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61.
62.
The role of grain size and selected microstructural parameters in strengthening fully lamellar TiAl alloys 总被引:2,自引:0,他引:2
Dennis M. Dimiduk Peter M. Hazzledine Triplicane A. Parthasarathy Madan G. Mendiratta Sriram Seshagiri 《Metallurgical and Materials Transactions A》1998,29(1):37-47
More than 5 years ago, wrought processing was first used to produce fully lamellar (FL) microstructures in TiAl alloys having
grain sizes less than ≈400 μm. These alloys exhibit an improvement in overall balance of properties, especially at high temperatures. More recently, such
microstructural forms led to exceptional yield strengths (500 to 1000 MPa at low temperatures) while maintaining attractive
high-temperature properties. The improvements appeared to be related to an unusually high apparent sensitivity of strength
to grain size. Studies reported an apparent value for the slope of the Hall-Petch (HP) plot approaching 5 MPa√m for FL gamma
alloys, while that for single-phase or duplex microstructures is near unity. The present investigations examine the slope
of the HP plot for FL microstructures, paying particular attention to the lamellar microstructural variables. Results show
that the α
2 lamellar thickness and spacing and the γ lamellar thickness can vary over more than two orders of magnitude with typical process methods. These spacings influence
the value of k
y
in the HP (grain size) relationship. Since they often change concomitantly with grain size in processing, they can give rise
to a large scatter in the HP plot. The investigations also examine the flow behavior, glide barriers, and slip multiplicity
for polysynthetically twinned (PST) crystals (the single-grain analogue of FL material), and then map this behavior into an
explanation of the yield behavior of high-strength FL gamma alloys.
This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the
TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations
Committees. 相似文献
63.
A surface processing method that combines electrostatic deposition of microparticles and dry etching is utilized to modify
the surface topography of silicon surfaces to reduce adhesion and friction force. Microscale adhesion and friction tests were
conducted on flat (smooth) and processed silicon surfaces with a low elastic modulus thermoplastic rubber (Santoprene) probe
that allowed a large enough contact area to observe the feature size effect. Both adhesion and friction force of the processed
surfaces were reduced comparing to that of the flat surfaces. 相似文献
64.
S. Sriram R. Balasubramaniam M. N. Mungole S. Bharagava R. G. Baligidad 《Bulletin of Materials Science》2005,28(6):547-554
The effect of Ce addition on the microstructure of carbon-alloyed Fe3Al-based intermetallic has been studied. Three different alloys of composition, Fe-18.5Al-3.6C, Fe-20.0Al-20C and Fe-19.2Al-3.3C-0.07Ce
(in at%), were prepared by electroslag remelting process. Their microstructures were characterized using optical and scanning
electron microscopies. Stereological methods were utilized to understand the observed microstructures. All the alloys exhibited
a typical two-phase microstructure consisting of Fe3AlC carbides in an iron aluminide matrix. In the alloy without Ce addition, large bulky carbides were equally distributed
throughout the matrix with many smaller precipitates interspersed in between. In the alloy with Ce addition, the carbide grain
sizes were finer and uniformly distributed throughout the matrix. The effect of Ce addition on the carbide morphology has
been explained based on the known effect of Ce in modifying carbide morphology in cast irons. 相似文献
65.
Sriram Ramaswamy 《Bulletin of Materials Science》1988,10(1-2):75-76
Calculations in a hydrodynamic model of quasicrystal dynamics show that dislocation motion in these systems is impeded by
a drag far greater than that in crystals. 相似文献
66.
Sriram Venkataramani Tharanikkarasu Kannan Ganga Radhakrishnan 《Polymer International》2006,55(11):1209-1214
1‐Vinylimidazole‐terminated telechelic polyurethanes were prepared from 1‐vinylimidazole and bromine‐terminated polyurethane. This vinyl‐terminated telechelic polyurethane (VTPU) and methyl methacrylate were polymerized in the presence of benzoyl peroxide to prepare novel AB crosslinked polymer networks (ABCPs). These were characterized by spectral, thermal and mechanical studies. The absence of the characteristic peak of vinyl group in infrared spectra of ABCP films confirms the occurrence of crosslinking. Static mechanical testing showed that the tensile strength of ABCP increases with increasing poly(methyl methacrylate) content. Dynamic mechanical studies revealed that ABCPs, at equal compositions of VTPU and methyl methacrylate, show good damping properties. Copyright © 2006 Society of Chemical Industry 相似文献
67.
B Sriram Shastry 《Bulletin of Materials Science》1979,1(3-4):195-199
The remarkable remanence effects observed in spin glasses are discussed. Some theoretical approaches and results are reviewed.
Invited talk given at the Indian Academy of Sciences, Bangalore, Academy discussion meeting on phase transitions, June 21st,
1978. 相似文献
68.
Sriram K. Varshney P. Shanthikumar J. 《Selected Areas in Communications, IEEE Journal on》1983,1(6):1124-1132
Discrete-time analysis of two schemes for multiplexing voice and data is presented. In each scheme voice and data are multiplexed using the movable boundary frame allocation scheme. In the first scheme, speech activity detectors (SAD's) are not used, and hence, the variations in the voice traffic are only due to the on/off characteristics of voice. In the second scheme, SAD's are employed so that talker silences can he utilized for transmission of additional voice and/or data. In this scheme, the multiplexer performs digital speech interpolation as well as movable boundary frame allocation. The performance measures considered are probability of loss for voice calls, probability of speech clipping, speech packet rejection ratio, and the expected data message delay. In the case of the multiplexer with SAD, a tradeoff exists between data message delay and speech interpolation advantage. Some numerical examples are presented which illustrate the performance of the two multiplexers. 相似文献
69.
Dynamic response of flexible-link mechanism (structure) when subjected to external dynamic load is analyzed. The non-linear equations of motion are discretized using the finite element method (FEM) and Newmark time integration method combined with Newton-Raphson iterative technique is used for solution. From the dynamic response of the structure, the required kinematic characteristics are derived. Typical examples are worked out for illustration. 相似文献
70.
Stress corrosion cracking of a commercial 0.19 pct C steel (SA-516 Grade 70) was studied in hot (92 ‡C) caustic solutions
of NaOH and NaOH plus aluminate (AlO−
2) species. Potentiostatically controlled tests were conducted near the active-passive transition, using fracture mechanics
testing techniques and fatigue precracked double cantilever beam specimens. Crack propagation rates (Ν) were determined for
a range of stress intensities (K
l). In simple NaOH solutions, Region I (K1-dependent) and Region II (K
1-independent) cracking behavior were observed. Increasing the concentration of NaOH from2m to8m decreasedK
ISCC
and displaced Region I and the onset of Region II to lowerK
1 levels. The presence of AlO−
2 produced a comparable effect, with Region II being extended to lowerK
I
-Ν levels relative to simple NaOH solutions of similar hydroxyl anion concentration. The overallK
I
-Νv behavior and fractography were consistent with a dissolution mechanism of crack advance based on the general principles of
the film rupture-dissolution model. The effect of environment composition uponK
I
— Ν behavior was attributed to changes in repassivation kinetics.
Formerly Graduate Student at the University of British Columbia 相似文献