全文获取类型
收费全文 | 1448篇 |
免费 | 109篇 |
国内免费 | 5篇 |
专业分类
化学 | 1061篇 |
晶体学 | 8篇 |
力学 | 17篇 |
数学 | 196篇 |
物理学 | 280篇 |
出版年
2024年 | 4篇 |
2023年 | 23篇 |
2022年 | 36篇 |
2021年 | 45篇 |
2020年 | 64篇 |
2019年 | 67篇 |
2018年 | 24篇 |
2017年 | 23篇 |
2016年 | 65篇 |
2015年 | 64篇 |
2014年 | 61篇 |
2013年 | 71篇 |
2012年 | 84篇 |
2011年 | 101篇 |
2010年 | 74篇 |
2009年 | 80篇 |
2008年 | 78篇 |
2007年 | 72篇 |
2006年 | 53篇 |
2005年 | 57篇 |
2004年 | 34篇 |
2003年 | 39篇 |
2002年 | 36篇 |
2001年 | 20篇 |
2000年 | 28篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 4篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1972年 | 8篇 |
排序方式: 共有1562条查询结果,搜索用时 15 毫秒
961.
962.
The electron configuration in single crystalline (sc-)titanium nitride (TiN) has been quantitatively studied using angle resolved X-ray photoelectron spectroscopy (AR-XPS). All samples were fabricated and transferred in situ so that only minimal surface contaminations were observed. The residual oxygen contamination was separated from the bulk information by extrapolating angle resolved measurements. Special attention is given to the quantitative evaluation of the spectra based on basic principles. Shake-up features are observed on core level lines and appear due two final ionized states. The ratio of this shake-up and the main Ti 2p energy line are investigated in this paper. In order to quantify this shake-up a precise evaluation is required. Here we present an approach to evaluate the XPS spectra of the Ti 2p photoemission line in TiN in a self-consistent manner that accounts for all features observable in an energy window of 80 eV. The evaluation considers the appropriate Tougaard background correction, shake-up features as well as surface and bulk plasmons. The ratio of the Ti 2p1/2 and Ti 2p3/2 and the corresponding peaks in the energy loss features fulfill the requirements given by quantum mechanics. The energy loss ΔE due to the shake-up process and the shake-up ratio have been determined quantitatively for oxygen-free bulk titanium nitride. The origin of the shake-up, its intensity and energy difference ΔE are explained by a two electron excitation process. 相似文献
963.
The kinematics and kinetics of a compliant mechanism are analyzed quasi-statically. The mechanism consists of a parallelkinematic (Biglide type) with the particular feature, that its revolute joints are implemented by flexure hinges. In the considered example the flexure hinges are uniform beams similar to leaf springs. The preliminary considerations with a rigid body system and by linear theory of elasticity result in an initial geometry. In order to predict the large displacement behavior more precisely the theory of Elastica is used. An optimization method is applied to solve the mechanism's state of deformation. It was found that some aspects can be approximated by a pseudo rigid body system, while others, namely the rotation, cannot be rendered. The decreased stiffness in the highly deformed operating state appears as key problem. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
964.
We prepared novel C5-modified triphosphates and phosphoramidites with a diamondoid functionally linked to the nucleobase. Using primer extension experiments with different length templates we investigated whether the modified triphosphates were enzymatically incorporated into DNA and whether they were further extended. We found that all three modified nucleotides can be incorporated into DNA using a single-nucleotide incorporation experiment, but only partially using two templates that demand for multiple incorporation of the modified nucleotides. The modified phosphoramidites were introduced into oligonucleotides utilizing DNA synthesizer technology. The occurring oligonucleotide structures were examined by circular dichroism (CD) and melting temperature (T(m)) measurements and were found to adapt similar helix conformations as their unmodified counterparts. 相似文献
965.
Four common parametrisations of spin-component-scaled second-order M?ller-Plesset (MP2) theory are benchmarked by calculating the anharmonic vibrational frequencies of a test suite consisting of eighteen diatomic and five small molecules. Of the four methods, the scaled opposite-spin MP2 (SOS-MP2), the variable-scaling opposite-spin MP2 (VOS-MP2) and the spin-component-scaled MP2 (SCS-MP2) methods perform statistically better than standard MP2 theory, while the spin-component scaled for nucleic bases MP2 (SCSN-MP2) performs worse. Vibrations of closed-shell diatomic molecules are slightly more accurately described by the SOS-MP2 method of Head-Gordon (ε(MAD) =51 cm(-1) ) than the SCS-MP2 method of Grimme (ε(MAD) =61 cm(-1)) or the size-consistent parametrisation of VOS-MP2 (ε(MAD) =54 cm(-1)). For open-shell diatomic molecules, the SOS-MP2 (ε(MAD) =83 cm(-1)) and SCS-MP2 (ε(MAD) =81 cm(-1)) methods are of similar accuracy, while VOS-MP2 is slightly better (ε(MAD) =77 cm(-1)). Since the VOS-MP2 and SOS-MP2 methods tend to have smaller deviations from experiment, and they can be made computationally more economical than the SCS-MP2 or MP2 methods, we suggest that they should be the preferred ab initio method for computing vibrational frequencies in large molecules. 相似文献
966.
967.
968.
Flier BM Baier M Huber J Müllen K Mecking S Zumbusch A Wöll D 《Physical chemistry chemical physics : PCCP》2011,13(5):1770-1775
Translational diffusion of single perylene diimide molecules in 25 nm thin polymer films was investigated by single molecule widefield fluorescence microscopy. Spatial heterogeneities in single molecule motion were detected and analyzed by a new, quantitative method which draws a comparison of log-Gaussian fits of experimentally determined diffusion coefficient-distributions and diffusion coefficient-distributions from Monte Carlo random walk simulations. Heterogeneities could be observed close to the glass transition temperature, but disappear at ca. 1.1 × T(g). At higher temperatures, heterogeneities do not exist or they average out on the time and length scales of observation. The observed heterogeneities also explain why the dependency of diffusion coefficients on temperature does not follow Vogel-Fulcher-Tammann behavior. 相似文献
969.
Stock C Moosbauer D Zugmann S Simbeck T Amereller M Gores HJ 《Chemical communications (Cambridge, England)》2011,47(24):6984-6986
We introduce here a novel in situ measurement method for solubility of solids in various liquids. Without any calibration the saturation point can be obtained in a relative manner. We exemplified the new method at four systems including water, organic carbonates and an ionic liquid as the solvents and various salts as dissolved solids. 相似文献
970.
Generalized Lie derivations on triangular algebras 总被引:1,自引:0,他引:1
Dominik Benkovi? 《Linear algebra and its applications》2011,434(6):1532-1544
Let A be a unital algebra and let M be a unitary A-bimodule. We consider generalized Lie derivations mapping from A to M. Our results are applied to triangular algebras, in particular to nest algebras and (block) upper triangular matrix algebras. We prove that under certain conditions each generalized Lie derivation of a triangular algebra A is the sum of a generalized derivation and a central map which vanishes on all commutators of A. 相似文献