全文获取类型
收费全文 | 121篇 |
免费 | 8篇 |
专业分类
化学 | 94篇 |
力学 | 2篇 |
数学 | 17篇 |
物理学 | 16篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 5篇 |
2012年 | 3篇 |
2011年 | 4篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 4篇 |
2007年 | 10篇 |
2006年 | 13篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2002年 | 1篇 |
2001年 | 2篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有129条查询结果,搜索用时 31 毫秒
21.
Faza ON López CS Alvarez R de Lera AR 《Journal of the American Chemical Society》2006,128(7):2434-2437
The mechanism of the stereospecific gold(I)-catalyzed Rautenstrauch rearrangement of (E)-1-ethynyl-2-methyl-but-2-en-yl acetate to 3,4-dimethyl-cyclopent-2-enone has been computationally addressed using DFT (B3LYP/6-31G, SDD for Au). Our results indicate that the bond formation event follows the Au(I)-induced acetyl transfer to the vicinal alkyne and that it is the helicity of the pentadienyl cation intermediate which keeps memory of the chiral information. The fidelity of the center-to-helix-to-center chirality transfer requires that the rates of helix interconversion and pivaloyl rotation are slower than the cyclization, as calculations predict. 相似文献
22.
Commercially-available 4,4'-dimethyloctafluorobiphenyl was converted in a single step to 4-(4'-methyltetrafluorophenyl)-2,3,5,6-tetrafluorobenzyl bromide (MTFP-TFBBr) for the purpose of providing a new electrophoric derivatizing reagent. When reacted with this reagent, 2-fluoro-O6-(2'-hydroxyethyl)hypoxanthine, a model analyte, gave a mixture of isomeric products (apparently substituted at N7 and N9, analogous to its known reaction with pentafluorobenzyl bromide), and 53 femtograms of the mixture was detected at S/N = 10 by gas chromatography electron capture mass spectrometry (GC-EC-MS). As intended, the volatility of the MTFB-TFBBr derivative was much less (two-fold) than that of the corresponding pentafluorobenzyl derivative. It is anticipated that MTFB-TFBBr sometimes will be useful in providing an electrophoric derivative that encounters less background noise in analysis by electrophore derivatization/GC-EC-MS. 相似文献
23.
E. Dafni J. Bendahan C. Broude G. Goldring M. Hass E. Naim M.H. Rafailovich C. Chasman O.C. Kistner S. Vajda 《Nuclear Physics A》1985,443(1):135-156
Time-differential perturbed-angular-distribution (TDPAD) experiments have been performed on polarized intermediate- and high-spin isomers . Excited Gd nuclei populated by reactions were polarized by the tilted-multifoil technique and implanted in a Gd single-crystal host. Observation of the subsequent electric quadrupole interaction with the known electric field gradient yielded negative values of the sign of the deformation for all isomers studied. The magnitude of the induced nuclear polarization PI was also determined from the TDPAD data and compared to model calculations in order to deduce the average atomic angular momentum and polarization of Gd ions at v/c ~ 0.018. 相似文献
24.
M. Naim Yunus 《The Journal of the Operational Research Society》1989,40(12):1153-1155
An exact expression for the transient expectation of traffic overflowing from an Erlang loss system with stationary offered traffic is presented. Its derivation is obtained by using an exact expression for the transient blocking probability. This exact expectation could be useful in approximating the expectation of real-life overflow traffic. 相似文献
25.
26.
We show that with any finite partially ordered set P (which need not be a lattice) one can associate a matrix whose determinant factors nicely. This was also noted by D.A. Smith, although his proof uses manipulations in the incidence algebra of P while ours is combinatorial, using nonintersecting paths in a digraph. As corollaries, we obtain new proofs for and generalizations of a number of results in the literature about GCD matrices and their relatives. 相似文献
27.
Sanagi MM Nasir Z Ling SL Hermawan D Ibrahim WA Naim AA 《Journal of AOAC International》2010,93(4):1322-1330
Linearity assessment as required in method validation has always been subject to different interpretations and definitions by various guidelines and protocols. However, there are very limited applicable implementation procedures that can be followed by a laboratory chemist in assessing linearity. Thus, this work proposes a simple method for linearity assessment in method validation by a regression analysis that covers experimental design, estimation of the parameters, outlier treatment, and evaluation of the assumptions according to the International Union of Pure and Applied Chemistry guidelines. The suitability of this procedure was demonstrated by its application to an in-house validation for the determination of plasticizers in plastic food packaging by GC. 相似文献
28.
H.H. See M. Marsin SanagiWan Aini Wan Ibrahim A.A. Naim 《Journal of chromatography. A》2010,1217(11):1767-1772
A novel microextraction technique termed solid phase membrane tip extraction (SPMTE) was developed. Selected triazine herbicides were employed as model compounds to evaluate the extraction performance and multiwall carbon nanotubes (MWCNTs) were used as the adsorbent enclosed in SPMTE device. The SPMTE procedure was performed in semi-automated dynamic mode and several important extraction parameters were comprehensively optimized. Under the optimum extraction conditions, the method showed good linearity in the range of 1–100 μg/L, acceptable reproducibility (RSD 6–8%, n = 5), low limits of detection (0.2–0.5 μg/L), and satisfactory relative recoveries (95–101%). The SPMTE device could be regenerated and reused up to 15 analyses with no analyte carry-over effects observed. Comparison was made with commercially available solid phase extraction-molecular imprinted polymer cartridge (SPE-MIP) for triazine herbicides as the reference method. The new developed method showed comparable or even better results against reference method and is a simple, feasible, and cost effective microextraction technique. 相似文献
29.
A convenient synthesis method was developed for the preparation of C-stapled homodimeric bis-lexitropsins connected through
the nitrogen atoms of the central pyrrole ring with a bis-methylene linker. This lexitropsin is designed as a standard for
other bis-lexitropsins with longer chains in biological evaluation and NMR studies. The key step in this method is the treatment
of ethyl 4-nitropyrrole-2-carboxylate with flame-dried potassium carbonate in DMF followed by the addition of 1,2-dibromoethane to form the 1,2-dipyrroloethane derivative. 相似文献
30.
Collaborative work between experimentalists and computational chemists have demonstrated a stong synergy which allowed the rationalization of allenyl azide chemistry and permited the development of an efficient synthetic tool aimed at the preparation of several alkaloids. Saturated allenyl azides undergo a reaction cascade involving key diradical intermediates that follow the Curtin-Hammett model whereas unsaturated allenyl azides form indolidene intermediates that furnish the final indole products via electrocyclic ring closure events taking place out of the Curtin-Hammett regime. The regiochemistry of the reaction cascade with the latter substrates can be manipulated by Cu(I) addition to the reaction mixture. 相似文献