首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   155篇
  免费   4篇
化学   107篇
晶体学   4篇
力学   3篇
数学   13篇
物理学   32篇
  2023年   1篇
  2022年   7篇
  2021年   5篇
  2020年   7篇
  2018年   2篇
  2017年   3篇
  2016年   7篇
  2015年   4篇
  2014年   2篇
  2013年   13篇
  2012年   8篇
  2011年   10篇
  2010年   9篇
  2009年   3篇
  2008年   5篇
  2007年   8篇
  2006年   7篇
  2005年   5篇
  2004年   7篇
  2003年   3篇
  2002年   6篇
  2001年   1篇
  2000年   2篇
  1999年   2篇
  1998年   2篇
  1997年   3篇
  1996年   3篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1991年   5篇
  1990年   3篇
  1989年   2篇
  1988年   1篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1979年   2篇
  1978年   1篇
排序方式: 共有159条查询结果,搜索用时 31 毫秒
51.
Intuitionistic fuzzy set plays a vital role in decision making, data analysis, and artificial intelligence. Many decision‐making problems consist of different types of datum, where fuzzy set theoretical approaches may fail to obtain the optimal decision. Numerous approaches for intuitionistic fuzzy decision‐making problem have been introduced in the literature to overcome these short comings. But there is no single approach that can be used to solve all kinds of problems because of the partial ordering defined on the collection of intuitionistic fuzzy numbers (IFNs). Even though ranking of fuzzy numbers have been studied from early seventies in the last century, a total order on the entire class of fuzzy numbers has been introduced by Wang and Wang (Fuzzy Sets Syst 2014, 243, 131–141) only on 2014. A total order on the collection of all IFN is an open problem till today. In this article, a total order on the entire class of IFN using upper lower dense sequence in the interval [0, 1] is proposed and compared with existing techniques using illustrative examples, further an algorithm (which is problem independent) for solving any intuitionistic fuzzy multicriteria decision‐making problem (Intuitionistic fuzzy MCDM) is introduced. This new total ordering on IFNs generalizes the total ordering defined in Wang and Wang ( 22 ) for fuzzy numbers. © 2016 Wiley Periodicals, Inc. Complexity 21: 54–66, 2016  相似文献   
52.
Let G be a finite group andA be a normal subgroup ofG. We denote by ncc(A) the number ofG-conjugacy classes ofA andA is calledn-decomposable, if ncc(A)= n. SetK G = {ncc(A)|A ⊲ G}. LetX be a non-empty subset of positive integers. A groupG is calledX-decomposable, ifK G =X. Ashrafi and his co-authors [1-5] have characterized theX-decomposable non-perfect finite groups forX = {1, n} andn ≤ 10. In this paper, we continue this problem and investigate the structure ofX-decomposable non-perfect finite groups, forX = {1, 2, 3}. We prove that such a group is isomorphic to Z6, D8, Q8, S4, SmallGroup(20, 3), SmallGroup(24, 3), where SmallGroup(m, n) denotes the mth group of ordern in the small group library of GAP [11].  相似文献   
53.
Many systems of ordinary differential equations are quadratic: the derivative can be expressed as a quadratic function of the dependent variable. We demonstrate that this feature can be exploited in the numerical solution by Runge-Kutta methods, since the quadratic structure serves to decrease the number of order conditions. We discuss issues related to construction design and implementation and present a number of new methods of Runge-Kutta and Runge-Kutta-Nyström type that display superior behaviour when applied to quadratic ordinary differential equations.  相似文献   
54.
Structural complexity of biological drug products presents an analytical challenge in terms of early detection of aggregation and/or degradation. In the present study, Raman and Raman optical activity (ROA) were evaluated for their sensitivity to detect heat‐induced molecular instability in an Immunoglobulin G4 subclass therapeutic monoclonal antibody present in its formulation matrix. The therapeutic antibody was subjected to heat stress at 50 °C and was analyzed at various time points up to 1 month. The current results suggest that Raman and ROA are sensitive to early‐stage detection of heat‐induced instability of the antibody, in which significant changes could be observed at 1 week of stress. ROA could provide early detection of the subtle differences at the tertiary structure level in a heat‐stressed monoclonal antibody and Raman/ROA spectra could provide early detection in secondary structural changes as well. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
55.
Base-catalyzed reaction of the nitroketene N,S-acetals and the ring substituted 2-hydroxybenzaldehydes afforded a combinatorial library of the 2-alkylamino-3-nitro-4-alkylsulfanyl 4H-chromenes in excellent yields. Nucleophilic displacement of the C4 alkylsulfanyl group with different thiols afforded 4H-chromenes with structural diversity.  相似文献   
56.
57.
Li-NH3 reduction of 1α-Ethynyl-1β-hydroxy-6-oxo-8a-methyl-1,2,3,4,6,7,8,8a octahydronaphthalene 5 furnishes, in addition to reported products, the tricyclic compound 8.  相似文献   
58.
The aim of this study was to evaluate the gastroprotective efficacy of andrographolide isolated from Andrographis paniculata in rats induced with duodenal ulcers. Duodenal ulcers were induced by cysteamine administration in rats pretreated with 3?mg?kg?1 BW?day?1 of andrographolide for 30 days. Ulcer score, myeloperoxidase activity, TBARS level, GSH/GSSG ratio and enzyme antioxidants were measured in the duodenal tissue. Brush border and basolateral membranes were isolated to assay sucrase, maltase, alkaline phosphatase and total ATPases. Ulcer score was significantly minimised in rats pretreated with andrographolide. Elevation in myeloperoxidase and TBARS levels were found to be minimised significantly due to andrographolide treatment. Membrane-bound enzyme activities and the thiol redox status of glutathione were significantly maintained in duodenal mucosa of rats that received andrographolide. This study reveals that the major component of A. paniculata, andrographolide, has potent antiulcer properties that are most likely caused by minimising inflammatory changes, counteracting free radical formation and maintaining the thiol redox status in the duodenum.  相似文献   
59.
The mineral crandallite CaAl3(PO4)2(OH)5·(H2O) has been identified in deposits found in the Jenolan Caves, New South Wales, Australia by using a combination of X-ray diffraction and Raman spectroscopic techniques. A comparison is made between the vibrational spectra of crandallite found in the Jenolan Caves and a standard crandallite. Raman and infrared bands are assigned to PO43− and HPO42− stretching and bending modes. The predominant features are the internal vibrations of the PO43− and HPO42− groups. A mechanism for the formation of crandallite is presented and the conditions for the formation are elucidated.  相似文献   
60.
The mechanism of biocidal action of nano titania on Escherichia coli and Staphylococcus aureus has been evaluated by various biochemical techniques like lipid peroxidation, hydrolysis of orthonitrophenol β-D-galactopyranoside, estimation of protein-amino acid and bacterial nucleic acids leakage into solution, in addition to morphology studies by electron microscopy (TEM and SEM) and K(+) ion leakage by inductively coupled plasma optical emission spectrometry. The active anatase phase of nano titania has been synthesized by sol-gel and pulverization techniques to obtain particle sizes averaging around 11 nm. The nano semiconductor with a bandgap of 3.2 eV responds well to the UV source to liberate reactive oxygen species (ROS). Gram negative bacteria easily succumb to the ROS at a faster rate than gram-positive bacteria with an observable difference in the mode of attack. The use of analytical techniques revealed the release of peroxidized lipid (26 nmol mL(-1) ) and protein content (370 μg mL(-1)) with a K(+) ion concentration of 22 000 ppb on complete destruction of E. coli.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号