全文获取类型
收费全文 | 2886篇 |
免费 | 81篇 |
国内免费 | 19篇 |
专业分类
化学 | 2150篇 |
晶体学 | 23篇 |
力学 | 66篇 |
综合类 | 1篇 |
数学 | 192篇 |
物理学 | 554篇 |
出版年
2022年 | 29篇 |
2021年 | 33篇 |
2020年 | 45篇 |
2019年 | 41篇 |
2018年 | 30篇 |
2017年 | 26篇 |
2016年 | 77篇 |
2015年 | 65篇 |
2014年 | 65篇 |
2013年 | 132篇 |
2012年 | 147篇 |
2011年 | 152篇 |
2010年 | 102篇 |
2009年 | 93篇 |
2008年 | 168篇 |
2007年 | 175篇 |
2006年 | 155篇 |
2005年 | 163篇 |
2004年 | 138篇 |
2003年 | 115篇 |
2002年 | 121篇 |
2001年 | 64篇 |
2000年 | 54篇 |
1999年 | 51篇 |
1998年 | 34篇 |
1997年 | 19篇 |
1996年 | 30篇 |
1995年 | 26篇 |
1994年 | 17篇 |
1993年 | 26篇 |
1992年 | 40篇 |
1991年 | 30篇 |
1990年 | 19篇 |
1989年 | 22篇 |
1988年 | 30篇 |
1987年 | 18篇 |
1985年 | 36篇 |
1984年 | 33篇 |
1983年 | 16篇 |
1982年 | 32篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 32篇 |
1978年 | 19篇 |
1977年 | 32篇 |
1976年 | 25篇 |
1975年 | 18篇 |
1974年 | 16篇 |
1973年 | 18篇 |
1969年 | 15篇 |
排序方式: 共有2986条查询结果,搜索用时 15 毫秒
991.
992.
Validation of an ultra‐performance liquid chromatography–tandem mass spectrometry method for the determination of flecainide in human plasma and its clinical application 下载免费PDF全文
Yuji Mano Yoshiki Asakawa Kenji Kita Takuho Ishii Koichiro Hotta Kazutomi Kusano 《Biomedical chromatography : BMC》2015,29(9):1399-1405
A simple and reproducible bioanalytical method for the determination of flecainide in human plasma was developed and validated using an ultra‐performance liquid chromatography with tandem mass spectrometry (UPLC‐MS/MS) to obtain higher sensitivity than the current available methods. After simple protein precipitation, flecainide and a stable isotope‐labeled internal standard (IS) were chromatographed on an Acquity UPLC BEH C18 column (2.1 × 100 mm, 1.7 µm) with isocratic elution of mobile phase consisting of 45% methanol containing 0.1% formic acid at a flow rate 0.25 mL/min. Detection was performed in positive electrospray ionization by monitoring the selected ion transitions at m/z 415.4/301.1 for flecainide and m/z 419.4/305.1 for the IS. The method was validated according to current bioanalytical method validation guidelines. The calibration standard curve was linear from 2.5 to 1000 ng/mL using 0.1 mL of plasma. No significant interferences were detected in blank human plasma. Accuracy and precision in the intra‐ and inter‐batch reproducibility study were within acceptance criteria. Neither hemolysis effects nor matrix effects were observed. The UPLC‐MS/MS method developed was successfully applied to determine plasma flecainide concentrations to support clinical studies and incurred sample reanalysis also ensured the reproducibility of the method. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
993.
Inside Back Cover: New Insights into the Hexaphenylethane Riddle: Formation of an α,o‐Dimer (Angew. Chem. Int. Ed. 13/2015) 下载免费PDF全文
994.
995.
996.
Insight into the Mechanism of Hydrogenation of Amino Acids to Amino Alcohols Catalyzed by a Heterogeneous MoOx‐Modified Rh Catalyst 下载免费PDF全文
Dr. Masazumi Tamura Riku Tamura Yasuyuki Takeda Dr. Yoshinao Nakagawa Prof. Keiichi Tomishige 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):3097-3107
Hydrogenation of amino acids to amino alcohols is a promising utilization of natural amino acids. We found that MoOx‐modified Rh/SiO2 (Rh–MoOx/SiO2) is an efficient heterogeneous catalyst for the reaction at low temperature (323 K) and the addition of a small amount of MoOx drastically increases the activity and selectivity. Here, we report the catalytic potential of Rh–MoOx/SiO2 and the results of kinetic and spectroscopic studies to elucidate the reaction mechanism of Rh–MoOx/SiO2 catalyzed hydrogenation of amino acids to amino alcohols. Rh–MoOx/SiO2 is superior to previously reported catalysts in terms of activity and substrate scope. This reaction proceeds by direct formation of an aldehyde intermediate from the carboxylic acid moiety, which is different from the reported reaction mechanism. This mechanism can be attributed to the reactive hydride species and substrate adsorption caused by MoOx modification of Rh metal, which results in high activity, selectivity, and enantioselectivity. 相似文献
997.
Frontispiece: Proton Order–Disorder Phenomena in a Hydrogen‐Bonded Rhodium–η5‐Semiquinone Complex: A Possible Dielectric Response Mechanism 下载免费PDF全文
Dr. Minoru Mitsumi Kazunari Ezaki Yuuki Komatsu Prof. Dr. Koshiro Toriumi Dr. Tatsuya Miyatou Prof. Dr. Motohiro Mizuno Nobuaki Azuma Prof. Dr. Yuji Miyazaki Prof. Dr. Motohiro Nakano Prof. Dr. Yasutaka Kitagawa Dr. Takayasu Hanashima Dr. Ryoji Kiyanagi Dr. Takashi Ohhara Prof. Dr. Kazuhiro Nakasuji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27)
998.
Dr. Yuji Kawato Hiromi Ono Akino Kubota Yoshihiro Nagao Naoki Morita Dr. Hiromichi Egami Prof. Dr. Yoshitaka Hamashima 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):2127-2133
The enantioselective bromocyclization of allylic amides catalyzed by phosphorus‐containing Lewis bases was examined in detail. A series of control experiments and NMR studies showed that a partially oxidized bis‐phosphine generated in situ serves as the actual enantioselective catalyst. The reaction mechanism involves distinct roles of two Lewis basic sites, P and P=O, with P+Br serving as a fine‐tuning element for substrate fixation in the chiral environment, and P+OBr as the Br+ transfer agent to the olefin. Catalyst loading could be reduced to as little as 1 mol %, and the reaction affords enantioenriched oxazolines with up to >99.5 % ee. 相似文献
999.
Yuta Ito Dr. Masafumi Ueda Dr. Norihiko Takeda Prof. Dr. Okiko Miyata 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(8):2616-2619
A novel reductive Fischer indolization of readily available N‐aryl conjugated hydrazones with tert‐butyl iodide has been developed. In this reaction, tert‐butyl iodide is used as anhydrous HI source, and the generated HI acts as a Brønsted acid and a reducing agent. This operationally simple method allows access to various indole derivatives. Furthermore, the procedure can be applied to the synthesis of biologically active compounds. 相似文献
1000.
Dr. Yoshihiro Nishimoto Yuji Kita Hiroki Ueda Hiroto Imaoka Kouji Chiba Prof. Dr. Makoto Yasuda Prof. Dr. Akio Baba 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11837-11845
A cross‐coupling reaction between enol derivatives and silyl ketene acetals catalyzed by GaBr3 took place to give the corresponding α‐alkenyl esters. GaBr3 showed the most effective catalytic ability, whereas other metal salts such as BF3?OEt2, AlCl3, PdCl2, and lanthanide triflates were not effective. Various types of enol ethers and vinyl carboxylates as enol derivatives are amenable to this coupling. The scope of the reaction with silyl ketene acetals was also broad. We successfully observed an alkylgallium intermediate by using NMR spectroscopy, suggesting a mechanism involving anti‐carbogallation among GaBr3, an enol derivative, and a silyl ketene acetal, followed by syn‐β‐alkoxy elimination from the alkylgallium. Based on kinetic studies, the turnover‐limiting step of the reaction using a vinyl ether and a vinyl carboxylate involved syn‐β‐alkoxy elimination and anti‐carbogallation, respectively. Therefore, the leaving group had a significant effect on the progress of the reaction. Theoretical calculations analysis suggest that the moderate Lewis acidity of gallium would contribute to a flexible conformational change of the alkylgallium intermediate and to the cleavage of the carbon?oxygen bond in the β‐alkoxy elimination process, which is the turnover‐limiting step in the reaction between a vinyl ether and a silyl ketene acetal. 相似文献