全文获取类型
收费全文 | 8291篇 |
免费 | 708篇 |
国内免费 | 1133篇 |
专业分类
化学 | 6802篇 |
晶体学 | 44篇 |
力学 | 243篇 |
综合类 | 46篇 |
数学 | 70篇 |
物理学 | 2927篇 |
出版年
2024年 | 10篇 |
2023年 | 198篇 |
2022年 | 277篇 |
2021年 | 334篇 |
2020年 | 369篇 |
2019年 | 269篇 |
2018年 | 193篇 |
2017年 | 366篇 |
2016年 | 440篇 |
2015年 | 414篇 |
2014年 | 511篇 |
2013年 | 512篇 |
2012年 | 657篇 |
2011年 | 522篇 |
2010年 | 448篇 |
2009年 | 547篇 |
2008年 | 546篇 |
2007年 | 547篇 |
2006年 | 457篇 |
2005年 | 414篇 |
2004年 | 409篇 |
2003年 | 282篇 |
2002年 | 238篇 |
2001年 | 194篇 |
2000年 | 137篇 |
1999年 | 135篇 |
1998年 | 134篇 |
1997年 | 120篇 |
1996年 | 69篇 |
1995年 | 75篇 |
1994年 | 48篇 |
1993年 | 56篇 |
1992年 | 35篇 |
1991年 | 39篇 |
1990年 | 35篇 |
1989年 | 21篇 |
1988年 | 25篇 |
1987年 | 19篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Sanjukta A. Kumar Neha Thakur Harshala J. Parab Shailaja P. Pandey Rakesh N. Shinde Ashok K. Pandey Sangita D. Kumar A.V.R. Reddy 《Analytica chimica acta》2014
A visual strip has been developed for sensing iron in different aqueous samples like natural water and fruit juices. The sensor has been synthesized by UV-radiation induced graft polymerization of acrylamide monomer in microporous poly(propylene) base. For physical immobilization of iron selective reagent, the in situ polymerization of acrylamide has been carried out in the presence of 1,10-phenanthroline. The loaded strip on interaction with Fe(II) in aqueous solution turned into orange red color and the intensity of the color was found to be directly proportional to the amount of Fe(II) in the aqueous sample. The minimal sensor response with naked eye was found for 50 ng mL−1 of Fe in 15 min of interaction. However, as low as 20 ng mL−1 Fe could be quantified using a spectrophotometer. The detection limit calculated using the 3s/S criteria, where ‘s’ is the standard deviation of the absorbance of blank reagent loaded strip and ‘S’ is the slope of the linear calibration plot, was 1.0 ng mL−1. The strip was applied to measure Fe in a variety of samples such as ground water and fruit juices. 相似文献
992.
A molecularly imprinted copolymer, poly(o-phenylenediamine-co-o-aminophenol) (PoPDoAP), was prepared as a new ascorbic acid (AA) sensor. The copolymer was synthesized by incorporation of AA as template molecules during the electrochemical copolymerization of o-phenylenediamine and o-aminophenol, and complementary sites were formed after the copolymer was electrochemically reduced in ammonium aqueous solution. The molecularly imprinted copolymer sensor exhibited a high sensitivity and selectivity toward AA. Differential pulse voltammograms (DPVs) showed a linear concentration range of AA from 0.1 to 10 mM, and the detection limit was calculated to be 36.4 μM. Compared to conventional polyaniline-based AA sensors, the analytical performance of the imprinted copolymer sensor was improved due to the broadened usable pH range of PoPDoAP (from pH 1.0 to pH 8.0). The sensor also exhibited a good reproducibility and stability. And it has been successfully applied in the determination of AA in real samples, including vitamin C tablet and orange juices, with satisfactory results. 相似文献
993.
Construction and Validation of New Electrochemical Carbon Nanotubes Sensors for Determination of Acebutolol Hydrochloride in Pharmaceuticals and Biological Fluids 下载免费PDF全文
A simple, rapid and a highly selective method for direct electrochemical determination of acebutolol hydrochloride (AC) was developed. The developed method was based on the construction of three types of sensors conventional polymer (I), carbon paste (II) and modified carbon nanotubes (MCNTs) carbon paste (III). The fabricated sensors depend mainly on the incorporation of acebutolol hydrochloride with phosphotungstic acid (PTA) forming ion exchange acebutolol‐phosphotungstate (AC‐PT). The performance characteristics of the proposed sensors were studied. The sensors exhibited Nernstian responses (55.6 ± 0.5, 57.14 ± 0.2 and 58.6 ± 0.4 mV mol L?1) at 25 °C over drug concentration ranges (1.0 × 10?6‐1.0 × 10?2, 1.0 × 10?7‐1.0 × 10?2 and 5.0 × 10?8‐1.0 × 10?2 mol L?1 with lower detection limits of (5.0 × 10?7, 5.0 × 10?8 and 2.5 × 10?8 mol L?1 for sensors (I), (II) and (III), respectively. The influence of common and possible interfering species, pharmaceutical additives and some related pharmacological action drugs was investigated using separate solution method and no interference was found. The stability indicating using forced degradation of acebutolol hydrochloride was studied. The standard addition method was used for determination of the investigated drug in its pharmaceutical dosage forms and biological fluids. The results were validated and statistically analysed and compared with those from previously reported methods. 相似文献
994.
995.
Manoj K. KesharwaniMoorthy Suresh Amitava Das Bishwajit Ganguly 《Tetrahedron letters》2011,52(28):3636-3639
The computational and experimental studies have revealed that even simple molecule like borazine can act as a sensor for fluoride ions. This study further reported the various binding modes of analytes using quantum chemical calculations and the nature of such interactions have been examined using electron density surface analysis. Total charge transfer analysis (qCT) correlates well with the binding affinities of analytes with the borazine receptor. 相似文献
996.
Jafar Ezzati Nazhad DolatabadiOmid Mashinchian Baharak AyoubiAli Akbar Jamali Ahmad MobedDusan Losic Yadollah Omidi Miguel de la Guardia 《Trends in analytical chemistry : TRAC》2011,30(3):459-472
In the past two decades, nanoscale advanced materials have been explored for biosensing molecules, so new horizons have opened up for identifying and quantifying biomolecules, and possible early diagnosis of diseases.DNA nanobiosensors show promise. This article provides an overview on their optical and electrochemical aspects. We discuss recent progress in this field, describing basic concepts of molecular beacons and quantum dots as optical nano-imaging systems. Also, carbon nanotubes provide a platform for development and advancement of electrochemical DNA nanobiosensors, which are increasingly being implemented as robust tools for detection in biomedical sciences. 相似文献
997.
A novel dipyrene ligand 1 has been designed which shows intramolecular excimer formation in solution. Its specific interaction with Cu2+ or Hg2+ leads to the disruption of the excimer and results in a fluorescence-mediated sensing of these ions in a mixed organic-aqueous solution. Apart from steady-state studies, time-resolved fluorescence measurements also reveal that excimer-switch off caused by metal ion coordination leads to the selective detection of these ions. 相似文献
998.
A simple analytical scheme for the detection and quantification of amitrol and triazine herbicides (atrazine, ametryn and atraton) and degradation product (2‐hydroxyatrazine) in environmental water samples by CZE is reported. On‐column preconcentration of analytes from untreated water samples (mineral, spring, tap and river water) is accomplished by introducing an acid plug (200 mM citrate of pH 2.0) after the sample and then proceeding with the CZE separation, using 100 mM formiate buffer of pH 3.5 as running buffer and 25.0 KV as separation voltage. UV detection at 200 nm provides LODs from 50 to 300 nM in untreated samples and they were lowered tenfold by sample preconcentration by evaporation. Calculated recoveries were typically higher than 90%. Minimal detectable concentration of the electroactive amitrol could be decreased about 20‐fold when electrochemical detection was employed by monitoring the amperometric signal at +800 mV using a carbon paste electrode (LOD of 9.6 nM, 0.81 μg/L, versus 170 nM, 14.3 μg/L, using amperometric and UV detection, respectively) in untreated water samples. 相似文献
999.
1000.