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   209篇
  免费   7篇
  国内免费   1篇
化学   140篇
晶体学   1篇
力学   6篇
数学   23篇
物理学   47篇
  2023年   1篇
  2021年   2篇
  2019年   2篇
  2017年   2篇
  2016年   3篇
  2015年   3篇
  2014年   2篇
  2013年   8篇
  2012年   13篇
  2011年   10篇
  2010年   13篇
  2009年   15篇
  2008年   12篇
  2007年   18篇
  2006年   19篇
  2005年   14篇
  2004年   9篇
  2003年   8篇
  2002年   7篇
  2001年   5篇
  2000年   5篇
  1999年   3篇
  1998年   3篇
  1997年   3篇
  1996年   9篇
  1995年   2篇
  1994年   1篇
  1993年   5篇
  1992年   1篇
  1991年   8篇
  1988年   1篇
  1987年   1篇
  1986年   3篇
  1985年   1篇
  1983年   3篇
  1982年   1篇
  1978年   1篇
排序方式: 共有217条查询结果,搜索用时 31 毫秒
41.
We report new approaches using alkali-hydroxide-doped matrices to facilitate structural characterization of neutral underivatized oligosaccharides by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) MS. The approaches involved pretreatment of the analytes with NaOH or LiOH in aqueous solution, followed by mixing them with MALDI matrices prior to MS analysis. It was found that for open-ended neutral underivatized oligosaccharides partial alkaline degradation occurred upon laser desorption and ionization of the hydroxide-pretreated analytes in 2,5-dihydroxybenzoic acid (DHBA). The effect intensified when nonacidic compounds such as 2,4,6-trihydroxyacetophenone (THAP) and 5-amino-2-mercapto-1,3,4-thiadiazole (AMT) were used as matrix. The degradation allowed facile identification of the reducing end residue of the analyte and facilitated its structural characterization by postsource decay TOF-MS. Applying the same technique using matrices composed of LiOH and THAP or AMT led to the production of singly as well as multiple lithiated ions of oligosaccharides containing hexoses with free 3-OH groups. Extensive lithiation through multiple hydrogen-lithium exchanges up to 6 Li atoms was observed for maltoheptaose, beta-cyclodextrin, and dextran 1500. Such a 'lithium tagging' technique makes it possible to differentiate positional isomers of milk-neutral oligosaccharides, lacto-N-difucohexaose I and II (LNDFH-I and LNDFH-II), without the need of chemical derivatization or tandem MS analysis.  相似文献   
42.
The semiconductor industry is shifting towards innovation and acquisition of intellectual property. Semiconductor-Intellectual-Property (SIP) design, a new industry, is also rapidly growing. This challenges both providers and users to develop infrastructure and standard interfaces. Establishing an SIP Mall to provide a full array of SIP business services is a new concept used to promote growth of the SIP industry. Many foundries and governments have been involved in setting up SIP Malls; however, the major services needed for an SIP Mall to attract SIP providers and SIP users must still be clarified. In this paper, the DEMATEL (DEcision MAking Trial and Evaluation Laboratory) method was used to discover and illustrate the key services needed to attract SIP users and SIP providers to an SIP Mall. Research enabled the derivation of the interrelated services and the structural interrelationship between them using the DEMATEL method. Overall, four key services were found to be vital for an SIP Mall to attract customers and to allocate resources efficiently.  相似文献   
43.
This paper reports normalized fifth-order spherical aberration coefficients C(5s)/R derived from Gaussian trajectory for rotationally symmetrical magnetic lenses, where S/D (the polepiece gap-width/bore-diameter ratio) is in the range 0.20-2.00, and k(2) (the lens-intensity parameter) is 0.10-100. It is noted that the normalized fifth-order spherical-aberration coefficient C(5s)/R changes its sign within the given parameter ranges.  相似文献   
44.
Cross-efficiency evaluation is a commonly used approach for ranking decision-making units (DMUs) in data envelopment analysis (DEA). The weights used in the cross-efficiency evaluation may sometimes differ significantly among the inputs and outputs. This paper proposes some alternative DEA models to minimize the virtual disparity in the cross-efficiency evaluation. The proposed DEA models determine the input and output weights of each DMU in a neutral way without being aggressive or benevolent to the other DMUs. Numerical examples are tested to show the validity and effectiveness of the proposed DEA models and illustrate their significant role in reducing the number of zero weights.  相似文献   
45.
A number of 2,4,5-triaryl-1H-imidazole derivatives were synthesized and evaluated for their antiproliferative activities against the growth of five cell lines including three non-small cell lung cancers (H460, H1299, and A549), one breast cancer (MCF-7), and one normal diploid embryonic lung cell line (MRC-5). Preliminary results indicated that both 2-(5-bromofuran-2-yl)-4,5-bis{4-[3-(dimethylamino) propoxy] phenyl}-1H-imidazole (10f) and 4,5-bis{4-[3-(dimethylamino)propoxy]phenyl}-2-(5-nitrofuran-2-yl)-1H -imidazole (10g) were selectively active against the growth of H1229 with an IC50 of less than 0.1???M, thus were more active than topotecan (IC50 >?10.0??? M). However, both 10f and 10g exhibited only marginal cytotoxicity against H460, A549, MCF-7, and MRC-5 requiring an IC 50 of at least 4.16???M. Our results also indicated that 10f induced H1299 cell cycle arrest at G0/G1 through the inactivation of p38 MAPK, JNK, ERK, as well as the expression of SIRT1 and survivin. These results suggested that 10f might have therapeutic potential against H1299 (non-small cell lung cancer cell).  相似文献   
46.
47.
The steering control of a ship during a course-changing maneuver is formulated as a Bolza optimal control problem, which is solved via the sequential gradient-restoration algorithm (SGRA). Nonlinear differential equations describing the yaw dynamics of a steering ship are employed as the differential constraints, and both amplitude and slew rate limits on the rudder are imposed. Two performance indices are minimized: one measures the time integral of the squared course deviation between the actual ship course and a target course; the other measures the time integral of the absolute course deviation. Numerical results indicate that a smooth transition from the initial set course to the target course is achievable, with a trade-off between the speed of response and the amount of course angle overshoot.  相似文献   
48.
In this paper, we propose some decision logic languages for rule representation in rough set-based multicriteria analysis. The semantic models of these logics are data tables, each of which is comprised of a finite set of objects described by a finite set of criteria/attributes. The domains of the criteria may have ordinal properties expressing preference scales, while the domains of the attributes may not. The validity, support, and confidence of a rule are defined via its satisfaction in the data table.  相似文献   
49.
50.
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