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141.
D. Q. Bai S. Yue W. P. Sun J. J. Jonas 《Metallurgical and Materials Transactions A》1993,24(10):2151-2159
The recrystallization behavior of three Nb-bearing high-strength low-alloy (HSLA) steels was investigated during multipass
deformation under continuous cooling conditions. The niobium concentrations of these steels varied from 0.05 to 0.09 wt pct.
The specimens were tested on a computerized torsion machine using a simulation schedule of 17 passes. Deformation tem-peratures
of 1180 °C to 700 °C were employed, together with pass strains of 0.1 to 0.7, strain rates of 0.2 to 10 s-1, and interpass times of 5 to 200 seconds. By means of mean flow stressvs 1000/T diagrams, the effect of the deformation conditions on the no-recrystallization tem-perature (T
nr
), the temperature at which recrystallization is no longer complete, was determined. It decreases with increasing strain and
also decreases slightly with increasing strain rate. There is aT
r
minimum at times of about 12∼15 seconds, and both increases and decreases from this value raise this characteristic temperature.
When the interpass times are short, solute atoms control the rate of recrystallization, the extent of which decreases as the
time is decreased. When the interpass times are long, precipitation takes place and retards recrystallization, so that the
extent of softening decreases.
Formerly Research Associate, McGill University, Department of Metallurgical Engineering. 相似文献
142.
T. R. Jonas J. A. Cornie K. C. Russell 《Journal of Materials Engineering and Performance》1993,2(3):375-381
The authors previously developed a capacitance technique to determine the position of the infiltration front as a function
of time during the pressure infiltration of ceramic particulate preforms with liquid metals. In the present work, the technique
was extended to higher temperatures and was used to monitor the infiltration of alumina particulate preforms with Al-Mg alloys
and silicon carbide particulate pre-forms with Sn and an Al-Si alloy. The infiltration front position could be determined
in the alumina pre-forms. However, it was not possible to clearly interpret the results obtained from the infiltration of
semiconducting silicon carbide preforms. The observed range of capacitance circuit voltage to infiltra-tion distance ratios
agreed with the predicted range for both simulated and alumina preform infiltration experiments. Formation of unstable infiltration
fronts could also be detected. 相似文献
143.
The following sequence of events is thought to underlie the stimulation of insulin release by hypoglycaemic sulphonylureas. Interaction of the drugs with a high-affinity binding site (sulphonylurea receptor) in the B-cell membrane leads to closure of ATP-sensitive K+ channels, depolarization, opening of voltage-dependent Ca2+ channels, Ca2+ influx and rise in cytoplasmic [Ca2+]i. Recent experiments using permeabilized islet cells or measuring changes in B-cell membrane capacitance have suggested that sulphonylureas can increase insulin release by a mechanism independent of a change in [Ca2+]i. This provocative hypothesis was tested here with intact mouse islets. When B-cells were strongly depolarized by 60 mM K+, [Ca2+]i was increased and insulin secretion stimulated. Under these conditions, tolbutamide did not further increase [Ca2+]i or insulin release, whether it was applied before or after high K+, and whether the concentration of glucose was 3 or 15 mM. This contrasts with the ability of forskolin and phorbol 12-myristate 13-acetate (PMA) to increase release in the presence of high K+. Tolbutamide also failed to increase insulin release from islets depolarized with barium (substituted for extracellular Ca2+) or with arginine in the presence of high glucose. Glibenclamide and its non-sulphonylurea moiety meglitinide were also without effect on insulin release from already depolarized B-cells. In the absence of extracellular Ca2+, acetylcholine induced monophasic peaks of [Ca2+]i and insulin secretion which were both unaffected by tolbutamide. Insulin release from permeabilized islet cells was stimulated by raising free Ca2+ (between 0.1 and 23 microM). This effect was not affected by tolbutamide and inconsistently increased by glibenclamide. In conclusion, the present study does not support the proposal that hypoglycaemic sulphonylureas can increase insulin release even when they do not also raise [Ca2+]i in B-cells. 相似文献
144.
145.
Solid state 27Al and 29Si NMR was used to examine the structures of aluminosilicates and sodium aluminosilicates prepared by the sol-gel method from metal alkoxides. In contrast to the borosilicate system, where B-O-Si bonds are not formed until heat treatment above 150° C, Al-O-Si formation appears complete upon gelation. Aluminium occupies tetrahedral [AlO4]– sites in the polymer network and octahedral [Al(H2O)6]3+ (or similar) sites in the intersticies for charge balance. When sodium is added as a counter ion the octahedral aluminium is converted to tetrahedral aluminium in the oxide network. In gels of high aluminium content prepared from (BusO)2Al-O-Si(OEt)3, some aluminium in five coordinate environments is also observed. All gels remain amorphous on heating to 800° C. 相似文献
146.
The choice of soft pulse shapes for chemical shift selective excitation in chemical shift imaging is discussed. In the presence of inhomogeneities in the static magnetic field resulting from susceptibility anomalies, it is important to optimise pulse bandshape and frequency offset as well as bandwidth, in order to minimize artefacts arising from excitation of unwanted resonances. A comparison of the use of Gaussian and sinc shaped excitation pulses in the chemical shift micro-imaging of grapes serves to illustrate some of the effects that may be observed. 相似文献
147.
148.
The history of microcomputer application in automotive electronics is briefly reviewed. American, Japanese, and European automobile manufacturer's microcomputer products are considered, and representative production designs are compared. Differences in approaches and problem solutions are examined. The chronological introduction of microcomputer-controlled functions is presented for engine, transmission, entertainment/comfort/convenience, and instrument panel control. Growth trends are noted for each category, and future automotive microcomputer applications are discussed. Projections are made of future semiconductor VLSI technology and automotive microcomputers. 相似文献
149.
Softening and microstructural change following the dynamic recrystallization of austenite 总被引:4,自引:0,他引:4
C. Roucoules P. D. Hodgson S. Yue J. J. Jonas 《Metallurgical and Materials Transactions A》1994,25(2):389-400
To characterize the dynamic recrystallization behavior of austenite, continuous-torsion tests were carried out on a Mo steel
over the temperature range 950 ‡C to {dy1000} ‡C, and at strain rates of 0.02, 0.2, and 2 s-1. Interrupted-torsion tests also were performed to study the characteristics of postdynamic recrystallization. Quenches were
performed after increasing holding times to follow the development of the postdynamic microstructure. Finally, torsion simulations
were carried out to assess the importance of metadynamic recrystallization in hot-strip mills. The postdynamic microstructure
shows that the growth of dynamically recrystallized grains is the first change that takes place. Then metadynamically recrystallized
grains appear and contribute to the softening of the material. The rate of metadynamic recrystallization and the meta-dynamically
recrystallized grain size depend on strain rate and temperature and are relatively independent of strain, in contrast to the
observations for static recrystallization. True dynamic recrystallization-controlled rolling (DRCR) is shown to require such
short interpass times that it does not occur in isolation in hot-strip mills. As these schedules involve 20 to 80 pct softening
by metadynamic recrystallization, a new concept known as metadynamic recrystallization-controlled rolling (MDRCR) is introduced
to describe this type of situation.
1 C. ROUCOULES, formerly with the Department of Mining and Metallurgical Engineering, McGill University, Montreal, PQ, Canada 相似文献
150.
G Raviv I Leibovitch O Shenfeld Y Mor P Jonas B Goldwasser 《Canadian Metallurgical Quarterly》1994,52(3):135-139
Ureteropelvic junction (UPJ) obstruction is a congenital anomaly either caused by intrinsic narrowing of the upper ureter or by extrinsic pressure on the ureter caused by aberrant vessels or fibrous bands. We reviewed 121 cases of pyeloplasties performed in our department for UPJ obstruction. The cases were grouped by age and by the underlying pathology. Postoperative urographic evaluation showed that dismembered pyeloplasty was successful in 98.4% of the patients, with no significant difference between age groups. Persistence or recurrence of preoperative symptoms occurred in some patients (16.6%). Extrinsic obstruction of the ureter was associated with better postoperative clinical results and less recurrence of symptoms. 相似文献