全文获取类型
收费全文 | 3938篇 |
免费 | 165篇 |
国内免费 | 75篇 |
专业分类
化学 | 2611篇 |
晶体学 | 30篇 |
力学 | 145篇 |
综合类 | 2篇 |
数学 | 582篇 |
物理学 | 808篇 |
出版年
2023年 | 32篇 |
2022年 | 27篇 |
2021年 | 54篇 |
2020年 | 54篇 |
2019年 | 54篇 |
2018年 | 48篇 |
2017年 | 30篇 |
2016年 | 88篇 |
2015年 | 77篇 |
2014年 | 108篇 |
2013年 | 211篇 |
2012年 | 264篇 |
2011年 | 277篇 |
2010年 | 146篇 |
2009年 | 146篇 |
2008年 | 240篇 |
2007年 | 224篇 |
2006年 | 225篇 |
2005年 | 196篇 |
2004年 | 178篇 |
2003年 | 152篇 |
2002年 | 117篇 |
2001年 | 95篇 |
2000年 | 97篇 |
1999年 | 59篇 |
1998年 | 62篇 |
1997年 | 41篇 |
1996年 | 77篇 |
1995年 | 54篇 |
1994年 | 52篇 |
1993年 | 49篇 |
1992年 | 44篇 |
1991年 | 37篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 27篇 |
1987年 | 26篇 |
1986年 | 20篇 |
1985年 | 48篇 |
1984年 | 29篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 38篇 |
1980年 | 29篇 |
1979年 | 25篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 20篇 |
1975年 | 25篇 |
1974年 | 37篇 |
排序方式: 共有4178条查询结果,搜索用时 15 毫秒
121.
Wong PS Yoshioka K Xie F Kissinger PT 《Rapid communications in mass spectrometry : RCM》1999,13(5):407-411
Liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been coupled to in vivo microdialysis for on-line monitoring of melatonin in a freely moving rat for a period of 15 hours. A microdialysis probe was surgically implanted into the jugular vein of the rat, and deionized water was used as the perfusion medium at a flow rate of 1.0 microL/min. Microdialysis samples were collected in an on-line injector with sample injection every 30 minutes. Melatonin was dosed by intraperitoneal (i.p.) injection and then monitored by microdialysis/LC/MS/MS. The whole experiment, including the microdialysis sampling and sample injection into the LC/MS system, was fully automated. Metabolites of melatonin were identified off-line by LC/MSn experiments. Two metabolites were identified as 6-hydroxymelatonin and cyclic 2-hydroxymelatonin, consistent with ones found previously in the literature. 相似文献
122.
维生素K1分子侧链上有一双键,因而存在几何异构体.天然维生素K1是2,3一反式构型,合成品为顺式和反式异构体的混合物,而顺式异构体几乎没有生理活性.故此,八十年代以后,各国药典均对维生素K;顺式异构体规定了限量,中国药典(1995版)规定顺式异构体的含量不得超过ZI.0%[’].目前国内流行的制备方法是以甲素配为起始原料,须经还原、乙酸化、水解、缩合、再水解和氧化五步反应制得[’],步骤长、收率低、对环境污染大.而用异植物酶合成引人侧链时,制备的维生素K;顺式异构体含量较高,达不到药典要求.为满足新版药典的… 相似文献
123.
The molecular structures of 1,3-benzodioxole and 1,3-indandione partially oriented in nematic solvents have been studied by NMR. Results for 1,3-indandione agree well with a planar model. The structural parameters are similar to those obtained by X-ray studies. No keto-enol tautomerism is observed. An anomalous structural result is obtained for 1,3-benzodioxole if the molecule is assumed to be planar. Dipolar couplings agree well with puckered model. The puckering angle is found to be about 15.5° ± 2°, similar to the values observed for TTF, TSeF and 2,5-dihydrofuran. 相似文献
124.
From proton magnetic resonance spectra of TTF and TCNQ partially oriented in nematic liquid crystal solvents the ratio of length to width of the proton rectangle is 3.124 ± 0.03 for TTF and 1.765 ± 0.024 for TCNQ. Values of JCH obtained for TTF dissolved in d6-acetone, are JCH = 187.9 ± 0.3 Hz, JCCH = 6.7 ±0.1 Hz and JCSCH = 9.0 ±0.2 Hz. 相似文献
125.
Angelo J. Amoroso Brian F. G. Johnson Jack Lewis Chi-Keung Li Catherine A. Morewood Paul R. Raithby Maria D. Vargas Wing-Tak Wong 《Journal of Cluster Science》1995,6(1):163-173
Reduction of the heptaosmium cluster [Os7(CO)21] With [Et4N][NH4) gives the cluster dianion [Os7(CO)20]2–,1, in high yield. The reaction of the dianion with [AuPR
3Cl] (R=Et or Ph) in the presence of TlPF6 forms [Os7((CO)20(AuPR
3)2] [R=Et (2a);R = Ph(2b)] in 80% yield, while the corresponding reaction with (Os(C6H6)(CH3CN)3]2+ gives [Os8(CO)20 (
6-C6H6)] (3) in reasonable yield (ca. 30%). The dianion,1, and the clusters2 and3 have been fully characterized by bout spectroscopic and crystallographic methods. The crystal structure of the [Ph4P]+ salt of1 shows that the metals in the anion adopt a capped octahedral geometry, with all twenty carbonyl ligands in terminal sites. The metal core geometry in2a is best described as a tricapped octahedron, and is based on the structure of the dianion1 with two adjacent octahedral faces capped by the Au atoms of the two AuPEt3 groups. In a similar fashion, the geometry of3 is related to that of1 with the addition of an Os(C6H6) unit capped to a triangular face, to give a bicapped octahedral framework. 相似文献
126.
Wei Y Guo X Shuang S Dong C Sun X Wong M 《Journal of photochemistry and photobiology. B, Biology》2005,81(3):190-194
Novel dimeric capsules are generated from the noncovalent assembly of 5, 10, 15, 20-tetrakis(4-N-ethylpyridiniurmyl)prophyrin (TEPyP) and tetracarboxyl-phenyl calix[4]arene. The self-assembly system was investigated based on UV-Vis absorption and fluorescent spectra. The factors affecting the interaction process including pH and concentration were examined in detail. The association constants between TEPyP and calix[4]arene were determined by the nonlinear least squares fit. The results showed that the basic medium is favourable to the interaction and electrostatic interaction was determinate in the processes of self-assembly process. The related mechanism was discussed. 相似文献
127.
Summary Two high-performance liquid chromatography (HPLC) techniques were developed for the determination of binding constants in
the interaction of serum albumin with L-tryptophan: internal calibration and external calibration. The results obtained were
compared with those obtained by the classical method of equilibrium dialysis and by gel filtration. While all the methods
are equally reliable, the internal and external calibration techniques seem to be superior in their simplicity, speed and
convenience. 相似文献
128.
129.
130.