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991.
The objective of this study was to evaluate the differences in ex-situ (starch treated by ultrasonication and oxidation sequentially, U-OS) and in-situ (starch treated by ultrasonication and oxidation simultaneously, UOS) ultrasonic assisted oxidation process of corn starch, which were studied in contrast to the traditional oxidized starches (OS). Fourier-transform infrared spectra confirmed the successful oxidation of all modified starches samples. In comparison to the OS, the carboxyl contents of U-OS and UOS increased by 56% and 112%, respectively. The same increase trend was also found for the carbonyl contents. The significance raise was attributed to the great increase of pores and specific surface areas in the starch granule after ultrasonic irradiation which promoted the penetration of the sodium hypochlorite into the starch granules with higher chances for chemical reactions. SEM and pore size distribution characterizations further verified this result. However, the method of in-situ ultrasonic assisted oxidation can simultaneously accelerate the increase of pores and the penetration process. Consequently, the starches with higher oxidation degree can be more efficiently prepared by the strategy of in-situ ultrasonic assisted oxidation. 相似文献
992.
The impact of ultrasound (US) reactor design on cavitation intensity distribution and disintegration efficiency was studied for sewage sludge pre-treatment, using a US flatbed reactor of variable reaction chamber height (RCH, 20–100 mm). Mapping of cavitation intensity and treatment effects was conducted using (i) hydrophone measurements, (ii) aluminum foil tests, and (iii) soluble chemical oxygen demand (COD) analyses. The overall disintegration efficiency was evaluated based on average COD solubilization. The impact of flow on treatment (in)homogeneity was additionally examined using computational fluid dynamics (CFD). Results of all measurement techniques suggest that small RCHs (20 mm, for instance) enable uniform and intense treatments, while large RCHs, which are subjected to strong sound wave attenuation, entail inhomogeneous treatments where large fractions of substrate are no longer exposed to notable cavitation activity. For instance, COD solubilization (relative to alkaline hydrolysis) measured in the channel center dropped from 6.4% to zero as RCH widened from 20 mm to 100 mm. Flow-through sonication further aggravates treatment inhomogeneity due to the high flow rates in the low-cavitation channel centers. Overall disintegration efficiency declined with increasing RCH, showing a drop in average COD solubilization by 73% from RCH = 20 mm to RCH = 100 mm. The drop correlated with average cavitation noise levels (R2 = 0.82), indicating that hydrophone measurements may be a suitable tool for US reactor design optimization. Overall, results suggest that reactor geometry has a critical impact on both treatment (in)homogeneity and treatment efficiency and that equal specific energy inputs do not imply equal US treatments. 相似文献
993.
994.
采用功率350W、40kHz超声波器和紫外光同时对水中的苯酚进行降解,考察了样品苯酚溶液的pH及浓度、加入6%H2O2和0.001mol/LFe2 (FeSO4)的量、超声波超声功率、紫外光照射的时间、紫外-超声联用降解的时间等条件的影响。结果表明,在苯酚的最佳降解条件(紫外-超声联用下作用60min,pH3~4,加入6%的H2O24mL和0.001mol/L的Fe2 (FeSO4)1.6mL)下,苯酚的降解率达91.8%,证明超声波诱导紫外光协同法是一种降解苯酚的有效方法。 相似文献
995.
Anisotropy of Seismic Attenuation in Fractured Media: Theory and Ultrasonic Experiment 总被引:1,自引:0,他引:1
This is a study on anisotropy of seismic attenuation in a transversely isotropic (TI) model, which is a long-wavelength equivalent
of an isotropic medium with embedded parallel fractures. The model is based on Schoenberg’s linear-slip theory. Attenuation
is introduced by means of a complex-valued stiffness matrix, which includes complex-valued normal and tangential weaknesses.
To study the peculiarities of seismic attenuation versus wave-propagation direction in TI media, numerical modeling was performed.
The model-input data were the complex-valued weaknesses found from the laboratory ultrasonic experiment made with a Plexiglas
plate-stack model, oil-saturated (wet) and air-filled (dry). The laboratory experiment and the numerical modeling have shown
that in the vicinity of the symmetry axis, in the wet model, P-wave attenuation is close to S-wave attenuation, while in the
dry model, P-wave attenuation is much greater than S-wave attenuation. Moreover, the fluid fill affects the P-wave attenuation
pattern. In the dry (air-saturated) model, the attenuation pattern in the vicinity of the symmetry axis exhibits steeper slope
and curvature than in the wet (oil-saturated) model. To define the slope or the curvature, a QVO gradient was introduced,
which was found to be proportional to the symmetry-axis Q
S/Q
P-ratio, which explains the differences between dry and wet models. Thus, depending on the Q
S/Q
P-ratio, the QVO gradient can serve as an indicator of the type of fluid in fractures, because the QVO gradient is greater
in gas-saturated than in liquid-saturated rocks. The analysis of P-wave attenuation anisotropy in seismic reflection and vertical
seismic profiling data can be useful in seismic exploration for distinguishing gas from water in fractures. 相似文献
996.
超声波清洗设备的发展方向目前有二个:一个是从单缸机到多缸机或自动化的超声清洗生产线;另一个是,从低频超声清洗机到高频超声清洗机。 相似文献
997.
998.
低温陈化超声波共沉淀法制得SO42-/ZrO2-La2O3前驱体, 经H2SO4处理, 在不同温度下焙烧得到纳米晶催化剂SO42-/ZrO2-La2O3;用Hammett指示剂法测定其酸性. 用XRD、BET、TEM、IR和XPS对样品进行表征,其催化活性用醋酸和甘油的酯化反应进行了评价. 结果表明经超声波搅拌和低温(-15 ºC)陈化,650 ºC焙烧4 h得到的固体超强酸表现出较高催化活性. 相似文献
999.
An FEM model is developed for a fundamental study of the time-dependent mechanical behavior of the substrate and its dimensions on ultrasonic consolidation. The simulation shows that for a given vibration condition, the amplitude of contact friction stress and displacement stabilizes to a saturated state after certain number of ultrasonic cycles. With the increased substrate height, the amplitude of contact frictional stress decreases, while that of contact interface displacement increases. The reason for the decrease in the frictional stress at the contact interface for certain substrate heights is the complicated wave interference occurring in the substrate. An analytical wave model has been built to validate the FEM model. A specific substrate geometry (height:width = 1.0) generates a minimum frictional strain state at the interface as a result of wave superposition. Such minimum strain state is believed to have produced the “lack of bonding” defect for the geometry. The energy density and transfer coefficient at the contact interface with different substrate heights is used as an indicator to correlate with the bond formation in ultrasonic bonding. 相似文献
1000.