全文获取类型
收费全文 | 261篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 168篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 26篇 |
物理学 | 80篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 14篇 |
2020年 | 13篇 |
2019年 | 4篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 18篇 |
2012年 | 18篇 |
2011年 | 19篇 |
2010年 | 11篇 |
2009年 | 9篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 1篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1990年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 5篇 |
1966年 | 2篇 |
1965年 | 4篇 |
1939年 | 1篇 |
排序方式: 共有277条查询结果,搜索用时 15 毫秒
81.
L. M. Korotaeva T. Ya. Rubinskaya L. V. Mikhal’chenko I. A. Rybakova V. P. Gul’tyai 《Russian Journal of Electrochemistry》2011,47(10):1139-1145
The electrochemical behavior of cinnamic acid (CA) on the cathodes with a high hydrogen overpotential (Hg, glassy carbon,
and carbositall) in the aprotic solvent (DMF) and in DMF with additions of H2O or Et4NOH is studied by the methods of polarography, preparative electrolysis, cyclic voltammetry (CVA), coulometry, and chronoammetry.
It is found that the mechanism of CA electroreduction is in conflict with the classical notion of the mechanism of electroreduction
of α,β-unsaturated carboxyl compounds. It is shown that in the aprotic solution, in contrast to similar carbonyl compounds
or ethers, which are the derivatives of organic acids, the products of double-bond hydrogenation, rather than the dimeric
compounds, are the only products of CA electroreduction, i.e the presence of carboxyl group changes essentially the direction
of electrochemical process. From the data of CVA, it is concluded that stable dimeric associates are present in the DMF solutions
in the equilibrium with nondissociated CA. 相似文献
82.
Carlos Torres J. Gulín-González E. Navas-Conyedo P. Demontis G. B. Suffritti 《Structural chemistry》2013,24(3):909-915
Completely siliceous zeolite ZSM-5 (silicalite-1) under high external pressures, up to 7 GPa, was investigated by energy minimization techniques. Classical empirical potentials have been used to study the phase transformation of the silicalite crystal to a new one with a lower symmetry. The analysis of the unit cell geometry and vibrational spectra at selected pressures suggest the loss of crystallinity of the silicalite structure. We found that a low-density amorphous phase is reached at pressures around 2.5–3.5 GPa. These results are compatible with recent Raman and X-Ray diffraction studies. We report the structural and vibrational properties of the new phase. In addition, we report the simulated elastic constants and the Young’s modulus of silicalite at selected pressures. The simulated results are in semi-quantitative agreement with the experiment. 相似文献
83.
T. Gamze Ulusoy Ghobadi Amir Ghobadi Muhammed Buyuktemiz Elif Akhuseyin Yildiz Dilara Berna Yildiz H. Gul Yaglioglu Yavuz Dede Ekmel Ozbay Ferdi Karadas 《Angewandte Chemie (International ed. in English)》2020,59(10):4082-4090
Herein, we establish a simple synthetic strategy affording a heterogeneous, precious metal‐free, dye‐sensitized photoelectrode for water oxidation, which incorporates a Prussian blue (PB) structure for the sensitization of TiO2 and water oxidation catalysis. Our approach involves the use of a Fe(CN)5 bridging group not only as a cyanide precursor for the formation of a PB‐type structure but also as an electron shuttle between an organic chromophore and the catalytic center. The resulting hetero‐functional PB‐modified TiO2 electrode demonstrates a low‐cost and easy‐to‐construct photoanode, which exhibits favorable electron transfers with a remarkable excited state lifetime on the order of nanoseconds and an extended light absorption capacity of up to 500 nm. Our approach paves the way for a new family of precious metal‐free robust dye‐sensitized photoelectrodes for water oxidation, in which a variety of common organic chromophores can be employed in conjunction with CoFe PB structures. 相似文献
84.
Hussain M. Sakhawat Ahmad Jamil Mazhar-ul-Haque Khattak Gul Dad 《Transition Metal Chemistry》1986,11(4):155-159
Summary We have carried out low temperature magnetic susceptibility measurements and a redetermination of the crystal and molecular structure of bis(1,5-diazacyclooctane)nickel(II) perchlorate dihydrate from three-dimensional intensity data collected on a CAD4 diffractometer. The structure was refined by full-matrix least-squares to the R value of 6.3% for 1501 observed reflections. The positions of the hydrogen atoms were obtained from the diffraction data. Contrary to our earlier conclusions drawn by inspection of molecular models of bis(diazacyclooctane) complexes, the axial sites in the actual crystal structure are open for ligation. The Ni-N bonds are, however, sterically protected by the coplanar N-H bonds, allowing maximum ligand-field stabilization for the squareplanar geometry around the nickel atom. The observed magnetic transition from a diamagnetic state at room temperature to a paramagnetic state at 78 K is explained on the basis of long-range exchange interactions along sterically unshieldedz axis. The crystal structure is compared with other similar structures. 相似文献
85.
Magnetic and electronic structure calculations are carried out for hypothetical zinc-blende (zb) phase of FeX (X=P, As, Sb) by using the full-potential linearized augmented plane wave (FLAPW) method. For zb FeSb, the total energy has been calculated as a function of lattice constant in ferromagnetic (FM) and antiferromagnetic (AFM) states. We found that the ground state of zb FeSb is very stable with respect to compression and expansion of the unit cell. The magnetic moment of zb FeSb in the AFM state is increasing with the lattice constant. The magnetic and electronic structures calculations of FeAs (FeP) are carried out for the lattice constants of GaAs (GaP), InAs (InP), and Si. Our finding shows that AFM is the ground state for all of our calculated zb FeX compounds and do not belong to the class of zb half metallic ferromagnets. 相似文献
86.
87.
Many theoretical works discuss the magnetic properties of the strongly repulsive Hubbard model near half filling. Several authors suggest that the system which contains a few holes does not behave as a ferromagnet, unlike in the one-hole case described by Nagaoka's famous result. We discuss the finite temperature properties of finite lattices. Using an efficient Monte Carlo method magnetic and specific heat results are presented for a 10 by 10 lattice with two holes. Our results show that the magnetization increases with decreasing temperature for such a finite system. 相似文献
88.
Concise,Enantioselective, and Versatile Synthesis of (−)‐Englerin A Based on a Platinum‐Catalyzed [4C+3C] Cycloaddition of Allenedienes 下载免费PDF全文
Ronald Nelson Dr. Moisés Gulías Prof. José L. Mascareñas Dr. Fernando López 《Angewandte Chemie (International ed. in English)》2016,55(46):14359-14363
A practical synthesis of (?)‐englerin A was accomplished in 17 steps and 11 % global yield from commercially available achiral precursors. The key step consists of a platinum‐catalyzed [4C+3C] allenediene cycloaddition that directly delivers the trans‐fused guaiane skeleton with complete diastereoselectivity. The high enantioselectivity (99 % ee) stems from an asymmetric ruthenium‐catalyzed transfer hydrogenation of a readily assembled diene–ynone. The synthesis also features a highly stereoselective oxygenation, and a late‐stage cuprate alkylation that enables the preparation of previously inaccessible structural analogues. 相似文献
89.
García-Fandiño R Gulías M Castedo L Granja JR Mascareñas JL Cárdenas DJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(1):272-281
The mechanism of the palladium-catalysed [3+2] intramolecular cycloaddition of alkylidenecyclopropanes to alkynes has been computationally explored at DFT level. The energies of the reaction intermediates and transition states for different possible pathways have been calculated in a model system that involves the use of PH3 as a ligand. The results obtained suggest that the most favourable reaction pathway involves the initial C--C oxidative addition of the cyclopropane to a Pd0 complex to give an alkylidenepalladacyclobutane, which isomerises to a methylenepalladacyclobutane intermediate. Subsequent cyclisation by alkyne carbometallation, followed by reductive elimination affords the final product. An alternative mechanism consisting of a palladaene-type rearrangement is less probable in terms of Gibbs energy, but cannot be fully discarded because it is competitive if one considers electronic energies. For substrates that present an ester group at the terminal position of the triple bond we have found an alternative, more favourable mechanistic route that explains why the [3+2] cycloaddition of these types of systems does not lead to the expected cycloadducts. 相似文献
90.