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991.
The reinforcing mechanisms of single-walled carbon nanotube-reinforced epoxy composites were studied by micromechanics models. The modeling results obtained from both Halpin-Tsai and Mori-Tanaka models are in good agreement with the experimental results. It has been found that these two models are also applicable to other single-walled carbon nanotube-reinforced, amorphous-polymer composites, given the existence of efficient load transfer. The reinforcing mechanisms that work in polymer-carbon nanotube composites were studied. The reasons responsible for the low mechanical property enhancement of single-walled carbon nanotube in polymer composites were discussed in conjunction with the effective fiber length concept, interface between nanotube bundles and the matrix, properties of the reinforcements and matrix, bundle effects, bundle curvature, and alignment.  相似文献   
992.
Resonance Raman spectroscopy offers a mechanism for the noninvasive measurement of in vivo and in situ hemoglobin oxygen saturation (HbO(2)Sat) in living tissue. Clinically informative signals can be provided by resonance enhancement with deep violet excitation. It is notable that fluorescence does not significantly degrade the quality of the signals. During the controlled hemorrhage and resuscitation of rats, signal intensity ratios of oxy- vs. deoxyhemoglobin from sublingual mucosa correlated with co-oximetry values of blood withdrawn from a central venous catheter. The spectroscopic application described here has potential as a noninvasive method for the diagnosis of clinical shock and guidance of its therapy.  相似文献   
993.
By using backing plates made out of materials with widely varying thermal diffusivity this work seeks to elucidate the effects of the root side thermal boundary condition on weld process variables and resulting joint properties. Welds were made in 25.4-mm-thick AA6061 using ceramic, titanium, steel, and aluminum as backing plate (BP) material. Welds were also made using a “composite backing plate” consisting of longitudinal narrow strip of low diffusivity material at the center and two side plates of high diffusivity aluminum. Stir zone temperature during the welding was measured using two thermocouples spot welded at the core of the probe: one at the midplane height and another near the tip of the probe corresponding to the root of the weld. Steady state midplane probe temperatures for all the BPs used were found to be very similar. Near root peak temperature, however, varied significantly among weld made with different BPs all other things being equal. Whereas the near root and midplane temperature were the same in the case of ceramic backing plate, the root peak temperature was 318 K (45 °C) less than the midplane temperature in the case of aluminum BP. The trends of nugget hardness and grain size in through thickness direction were in agreement with the measured probe temperatures. Hardness and tensile test results show that the use of composite BP results in stronger joint compared to monolithic steel BP.  相似文献   
994.
We demonstrate that blend films containing poly(3-hexylthiophene-2,5-diyl) and in situ grown CdS display a greater yield of photogenerated charges than a blend containing an equivalent amount of pre-synthesised CdS quantum dots. Moreover, we show that the greater charge yield in the in situ grown films leads to an improvement in device efficiency. The present findings also appear to suggest that charge photogeneration at the CdS/polymer heterojunction is facilitated by the formation of nanoparticle networks as a result of CdS aggregation.  相似文献   
995.
ABSTRACT

Sunnyside (Utah) tar sand was subjected to programmed temperature pyrolysis and the volatile products were detected by tandem on-line mass spectrometry (MS/MS) in real time analyses. A heating rate of 4°C/min from room temperature to 900°C was employed.

Evolution of hydrogen, light hydrocarbons, nitrogen-, sulfur-, and oxygen-containing compounds was monitored by MS or MS/MS detection. Evolution of volatile organic compounds occurred in two regimes: 1) low temperature (maximum evolution at 150 to 175°C), corresponding to entrained organics, and 2) high temperature (maximum evolution at 440 to 460°C), corresponding to cracking of large organic components. Alkanes and alkenes of two carbons and higher had temperatures of maximum evolution at approximately 440°C, and methane at approximately 474°C. Aromatic hydrocarbons had temperatures of maximum evolution slightly higher, at approximately 450° C. Some nitrogen-, sulfur-, and oxygen-'ccntaining compounds were also detected in the volatile products.

Comparing the Sunnyside pyrolysis to the pyrolysis of other domestic tar sands indicated the following for hydrocarbon evolution: 1) the evolution of entrained organics relative to the total evolution was much less for Sunnyside tar sand, 2) the temperatures of maximum evolution of hydrocarbons due t o cracking reactions were slightly lower, and 3) the temperatures of maximum evolution for benzene and toluene are slightly higher than observed for other tar sands.

In general, the noncondensible gases, H2, CO, and CO2, exhibited evolution associated with hydrocarbon cracking reactions, and high temperature evolution associated with mineral decomposition, the water-gas shift reaction, and gasification reactions. Pyrolysis yields were dominated by the evolution of carbon oxides and water. The CO2 primarily appeared t o cane from the decomposition of carbonate minerals. Compared t o other domestic tar sands, the gas evolution reflected more mineral decomposition character for Sunnyside tar sand.  相似文献   
996.
ABSTRACT

We have applied size-exclusion chromatography (SEC-HPLC) and reversed-phase chromatography (RP-HPLC), with element specific detection, [Inductively coupled and direct current plasma atomic emission spectroscopy (ICP and DCP)], to selected crude oils –– Boscan, Beta, Morichal, Arabian Heavy, and Maya –– and their separated fractions. By these procedures, we have further characterized both the V porphyrin and the V non-porphyrin compounds.

From the SEC-HPLC-ICP profiles of the heavy crude oils we found the V compounds generally have a bimodal distribution, with maxima at approx. 800 and 9000 polystyrene equivalent (PS) molecular weight (MW). Arabian Heavy, though, had relatively few of the small V compounds.

The crude oils were separated into porphyrin and non-porphyrin fractions by methanol extraction. From the SEC-HPLC-ICP profiles of the porphyrin fraction, we Identified and quantitated the maximum at approx. MW 800 (PS) as being V porphyrins. The remaining V compounds are non-porphyrin.  相似文献   
997.
The incubation time for both whisker growth and corrosion in thin Sn platings (3–10 $mu{hbox {m}}$ thick) on Cu-based alloys have been found to be well represented by an exponential function of humidity and an Arrhenius function of temperature for both as-deposited and reflowed tin platings. Furthermore, whisker growth was found to follow the same functionality in both corroded and non-corroded regions of the plating. The effective activation energies and humidity coefficients were found to depend upon plating thickness, exposure to reflow, and presence of corrosion. The effective activation energies ranged from 0.23 eV to 0.41 eV and the humidity coefficients ranged from $-$0.012% to $-$0.031%. Corrosion enhanced whisker growth occurred by lowering the effective activation energy for whisker growth. A theory based on excess, non-creep relaxed, oxidation induced strain was developed to explain the corrosion induced energy barrier lowering. The data showed that 60 $^{circ}{hbox {C}}/{hbox {87}}%{hbox {RH}}$ appears to be the optimal high temperature/high humidity test condition at this time for Sn over Cu substrates. Within the limits of the whisker and corrosion (incubation) acceleration functions developed in this study, it is concluded that the JEDEC tests can be used to indicate behavior at other temperature/humidity points that could be relevant storage or service conditions.   相似文献   
998.
In organic solar cells, high open circuit voltages may be obtained by choosing materials with a high offset between the donor highest occupied molecular orbital (HOMO) and acceptor lowest unoccupied molecular orbital (LUMO). However, increasing this energy offset can also lead to photophysical processes that compete with charge separation. In this paper the formation of triplet states is addressed in blends of polyfluorene polymers with a series of PCBM multi‐adducts. Specifically, it is demonstrated that the formation of such triplets occurs when the offset energy between donor ionization potential and acceptor electron affinity is ~1.6 eV or greater. Spectroscopic measurements support a mechanism of resonance energy transfer for triplet formation, influenced by the energy levels of the materials, but also demonstrate that the competition between processes at the donor–acceptor interface is strongly influenced by morphology.  相似文献   
999.
在不超过10年的发展时间里,超级电容器已经很成熟了,这种可以贮藏高电荷能量的电化学器件从最初只为直流应用(例如,微波炉或VCR中的时钟电压保持)设计的大容量、低耐压圆柱形器件发展到目前的两大分支:处于实用阶段为混合动力汽车提供电力,并具有很高耐压和法拉容量的电容器和新型小体积、低高度的柱形脉冲超级电容器。  相似文献   
1000.
This study revisits the OPEC cartel hypothesis using a case study. A test is conducted to see if Venezuela has its production Granger cause its OPEC quota or whether the OPEC quota for Venezuela Granger causes Venezuelan production. The results show both occur at different times. In the short run, OPEC’s oil production quota for Venezuela Granger causes Venezuelan production. However, shortly after cuts, Venezuela cheats on agreements, suggesting a tit-for-tat oligopoly game, which is not anti-competitive. In the long run, we show that Venezuelan oil production Granger causes OPEC’s quota for Venezuela, but not vice versa. Having Venezuelan oil production Granger cause OPEC quotas for Venezuela in the long run suggests OPEC does not coordinate outputs as much as it reacts to them. The evidence suggests Venezuela is not a part of an OPEC anti-competitive syndicate even though we show that Venezuelan oil production is low. An alternative explanation for why Venezuela and possibly other OPEC members have low oil production outputs is that institutions and risk aversion, not cartel participation, is the cause. A vector error correction model shows that there is no tendency for Venezuelan oil production to converge to OPEC’s quota for Venezuela.  相似文献   
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