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排序方式: 共有884条查询结果,搜索用时 15 毫秒
61.
62.
Crawford M.H. Schneider R.P. Jr. Choquette K.D. Lear K.L. 《Photonics Technology Letters, IEEE》1995,7(7):724-726
We report on temperature dependent characteristics and single mode performance of one-wave cavity, planar implanted, AlGaInP-based vertical-cavity surface emitting lasers. By optimizing the overlap between the gain peak and the cavity mode of the structure, we demonstrate record device performance, including 8.2 mW maximum output power and 11% power conversion efficiency for multimode operation and 1.9 mW and 9.6% power conversion efficiency for single mode operation at 687 nm. Improved performance at elevated temperatures is also achieved, with 1.5 mW output power demonstrated at 50°C from a 15-μm-diameter device 相似文献
63.
Dead-beat feedforward control is achievable if the Laplace transform of the switched level control waveform is zero for every pole in the plant transfer function except for any system type poles. The correct switching instants then follow from the simultaneous solution of some simple transcendental equations of pole positions.<> 相似文献
64.
Emily Crawford 《Urban Policy and Research》2003,21(1):81-92
This article examines the Commonwealth Government's urban planning initiative, the Building Better Cities Program, as it was implemented in the East Perth redevelopment. It analyses the disparity between one of the Program's key objectives, improved social justice, and the outcomes evident in East Perth. The nature of Commonwealth-State relations is examined to reveal that the tensions inherent in a federal polity are a cause of the redevelopment failing to achieve the objective of improved social justice outcomes. 相似文献
65.
66.
Hongyu Chen Bin Qi Thomas Moore Daniel C. Colvin Thomas Crawford John C. Gore Frank Alexis O. Thompson Mefford Jeffrey N. Anker 《Small (Weinheim an der Bergstrasse, Germany)》2014,10(1):160-168
A method is developed to fabricate monodispersed biocompatible Yb/Er or Yb/Tm doped β‐NaGdF4 upconversion phosphors using polyelectrolytes to prevent irreversible particle aggregation during conversion of the precursor, Gd2O(CO3)2?H2O:Yb/Er or Yb/Tm, to β‐NaGdF4:Yb/Er or Yb/Tm. The polyelectrolyte on the outer surface of nanophosphors also provided an amine tag for PEGylation. This method is also employed to fabricate PEGylated magnetic upconversion phosphors with Fe3O4 as the core and β‐NaGdF4 as a shell. These magnetic upconversion nanophosphors have relatively high saturation magnetization (7.0 emu g?1) and magnetic susceptibility (1.7 × 10?2 emu g?1 Oe?1), providing them with large magnetophoretic mobilities. The magnetic properties for separation and controlled release in flow, their optical properties for cell labeling, deep tissue imaging, and their T1‐ and T2‐weighted magnetic resonance imaging (MRI) relaxivities are studied. The magnetic upconversion phosphors display both strong magnetophoresis, dual MRI imaging (r1 = 2.9 mM?1 s?1, r2 = 204 mM?1 s?1), and bright luminescence under 1 cm chicken breast tissue. 相似文献
67.
The continued outward growth from a central business district has been the dominant characteristic of most cities in Australia.
However, this feature is seen as unsustainable and alternative scenarios to contain the outward growth are being proposed.
Melbourne is currently grappling with this issue while simultaneously trying to reduce per capita greenhouse gas emissions.
Housing size, style and its location are the three principal factors which determine the emissions from the residential sector.
This paper describes a methodology to assess the combined impact of these factors on past and possible future forms of residential
development in Melbourne. The analysis found that the location of the housing and its size are the dominant factors determining
energy use and greenhouse gas emissions. 相似文献
68.
High-resolution electron-microscope images of high-modulus carbon-fibre fragments have been recorded under conditions which allow resolution of the individual 0.34 nm graphite layer planes. Extinction bands previously observed at low resolution are now seen to originate from several different structural features. Single bands are caused by lattice distortion due to non-basal edge dislocations and low-angle boundaries of tilt or twist character; periodic bands are the result of Moiré effects from overlapping or interlinked crystallites. Accurately controlled tilting experiments give further insight into the complex interlinked nature of the crystallites and the results are summarized in terms of a model which is also capable of explaining the partial recrystallization observed with boron doping. 相似文献
69.
SM Kurtz L Pruitt CW Jewett RP Crawford DJ Crane AA Edidin 《Canadian Metallurgical Quarterly》1998,19(21):1989-2003
The yielding, plastic flow, and fracture behavior of UHMWPE plays an important role in wear and failure mechanisms of total joint replacement components. The primary objective of this study was to compare the yielding, plastic flow, and fracture behavior of two implantable grades of UHMWPE (GUR 1120 vs 4150 HP). The first part of this work explored the hypothesis that up to the polymer yield point, the monotonic loading behavior of UHMWPE displays similar true stress strain behavior in tension and compression. Uniaxial tension and compression tests were conducted to compare the equivalent true stress vs strain response of UHMWPE up to 0.12 true strain. During monotonic loading, the equivalent true stress strain behavior was similar in tension and compression up to the yield point. However, investigation of the unloading behavior and permanent plastic deformations showed that classical deviatoric rate independent plasticity theory may dramatically overpredict the permanent strains in UHMWPE. A secondary goal of this study was to determine the ultimate true stress and strain for UHMWPE and to characterize the fracture surfaces after failure. Using a fracture mechanics approach, the critical flaw sizes were used in combination with the true ultimate stresses to predict the fracture toughness of the two resins. A custom video-based strain measurement system was developed and validated to characterize the true stress-strain behavior up to failure and to verify the accuracy of the incompressibility assumption in calculating the true stress-strains up to failure. In a detailed uncertainty analysis, theoretical expressions were derived for the relative uncertainty in digital video-based estimates of nominal strain, true strain, homogeneous stress, and true stress. Although the yielding behavior of the two UHMWPE resins was similar, the hardening and plastic flow behavior clearly discriminated between the GUR 1120 and 4150 HP. A statistically significant difference between the fracture toughness of the two resins was also evident. The long-term goal of this research is to provide detailed true stress strain data for UHMWPE under uniaxial tension and compression for future numerical simulations and comparison with more complex multiaxial loading conditions. 相似文献
70.
MA Dobbs M Lueker KA Aird AN Bender BA Benson LE Bleem JE Carlstrom CL Chang HM Cho J Clarke TM Crawford AT Crites DI Flanigan T de Haan EM George NW Halverson WL Holzapfel JD Hrubes BR Johnson J Joseph R Keisler J Kennedy Z Kermish TM Lanting AT Lee EM Leitch D Luong-Van JJ McMahon J Mehl SS Meyer TE Montroy S Padin T Plagge C Pryke PL Richards JE Ruhl KK Schaffer D Schwan E Shirokoff HG Spieler Z Staniszewski AA Stark K Vanderlinde JD Vieira C Vu B Westbrook R Williamson 《The Review of scientific instruments》2012,83(7):073113
A technological milestone for experiments employing transition edge sensor bolometers operating at sub-Kelvin temperature is the deployment of detector arrays with 100s-1000s of bolometers. One key technology for such arrays is readout multiplexing: the ability to read out many sensors simultaneously on the same set of wires. This paper describes a frequency-domain multiplexed readout system which has been developed for and deployed on the APEX-SZ and South Pole Telescope millimeter wavelength receivers. In this system, the detector array is divided into modules of seven detectors, and each bolometer within the module is biased with a unique ~MHz sinusoidal carrier such that the individual bolometer signals are well separated in frequency space. The currents from all bolometers in a module are summed together and pre-amplified with superconducting quantum interference devices operating at 4 K. Room temperature electronics demodulate the carriers to recover the bolometer signals, which are digitized separately and stored to disk. This readout system contributes little noise relative to the detectors themselves, is remarkably insensitive to unwanted microphonic excitations, and provides a technology pathway to multiplexing larger numbers of sensors. 相似文献