全文获取类型
收费全文 | 624篇 |
免费 | 21篇 |
国内免费 | 11篇 |
专业分类
化学 | 430篇 |
晶体学 | 5篇 |
力学 | 10篇 |
数学 | 90篇 |
物理学 | 121篇 |
出版年
2023年 | 2篇 |
2022年 | 13篇 |
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 21篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 34篇 |
2011年 | 47篇 |
2010年 | 34篇 |
2009年 | 24篇 |
2008年 | 42篇 |
2007年 | 48篇 |
2006年 | 34篇 |
2005年 | 34篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 18篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有656条查询结果,搜索用时 31 毫秒
111.
Yoshizawa K Nakayama T Kamachi T Kozlowski PM 《The journal of physical chemistry. A》2007,111(5):852-857
The vibronic (vibrational-electronic) interactions in the pi-anion radicals of the metalloporphyrins (M=Cr, Mn, Fe, Co, Ni, Cu, and Zn), which show delocalized D4h structures in the neutral states, are discussed using B3LYP density-functional-theory calculations. The B1g and B2g modes of vibration can remove the degenerate 2Eg state of the pi-anion radicals in the D4h symmetric structures to lead to rectangular and diamond D2h distortions, respectively. Calculated vibronic coupling constants demonstrate that the B1g modes of vibration better couple with the degenerate electronic state, leading to the rectangular D2h distortion. In particular, the B1g modes of nu10 and nu11, which have dominant contributions from Calpha-Cm and Cbeta-Cbeta stretching, give large vibronic coupling constants in the pi-anion radicals. The vibronic coupling constant can be viewed as the Jahn-Teller distortion force, and therefore these C-C stretching B1g modes will play a central role in the Jahn-Teller effect of the pi-anion radicals of the metalloporphyrins. 相似文献
112.
Theoretical studies on the electronic and thermodynamic properties of several electronic states of CeC(2) and CeC(2)(+) have been carried out employing state-of-the-art single- and multireference techniques. The ground and the low-lying electronic states of these two species have been found to possess C(2v) triangular structures. A (3)B(2) state has been found to be the ground state of CeC(2) while for CeC(2)(+) (2)A(2) is the ground state. The computed electron ionization energy is in excellent agreement with experiment. The experimentally observed thermodynamic properties (dissociation and atomization energies) of reactions involving CeC(2) dissociation are corrected using the computed gas-phase properties of the molecule and the partition functions. The bent triplet and singlet state of CeC(2) exhibit large dipole moments (7.0-10.5 D) and it is consistent with the ionic character (through dative charge transfer) of the cluster in ground and excited states. 相似文献
113.
Pawel Bechler Ronald DeVore Anna Kamont Guergana Petrova Przemyslaw Wojtaszczyk 《Transactions of the American Mathematical Society》2007,359(2):619-635
Let be the space of functions of bounded variation on with . Let , , be a wavelet system of compactly supported functions normalized in , i.e., , . Each has a unique wavelet expansion with convergence in . If is the set of indicies for which are largest (with ties handled in an arbitrary way), then is called a greedy approximation to . It is shown that with a constant independent of . This answers in the affirmative a conjecture of Meyer (2001).
114.
Gjertrud Maurstad Andreas R. Bausch Pawel Sikorski Bjørn T. Stokke 《Macromolecular Symposia》2005,227(1):161-172
The thickness and surface morphology of electrostatically self-assembled films of chitosan and xanthan (persistence length of ∼120nm) have been studied using dual-wavelength Reflection Interference Contrast Microscopy (DW-RICM) and tapping mode Atomic Force Microscopy (AFM). The multilayers were prepared at two ionic strengths (5mM and 150mM). When the multilayers were assembled at 150 mM a network like morphology was observed after one bilayer. This structure was found to be of large influence in the further growth of the multilayers, with the same kind of network structure being observed at all number of bilayers. A lack of swelling behaviour, as well as the network structure and the poresize of the network, is suggested to originate from the high chain stiffness of xanthan. 相似文献
115.
Luca Sancineto Carmine Ostacolo David Ortega-Alarcon Ana Jimenez-Alesanco Laura Ceballos-Laita Sonia Vega Olga Abian Adrian Velazquez-Campoy Silvia Moretti Agnieszka Dabrowska Pawel Botwina Aleksandra Synowiec Anna Kula-Pacurar Krzysztof Pyrc Nunzio Iraci Claudio Santi 《Molecules (Basel, Switzerland)》2021,26(19)
The COVID-19 pandemic outbreak prompts an urgent need for efficient therapeutics, and repurposing of known drugs has been extensively used in an attempt to get to anti-SARS-CoV-2 agents in the shortest possible time. The glycoside rutin shows manifold pharmacological activities and, despite its use being limited by its poor solubility in water, it is the active principle of many pharmaceutical preparations. We herein report our in silico and experimental investigations of rutin as a SARS-CoV-2 Mpro inhibitor and of its water solubility improvement obtained by mixing it with l-arginine. Tests of the rutin/l-arginine mixture in a cellular model of SARS-CoV-2 infection highlighted that the mixture still suffers from unfavorable pharmacokinetic properties, but nonetheless, the results of this study suggest that rutin might be a good starting point for hit optimization. 相似文献
116.
We derive sharp upper bounds for eigenvalues of the Laplacian under Neumann boundary conditions on convex domains with given diameter in Euclidean space. We use the Brunn-Minkowski theorem in order to reduce the problem to a question about eigenvalues of certain classes of Sturm-Liouville problems.
117.
Edwin Haselbach Michael Allan Thomas Bally Pawel Bednarek Anne‐Christelle Sergenton Armin deMeijere Sergej Kozhushkov Manuel Piacenza Stefan Grimme 《Helvetica chimica acta》2001,84(6):1670-1693
The electronic structure of spiro[4.4]nonatetraene 1 as well as that of its radical anion and cation were studied by different spectroscopies. The electron‐energy‐loss spectrum in the gas phase revealed the lowest triplet state at 2.98 eV and a group of three overlapping triplet states in the 4.5 – 5.0 eV range, as well as a number of valence and Rydberg singlet excited states. Electron‐impact excitation functions of pure vibrational and triplet states identified various states of the negative ion, in particular the ground state with an attachment energy of 0.8 eV, an excited state corresponding to a temporary electron attachment to the 2b1 MO at an attachment energy of 2.7 eV, and a core excited state at 4.0 eV. Electronic‐absorption spectroscopy in cryogenic matrices revealed several states of the positive ion, in particular a richly structured first band at 1.27 eV, and the first electronic transition of the radical anion. Vibrations of the ground state of the cation were probed by IR spectroscopy in a cryogenic matrix. The results are discussed on the basis of density‐functional and CASSCF/CASPT2 quantum‐chemical calculations. In their various forms, the calculations successfully rationalized the triplet and the singlet (valence and Rydberg) excitation energies of the neutral molecule, the excitation energies of the radical cation, its IR spectrum, the vibrations excited in the first electronic absorption band, and the energies of the ground and the first excited states of the anion. The difference of the anion excitation energies in the gas and condensed phases was rationalized by a calculation of the Jahn‐Teller distortion of the anion ground state. Contrary to expectations based on a single‐configuration model for the electronic states of 1 , it is found that the gap between the first two excited states is different in the singlet and the triplet manifold. This finding can be traced to the different importance of configuration interaction in the two multiplicity manifolds. 相似文献
118.
Viktor Bezugly Pawel Wielgus Miroslav Kohout Frank R. Wagner 《Journal of computational chemistry》2010,31(7):1504-1519
Electron localizability indicators based on the parallel‐spin electron pair density (ELI–D) and the antiparallel‐spin electron pair density (ELIA) are studied for the correlated ground‐state wavefunctions of Li2, Be2, B2, and C2 diatomic molecules. Different basis sets and reference spaces are used for the multireference configuration interaction method following the complete active space calculations to investigate the local effect of electron correlation on the extent of electron localizability in position space determined by the two functionals. The results are complemented by calculations of effective bond order, vibrational frequency, and Laplacian of the electron density at the bond midpoint. It turns out that for Li2, B2, and C2 the reliable topology of ELI–D is obtained only at the correlated level of theory. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
119.
Rafal Nowaczynski Marcin Gajc Hancza B. Surma Pawel Osewski Adam Strzep Witold Ryba‐Romanowski Dorota A. Pawlak 《Particle & Particle Systems Characterization》2019,36(1)
Quantum dot (QD)‐based light‐emitting materials are gaining increased attention because of their easily tunable optical properties desired for various applications in biology, optoelectronics, and photonics. However, few methods can be used to manufacture volumetric materials doped with more than one type of QD other than QD‐polymer hybrids, and they often require complicated preparation processes and are prone to luminescence quenching by QD aggregation and separation from the matrix. Here, simultaneous doping of a volumetric glass‐based nanocomposite with two types of QDs is demonstrated for the first time in a single‐step process using the nanoparticle direct doping method. Glass rods doped with CdTe, CdSe/ZnS, or co‐doped with both QDs, are obtained. Photoluminescence and lifetime experiments confirm temperature‐dependent double emission with maxima at 596 and 720 nm with mean lifetimes up to 16 ns, as well as radiative energy transfer from the short wavelength–emitting QDs to the long wavelength–emitting QDs. This approach may enable the simple and cost‐efficient manufacturing of bulk materials that produce multicolor luminescence with cascade excitation pumping. Applications that could benefit from this include broadband optical fiber amplifiers, backlight systems in LCD screens, high‐power LEDs, or down‐converting solar concentrators used to increase the efficiency of solar panels. 相似文献
120.
Pawel Dziedzic 《Tetrahedron letters》2009,50(52):7242-7245
Inorganic ammonium salts catalyze the direct aldol reaction between unmodified ketones and aldehydes to furnish the corresponding β-hydroxy ketones in aqueous media. The reactions are highly chemoselective and operationally simple. 相似文献