全文获取类型
收费全文 | 445篇 |
免费 | 49篇 |
国内免费 | 36篇 |
专业分类
化学 | 290篇 |
晶体学 | 5篇 |
力学 | 7篇 |
综合类 | 3篇 |
数学 | 56篇 |
物理学 | 169篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 16篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 17篇 |
2011年 | 20篇 |
2010年 | 13篇 |
2009年 | 19篇 |
2008年 | 26篇 |
2007年 | 25篇 |
2006年 | 21篇 |
2005年 | 29篇 |
2004年 | 20篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 16篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1972年 | 6篇 |
排序方式: 共有530条查询结果,搜索用时 78 毫秒
91.
Diego A. Manjarrs William J. Herrera Shirley Gmez 《Physica B: Condensed Matter》2009,404(18):2799-2801
In order to consider the Dirac-like spectrum of graphene we employ the Bogoliubov de Gennes–Dirac formalism to determine the quasiparticle Andreev levels in an NS surface (normal–superconductor). The normal region is characterized by a width L while the superconducting region is semi-infinite and both regions are made of doped graphene. The quasiparticle energy spectrum is originated by the Andreev reflections that occur in the NS interface. It is shown that this spectrum depends on the width of the normal region and the Fermi energy in each region. When the Fermi energy in the normal metal is lower than the gap of the superconductor region, the spectrum is affected by specular Andreev reflections. The equation that is obtained to find the spectrum is very general and we solve it for some particular cases. We find that the energy spectrum oscillates when the Fermi energy in graphene is changed. Finally we obtain under some approximations an equation for the energy spectrum which is similar in structure as those obtained for an INS conventional junction. 相似文献
92.
以二硫化碳和金属钠为基础物质合成了四硫富瓦烯(TTF)锌的配合物(TTF)Zn(NBu4)2。利用该化合物与苯甲酰氯反应得到的稳定化合物C17H10O2S5在甲醇钠溶液中与2,3-二溴丙醇反应成功合成出目标化合物(一种新配体),其化学组成为C6H6OS5。利用IR谱、^1HNMR谱及元素分析对此化合物进行了表征。 相似文献
93.
94.
Synthesis and characterization of multifunctional silica core-shell nanocomposites with magnetic and fluorescent functionalities 总被引:1,自引:0,他引:1
Zhiya Ma Mikaela Nichkova Shirley J. Gee Kai Liu 《Journal of magnetism and magnetic materials》2009,321(10):1368-1371
Multifunctional core-shell nanocomposites with a magnetic core and a silica shell doped with lanthanide chelate have been prepared by a simple method. First, citric acid-modified magnetite nanoparticles were synthesized by a chemical coprecipitation method. Then the magnetite nanoparticles were coated with silica shells doped with terbium (Tb3+) complex by a modified Stöber method based on hydrolyzing and condensation of tetraethyl orthosilicate (TEOS) and a silane precursor. These multifunctional nanocomposites are potentially useful in a variety of biological areas such as bio-imaging, bio-labeling and bioassays because they can be simultaneously manipulated with an external magnetic field and exhibit unique phosphorescence properties. 相似文献
95.
对-叔丁基杯[8]芳烃键合硅胶制备及其毛细管电色谱性能研究 总被引:1,自引:0,他引:1
以γ-(环氧丙氧)丙基键合硅胶为前体,于硅胶表面键合环氧基,在催化剂存在下以杯芳烃钠盐开环制备杯芳烃键合硅胶固定相.该方法反应条件温和,适用性强.将这个新方法首次用于制备对-叔丁基杯[8]芳烃电色谱键合固定相(C8BS),采用加压电色谱初步评价其电色谱性能.研究结果表明,C8BS电渗流(Electrosmoticflow,EOF)较小,但通过控制键合反应及使用压力辅助电色谱可部分弥补上述不足.该固定相的EOF受流动相pH影响小(pH=3-8),同时大环配体屏蔽效应能有效地克服硅羟基引起的碱性化合物拖尾现象,这对电色谱分离具有重要意义.通过分步封尾研究EOF的来源发现,杯芳烃酚羟基对EOF有弱的贡献,这与报道的杯芳烃涂层具有径向电渗流调控能力相一致. 相似文献
96.
97.
98.
Shirley H. Lomeli Sheng Yin Rachel R. Ogorzalek Loo Joseph A. Loo 《Journal of the American Society for Mass Spectrometry》2009,20(4):593-596
Increased multiple charging of native proteins and noncovalent protein complexes is observed in electrospray ionization (ESI)
mass spectra obtained from nondenaturing protein solutions containing up to 1% (vol/vol) m-nitrobenzyl alcohol (m-NBA). The increases in charge ranged from 8% for the 690 kDa α7β7β7α7 20S proteasome complex to 48% additional charge for the zinc-bound 29 kDa carbonic anhydrase-II protein. No dissociation
of the noncovalently bound ligands/subunits was observed upon the addition of m-NBA. It is not clear if the enhanced charging is related to altered surface tension as proposed in the “supercharging” model
of Iavarone and Williams (Iavarone, A. T.; Williams, E. R. J. Am. Chem. Soc.
2003, 125, 2319–2327). However, more highly charged noncovalent protein complexes have utility in relaxing slightly the mass-to-charge
(m/z) requirements of the mass spectrometer for detection and will be effective for enhancing the efficiency for tandem mass spectrometry
studies of protein complexes. 相似文献
99.
Silvana T. Castaman Shirley Nakagaki Ronny R. Ribeiro Ktia J. Ciuffi Sueli M. Drechsel 《Journal of molecular catalysis. A, Chemical》2009,300(1-2):89-97
The synthesis and characterization of a binuclear carboxylated bridged manganese complex containing the heptadentate ligand N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)-2-ol-1,3-propanediamine (H3bbppnol) is reported. This complex was characterized by elemental analysis; infrared, electronic (UV–vis) and EPR spectroscopy; and conductivity measurements. The complex was immobilized on silica by either adsorption or entrapment via a sol–gel route. The obtained solids were characterized by thermogravimetric analyses (TG and DSC), UV–vis and infrared spectroscopy, and X-ray diffraction. The catalytic performance of the binuclear manganese complex in epoxidation reactions was evaluated for both homogeneous and heterogeneous systems. The catalytic investigation revealed that the complex performs well as an epoxidation catalyst for the substrates cyclohexene (26–39%) and cyclooctene (29–74%). The solids containing the immobilized complex can be recovered from the reaction medium and reused, maintaining good catalytic activity. 相似文献
100.
Matilte Halma Kelly Aparecida Dias de Freitas Castro Vanessa Prvot Claude Forano Fernando Wypych Shirley Nakagaki 《Journal of molecular catalysis. A, Chemical》2009,310(1-2):42-50
The first generation anionic iron(III) porphyrin [Fe(TSPP)] and the second generation anionic complexes [Fe(TDFSPP)], [Fe(TCFSPP)], and [Fe(TDCSPP)] were immobilized into three-dimensionally macroporous layered double hydroxide (3DM-LDH), using the direct reconstruction of 3DM-LDH from macroporous mixed oxides MOX or the anionic exchange on DDS intercalated 3DM-LDH. The macroporous layered double hydroxides were obtained at the surface of nanometric polystyrene spheres, which were synthesized by an inverse opal method. Polystyrene was removed after calcination in oxidizing atmosphere, nanostructured mixed oxides (3DM-MOX) were obtained, which after reconstruction give origin to macroporous layered double hydroxide (3DM-LDH). Following metalloporphyrin immobilization, the resulting materials were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), UV–vis (glycerin mull) spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FTIR), and electron paramagnetic resonance (EPR). Results revealed that the complexes are either immobilized at the surface of the macroporous layered double hydroxide or intercalated between the layers, displacing some dodecylsufate anions. The obtained materials were investigated as catalysts for oxidation reactions, to find out whether they function as cytochrome P-450 models. 相似文献