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991.
Mohammad Ghalambaz Seyed Abdollah Mansouri Mehryan Kasra Ayoubi Ayoubloo Ahmad Hajjar Mohamad El Kadri Obai Younis Mohsen Saffari Pour Christopher Hulme-Smith 《Molecules (Basel, Switzerland)》2021,26(5)
Thermal energy storage units conventionally have the drawback of slow charging response. Thus, heat transfer enhancement techniques are required to reduce charging time. Using nanoadditives is a promising approach to enhance the heat transfer and energy storage response time of materials that store heat by undergoing a reversible phase change, so-called phase change materials. In the present study, a combination of such materials enhanced with the addition of nanometer-scale graphene oxide particles (called nano-enhanced phase change materials) and a layer of a copper foam is proposed to improve the thermal performance of a shell-and-tube latent heat thermal energy storage (LHTES) unit filled with capric acid. Both graphene oxide and copper nanoparticles were tested as the nanometer-scale additives. A geometrically nonuniform layer of copper foam was placed over the hot tube inside the unit. The metal foam layer can improve heat transfer with an increase of the composite thermal conductivity. However, it suppressed the natural convection flows and could reduce heat transfer in the molten regions. Thus, a metal foam layer with a nonuniform shape can maximize thermal conductivity in conduction-dominant regions and minimize its adverse impacts on natural convection flows. The heat transfer was modeled using partial differential equations for conservations of momentum and heat. The finite element method was used to solve the partial differential equations. A backward differential formula was used to control the accuracy and convergence of the solution automatically. Mesh adaptation was applied to increase the mesh resolution at the interface between phases and improve the quality and stability of the solution. The impact of the eccentricity and porosity of the metal foam layer and the volume fraction of nanoparticles on the energy storage and the thermal performance of the LHTES unit was addressed. The layer of the metal foam notably improves the response time of the LHTES unit, and a 10% eccentricity of the porous layer toward the bottom improved the response time of the LHTES unit by 50%. The presence of nanoadditives could reduce the response time (melting time) of the LHTES unit by 12%, and copper nanoparticles were slightly better than graphene oxide particles in terms of heat transfer enhancement. The design parameters of the eccentricity, porosity, and volume fraction of nanoparticles had minimal impact on the thermal energy storage capacity of the LHTES unit, while their impact on the melting time (response time) was significant. Thus, a combination of the enhancement method could practically reduce the thermal charging time of an LHTES unit without a significant increase in its size. 相似文献
992.
The development of highly efficient, inexpensive, abundant and non-precious metal electrocatalysts is the lifeblood of the hydrogen production industry, especially the hydrogen production industry by electrolysis of water. A Fe-Co-S/NF bifunctional electrocatalyst with nanoflower-like structure was synthesized on three-dimensional porous nickel foam through one-step hydrothermal and one-step high-temperature sulfuration operations, and the material displays high-efficiency electrocatalytic performance. As a catalyst for the hydrogen evolution reaction, Fe-Co-S/NF can drive a current density of 10 mA/cm2 at an overpotential of 143 mV with a Tafel slope of 80.2 mV/dec. When it was used as an oxygen evolution reaction catalyst, it exhibits good OER reactivity with a low Tafel slope (82.6 mV/dec) and with requiring only 117 mV overpotential to drive current densities up to 50 mA/cm2. In addition, the Fe-Co-S/NF//Fe-Co-S/NF electrolytic cell was assembled, an electrolysis voltage of 1.64 V is required to drive a current density of 50 mA/cm2, which is one of the most active catalysts reported so far. This work indicates that the introduction of S, P and Se treating processes could effectively improve electrical conductivity of the material and enhance the catalytic activity of the material. This work offers an effective and convenient method for improving the morphology of the catalyst, increasing the surface area of the catalyst and developing high-efficiency and low-cost catalysts. 相似文献
993.
Rika Fukushima Olivier Tardif Shojiro Kaita Yasuo Wakatsuki Nobuaki Koga 《化学:亚洲杂志》2021,16(11):1403-1416
The cationic gadolinium metallocene [(C5Me5)2Gd][B(C6F5)4], when combined with an excess amount of Al(iBu)3, efficiently produces polyethylene at 80 °C under 0.8 MPa pressure of ethylene. After quenching, the resulting polyethylene has ethyl group at one end and isobutyl group at the other terminal. Because no Gd-alkyl species appears to be involved, a mechanism with conventional coordinative chain transfer polymerization (CCTP) is not feasible. Density functional theory (DFT) analyses indicate a novel mechanism in which the cationic Gd plays a crucial role by coordinating ethylene and assists the insertion of the coordinated ethylene into Al−C bond. 相似文献
994.
995.
Poly (vinyl alcohol) (PVA) foam is a promising environment‐friendly packaging material due to the good biodegradability and excellent mechanical properties. Besides, PVA can be produced on a large scale viathe non‐petroleum routes. However, the preparation of complex‐shaped PVA foam products has not been realized, because PVA is a water‐soluble and semi‐crystalline polymer with a high melting temperature (226°C), which cannot be welded through the conventional bead foaming technology. In this article, a clean and efficient strategy based on microwave foaming and sintering was innovatively developed to manufacture the PVA bead foam products. First, the expandable PVA beads were prepared through polar solvent‐plasticization, followed by supercritical carbon dioxide (scCO2)‐impregnation in solid‐state. The impregnated beads were then surface plasticized with polar solvent by simple coating. Thus, the incorporated polar solvent in the internal and superficial regions of PVA beads was rapidly heated upon exposure to the microwave irradiation, which simultaneously induced the CO2 foaming and interfacial melting, respectively. In this way, the expansion and welding of PVA beads were completed in a one‐step procedure. Meanwhile, the complex‐shaped PVA bead foam products with excellent elasticity and intra‐bead adhesive strength were prepared within a short period of 30 seconds. Therefore, the microwave heating can be considered as an efficient strategy for preparing the high‐performance polymer bead foam products, especially for these high‐melting temperature or glass‐transition temperature polymers. 相似文献
996.
New ambient sound absorption material, lightweight isocyanate-based polyimide foam(IBPIF), was fabricated by operable combination between different distinctive acoustic IBPIF. Cellular structure of IBPIF was facilely and obviously adjusted by increased slurry temperature corresponding to change in distinctive acoustic properties. Moreover, density of all IBPIF kept at only 12-17 kg/m~3. With increasing slurry temperature from 0 ℃ to 40 ℃, cell size and window opening rate gradually increased from 553 μm to 791 μm and from 6.85% to 58.46%,respectively. In this study, IBPIF generated by slurries at 0 ℃(marked as PIF-2) and 40 ℃(marked as PIF-6) showed best and distinctive acoustic behavior in 315-800 Hz and 800-6300 Hz regions, respectively. After acoustic behavior study of combined IBPIF prepared by stitching combination between two distinctive acoustic IBPIFs, results showed that only when PIF-6 sheet used as sound receiving surface even though with thickness of only 10 mm could the combined IBPIF possess the best acoustic level in 800-6300 Hz region as PIF-6. Furtherly, acoustic behavior in 315-800 Hz region could be significantly enhanced by increasing thickness of PIF-2 and could reach or close to the best acoustic level. 相似文献
997.
通过一步液滴法在不同的反应溶剂体系下制备了一系列无定形硅铝酸盐载体, 并进一步制备出Pd基负载型多孔催化材料, 探究了反应溶剂极性和反应物Si/Al比对载体材料和催化剂的影响, 实现了通过一步液滴法调控硅铝酸盐酸性和孔道属性. 结果表明, 在极性较小的反应溶剂体系中制得了富含介孔的无定形硅铝酸盐载体材料, 并且通过改变Si/Al比可实现载体材料的酸性、 比表面积及孔道尺寸的调控, 比表面积和总酸量分别达到349.6 m2/g和1.389 mmol/g. 由于该载体材料高的比表面积及丰富的介孔孔道, 所制得的Pd基负载型多孔催化材料的Pd金属分散性达到了63.17%, 在硝基苯加氢反应中实现了99.75%的转化率和94.62%的选择性, 在苯甲醇氧化反应中表现出40.61%的转化率及38.09%的选择性, 远远优于利用商用载体合成的 Pd/Al2O3催化材料. 这种简单有效的合成方法使得按照目标催化反应的类型来设计高效催化剂成为可能. 相似文献
998.
The worm-like AlN nanowires are fabricated by the plasma-enhanced chemical vapor deposition (PECVD) on Si substrates through using Al powder and N2 as precursors, CaF2 as fluxing medium, Au as catalyst, respectively. The as-grown worm-like AlN nanowires each have a polycrystalline and hexagonal wurtzite structure. Their diameters are about 300 nm, and the lengths are over 10 μm. The growth mechanism of worm-like AlN nanowires is discussed. Hydrogen plasma plays a very important role in forming the polycrystalline structure and rough surfaces of worm-like AlN nanowires. The worm-like AlN nanowires exhibit an excellent field-emission (FE) property with a low turn-on field of 4.5 V/μm at a current density of 0.01 mA/cm2 and low threshold field of 9.9 V/μm at 1 mA/cm2. The emission current densities of worm-like AlN nanowires each have a good stability. The enhanced FE properties of worm-like AlN nanowires may be due to their polycrystalline and rough structure with nanosize and high aspect ratio. The excellent FE properties of worm-like AlN nanowires can be explained by a grain boundary conduction mechanism. The results demonstrate that the worm-like AlN nanowires prepared by the proposed simple and the PECVD method possesses the potential applications in photoelectric and field-emission devices. 相似文献
999.
Mohammad Javad Jafari Mohsen Niknam Sharak Ali Khavanin Touraj Ebadzadeh Mahmood Fazlali Rohollah Fallah Madvari 《声与振动》2021,55(2):117-130
Fabricating of metal foams with desired morphological parameters including pore size, porosity and pore opening is possible now using sintering technology. Thus, if it is possible to determine the morphology of metal foam to absorb sound at a given frequency, and then fabricate it through sintering, it is expected to have optimized metal foams for the best sound absorption. Theoretical sound absorption models such as Lu model describe the relationship between morphological parameters and the sound absorption coefficient. In this study, the Lu model was used to optimize the morphological parameters of Aluminum metal foam for the best sound absorption coefficient. For this purpose, the Lu model was numerically solved using written codes in MATLAB software. After validating the proposed codes with benchmark data, the genetic algorithm (GA) was applied to optimize the affecting morphological parameters on the sound absorption coefficient. The optimization was carried out for the thicknesses of 5 mm to 40 mm at the sound frequency range of 250 Hz–8000 Hz. The optimized parameters ranged from 50% to 95% for porosity, 0.1 mm to 4.5 mm for pore size, and 0.07 mm to 0.6 mm for pore opening size. The result of this study was applied to fabricate the desired Aluminum metal foams for the best sound absorption. The novel approach applied in this study, is expected to be successfully applied in for best sound absorption in desired frequencies. 相似文献
1000.
燃煤烟气汞的大量排放对公众健康和生态系统造成了严重威胁,开发新型高效脱汞技术和材料对汞污染防治具有重要意义。本文采用原位硒化方法制备了泡沫硒化铜(Cu-hs),与采用水热法制备的泡沫硒化铜(Cu-hd-1和Cu-hd-12)相比,Cu-hs具有更优的单质汞(Hg0)吸附性能。Cu-hs具有良好的抗H2O和SO2干扰能力,O2对Cu-hs吸附Hg0有一定的促进作用,而HCl的存在对Hg0吸附没有明显影响。Cu-hs表面的汞饱和吸附量为3743 g/m3(约为15 mg/g),显著高于目前文献中报道的活性炭的饱和吸附量,具有很好的燃煤烟气脱汞应用潜力。 相似文献