全文获取类型
收费全文 | 308333篇 |
免费 | 4406篇 |
国内免费 | 988篇 |
专业分类
化学 | 171661篇 |
晶体学 | 4022篇 |
力学 | 11760篇 |
综合类 | 4篇 |
数学 | 39125篇 |
物理学 | 87155篇 |
出版年
2021年 | 2387篇 |
2020年 | 2719篇 |
2019年 | 2979篇 |
2018年 | 4135篇 |
2017年 | 3688篇 |
2016年 | 5974篇 |
2015年 | 4393篇 |
2014年 | 5802篇 |
2013年 | 15078篇 |
2012年 | 12361篇 |
2011年 | 14404篇 |
2010年 | 9212篇 |
2009年 | 8807篇 |
2008年 | 12759篇 |
2007年 | 12929篇 |
2006年 | 11725篇 |
2005年 | 11064篇 |
2004年 | 9782篇 |
2003年 | 8454篇 |
2002年 | 8142篇 |
2001年 | 8309篇 |
2000年 | 6429篇 |
1999年 | 5013篇 |
1998年 | 4129篇 |
1997年 | 4140篇 |
1996年 | 4000篇 |
1995年 | 3586篇 |
1994年 | 3504篇 |
1993年 | 3527篇 |
1992年 | 3823篇 |
1991年 | 3779篇 |
1990年 | 3616篇 |
1989年 | 3529篇 |
1988年 | 3520篇 |
1987年 | 3386篇 |
1986年 | 3242篇 |
1985年 | 4493篇 |
1984年 | 4644篇 |
1983年 | 3731篇 |
1982年 | 4178篇 |
1981年 | 4060篇 |
1980年 | 3895篇 |
1979年 | 3879篇 |
1978年 | 4114篇 |
1977年 | 3894篇 |
1976年 | 4137篇 |
1975年 | 3692篇 |
1974年 | 3794篇 |
1973年 | 4096篇 |
1972年 | 2453篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
The influence of different referencing methods on the accuracy of δ13C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry 下载免费PDF全文
3.
The European Physical Journal Special Topics - The removal of suspended particles from the interior of a thermocapillary liquid bridge via a finite-particle-size effect restricting the particle... 相似文献
4.
Nano palladium supported on high‐surface‐area metal–organic framework MIL‐101: an efficient catalyst for Sonogashira coupling of aryl and heteroaryl bromides with alkynes 下载免费PDF全文
Manne Annapurna T. Parsharamulu P. Vishnuvardhan Reddy M. Suresh Pravin R. Likhar Mannepalli Lakshmi Kantam 《应用有机金属化学》2015,29(4):234-239
Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
5.
6.
7.
Pd0‐Catalyzed Intramolecular α‐Arylation of Sulfones: Domino Reactions in the Synthesis of Functionalized Tetrahydroisoquinolines 下载免费PDF全文
Prof.Dr. Daniel Solé Ferran Pérez‐Janer Dr. Raffaella Mancuso 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4580-4584
A new strategy for the synthesis of tetrahydroisoquinolines based on the Pd0‐catalyzed intramolecular α‐arylation of sulfones is reported. The combination of this Pd‐catalyzed reaction with intermolecular Michael and aza‐Michael reactions allows the development of two‐ and three‐step domino processes to synthesize diversely functionalized scaffolds from readily available starting materials. 相似文献
8.
9.
Biodistribution study of free and microencapsulated 6‐methylcoumarin in Wistar rats by HPLC 下载免费PDF全文
Aura Rocío Hernández Luis Fernando Ospina Diana Marcela Aragón 《Biomedical chromatography : BMC》2015,29(2):176-181
A sensitive, specific and reproducible HPLC method has been developed and validated for the quantitative determination of 6‐methylcoumarin (6MC) in plasma and other tissues in Wistar rats. A C18 column was used with UV detection at 321 nm and a gradient system consisting of methanol‐deionized water was used as mobile phase. The retention time for 6MC was 14.921 min and no interfering peaks were observed for any of the matrices. Linear relationships (r2 > 0.997) were obtained between the peak height ratios and the corresponding biological sample concentrations over the range 0.4–12.8 µg/mL. Precision and accuracy were evaluated; the coefficient of variation and the relative error for all of the organs were <2 and 7%, respectively. The limit of quantitation was 0.20 µg/mL for the heart and 0.30 µg/mL for the other tissues evaluated. This HPLC method was successfully used in the determination of 6MC in the biodistribution study after administration of 200 mg/kg of both 6MC‐free and 6MC‐loaded polymeric microparticles. In this study, extensive 6MC was found, in both free and microencapsulated forms, in all the organs tested. The 6MC‐free showed a range of between 1.7 and 11.5 µg/g, while the microencapsulated 6MC showed concentrations of between 6.35 and 17.7 µg/g, suggesting that 6MC improved absorption rate. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
10.