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161.
E-SPART Analysis of Poly (D, L-lactide-co-glycolide) Microspheres Formulated for Dry Powder Aerosols
Vinod A. Philip Rahul C. Mehta Patrick P. Deluca Malak K. Mazumder 《Particulate Science and Technology》1997,15(3):303-316
Electrical-single particle aerodynamic relaxation time (E-SPART) analysis was studied as a tool in formulation screening of diy powders for use in aerosol delivery to the lung. The respirable fraction (RF) of drugs delivered by dry powder inhalers (DPIs) can be improved more effectively by using hydrophobic microspheres as carriers. Poly (D,L-lacttde-co-grycolide) microspheres (PLGA) prepared in die respirable size range (3-7 mm) were treated with poryamino acids and isopropanol in order to obtain particles of surface charge suitable for use in DPIs.
The powder formulations were evaluated for their degree of aggregation by cascade impaction following delivery by the Pfeifler® DPI. The IPA treated PLGA microspheres had a significantly higher RF (12.9%) as compared to the PL and PGA treated microspheres (3.3 and 2.4%, respectively), and untreated microspheres (3.8%). Results of electrostatic charge determined by E-SPART analysis suggested that die higher RF for the IPA formulation may be due to hs highly unipolar nature (+ 56.3 mC/g). 相似文献
The powder formulations were evaluated for their degree of aggregation by cascade impaction following delivery by the Pfeifler® DPI. The IPA treated PLGA microspheres had a significantly higher RF (12.9%) as compared to the PL and PGA treated microspheres (3.3 and 2.4%, respectively), and untreated microspheres (3.8%). Results of electrostatic charge determined by E-SPART analysis suggested that die higher RF for the IPA formulation may be due to hs highly unipolar nature (+ 56.3 mC/g). 相似文献
162.
The laser surface cladding technique was used to formin situ Fe-Cr-Mn-C alloys on AISI 1016 steel substrate. In this process mixed powders containing Cr, Mn, and C with a ratio of 10∶1∶1
were delivered using a screw feed, gravity flow carrier gas aided system into the melt pool generated by a 10 kw CO2 laser. This technique produced ultrafine microstructure in the clad alloy. The microstructure of the laser surface clad region
was investigated by optical, scanning, and transmission electron microscopy and X-ray microanalysis techniques. Microstructural
study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced
a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy
of this composition does not show any martensitic or retained austenite phase. In preliminary wear studies the laser clad
Fe-Cr-Mn-C alloys exhibited far superior wear properties compared to Stellite 6 during block-on-cylinder tests. The improved
wear resistance is attributed to the fine distribution of metastable M6C carbides. 相似文献
163.
A two-dimensional transient model for convective heat transfer and surface tension driven fluid flow is developed. The model
describes the transient behavior of the heat transfer process of a stationary band source. Semi-quantitative understanding
of scanning is obtained by a coordinate transformation. The non-dimensional forms of the equations are derived and four dimensionless
parameters are identified, namely, Peclet number (Pe), Prandtl number (Pr), surface tension number(S), and dimensionless melting temperature(@#@ Tm
*
@#@). Their governing characteristics and their effects on pool shape, cooling rate, velocity field, and solute redistribution
are discussed. A numerical solution is obtained and presented. Quantitative effects of Prandtl number and surface tension
number on surface velocity, surface temperature, pool shape, and cooling rate are presented graphically.
This paper is based on a presentation made at the symposium “Fluid Flow at Solid-Liquid Interfaces” held at the fall meeting
of the TMS-AIME in Philadelphia, PA on October 5, 1983 under the TMS-AIME Solidification Committee. 相似文献
164.
Hui Zhang Mazumder P. Li Ding Kyounghoon Yang 《Nanotechnology, IEEE Transactions on》2005,4(4):472-480
Resonant tunneling-based random-access memories (TRAMs) have recently garnered a great amount of interest among memory designers due to their intrinsic merits such as reduced power consumption by elimination of refreshing operation, faster read and write cycles, and improved reliability in comparison to conventional silicon dynamic random access memories (DRAMs). In order to understand the precise principle of operation of TRAM memories, an in-depth circuit analysis has been attempted in this paper and analytical models for memory cycle time, soft error rate, and power consumption have been derived. The analytical results are then validated by simulation experiments performed with HSPICE. These results are then compared with conventional DRAMs to establish the claim of superiority of TRAM performance to DRAM performance. 相似文献
165.
A. S. Biris S. De M. K. Mazumder R. A. Sims D. A. Buzatu R. Mehta 《Particulate Science and Technology》2004,22(4):405-416
A corona discharge ion bombardment technique was used successfully to generate gold particles of submicron diameters. In a negative corona discharge, the glow region contains electrons, negative ions, and positive ions. Positive ions collided with the negative corona tip electrode, causing it to sputter and emit fine particles of the electrode material. These nanoparticles were deposited on grounded metal substrates or thin mica sheets supported by grounded metal substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the size distribution and deposition pattern of the metal nanoparticles. The diameter of these nanoparticles was dependent upon the material of the electrode and ranged from 20 to 450 nm for gold and from 15 to 240 nm for tungsten. The nanoparticles were deposited on aluminum, mica, and carbon steel test panels for different amounts of time. The electrochemical response of the carbon steel panels exposed to aerated salt solution was measured by direct current (DC) polarization technique before and after the gold nanoparticles were deposited. This technique was employed to determine the changes in the surface chemistry because of the presence of gold nanoparticles, and it proved to be a sensible method for detecting the presence of fine layers of nanoparticles on the metallic substrate. The presence of the gold nanoparticles increased the electrochemical potential Ecorr from -0.640 V to -0.211 V, compared with the value for a noncorrosive surface, like that of pure gold, which is 0 V. 相似文献
166.
Resonant tunneling devices are promising candidates for comingling with traditional CMOS circuits, yielding better performance in terms of reduced silicon area, faster circuit speeds, lower power consumption, and improved circuit noise margin. These resonant tunneling devices have several intrinsic merits that include: high current density, low intrinsic capacitance, the negative differential resistance effect, and relative ease of fabrication. In this paper, we briefly describe some circuit configurations of Silicon quantum MOS logic family, with a special emphasis on noise-tolerant design that is now becoming an important constraint for robust and reliable operation of very deep submicron VLSI chips. More specifically, we discuss a novel strategy to incorporate quantum-tunneling devices into mainstream dynamic CMOS circuits with a view to improving the noise immunity of the latter. Dynamic CMOS circuits are rampantly used in modern high-performance VLSI chips achieving the best tradeoff between circuit speed, silicon area, and power consumption. However, they are inherently less noise-tolerant than their static CMOS counterparts. With the continuously deteriorating noise margins due to aggressive down scaling of the CMOS fabrication technologies, the performance overhead due to existing remedial noise-tolerant circuit techniques becomes prohibitively high. In this paper, we propose a novel method that utilizes the negative differential resistance property of quantum tunneling devices. The performance and noise immunity of the proposed circuits are evaluated through both analytical studies and SPICE simulations. We demonstrate that the noise tolerance of dynamic CMOS circuits can be greatly improved with very little degradation in circuit speed. The benefit of the proposed technique is evident even for currently available Silicon-based resonant tunneling devices with a relatively small peak-to-valley current ratio. 相似文献
167.
B. S. Mazumder 《Acta Mechanica》1979,32(4):211-216
Summary Dispersion of a solute in combined free and forced convective laminar flow through a parallel plate channel has been considered, when there is a uniform axial temperature variation along the channel walls. It is observed that the effective Taylor diffusion coefficient increases with increase in Grashof number and also the interesting fact that it is same for both heating and cooling of the plates.
With 1 Figure 相似文献
Dispersion von Lösungen bei freier und erzwungener Konvektion in einem Kanal
Zusammenfassung Es wird die Dispersion einer Lösung bei freier und erzwungener Konvektion in einem Kanal mit parallelen Wänden untersucht, falls ein konstanter horizontaler Temperaturgradient an den Kanalwänden auftritt. Es wird festgestellt, daß der effektive Taylor-Diffusionskoeffizient ansteigt mit wachsender Grashof-Zahl, und zwar gilt dies unverändert für Kühlung oder Heizung der Wände.
With 1 Figure 相似文献
168.
Coupled-line circuit with adjustable input conductance 总被引:1,自引:0,他引:1
A new matching circuit was developed, for which the input conductance (real part of the input admittance) can be adjusted by simply changing the length of one open-ended stub. This circuit can be utilised for matching of microstrip devices as well as for tuning of solid-state amplifiers and oscillators (such as transistors, Impatt or Gunn diodes). 相似文献
169.
Origins and implications of drinking water odours in lakes and reservoirs of British Columbia, Canada 总被引:3,自引:0,他引:3
The relationship between commonly measured limnological parameters and odours was examined in 16 reservoirs and lakes used as sources for drinking water and three reference lakes. Odour analysis was conducted using flavour profile analysis (FPA) and, on select lakes, gas chromatography ion-trap mass spectrometry (GC-ITMS) for target compounds. Total phosphorus (TP) was the best single predictor of FPA intensity and multiple regression models accounted for 37-39% of intensity variance in the epilimnion and metalimnion, respectively. Earthy odours were more prevalent in reservoirs and lakes with higher TP, whereas decomposing vegetation and green vegetation+grassy odours almost exclusively occurred when TP was lower (<13 microg P/L). Only geosmin was identified with GC-ITMS, and it was found to occur in lakes and reservoirs of higher trophic status (e.g. more algal biomass). Infrequent episodic events in the Greater Victoria's principal reservoir (e.g. algal blooms) have previously been linked with taste and odour problems in their tap water. However, analysis of odours under the conditions of this study (i.e. no strong odour episodes in the source reservoir) suggest that typical odours prevalent in tap water originating from Sooke Lake Reservoir are derived from treatment processes or the distribution system, not directly from the reservoir. This study demonstrates the utility of employing relatively simple and established methods to better understand management issues of a drinking water system. 相似文献
170.
Dense BiFeO3 ceramics were prepared by a novel spark plasma sintering (SPS) technique. The sintering was conducted at temperatures ranging from 675 to 750 °C under 70 MPa pressure. A bulk density value up to 96% of theoretical density was achieved in the process. This contrast to around 90% of the theoretical density achieved by conventional sintering at around 830 °C. It was found that the tendency to form unwanted Bi2Fe4O9 phase is higher at a high sintering temperature for SPS. The dielectric and ferroelectric properties also improved (with respect to conventionally sintered sample) for spark plasma-sintered samples. 相似文献