全文获取类型
收费全文 | 658篇 |
免费 | 135篇 |
国内免费 | 103篇 |
专业分类
化学 | 480篇 |
晶体学 | 16篇 |
力学 | 34篇 |
综合类 | 16篇 |
数学 | 66篇 |
物理学 | 284篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 22篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 23篇 |
2015年 | 28篇 |
2014年 | 28篇 |
2013年 | 50篇 |
2012年 | 62篇 |
2011年 | 58篇 |
2010年 | 51篇 |
2009年 | 43篇 |
2008年 | 56篇 |
2007年 | 38篇 |
2006年 | 32篇 |
2005年 | 29篇 |
2004年 | 28篇 |
2003年 | 46篇 |
2002年 | 56篇 |
2001年 | 51篇 |
2000年 | 33篇 |
1999年 | 31篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有896条查询结果,搜索用时 187 毫秒
51.
Determination of Fatty Acid Methyl Esters in Biodiesel Produced from Yellow Horn Oil by LC 总被引:2,自引:0,他引:2
Yu-Jie Fu Yuan-Gang Zu Li-Li Wang Nai-Jing Zhang Wei Liu Shuang-Ming Li Su Zhang 《Chromatographia》2008,67(1-2):9-14
A simple and accurate HPLC method with refractive index detection was developed to determine the main fatty acid methyl esters
in biodiesel produced from yellow horn oil. Methyl linoleate, methyl linolenate, methyl arachidate, methyl stearate, methyl
palmitate and methyl oleate were separated on a HIQ SIL C18W column using methanol as mobile phase. The method has good repeatability
and precision, the intraday and interday RSD for both retention time and peak area was less than 3.2%. The LOD (S/N = 3) and
LOQ (S/N = 9) were less than 0.004 and 0.015 mg mL−1, respectively. 相似文献
52.
Li Liu Ling‐Xiang Qiao Shi‐Zhong Liu Dong‐Mei Cui Chun‐Mei Zhang Zheng‐Ji Zhou Zu‐Liang Du Wai‐Yeung Wong 《Journal of polymer science. Part A, Polymer chemistry》2008,46(10):3193-3206
A new family of organometallic/inorganic composite Langmuir‐Blodgett (LB) films consisting of rigid‐rod polyplatinayne polymer ([Pt‐T(OMe‐Fl)T]∞ or [Pt‐T(F‐Fl)T]∞, where the triplet bonds are abbreviated by T, and fluorene ring by Fl) as the π‐conjugated organometallic molecule, polyoxometalate (POM, POM = K3PMo12O40, H3PW12O40, or H6P2W18O62) of the Keggin and Dawson structures as the inorganic component, and dimethyldioctadecylammonium bromide (DODA) or a mixture of octadecanoic acid (OA) and docosanoic acid (DA) as the auxiliary film‐forming agent were prepared and characterized by π–A isotherms, UV–Vis absorption spectra, photoluminescence spectra, atomic force microscopy imaging, scanning tunneling microscopy, and low‐angle X‐ray diffraction. Our experimental results indicate that steady, even, and ordered Langmuir and LB films are formed in pure water and polyoxometalate subphases. It was shown that the POM molecules are probably embedded inside the polyplatinayne molecules in the LB film structure and they can quench the luminescence of the Pt polyyne. These Pt‐polyyne based LB films display interesting electric conductivity behavior. [Pt‐T(OMe‐Fl)T]∞/DODA/HPW12 monolayer film shows a good electrical conductivity, and the tunneling current amounts to ±100 nA when the voltage is set at ±8 V. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3193–3206, 2008 相似文献
53.
N-Octadecyl-N′-maleoyl-L-phenylalanine(ODMA-L-Phe)was synthesized through the condensation,deprotection and acid- ylation reaction of BOC-L-phenylalauine,octadecylamine and maleic anhydride,ODMA-L-Phe can self-assemble in some organic solvents and turned them into thermally reversible physical supramolecular organogels.The morphology of ODMA-L-Phe aggregates was characterized by polarized optical microscopy(POM)and field emission scanning electron microscope(FE-SEM). The aggregates of ODMA-L-Phe were needle-like fibrils with diameters of approximately 100-200 nm.The mechanism of ODMA- L-Phe serf-assembly in organic solvents was investigated using ~1H NMR and circular dichroism(CD).The results indicated that hydrogen bonding was one of the main driving forces for the self-assembly of ODMA-L-Phe. 相似文献
54.
本文以量级分析为基础,建立了一般曲线坐标系上的三维旋转边界层方程。对旋转在边界层中的影响进行分析之后,提出了一个能够处理壁面法向压力梯度不为零问题的压力梯度迭代方法。在传统的Box法的基础上发展了一套完整的求解三维旋转边界层的方法和程序,并对螺旋面、压气机转子叶面以及圆柱面上的旋转边界层进行了计算,与他人的计算和实验的对比分析表明,该方法和程序是正确的,可用于求解任意几何物面上的三维旋转边界层。 相似文献
55.
Miao Yu Sheng‐Zhen Zu Dr. Yong Chen Dr. Yu‐Ping Liu Dr. Bao‐Hang Han Prof. Dr. Yu Liu Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(4):1168-1174
A supramolecular hybrid is prepared by the supramolecular surface modification of single‐walled carbon nanotube (SWCNT) with cationic β‐cyclodextrin‐tethered ruthenium complexes through a spacer molecule that contains both an adamantane and a pyrene moiety. By employing the supramolecular hybrid, spatially controllable DNA condensation along the SWCNT skeleton is achieved by anchoring cationic ruthenium complexes on the surface. Furthermore, because of the unique physiological properties of SWCNTs, the cationic supramolecular hybrid can be used as a nonviral gene delivery system with the ruthenium complexes as a fluorescent probe to monitor uptake of DNA by cells. 相似文献
56.
Juan Peng Lily Zu Weihai Fang Lingyun Huang Yaru Wang Dacheng He 《Journal of mass spectrometry : JMS》2010,45(6):627-634
An understanding of the dissociation of penetratin is important for improving its metabolic stability and cargo‐delivery efficiency. In this study, we describe the selective cleavage of the K15–K16 amide bond of penetratin under the low‐energy collision‐induced dissociation condition in mass spectrometry. A variety of penetratin substitutes have been studied in which key basic amino acids have been substituted within the sequence. The calculated structure indicates that an α‐helix structure prevents the fragmentation of the central peptide domain and the side chain of lysine is involved in the proton translocation process. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
57.
58.
A novel method using liquid chromatography coupled to electrospray ionization mass spectrometry (LC-ESI-MS) has been optimized and established for the qualitative and quantitative analysis of ten active phenolic compounds originating from the pigeon pea leaves and a medicinal product thereof (Tongluo Shenggu capsules). In the present study, the chromatographic separation was achieved by means of a HiQ Sil C18V reversed-phase column with a mobile phase consisting of methanol and 0.1% formic acid aqueous solution. Low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) using the selected reaction monitoring (SRM) analysis was employed for the detection of ten analytes which included six flavonoids, two isoflavonoids and two stilbenes. All calibration curves showed excellent coefficients of determination (r(2) ≥ 0.9937) within the range of tested concentrations. The intra- and inter-day variations were below 5.36% in terms of relative standard deviation (RSD). The recoveries were 95.08-104.98% with RSDs of 2.06-4.26% for spiked samples of pigeon pea leaves. The method developed was a rapid, efficient and accurate LC-MS/MS method for the detection of phenolic compounds, which can be applied for quality control of pigeon pea leaves and related medicinal products. 相似文献
59.
60.
In this paper,kinematic formulae in a real space form are investigated.A kinematic formula for homogeneous polynomial of degree 4 on the second fundamental forms in a real space form is obtained.The formula obtained is a concrete form of the result of Howard and the analogue of the known formula of Chen and Zhou. 相似文献