全文获取类型
收费全文 | 2854篇 |
免费 | 32篇 |
国内免费 | 6篇 |
专业分类
化学 | 2052篇 |
晶体学 | 9篇 |
力学 | 44篇 |
综合类 | 1篇 |
数学 | 460篇 |
物理学 | 326篇 |
出版年
2016年 | 32篇 |
2015年 | 30篇 |
2014年 | 34篇 |
2013年 | 96篇 |
2012年 | 76篇 |
2011年 | 71篇 |
2010年 | 49篇 |
2009年 | 46篇 |
2008年 | 76篇 |
2007年 | 93篇 |
2006年 | 71篇 |
2005年 | 69篇 |
2004年 | 58篇 |
2003年 | 62篇 |
2002年 | 49篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 28篇 |
1998年 | 25篇 |
1997年 | 36篇 |
1996年 | 32篇 |
1995年 | 38篇 |
1994年 | 49篇 |
1993年 | 31篇 |
1992年 | 28篇 |
1991年 | 35篇 |
1990年 | 29篇 |
1989年 | 40篇 |
1988年 | 32篇 |
1987年 | 37篇 |
1986年 | 37篇 |
1985年 | 50篇 |
1984年 | 58篇 |
1983年 | 30篇 |
1982年 | 53篇 |
1981年 | 50篇 |
1980年 | 43篇 |
1979年 | 37篇 |
1978年 | 64篇 |
1977年 | 60篇 |
1976年 | 45篇 |
1975年 | 38篇 |
1974年 | 34篇 |
1973年 | 47篇 |
1972年 | 31篇 |
1971年 | 46篇 |
1970年 | 30篇 |
1969年 | 20篇 |
1968年 | 19篇 |
1966年 | 24篇 |
排序方式: 共有2892条查询结果,搜索用时 15 毫秒
121.
3-Amino-1H,3H-quinoline-2,4-diones react with thiourea or potassium thiocyanate in boiling acetic acid to give novel 2,3-dihydro-3-thioxoimidazo[1,5-c]quinazolin-5(6H)-ones in high yields. However, if the starting compounds are substituted with a benzyl group at position 3, a C-debenzylation proceeds to give 2,3-dihydro-2-thioxo-1H-imidazo[4,5-c]quinolin-4(5H)-ones. According to a proposed reaction mechanism, a molecular rearrangement of the primarily formed mono-substituted thiourea takes place. All compounds were characterized by 1H, 13C and 15N NMR and IR spectroscopy as well as by mass spectrometry. 相似文献
122.
123.
Krska R Schubert-Ullrich P Josephs RD Emteborg H Buttinger G Pettersson H van Egmond HP Schothorst RC Macdonald S Chan D 《Analytical and bioanalytical chemistry》2007,388(5-6):1215-1226
This paper presents results from the European Commission-funded project Doncalibrant, the objective of which was to produce
calibrators with certified mass fractions of the Fusarium toxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-Ac-DON), 15-acetyldeoxynivalenol (15-Ac-DON), and nivalenol (NIV),
in acetonitrile. The calibrators, available in ampoules, were sufficiently homogeneous, with between-bottle variations (s
bb) of less than 2%. Long-term stability studies performed at four different temperatures between −18 and 40 °C revealed no
significant negative trends (at a confidence level of 95%). Molar absorptivity coefficients (in L mol−1 cm−1) were determined for all four toxins (DON: 6805 ± 126, NIV: 6955 ± 205, 3-Ac-DON: 6983 ± 141, 15-Ac-DON: 6935 ± 142) on the
basis of a mini-interlaboratory exercise. The overall uncertainty of the calibrators’ target values for DON and NIV were evaluated
on the basis of gravimetric preparation data and include uncertainty contributions from possible heterogeneity, storage, and
transport. The Doncalibrant project resulted in the production of calibrators for DON (IRMM-315) and NIV (IRMM-316) in acetonitrile
with certified mass fractions of 25.1 ± 1.2 μg g−1 and 24.0 ± 1.1 μg g−1, respectively. Both CRMs became commercially available from the Institute for Reference Materials and Measurements (IRMM,
Geel, Belgium) at the beginning of 2007. 相似文献
124.
Electroactive conducting copolymers of aniline (ANI) and o-aminophenol (OAP) and two-layered poly(o-aminophenol) (POAP)/polyaniline (PANI) composites were prepared in aqueous acidic solution by electrode potential cycling.
Copolymerization was carried out at different feed concentrations of OAP and ANI on a gold electrode. A strong inhibition
of electropolymerization was found at a high molar fraction of OAP in the feed. The copolymers showed good adherence on the
electrode surface and gave a redox response up to pH=10.0. Two transitions were observed in the in situ conductivities of
the copolymers (as with PANI), but the conductivities were lower by 2.5–3 orders of magnitude as compared to PANI. Electrosynthesis
of PANI on POAP modified electrodes showed copolymer formation after reaction initiation and finally formation of a PANI layer
at the copolymer/solution interface. The ‘memory effect’ of the bilayer structures of both polymers was discussed in terms
of protonation/deprotonation and anion consumption taking place during redox processes of both polymers. 相似文献
125.
126.
127.
Zellner M Winkler W Hayden H Diestinger M Eliasen M Gesslbauer B Miller I Chang M Kungl A Roth E Oehler R 《Electrophoresis》2005,26(12):2481-2489
For the preparation of proteins for proteome analysis, precipitation is frequently used to concentrate proteins and to remove interfering compounds. Various methods for protein precipitation are applied, which rely on different chemical principles. This study compares the changes in the protein composition of human blood platelet extracts after precipitation with ethanol (EtOH) or trichloroacetic acid (TCA). Both methods yielded the same amount of proteins from the platelet preparations. However, the EtOH-precipitated samples had to be dialyzed because of the considerable salt content. To characterize single platelet proteins, samples were analyzed by two-dimensional fluorescence differential gel electrophoresis. More than 90% of all the spots were equally present in the EtOH- and TCA-precipitated samples. However, both precipitation methods showed a smaller correlation with nonprecipitated samples (EtOH 74.9%, TCA 79.2%). Several proteins were either reduced or relatively enriched in the precipitated samples. The proteins varied randomly in molecular weight and isoelectric point. This study shows that protein precipitation leads to specific changes in the protein composition of proteomics samples. This depends more on the specific structure of the protein than on the precipitating agent used in the experiment. 相似文献
128.
Mendoza SM Whelan CM Jalkanen JP Zerbetto F Gatti FG Kay ER Leigh DA Lubomska M Rudolf P 《The Journal of chemical physics》2005,123(24):244708
Thin films of fumaramide [2]rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface. 相似文献
129.
ZHANG Yong HONG Hua-Sheng Michael H W Lam Ka-Fai Poon Bruce J Richardson Rudolf S S Wu Gene J S Zheng 《高等学校化学学报》1999,20(Z1):554
A new mimic biological sampling devices, which consisted of lipid-containing semipermeable-membrane (SPMD) for sampling organic pollutants has been introduced. 相似文献
130.