全文获取类型
收费全文 | 1180篇 |
免费 | 144篇 |
国内免费 | 18篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 10篇 |
2021年 | 3篇 |
2020年 | 48篇 |
2019年 | 51篇 |
2018年 | 38篇 |
2017年 | 41篇 |
2016年 | 46篇 |
2015年 | 51篇 |
2014年 | 45篇 |
2013年 | 84篇 |
2012年 | 53篇 |
2011年 | 46篇 |
2010年 | 47篇 |
2009年 | 32篇 |
2008年 | 31篇 |
2007年 | 53篇 |
2006年 | 43篇 |
2005年 | 44篇 |
2004年 | 56篇 |
2003年 | 58篇 |
2002年 | 40篇 |
2001年 | 26篇 |
2000年 | 6篇 |
1999年 | 40篇 |
1998年 | 19篇 |
1997年 | 45篇 |
1996年 | 33篇 |
1995年 | 41篇 |
1994年 | 38篇 |
1993年 | 49篇 |
1992年 | 42篇 |
1991年 | 30篇 |
1990年 | 12篇 |
1989年 | 18篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1342条查询结果,搜索用时 31 毫秒
991.
A set of phenyl ring‐substituted N‐t‐butoxycarbonyl‐phenylalanine analogs were chirally resolved using an α‐Burke 2 Pirkle‐type chiral column under subcritical fluid conditions. Various mobile phase modifiers were used to elute the chiral analytes, resulting in different selectivity factors for each analog. The observed selectivity factors were accurately modeled based on the bulk solvation parameters for each mobile phase modifier. The resulting model equation was used to predict the selectivity factors using an additional modifier not included in the model building data set. The predictive ability of the model was demonstrated to be quite good for this limited range of analogs and mobile phase modifiers. Chirality 11:98–102, 1999. © 1999 Wiley‐Liss, Inc. 相似文献
992.
Stirred crystallization of racemic (D/L)‐glutamic acid (Glu) in the presence of small amounts of L‐ or D‐lysine (Lys) was studied for the effect of transient chiral resolution by monitoring the time evolution of optical rotation and the concentration of the solution. The presence of a small amount of L‐ or D‐Lys retards the crystallization rate of the corresponding enantiomer of Glu in a chirally selective manner, giving rise to transient optical resolution of racemic Glu during crystallization. The optical rotation of the Glu solution was found to increase from zero to a value corresponding to an enantiomeric excess (ee) of 22–35% and subsequently decreases to zero over a period of many hours. During this process, the ee of the crystallized Gu is nearly 100% during the first 35 min and then it decreases slowly to zero. Our results indicate that the time at which the ee of the solution reaches its maximum and the maximum value of the ee show a nonlinear dependence on the initial mole fraction of the chiral impurity. The effect of the impurity is highly chirally selective, indicating “molecular recognition.” Chirality 11:343–348, 1999. © 1999 Wiley‐Liss, Inc. 相似文献
993.
Esters of 1-(1-naphthly)ethylurea derivatives of L-valine, L-leucine, L-tert-leucine, and L-proline are examined as organic-soluble chiral nuclear magnetic resonance (NMR) resolving agents. The reagents are useful for resolving the spectra of chiral sulfoxides, amines, alcohols, and carboxylic acids. Enantiomeric resolution is caused by a combination of diastereomeric effects and the different association constants of the substrates with the resolving agents. Organic-soluble lanthanide species are added to resolving agent-substrate mixtures and often enhance the enantiomeric resolution. The enhancement occurs because the substrate that exhibits weaker binding with the resolving agent is more available to bond to the lanthanide. Broadening in the spectra with lanthanides is reduced at 50°C. Enantiomeric resolution is still observed at elevated temperatures. Chirality 9:1–9, 1997. © 1997 Wiley-Liss, Inc. 相似文献
994.
Soo Choon Tan James A. Baker Nichola Stevens Vern de Biasi Colin Salter Maria Chalaux Kamyar Afarinkia Andrew J. Hutt 《Chirality》1997,9(1):75-87
The chromatographic resolution of the four stereoisomers of carboxyibuprofen, a major metabolite of ibuprofen in man, was achieved using a Chiralpak AD chiral stationary phase (CSP) (J.T. Baker, Milton, Keynes, UK). The elution order of the stereoisomers was determined to be 2′S,2R; 2′R,2R; 2′R,2S; 2′S,2S by a combination of stereoselective synthesis of diastereoisomeric mixtures and analysis of the two diastereoisomers isolated from human urine following the administration of (S)-ibuprofen. The individual stereoisomers were isolated by semipreparative chiral phase chromatography and characterized by circular dichroism spectroscopy. Chirality 9:75–87, 1997. © 1997 Wiley-Liss, Inc. 相似文献
995.
Mtys Czugler Petros P. Korkas Petra Bombicz Wilhelm Seichter Edwin Weber 《Chirality》1997,9(3):203-210
New chiral host molecules 1 and 2 involving a bulky terpenoid unit and aromatic ethyne spacer groups were synthesized using Pd-catalyzed cross-coupling reactions of (+)-2α-ethynyl-2β-hydroxybornane (4) or (+)-2α-ethynyl-2β-hydroxyfenchane (5) with 9,10-dibromoanthracene. Host compounds 1 and 2 from crystalline inclusions with 1-methoxy-2-propanol (3) in 1:1 and 1:2 stoichiometry, respectively. In the case of 1, complete enantiomer resolution (ee > 99%) of 3 is effected in one cocrystallization step. However, constitutional isomer 2 failed in the enantiomer separation of 3, which might be explained due to the different crystal lattice buildup of these cocrystals. Chirality 9:203–210, 1997. © 1997 Wiley-Liss, Inc. 相似文献
996.
The aim of this study was to rationalise retention behaviour of a chiral solute on molecularly imprinted polymer (MIP) HPLC stationary phases in terms of variation of the mobile phase. It is generally held that the most important interaction governing the separation of enantiomers on such materials is H-bonding, and that retention times increase with decreasing H-bonding potential of the mobile phase. Previous studies have largely concerned mobile phases containing chloroform with acetic acid as a polar modifier. Boc-L-Phenylalanine (Boc-L-Phe-OH) MIPs were prepared, processed, and packed into HPLC columns, which were then used to investigate the retention characteristics of Boc-L-Phe-OH and Boc-D-Phe-OH with a range of mobile phases. The main observations were as follows: (1) in chloroform-based mobile phases there was generally a linear relationship between the H-bond donator factor of the polar modifier and capacity (K′). Results also indicated a hydrogen bond donor parameter value for a polar modifier at which retention became concentration independent; (2) For given values of K′L, K′D varied depending on the polar modifier, indicating that enantiomer resolution was solvent dependent; (3) Using mobile phases based on solvents of lower polarity/H-bonding potential than chloroform, substantial increases in K′ were observed, although enantioselectivity was greatly reduced. Chirality 9:238–242, 1997. © 1997 Wiley-Liss, Inc. 相似文献
997.
A high-performance liquid chromatographic method has been developed for the analysis of the intermediate imines and end products in an asymmetric isomerization route toward optically active amines. Separation of the imine enantiomers was performed on commercially available Chiralcel OD-H, Chiralcel OJ, and Chiralpak AD chiral stationary phases. All substituted imine enantiomers could be readily resolved with selectivities (α) higher than 1.10 using the Chiralpak AD column. By derivatization with ring-substituted benzaldehydes, aromatic amines were converted into Schiff base derivatives and the enantiopurity of these amines was determined. Chirality 9:727–731, 1997. © 1997 Wiley-Liss, Inc. 相似文献
998.
Optimization of chiral resolution, using carbon dioxide based mobile phases, must take into consideration the individual contributions of analyte retention, selectivity, and efficiency. Each of these factors may be independently affected by changes in pressure, temperature, or state of the mobile phase. The ability to control retention by different means reflects an advantage of carbon dioxide based mobile phases over conventional HPLC mobile phases. Utilization of this advantage requires that the effects of each of these factors on each contributor to resolution be known. The cumulative effect that each of these variables has on retention, selectivity and efficiency suggests that maximum resolution is obtained using low pressures and temperatures. Maximum resolution (at fixed k′) results from low temperatures and high pressures. The latter may be of more practical importance when speed of analyses and detection limits are considered. Chirality 9:672–677, 1997. © 1997 Wiley-Liss, Inc. 相似文献
999.
Derivatization of the free cys34 in human serum albumin (HSA) anchored to a silica matrix has been performed by in situ reaction with ethacrynic acid. This modification, which is reported to occur under physiological conditions, gives rise in practice to a new column with different binding properties with respect to the column based on the native protein. Significant differences were observed in the binding of drugs known to bind to site I, (R)-(S)-warfarin and phenylbutazone, and to site II, 1,4-benzodiazepin-2-ones and nonsteroidal anti-inflammatory agents. In particular, the chromatographic retentions markedly decreased for most of the drugs, and, in the case of chiral compounds, significant differences were often observed in the behavior of the two enantiomers, with higher values of enantioselectivity obtained for some of the examined compounds. Furthermore, the noncovalent binding of ethacrynic acid to the protein modifies the binding properties of the albumin. Chirality 9:335–340, 1997. © 1997 Wiley-Liss, Inc. 相似文献
1000.
Chiral asymmetry generation, the predominant production of one enantiomer in a non-chiral environment, could occur in the production of the chiral complex cis-[CoBr(NH3)(en)2]Br2 by the reaction of [Co(H2O)2{(OH)2Co(en)2}2](SO4)2 with ammonium bromide in an aqueous medium. The main kinetic steps in the reaction system have been determined. During the reaction, the product crystallizes at an early stage. When a very small amount of crystalline enantiomer was added to the reaction system at an early stage, the same enantiomer was produced preferentially; in addition, the enantiomeric excess of the product increased with increasing the stirring rate. Thus, it seems that each enantiomer generates chiral crystals that could self-replicate through secondary nucleation when the solution is stirred; these crystals in turn enhance the production of the same enantiomer. With a computer code that simulates such a kinetic mechanism, it is shown that enantiomeric excess observed in the experiments could be reproduced. Chirality 10:343–348, 1998. © 1998 Wiley-Liss, Inc. 相似文献