全文获取类型
收费全文 | 1816篇 |
免费 | 52篇 |
国内免费 | 21篇 |
专业分类
化学 | 1089篇 |
晶体学 | 5篇 |
力学 | 44篇 |
数学 | 305篇 |
物理学 | 446篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 28篇 |
2021年 | 29篇 |
2020年 | 43篇 |
2019年 | 52篇 |
2018年 | 42篇 |
2017年 | 33篇 |
2016年 | 59篇 |
2015年 | 54篇 |
2014年 | 53篇 |
2013年 | 124篇 |
2012年 | 100篇 |
2011年 | 117篇 |
2010年 | 80篇 |
2009年 | 65篇 |
2008年 | 136篇 |
2007年 | 128篇 |
2006年 | 129篇 |
2005年 | 118篇 |
2004年 | 98篇 |
2003年 | 70篇 |
2002年 | 74篇 |
2001年 | 38篇 |
2000年 | 24篇 |
1999年 | 21篇 |
1998年 | 26篇 |
1997年 | 28篇 |
1996年 | 27篇 |
1995年 | 19篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1889条查询结果,搜索用时 31 毫秒
91.
Dr. Bhupendra Goswami Dr. Thomas J. Feuerstein Dr. Ravi Yadav Dr. Ralf Köppe Dr. Sergei Lebedkin Prof. Dr. Manfred M. Kappes Prof. Dr. Peter W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(13):4401-4411
The synthesis of calcium complexes ligated by three different chiral iminophosphonamide ligands, L- H ( L =[Ph2P{N(R)CH(CH3)Ph}2]), L′ -H ( L′ =[Ph2P{NDipp}{N(R)CH(CH3)Ph}]), (Dipp=2,6-iPr2C6H3), and L′′ -H ( L′′ =[Ph2P{N(R)CH(CH3)naph}2]), (naph=naphthyl) is presented. The resulting structures [ L 2Ca], [ L′ 2Ca], and [ L′′ 2Ca] represent the first examples of enantiopure homoleptic calcium complexes based on this type of ligands. The calcium complexes show blue–green photoluminescence (PL) in the solid state, which is especially bright at low temperatures. Whereas the emission of [ L′′ 2Ca] is assigned to the fluorescence of naphthyl groups, the PL of [ L 2Ca] and [ L′ 2Ca] is contributed by long-lived phosphorescence and thermally activated delayed fluorescence (TADF), with a strong variation of the PL lifetimes over the temperature range of 5–295 K. Furthermore, an excellent catalytic activity was found for these complexes in hydroboration of ketones at room temperature, although no enantioselectivity was achieved. 相似文献
92.
Iván da Silva Germán R. Castro Zakariae Amghouz Aránzazu Espina Sergei A. Khainakov Santiago García-Granda José R. García 《Journal of Thermal Analysis and Calorimetry》2014,117(3):1179-1186
(C4N2H12)CrO(H1.5PO4)2·H2O has been synthesized hydrothermally using piperazine as organic template. Its crystal structure was solved ab initio using synchrotron powder X-ray diffraction data [monoclinic, a = 16.9649(4) Å, b = 9.8609(2) Å, c = 7.14375(14) Å, and β = 94.896(3)°, space group P21/a, Z = 4]. 1D structure is composed by isolated infinite anionic chains [CrO(H1.5PO4)2]n (vertex-sharing {CrO6} octahedra joined by phosphate moieties). Their 2D plate-like morphology is propitiated by a very strong inter-chain interaction (P–O···H···O–P symmetric hydrogen bonds). KAS isoconversional method was applied to determine the activation energy for both thermal and thermo-oxidative decomposition of (C4N2H12)CrO(H1.5PO4)2·H2O. 相似文献
93.
Valerii F. Traven Dmitriy A. Cheptsov Zarina Z. Mamirgova Natalya P. Solovjova Vyacheslav M. Martynenko Sergei M. Dolotov Michail M. Krayushkin Ivan V. Ivanov 《Photochemistry and photobiology》2020,96(4):798-804
Photophysical characteristics of new 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins have been measured. These coumarin derivatives are found to be effective fluorophores and show high values of quantum yields of fluorescence both in nonpolar and in polar solvents. The 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins turned to be photosensitive compounds and undergo photolysis under irradiation in the range of 310–465 nm. Photolysis is suggested to include retro-cyclization and retro-condensation steps. The process is accompanied by a sharp drop of fluorescence that can be of interest for the creation of new media in optical recording of information. 相似文献
94.
Kirill T. Kalinin Dr. Nikita G. Sedush Petr V. Dmitryakov Prof. Sergei N. Chvalun 《ChemistryOpen》2020,9(10):1027-1032
The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol−1. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy Ea=44.51±5.35 kJ mol−1, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol−1 K−1. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown. 相似文献
95.
Joji Tanaka Satu Hkkinen Parker T. Boeck Yidan Cong Sbastien Perrier Sergei S. Sheiko Wei You 《Angewandte Chemie (International ed. in English)》2020,59(18):7203-7208
An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side‐chain polymers to be grafted from the pendant RAFT agent by a radical‐mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one‐pot tandem without intermediate purification. 相似文献
96.
Chen‐Xi Ye Shuming Chen Feng Han Xiulan Xie Sergei Ivlev K. N. Houk Eric Meggers 《Angewandte Chemie (International ed. in English)》2020,59(32):13552-13556
A transformation of fluxional into configurationally stable axially chiral N‐arylpyrroles was achieved with a highly atroposelective electrophilic aromatic substitution catalyzed by a chiral‐at‐metal rhodium Lewis acid. Specifically, N‐arylpyrroles were alkylated with N‐acryloyl‐1H‐pyrazole electrophiles in up to 93 % yield and with up to >99.5 % ee, and follow‐up conversions reveal the synthetic utility of this new method. DFT calculations elucidate the origins of the observed excellent atroposelectivity. 相似文献
97.
98.
99.
Alexei R. Khokhlov Elena Yu. Kramarenko Elena E. Makhaeva Sergei G. Starodubtzev 《Macromolecular theory and simulations》1992,1(3):105-118
A very simple theory of swelling and collapse of weakly charged polyelectrolyte networks in the solution of an oppositely charged surfactant has been developed. The following contributions to the free energy were taken into account: free energy of volume interaction and of elastic deformation of the network chains, free energy connected with micelle formation and free energy of translational motion of all mobile ions in the system (translational entropy). Both the cases of a solution of charged surfactant and that of a mixed solution of charged and neutral surfactant components have been taken into account. It has been shown that the behaviour of the network depends on the total surfactant concentration in the system and corresponds to one of the three following regimes: At low concentration, micelles inside the network are not formed and the behaviour of the polymer network is similar to that of a network swelling in the solution of a lowmolecular-weight salt (regime 1). In the second regime, surfactant concentration inside the network exceeds the critical micelle concentration and micelles are formed; in this regime the network collapses because surfactant molecules, aggregated in micelles, cease to create “exerting” osmotic pressure in the network sample. In the third regime, at very high surfactant concentration, formation of additional micelles inside the network ceases, and the network dimensions coincide with those of the corresponding neutral network. 相似文献
100.