.)》2019,31(14)
A new concept for the design of self‐toughening thermoplastic polymers is presented. The approach involves the incorporation of plasticizer‐filled microcapsules (MCs) in an intrinsically rigid and brittle matrix polymer. The intriguing adaptability that this simple tactic enables is demonstrated with composites composed of a poly(lactic acid) (PLA) matrix and 5–20% w/w poly(urea‐formaldehyde) (PUF) MCs that contained hexyl acetate as plasticizer. At low strain (<1.5%), the glassy PLA/MC composites remain rigid, although the intact MCs reduce the Young's modulus and tensile strength by up to 50%. While the neat PLA shows brittle failure at a strain of around 2.5%, the composites yield in this regime, because the MCs rupture and release their plasticizing cargo. This effect leads up to 25‐fold increase of the elongation at break and 20‐fold increase of the toughness vis‐à‐vis the neat PLA, while the impact on modulus and ultimate stress is much smaller. Ballistic impact tests show that the self‐toughening mechanism also works at much higher strain rates than applied in tensile tests and the operating mechanism is corroborated through systematic thermomechanical studies that involved dynamic mechanical testing and thermal analysis. 相似文献
958.
Oliver Schüler Lars Krause Mark Görög Jens Hauslage Leona Kesseler Maik Böhmer Ruth Hemmersbach 《Microgravity science and technology》2016,28(3):297-305
Plant development strongly relies on environmental conditions. Growth of plants in Biological Life Support Systems (BLSS), which are a necessity to allow human survival during long-term space exploration missions, poses a particular problem for plant growth, as in addition to the traditional environmental factors, microgravity (or reduced gravity such as on Moon or Mars) and limited gas exchange hamper plant growth. Studying the effects of reduced gravity on plants requires real or simulated microgravity experiments under highly standardized conditions, in order to avoid the influence of other environmental factors. Analysis of a large number of biological replicates, which is necessary for the detection of subtle phenotypical differences, can so far only be achieved in Ground Based Facilities (GBF). Besides different experimental conditions, the usage of a variety of different plant growth chambers was a major factor that led to a lack of reproducibility and comparability in previous studies. We have developed a flexible and customizable plant growth chamber, called ARAbidopsis DISH (ARADISH), which allows plant growth from seed to seedling, being realized in a hydroponic system or on Agar. By developing a special holder, the ARADISH can be used for experiments with Arabidopsis thaliana or a plant with a similar habitus on common GBF hardware, including 2D clinostats and Random Positioning Machines (RPM). The ARADISH growth chamber has a controlled illumination system of red and blue light emitting diodes (LED), which allows the user to apply defined light conditions. As a proof of concept we tested a prototype in a proteomic experiment in which plants were exposed to simulated microgravity or a 90° stimulus. We optimized the design and performed viability tests after several days of growth in the hardware that underline the utility of ARADISH in microgravity research. 相似文献
959.
960.
Jürgen G. Heinrich André Gahler Jens Günster Martin Schmücker Jingxian Zhang Dongliang Jiang Meiling Ruan 《Journal of Materials Science》2007,42(14):5307-5311
The microstructural evolution during direct laser sintering of LSD (Layerwise Slurry Deposition)—samples in the Al2O3–SiO2 system has been investigated. Slurries with a water content of 34 wt.% and a SiO2/Al2O3—ratio of about 3:1 have been used to manufacture layers which—after consecutive drying—have been sintered and laminated by
laser treatment. Densified samples can be obtained with laser irradiances from 190 to 270 kW/cm2 and scan velocities between 35 and 65 mm/s. Elemental mappings of the layers’ cross sections suggest an inhomogeneous phase
distribution in the laser sintered LSD samples with a slight alumina concentration gradient. A lower degree of particle melting
in the bottom region of the layers is plausible due to attenuation of the laser beam intensity. SEM and HRTEM micrographs
show that after a few seconds of laser treatment relictic starting phase, crystalline alumina plus amorphous silica, occur
together with needle like mullite, the latter formed within an amorphous aluminosilicate phase. The resulting phase assemblage
reflects the non-equilibrium conditions which can be expected for short time laser treatments. Mullite nucleation within the
bulk of the liquid phase rather than in the vicinity of the parent alumina phase suggests that dissolution of alumina is the
rate controlling step. Subsequent thermal post treatment in air in a conventional sintering furnace causes an increase of
density to about 96% and leads to additional phase reactions. Amorphous silica transforms into cristobalite and the amount
of alumina is reduced by additional mullite formation. By both coalescence of individual crystals and grain growth the morphology
of the newly formed mullite changes during post heat treatment. 相似文献