全文获取类型
收费全文 | 29524篇 |
免费 | 5642篇 |
国内免费 | 3189篇 |
专业分类
化学 | 21152篇 |
晶体学 | 321篇 |
力学 | 1763篇 |
综合类 | 136篇 |
数学 | 2970篇 |
物理学 | 12013篇 |
出版年
2024年 | 47篇 |
2023年 | 666篇 |
2022年 | 739篇 |
2021年 | 1063篇 |
2020年 | 1376篇 |
2019年 | 1344篇 |
2018年 | 1130篇 |
2017年 | 997篇 |
2016年 | 1555篇 |
2015年 | 1436篇 |
2014年 | 1873篇 |
2013年 | 2305篇 |
2012年 | 2810篇 |
2011年 | 2867篇 |
2010年 | 1867篇 |
2009年 | 1780篇 |
2008年 | 1992篇 |
2007年 | 1736篇 |
2006年 | 1624篇 |
2005年 | 1279篇 |
2004年 | 973篇 |
2003年 | 747篇 |
2002年 | 713篇 |
2001年 | 562篇 |
2000年 | 446篇 |
1999年 | 579篇 |
1998年 | 503篇 |
1997年 | 487篇 |
1996年 | 480篇 |
1995年 | 420篇 |
1994年 | 342篇 |
1993年 | 276篇 |
1992年 | 276篇 |
1991年 | 223篇 |
1990年 | 200篇 |
1989年 | 151篇 |
1988年 | 92篇 |
1987年 | 79篇 |
1986年 | 103篇 |
1985年 | 73篇 |
1984年 | 37篇 |
1983年 | 43篇 |
1982年 | 26篇 |
1981年 | 22篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1957年 | 4篇 |
1923年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
An LC‐MS/MS method for simultaneous determination of cefprozil diastereomers in human plasma and its application for the bioequivalence study of two cefprozil tablets in healthy Chinese volunteers 下载免费PDF全文
Min Liu Jing‐Yi Ma Yanan Zhang Xiaolin Wang Hongna Zhao Aihua Du Man Yang Lingjie Meng Ming Deng Huichen Liu 《Biomedical chromatography : BMC》2016,30(3):288-293
A rapid and sensitive liquid chromatography–tandem mass spectrometric method was developed for the first time and validated for the determination of cefprozil diastereomers in human plasma. The plasma samples were prepared by protein precipitation using acetonitrile. Detection was performed using an electronic spray ion source in the negative ion mode, operating in the multiple reaction monitoring of the transitions m/z 388.0 to m/z 205.0 for cefprozil diastereomers and m/z 346.1 to m/z 268.1 for cephalexin (the internal standard). The calibration curves of cis‐cefprozil and trans‐cefprozil were linear in the ranges 0.125–16.0 µg/mL and 0.0403–1.72 µg/mL, respectively. The lower limits of quantification of cis‐ and trans‐cefprozil were 0.125 and 0.0403 µg/mL in human plasma, respectively. The intra‐ and inter‐day precisions of cis‐ and trans‐cefprozil were all <9.7%, and the accuracy ranged from 99.2 to 104.7% and from 100.6 to 102.2%, respectively. The validated method was successfully applied to a bioequivalence study of two cefprozil formulations in 24 healthy Chinese volunteers. The two cefprozil tablets were bioequivalent by measurement of cis‐, trans‐ and total cefprozil. We suggest that the bioequivalence of cefprozil formulations can be evaluated only using cis‐cefprozil as the analyte in future studies. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
992.
A unique structured hollow carbon nanofiber–sulfur composite material (HCF–S) was fabricated and characterized in lithium-sulfur batteries. It is found that a part of spherical sulfur particles are located in the voids formed by the intertwined fibers and the others are confined in hollow channel of the HCF. The high conductive and porous HCF favors the construction of stable three-dimensional conducting network and convenient infiltration of the electrolytes into the cathode. The HCF–S cathode exhibits excellent electrochemical performance in the electrolyte with LiNO3. By contrast, the ionic liquid electrolyte provides insufficient shuttle suppression and weakens ion transport, which leads to poor cycle and rate capability. 相似文献
993.
994.
Conductivity as a Sensor for Monitoring Relative Magnesium Corrosion Rates in Real‐time,in Serum‐containing Media under Cell Culture Conditions 下载免费PDF全文
Kolade Ojo Tracy Hopkins Madhura Joshi Pravahan Salunke Guangqi Zhang Keaton Nahan Zhannping Zhang Daoli Zhao Sarah K. Pixley Vesselin Shanov William R. Heineman 《Electroanalysis》2016,28(12):3000-3008
Because controlling the corrosion rate of magnesium metal will be crucial to the success of biomedical implants containing pure magnesium or magnesium alloys, many ways have been sought to improve in vitro tests to analyze corrosion rates, and also to identify new methods of preparing or post‐processing magnesium. In this work, for an in vitro assay, we explored the use of a commercially available conductivity sensor to study magnesium corrosion under cell culture conditions that duplicate many physiologically appropriate parameters. With this sensor, we studied the corrosion of two previously untested magnesium single crystal samples that differed in surface treatments that could alter corrosion rates. The results show that the relative conductivity changes in (mS/cm) over the total time of immersion were proportional to the corrosion rates in (mm/y) and also to the total magnesium released, as detected by inductively coupled plasma mass spectrometry (ICP‐MS). 相似文献
995.
Based on some iteration schemes, we study the viscosity approximation results for multivalued nonexpansive mappings in Hilbert space and Banach space. For that mapping, we obtain a fixed point to solve its related variational inequality. 相似文献
996.
997.
Determination of ecliptasaponin A in rat plasma and tissues by liquid chromatography‐tandem mass spectrometry 下载免费PDF全文
Jing Zhao Erwei Liu Lifeng Han Linlin Wang Yi Zhang Tao Wang Shiming Fang Xiumei Gao 《Biomedical chromatography : BMC》2016,30(6):846-851
A sensitive, rapid and specific high‐performance liquid chromatography tandem mass spectrometry method (HPLC‐MS/MS) was developed to determine ecliptasaponin A in rat plasma and tissues after oral administration. Ginsenoside Rg1 was used as the internal standard (IS). The plasma and tissues samples were prepared by liquid‐liquid extraction with ethyl acetate and separated on an Eclipse Plus C18 column (2.1 mm × 150 mm, 5 µm) at a flow rate of 0.4 mL/min using acetonitrile and water (containing 0.05% acetic acid) as the mobile phase. The tandem mass detection was carried out with eletrospray ionization in negative mode. Quantification was performed by using multiple reaction monitoring (MRM), which monitored the fragmentation of m/z 633.4→587.2 for ecliptasaponin A and m/z 859.4→637.4 for the IS. The calibration curves obtained were linear in different matrices, and the lower limit of quantification (LLOQ) achieved was 0.5 ng/mL both for rat plasma and tissues. The intra‐ and inter‐day precisions were below 15%. This method was successfully applied to pharmacokinetic study of ecliptasaponin A in rat plasma and tissues after oral administration. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
998.
A simple LC‐MS method for determination of cyasterone in rat plasma: application to a pilot pharmacokinetic study 下载免费PDF全文
Fuqiang Li Guangyu Li Jinsong Zhao Jun Xiao Zaoxia Liu Guanfang Su 《Biomedical chromatography : BMC》2016,30(6):867-871
A simple, specific, and sensitive liquid chromatography–mass spectrometry (LC‐MS) method for determination of cyasterone in rat plasma was developed in our laboratory. Cucurbitacin B was used as an internal standard (IS). After protein precipitation with twofold volume of acetonitrile, the analyte and IS were separated on a Luna C18 column (100 × 4.6 mm, i.d., 3.0 µm; Phenomenex) by isocratic elution with acetonitrile–water (80:20, v/v) as the mobile phase at a flow rate of 0.4 mL/min. An electrospray ionization source was applied and operated in the positive ion mode; selected ion monitoring scan mode was used for quantification, and the target ions m/z 543.3 for cyasterone and m/z 581.3 for IS were chosen. Good linearity was observed in the concentration range of 0.40–400 ng/mL for cyasterone in rat plasma. Intra‐day and inter‐day precision were both <7.4%. This method was proved to be suitable for pharmacokinetic studies after oral (5.0 mg/kg) or intravenous (0.5 mg/kg) administration of cyasterone in rats. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
999.
1000.
With [5,10,15,20‐tetra(4‐carboxyphenyl)porphyrin]Mn(III) and sterically controlled 2,2¢‐dimethyl‐4,4¢‐pyridine as the main raw materials, metal–organic framework thin films containing metalloporphyrin (MnPor‐MOF) with catalytically active sites were built up on functionalized quartz glass surfaces using a layer‐by‐layer self‐assembly method. Retaining active catalytic sites and having a porous reticular structure, the MnPor‐MOF films possessed remarkable photocatalytic activity for oxidative degradation of methylene blue in the presence of hydrogen peroxide under visible‐light irradiation. Most meaningfully, the MnPor‐MOF films were highly stable and simply and conveniently reusable, and are thus a potentially new organic material for photocatalytic wastewater treatment. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献