全文获取类型
收费全文 | 92943篇 |
免费 | 799篇 |
国内免费 | 708篇 |
专业分类
化学 | 33651篇 |
晶体学 | 892篇 |
力学 | 7124篇 |
综合类 | 30篇 |
数学 | 33814篇 |
物理学 | 18939篇 |
出版年
2022年 | 170篇 |
2021年 | 196篇 |
2020年 | 201篇 |
2019年 | 204篇 |
2018年 | 10558篇 |
2017年 | 10337篇 |
2016年 | 6367篇 |
2015年 | 1145篇 |
2014年 | 666篇 |
2013年 | 1122篇 |
2012年 | 4385篇 |
2011年 | 11165篇 |
2010年 | 6129篇 |
2009年 | 6502篇 |
2008年 | 7223篇 |
2007年 | 9396篇 |
2006年 | 821篇 |
2005年 | 1915篇 |
2004年 | 2133篇 |
2003年 | 2574篇 |
2002年 | 1641篇 |
2001年 | 696篇 |
2000年 | 695篇 |
1999年 | 475篇 |
1998年 | 420篇 |
1997年 | 350篇 |
1996年 | 427篇 |
1995年 | 357篇 |
1994年 | 317篇 |
1993年 | 280篇 |
1992年 | 232篇 |
1991年 | 250篇 |
1990年 | 251篇 |
1989年 | 220篇 |
1988年 | 201篇 |
1987年 | 197篇 |
1986年 | 185篇 |
1985年 | 287篇 |
1984年 | 296篇 |
1983年 | 213篇 |
1982年 | 252篇 |
1981年 | 217篇 |
1980年 | 215篇 |
1979年 | 194篇 |
1978年 | 166篇 |
1977年 | 189篇 |
1976年 | 174篇 |
1975年 | 149篇 |
1974年 | 136篇 |
1973年 | 152篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Spherical molecularly imprinted polymer particles: a promising tool for molecular recognition in capillary electrokinetic separations 总被引:2,自引:0,他引:2
De Boer T Mol R De Zeeuw RA De Jong GJ Sherrington DC Cormack PA Ensing K 《Electrophoresis》2002,23(9):1296-1300
Spherical molecularly imprinted polymer particles obtained via precipitation polymerization, were introduced as a pseudostationary phase in capillary electrophoresis (CE) to study molecular recognition. Analyses were performed via a partial filling technique using (+)-ephedrine-imprinted microspheres (100-200 nm) which were polymerized from methacrylic acid and 1,1,1-Tris(hydroxymethyl)propanetrimethacrylate using acetonitrile as the solvent. The influence of pH and the modifier content on the separation was investigated. A 0.1% w/v suspension in an aqueous 10 mM phosphate buffer (pH 2.5 with 40% acetonitrile) was hydrodynamically injected into the CE system (80% of the effective capillary length) and led to full baseline separation of racemic ephedrine within 10 min. 相似文献
972.
Armentano D De Munno G Mastropietro TF Julve M Lloret F 《Journal of the American Chemical Society》2005,127(31):10778-10779
Intermolecular proton transfer in solid phase from the hydroxo bridge to a water molecule occurs in a new mu-hydroxo iron(III) compound of formula {EtNH3[Fe2(ox)2Cl2(mu-OH)].2H2O}n leading to a still crystalline compound in which the mu-oxo bridge replaces the mu-hydroxo one. Both three-dimensional compounds exhibit magnetic ordering at Tc ca. 70 K due to a spin canting. 相似文献
973.
De Wasch K Le Bizec B De Brabander H André F Impens S 《Rapid communications in mass spectrometry : RCM》2001,15(16):1442-1447
In previous work (Le Bizec et al., Rapid Commun. Mass Spectrom. 2000; 14: 1058), it was demonstrated that a boar meal intake could lead to possible false accusations of abuse of 17beta-nortestosterone in antidoping control. The aim of the present study was to identify and quantify endogenous 19-norsteroids in boar edible tissue at concentrations that can alter the steroid urinary profile in humans, and lead to excretion of 19-norandrosterone (19-NA) and 19-noretiocholanolone (19-NE). The samples were analysed in two laboratories. The methodologies used for extraction and detection (GC/MS(EI) and LC/MS/MS(APCI+)) are compared and discussed. 19-Norandrostenedione (NAED), 17beta- and 17alpha-nortestosterone (bNT, aNT), and 17beta- and 17alpha-testosterone (bT, aT) were quantified. The largest concentrations of NAED and bNT were observed in testicles (83 and 172 microg/kg), liver (17 and 63 microg/kg) and kidney (45 and 38 microg/kg). A correlation between the bNT and NAED content of a typical meal prepared with boar parts and the excreted concentrations of 19-NA and 19-NE in human urine was demonstrated. 相似文献
974.
Naert C De Saeger S Van Peteghem C 《Rapid communications in mass spectrometry : RCM》2004,18(19):2317-2322
A combined gas chromatographic mass spectrometric (GC/MS/MS) method for the determination of seven polybrominated diphenyl ethers (PBDEs) and seven marker polychlorinated biphenyls (PCBs) in adipose tissue has been developed. Adipose tissue was melted and filtered through anhydrous sodium sulphate to obtain pure fat. Clean-up was performed using a glass column containing acidified silica, deactivated alumina and anhydrous sodium sulphate. Polybrominated biphenyl (PBB) 155 and Mirex were added as internal standards for PBDEs and PCBs, respectively. Injection standards, PBB 103 and PCB 143, for PBDEs and PCBs, respectively, were added before analysis with GC/MS/MS. The developed GC/MS/MS method has the advantage of being more selective than single MS methods because matrix effects are largely eliminated. Validation of this method was conducted according to Commission Decision 2002/657/EC. Decision limits for PBDEs and PCBs ranged from 0.06-0.15 ng g(-1) and from 0.35-1.22 ng g(-1), respectively. Detection capabilities were all between 0.23-0.55 ng g(-1) for PBDEs and between 0.98-2.29 ng g(-1) for PCBs. Precision, recovery, bias and selectivity were tested, with satisfactory results. 相似文献
975.
976.
Fernandez E Ford WT Qi N Read AL Smith JG Camporesi T De Sangro R Marini A Peruzzi I Piccolo M Ronga F Blume HT Hurst RB Venuti JP Wald HB Weinstein R Band HR Gettner MW Goderre GP Meyer OA Moromisato JH Shambroom WD Sleeman JC von Goeler E Ash WW Chadwick GB Clearwater SH Coombes RW Kaye HS Lau KH Leedy RE Lynch HL Messner RL Moss LJ Muller F Nelson HN Ritson DM Rosenberg LJ Wiser DE Zdarko RW Groom DE Lee H Delfino MC Heltsley BK Johnson JR Lavine TL Maruyama T Prepost R 《Physical review letters》1985,54(15):1620-1623
977.
Miniaturizing all dimensions of apparatus, such as electronics and computers, is the current trend followed by scientists
in various fields. The idea of Lab-on-a-Chip has significantly expanded and found its broad applications in analytical chemistry.
Microplasmas can act as a sample excitation source and are the miniaturized versions of full-sized plasmas. These can be created
in various forms, such as direct current, microwave induced, capacitively coupled and inductively coupled plasmas. Scaling
down the size would reduce the amount of gases, liquids and consumables required, as well as the sample analysis time, which
in turn would decrease the operating costs. Therefore, several research groups are involved in the development of microplasmas
for utilisation in analytical instruments. 相似文献
978.
An activated D-residue of a protected dipeptide when coupled racemizes twice as much as an activated L-residue, which is contrary to the case for couplings of acylamino acids. 相似文献
979.
980.