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排序方式: 共有810条查询结果,搜索用时 437 毫秒
71.
Min Liu Kin Seng Chiang Ping Shum 《Quantum Electronics, IEEE Journal of》2004,40(11):1597-1602
The switching dynamics of short pulses in an active nonlinear two-core fiber coupler is investigated theoretically. The analysis takes into account the effects of coupling-coefficient dispersion, gain bandwidth, and gain saturation. In particular, we demonstrate that the pulse breakup effect due to coupling-coefficient dispersion can be suppressed by limiting the bandwidth of the linear gain, whether gain saturation is considered or not. 相似文献
72.
Electrochemical copolymerization of diphenylamine (DPA) with o‐chloroaniline (OCA) was performed in aqueous 4M sulfuric acid using the pulse potentiostatic method (PPSM). By employing the tunable parameters in PPSM, polymeric films were deposited under different conditions. Cyclic voltammetry was used for evaluating the characteristics of the deposited polymeric films. A suitable growth equation for the deposition of polymer, relating the charge associated for the film deposition and the pulse parameters in PPSM, was deduced. Various surface parameters are evaluated. The formation of copolymer during PPSM deposition was revealed through critical analysis of the results. The characteristic differences between the individual homopolymers, poly(diphenylamine) and poly(o‐chloroaniline) and the copolymer, poly(diphenylamine‐co‐o‐chloroaniline), were brought out. The copolymer was also synthesized through a chemical method and characterized through infrared and ultraviolet‐visible spectroscopic analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 389–397, 2003 相似文献
73.
Kaixue Ma Jianguo Ma Jianbo Sun Jianmin Miao Manh Anh Do Kiat Seng Yeo 《Microwave and Wireless Components Letters, IEEE》2005,15(7):478-480
A new miniaturized ground ring guided microstrip patch filter developed on the silicon wafer using micromachined technology is reported. The ground shunt can be used to lower the operating frequency up to one-third as compared to the traditional patch resonator. The size of the designed band pass filter operating in 5.17 GHz is only 8.7 mm/spl times/2.9 mm. 相似文献
74.
Ong Lin Seng Chan Yiu Wing Gerald Seet 《International Journal of Pressure Vessels and Piping》1989,38(5):369-383
The elastic analysis of a dent on a pressurised cylinder is investigated. The predetermined shapes of the dent are grouped into three categories according to the physical geometry of the dent width, namely the local dent, the short dent, and the long dent. The induced bending stresses associated with the dent are evaluated using Sanders's non-linear shell theory. The geometry of the dent is treated as an initial geometric imperfection and incorporated in the expressions of strain. The non-linear cylindrical shell equations thus obtained are linearised and then solved by a Fourier series expansion technique. Comparison of theoretical results with the finite element approach is made for a pipe of assumed dimensions and pressure. Good agreement of the results is observed. The analytical approach of this paper is suitable for pipe or cylinder with a dent depth of up to five times the wall thickness. 相似文献
75.
JM Balter KL Lam HM Sandler JF Littles RL Bree RK Ten Haken 《Canadian Metallurgical Quarterly》1995,33(5):1281-1286
PURPOSE: Prostate movement is a major consideration in the formation of target volumes for conformal radiation therapy of prostate cancer. The goal of this study was to determine the technical feasibility of using implanted radiopaque markers and digital imaging to localize the prostate at the time of treatment, thus allowing for reduction of the margin required for uncertainty in target position. METHODS AND MATERIALS: Radiopaque markers implanted around the prostate prior to treatment are visible on electronic radiographs generated with a portal imager or diagnostic imaging device. The locations of the images of these markers on the digital radiographs were automatically determined by a template-matching algorithm. The coordinates of the markers were found by projecting rays through the marker locations on orthogonal radiographs using a three-dimensional (3D) point-matching algorithm. Prostate and/or patient movement was inferred from the marker displacements. Images generated from known movements of a phantom with implanted markers were tested with this algorithm. Locations of markers from daily images of patients with implanted markers were determined by both manual and automatic techniques to determine the efficacy of automated localization on typical clinical images. RESULTS: Prostate movements can be automatically detected in a phantom using low-energy photons within 30 s after image acquisition and with a precision of better than 1 mm in translation and 1 degree in rotation (indistinguishable from the uncertainty in measuring precision). CONCLUSION: The studies show that on-line repositioning of the patient based on localization of the markers at the time of treatment is feasible, and may reduce the uncertainty in prostate location when combined with practical on-line repositioning techniques. 相似文献
76.
Kwok Wah Hui Kin Seng Chiang Boyu Wu Zhang Z.H. 《Lightwave Technology, Journal of》1998,16(2):232-238
Different electrode configurations for LiNbO3-based Mach-Zehnder traveling-wave electrooptic modulators are analyzed. It is found that the Z-cut coplanar waveguide (CPW) configuration provides the best compromise between the characteristic impedance, the half-wave voltage, and the driving power. To increase the bandwidth and simultaneously reduce the half-wave voltage, an optimum design of multisection phase reversal electrode is proposed. To verify the theoretical predictions experimentally, two modulators, both using the Z-cut LiNbO3 CPW configuration, were fabricated and characterized, one with an optimized five-section phase reversal electrode and the other with a conventional single-section electrode. By comparing the performances of these two devices, it is confirmed that significant improvements on the bandwidth to half-wave voltage ratio and the flatness of the frequency response can indeed be obtained from using an optimized multisection phase reversal electrode 相似文献
77.
K. Y. Liew C. E. Seng C. G. Lee 《Journal of the American Oil Chemists' Society》1994,71(11):1297-1299
Densities of sevenn-alkylamines from 1-butylamine to 1-decylamine were determined from 15 to 80°C. The density was found to be a linear function
of the temperature within this temperature range. At constant temperature, the molal volume was a linear function of the number
of methylene units in the chain for the homologous series.
A simple equation with four constants correlating the molal volume with the number of methylene units and temperature of then-alkylamines was formulated. Excellent agreement between the calculated, the measured and the literature values were obtained.
Accurate molal volumes, and hence the densities of anyn-alkylamines, other than methylamine, within the temperature range can be calculated from the equation. 相似文献
78.
The development of materials with unique nanostructures is an effective strategy for the improvement of sodium storage in sodium ion batteries to achieve stable cycling performance and good rate capability. In this work, SnSbcore/carbon-shell nanocables directly anchored on graphene sheets (GS) were synthesized by the hydrothermal technique and chemical vapor deposition. The simultaneous carbon coating and the encapsulation of SnSb alloy is effective for alleviating the volume-change problem in sodium ion batteries. After optimizing the electrolyte for SnSb in the sodium ion batteries, the optimized coaxial SnSb/carbon nanocable/GS (SnSb/CNT@GS) nanostructure demonstrated stable cycling capability and rate performance in 1 M NaClO4 with propylene carbonate (PC) + 5% fluoroethylene carbonate (FEC). The SnSb/CNT@GS electrode can retain a capacity of 360 mAh/g for up to 100 cycles, which is 71% of the theoretical capacity. This is higher than in the other three electrolytes tested (1 M NaClO4 in PC, 1 M NaClO4 in PC/FEC (1:1 v/v) and 1 M NaPF6 + PC), and higher than that of the sample without the addition of graphene. The good electrochemical performance can be attributed to the efficient buffering provided by the outer carbon nanocable layer and the graphene inhibiting the agglomeration of SnSb particles, as well as its high conductivity. 相似文献
79.
Creamean JM Ault AP Ten Hoeve JE Jacobson MZ Roberts GC Prather KA 《Environmental science & technology》2011,45(19):8208-8216
Determining the major sources of particles that act as cloud condensation nuclei (CCN) represents a critical step in the development of a more fundamental understanding of aerosol impacts on cloud formation and climate. Reported herein are direct measurements of the CCN activity of newly formed ambient particles, measured at a remote rural site in the Sierra Nevada Mountains of Northern California. Nucleation events in the winter of 2009 occurred during two pristine periods following precipitation, with higher gas-phase SO(2) concentrations during the second period, when faster particle growth occurred (7-8 nm/h). Amines, as opposed to ammonia, and sulfate were detected in the particle phase throughout new particle formation (NPF) events, increasing in number as the particles grew to larger sizes. Interestingly, long-range transport of SO(2) from Asia appeared to potentially play a role in NPF during faster particle growth. Understanding the propensity of newly formed particles to act as CCN is critical for predicting the effects of NPF on orographic cloud formation during winter storms along the Sierra Nevada Mountain range. The potential impact of newly formed particles in remote regions needs to be compared with that of transported urban aerosols when evaluating the impact of aerosols on clouds and climate. 相似文献
80.
Enhanced friction model for high-speed right-angle gear dynamics 总被引:1,自引:0,他引:1
Zhiheng Feng Shilong Wang Teik C. Lim Tao Peng 《Journal of Mechanical Science and Technology》2011,25(11):2741-2753
The modeling of elastohydrodynamic lubrication friction and the analysis of its dynamic effect on right-angle gears, such
as hypoid and spiral bevel types are performed in the present study. Unlike the classically applied empirical constant coefficient
of friction at the contacting tooth surfaces, the enhanced physics-based gear mesh friction model is both spatial and time-varying.
The underlying formulation assumes mixed elastohydrodynamic lubrication (EHL) condition in which the division and load distribution
between the full film and asperity contact zones are determined by the film thickness ratio and load sharing coefficient.
In the proposed time-varying friction model, the calculation of friction coefficient is performed at each contact grid inside
the instantaneous contact area that is being subjected to mineral oil lubrication. The effective friction coefficient and
directional parameters synthesized from the net frictional and normal contact forces are then incorporated into a nonlinear
time-varying right-angle gear dynamic model. Using this model, the effect of friction on the gear dynamic response due to
the transmission error and mesh excitations is analyzed. Also, parametric studies are performed by varying torque, surface
roughness and lubrication properties to understand the salient role of tooth sliding friction in gear dynamics. The simulation
results are included. But experimental verification is needed. 相似文献