全文获取类型
收费全文 | 3524篇 |
免费 | 550篇 |
国内免费 | 389篇 |
专业分类
化学 | 2677篇 |
晶体学 | 41篇 |
力学 | 135篇 |
综合类 | 3篇 |
数学 | 363篇 |
物理学 | 1244篇 |
出版年
2024年 | 6篇 |
2023年 | 71篇 |
2022年 | 120篇 |
2021年 | 153篇 |
2020年 | 143篇 |
2019年 | 132篇 |
2018年 | 117篇 |
2017年 | 113篇 |
2016年 | 166篇 |
2015年 | 183篇 |
2014年 | 195篇 |
2013年 | 276篇 |
2012年 | 357篇 |
2011年 | 346篇 |
2010年 | 202篇 |
2009年 | 241篇 |
2008年 | 202篇 |
2007年 | 212篇 |
2006年 | 191篇 |
2005年 | 133篇 |
2004年 | 123篇 |
2003年 | 86篇 |
2002年 | 80篇 |
2001年 | 48篇 |
2000年 | 63篇 |
1999年 | 71篇 |
1998年 | 50篇 |
1997年 | 37篇 |
1996年 | 59篇 |
1995年 | 30篇 |
1994年 | 31篇 |
1993年 | 31篇 |
1992年 | 30篇 |
1991年 | 22篇 |
1990年 | 22篇 |
1989年 | 27篇 |
1988年 | 15篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有4463条查询结果,搜索用时 15 毫秒
61.
62.
本文利用红外光解离光谱研究了第三族金属氧化物离子对二氧化碳分子的转化机制. 研究表明,对于[ScO(CO2)n]+体系,在n≤4时,形成了溶剂化结构;在n=5时,形成了碳酸盐结构,实现了二氧化碳的转化. 对于[YO(CO2)n]+体系,需要4个二氧化碳分子就可以实现二氧化碳的转化. 而在[YO(CO2)n]+体系中,只发现了溶剂化结构,没有观察到碳酸盐结构. 理论计算表明,[YO(CO2)n]+体系拥有最小的溶剂化结构向碳酸盐结构转化能垒,[LaO(CO2)n]+体系拥有最大的溶剂化结构向碳酸盐结构转化能垒. 本文从分子水平揭示了不同金属氧化物离子对二氧化碳分子转化的影响规律. 相似文献
63.
Electrical, dielectric and surface wetting properties of multi-walled carbon nanotubes/nylon-6 nanocomposites 下载免费PDF全文
This paper reports that the multi-walled carbon nanotubes(MWCNT)/nylon-6 (PA6) nanocomposites with different MWCNT loadingshave been prepared by a simple melt-compounding method. Theelectrical, dielectric, and surface wetting properties of theCNT/PA6 composites have been studied. The temperature dependence ofthe conductivity of the CNT/PA6 composite with 10.0 wt{\%} CNTloading ($\sigma _{\rm RT} \sim 10^{-4}$ S/cm) are measured, andafterwards a charge-energy-limited tunnelling model (ln $\sigma (T)\sim T^{-1/2})$ is found. With increasing CNT weight percentage from0.0 to 10.0 wt%, the dielectric constant of the CNT/PA6composites enhances and the dielectric loss tangent increases twoorders of magnitude. In addition, water contact angles of theCNT/PA6 composites increase and the composites with CNT loadinglarger than 2.0 wt%even become hydrophobic. The obtainedresults indicate that the electrical and surface properties of thecomposites have been significantly enhanced by the embedded carbonnanotubes. 相似文献
64.
Spiders in electro-dynamic loudspeakers are most commonly concentrically corrugated fabric disks, and their viscoelastic behaviors affect the loudspeaker reproductions. A noncontact dynamic measuring technology is presented by a subwoofer closed box to excite the tested spiders pneumatically with a Laser Doppler Vibrometer (LDV) to measure the velocity of the moving spiders. Correlation techniques were employed to get an accurate and reliable acoustical transfer function between the measured velocity and sound pressure. The Young’s moduli of the tested spider composite materials were derived from the measured vibration modes. The creep effect and the level dependent behaviors of tested spiders were investigated. The results indicate that, the Young’s moduli of the tested spiders are frequency dependent. The mechanical stiffness increases with a small slope in low frequency range while a large slope in high frequency range. The loss factor exhibits the maximum around the resonance frequency, and after that it decreases with increasing frequency. The effective stiffness has a monotonic decrease with input voltage levels and the harder the spider, the less stiffness changes with input levels. 相似文献
65.
66.
Fen Ran Huili Fan Lingren Wang Lei Zhao Yongtao Tan Xuanxuan Zhang Lingbin Kong Long Kang 《天然气化学杂志》2013,(6):928-934
A novel bird nest-like nanostructured MnO2(BNNS-MnO2) was prepared by a facile and cost-effective strategy. Their structures and morphologies were characterized by field emission scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. Capacitive behaviors were investigated by cyclic voltammetry and galvanostatic charge-discharge. The obtained nano-MnO2 possesses a well designed loose-assembled hierarchical nanoarchitecture with an appropriate crystallinity which gives rise to excellent performances as an electrode material for supercapacitors. A maximum specific capacitance of 917 F/g has been obtained at a current density of 5 mA/cm2 in 6 mol/L KOH aqueous solution, and a specific capacitance of 210 F/g has been maintained for 500 cycles. As the low cost of MnSO4 and KCr2O7 and the low reaction temperature, the present method avoids the requirements for complicated operations, time/energy-consuming and expensive reagents, and perhaps is ready for the industrialization of nano-MnO2 production. 相似文献
67.
The adsorptive denitrogenation from fuels over three metal-organic frameworks(MIL-96(Al),MIL-53(Al)and MIL-101(Cr))was studied by batch adsorption experiments.Four nitrogen-containing compounds(NCCs)pyridine,pyrrole,quinoline and indole were used as model NCCs in fuels to study the adsorption mechanism.The physicochemical properties of the adsorbents were characterized by XRD,N2physical adsorption,FT-IR spectrum and Hammett indicator method.The metal-organic frameworks(MOFs),especially the MIL-101(Cr)containing Lewis acid sites as well as high specific surface area,can adsorb large quantities of NCCs from fuels.In addition,the adsorptive capacity over MIL-101(Cr)will be different for NCCs with different basicity.The stronger basicity of the NCC is,the more it can be absorbed over MIL-101(Cr).Furthermore,pore size and shape also affect the adsorption capacity for a given adsorbate,which can be proved by the adsorption over MIL-53(Al)and MIL-96(Al).The pseudo-second-order kinetic model and Langmuir equation can be used to describe kinetics and thermodynamics of the adsorption process,respectively.Finally,the regeneration of the used adsorbent has been conducted successfully by just washing it with ethanol. 相似文献
68.
A novel one-step protocol for the preparation of porous polyurea material (PPU) through precipitation polymerization of toluene diisocynate (TDI) is presented. The process is based on step polymerization of one singlemonomer, TDI, with water in water-acetonemixed solvent. PPU is obtained without need for any porogen or additives, and no any chemical modification on the outcome polymer is necessary. The morphology, pore size and size distribution of PPU are characterized by scanning electron microscope and BET nitrogen adsorption. Taking acid fuchsine (AF) and Congo Red as dye examples in wastewaters, their adsorption on, desorption from PPU and the reusability of PPU were tested. Experimental conditions for AF adsorption were optimized with regard to pH, adsorption time, AF concentration and amount of PPU. Results demonstrate that the as-prepared PPU is of high performance in dyes adsorption and recycled use. This work presents therefore a novel and attractive candidate for removal of anionic dyes from wastewaters. 相似文献
69.
70.