全文获取类型
收费全文 | 64178篇 |
免费 | 2221篇 |
国内免费 | 294篇 |
专业分类
化学 | 37077篇 |
晶体学 | 364篇 |
力学 | 1533篇 |
综合类 | 9篇 |
数学 | 10874篇 |
物理学 | 16836篇 |
出版年
2023年 | 396篇 |
2021年 | 801篇 |
2020年 | 906篇 |
2019年 | 837篇 |
2018年 | 939篇 |
2017年 | 896篇 |
2016年 | 1866篇 |
2015年 | 1516篇 |
2014年 | 1696篇 |
2013年 | 3319篇 |
2012年 | 3294篇 |
2011年 | 3688篇 |
2010年 | 2372篇 |
2009年 | 2137篇 |
2008年 | 3336篇 |
2007年 | 3150篇 |
2006年 | 2969篇 |
2005年 | 2731篇 |
2004年 | 2261篇 |
2003年 | 1875篇 |
2002年 | 1636篇 |
2001年 | 1377篇 |
2000年 | 1143篇 |
1999年 | 863篇 |
1998年 | 706篇 |
1997年 | 687篇 |
1996年 | 818篇 |
1995年 | 703篇 |
1994年 | 737篇 |
1993年 | 751篇 |
1992年 | 791篇 |
1991年 | 565篇 |
1990年 | 575篇 |
1989年 | 496篇 |
1988年 | 456篇 |
1987年 | 492篇 |
1986年 | 451篇 |
1985年 | 670篇 |
1984年 | 656篇 |
1983年 | 523篇 |
1982年 | 568篇 |
1981年 | 548篇 |
1980年 | 540篇 |
1979年 | 494篇 |
1978年 | 476篇 |
1977年 | 473篇 |
1976年 | 433篇 |
1975年 | 415篇 |
1974年 | 394篇 |
1973年 | 360篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
41.
Ortiz Adolfo Yang Jianhua Coccolo Mattia Seoane Jesús M. Sanjuán Miguel A. F. 《Nonlinear dynamics》2020,102(4):2323-2337
Nonlinear Dynamics - The main purpose of this paper is to study both the underdamped and the overdamped dynamics of the nonlinear Helmholtz oscillator with a fractional-order damping. For that... 相似文献
42.
Thomas Wittmann Dr. Renée Siegel Nele Reimer Dr. Wolfgang Milius Prof. Dr. Norbert Stock Prof. Dr. Jürgen Senker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):314-323
The resistance of metal–organic frameworks towards water is a very critical issue concerning their practical use. Recently, it was shown for microporous MOFs that the water stability could be increased by introducing hydrophobic pendant groups. Here, we demonstrate a remarkable stabilisation of the mesoporous MOF Al‐MIL‐101‐NH2 by postsynthetic modification with phenyl isocyanate. In this process 86 % of the amino groups were converted into phenylurea units. As a consequence, the long‐term stability of Al‐MIL‐101‐URPh in liquid water could be extended beyond a week. In water saturated atmospheres Al‐MIL‐101‐URPh decomposed at least 12‐times slower than the unfunctionalised analogue. To study the underlying processes both materials were characterised by Ar, N2 and H2O sorption measurements, powder X‐ray diffraction, thermogravimetric and chemical analysis as well as solid‐state NMR and IR spectroscopy. Postsynthetic modification decreased the BET equivalent surface area from 3363 to 1555 m2 g?1 for Al‐MIL‐101‐URPh and reduced the mean diameters of the mesopores by 0.6 nm without degrading the structure significantly and reducing thermal stability. In spite of similar water uptake capacities, the relative humidity‐dependent uptake of Al‐MIL‐101‐URPh is slowed and occurs at higher relative humidity values. In combination with 1H‐27Al D ‐HMQC NMR spectroscopy experiments this favours a shielding mechanism of the Al clusters by the pendant phenyl groups and rules out pore blocking. 相似文献
43.
44.
45.
Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献
46.
47.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
48.
49.
50.
P. Seelig A. Dax S. Faber M. Gerlach G. Huber T. Kühl D. Marx P. Merz W. Quint F. Schmitt H. Winter M. Würtz 《Hyperfine Interactions》1998,114(1-4):135-139
The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric
and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in 207Pb81+. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique
using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics
from an ion beam at relativistic velocities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献