全文获取类型
收费全文 | 909篇 |
免费 | 47篇 |
国内免费 | 1篇 |
专业分类
化学 | 656篇 |
晶体学 | 1篇 |
力学 | 23篇 |
数学 | 126篇 |
物理学 | 151篇 |
出版年
2023年 | 11篇 |
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 33篇 |
2019年 | 23篇 |
2018年 | 11篇 |
2017年 | 7篇 |
2016年 | 34篇 |
2015年 | 25篇 |
2014年 | 32篇 |
2013年 | 31篇 |
2012年 | 53篇 |
2011年 | 69篇 |
2010年 | 34篇 |
2009年 | 33篇 |
2008年 | 54篇 |
2007年 | 49篇 |
2006年 | 44篇 |
2005年 | 49篇 |
2004年 | 40篇 |
2003年 | 22篇 |
2002年 | 23篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1983年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1972年 | 4篇 |
1923年 | 6篇 |
1892年 | 4篇 |
1890年 | 3篇 |
1888年 | 5篇 |
1887年 | 4篇 |
1885年 | 3篇 |
1884年 | 3篇 |
1882年 | 5篇 |
1881年 | 6篇 |
排序方式: 共有957条查询结果,搜索用时 15 毫秒
61.
Dongyi Liu Ahmed M. El‐Zohry Maria Taddei Clemens Matt Laura Bussotti Zhijia Wang Jianzhang Zhao Omar F. Mohammed Mariangela Di Donato Stefan Weber 《Angewandte Chemie (International ed. in English)》2020,59(28):11591-11599
We prepared conceptually novel, fully rigid, spiro compact electron donor (Rhodamine B, lactam form, RB)/acceptor (naphthalimide; NI) orthogonal dyad to attain the long‐lived triplet charge‐transfer (3CT) state, based on the electron spin control using spin‐orbit charge transfer intersystem crossing (SOCT‐ISC). Transient absorption (TA) spectra indicate the first charge separation (CS) takes place within 2.5 ps, subsequent SOCT‐ISC takes 8 ns to produce the 3NI* state. Then the slow secondary CS (125 ns) gives the long‐lived 3CT state (0.94 μs in deaerated n‐hexane) with high energy level (ca. 2.12 eV). The cascade photophysical processes of the dyad upon photoexcitation are summarized as 1NI*→1CT→3NI*→3CT. With time‐resolved electron paramagnetic resonance (TREPR) spectra, an EEEAAA electron‐spin polarization pattern was observed for the naphthalimide‐localized triplet state. Our spiro compact dyad structure and the electron spin‐control approach is different to previous methods for which invoking transition‐metal coordination or chromophores with intrinsic ISC ability is mandatory. 相似文献
62.
Synthesis and characterisation of the SrxBa1−xFeO3−y-system and the fluorinated phases SrxBa1−xFeO2F
Oliver Clemens Robert Haberkorn Peter R. Slater Horst Philipp Beck 《Solid State Sciences》2010,12(8):1455-1463
Compounds in the system SrxBa1?xFeO3?y have been prepared under different partial pressures of oxygen. In this system, different perovskite-type structures are found depending highly on the values of x and y. Fluorination using polyvinylidenedifluoride (PVDF) gives oxyfluoride materials of composition SrxBa1?xFeO2F, which normally crystallize in the cubic perovskite structure. Rietveld refinement results provide information about the packing density for oxide and oxyfluoride samples and allow a general comparison between these two different types of materials. Furthermore, the determination of the average iron oxidation state also showed that the oxygen deficiency, y, depends significantly on the value of x and the structure determined by the Sr/Ba ratio. 相似文献
63.
Gary E. Martin R. Thomas Williamson Kirill A. Blinov Clemens G. Anklin Wolfgang Bermel 《Magnetic resonance in chemistry : MRC》2012,50(10):691-695
1,1‐ADEQUATE and the related long‐range 1,n‐ and n,1‐ADEQUATE variants were developed to provide an unequivocal means of establishing 2JCH and the equivalent of nJCH correlations where n = 3,4. Whereas the 1,1‐ and 1,n‐ADEQUATE experiments have two simultaneous evolution periods that refocus the chemical shift and afford net single quantum evolution for the carbon spins, the n,1‐variant has a single evolution period that leaves the carbon spin to be observed at the double quantum frequency. The n,1‐ADEQUATE experiment begins with an HMBC‐type nJCH magnetization transfer, which leads to inherently lower sensitivity than the 1,1‐ and 1,n‐ADEQUATE experiments that begin with a 1JCH transfer. These attributes, in tandem, serve to render the n,1‐ADEQUATE experiment less generally applicable and more difficult to interpret than the 1,n‐ADEQUATE experiment, which can in principle afford the same structural information. Unsymmetrical and generalized indirect covariance processing methods can complement and enhance the structural information encoded in combinations of experiments e.g. HSQC‐1,1‐ or ?1,n‐ADEQUATE. Another benefit is that covariance processing methods offer the possibility of mathematically combining a higher sensitivity 2D NMR spectrum with for example 1,1‐ or 1,n‐ADEQUATE to improve access to the information content of lower sensitivity congeners. The covariance spectrum also provides a significant enhancement in the F1 digital resolution. The combination of HMBC and 1,1‐ADEQUATE spectra is shown here using strychnine as a model compound to derive structural information inherent to an n,1‐ADEQUATE spectrum with higher sensitivity and in a more convenient to interpret single quantum presentation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
64.
65.
Elisabeth Eidenberger Erich Stergar Harald Leitner Peter Staron Jürgen Spitaler Claudia Ambrosch-Draxl Helmut Clemens 《Applied Physics A: Materials Science & Processing》2009,97(2):331-340
Atom probe tomography (APT) measurements were conducted to analyze nm-sized precipitates in a Fe-25 m% Co-15 m% Mo model alloy.
Calculation of isoconcentration surfaces and application of cluster-search algorithms yielded the chemical compositions of
matrix and precipitates. Small-angle neutron scattering (SANS) was performed in order to calculate the ratio of magnetic to
nuclear scattering. This so-called A-ratio was compared with values calculated from the chemical information derived from the atom probe data. For this, the magnetism
of the precipitates has to be taken into account. Ab-initio studies have been carried out to determine the magnetic moment
of the precipitate phase. The results show that the extremely fine precipitates are ferromagnetic and exhibit near-equilibrium
composition. In the very early stage of decomposition, however, the composition is different from near-equilibrium. The influences
of the magnetism of the precipitates as well as of artifacts from atom probe measurements on the obtained results are discussed. 相似文献
66.
67.
Weisshoff H Preiss A Nehls I Win T Mügge C 《Analytical and bioanalytical chemistry》2002,373(8):810-819
A hyphenated HPLC-(1)H NMR method for the identification and quantification of PAHs in soil samples has been developed and applied to a PAH reference sample provided by the Federal Institute for Materials Research and Testing (BAM, Berlin, Germany). The results were compared with those obtained by HPLC-DAD, HPLC-F, and GC-MS analyses of the same sample. 相似文献
68.
Clemens Berger 《Advances in Mathematics》2002,169(1):118-175
69.
70.
Wagner C Rist M Mayer-Enthart E Wagenknecht HA 《Organic & biomolecular chemistry》2005,3(11):2062-2063
1-ethynylpyrene shows remarkable absorption changes upon DNA hybridization when it is covalently attached to the 8-position of guanine. An absorption band at approximately 420 nm is only present in the duplex, exhibits thermal melting behaviour and provides the basis for a molecular beacon together with 1-ethynylpyrene-modified cytosine. 相似文献