全文获取类型
收费全文 | 618篇 |
免费 | 38篇 |
专业分类
化学 | 534篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 42篇 |
物理学 | 66篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 10篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 16篇 |
2015年 | 22篇 |
2014年 | 16篇 |
2013年 | 45篇 |
2012年 | 34篇 |
2011年 | 61篇 |
2010年 | 22篇 |
2009年 | 19篇 |
2008年 | 50篇 |
2007年 | 34篇 |
2006年 | 29篇 |
2005年 | 52篇 |
2004年 | 36篇 |
2003年 | 35篇 |
2002年 | 35篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 1篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有656条查询结果,搜索用时 15 毫秒
581.
Chun‐Lin Deng Jeremy P. Bard Jessica A. Lohrman Joshua E. Barker Lev N. Zakharov Darren W. Johnson Michael M. Haley 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(12):3974-3978
We describe two novel hybrid receptors combining a phosphorus‐/nitrogen‐containing (PN) phosphonamidate heterocycle with urea recognition units in an arylethynyl backbone. Structural, spectroscopic and computational studies reveal that the origin of superior binding for hydrogen sulfate (HSO4?) anion is correlated with the formation of strong hetero‐complementary hydrogen bonds with the phosphonamidate motif. We further demonstrate that the hybrid host system is capable of capturing/transporting the HSO4? anion from an aqueous, biphasic system. 相似文献
582.
The efficient oxidative construction of benzo[1,4]oxazines from simple α-branched amines and ortho-benzoquinones is reported. The procedure pivots on a triethylamine and iodine mediated oxidative ring closure from the ketimine intermediate formed upon their condensation. This reaction was shown to tolerate a variety of α-branched benzylamines and downstream derivatization to substituted benzomorpholine structures was also demonstrated. 相似文献
583.
Palmblad M Buchholz BA Hillegonds DJ Vogel JS 《Journal of mass spectrometry : JMS》2005,40(2):154-159
Accelerator mass spectrometry (AMS) is a mass spectrometric method for quantifying rare isotopes. It has had a great impact in geochronology and archaeology and is now being applied in biomedicine. AMS measures radioisotopes such as 3H, 14C, 26Al, 36Cl and 41Ca, with zepto- or attomole sensitivity and high precision and throughput, allowing safe human pharmacokinetic studies involving microgram doses, agents having low bioavailability or toxicology studies where administered doses must be kept low (<1 microg kg(-1)). It is used to study long-term pharmacokinetics, to identify biomolecular interactions, to determine chronic and low-dose effects or molecular targets of neurotoxic substances, to quantify transport across the blood-brain barrier and to resolve molecular turnover rates in the human brain on the time-scale of decades. We review here how AMS is applied in neurotoxicology and neuroscience. 相似文献
584.
585.
Versatile and conveniently operated microreactor devices, suitable for long term chemical synthesis for both laboratory and industrial use, are described. Direct fluorination of ethyl acetoacetate by fluorine gas is used as a model reaction to illustrate the successful application of reactors having either 9, 18 or 30 microchannels, with all channels supplied from single reagent sources, to provide significant quantities of fluorinated products. Convenient reactor maintenance, simple design, versatility and the enhanced safety features of using such modular microreactor devices, make these systems appropriate for synthesis on the large scale. 相似文献
586.
Lanthanide metals react with PhTeTePh and elemental Te in pyridine to give (py)(y)Ln(4)(Te)(TeTe)(2)(TeTeTe(Ph)TeTe)(Te(x)TePh) (Ln = Sm (y = 9; x = 0); Tb, Ho (y = 8, x = 0.1)), and (py)(7)Tm(4)(Te)[(TeTe)(4)TePh](Te(0.6)TePh) clusters. The Sm, Tb, and Ho compounds contain a square array of Ln(III) ions all connected to a central Te(2-) ligand. Two adjacent edges of the square are bridged by ditelluride ligands, with the Ln ion that is eta(2) bound to both of these TeTe ligands also coordinating to a terminal TePh ligand. The other two edges of the square are spanned by ditellurides that both coordinate a TePh ligand that has been displaced from the Ln ion by pyridine, to give the pentaanion (mu-eta(2)-eta(2)-Te(2)Te(Ph)Te(2)).(5-) In the Tm compound, the displaced TePh interacts with all four TeTe units. The compounds are air-, light-, and temperature-sensitive. Upon thermolysis, they decompose to give solid-state TbTe(2-x), HoTe, or TmTe, with elimination of Te and TePh(2). 相似文献
587.
High silicon content SAPO(4)-5 (up to 0.511 atoms per unit cell) has been synthesised, using sodium 3-bromopropanesulfonate, sodium 1-butanesulfonate, sodium naphthalene-1-sulfonate or sodium n-decyl sulfate as surfactants; the SiO2 in the reaction gels ranged up to 3.0 (molar ratio), silicon incorporation was confirmed by XRD, XRF, TG-DTA, FT-IR and SEM techniques. 相似文献
588.
A series of three bis-tridentate bridging ligands has been prepared in which two 1,10-phenanthroline units have been symmetrically appended to a central pyridazine, pyrimidine, or pyrazine ring. These ligands have been treated with [Ru(tpy-d(11))Cl(3)] to afford both mono- and bimetallic complexes that show very self-consistent NMR properties. [structure: see text] 相似文献
589.
Seeds of the endangered species Zizania texana are recalcitrant, making it difficult to preserve the remaining genetic diversity of this species in genebanks. Excised embryos can be cryopreserved using solution-based cryoprotection protocols. Survival following cryoexposure increased from less than 5% to about 75% by preculturing embryos in high concentrations of sugars, bathing them in cryoprotectant solutions, and partially drying them to water contents of about 0.6 g H2O/g dry mass. 相似文献
590.
Patchanee Charoenying Karl Hemming Darren McKerrecher Richard J. K. Taylor 《Journal of heterocyclic chemistry》1996,33(4):1083-1089
The unsubstituted pyrylium nucleus is shown to undergo reaction with cuprate or secondary Grignard organometallic reagents to give intermediate 4-substituted pyrans which are converted into the corresponding 4-substituted pyrylium salts (7 examples) in fair to good overall yield. The synthetic utility of the 4-substituted pyrylium heterocycles is demonstrated by their reaction with organolithium reagents to give 3,5-disubstituted dienals in a highly stereospecific manner (7 examples) via electrocyclic ring opening of the intermediate 2-substituted pyrans. 相似文献