全文获取类型
收费全文 | 837篇 |
免费 | 16篇 |
国内免费 | 6篇 |
专业分类
化学 | 444篇 |
晶体学 | 9篇 |
力学 | 17篇 |
数学 | 112篇 |
物理学 | 277篇 |
出版年
2020年 | 5篇 |
2019年 | 8篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 28篇 |
2012年 | 34篇 |
2011年 | 39篇 |
2010年 | 20篇 |
2009年 | 10篇 |
2008年 | 44篇 |
2007年 | 58篇 |
2006年 | 58篇 |
2005年 | 33篇 |
2004年 | 28篇 |
2003年 | 17篇 |
2002年 | 46篇 |
2001年 | 23篇 |
2000年 | 26篇 |
1999年 | 9篇 |
1998年 | 16篇 |
1997年 | 19篇 |
1996年 | 12篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 17篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 15篇 |
1976年 | 10篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 11篇 |
1972年 | 8篇 |
1971年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有859条查询结果,搜索用时 15 毫秒
851.
Venugopal N McCurdy B Al Mehairi S Alamri A Sandhu GS Sivalingam S Drachenberg D Ryner L 《Magnetic resonance imaging》2012,30(2):195-204
Visualization of short echo time (TE) metabolites in prostate magnetic resonance spectroscopic imaging is difficult due to lipid contamination and pulse timing constraints. In this work, we present a modified pulse sequence to permit short echo time (TE=40ms) acquisitions with reduced lipid contamination for the detection of short TE metabolites. The modified pulse sequence employs the conformal voxel MRS (CV-MRS) technique, which automatically optimizes the placement of spatial saturation planes to adapt the excitation volume to the shape of the prostate, thus reducing lipid contamination in prostate magnetic resonance spectroscopic imaging (MRSI). Metabolites were measured and assessed using a modified version of LCModel for analysis of in vivo prostate spectra. We demonstrate the feasibility of acquiring high quality spectra at short TEs, and show the measurement of short TE metabolites, myo-inositol, scyllo-inositol, taurine and glutamine/glutamate for both single and multi-voxel acquisitions. In single voxels experiments, the reduction in TE resulted in 57% improvement in the signal-to-noise ratio (SNR). Additional 3D MRSI experiments comparing short (TE=40 ms), and long (TE=130 ms) TE acquisitions revealed a 35% improvement in the number of adequately fitted metabolite peaks (775 voxels over all subjects). This resulted in a 42 ± 24% relative improvement in the number of voxels with detectable citrate that were well-fitted using LCmodel. In this study, we demonstrate that high quality prostate spectra can be obtained by reducing the TE to 40 ms to detect short T2 metabolites, while maintaining positive signal intensity of the spin-coupled citrate multiplet and managing lipid suppression. 相似文献
852.
Influence of atmospheric turbulence on states of light carrying orbital angular momentum 总被引:2,自引:0,他引:2
B Rodenburg MP Lavery M Malik MN O'Sullivan M Mirhosseini DJ Robertson M Padgett RW Boyd 《Optics letters》2012,37(17):3735-3737
We have experimentally studied the degradation of mode purity for light beams carrying orbital angular momentum (OAM) propagating through simulated atmospheric turbulence. The turbulence is modeled as a randomly varying phase aberration, which obeys statistics postulated by Kolmogorov turbulence theory. We introduce this simulated turbulence through the use of a phase-only spatial light modulator. Once the turbulence is introduced, the degradation in mode quality results in crosstalk between OAM modes. We study this crosstalk in OAM for 11 modes, showing that turbulence uniformly degrades the purity of all the modes within this range, irrespective of mode number. 相似文献
853.
Erdman A. A. Zubreichuk Z. P. Knizhnikov V. A. Maier A. A. Aleksandrov G. G. Nefedov S. E. Eremenko I. L. 《Russian Chemical Bulletin》2001,50(11):2248-2250
The reaction of bis(o-dicarbollyl)nickel(iv) with PPh3 in EtOH gave rise to the complex 3,3-(PPh3)2-3,1,2-NiC2B9H11 (2) whose structure was established by X-ray diffraction analysis. 相似文献
854.
J.-Y. Zhang I.W. Boyd M.B. Mooney P.K. Hurley J.T. Beechinor B.J. O’Sullivan P.V. Kelly G.M. Crean J.-P. Senateur C. Jimenez M. Paillous 《Applied Physics A: Materials Science & Processing》2000,70(6):647-649
We report the growth of thin tantalum pentoxide films on Si (100) by ultraviolet-assisted injection liquid source (UVILS) chemical vapor deposition (CVD) at low temperatures (200-350 °C). This new technique combines the intense radiation from an excimer lamp (5=222 nm) with a novel injection liquid source capable of delivering precisely controllable quantities of a liquid metalorganic precursor into the CVD chamber. The composition and optical properties of the oxides were determined using a variety of standard characterization methods. After optimization of the deposition parameters, the best layers were incorporated into simple MOS test structures to enable electrical characterization. Refractive index values of 2.09ǂ.07, fixed oxide charge content of <5᎒10 cm-2, breakdown fields higher than 2 MV/cm and dielectric constant values of 18-24 were readily achievable in the as-deposited films. These properties compare favorably with those for layers prepared by conventional thermal-CVD at significantly higher temperatures of 500 °C. 相似文献
855.
Christopher Boyd 《Monatshefte für Mathematik》2000,130(3):177-188
We develop a duality theory for spaces of approximable n-homogeneous polynomials on locally convex spaces, generalising results previously obtained for Banach spaces. For E a Fréchet space with its dual having the approximation property and with E′
b
locally Asplund we show that the space of n-homogeneous polynomials on (E′
b
)′
b
is the inductive dual of the space of boundedly weakly continuous n-homogeneous polynomials on E. We show that when E is a reflexive Fréchet space, the space of n-homogeneous polynomials on E is reflexive if and only if every n-homogeneous polynomial on E is boundedly weakly continuous.
(Received 24 March 1999; in final form 14 February 2000) 相似文献
856.
857.
858.
859.
Md Shahabuddin Alam Xinlin Li Drew O. Brittin Saiful Islam Prof. Dr. Pravas Deria Prof. Dr. Eduard Y. Chekmenev Prof. Dr. Boyd M. Goodson 《Angewandte Chemie (International ed. in English)》2023,62(8):e202213581
Hyperpolarized orthohydrogen (o-H2) is a frequent product of parahydrogen-based hyperpolarization approaches like signal amplification by reversible exchange (SABRE), where the hyperpolarized o-H2 signal is usually absorptive. We describe a novel manifestation of this effect wherein large antiphase o-H2 signals are observed, with 1H enhancements up to ≈500-fold (effective polarization PH≈1.6 %). This anomalous effect is attained only when using an intact heterogeneous catalyst constructed using a metal–organic framework (MOF) and is qualitatively independent of substrate nature. This seemingly paradoxical observation is analogous to the “partial negative line” (PNL) effect recently explained in the context of Parahydrogen Induced Polarization (PHIP) by Ivanov and co-workers. The two-spin order of the o-H2 resonance is manifested by a two-fold higher Rabi frequency, and the lifetime of the antiphase HP o-H2 resonance is extended by several-fold. 相似文献