全文获取类型
收费全文 | 156篇 |
免费 | 17篇 |
专业分类
化学 | 142篇 |
数学 | 9篇 |
物理学 | 22篇 |
出版年
2023年 | 7篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 12篇 |
2013年 | 9篇 |
2012年 | 19篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 4篇 |
2007年 | 5篇 |
2006年 | 12篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有173条查询结果,搜索用时 46 毫秒
21.
Covalent side-chain cross-linking has been shown to be a viable strategy to control peptide folding. We report here that an oxime side-chain linkage can elicit α-helical folds from peptides in aqueous solution. The bio-orthogonal bridge is formed rapidly under neutral buffered conditions, and the resulting cyclic oximes are capable of dynamic covalent exchange. 相似文献
22.
Conor S. Barry 《Tetrahedron letters》2007,48(46):8192-8195
Hydroamination of cinnamyl alcohol is possible by reaction with lithium amides derived from primary or cyclic secondary amines. 相似文献
23.
Burke CS McGaughey O Sabattié JM Barry H McEvoy AK McDonagh C MacCraith BD 《The Analyst》2005,130(1):41-45
This paper describes the development of a generic platform for enhanced, integrated optic sensors based on fluorescence detection. The platform employs a novel optical configuration in order to achieve enhanced performance and has inherent multianalyte detection capability. The sensor element comprises a multimode ridge waveguide that has been patterned with an analyte-sensitive fluorescent spot, which is excited directly using a LED. The platform was applied to the detection of gaseous oxygen as a proof of principle. The sol-gel-derived sensor spots were doped with an oxygen-sensitive fluorescent dichlororuthenium dye complex and intensity-based calibration data were generated from the oxygen-dependent waveguide output. The sensor achieved a LOD of 0.62% and a resolution of less than 0.96% gaseous oxygen, which compares favourably with a similar, recently reported system. This device highlights the combination of inexpensive rapid prototyping techniques and a dedicated sensor enhancement strategy that together facilitate the production of an effective prototype sensor platform. 相似文献
24.
Reingold JA Uk Son S Bok Kim S Dullaghan CA Oh M Frake PC Carpenter GB Sweigart DA 《Dalton transactions (Cambridge, England : 2003)》2006,(20):2385-2398
Coordination of the carbocyclic ring of hydroquinones to electrophilic transition-metal fragments such as Mn(CO)3+ and Rh(COD)+ produces stable pi-bonded eta6-complexes that are activated to facile reversible deprotonation of the -OH groups. The deprotonations are accompanied by electron transfer to the transition metal, which acts as an internal oxidizing agent or electron sink. With manganese as the metal, the resulting eta5-semiquinone and eta4-quinone complexes have been used to synthesize one- two- and three-dimensional polymeric metal-organometallic coordination networks. With rhodium as the metal, the pi-quinonoid complexes have been demonstrated to play a unique role in multifunctional C-C coupling catalysis and in the synthesis of new organolithium reagents. Both classes of pi-quinonoid complexes appear to have significant applications in nanochemistry by providing an excellent vehicle for templating the directed self-assembly of nanoparticles into functional materials. 相似文献
25.
High-order differentiation matrices as calculated in spectral collocation methods usually include a large round-off error and have a large condition number (Baltensperger and Berrut Computers and Mathematics with Applications 37(1), 41–48 1999; Baltensperger and Trummer SIAM J. Sci. Comput. 24(5), 1465–1487 2003; Costa and Don Appl. Numer. Math. 33(1), 151–159 2000). Wang et al. (Wang et al. SIAM J. Sci. Comput. 36(3), A907–A929 2014) present a method to precondition these matrices using Birkhoff interpolation. We generalize this method for all orders and boundary conditions and allowing arbitrary rows of the system matrix to be replaced by the boundary conditions. The preconditioner is an exact inverse of the highest-order differentiation matrix in the equation; thus, its product with that matrix can be replaced by the identity matrix. We show the benefits of the method for high-order differential equations. These include improved condition number and, more importantly, higher accuracy of solutions compared to other methods. 相似文献
26.
Although some of the earliest Estimation of Distribution Algorithms (EDAs) utilized bivariate marginal distribution models, up to now, all discrete bivariate EDAs had one serious limitation: they were constrained to exploiting only a limited O(d) subset out of all possible \(O(d^{2})\) bivariate dependencies. As a first we present a family of discrete bivariate EDAs that can learn and exploit all \(O(d^{2})\) dependencies between variables, and yet have the same run-time complexity as their more limited counterparts. This family of algorithms, which we label DICE (DIscrete Correlated Estimation of distribution algorithms), is rigorously based on sound statistical principles, and particularly on a modelling technique from statistical physics: dichotomised multivariate Gaussian distributions. Initially (Lane et al. in European Conference on the Applications of Evolutionary Computation, Springer, 1999), DICE was trialled on a suite of combinatorial optimization problems over binary search spaces. Our proposed dichotomised Gaussian (DG) model in DICE significantly outperformed existing discrete bivariate EDAs; crucially, the performance gap increasingly widened as dimensionality of the problems increased. In this comprehensive treatment, we generalise DICE by successfully extending it to multary search spaces that also allow for categorical variables. Because correlation is not wholly meaningful for categorical variables, interactions between such variables cannot be fully modelled by correlation-based approaches such as in the original formulation of DICE. Therefore, here we extend our original DG model to deal with such situations. We test DICE on a challenging test suite of combinatorial optimization problems, which are defined mostly on multary search spaces. While the two versions of DICE outperform each other on different problem instances, they both outperform all the state-of-the-art bivariate EDAs on almost all of the problem instances. This further illustrates that these innovative DICE methods constitute a significant step change in the domain of discrete bivariate EDAs. 相似文献
27.
Barry CS Elsworth JD Seden PT Bushby N Harding JR Alder RW Willis CL 《Organic letters》2006,8(15):3319-3322
[Structure: see text] The total synthesis of the marine metabolite clavosolide A is reported which confirms the structure and absolute configuration of the natural product as the symmetrical diolide glycosylated by permethylated D-xylose moieties, 2. 相似文献
28.
Conor T. Graham Simon S.C. Harrison Chris Harrod 《Isotopes in environmental and health studies》2013,49(4):555-566
The preferred tissue for analyses of fish stable isotope ratios for most researchers is muscle, the sampling of which typically requires the specimen to be sacrificed. The use of non-destructive methods in fish isotopic research has been increasing recently, but as yet is not a standard procedure. Previous studies have reported varying levels of success regarding the utility of non-lethally obtained stable isotope materials, e.g. fins, but none have accounted for the potential compounding effects of inorganic components of fin rays or lipids. Comparisons of carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of muscle with adipose and caudal fin of two salmonids, Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.), revealed that caudal fin can be used as a non-destructive surrogate for muscle in stable isotope analysis, but that adipose fin, where available, is a better proxy. The use of a published model to inexpensively counteract the confounding effect of lipids, which are depleted in 13C, greatly improved the relationship between fish muscle and fins. However, efforts to account for the inorganic components of fin rays were counterproductive and required twice the biomass of fins clipped from each fish. As this experiment was conducted on wild fish, controlled laboratory studies are required to confirm these field observations. 相似文献
29.
Natasha S. Adamson Ashton G. Theakstone Lachlan C. Soulsby Egan H. Doeven Emily Kerr Conor F. Hogan Paul S. Francis Lynn Dennany 《Chemical science》2021,12(28):9770
We present a new approach to explore the potential-dependent multi-colour co-reactant electrochemiluminescence (ECL) from multiple luminophores. The potentials at both the working and counter electrodes, the current between these electrodes, and the emission over cyclic voltammetric scans were simultaneously measured for the ECL reaction of Ir(ppy)3 and either [Ru(bpy)3]2+ or [Ir(df-ppy)2(ptb)]+, with tri-n-propylamine as the co-reactant. The counter electrode potential was monitored by adding a differential electrometer module to the potentiostat. Plotting the data against the applied working electrode potential and against time provided complementary depictions of their relationships. Photographs of the ECL at the surface of the two electrodes were taken to confirm the source of the emissions. This provided a new understanding of these multifaceted ECL systems, including the nature of the counter electrode potential and the possibility of eliciting ECL at this electrode, a mechanism-based rationalisation of the interactions of different metal-complex luminophores, and a previously unknown ECL pathway for the Ir(ppy)3 complex at negative potentials that was observed even in the absence of the co-reactant.Exploration of potential-dependent, multi-colour co-reactant electrochemiluminescence from multiple luminophores at the working and counter electrodes reveals new pathways to emission. 相似文献
30.