全文获取类型
收费全文 | 643篇 |
免费 | 37篇 |
专业分类
化学 | 550篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 70篇 |
物理学 | 54篇 |
出版年
2023年 | 7篇 |
2022年 | 24篇 |
2021年 | 30篇 |
2020年 | 24篇 |
2019年 | 26篇 |
2018年 | 12篇 |
2017年 | 15篇 |
2016年 | 21篇 |
2015年 | 32篇 |
2014年 | 36篇 |
2013年 | 40篇 |
2012年 | 53篇 |
2011年 | 48篇 |
2010年 | 30篇 |
2009年 | 19篇 |
2008年 | 44篇 |
2007年 | 29篇 |
2006年 | 36篇 |
2005年 | 30篇 |
2004年 | 42篇 |
2003年 | 29篇 |
2002年 | 23篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 6篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有680条查询结果,搜索用时 31 毫秒
81.
Human serum albumin consists of a single polypeptide of 585 amino acid residues with 1 Trp residue. In the present work, we
measured fluorescence lifetimes of the protein in both native and denatured states. The results indicate that Trp emission
occurs with three lifetimes in both states. Lifetimes values and contribution to the global emission decay differ between
the two states. Data are interpreted as the results of an emission occurring from three substructures of the tryptophan formed
in the excited state. Two of these substructures are already present for the tryptophan free in solution. The third lifetime
is the result of the interaction between the tryptophan residue and surrounding microenvironment. The populations of these
substructures characterized by the pre-exponential parameters of the fluorescence lifetimes are dependent on the fluorophore
microenvironment and on the global protein structure. 相似文献
82.
Cole ML Deacon GB Forsyth CM Konstas K Junk PC 《Dalton transactions (Cambridge, England : 2003)》2006,(27):3360-3367
Treatment of calcium or strontium with 2.0 equivalents of N,N-bis(o-methylphenyl)formamidine (o-TolFormH), N,N-bis(2,6-dimethylphenyl)formamidine (XylFormH) or N,N-bis(o-phenylphenyl)formamidine (o-PhPhFormH) in the presence of 1.0 equivalent of Hg(C6F5)2 in tetrahydrofuran (thf) affords the bis(formamidinate) complexes [Ca(o-TolForm)2(thf)2] (1), [Ca(XylForm)2(thf)2] (2), [Ca(o-PhPhForm)2(thf)2].thf (3), [Sr(o-TolForm)2(thf)3] (4), [Sr(XylForm)2(thf)3].3thf (5) and [Sr(o-PhPhForm)2(thf)3].2thf (6). Analogous reactions with barium were generally unsatisfactory but [Ba(o-PhPhForm)2(thf)3].2thf (7) was successfully prepared. Compounds 1-7 have been characterised by various spectroscopic methods (1H, 13C{1H} NMR and IR), elemental analyses and, for 1, 2 and 4-6, X-ray crystallography. The calcium complexes are monomeric and six-coordinate with either transoid octahedral or trigonal prismatic geometry, whilst the larger radius of strontium accommodates an additional thf solvent donor to give seven-coordinate structures with two types of coordination polyhedra. 相似文献
83.
Hartung J Daniel K Gottwald T Gross A Schneiders N 《Organic & biomolecular chemistry》2006,4(11):2313-2322
Microwave irradiation (2.45 GHz, 300-500 W) of N-(alkoxy)thiazole-2(3H)-thiones in low-absorbing solvents affords alkoxyl radicals, which were identified by (i) spin adduct formation (EPR-spectroscopy) and (ii) fingerprint-type selectivities in intramolecular additions (stereoselective synthesis of disubstituted tetrahydrofurans), beta-fragmentations (formation of carbonyl compounds), and C,H-activation of aliphatic subunits, by delta-selective hydrogen atom transfer. C-Radicals formed from oxygen-centered intermediates were trapped either by Bu(3)SnH, L-cysteine ethyl ester, the reduced form of glutathione (reductive trapping), or by bromine atom donor BrCCl(3) (heteroatom functionalization) The results suggest that microwave activation is superior to UV/Vis-photolysis and conductive heating for alkoxyl radical generation from N-(alkoxy)thiazolethiones. It offers by far the shortest reaction times along with the option to reduce the amount of trapping reagent significantly. 相似文献
84.
Mass spectrometry (MS) is extensively used for the identification and sequencing of nucleic acids but has so far seen limited
use for characterization of their higher order structures. Here, we have applied a range of different tandem mass spectrometry
techniques, including electron detachment dissociation (EDD), infrared multiphoton dissociation (IRMPD), activated ion (AI)
EDD, and EDD/IRMPD MS3, in a Fourier transform ion cyclotron resonance mass spectrometer to the characterization of three isomeric 15mer DNAs with
different sequences and predicted solution-phase structures. Our goal was to explore whether their structural differences
could be directly probed with these techniques. We found that all three 15mers had higher order structures in the gas phase,
although preferred structures were predicted for only two of them in solution. Nevertheless, EDD, AI EDD, and EDD/IRMPD MS3 experiments yielded different cleavage patterns with less backbone fragmentation for the more stable solution-phase structure
than for the other two 15mers. By contrast, no major differences were observed in IRMPD, although the extent of backbone cleavage
was higher with that technique for all three 15mers. Thus, experiments utilizing the radical ion chemistry of EDD can provide
complementary structural information compared to traditional slow heating methods, such as IRMPD, for structured nucleic acids. 相似文献
85.
86.
87.
In a reaction-diffusion system, diffusion can induce the instability of a uniform equilibrium which is stable with respect to a constant perturbation, as shown by Turing in 1950s. We show that cross-diffusion can destabilize a uniform equilibrium which is stable for the kinetic and self-diffusion reaction systems; on the other hand, cross-diffusion can also stabilize a uniform equilibrium which is stable for the kinetic system but unstable for the self-diffusion reaction system. Application is given to predator-prey system with preytaxis and vegetation pattern formation in a water-limited ecosystem. 相似文献
88.
We apply the method of homotopy analysis to the Zakharov system with dissipation in order to obtain analytical solutions, treating the auxiliary linear operator as a time evolution operator. Evolving the approximate solutions in time, we construct approximate solutions which depend on the convergence control parameters. In the situation where solutions are strongly coupled, there will be multiple convergence control parameters. In such cases, we will pick the convergence control parameters to minimize a sum of squared residual errors. We explain the error minimization process in detail, and then demonstrate the method explicitly on several examples of the Zakharov system held subject to specific initial data. With this, we are able to efficiently obtain approximate analytical solutions to the Zakharov system of minimal residual error using approximations with relatively few terms. 相似文献
89.
Kristina Rognlien Dahl 《Applied Mathematics and Optimization》2013,68(2):145-155
We consider the pricing problem of a seller with delayed price information. By using Lagrange duality, a dual problem is derived, and it is proved that there is no duality gap. This gives a characterization of the seller’s price of a contingent claim. Finally, we analyze the dual problem, and compare the prices offered by two sellers with delayed and full information respectively. 相似文献
90.
Lena Quambusch Ina Landel Laura Depta Jrn Weisner Niklas Uhlenbrock Matthias P. Müller Franziska Glanemann Kristina Althoff Jens T. Siveke Daniel Rauh 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(52):18999-19005
Isoforms of protein kinase Akt are involved in essential processes including cell proliferation, survival, and metabolism. However, their individual roles in health and disease have not been thoroughly evaluated. Thus, there is an urgent need for perturbation studies, preferably mediated by highly selective bioactive small molecules. Herein, we present a structure‐guided approach for the design of structurally diverse and pharmacologically beneficial covalent‐allosteric modifiers, which enabled an investigation of the isoform‐specific preferences and the important residues within the allosteric site of the different isoforms. The biochemical, cellular, and structural evaluations revealed interactions responsible for the selective binding profiles. The isoform‐selective covalent‐allosteric Akt inhibitors that emerged from this approach showed a conclusive structure–activity relationship and broke ground in the development of selective probes to delineate the isoform‐specific functions of Akt kinases. 相似文献