全文获取类型
收费全文 | 298篇 |
免费 | 13篇 |
专业分类
化学 | 233篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 1篇 |
物理学 | 74篇 |
出版年
2021年 | 2篇 |
2019年 | 8篇 |
2017年 | 2篇 |
2016年 | 16篇 |
2015年 | 10篇 |
2014年 | 3篇 |
2013年 | 13篇 |
2012年 | 16篇 |
2011年 | 14篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 16篇 |
1993年 | 2篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1985年 | 2篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1969年 | 4篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1961年 | 2篇 |
1935年 | 2篇 |
1932年 | 2篇 |
1921年 | 2篇 |
排序方式: 共有311条查询结果,搜索用时 406 毫秒
31.
32.
A. Tojiboev R. Wang F. Pan U. Englert K. Turgunov R. Okmanov 《Journal of Structural Chemistry》2013,54(6):1012-1017
2,3-Trimethylene-3,4-dihydroquinazoline shares the heterocyclic core with natural compounds and synthetic drugs. The hydrochloride of the compound forms excellent dihydrate crystals which have allowed us to collect high-resolution X-ray diffraction data and obtain the experimental charge density. The solid may be understood as built up from pairs of heterocyclic cations and chloride anions; a direct hydrogen bond links the halide to the formally cationic pyrimidine NH group. The hydrate water molecules interact with the anions, forming an infinite chain along the crystallographic a axis between the stacks of the heterocyclic cations. Based on the experimental charge density, a dipole moment of 16.1 Debye is calculated for a pair of the hydrogen-bonded quinazolinium cation and the chloride anion in the extended crystal structure. 相似文献
33.
34.
35.
Borabenzene Derivatives. 25 [1]. Methylbis(1-methylboratabenzene)indium: Synthesis and Structure. An Example for the Variability of Soft Structural Parameters in the Crystalline Environment The new boratabenzene derivative InMe(C5H5BMe)2 has been synthesized from 2-(Me3Sn)C5H5BMe and InMe3. The compound proves fluxional on the nmr time scale with average C2v symmetry in solution. An x-ray structure determination shows the existence of four molecules in the asymmetric unit differing mainly in the bonding geometry of the metal atoms with respect to the eight symmetrically independent boratabenzene ligands. Thus the dynamical behaviour in solution is reflected in the solid state by the soft structural parameters of the indium-ring coordination, with their variability exceeding the standard deviations of the corresponding individual observations by an order of magnitude. 相似文献
36.
The presumably "small molecule structure" of the organopalladium complex rac-PdCl(C(6)H(3)-4-OMe-CHMeNH(2))(py) crystallizes with 16 molecules in the asymmetric unit, a highly unusual situation according to the CSD database. The symmetrically independent residues differ with respect to soft conformational degrees of freedom. Packing in the acetonitrile solvate of the same compound is unexceptional. 相似文献
37.
Irmgard Kalf Ulli Englert 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(6):o206-o208
The crystal structure of cholic acid–pentan‐3‐one (1/1), C5H10O·C24H40O5, has been determined in order to deduce the molecular conformation of the small volatile ketone. Data were collected at 100 K to a resolution of (sin θ)/λ = 0.91 Å−1. The structure contains a hydrogen‐bonded cholic acid host network, forming only van der Waals interactions with the guest pentan‐3‐one molecules. The ketone molecules are disordered on general positions, with two clearly identifiable conformations. The majority conformer exhibits approximate C2 symmetry and is similar to that recently observed by microwave spectroscopy in the gas phase. 相似文献
38.
Steven van Terwingen Daniel Brüx Ruimin Wang Ulli Englert 《Molecules (Basel, Switzerland)》2021,26(13)
In the hydrochloride of a pyrazolyl-substituted acetylacetone, the chloride anion is hydrogen-bonded to the protonated pyrazolyl moiety. Equimolar co-crystallization with tetrafluorodiiodobenzene (TFDIB) leads to a supramolecular aggregate in which TFDIB is situated on a crystallographic center of inversion. The iodine atom in the asymmetric unit acts as halogen bond donor, and the chloride acceptor approaches the -hole of this TFDIB iodine subtending an almost linear halogen bond, with Cl···I = Å and Cl···I–C = 179.32(6)°. This contact is roughly orthogonal to the N–H···Cl hydrogen bond. An analysis of the electron density according to Bader’s Quantum Theory of Atoms in Molecules confirms bond critical points (bcps) for both short contacts, with = 0.129 for the halogen and e for the hydrogen bond. Our halogen-bonded adduct represents the prototype for a future class of co-crystals with tunable electron density distribution about the -hole contact. 相似文献
39.
Hendricks K.J. Haworth M.D. Englert T. Shiffler D. Baca G. Coleman P.D. Bowers L. Lemke R.W. Spencer T.A. Arman M.J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1998,26(3):320-325
The Air Force Research Laboratory RKO source has recently demonstrated the ability to convert electron beam power to RF power until the termination of the electron beam pulse, achieving a power of 1.5 GW at an energy of 170 J. These results represent an increase in power of 25-30% in power and energy extracted from this source. This paper discusses the principal research areas encountered in lengthening the RF pulse (FWHM) from 50 ns to the present 120 ns and the associated increase in the RF energy 相似文献
40.
Berthold-Georg Englert Nicoletta Sterpi Herbert Walther 《Optics Communications》1993,100(5-6):526-535
An experiment to determine the parity of the photon field of one privileged mode in a high-Q resonator is proposed. Even parity indicates that the photon number equals zero, two, four or any other even integer; likewise, odd parity states are mixtures of states with any odd number of photons. The parity measurement can be performed while the resonator is pumped as in standard one-atom maser operation. The time dependence of the parity expectation value is studied theoretically, and we suggest its experimental verification, which would serve as a test of the standard models describing both the relaxation of the cavity field toward thermal equilibrium and the pumping process. The connection between parity expectation values and Wigner's phase space function is recalled; the central value of the Wigner function equals twice the mean parity and it is, therefore, a measurable quantity. 相似文献