全文获取类型
收费全文 | 920篇 |
免费 | 28篇 |
国内免费 | 5篇 |
专业分类
化学 | 594篇 |
晶体学 | 11篇 |
力学 | 29篇 |
数学 | 109篇 |
物理学 | 210篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 38篇 |
2021年 | 50篇 |
2020年 | 22篇 |
2019年 | 31篇 |
2018年 | 52篇 |
2017年 | 33篇 |
2016年 | 41篇 |
2015年 | 37篇 |
2014年 | 34篇 |
2013年 | 65篇 |
2012年 | 71篇 |
2011年 | 71篇 |
2010年 | 45篇 |
2009年 | 30篇 |
2008年 | 59篇 |
2007年 | 59篇 |
2006年 | 39篇 |
2005年 | 39篇 |
2004年 | 37篇 |
2003年 | 29篇 |
2002年 | 15篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有953条查询结果,搜索用时 0 毫秒
51.
Dr. Nikolay A. Pushkarevsky Elena A. Chulanova Prof. Dr. Leonid A. Shundrin Dr. Anton I. Smolentsev Dr. Georgy E. Salnikov Dr. Elena A. Pritchina Dr. Alexander M. Genaev Dr. Irina G. Irtegova Prof. Dr. Irina Yu. Bagryanskaya Prof. Dr. Sergey N. Konchenko Prof. Dr. Nina P. Gritsan Prof. Dr. Jens Beckmann Prof. Dr. Andrey V. Zibarev 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(3):806-816
By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron-acceptor ability of 2,1,3-benzochalcogenadiazoles 1 – 3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the chalcogen. This trend is nontrivial, since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [ 1 ].− and [ 2 ].−, RA [ 3 ].− was not detected by EPR spectroscopy under CV conditions. Chemical reduction of 1 – 3 was performed and new thermally stable RA salts [K(THF)]+[ 2 ].− ( 8 ) and [K(18-crown-6)]+[ 2 ].− ( 9 ) were isolated in addition to known salt [K(THF)]+[ 1 ].− ( 7 ). On contact with air, RAs [ 1 ].− and [ 2 ].− underwent fast decomposition in solution with the formation of anions [ECN]−, which were isolated in the form of salts [K(18-crown-6)]+[ECN]− ( 10 , E=S; 11 , E=Se). In the case of 3 , RA [ 3 ].− was detected by EPR spectroscopy as the first representative of tellurium–nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]+2[ 3 -Te2]2− ( 12 ) featuring a new anionic complex with coordinate Te−Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18-crown-6)]+2[ 3 -Te4- 3 ]2− ( 13 ) containing an anionic complex with two coordinate Te−Te bonds. The structures of 8 – 13 were confirmed by XRD, and the nature of the Te−Te coordinate bond in [ 3 -Te2]2− and [ 3 -Te4- 3 ]2− was studied by DFT calculations and QTAIM analysis. 相似文献
52.
Jordanka Petrova Snejana Momchilova Nikolay G. Vassilev 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):45-52
Abstract The interaction of Li-diethylbenzylphosphonate 1-Li with aldehydes 2 is studied at different reaction conditions, the corresponding β-hydroxyethanephosphonate 3 being isolated. It is found that in these cases the aldol stage of the HWE reaction is not stereoselective or threo isomers predominate. The elimination stage leads only to trans-alkene due to the electron and steric influence of the substituents at the phosphorus atom. 相似文献
53.
Larisa G. Shaidarova Larisa G. Popesku Nikolay A. Ulakhovich Herman C. Budnikov Nail G. Zabirov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract Crown-containing N-(thio)phosphoryl(thio)ureas are related to a class of NH-acids due to the presence of two acceptor-groups: (thio)phosphorylic and (thio)acylic. In agreement with structure of lariat ether, it was observed a stage corresponding to the step ejection of two H* ion on the potentiometric titration curve of ligand by alkaline. Calculated step ionization constants demonstrate that these compounds are weak acids with relative values of pK1 and pK2. 相似文献
54.
Alexey V. Laptev Dmitrii E. Pugachev Alexey Yu. Lukin Andrei V. Nechaev Nikolay E. Belikov Olga V. Demina Petr P. Levin Andrey A. Khodonov Andrey F. Mironov Sergei D. Varfolomeev Vitalii I. Shvets 《Mendeleev Communications》2013,23(4):199-201
A new 5,10,15,20-tetrasubstituted porphyrin containing four 6’-nitro-1,3,3-trimethylspiro(indolino-2,2’-2H-chromene) substituents and its complexes with Zn2+ and Cu2+ ions were prepared and characterized by physicochemical methods of analysis. 相似文献
55.
Novella F. Kazanskaya Margarita A. Manenkova Nikolay L. Eremeev 《Applied biochemistry and biotechnology》1996,61(1-2):57-65
The coupling of photosensitive reagents has been carried out with the goal of obtaining the predetermined distribution of binding sites either for “surface” or “spacial” immobilization of biomacromolecules. The correlation holds between light intensity and the number of readant groups emerged in a matrix. 相似文献
56.
Lukyanenko NG Kirichenko TI Lyapunov AY Mazepa AV Simonov YA Fonari MS Botoshansky MM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,11(1):262-270
The first three representatives of the new family of oxacyclophanes incorporating two 2,7-dioxyfluorenone fragments, connected by [-CH(2)CH(2)O-](m) spacers (m=2-4), have been synthesized. The yield of the smallest oxacyclophane (m=2) is considerably higher with respect to the larger ones (m=3 and m=4), which are formed in comparable yields. Molecular modeling and NMR spectra analysis of the model compounds suggest that an essential difference in oxacyclophanes yields is caused by formation of quasi-cyclic intermediates, which are preorganized for macrocyclization owing to intramolecular pi-pi stacking interactions between the fluorenone units. The solid-state structures of these oxacyclophanes exhibit intra- and intermolecular pi-pi stacking interactions that dictate their rectangular shape in the fluorenone backbone and crystal packing of the molecules with the parallel or T-shape arrangement. The crystal packing in all cases is also sustained by weak C--HO hydrogen bonds. FAB mass spectral analysis of mixtures of the larger oxacyclophanes (m=3 and m=4) and a paraquat moiety revealed peaks corresponding to the loss of one and two PF(6) (-) counterions from the 1:1 complexes formed. However, no signals were observed for complexes of the paraquat moiety with the smaller oxacyclophane (m=2). Computer molecular modeling of complexes revealed a pseudorotaxane-like incorporation of the paraquat unit, sandwiched within a macrocyclic cavity between the almost parallel-aligned fluorenone rings of the larger oxacyclophanes (m=3 and m=4). In contrast to this, only external complexes of the smallest oxacyclophane (m=2) with a paraquat unit have been found in the energy window of 10 kcal mol(-1). 相似文献
57.
Nikolay Manov 《Tetrahedron》2004,60(10):2387-2391
A solid-phase route for synthesis of 15N-labeled acylpolyamines is described. Utilizing alkylation at benzylic N-atom as a key step, 15N-atoms are incorporated by stepwise construction of the polyamine framework on the solid support. The derivatives were used as reference compounds for the investigation of the MS/MS behavior of spider toxins. 相似文献
58.
Oxana Nipruk Nikolay Chernorukov Natalya Zakharycheva Elena Kostrova 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(1):519-529
Uranyl silicates with formula MII(HSiUO6)2·6H2O (MII=Mn, Co, Ni, Cu, Zn) were investigated in aqueous solutions in the pH range of 0÷14. The pH interval was established where compounds preserve their composition and structure. It varies in the pH range of (3.5–4.0)÷(10.8–11.4) and depends on MII type. Out of this pH interval investigated uranyl silicates convert to the compounds of other composition and structure, such as amorphous silica, polyuranates and hydroxides of 3d-transition elements. The solubility of MII(HSiUO6)2·6H2O was determined, it’s value changes on the several orders of magnitude from 10?6 M in subalkali solutions to 10?3 M in acid and strongly alkaline media. Using obtained experimental data the solubility products and solubility curves of uranyl silicates were calculated by mathematical modeling. Also the speciation diagrams of uranium (VI), silicon (IV) and M (II) in solutions and solids were plotted. 相似文献
59.
Mircho Georgiev Tatiana Popova Zhorro S. Nickolov Nikolay Goutev Georgi Georgiev Hiroatsu Matsuura 《Central European Journal of Chemistry》2004,2(4):617-626
The hypothesis that the degree of hydration of poly(oxyethylene) (POE) in aqueous solution depends on the mole ratio of water
molecules to ether oxygen atoms in the molecule has been verified by studying the isotropic Raman spectra in the O−H stretching
region for four short-chain POEs (C 1E
n
C 1 withn=1−4). Excellent coincidence of the O−H stretching Raman band for all four POEs studied in the range of mole ratio H2O/O
ether
from 25 to 0.6 was observed, thus confirming the assumption stated above. A conclusion that all ether oxygen atoms in the
POE molecule participate in hydrogen bonding with water molecules has been made. 相似文献
60.
The relationship of the microstructure of supercooled, highly viscous glycerol to the temperature dependence of its density, thermal expansion coefficient, and shear viscosity are discussed. The character of this temperature dependence at the transition from low viscosity state to the solid amorphous state (solidified state without nuclei) is described with help of function psi, which can be interpreted as the effective number of degrees of freedom responsible for the change of viscosity of glycerol over a broad range; these degrees of freedom are those related to the alpha-relaxation process. It is shown that the change in effective activation energy of the viscosity is completely determined by the parameter psi. The change in the shear viscosity of glycerol due to the influence of the solid-phase nuclei is considered. It is shown that the introduction of the parameter phi, equal to the specific volume occupied by the nuclei of the solid phase, together with psi provides a natural explanation of the temperature dependence of density and thermal expansion coefficients of glycerol in its liquid, solid amorphous, glassy, and crystal states. The peculiarities of the temperature dependence of phi(T) and psi(T) for glycerol and o-terphenyl are compared. 相似文献