全文获取类型
收费全文 | 129篇 |
免费 | 10篇 |
专业分类
化学 | 87篇 |
力学 | 7篇 |
数学 | 10篇 |
物理学 | 35篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 10篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 14篇 |
2012年 | 5篇 |
2011年 | 11篇 |
2010年 | 4篇 |
2009年 | 5篇 |
2008年 | 3篇 |
2007年 | 6篇 |
2006年 | 4篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 1篇 |
2002年 | 2篇 |
2000年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 2篇 |
排序方式: 共有139条查询结果,搜索用时 15 毫秒
1.
Karam Asad Dr. Anastasios Stergiou Dr. Andreas Kourtellaris Prof. Nikos Tagmatarchis Prof. Nikos Chronakis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(55):13879-13886
The multiaddition chemistry of azafullerene C59N has been scarcely explored, and the isolation of pure bisadducts is in its infancy. Encouraged by the recent regioselective synthesis of the inherently chiral equatorialface bisadduct of C59N, we focused on the isolation of the first trans-4 bisadduct in a simple two-step approach. The first regioselective synthesis of the trans-4 bisadduct of C59N by using cyclo-[2]-dodecylmalonate as a tether is now reported. The newly synthesized bisadduct has C1 symmetry, as evidenced by 13C NMR, while X-ray crystallography validated the trans-4′ addition pattern. Furthermore, the inherently chiral trans-4′ C59N bisadduct was enantiomerically resolved, and the mirror-image relation of the two enantiomers was probed by circular dichroism spectroscopy. Finally, UV-Vis and redox assays suggested that the addition pattern has a reflection in the light-harvesting and redox properties of the bisadduct. 相似文献
2.
Abdul Qadir Nausheen Khan Muhammad Arif Shehla Nasar Mir Najib Ullah Sauban Ahmed Khan Asad Ali Mohd Imran 《印度化学会志》2022,99(2):100354
Simmondsia chinensis L. commonly called as Jojoba and belongs to family Simmondsiaceae. It has shown positive pharmacological activities of these compounds which include antidiabetic, antirheumatic, anthelminthic, antipsoriatic, antioxidant, antiepileptic, antigonorrheal, analgesic, anti-inflammatory, and pesticidal activity of jojoba. The multifaceted action of numerous bioactives existing in the seed extract with therapeutic activity have attracted great research interest by pharmaceutical industries. n-hexane extract of Simmondsia chinensis L. (SC) Seeds was analysed by gas chromatography-mass spectroscopy for identification and characterization of phytobioconstituents and its therapeutic claim by traditional system. The major compounds discovered in SC seeds extract are cis-9-octadecen-1-ol (24.85%), 9-octadecen-1-ol, (Z)- (18.24%), Stigmast-5-en-3-ol (14.10%), Ergost-5-en-3-ol, (3-β)-ol (5.26%), (Z)-14-tricosenyl formate (5.24%), Thiositosteroldisulfide (3.64%), Silane, Dimethyl (dimethylpentyloxysilyloxy) tetradecyloxy- (3.41%), Ergost-5-ene, 3-methoxy-, (3β,24R)- (2.55%), Ergosta-5,22-dien-3-ol (2.22%), 1,19-eicosadiene (2.17%), Pentacosane (2.02%), Stigmasta-5,22-dien-3-ol (1.64%), 1,19-eicosadiene (1.57%), 9-octadecen-1-ol, (Z)- (1.46%), 9,19-cyclo-9β-lanostan-3β-ol, 24-methylene- (1.14%), (9Z)-9-octadecenyl palmitate (1.50%), Hexadecanoic acid, 9-octadecenyl ester, (Z) (1.37%), 9Z)-9-octadecenyl (9Z)-9-hexadecenoate (1.01%). The hexane extract of Simmondsia chinensis seeds comprises various polar and nonpolar phytobioconstituents. These compounds were established qualitatively via GC-MS evaluation. GC-MS reports will be promising in pharmaceutical sector in identification of variety of Phytobioconstituents in distinct plant extracts, polyherbal extract and the standardization of particular plant materials. 相似文献
3.
Vijayakumar Uppar Sandeep Chandrashekharappa Chandan Shivamallu Sushma P Shiva Prasad Kollur Joaquín Ortega-Castro Juan Frau Norma Flores-Holguín Atiyaparveen I. Basarikatti Mallikarjun Chougala Mrudula Mohan M Govindappa Banuprakash Jayadev Katharigatta N. Venugopala Belakatte P. Nandeshwarappa Ravindra Veerapur Abdulaziz A. Al-Kheraif Abdallah M. Elgorban Asad Syed Kiran K. Mudnakudu-Nagaraju Basavaraj Padmashali Daniel Glossman-Mitnik 《Molecules (Basel, Switzerland)》2021,26(9)
4.
Heck cross-coupling reactions of 2,3-dichloropyrazine provide a convenient approach to 2,3-dialkenyl-, 2-alkenyl-3-alkyl-, and 2,3-dialkylpyrazines depending on the reaction conditions. 相似文献
5.
The single crystalline form of an insulator, Sr(3)CuIrO(6+delta), is shown to exhibit unexpectedly more than one magnetic transition (at 5 and 19 K) with spin-glass-like magnetic susceptibility behavior. On the basis of this finding, viz., inhomogeneous magnetism in a chemically homogeneous material, we propose that the idea of "phase separation" described for manganites is more widespread in different ways. The observed experimental features enable us to make a comparison with the predictions of a recent toy model on magnetic phase separation in an insulating environment. 相似文献
6.
J.?H.?Asad R.?S.?Hijjawi A.?Sakaj J.?M.?KhalifehEmail author 《International Journal of Theoretical Physics》2005,44(4):471-483
The resistance between arbitrary sites of infinite square network of identical resistors is studied when the network is perturbed by removing two bonds from the perfect lattice. A connection is made between the resistance and the lattice Green’s function of the perturbed network. By solving Dyson’s equation the Green’s function and the resistance of the perturbed lattice are expressed in terms of those of the perfect lattice. Some numerical results are presented for an infinite square lattice. 相似文献
7.
We explore the phases of
supersymmetric U(N) gauge theories with fundamental matter that arise as deformations of
SQCD by the addition of a superpotential for the adjoint chiral multiplet. As the parameters in the superpotential are varied, the vacua of this theory sweep out various branches, which in some cases have multiple semiclassical limits. In such limits, we recover the vacua of various product gauge group theories, with flavors charged under some group factors. We describe in detail the structure of the vacua in both classical and quantum regimes, and develop general techniques such as an addition and a multiplication map which relate vacua of different gauge theories. We also consider possible indices characterizing different branches and potential relationships with matrix models. 相似文献
8.
Asad Ali Munawar Hussain Imran Malik Alexander Villinger Christine Fischer Peter Langer 《Helvetica chimica acta》2010,93(9):1764-1772
Double Heck cross‐coupling reactions of 2,3‐ and 3,5‐dibromopyridine with various alkenes afforded the corresponding novel di(alkenyl)pyridines. The Heck reaction of 2,5‐dibromopyridine unexpectedly afforded 5,5′‐di(alkenyl)‐2,2′‐bipyridines by palladium‐catalyzed dimerization to give 5,5′‐dibromo‐2,2′‐bipyridine and subsequent twofold Heck reaction. 相似文献
9.
We study the message queueing delays in a node of a communication system, where a message consists of a block of consecutive packets. The message delay is defined as the time elapsing between the arrival epoch of the first packet of the message to the system until after the transmission of the last packet of that message is completed. We distinguish between two types of message generation processes. The message can be generated as abatch or it can bedispersed over time. In this paper we focus on the dispersed generation model. The main difficulty in the analysis is due to the correlation between the system states observed by different packets of the same message. This paper introduces a new technique to analyze the message delay in such systems for different arrival models and different number of sessions. For anM/M/1 system with variable size messages and for the bursty traffic model, we obtain an explicit expression for the Laplace-Stieltjes transform (LST) of the message delay. Derivations are also provided for anM/G/1 system, for multiple session systems and for fixed message sizes. We show that the correlation has a strong effect on the performance of the system, and that the commonly usedindependence assumption, i.e., the assumption that the delays of packets are independent from packet to packet, can lead to wrong conclusions. 相似文献
10.
We provide solution techniques for the analysis of multiplexers with periodic arrival streams, which accurately account for the effects of active and idle periods and of gradual arrival. In the models considered in this paper, it is assumed that each source alternates (periodically) between active and idle periods of fixed durations. Incoming packets are transmitted on the network link and excess information is stored in the multiplexing buffer when the aggregate input rate exceeds the capacity of the link. We are interested in the probability distribution of the buffer content for a given network link speed as a function of the number of sources and their characteristics, i.e., rate and duration of idle and active periods. We derive this distribution from two models: discrete time and continuous time systems. Discrete time systems operate in a slotted fashion, with a slot defining the base unit for data generation and transmission. In particular, in each slot the link is capable of transmitting one data unit and conversely an active source generates one data unit in that time. The continuous time model of the paper falls in the category of fluid models. Compared to previous works we allow a more general model for the periodic packet arrival process of each source. In discrete time, this means that the active period of a source can now extend over several consecutive slots instead of a single slot as in previous models. In continuous time, packet arrivals are not required to be instantaneous, but rather the data generation process can now take place over the entire duration of the active period. In both cases, these generalizations allow us to account for the progressive arrival of source data as a function of both the source speed and the amount of data it generates in an active period.This work was done while at the IBM T.J. Watson Research Center.This work was done while at the IBM T.J. Watson Research Center.Part of the work was done while visiting the IBM T.J. Watson Research Center. 相似文献