全文获取类型
收费全文 | 458篇 |
免费 | 15篇 |
专业分类
化学 | 325篇 |
晶体学 | 8篇 |
力学 | 7篇 |
数学 | 30篇 |
物理学 | 103篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 14篇 |
2013年 | 12篇 |
2012年 | 27篇 |
2011年 | 25篇 |
2010年 | 16篇 |
2009年 | 20篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 23篇 |
2005年 | 18篇 |
2004年 | 29篇 |
2003年 | 24篇 |
2002年 | 23篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有473条查询结果,搜索用时 781 毫秒
91.
Kazuhisa Makino Yushi Uno Toshihide Ibaraki 《Journal of Algorithms in Cognition, Informatics and Logic》2001,38(2):411
In this paper, we introduce the problem of computing a minimum edge ranking spanning tree (MERST); i.e., find a spanning tree of a given graph G whose edge ranking is minimum. Although the minimum edge ranking of a given tree can be computed in polynomial time, we show that problem MERST is NP-hard. Furthermore, we present an approximation algorithm for MERST, which realizes its worst case performance ratio
where n is the number of vertices in G and Δ* is the maximum degree of a spanning tree whose maximum degree is minimum. Although the approximation algorithm is a combination of two existing algorithms for the restricted spanning tree problem and for the minimum edge ranking problem of trees, the analysis is based on novel properties of the edge ranking of trees. 相似文献
92.
93.
94.
C. Harada H. Goto T. Minegishi T. Suzuki H. Makino M. W. Cho T. Yao 《Current Applied Physics》2004,4(6):633-636
We report on a surface property of bulk ZnO crystals and an optical method to evaluate it. Bulk ZnO crystals have a damaged surface layer due to chemomechanical polishing. We prepared the ZnO crystals by etching, and evaluated the improvement of the surface by high-resolution X-ray diffraction (XRD) and photoluminescence (PL). In PL measurements, the relative intensity of the first order longitudinal optical phonon replica of free exciton (FX-1LO) to second order process (FX-2LO) was compared. The relative intensity becomes weak with increasing etched depth and finally saturates at the etched depth of 5 μm. This result agrees well with XRD results. 相似文献
95.
Voltammetric study of the transfer of polyammonium ions at nitrobenzene / water interface. 总被引:1,自引:0,他引:1
Hajime Katano Ikuo Kameoka Yuji Murayama Hirosuke Tatsumi Toshihide Tsukatani Masahiro Makino 《Analytical sciences》2004,20(11):1581-1585
The transfer of polyammonium ions, poly[(dimethylimino)-1,6-hexanediyl] (n = 140, n being the degree of polymerization) ion and poly[(dimethylimino)(2-oxo-1,2-ethanediyl)imino-alpha,omega-alkanediylimino(1-oxo-1,2-ethanediyl)(dimethylimino)-alpha',omega'-alkanediyl] ([-N+ (CH3)2CH2CONH(CH2)x NHCOCH2N+ (CH3)2(CH2)y-]n, x = 2, 3, 4, or 6, y = 3 or 6, and n = 30-130) ions, at a polarizable nitrobenzene / water interface has been studied by normal pulse voltammetry and cyclic voltammetry. Despite the polydispersity of the preparations, by normal pulse voltammetry, an S-shaped current-potential curve with a well-defined limiting current, and, by cyclic voltammetry, a pair of anodic and cathodic peak currents due to the transfer of polyammonium ions across the interface were observed within the potential window. The voltammetric behavior is described. Also, the effect of ion-pair formation of the polyammonium ions with supporting electrolyte anions in nitrobenzene- and water-phases on the half-wave or midpoint potential of the ion-transfer, and the relation between the structure of the polyammonium ions and the transfer potentials are discussed. 相似文献
96.
97.
Silver‐Catalyzed Efficient Synthesis of Oxindoles and Pyrroloindolines via α‐Aminoalkylation of N‐Arylacrylamides with Amino Acid Derivatives
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
α‐Aminoalkylation of N‐arylacrylamides with amino acid derivatives was achieved by silver‐catalysis in moderate to high yields. The reaction provides an efficient strategy for the synthesis of functionalized oxindoles, and is suitable for a wide range of N‐arylacrylamides and amino acids, both of which are inexpensive and readily available. The oxindoles obtained were readily transformed into densely functionalized pyrroloindolines by deprotection and cyclization in one pot. 相似文献
98.
Chetiyanukornkul T Toriba A Kizu R Makino T Nakazawa H Hayakaw K 《Journal of chromatography. A》2002,961(1):107-112
A high-performance liquid chromatographic method has been developed for the quantification of 1-hydroxypyrene (1-OHP) in human urine using deuterated 1-hydroxypyrene ([2H9]1-OHP) as an internal standard with fluorescence detection. [2H9]1-OHP was prepared enzymatically from deuterated pyrene ([2H10]Pyr) with cytochrome P450 1A1. It eluted immediately prior to non-deuterated 1-OHP on alkylamide-type reversed-phase columns and had nearly the same fluorescence characteristics as non-deuterated 1-OHP. The detection limit was 0.1 microg/L and the calibration range was from 1 to 100 nmol/L. Urine sample treatment involved enzymatic hydrolysis followed by solid-phase extraction using Sep-Pak C18 cartridges. The proposed method was used to determine urinary 1-OHP in smokers and non-smokers. 相似文献
99.
The iron-catalyzed Kirmse reaction was used to generate neopentyl alpha-silyl thioethers that were elaborated to meroterpenes using two complementary routes: one route involved a sila-Pummerer rearrangement, and the other route involved a Peterson olefination. While severe eclipsing interactions undermined the efficiency of the stereospecific sila-Pummerer rearrangement, they made it possible to stereoselectively generate E olefins without isolation or separation of syn- and anti-beta-silyl alkoxides. Addition of a neopentyl alpha-silyl alkyllithium intermediate to an aryl aldehyde generated a mixture of syn- and anti-beta-silyl alkoxides. The syn-beta-silyl alkoxide eliminated stereospecifically at -78 degrees C to give an E olefin, whereas the anti-beta-silyl alkoxide was unreactive. The reaction mixture was then acidified and heated to induce stereospecific elimination of the anti isomer to give the same E olefin via a complementary cationic pathway. This route was used to complete the first synthesis of the meroterpene (+/-)-3-hydroxybakuchiol. In addition, we synthesized another meroterpene corresponding to the natural product corylifolin and offer evidence that the structure of corylifolin was misassigned. 相似文献
100.
Therapeutic drug monitoring of anti-inflammatory drugs is necessary for the identification of the agents that cause toxic events and for the decision on the treatment for intoxication. Recently, capillary electrophoresis (CE) has been developed for the simple and rapid analyses of a variety of chemical agents. Micellar electrokinetic chromatography (MEKC) can separate acidic, neutral and basic anti-inflammatory drugs in serum. Furthermore, serum samples are directly applied to the CE system without any pretreatments, and some anti-inflammatory drugs can be separated from serum albumin in the MEKC analysis. On the other hand, capillary zone electrophoresis (CZE) enables us to determine a few microg/mL levels of acidic anti-inflammatory drugs with simple running buffer and stacking technique. A rapid and simultaneous determination of several analgesic anti-inflammatory agents, including ibuprofen, acetaminophen, indomethacin, and salicylic acid in human serum has been developed by using CZE. Therefore, the CZE and MEKC analysis may become a potentially useful alternative to high-performance liquid chromatography (HPLC) and fluorescence polarization immunoassay (FPIA) for therapeutic drug monitoring, particularly in serum of patients suffering from intoxication by overdosage of nonsteroidal anti-inflammatory agents. 相似文献