全文获取类型
收费全文 | 1132篇 |
免费 | 60篇 |
国内免费 | 19篇 |
专业分类
化学 | 698篇 |
晶体学 | 3篇 |
力学 | 14篇 |
数学 | 216篇 |
物理学 | 280篇 |
出版年
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 30篇 |
2020年 | 40篇 |
2019年 | 35篇 |
2018年 | 24篇 |
2017年 | 23篇 |
2016年 | 56篇 |
2015年 | 46篇 |
2014年 | 41篇 |
2013年 | 77篇 |
2012年 | 80篇 |
2011年 | 77篇 |
2010年 | 58篇 |
2009年 | 39篇 |
2008年 | 50篇 |
2007年 | 56篇 |
2006年 | 53篇 |
2005年 | 65篇 |
2004年 | 39篇 |
2003年 | 31篇 |
2002年 | 35篇 |
2001年 | 32篇 |
2000年 | 21篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 4篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1987年 | 4篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1970年 | 2篇 |
1967年 | 2篇 |
1915年 | 2篇 |
排序方式: 共有1211条查询结果,搜索用时 156 毫秒
61.
Dr. Louwanda Lakiss Dr. Aurélie Vicente Prof. Jean-Pierre Gilson Dr. Valentin Valtchev Dr. Svetlana Mintova Dr. Alexandre Vimont Dr. Robert Bedard Dr. Suheil Abdo Dr. Jeffery Bricker 《Chemphyschem》2020,21(16):1873-1881
We outline two methodologies to selectively characterize the Brønsted acidity of the external surface of FAU-type zeolites by IR and NMR spectroscopy of adsorbed basic probe molecules. The challenge and goal are to develop reliable and quantitative IR and NMR methodologies to investigate the accessibility of acidic sites in the large pore FAU-type zeolite Y and its mesoporous derivatives often referred to as ultra-stable Y (USY). The accessibility of their Brønsted acid sites to probe molecules (n-alkylamines, n-alkylpyridines, n-alkylphosphine- and phenylphosphine-oxides) of different molecular sizes is quantitatively monitored either by IR or 31P NMR spectroscopy. It is now possible, for the first time to quantitatively discriminate between the Brønsted acidity located in the microporosity and on the external surface of large pore zeolites. For instance, the number of external acid sites on a Y (LZY-64) zeolite represents 2 % of its total acid sites while that of a USY (CBV760) represents 4 % while the latter has a much lower framework Si/Al ratio. 相似文献
62.
Nikita K. Kulachenkov Dapeng Sun Yuri A. Mezenov Andrei N. Yankin Sergey Rzhevskiy Vyacheslav Dyachuk Alexandre Nomin Ghouti Medjahdi Evgeny A. Pidko Valentin A. Milichko 《Angewandte Chemie (International ed. in English)》2020,59(36):15522-15526
We demonstrate herein an all‐optical switch based on stimuli‐responsive and photochromic‐free metal–organic framework (HKUST‐1). Ultrafast near‐infrared laser pulses stimulate a reversible 0.4 eV blue shift of the absorption band with up to 200 s?1 rate due to dehydration and concomitant shrinking of the structure‐forming [Cu2C4O8] cages of HKUST‐1. Such light‐induced switching enables the remote modulation of intensities of photoluminescence of single crystals of HKUST‐1 as well visible radiation passing through the crystal by 2 order of magnitude. This opens up the possibility of utilyzing stimuli‐responsive MOFs for all‐optical data processing devices. 相似文献
63.
64.
Yury Yu. Rusakov Leonid B. Krivdin Valentina M. Nosova Alexander V. Kisin Valentin G. Lakhtin 《Magnetic resonance in chemistry : MRC》2012,50(10):665-671
The calculations of geminal and vicinal 29Si–1H spin–spin coupling constants across double bond in 15 alkenylmethylsilanes and alkenylchlorosilanes were carried out at the second‐order polarization propagator approach level in a good agreement with experiment. Two structural trends, namely, (i) the geometry of the coupling pathway and (ii) the effect of the electrowithdrawing substituent, have been interpreted in terms of the natural J‐coupling analysis within the framework of the natural bond orbital approach. Thus, the marked difference between cisoidal and transoidal 29Si–1H spin–spin coupling constants across double bond was accounted for the delocalization contributions including bonding and antibonding Si–C and C–H orbitals, whereas the chlorine effect was explained in terms of the steric contributions including bonding Si–Cl orbitals. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
65.
D Hurtmans G DufourW Bell A HenryA Valentin C Camy-Peyret 《Journal of Molecular Spectroscopy》2002,215(1):128-133
We have determined the spectroscopic parameters that are necessary to describe accurately the R(0) line profile of the CH4 2ν3 band from about 1 Torr to a few hundred Torr of pure CH4. The intensities determined at each pressure are in overall agreement to better than 0.7%. The R(3) manifold of the same band has also been investigated. Relative positions and absolute intensities of the three transitions composing the triplet have been determined. The intensity distribution inside the triplet is in fair agreement with recent theoretical predictions. 相似文献
66.
Sebban S Mocek T Ros D Upcraft L Balcou P Haroutunian R Grillon G Rus B Klisnick A Carillon A Jamelot G Valentin C Rousse A Rousseau JP Notebaert L Pittman M Hulin D 《Physical review letters》2002,89(25):253901
We report the first experimental demonstration of a Ni-like optical-field ionization collisional soft x-ray laser. The amplifying medium is generated by focusing a circularly polarized 760 mJ, 30 fs, 10-Hz Ti:sapphire laser beam in a few mm cell filled with krypton. We have measured a gain coefficient of 78 cm(-1) on the 3d(9)4d 1S0-3d(9)4p(1)P1 transition at 32.8 nm, which is here amplified for the first time. This radiation source represents the shortest wavelength optical-field ionization collisional soft x-ray laser ever produced. The influence of the gas pressure and the pumping energy on the lasing output are also presented. 相似文献
67.
A. Valentin A. Henry Ph. Cardinet M.F. Le Moal Da-Wun Chen K. Narahari Rao 《Journal of Molecular Spectroscopy》1978,70(1):9-17
The wavenumbers of the vibration rotation band lines of 14N16O are reported for the , and subbands of the 1-0 transition in the infrared. The full set of spectroscopic constants for this band has been determined by direct approach using the analysis of Zare, Schmeltekopf, Harrop, and Albritton. In addition to the band origin ν0 and the B, D, H constants for the lower and upper vibrational levels, the following spin-orbit coupling constants have been derived: and (in cm?1). Apparent centrifugal corrections to these constants have been determined and the values obtained for them are and . Λ-Type doubling constants evaluated by using both grating and tunable laser data are also reported. 相似文献
68.
A. Kimura H. Kobayashi M. Nishida P. Valentin 《Journal of Quantitative Spectroscopy & Radiative Transfer》1985,34(2):189-215
Average radiative transition probabilities for argon atoms have been calculated for transitions between 24 levels in two groups characterized by the atomic core terms 2P1/2 and 2P3/2 by using the method of Bates and Damgaard. The results are compared with data in the NBS tables (Wiese et al.) and with those of Katsonis and Drawin. We find satisfactory agreement for the order of magnitude, even for transitions between lower lying levels. Parameters, which appear in Drawin's semiempirical cross-section expressions for electronic excitation of optically allowed and parity-forbidden transitions, are determined with the multipole expansion method proposed by Sobel'man for transitions between the specified levels. Most of these are easily obtained, but the method must be improved for transitions between levels having the same azimuthal quantum number because the summation over the constituent terms does not converge. 相似文献
69.
Elena?F.?ShekaEmail author Ekaterina?A.?Nikitina Valentin?A.?Zayets Ilya?Ya.?Ginzburg Joop?Schoonman 《Journal of nanoparticle research》2005,7(2-3):171-186
The current paper presents results of a quantum-chemical study of the surface structure of nanoparticles of both rutile and anatase crystallographic modifications. Different stages of the surface relaxation are discussed. Water adsorption is considered. The calculations were performed in the spd-basis by using semi-empirical quantum-chemical codes, both sequential and parallel. The results are mainly addressed to the study of the interface formed by titania nanoparticles and a set of carboxylated species, namely, benzoic, bi-isonicotinic acids as well as tris-(2,2′-dcbipyridine) Fe(II) complex placed on the surface of either rutile or anatase polymorphs.This revised version was published online in August 2005 with a corrected issue number. 相似文献
70.
Johnsson P López-Martens R Kazamias S Mauritsson J Valentin C Remetter T Varjú K Gaarde MB Mairesse Y Wabnitz H Salières P Balcou P Schafer KJ L'Huillier A 《Physical review letters》2005,95(1):013001
We use a train of sub-200 attosecond extreme ultraviolet (XUV) pulses with energies just above the ionization threshold in argon to create a train of temporally localized electron wave packets. We study the energy transfer from a strong infrared (IR) laser field to the ionized electrons as a function of the delay between the XUV and IR fields. When the wave packets are born at the zero crossings of the IR field, a significant amount of energy (approximately 20 eV) is transferred from the field to the electrons. This results in dramatically enhanced above-threshold ionization in conditions where the IR field alone does not induce any significant ionization. Because both the energy and duration of the wave packets can be varied independently of the IR laser, they are valuable tools for studying and controlling strong-field processes. 相似文献