全文获取类型
收费全文 | 2311篇 |
免费 | 73篇 |
国内免费 | 446篇 |
专业分类
化学 | 2625篇 |
晶体学 | 32篇 |
力学 | 3篇 |
综合类 | 15篇 |
数学 | 2篇 |
物理学 | 153篇 |
出版年
2023年 | 12篇 |
2022年 | 39篇 |
2021年 | 22篇 |
2020年 | 48篇 |
2019年 | 40篇 |
2018年 | 74篇 |
2017年 | 76篇 |
2016年 | 66篇 |
2015年 | 66篇 |
2014年 | 91篇 |
2013年 | 261篇 |
2012年 | 131篇 |
2011年 | 111篇 |
2010年 | 102篇 |
2009年 | 119篇 |
2008年 | 139篇 |
2007年 | 136篇 |
2006年 | 141篇 |
2005年 | 130篇 |
2004年 | 123篇 |
2003年 | 110篇 |
2002年 | 81篇 |
2001年 | 72篇 |
2000年 | 79篇 |
1999年 | 91篇 |
1998年 | 61篇 |
1997年 | 58篇 |
1996年 | 48篇 |
1995年 | 53篇 |
1994年 | 48篇 |
1993年 | 38篇 |
1992年 | 52篇 |
1991年 | 20篇 |
1990年 | 23篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
排序方式: 共有2830条查询结果,搜索用时 15 毫秒
71.
Determination of medroxyprogesterone acetate residues by CE immunoassay with chemiluminescence detection 总被引:1,自引:0,他引:1
A rapid and simple method is developed for the determination of medroxyprogesterone acetate (MPA) by CE immunoassay with chemiluminescence (CL). This method is based on the competitive reactions between horseradish peroxidase (HRP)-labeled MPA (MPA-HRP) and free MPA with anti-MPA antiserum. The influencing factors on the electrophoresis and CL detection were studied completely and the optimal conditions of separation and determination were obtained. The linear range was 2.0-50 nmol/L and the LOD for MPA was 0.9 nmol/L. The present method was applied to the analysis of pork tissues. 相似文献
72.
A procedure was developed for the synthesis of tertiary phosphine oxides by alkylation of secondary phosphine oxides with
quaternary ammonium salts.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 390–392, February, 1999 相似文献
73.
Endoglucanases were used as a selective tool to determine the substituent distribution along the chains of partially substituted cellulose acetates. Unsubstituted segments are intensively fragmented while highly substituted segments are only slightly degraded or not affected at all. Two different procedures were developed to perform a preparative separation of the fragments by size exclusion chromatography. One system is based on a direct separation of the fragmentation products using pyridine : water (9 : 1) as an eluent. The isolated fragments can be analysed regarding to their DS values by ATR/FTIR spectroscopy or by hydrolysis and HPLC. The second system is based on deutero-acetylation of endoglucanase fragmented samples. The complete acetylation of all OH groups enables a chromatographic separation in chloroform. Afterwards the isolated fragments can be analysed regarding to their partial DS values by 1H-NMR spectroscopy. 相似文献
74.
A facile synthesis of benzofuro[2,3‐c]pyridines has been achieved under mild conditions by using ammonium acetate as the nitrogen source through intramolecular cascade annulation. This reaction could efficiently construct pyridine ring and furan ring in one step. Moreover, the key annulation step was demonstrated through dihydrobenzofuran intermediates. 相似文献
75.
In this study the effect of the membrane preparation methods on the release of theophylline through cellulose acetate (CA) membranes was studied at in vitro conditions. CA/acetone binary and CA/acetone/water ternary systems were used as casting solutions and poly(ethylene glycol) (PEG) was used as the pore forming, plasticizing agent in the study. Membranes were characterized by FTIR, SEM, and DSC analysis. It was determined that pH, temperature and drug concentration affected the release of theophylline. A decrease in pH, increase in temperature and drug concentration increased the permeated amount of theophylline through the membranes. In addition, receiver solution circulation at a capillary blood rate increased the permeation of theophylline. As a result of the study, it was concluded that the release of theophylline could be controlled for a prolonged period of time and modified CA membranes prepared in the study could be as an advisable membrane material for potential release of theophylline at transdermal conditions. 相似文献
76.
77.
Adiabatic calorimetry is a suitable method for investigations of reactions because the generated heat remains completely in the reactor. For the investigation of organic reactions, the adiabatic precision calorimeter ACTRON 5 is used. The alcoholyses of phenyl isocyanate and 1,2-butyleneoxide were investigated. The temperature-time course was estimated by means of the nonlinear program TA-kin. Inclusion of the concentration-time course in the estimation procedure led to an increase in the reliability of the parameters. Probes were taken during isoperibolic measurements and were analysed by means of HPLC. 相似文献
78.
Maryam Sadat Hosseini-ZareMohammad Mahdavi Mina SaeediMehdi Asadi Shahrzad JavanshirAbbas Shafiee Alireza Foroumadi 《Tetrahedron letters》2012,53(27):3448-3451
We describe a new one-pot synthesis of 2,3-diaryl-5H-imidazo[2,1-a]isoindol-5-ones via the reaction of 1,2-diketones, 2-formylbenzoic acids, and ammonium acetate in acetic acid under reflux conditions and in the absence of a catalyst. 相似文献
79.
Miscibility studies on cellulose secondary acetate(CA)/Nylon 6(N6) blends have been carried out in this work. Dilute solution viscometry for the blend solutions using formic acid as the common solvent shows the existence of miscibility window. 相似文献
80.
1 Introduction Gaschromatography/massspectrometry (GC/MS)andliquidchromatography/massspectrometry (LC/MS) ,representativesofthehyphenatedtechniques ,aresomeofthemostreliableanalyticalmethods ,whicharethesynergisticcombinationoftwopowerfulanalyticaltechniques;… 相似文献