全文获取类型
收费全文 | 4688篇 |
免费 | 227篇 |
国内免费 | 20篇 |
专业分类
化学 | 3279篇 |
晶体学 | 20篇 |
力学 | 99篇 |
数学 | 631篇 |
物理学 | 906篇 |
出版年
2023年 | 48篇 |
2022年 | 65篇 |
2021年 | 98篇 |
2020年 | 136篇 |
2019年 | 133篇 |
2018年 | 90篇 |
2017年 | 73篇 |
2016年 | 218篇 |
2015年 | 158篇 |
2014年 | 188篇 |
2013年 | 256篇 |
2012年 | 387篇 |
2011年 | 486篇 |
2010年 | 231篇 |
2009年 | 147篇 |
2008年 | 313篇 |
2007年 | 330篇 |
2006年 | 297篇 |
2005年 | 278篇 |
2004年 | 190篇 |
2003年 | 131篇 |
2002年 | 110篇 |
2001年 | 45篇 |
2000年 | 30篇 |
1999年 | 27篇 |
1998年 | 22篇 |
1997年 | 22篇 |
1996年 | 39篇 |
1995年 | 35篇 |
1994年 | 30篇 |
1993年 | 34篇 |
1992年 | 28篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 18篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1973年 | 35篇 |
排序方式: 共有4935条查询结果,搜索用时 15 毫秒
101.
102.
Benjamin Prek Jure Bezenšek Marta Kasunič Uroš Grošelj Jurij Svete Branko Stanovnik 《Tetrahedron》2014
Herein a simple one-pot metal-free synthesis of alkyl-, aryl-, heteroaryl- and alkoxycarbonyl substituted 1,3-bis(dimethylamino)benzene derivatives is described. The products were prepared from the corresponding methyl ketones or compounds with an α-methylene group in regard to the carbonyl group, using N,N-dimethylacetamide dimethyl acetal (DMADMA) as the reagent. 相似文献
103.
104.
Eve Kozari Dr. Mark Sigalov Dr. Dina Pines Dr. Benjamin P. Fingerhut Prof. Dr. Ehud Pines 《Chemphyschem》2021,22(8):716-725
Infrared (IR) absorption in the 1000–3700 cm−1 range and 1H NMR spectroscopy reveal the existence of an asymmetric protonated water trimer, H7+O3, in acetonitrile. The core H7+O3 motif persists in larger protonated water clusters in acetonitrile up to at least 8 water molecules. Quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations reveal irreversible proton transport promoted by propagating the asymmetric H7+O3 structure in solution. The QM/MM calculations allow for the successful simulation of the measured IR absorption spectra of H7+O3 in the OH stretch region, which reaffirms the assignment of the H7+O3 spectra to a hybrid-complex structure: a protonated water dimer strongly hydrogen-bonded to a third water molecule with the proton exchanging between the two possible shared-proton Zundel-like centers. The H7+O3 structure lends itself to promoting irreversible proton transport in presence of even one additional water molecule. We demonstrate how continuously evolving H7+O3 structures may support proton transport within larger water solvates. 相似文献
105.
We consider a model for magnetic memory that consists of strongly coupled dipolar or antiferromagnetic (AF) pairs with inequivalent perpendicular anisotropy K1 and K2. For appropriate parameter values, determined in this work, they have two inequivalent storage states with zero net magnetic moment. Both analytical and numerical calculations are performed, in some cases yielding different results because of relaxation effects (i.e., a dependence on the damping parameter α). Hysteresis loops for a wide variety of parameter values are obtained, both for the AF case and the dipole case. An Appendix gives analytic results for slightly non-collinear spins in an applied field, which were used to test the numerical results. 相似文献
106.
Starting from first‐principle many‐body quantum dynamics, we show that the dynamics of Bose‐Einstein condensates can be approximated by the time‐dependent nonlinear Gross‐Pitaevskii equation, giving a bound on the rate of the convergence. Initial data are constructed on the bosonic Fock space applying an appropriate Bogoliubov transformation on a coherent state with expected number of particles N. The Bogoliubov transformation plays a crucial role; it produces the correct microscopic correlations among the particles. Our analysis shows that, on the level of the one‐particle reduced density, the form of the initial data is preserved by the many‐body evolution, up to a small error that vanishes as N?1/2 in the limit of large N.© 2015 Wiley Periodicals, Inc. 相似文献
107.
Antonio Dell'Isola Dr. Matthew M. W. McLachlan Dr. Benjamin W. Neuman Hawaa M. N. Al‐Mullah Alexander W. D. Binks Warren Elvidge Dr. Kenneth Shankland Dr. Alexander J. A. Cobb 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11685-11689
An efficient synthesis of spirocyclic triazolooxazine nucleosides is described. This was achieved by the conversion of β‐D ‐psicofuranose to the corresponding azido‐derivative, followed by alkylation of the primary alcohol with a range of propargyl bromides, obtained by Sonogashira chemistry. The products of these reactions underwent 1,3‐dipolar addition smoothly to generate the protected spirocyclic adducts. These were easily deprotected to give the corresponding ribose nucleosides. The library of compounds obtained was investigated for its antiviral activity using MHV (mouse hepatitis virus) as a model wherein derivative 3 f showed the most promising activity and tolerability. 相似文献
108.
James A. Phillips Anna R. Ley Patrick W. Treacy Benjamin M. Wahl Brittany C. Zehner Kelling J. Donald Samuel Gillespie 《International journal of quantum chemistry》2020,120(20):e26383
We have explored the structural and energetic properties of a series of RMX3-NH3 (M=Si, Ge; X=F, Cl; R=CH3, C6H5) complexes using density functional theory and low-temperature infrared spectroscopy. In the minimum-energy structures, the NH3 binds axially to the metal, opposite a halogen, while the organic group resides in an equatorial site. Remarkably, the primary mode of interaction in several of these systems seems to be hydrogen bonding (C-H--N) rather than a tetrel (N→M) interaction. This is particularly clear for the RMCl3-NH3 complexes, and analyses of the charge distributions of the acid fragment corroborate this assessment. We also identified a set of metastable geometries in which the ammonia binds opposite the organic substituent in an axial orientation. Acid fragment charge analyses also provide a clear rationale as to why these configurations are less stable than the minimum-energy structures. Matrix-isolation infrared spectra provide clear evidence for the occurrence of the minimum-energy form of CH3SiCl3–NH3, but analogous results for CH3GeCl3–NH3 are less conclusive. Computational scans of the M-N distance potentials for CH3SiCl3–NH3 and CH3GeCl3–NH3, both in the gas phase and bulk dielectric media, reveal a great deal of anharmonicity and a propensity for condensed-phase structural change. 相似文献
109.
Paracyclophene based monomers can be polymerized in a living fashion using the alkylidene initiator Mo(NAr)(CHCMe2Ph)(OCMe(CF3)2)2. The cis-specific nature of the polymerization is critical, since small amounts of trans olefin in the backbone renders the material insoluble. These polymers have complex photophysical behavior, probably a consequence of the close proximity of chromophores along the polymer backbone. Polymerization of 9-(tert-butyldimethylsilyloxy)-[2.2]-paracyclophan-1-ene produces a new precursor material which furnishes PPV under remarkably mild conditions. 相似文献
110.
Benjamin L. Solomon Christopher P. Landee Jan L. Wikaira 《Journal of Coordination Chemistry》2014,67(23-24):3953-3971
Using 2-amino-5-chloro-3-fluoropyridine, two new copper halide coordination complexes and two new salts have been synthesized: [(3,5-FCAP)2CuCl2] (1), [(3,5-FCAP)2CuBr2](2), (3,5-FCAPH)2[CuCl4] (3) and (3,5-FCAPH)2[CuBr4] (4) [3,5-FCAP?=?2-amino-5-chloro-3-fluoropyridine; 3,5-FCAPH?=?2-amino-5-chloro-3-fluoropyridinium]. These complexes have been analyzed through single-crystal X-ray diffraction and temperature-dependent magnetic susceptibility. Compounds 1 and 2 crystallize in the triclinic space group P-1, while 3 and 4 crystallize in the monoclinic space group P21/c. All structures were distinct, with 1 giving a bihalide bridged chain, 2 yielding a halide bridged dimer, 3 forming a two-halide bridged chain via short Cl???Cl contacts, and 4 producing a rectangular sheet via short Br???Br contacts. All four compounds exhibit anti-ferromagnetic interactions and were fit to linear chain (1 and 3), dimer (2), and rectangular 2-D sheet (4) models. The resulting J/kB values are ?3.4(1), ?31.3(8), ?0.9(1), and ?9.46(6)?K with an α value (α?=?J?/J) of 0.06(2), respectively. 相似文献