全文获取类型
收费全文 | 887篇 |
免费 | 113篇 |
国内免费 | 113篇 |
专业分类
化学 | 586篇 |
晶体学 | 11篇 |
力学 | 63篇 |
综合类 | 1篇 |
数学 | 130篇 |
物理学 | 322篇 |
出版年
2024年 | 3篇 |
2023年 | 19篇 |
2022年 | 40篇 |
2021年 | 34篇 |
2020年 | 38篇 |
2019年 | 37篇 |
2018年 | 25篇 |
2017年 | 24篇 |
2016年 | 40篇 |
2015年 | 46篇 |
2014年 | 45篇 |
2013年 | 51篇 |
2012年 | 91篇 |
2011年 | 92篇 |
2010年 | 60篇 |
2009年 | 60篇 |
2008年 | 60篇 |
2007年 | 39篇 |
2006年 | 62篇 |
2005年 | 42篇 |
2004年 | 39篇 |
2003年 | 24篇 |
2002年 | 16篇 |
2001年 | 17篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 4篇 |
1997年 | 14篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1113条查询结果,搜索用时 15 毫秒
81.
C. Guo L. Luan X. Ding F. Zhang F. G. Shi F. Gao L. Liang 《Applied physics. B, Lasers and optics》2009,95(4):779-785
Eu2+ and Mn2+ co-activated Sr5(PO4)3Cl phosphors with blue and orange color double emission bands, under a broad-band excitation wavelength range of 340–400 nm,
were synthesized by the solid-state reaction. It was found that the processing parameters, including the fluxes, annealing
time and activators concentrations, affect the emission intensity and other luminescent properties. Energy transfer between
Eu2+ and Mn2+ was discovered and the transfer efficiency was also estimated based on relative intensities of Eu2+ and Mn2+ emission. Thus the relative strength of blue and orange emission intensities could be tuned by varying the relative concentration
of Eu2+ and Mn2+. Since the photoluminescence excitation spectra of the newly developed Sr5(PO4)3Cl:Eu2+, Mn2+ phosphors exhibit a strong absorption in the range of 340–400 nm, they are promising for producing UV-LED-based white LEDs. 相似文献
82.
A novel polyaniline/Bi(2)SnTiO(7 )composite polymer was synthesized by chemical oxidation in-situ polymerization method and sol-gel method for the first time. The structural properties of novel polyaniline/Bi(2)SnTiO(7) have been characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray spectrometry. The lattice parameter of Bi(2)SnTiO(7) was found to be a = 10.52582(8) ?. The photocatalytic degradation of methylene blue was realized under visible light irradiation with the novel polyaniline/Bi(2)SnTiO(7) as catalyst. The results showed that novel polyaniline/Bi(2)SnTiO(7 )possessed higher catalytic activity compared with Bi(2)InTaO(7) or pure TiO(2) or N-doped TiO(2) for photocatalytic degradation of methylene blue under visible light irradiation. The photocatalytic degradation of methylene blue with the novel polyaniline/Bi(2)SnTiO(7) or N-doped TiO(2) as catalyst followed first-order reaction kinetics, and the first-order rate constant was 0.01504 or 0.00333 min(-1). After visible light irradiation for 220 minutes with novel polyaniline/Bi(2)SnTiO(7 )as catalyst, complete removal and mineralization of methylene blue was observed. The reduction of the total organic carbon, the formation of inorganic products, SO(4)2- and NO(3-), and the evolution of CO(2) revealed the continuous mineralization of methylene blue during the photocatalytic process. The possible photocatalytic degradation pathway of methylene blue was obtained under visible light irradiation. 相似文献
83.
微波辅助萃取-固相微萃取联用气相色谱-质谱法测定土壤中的扑草净 总被引:17,自引:0,他引:17
研究了微波辅助萃取-固相微萃取联用、气相色谱-质谱联用测定土壤中除草剂扑草净的分析方法。采用正交设计实验优化了萃取溶剂种类和体积、微波辐射时间和微波功率等微波辅助萃取条件;研究了SPME萃取涂层、搅拌速度、萃取时间和解吸时间等对萃取效率的影响。方法的检出限为0.01ng/g;线性范围为0.2—200μg/L。在优化的条件下测定了5和50ng/g的合成土壤样品,回收率分别为90.1%和91.6%;相对标准偏差分别为9.4%和8.8%(n=6)。本法综合了微波辅助萃取和固相微萃取的优点,操作简便.灵敏度高,特别适合于固体样品中痕量有机物的萃取分离。 相似文献
84.
85.
In a capillary discharge experiment for the neon-like argon lasing, we have proposed an experimental scheme to verify that the multi-spike of X-ray diode (XRD) signal is a multi-pulse laser or is a reflection of the laser pulse in the XRD.The ceramic capillary has an inner diameter of 3mm and a length of 200mm.At the gas pressure of 28Pa and discharge current of 27kA, stable lasing has been realized.The experimental results prove that the multi-spike of XRD signal is a reflection of the electromagnetic signal produced by the laser pulse in the XRD.The improved electrocircuit scheme of the XRD to minimize the reflection phenomena is also found. 相似文献
86.
87.
Hongtao Liu Ling Liu Yiquan Xiong Xuemei Yang Tiangang Luan 《Journal of chromatography. A》2010,1217(43):6747-6753
A simple, precise and accurate method for the simultaneous determination of four UV filters and five polycyclic musks (PCMs) in aqueous samples was developed by solid-phase microextraction coupled with gas chromatography–mass spectrometry (SPME-GC–MS). The operating conditions affecting the performance of SPME-GC–MS, including fiber thickness, desorption time, pH, salinity, extraction time and temperature have been carefully studied. Under optimum conditions (30 μm PDMS fiber, 7 min desorption time, pH 7, 10% NaCl, 90 min extraction time at 24 °C), the correlation coefficients (r2) of the calibration curves of target compounds ranged from 0.9993 to 0.9999. The limit of detection (LOD) and limit of quantification (LOQ) ranged from 0.2 to 9.6 ng L−1 and 0.7 to 32.0 ng L−1, respectively. The developed procedure was applied to the determinations of four UV filters and five PCMs in river water samples and internal standard was used for calibration to compensate the matrix effect. Good relative recoveries were obtained for spiked river water at low, medium and high levels. The proposed SPME method was compared with traditional SPE procedure and the results found in river water using both methods were in the same order of magnitude and both are quite agreeable. 相似文献
88.
报道了多核铜配合物[Cu(en)_2]·[Cu(pht)_2]_2(Hpht:苯妥英,即5,5-二苯基-2,2-咪唑烷酮;en:乙二胺)的溶剂热合成、晶体结构及其与DNA的相互作用.该晶体属三斜晶系,P_1~-空间群,晶胞参数:a=0.8453(2)nm,b=1.1878(3)nm,c=1.5674(4)nm,a=101.197(3)°,β=97.690(3)°,γ=103.283(3)°,V=1.476(6)nm~3,D_c=1.480 g/cm~3,Z=1,F(000)=679,μ=1.139nm~(-1),R_1=0.0402,wR_2=0.0962[I>2σ(Ⅰ)],GOF=1.035.XPS和X射线单晶衍射数据显示该配合物分子由混价铜组成,包括两个一价铜和一个二价铜,其中每个Cu(Ⅰ)分别与两个苯妥英配体提供的氮原子配位,N-Cu(Ⅰ)-N的夹角为177°,一个Cu(Ⅱ)与六个配位原子配位(CuN_4O_2),形成一个稍变形八面体结构.配合物与DNA相互作用研究表明,该配合物主要是以插入方式与小牛胸腺DNA结合. 相似文献
89.
Jiming Yang Yanping Chen Zhiguang Xiong 《Numerical Methods for Partial Differential Equations》2013,29(6):1801-1820
An efficient time‐stepping procedure is investigated for a two‐dimensional compressible miscible displacement problem in porous media in which the mixed finite element method with Raviart‐Thomas space is applied to the flow equation, and the transport one is solved by the symmetric interior penalty discontinuous Galerkin approximation on Cartesian meshes. Based on the projection interpolations and the induction hypotheses, a superconvergence error estimate is obtained. During the analysis, an extension of the Darcy velocity along the Gauss line is also used in the evaluation of the coefficients in the Galerkin procedure for the concentration. © 2013 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2013 相似文献
90.
Yongjin Fang Deyan Luan Ye Chen Shuyan Gao Xiong Wen Lou 《Angewandte Chemie (International ed. in English)》2020,59(18):7178-7183
Hybrid materials, integrating the merits of individual components, are ideal structures for efficient sodium storage. However, the construction of hybrid structures with decent physical/electrochemical properties is still challenging. Now, the elaborate design and synthesis of hierarchical nanoboxes composed of three‐layered Cu2S@carbon@MoS2 as anode materials for sodium‐ion batteries is reported. Through a facile multistep template‐engaged strategy, ultrathin MoS2 nanosheets are grown on nitrogen‐doped carbon‐coated Cu2S nanoboxes to realize the Cu2S@carbon@MoS2 configuration. The design shortens the diffusion path of electrons/Na+ ions, accommodates the volume change of electrodes during cycling, enhances the electric conductivity of the hybrids, and offers abundant active sites for sodium uptake. By virtue of these advantages, these three‐layered Cu2S@carbon@MoS2 hierarchical nanoboxes show excellent electrochemical properties in terms of decent rate capability and stable cycle life. 相似文献