全文获取类型
收费全文 | 438篇 |
免费 | 17篇 |
国内免费 | 3篇 |
专业分类
化学 | 294篇 |
晶体学 | 10篇 |
力学 | 9篇 |
数学 | 59篇 |
物理学 | 86篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 6篇 |
2015年 | 16篇 |
2014年 | 14篇 |
2013年 | 17篇 |
2012年 | 33篇 |
2011年 | 38篇 |
2010年 | 26篇 |
2009年 | 24篇 |
2008年 | 34篇 |
2007年 | 34篇 |
2006年 | 23篇 |
2005年 | 26篇 |
2004年 | 16篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 12篇 |
2000年 | 14篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 16篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1972年 | 1篇 |
1930年 | 2篇 |
排序方式: 共有458条查询结果,搜索用时 46 毫秒
141.
In order to investigate the secondary cluster ion emission process of organo-metallic compounds under keV ion bombardment, self-assembled monolayers (SAMs) of alkanethiols on gold are ideal model systems. In this experimental study, we focussed on the influence of the primary ion species on the emission processes of gold-alkanethiolate cluster ions from a hexadecanethiol SAM on gold. For this purpose, we carried out time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements using the following primary ion species and acceleration voltages: Ar+, Xe+, SF5+ (10 kV), Bi+, Bi3+(25 kV), Bi32+, Bi52+, Bi72+ (25 kV).It is well known that molecular ions M− and gold-alkanethiolate cluster ions AuxMy− with M = S-(CH2)15-CH3, x − 3 ≤ y ≤ x + 1, x, y > 0, show intense peaks in negative mass spectra. We derived yields YSI exemplarily for the molecular ions M− and the gold-hexadecanethiolate cluster ions Auy+1My− up to y = 8 and found an exponentially decreasing behaviour for increasing y-values for the cluster ions.In contrast to the well-known increase in secondary ion yield for molecular secondary ions when moving from lighter to heavier (e.g. Ar+ to Xe+) or from monoatomic to polyatomic (e.g. Xe+ to SF5+) primary ions, we find a distinctly different behaviour for the secondary cluster ions. For polyatomic primary ions, there is a decrease in secondary ion yield for the gold-hexadecanethiolate clusters whereas the relative decrease of the secondary ion yield ξY with increasing y remains almost constant for all investigated primary ions. 相似文献
142.
Seong-Dae Oh Seong-Ho Choi A. Gopalan Sang-Ho Sohn Insung S. Choi 《Journal of Non》2006,352(4):355-360
(PVP)-protected Pt-Ru alloy nanoparticles were prepared using γ-irradiation at room temperature. Pt-Ru alloy particles were successfully dispersed onto various carbon structures, including Vulcan XC-71, Ketjen-300, Ketjen-600, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs) to form new types of Pt-Ru/carbon-based composites. While Pt-Ru alloy nanoparticles were mainly aggregated on Vulcan XC-71, Ketjen-300 and Ketjen-600, SWCNTs and MWCNTs provided hydrophilic sites for improving the distribution of alloy particles. FT-IR spectroscopy provided evidence for the formation of carboxylate and hydroxyl groups on the surface of the nanotubes after γ-irradiation. These functional groups serve as the nuclei that resulted in the improved dispersion of alloy nanoparticles onto SWCNTs and MWCNTs. 相似文献
143.
George E. Andrews Bruce C. Berndt Jaebum Sohn Alexandru Zaharescu 《Advances in Mathematics》2005,192(2):231-258
On page 45 in his lost notebook, Ramanujan asserts that a certain q-continued fraction has three limit points. More precisely, if An/Bn denotes its nth partial quotient, and n tends to ∞ in each of three residue classes modulo 3, then each of the three limits of An/Bn exists and is explicitly given by Ramanujan. Ramanujan's assertion is proved in this paper. Moreover, general classes of continued fractions with three limit points are established. 相似文献
144.
Park EJ Ji HY Kim NJ Song WY Kim YH Kim YC Sohn DH Lee HS 《Biomedical chromatography : BMC》2008,22(5):548-555
A rapid, sensitive and selective liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for the simultaneous determination of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone, the active components of Salvia miltiorrhiza in rat plasma, was developed. After liquid-liquid extraction with tariquidar as an internal standard, tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone were eluted from an Atlantis dC18 column within 5 min with a mixture of methanol and ammonium formate (10 mm, pH 6.5; 85:15, v/v). The analytes were detected by an electrospray ionization tandem mass spectrometry in the selected reaction monitoring (SRM) mode. The standard curves were linear (r=0.999) over the concentration range of 0.25-80 ng/mL for tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone in rat plasma. The coefficients of variation and the relative errors of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone for intra- and inter-assay at four quality control (QC) concentrations were 1.1-5.1% and -4.0-6.0%, respectively. The lower limit of quantification for tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone was 0.25 ng/mL from 100 microL of plasma. This method was successfully applied to the pharmacokinetic study of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone after oral administration of PF2401-SF, the standardized fraction of Salvia miltiorrhiza enriched with tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone to male Sprague-Dawley rats. 相似文献
145.
Yun-Hyeok Choi Jae-Hak Sohn Joong Kyun Kim Soon Cheol Ahn Hyuncheol Oh 《Tetrahedron letters》2008,49(50):7128-7131
Two new 17-membered carbocyclic tetraenes, chejuenolides A and B (1 and 2), have been isolated from the EtOAc extract of the marine bacterium Hahella chejuensis by various chromatographic methods. The structures and relative configurations of 1 and 2 were mainly determined by analysis of the NMR spectroscopic data, and their absolute configurations were assigned by application of modified Mosher method. 相似文献
146.
High aspect ratio gold nanowires with single crystalline surface have long been a missing piece in the toolbox of plasmonics metal nanostructures. Such wires are now made with a room temperature, surfactant assisted chemical synthesis in acidic aqueous solution. The diameters and lengths of the multiply twinned gold nanowires can be tuned by varying the amount of seed particles and acid in the growth solution. Nanowires with diameters around 35 nm and lengths up to 10 micron were made with a low seed concentration in pH approximately 1 solution. 相似文献
147.
Chen W Qu L Chang D Dai L Ganguli S Roy A 《Chemical communications (Cambridge, England)》2008,(2):163-165
We have demonstrated that the infiltration of temperature-responsive polymers (e.g., PNIPAAm) into vertically-aligned carbon nanotube forests created synergetic effects, which provided the basis for the development of smart nanocomposite films with temperature-induced self-cleaning and/or controlled release capabilities. 相似文献
148.
DA-5018 is a new capsaicin derivative and has analgesic effect. The objective of this work was to investigate the existence of polymorphs and pseudopolymorphs of DA-5018 and the transformation of crystal forms. Eight crystal forms of DA-5018 have been isolated by recrystallization and characterized by powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TG). The PXRD and DSC patterns of the eight crystal forms were different respectively. In the dissolution studies in simulated intestinal fluid at 37±0.5°C, the solubility of Form 2 was the highest. And the solubility in water decreased in rank order: Form 2>Form 3>Form 1>Form 5>Form 7>Form 4>Form 6>Form 8. Eight crystal forms were shown to have a good physical stability at room temperature for 60 days. 相似文献
149.
On the basis of density functional theory (DFT) and high level ab initio theory, we report the structures, binding energies, thermodynamic quantities, IR spectra, and electronic properties of the hydride anion hydrated by up to six water molecules. Ground state DFT molecular dynamics simulations (based on the Born-Oppenheimer potential surface) show that as the temperature increases, the surface-bound hydride anion changes to the internally bound structure. Car-Parrinello molecular dynamics simulations are also carried out for the spectral analysis of the monohydrated hydride. Excited-state ab initio molecular dynamics simulations show that the photoinduced charge-transfer-to-solvent phenomena are accompanied by the formation of the excess electron-water clusters and the detachment of the H radical from the clusters. The dynamics of the detachment process of a hydrogen radical upon the excitation is discussed. 相似文献
150.
Two types of solid electrolytes have reached technological relevance in the field of sodium batteries: ß/ß”-aluminas and NaSICON-type materials. Today, significant attention is paid to room-temperature stationary electricity storage technologies and all-solid-state Na batteries used in combination with these solid electrolytes are an emerging research field besides sodium-ion batteries. In comparison, NaSICON materials can be processed at lower sintering temperatures than the ß/ß”-aluminas and have a similarly attractive ionic conductivity. Since Na2O−SiO2−ZrO2−P2O5 ceramics offer wider compositional variability, the series Na3Zr3–xSi2PxO11.5+x/2 with seven compositions (0≤x≤3) was selected from the quasi-quaternary phase diagram in order to identify the predominant stability region of NaSICON within this series and to explore the full potential of such materials, including the original NaSICON composition of Na3Zr2Si2POl2 as a reference. Several characterization techniques were used for the purpose of better understanding the relationships between processing and properties of the ceramics. X-ray diffraction analysis revealed that the phase region of NaSICON materials is larger than expected. Moreover, new ceramic NaSICON materials were discovered in the system crystallizing with a monoclinic NaSICON structure (space group C2/c). Impedance spectroscopy was utilized to investigate the ionic conductivity, giving clear evidence for a dependence on crystal symmetry. The monoclinic NaSICON structure showed the highest ionic conductivity with an optimum ionic conductivity of 1.22×10−3 at 25 °C for the composition Na3Zr2Si2PO12. As the degree of P5+ content increases, the total ionic conductivity is initially enhanced until x=1 and then decreases again. Simultaneously, the increasing amount of phosphorus leads a decrease in the sintering temperatures for all samples, which was confirmed by dilatometry measurements. The thermal and microstructural properties of the prepared samples are also evaluated and discussed. 相似文献