全文获取类型
收费全文 | 475篇 |
免费 | 5篇 |
国内免费 | 3篇 |
专业分类
化学 | 377篇 |
晶体学 | 1篇 |
力学 | 15篇 |
数学 | 38篇 |
物理学 | 52篇 |
出版年
2022年 | 7篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 24篇 |
2012年 | 30篇 |
2011年 | 28篇 |
2010年 | 17篇 |
2009年 | 14篇 |
2008年 | 24篇 |
2007年 | 24篇 |
2006年 | 21篇 |
2005年 | 27篇 |
2004年 | 29篇 |
2003年 | 33篇 |
2002年 | 33篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有483条查询结果,搜索用时 125 毫秒
111.
Bravo M Lespes G De Gregori I Pinochet H Potin-Gautier M 《Journal of chromatography. A》2004,1046(1-2):217-224
Because of the high toxicity of organotin compounds and the current regulation about their applications, analytical method usable in routine analysis is required. A speciation procedure based on NaBEt4 ethylation and GC-PFPD analysis has shown to be suitable for the organotin determination. Unfortunately, some matrix effects were observed during the analysis of harbour sediments from Chile. These effects were identified as the alkylation of elemental sulfur and the coelution between the organotin compounds and some dialkylsulfides. The re-optimization of GC parameters and application of solid phase microextraction (SPME) were proposed to solve these analytical problems. Certified reference materials and different harbour sediment samples were analysed in order to evaluate the suitability of the methods for organotin control in complex environment samples. 相似文献
112.
Martine Croisy-Delcey Emile Bisagni Christiane Huel Danielle Zilberfarb Alain Croisy 《Journal of heterocyclic chemistry》1991,28(1):65-71
Using 2-methoxy- and 2,5-dimethoxyacetophenones 8a and 8b as starting materials, 1-chloro-4-methylisoquinoline-5,8-quinone ( 6 ) and its 6-bromo derivative 7 were obtained via multistep sequences. Whereas Diels-Alder condensation of the former compound with homophthalic anhydride ( 22 ) led to a mixture of the two possible isomers: 1-chloro-11-hydroxy-4-methylnaphtho[2,3-g]isoquinoline-5,12-quinone ( 23 ) and 1-chloro-6-hydroxy-4-methylnaphtho[2,3-g]isoquinoline-5,12-quinone ( 24 ), this last tetracyclic chloroquinone was specifically obtained from 6-bromo-1-chloro-4-methylisoquinoline-5,8-quinone ( 7 ) and homophthalic anhydride. The 6,11-dihydroxy derivative was then prepared by ammonium nitrate oxidation or photochemically by cycloaddition of benzocyclobutenedione ( 28 ) and 1-chloro-4-methylisoquinoline-5,8-quinone ( 6 ). Chloro compounds were easily substituted by diamines to provide corresponding 1-amino substituted hydroxy tetracyclic quinones. 相似文献
113.
Luna AP Bonin M Micouin L Husson HP 《Journal of the American Chemical Society》2002,124(41):12098-12099
The Ir-catalyzed asymmetric hydroboration of bicyclic hydrazines with ee and chemical yields up to 64% is reported. The switch from rhodium to iridium leads systematically to opposite enantiomers in this desymmetrization reaction. 相似文献
114.
[reaction: see text] Alkynyldimethylaluminum reagents are easily available from terminal alkynes and trimethylaluminum via a triethylamine-catalyzed metalation. These compounds can react with various aromatic and heterocyclic halides in the presence of palladium in a fast and efficient way. This catalyzed cross-coupling reaction provides a simple entry to numerous internal alkynes, using a readily available, inexpensive, and nontoxic metalating agent. 相似文献
115.
Corset J Castellà-Ventura M Froment F Strzalko T Wartski L 《The Journal of organic chemistry》2003,68(10):3902-3911
It is evidenced through vibrational spectroscopy that a heterodimer or "Quadac" is formed when an excess of base (LHMDS, LDA, or n-BuLi) is added to PhCH(2)CN in THF, THF-hexane, or THF-toluene solution. The amount of heterodimer increases with the pK(H)(a) of the lithiated base. A dianionic species may be formed through decomposition of this heterodimer if the pK(H)(a) of the base is sufficiently high, as in the case of n-BuLi. With LDA, only a very small amount of dianion is observed, and with LHMDS, no dianion is detected. The predominant dianionic species observed are the linear and bridged separated ion pairs of the dilithiated dianion. The presence of the amine in the medium is of paramount importance. The PhCHCNLi monomer-dimer equilibrium is entropy driven toward the dimer solvated by the amine. 相似文献
116.
The recombinantly produced different forms of protein G, namely monofunctional immunoglobulin G (IgG) binding, monofunctional serum albumin (SA) binding and bifunctional IgG/SA binding proteins G, are compared with respect to their specific affinities to blood IgG and SA. The affinity mode of the recently developed high-performance monolithic disk chromatography has been used for fast quantitative investigations. Using single affinity disks as well as two discs stacked into one separation unit, one order of magnitude in adsorption capacities for IgG and SA were found both for monofunctional and bifunctional protein G forms used as specific affinity ligands. However, despite the adsorption difference observed, the measured dissociation constants of the affinity complexes seemed to be very close. The analytical procedure developed can be realized within a couple of minutes. Up-scaling of the developed technology was carried out using another type of monolithic materials, i.e. CIM affinity tubes. 相似文献
117.
Marek Koutny Martine Sancelme Nicolas Pichon Jacques Lemaire 《Polymer Degradation and Stability》2006,91(7):1495-1503
Biodegrability of high density polyethylene film (HDPE) and low density polyethylene film (LDPE) both containing a balance of antioxidants and pro-oxidants was studied with defined microbial strains particularly with Rhodococcus rhodochrous and Nocardia asteroides in mineral medium. After an abiotic pre-treatment consisting of photooxidation and thermo-oxidation corresponding to about 3 years of outdoor weathering the samples were inoculated, incubated up to 200 days and during the period their metabolic activities were followed by measuring adenosine triphosphate content. Simultaneously the cultures were also monitored by optical microscopy and FTIR spectroscopy. The first initial phase of fast growth caused by the presence of low molecular extractable compounds was followed by a long period of stabilized metabolic activity suggesting that microorganisms continued to gain energy from the substrate but evidently at a much slower rate. Complementary analysis performed at the end of incubation revealed that during the experiment time biodegradation processes probably affected surface layer of materials only. 相似文献
118.
Martine Croisy-Delcey Christiane Huel Emile Bisagni 《Journal of heterocyclic chemistry》1988,25(2):661-665
Under the conditions of the Bischler-Napieralski reaction the cyclization of 2-(1,4-dimethoxy and 1,4,8-trimethoxynaphthyl)ethylacetamides derivatives take place essentially at the 1 position by substitution of the 1-methoxy group. Nevertheless, 1-aminomethyl-9,10-azaanthraquinones are accessibles by condensation of 1-aminomethylisoquinoline-5,8-diones with a 1,4-diacetoxy-1,3-butadiene. 相似文献
119.
The four complexes [Pd(H)(Cl)L2] and [Pd(H)(SnCl3)L2], L = PPh3, PCy3, have been synthesized and fully characterized by multinuclear NMR. They represent the active species of the hydride palladium-catalyzed alkoxycarbonylation of terminal alkenes. Isolation of the model acylplatinum complex, resulting from the carbonylation of dihydromyrcene, clearly shows that SnCl2 as co-catalyst produces a SnCl3 ligand which modulates the metal center electron density. 相似文献
120.
A rapid procedure, based on closed vessels microwave digestion and inductively coupled plasma-mass spectrometry (ICP-MS), was evaluated to ascertain the effect of chronic exposure to cadmium on intracellular accumulation of minor and essential trace elements in cultured epithelial cells (Caco-2 TC7). For all measurements, the method of external calibration was used and 3 elements (Be, Sc, In) were selected as internal standards. Optimization procedures are discussed and results are presented for the total determination of 9 key analytes (Na, Mg, Ca, Cr, Mn, Cu, Zn, Mo, and Cd) in certified reference materials (CRMs) and 20 samples of Caco-2 TC7 cells long-term exposed to Cd. The performance characteristics of the analytical system were evaluated by calibration and linearity, limits of detection and quantitation, accuracy with spiking, trueness and repeatability with available CRMs. As a complement to the ICP-MS determinations, both available CRMs and cell samples were analyzed either by electro thermal- or flame atomic absorption spectrometry. The results were in good agreement with the ICP-MS results. 相似文献