全文获取类型
收费全文 | 351篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 166篇 |
晶体学 | 7篇 |
力学 | 13篇 |
数学 | 84篇 |
物理学 | 95篇 |
出版年
2022年 | 4篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 20篇 |
2012年 | 16篇 |
2011年 | 14篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 16篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1966年 | 2篇 |
1957年 | 2篇 |
1956年 | 6篇 |
1955年 | 4篇 |
1936年 | 13篇 |
排序方式: 共有365条查询结果,搜索用时 15 毫秒
281.
282.
Blue light-emitting and hole-transporting amorphous molecular materials based on diarylaminobiphenyl-functionalized bimesitylenes 总被引:1,自引:0,他引:1
Moorthy JN Venkatakrishnan P Huang DF Chow TJ 《Chemical communications (Cambridge, England)》2008,(18):2146-2148
The diarylaminobiphenyl-functionalized bimesityls and exhibit amorphous nature, high thermal stability and excellent blue emission in the solid state. They serve as both hole-transporting and emissive materials in OLEDs for blue emission with high external quantum efficiencies. 相似文献
283.
284.
A rhodium-catalyzed chelation-assisted C-H activation of alpha,beta-unsaturated ketoximes and the reaction with alkynes to afford highly substituted pyridine derivatives is described. 相似文献
285.
Parthasarathy M Singh S Hazra S Pillai VK 《Analytical and bioanalytical chemistry》2008,391(6):2227-2233
The stomatal physiology, chlorophyll distribution and photosynthetic activity of somatic embryo (SE)- and seedling-derived
peanut plants grown in vitro (test tube-grown) and extra vitrum (soil-grown) are investigated using scanning electrochemical microscopy (SECM). This SECM
imaging is performed in two different feedback modes, corresponding to oxygen evolution and chlorophyll distribution. More
specifically, the oxygen evolution profiles of the in vitro leaves indicate important differences in leaf anatomy between the SE- and seedling-derived leaves. On the other hand, the
chlorophyll distribution images show individual stomata of size ca. 27 ± 5μm. Further studies on senescing (aged) leaves reveal
interesting voltammograms that vary widely over the stomatal complexes and the surrounding tissues, probably due to the release
of electroactive metabolites during chlorophyll breakdown when the leaves turn yellow. Thus, the present investigation could
open up new opportunities for characterizing botanical systems using electroanalytical techniques. In addition, it could provide
further insights into various areas of current relevance, including signal transduction, cell fate/differentiation and developmental
biology.
Schematic representation of SECM imaging used in this investigation. The SECM probe is a Pt UME disk (25 μm diameter) embedded
in an insulating glass sheath so that the ratio of the diameter of the death to that of the electrode surface (RG) is 7. RE denotes the reference electrode Ag/AgCl, sat. KCl and CE refers to the counter electrode, a Pt wire. Oxygen evolving from the leaf surface during photosynthesis diffuses into the
electrolyte (0.1 M KCl) and gets reduced at the Pt UME, biased to a potential of −0.5 V, at a diffusion-limited rate to produce
a change in the tip-current 相似文献
286.
Crystal structures are viewed as being determined by ranges and constraints on interatomic contact distances between neighboring molecules. These distances are considered to arise from environment‐dependent atomic sizes, that is, larger sizes for isotropic, van der Waals type contacts and smaller sizes for more‐polar, possibly ionic contacts. Although the idea of different, or anisotropic, radii for atoms is not new, we developed a method of obtaining atomic sizes that is based on a theoretical framework. Using different atomic sizes for the same atom in different environments, we were able to rationalize some structural observations and anomalies. For example, benzene with the Pbca structure may be described in terms of two types of C???H interactions: a longer contact largely of the van der Waals type, and a shorter, structure‐determining type (Cδ????Hδ+), which we term “n‐polar”. Our approach is illustrated with three examples: 1) the equivalence in crystal packing of fluorobenzene, benzonitrile, pyridine N‐oxide, and pyridine/HF 1:1 molecular complex, all of which take the not‐so‐common tetragonal P41212 space group and are practically isomorphous; 2) the similarity of the Pa3 acetylene and Pbca benzene crystal structures; and 3) the equivalence between an increase in pressure and an increase in the “n‐polar” contacts in Pbca benzene; in other words, the equivalence between hydrostatic pressure and chemical pressure. In the context of crystal engineering, we describe a method whereby the topological information conveyed in a supramolecular synthon is recast in a more quantitative manner. A particular synthon, and in turn the crystal structure to which it leads, is viable within small ranges of distances of its constituent atoms, and these distances are determined by chemical factors. 相似文献
287.
Uniform distribution of projection data for improved reconstruction quality of 4D EPR imaging 总被引:2,自引:2,他引:0
Ahmad R Vikram DS Clymer B Potter LC Deng Y Srinivasan P Zweier JL Kuppusamy P 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,187(2):277-287
In continuous wave (CW) electron paramagnetic resonance imaging (EPRI), high quality of reconstruction in a limited acquisition time is a high priority. It has been shown for the case of 3D EPRI, that a uniform distribution of the projection data generally enhances reconstruction quality. In this work, we have suggested two data acquisition techniques for which the gradient orientations are more evenly distributed over the 4D acquisition space as compared to the existing methods. The first sampling technique is based on equal solid angle partitioning of 4D space, while the second technique is based on Fekete points estimation in 4D to generate a more uniform distribution of data. After acquisition, filtered backprojection (FBP) is applied to carry out the reconstruction in a single stage. The single-stage reconstruction improves the spatial resolution by eliminating the necessity of data interpolation in multi-stage reconstructions. For the proposed data distributions, the simulations and experimental results indicate a higher fidelity to the true object configuration. Using the uniform distribution, we expect about 50% reduction in the acquisition time over the traditional method of equal linear angle acquisition. 相似文献
288.
Sujatha Babu Nagarajan Krishnamurthy T. Parthasarathy 《International Journal of Game Theory》2017,46(3):761-782
In this paper, we address various types of two-person stochastic games—both zero-sum and nonzero-sum, discounted and undiscounted. In particular, we address different aspects of stochastic games, namely: (1) When is a two-person stochastic game completely mixed? (2) Can we identify classes of undiscounted zero-sum stochastic games that have stationary optimal strategies? (3) When does a two-person stochastic game possess symmetric optimal/equilibrium strategies? Firstly, we provide some necessary and some sufficient conditions under which certain classes of discounted and undiscounted stochastic games are completely mixed. In particular, we show that, if a discounted zero-sum switching control stochastic game with symmetric payoff matrices has a completely mixed stationary optimal strategy, then the stochastic game is completely mixed if and only if the matrix games restricted to states are all completely mixed. Secondly, we identify certain classes of undiscounted zero-sum stochastic games that have stationary optima under specific conditions for individual payoff matrices and transition probabilities. Thirdly, we provide sufficient conditions for discounted as well as certain classes of undiscounted stochastic games to have symmetric optimal/equilibrium strategies—namely, transitions are symmetric and the payoff matrices of one player are the transpose of those of the other. We also provide a sufficient condition for the stochastic game to have a symmetric pure strategy equilibrium. We also provide examples to show the sharpness of our results. 相似文献
289.
Rhodium(III)‐Catalyzed [4+1] Annulation of Aromatic and Vinylic Carboxylic Acids with Allenes: An Efficient Method Towards Vinyl‐Substituted Phthalides and 2‐Furanones
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. Parthasarathy Gandeepan Dr. Pachaiyappan Rajamalli Prof. Dr. Chien‐Hong Cheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):9198-9203
A highly regio‐ and stereoselective synthesis of 3,3‐disubstituted phthalides from aryl carboxylic acids and allenes using a rhodium(III) catalyst has been demonstrated. The reaction features broad functional group tolerance and provides a simple and straightforward route to the synthesis of various 3‐vinyl‐substituted phthalides. Furthermore, the catalytic reaction can also be applied to the synthesis of biologically active 5‐vinyl‐substituted 2‐furanones from α,β‐unsaturated carboxylic acids and allenes. The reactions proceed through a carboxylate‐assisted ortho‐C?H activation and [4+1] annulation. The preliminary mechanistic studies suggest that a C?H cleavage is the rate‐determining step. 相似文献
290.
A. Abdul Ajees S. Parthasarathy S. Manikandan R. Raghunathan 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(4):473-475
The title compound, C23H15Cl2NO3, crystallizes with two independent molecules in the asymmetric unit. The chromanone moiety consists of a benzene ring fused with a six‐membered heterocyclic ring which adopts a sofa conformation. The five‐membered spiroisoxazoline ring is in an envelope conformation. The p‐chlorophenyl rings bridged by the five‐membered ring are nearly perpendicular to each other. The chromanone moiety of one molecule packs into the cavity formed by the p‐chlorophenyl rings of a second molecule through the formation of C—H?π interactions. The structure is stabilized by weak C—H?O, C—H?Cl and C—H?π interactions. 相似文献