全文获取类型
收费全文 | 6435篇 |
免费 | 267篇 |
国内免费 | 46篇 |
专业分类
化学 | 4789篇 |
晶体学 | 35篇 |
力学 | 177篇 |
数学 | 890篇 |
物理学 | 857篇 |
出版年
2023年 | 43篇 |
2022年 | 64篇 |
2021年 | 113篇 |
2020年 | 122篇 |
2019年 | 127篇 |
2018年 | 96篇 |
2017年 | 74篇 |
2016年 | 170篇 |
2015年 | 176篇 |
2014年 | 194篇 |
2013年 | 340篇 |
2012年 | 424篇 |
2011年 | 507篇 |
2010年 | 241篇 |
2009年 | 196篇 |
2008年 | 431篇 |
2007年 | 429篇 |
2006年 | 433篇 |
2005年 | 346篇 |
2004年 | 308篇 |
2003年 | 274篇 |
2002年 | 228篇 |
2001年 | 75篇 |
2000年 | 55篇 |
1999年 | 51篇 |
1998年 | 57篇 |
1997年 | 59篇 |
1996年 | 91篇 |
1995年 | 50篇 |
1994年 | 48篇 |
1993年 | 54篇 |
1992年 | 38篇 |
1991年 | 51篇 |
1990年 | 44篇 |
1989年 | 32篇 |
1988年 | 33篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 54篇 |
1984年 | 54篇 |
1983年 | 26篇 |
1982年 | 42篇 |
1981年 | 39篇 |
1980年 | 33篇 |
1979年 | 44篇 |
1978年 | 37篇 |
1977年 | 41篇 |
1976年 | 35篇 |
1975年 | 32篇 |
1974年 | 33篇 |
排序方式: 共有6748条查询结果,搜索用时 15 毫秒
51.
Kinetic studies of PET glycolysis by diethylene glycol (DEG), dipropylene glycol (DPG), glycerol (Gly) and mixtures of these glycols have shown, in a previous study, that the order of reactivity of the glycols differs according to the conditions of temperature and catalysis. Indeed, their global reactivity depends both on their chemical reactivity and physico-chemical properties.Glycolysis of model polyesters which are liquid at the reaction temperature, which allows us to overcome the problem of the polyesters' solubility, were studied to compare the chemical reactivity of these glycols. Three oligoesters were synthesized from dimethyl terephthalate and three different glycols namely triethylene glycol, ethylene glycol and hexanediol to form, respectively, PE3T, OET and PTHD.Results showed that the order of reactivity of the glycols is the same for PET, OET and PTHD but different for PE3T. Indeed, DPG without catalyst has a particular and unexpected behaviour: its reactivity seems to be strongly influenced by the presence of oxygen atoms in the chain. 相似文献
52.
53.
54.
55.
Kevin J. Luebke 《Chemistry & biology》1998,5(12):R317
Genetically encoded fluorescent labels, such as green fluorescent protein, make it possible to visualize a protein's natural distribution and environment in living cells. A new approach to protein labeling in living cells has been devised in which a small, membrane-permeable ligand binds with high affinity and specificity to a short peptide motif that can be incorporated into the protein of interest; the ligand becomes brightly fluorescent after binding to the peptide. 相似文献
56.
57.
58.
1,4-Diamino-2-butyne was prepared from 1,4-dichloro-2-butyne via 1,4-diazido-2-butyne. Bis(amino acid) derivatives of 1,4-diamino-2-butyne having the general structure (Boc-Xxx-NHCH2C[triple bond])2 (Xxx = Ala, Phe and Met) were prepared and examined by 1H NMR spectroscopy. Using chemical shift, coupling constant and DMSO titration data it is found that these compounds adopt a C2-symmetric turn conformation featuring two intramolecular hydrogen bonds. 相似文献
59.
Application of stir bar sorptive extraction for wine analysis 总被引:4,自引:0,他引:4
Yoji?Hayasaka Kevin?MacNamara Gayle?A.?Baldock Randell?L.?Taylor Alan?P.?PollnitzEmail author 《Analytical and bioanalytical chemistry》2003,375(7):948-955
Stir bar sorptive extraction (SBSE) coupled with gas chromatography/mass spectrometry (GC/MS) was used to analyse wine samples for three applications: flavour and compositional analysis; 2,4,6-trichloroanisole (TCA), a common off-aroma in wine; and agrochemicals. SBSE was found to be orders of magnitude more sensitive than modern conventional methodology, allowing for lower detection and quantitation levels, and improved confirmation of identity; SBSE often gave better signal to noise in scan mode than other methods in selective ion monitoring (SIM) mode. With the help of their characteristic mass spectra all agrochemicals could be identified unambiguously at concentrations of 10 microg L(-1) in wine and a further 100 constituents were detected in a Cabernet Sauvignon sample. Thus it is now possible to analyse complex samples such as wine by scan mode, with better confirmation of identity, and without sacrificing sensitivity, where previously SIM methodology had to be used. 相似文献
60.