全文获取类型
收费全文 | 300篇 |
免费 | 1篇 |
专业分类
化学 | 127篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 8篇 |
物理学 | 161篇 |
出版年
2015年 | 3篇 |
2013年 | 5篇 |
2012年 | 20篇 |
2011年 | 41篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 14篇 |
2007年 | 22篇 |
2006年 | 34篇 |
2005年 | 38篇 |
2004年 | 30篇 |
2003年 | 19篇 |
2002年 | 18篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有301条查询结果,搜索用时 0 毫秒
1.
H. Gallart-Ayala F. Courant S. Severe J.-P. Antignac F. Morio J. Abadie B. Le Bizec 《Analytica chimica acta》2013
Lipids represent an extended class of substances characterized by such high variety and complexity that makes their unified analyses by liquid chromatography coupled to either high resolution or tandem mass spectrometry (LC–HRMS or LC–MS/MS) a real challenge. In the present study, a new versatile methodology associating ultra high performance liquid chromatography coupled to high resolution tandem mass spectrometry (UHPLC–HRMS/MS) have been developed for a comprehensive analysis of lipids. The use of polarity switching and “all ion fragmentation” (AIF) have been two action levels particularly exploited to finally permit the detection and identification of a multi-class and multi-analyte extended range of lipids in a single run. For identification purposes, both higher energy collision dissociation (HCD) and in-source CID (collision induced dissociation) fragmentation were evaluated in order to obtain information about the precursor and product ions in the same spectra. This approach provides both class-specific and lipid-specific fragments, enhancing lipid identification. Finally, the developed method was applied for differential phenotyping of serum samples collected from pet dogs developing spontaneous malignant mammary tumors and health controls. A biological signature associated with the presence of cancer was then successfully revealed from this lipidome analysis, which required to be further investigated and confirmed at larger scale. 相似文献
2.
The hierarchies of evolution equations associated with the spectral operators ?x?y ? R?y ? Q and ?x?y ? Q in the plane are considered. In both cases a recursion operator Ф12, which is nonlocal and generates the hierarchy, is obtained. It is shown that only in the first case does the recursion operator satisfy the canonical geometrical scheme in 2 + 1 dimensions proposed by Fokas and Santini. The general procedure proposed allows one to derive, at the same time, the evolution equations associated with a given linear spectral problem and their Backlund transformations (if they exist), with no need to verify by long and tedious computations the algebraic properties of Ф12. Two equations in the first hierarchy can be considered as two different integrable generalizations in the plane of the dispersive long wave equation. All equations in this hierarchy are shown to be both a dimensional reduction of bi-Hamiltonian n × n matrix evolution equations in multidimensions and a generalization in the plane of bi-Hamiltonian n × n matrix evolution equations on the line. 相似文献
3.
A study by B11 NMR of the system tripropylborane–boron trioxide shows that scrambling reactions occur between the alkylborane and its oxidation products; this involves a redistribution of the mono-(? C3H7) and difunctional (? O? ) substituents attached to boron, leading to molecules of varying size and structure. 相似文献
4.
5.
J. Boxus B. Poulaert J-P. Issi H. Mazurek M.S. Dresselhaus 《Solid State Communications》1981,38(12):1117-1119
The low-temperature variation of the in-plane thermal conductivity of graphite- FeCl3 intercalation compounds is reported. Around room temperature, though holes are participating, there is an important lattice contribution, but much smaller than in pristine graphite. The electronic contribution dominates in the liquid helium range. These preliminary results suggest lattice thermal conductivity measurements as a new tool to investigate defects introduced by intercalation. 相似文献
6.
7.
Metastable 23S1 He atoms are optically oriented and their orientation is transferred to metallic ions produced by Penning collisions . If r.f. transitions are induced in the 23S1 He level, the circularly polarized light emitted by the ions in a direction perpendicular to the static magnetic field is modulated at the r.f. frequency. The variation of the modulation amplitude with frequency depends on the lifetime of the level of the excited ion.We describe an experimental apparatus with which we measure the modulation amplitude from 1 MHz to 110 MHz. In this way the lifetime of the 4f2F and 2F Mg+ levels has been determined. 相似文献
8.
Results on the temperature variation from 2 ? T ? 300 K of the c-axis electrical resistivity and thermopower of a donor stage-5 potassium and an acceptor stage-2 FeCl3 graphite intercalation compounds are reported. Comparing the data with those of the literature reveals for both compounds a different qualitative behavior for low and high stages. 相似文献
9.
Experimental study of vortex emission behind bluff obstacles in a gas liquid vertical two-phase flow
Vortex emission behind cylinders with trapezoidal cross section was experimentally studied in air-water vertical two-phase flows (liquid velocities vary from 45 cm/s to 2 m/s inside a 15 cm ID pipe); the void fraction ranged from 0 to 25%. The measurements were performed at room pressure and temperature. Two flow regimes were observed. For void fraction smaller than 10% vortex emission remained stable and its frequency sharply defined. However, the rms amplitude of the associated pressure fluctuations strongly decreased. These results were explained by bubble trapping inside the vortex cores. This effect was verified experimentally and analyzed using optical fiber probe measurements. Above a 10% void fraction, vortex emission became erratic. Its spectrum became broader but could be identified up to 25% void fraction. 相似文献
10.
J-P Boussemart W Briec H Leleu 《The Journal of the Operational Research Society》2010,61(8):1297-1301
This note generalizes analytical relationships among activity variables of Dataenvelopment analysis models previously derived in a previous article by theauthors of this note. We relax the assumption of constant returns to scale byshowing that the key results hold under a weaker assumption of homogeneity. Weuse the notion of α-returns to scale to extend the analysis tostrictly increasing and decreasing returns, covering now the whole range ofreturns to scale for multi-output homogenous technologies. 相似文献