全文获取类型
收费全文 | 1149篇 |
免费 | 38篇 |
国内免费 | 7篇 |
专业分类
化学 | 864篇 |
晶体学 | 5篇 |
力学 | 21篇 |
数学 | 93篇 |
物理学 | 211篇 |
出版年
2022年 | 15篇 |
2021年 | 10篇 |
2020年 | 22篇 |
2019年 | 11篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 21篇 |
2015年 | 14篇 |
2014年 | 22篇 |
2013年 | 40篇 |
2012年 | 47篇 |
2011年 | 71篇 |
2010年 | 31篇 |
2009年 | 18篇 |
2008年 | 63篇 |
2007年 | 76篇 |
2006年 | 75篇 |
2005年 | 58篇 |
2004年 | 65篇 |
2003年 | 55篇 |
2002年 | 27篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1998年 | 15篇 |
1997年 | 23篇 |
1996年 | 25篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 16篇 |
1976年 | 19篇 |
1975年 | 20篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1971年 | 7篇 |
1932年 | 7篇 |
排序方式: 共有1194条查询结果,搜索用时 93 毫秒
71.
The gas‐phase acidities (GA) of various aryl‐substituted fluoroalkanes, XC6H4CH(R1)R2, were calculated at the B3LYP/6‐311 + G(d,p)//B3LYP/6‐311 + G(d,p). The acidity values of alkanes having a common substituent X varied significantly with the change of R1 and R2. Their changes in acidity of 1 and 2 having two strong electron‐withdrawing groups (CF3 or C2F5) at the deprotonation site and 8 , 9 , 10 , 11 having no fluorine atom at β‐position were linearly correlated with the corrected number of fluorine atoms contained in the fluorinated alkyl group (R2 > 0.999). On the other hand, the GA values of β‐fluorine substituted alkanes ( 3 , 4 , 5 , 6 , 7 ) deviated in a stronger acid direction from the line. The enhanced acidity was attributed to the additional stabilization of the conjugate anion caused by the β‐fluorine negative hyperconjugation. The magnitude of β‐fluorine negative hyperconjugation of the fluorinated alkyl group (ΔGoβ‐F) given by the deviations from the line decreased with increasing electron‐withdrawing ability of substituent X on the benzene ring, indicating that β‐fluorine negative hyperconjugation competes with the electronic effect of the substituent X. The GAel values obtained by subtraction ΔGoβ‐F from the apparent GA value were successfully correlated in terms of the Yukawa–Tsuno equation. The obtained ρel and r?el values were linearly related to the GAel value of the respective phenyl‐substituted fluoroalkanes, supporting our previous conclusion that the ρ and r? values for the substituent effect caused by the electronic effects of the substituent on the acidity are determined by the thermodynamic stability of the parent ion (ring substituent = H). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
72.
Evolution of Actinyl Peroxide Clusters U28 in Dilute Electrolyte Solution: Exploring the Transition from Simple Ions to Macroionic Assemblies
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Dong Li Silas Simotwo Prof. Dr. May Nyman Prof. Dr. Tianbo Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1683-1690
Actinyl peroxide clusters, a unique class of uranyl‐containing nanoclusters discovered in recent years, are crucial intermediates between the (UO2)2+ aqua‐ion monomer and bulk uranyl minerals. Herein, two actinyl polyoxometalate nanoclusters of Cs15[(Ta(O2)4)Cs4K12(UO2(O2)1.5)28] ? 20 H2O (CsK U28 ) and Na6K9[(Ta(O2)4)Rb4Na12(UO2(O2)1.5)28] ? 20 H2O (RbNa U28 ) were synthesized by incorporating a central Ta(O2)43? anion that templates a hollow shell of 28 uranyl peroxide polyhedra. When dissolved in aqueous solutions with additional electrolytes, those 1.8 nm‐size macroanions self‐assembled into spherical, hollow, blackberry‐type supramolecular structures, as was characterized by laser‐light scattering (LLS) and TEM techniques. These clusters are the smallest macroions reported to date that form blackberry structures in solution, therefore, can be treated as valuable models for investigating the transition from simple ions to macroions. Kinetic studies showed an unusually long lag phase in the initial self‐assembly process, which is followed by a rapid formation of the blackberry structures in solution. The small cluster size and high surface‐charge density are essential in regulating the supramolecular structure formation, as was shown from the high activation energy barrier of 51.2±2 kJ mol?1. Different countercations were introduced into the system to investigate the effect of ion binding to the length of the lag phase. The current research provides yet another scale of self‐assembly of uranyl peroxide complexes in aqueous media. 相似文献
73.
74.
Jens Moons Dr. Francisco de Azambuja Jelena Mihailovic Karoly Kozma Dr. Katarina Smiljanic Mehran Amiri Prof. Tanja Cirkovic Velickovic Prof. May Nyman Prof. Tatjana N. Parac-Vogt 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9179-9186
The selective hydrolysis of proteins by non-enzymatic catalysis is difficult to achieve, yet it is crucial for applications in biotechnology and proteomics. Herein, we report that discrete hafnium metal-oxo cluster [Hf18O10(OH)26(SO4)13⋅(H2O)33] ( Hf18 ), which is centred by the same hexamer motif found in many MOFs, acts as a heterogeneous catalyst for the efficient hydrolysis of horse heart myoglobin (HHM) in low buffer concentrations. Among 154 amino acids present in the sequence of HHM, strictly selective cleavage at only 6 solvent accessible aspartate residues was observed. Mechanistic experiments suggest that the hydrolytic activity is likely derived from the actuation of HfIV Lewis acidic sites and the Brønsted acidic surface of Hf18 . X-ray scattering and ESI-MS revealed that Hf18 is completely insoluble in these conditions, confirming the HHM hydrolysis is caused by a heterogeneous reaction of the solid Hf18 cluster, and not from smaller, soluble Hf species that could leach into solution. 相似文献
75.
76.
Coy L. May 《代数通讯》2013,41(11):4078-4095
Let G be a finite group. The symmetric genus σ (G) is the minimum genus of any compact Riemann surface on which G acts faithfully as a group of automorphisms. Here we classify the groups of symmetric genus σ, for all values of σ such that 4 ≤ σ ≤ 8. In addition, we obtain some general results about the partial presentations that groups acting on surfaces must have. We show that a group with even genus and no “large order” elements in its Sylow 2-subgroup has restrictions on its Sylow 2-subgroup. As a consequence, we show that if G is a 2-group with positive symmetric genus, then σ(G) is odd. The software package MAGMA was employed to help with the calculations, and the MAGMA library of small groups was essential to the classification. 相似文献
77.
Dr. Pere Miró Dr. Bess Vlaisavljevich Dr. Adria Gil Dr. Peter C. Burns Dr. May Nyman Dr. Carles Bo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8571-8578
A wide range of uranyl–peroxide nanocapsules have been synthesized using very simple reactants in basic media; however, little is known about the process to form these species. We have performed a density functional theory study of the speciation of the uranyl ions under different experimental conditions and explored the formation of dimeric species via a ligand exchange mechanism. We shed some light onto the importance of the excess of peroxide and alkali counterions as a thermodynamic driving force towards the formation of larger uranyl–peroxide species. 相似文献
78.
79.
80.
Christopher J. Morris Brian Mary Sara Barron Omar Knio Ralph Hodgin Chadd May 《Journal of Physics and Chemistry of Solids》2010,71(2):84-1650
Research into nanoenergetic materials is enabling new capabilities for controlling exothermic reaction rates and energy output, as well as new methods for integrating these materials with conventional electronics fabrication techniques. Many reactions produce primarily heat, and in some cases it is desirable to increase the rate of heat release beyond what is typically observed. Here we investigate the Al-Ni intermetallic reaction, which normally propagates across films or foils at rates lower than 10 m/s. However, models and experiments indicate that local heating rates can be very high (107 K/s), and uniform heating of such a multilayer film can lead to a rapid, thermally explosive type of reaction. With the hopes of using a device to transduce electrical energy to kinetic energy of a flyer plate in the timescale of 100's of nanoseconds, we have incorporated a Ni/Al nanolayer film that locally heats upon application of a large electrical current. We observed flyer plate velocities in the 2-6 km/s range, corresponding to 4-36 kJ/g in terms of specific kinetic energy. Several samples containing Ni/Al films with different bilayer thicknesses were tested, and many produced additional kinetic energy in the 1.1-2.3 kJ/g range, as would be expected from the Ni-Al intermetallic reaction. These results provide evidence that nanoscale Ni/Al layers reacted in the timescale necessary to contribute to device output. 相似文献