全文获取类型
收费全文 | 3506篇 |
免费 | 69篇 |
国内免费 | 16篇 |
专业分类
化学 | 2636篇 |
晶体学 | 37篇 |
力学 | 43篇 |
数学 | 176篇 |
物理学 | 699篇 |
出版年
2022年 | 18篇 |
2021年 | 20篇 |
2020年 | 38篇 |
2019年 | 54篇 |
2018年 | 43篇 |
2017年 | 20篇 |
2016年 | 60篇 |
2015年 | 52篇 |
2014年 | 74篇 |
2013年 | 162篇 |
2012年 | 169篇 |
2011年 | 195篇 |
2010年 | 115篇 |
2009年 | 108篇 |
2008年 | 187篇 |
2007年 | 184篇 |
2006年 | 174篇 |
2005年 | 183篇 |
2004年 | 152篇 |
2003年 | 155篇 |
2002年 | 145篇 |
2001年 | 87篇 |
2000年 | 92篇 |
1999年 | 57篇 |
1998年 | 39篇 |
1997年 | 38篇 |
1996年 | 49篇 |
1995年 | 31篇 |
1994年 | 35篇 |
1993年 | 44篇 |
1992年 | 40篇 |
1991年 | 46篇 |
1990年 | 48篇 |
1989年 | 33篇 |
1988年 | 43篇 |
1987年 | 45篇 |
1986年 | 38篇 |
1985年 | 68篇 |
1984年 | 50篇 |
1983年 | 27篇 |
1982年 | 40篇 |
1981年 | 40篇 |
1980年 | 24篇 |
1979年 | 37篇 |
1978年 | 35篇 |
1977年 | 42篇 |
1976年 | 31篇 |
1975年 | 26篇 |
1974年 | 19篇 |
1973年 | 23篇 |
排序方式: 共有3591条查询结果,搜索用时 15 毫秒
161.
T Yoshida 《Journal of chromatography. A》1991,570(2):321-328
A simple, accurate and precise isocratic reversed-phase high-performance liquid chromatographic method was developed and validated for the determination of p-chloronitrobenzene (p-CNB) in rat plasma. A plasma sample was deproteinized with methanol containing the internal standard (p-bromonitrobenzene). The resulting methanol eluate obtained after centrifugation was filtered and injected into a high-performance liquid chromatograph (50 microliters each). A column packed with 5 microns octadecylsilane (ODS) spherical particles was used with isocratic elution of methanol-water (45:55, v/v) at a flow-rate of 1.0 ml/min. The compounds were detected by ultraviolet absorbance at 280 nm. The retention times of p-CNB and the internal standard were 12.5 and 15.5 min, respectively, at a column oven temperature of 30 degrees C. The results were linear from 0.05 to 100 micrograms/ml (r = 0.999), and the detection limit was 0.01 microgram/ml. The relative error and the coefficient of variation on replicate assays were less than 7 and 10%, respectively, for all concentrations studied. The overall recoveries of p-CNB were between 97 and 105%. Plasma samples could be stored for up to one month at -20 degrees C. 相似文献
162.
M Imuta H Itani H Ona Y Hamada S Uyeo T Yoshida 《Chemical & pharmaceutical bulletin》1991,39(3):663-671
The synthesis and antibacterial activity of the 1-methylcarbapenems, 2-heteroaromatic-thiomethyl and 2-carbamoyloxymethyl derivatives having a 6-[(R)-1-hydroxyethyl] side chain, are described. The introduction of a methyl substituent at the C-1 position was accomplished by a newly developed procedure using crotyl halides and zinc dust. The 2-hydroxymethyl carbapenems as key intermediates allowed an easy entry into the preparation of title carbapenems. 相似文献
163.
The synthesis of 1 alpha- and/or 1 beta-methylcarbapenems, 2-unsubstituted and 2-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl derivatives having a 1-(hydroxy)methylethylidene or cyclic carbonate side chain at the C-6 position, is described. The in vitro antibacterial activities of these compounds and their corresponding 1-unsubstituted carbapenems are compared. 相似文献
164.
165.
166.
Takuma Shinya Nakashima Noriyuki Tantirungkij Manee Kinoshita Shinichi Okada Hirosuke Sew TatsÜji Yoshida Toshiomi 《Applied biochemistry and biotechnology》1991,28(1):327-340
Applied Biochemistry and Biotechnology - A NADPH/NADH-dependent xylose reductase gene was isolated from the xylose-assimilating yeast,Pichia stipitis. DNA sequence analysis showed that the gene... 相似文献
167.
Dr. Yusaku Nomura Dr. Frédéric Thuaud Dr. Daisuke Sekine Prof. Dr. Akihiro Ito Satoko Maeda Dr. Hiroyuki Koshino Dr. Daisuke Hashizume Dr. Atsuya Muranaka Dr. Thomas Cruchter Prof. Dr. Masanobu Uchiyama Prof. Dr. Satoshi Ichikawa Prof. Dr. Akira Matsuda Prof. Dr. Minoru Yoshida Prof. Dr. Go Hirai Prof. Dr. Mikiko Sodeoka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(35):8387-8392
A synthetic methodology to access all possible stereoisomers of spectomycin A1 (SMA1) and A2 (SMA2) has been established through late-stage diversification. The key reaction for the construction of all four diastereomers is an intramolecular cyclization based on the umpolung of π-allyl palladium species with bis(pinacolato)diborane (B2(pin)2). Silyl group assisted direct benzylic oxidation of each isomer enabled construction of the fragile β-hydroxytetralone skeleton to provide the SMAs. The relative and absolute stereochemistry of SMA2 was also determined, and the absolute stereochemistry of SMA1 was extrapolated based on the optical rotation of SMA2. The axial chirality of SMAs is discussed based on circular dichroism spectra and DFT calculations, and it is concluded that the M isomer is predominant in solution. Biochemical assessment of all isomers in vitro revealed that the C9 hydroxyl group and dimeric structure were both important for protein SUMOylation-inhibitory activity. 相似文献
168.
S Sugai Y Kajiwara T Kanbara Y Naito S Yoshida S Akaboshi S Ikegami Y Kamano 《Chemical & pharmaceutical bulletin》1986,34(4):1613-1618
169.
170.
Treatment of 3,4-alkadienyl carbonates 2a-i with a low-valent titanium reagent diisopropoxy(eta(2)-propene)titanium (1), readily generated by the reaction of Ti(O-i-Pr)(4) with 2 i-PrMgCl, resulted in an intramolecular nucleophilic acyl substitution (INAS) reaction to afford vinyltitanium compounds 3 which, in turn, reacted with H(3)O(+), D(2)O, or iodine to give alpha-substituted beta,gamma-unsaturated esters 4 in good to excellent yields. The olefin moiety of the hydrolysis product 4 has (Z)-geometry mainly except for 4h. Starting from chiral 2f or 2g, the reaction proceeded stereospecifically to give optically active alpha-substituted beta,gamma-unsaturated ester 4f or 4g having (Z)-olefin geometry exclusively. 相似文献