全文获取类型
收费全文 | 654篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
化学 | 423篇 |
晶体学 | 10篇 |
力学 | 26篇 |
数学 | 125篇 |
物理学 | 85篇 |
出版年
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 13篇 |
2014年 | 21篇 |
2013年 | 33篇 |
2012年 | 30篇 |
2011年 | 34篇 |
2010年 | 18篇 |
2009年 | 23篇 |
2008年 | 39篇 |
2007年 | 40篇 |
2006年 | 23篇 |
2005年 | 20篇 |
2004年 | 32篇 |
2003年 | 18篇 |
2002年 | 23篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 11篇 |
1974年 | 5篇 |
1973年 | 9篇 |
排序方式: 共有669条查询结果,搜索用时 15 毫秒
581.
Giorgio Stefancich Marino Artico Romano Silvestri 《Journal of heterocyclic chemistry》1992,29(4):1005-1007
Reaction of di-4-morpholinylphosphinic chloride on 5,10-dihydro-9H-pyrrolo[2,1-c][1,4]benzodiazepin-11-one 9 afforded 11-(di-4-morpholinylphosphinyloxy)-5H-pyrrolo[2,1-c][1,4]benzodiazepine 10 . Displacement of di-4-morpholinylphosphinyloxy group of 10 by formylhydrazine with concomitant intramolecular cyclization led directly to 9H-pyrrolo[2,1-c]-s-triazolo[4,3-a][1,4]benzodiazepine 7, a novel nitrogen heterocyclic ring of pharmaceutical interest. A new procedure for the synthesis of 9 is also described. 相似文献
582.
583.
Gomes Silva C Juárez R Marino T Molinari R García H 《Journal of the American Chemical Society》2011,133(3):595-602
Gold nanoparticles supported on P25 titania (Au/TiO(2)) exhibit photocatalytic activity for UV and visible light (532 nm laser or polychromatic light λ > 400 nm) water splitting. The efficiency and operating mechanism are different depending on whether excitation occurs on the titania semiconductor (gold acting as electron buffer and site for gas generation) or on the surface plasmon band of gold (photoinjection of electrons from gold onto the titania conduction band and less oxidizing electron hole potential of about -1.14 V). For the novel visible light photoactivity of Au/TiO(2), it has been determined that gold loading, particle size and calcination temperature play a role in the photocatalytic activity, the most active material (Φ(H2) = 7.5% and Φ(O2) = 5.0% at 560 nm) being the catalyst containing 0.2 wt % gold with 1.87 nm average particle size and calcined at 200 °C. 相似文献
584.
Conway JM Birnbaum AK Marino SE Cloyd JC Remmel RP 《Biomedical chromatography : BMC》2012,26(9):1071-1076
Topiramate (Topamax®) is an antiepileptic medication used as adjunctive and monotherapy in patients with epilepsy and for migraine prophylaxis. A GC‐MS assay was developed that was capable of detecting topiramate plasma concentrations following a single rectal or oral dose administration. Topiramate plasma samples were prepared by solid‐phase extraction and were quantified by GC‐MS analysis. The topiramate standard curves were split from 0.1 to 4 µg/mL and from 4 to 40 µg/mL in order to give a more accurate determination of the topiramate concentration. The accuracy of the standards ranged from 94.6 to 107.3% and the precision (%CV) ranged from 1.0 to 5.3% for both curves at all concentrations. The %CV for quality controls was <7.6%. The assay is both accurate and precise and will be used to complete future pharmacokinetic studies. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
585.
Supercharged proteins (SCPs) can deliver functional macromolecules into the cytoplasm of mammalian cells more potently than unstructured cationic peptides. Thus far, neither the structural features of SCPs that determine their delivery effectiveness nor their intracellular fate postendocytosis, has been studied. Using a large set of supercharged GFP (scGFP) variants, we found that the level of cellular uptake is sigmoidally related to net charge and that scGFPs enter cells through multiple pathways, including clathrin-dependent endocytosis and macropinocytosis. SCPs activate Rho and ERK1/2 and also alter the endocytosis of transferrin and EGF. Finally, we discovered that the intracellular trafficking of endosomes containing scGFPs is altered in a manner that correlates with protein delivery potency. Collectively, our findings establish basic structure-activity relationships of SCPs and implicate the modulation of endosomal trafficking as a determinant of macromolecule delivery efficiency. 相似文献
586.
Reduction of ketosulfonyl indoles with sodium borohydride provides a ready entry to tryptophols in a regiocomplementary fashion with respect to the traditional oxirane ring-opening by indoles under Friedel-Crafts conditions. Compared to traditional β-ketosulfones, ketosulfonyl indoles show a peculiar behavior since they undergo a Lewis acid promoted elimination of the arylsulfonyl group allowing the preparation of indolyl-substituted 1,4-dicarbonyl derivatives. 相似文献
587.
Orazio Nicolotti Ilenia Giangreco Teresa Fabiola Miscioscia Marino Convertino Francesco Leonetti Leonardo Pisani Angelo Carotti 《Journal of computer-aided molecular design》2010,24(2):117-129
Abstract
A series of 27 benzamidine inhibitors covering a wide range of biological activity and chemical diversity was analysed to derive a Linear Interaction Energy in Continuum Electrostatics (LIECE) model for analysing the thrombin inhibitory activity. The main interactions occurring at the thrombin binding site and the preferred binding conformations of inhibitors were explicitly biased by including into the LIECE model 10 compounds extracted from X-ray solved thrombin-inhibitor complexes available from the Protein Data Bank (PDB). Supported by a robust statistics (r 2 = 0.698; q 2 = 0.662), the LIECE model was successful in predicting the inhibitory activity for about 76% of compounds (r ext2 ≥ 0.600) from a larger external test set encompassing 88 known thrombin inhibitors and, more importantly, in retrieving, at high sensitivity and with better performance than docking and shape-based methods, active compounds from a thrombin combinatorial library of 10240 mimetic chemical products. The herein proposed LIECE model has the potential for successfully driving the design of novel thrombin inhibitors with benzamidine and/or benzamidine-like chemical structure. 相似文献588.
The deformation and breakup of a drop in an immiscible equiviscous liquid undergoing unbounded shear flow has been extensively investigated in the literature, starting from the pioneering work of Taylor. In this Letter, we address the case of microconfined shear flow, a problem which is relevant for microfluidics and emulsion processing applications. The main effects of confinement include complex oscillating transients and drop stabilization against breakup. In particular, very elongated drop shapes are observed, which would be unstable in the unbounded case and can be explained in terms of wall-induced distortion of the shear flow field. We show that wall effects can be exploited to obtain nearly monodisperse emulsions in microconfined shear flow. 相似文献
589.
590.
Resendiz MJ Pottiboyina V Sevilla MD Greenberg MM 《Journal of the American Chemical Society》2012,134(8):3917-3924
Nucleobase radicals are the major family of reactive intermediates produced when nucleic acids are exposed to γ-radiolysis. The 5,6-dihydrouridin-5-yl radical (1), the formal product of hydrogen atom addition and a model for hydroxyl radical addition, was independently generated from a ketone precursor via Norrish Type I photocleavage in single and double stranded RNA. Radical 1 produces direct strand breaks at the 5'-adjacent nucleotide and only minor amounts of strand scission are observed at the initial site of radical generation. Strand scission occurs preferentially in double stranded RNA and in the absence of O(2). The dependence of strand scission efficiency from the 5,6-dihydrouridin-5-yl radical (1) on secondary structure under anaerobic conditions suggests that this reactivity may be useful for extracting additional RNA structural information from hydroxyl radical reactions. Varying the identity of the 5'-adjacent nucleotide has little effect on strand scission. Internucleotidyl strand scission occurs via β-elimination of the 3'-phosphate following C2'-hydrogen atom abstraction by 1. The subsequently formed olefin cation radical yields RNA fragments containing 3'-phosphate or 3'-deoxy-2'-ketonucleotide termini from competing deprotonation pathways. The ketonucleotide end group is favored in the presence of low concentrations of thiol, presumably by reducing the cation radical to the enol. Competition studies with thiol show that strand scission from the 5,6-dihydrouridin-5-yl radical (1) is significantly faster than from the 5,6-dihydrouridin-6-yl radical (2) and is consistent with computational studies using the G3B3 approach that predict the latter to be more stable than 1 by 2.8 kcal/mol. 相似文献