全文获取类型
收费全文 | 886篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 797篇 |
晶体学 | 7篇 |
力学 | 6篇 |
数学 | 51篇 |
物理学 | 46篇 |
出版年
2023年 | 6篇 |
2022年 | 37篇 |
2021年 | 32篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 8篇 |
2016年 | 30篇 |
2015年 | 14篇 |
2014年 | 43篇 |
2013年 | 49篇 |
2012年 | 45篇 |
2011年 | 67篇 |
2010年 | 55篇 |
2009年 | 40篇 |
2008年 | 71篇 |
2007年 | 68篇 |
2006年 | 63篇 |
2005年 | 54篇 |
2004年 | 47篇 |
2003年 | 35篇 |
2002年 | 33篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有907条查询结果,搜索用时 15 毫秒
881.
Filippini M Ortelli C Svercel M Bagheri HC 《Journal of photochemistry and photobiology. B, Biology》2011,103(3):234-242
Ultraviolet radiation is an important environmental constraint on the evolution of life. In addition to its harmful effects, ultraviolet radiation plays an important role in generating genetic polymorphisms and acting as a selective agent. Understanding how prokaryotes cope with high radiation can give insights on the evolution of life on Earth. Four representative filamentous bacteria from the family Cytophagaceae with different pigmentation were selected and exposed to different doses of UVC radiation (15-32,400Jm(-2)). The effect of UVC radiation on bacterial survival, growth and morphology were investigated. Results showed high survival in response to UVC for Rudanella lutea and Fibrisoma limi, whereas low survival was observed for Fibrella aestuarina and Spirosoma linguale. S. linguale showed slow growth recovery after ultraviolet exposure, R. lutea and F. limi showed intermediate growth recovery, while F. aestuarina had the fastest recovery among the four tested bacteria. In terms of survival, S. linguale was the most sensitive bacterium whereas R. lutea and F. limi were better at coping with UVC stress. The latter two resumed growth even after 2h exposure (~10,800Jm(-2)). Additionally, the ability to form multicellular filaments after exposure was tested using two bacteria: one representative of the high (R. lutea) and one of the low (F. aestuarina) survival rates. The ability to elongate filaments due to cell division was preserved but modified. In R. lutea 10min exposure reduced the average filament length. The opposite was observed in F. aestuarina, where the 5 and 10min exposures increased the average filament length. R. lutea and F. limi are potential candidates for further research into survival and resistance to ultraviolet radiation stress. 相似文献
882.
Yurii M. Chumakov Yurii A. Simonov Mata Grozav Manuela Crisan Gabriele Bocelli Andrey A. Yakovenko Dmitry Lyubetsky 《Central European Journal of Chemistry》2006,4(3):458-475
The crystal structures of six novel salts of 4-nitrobenzoic acid — namely, 2-hydroxyethylammonium 4-nitrobenzoate (I), 2-hydroxypropylammonium 4-nitrobenzoate (II), 1-(hydroxymethyl)propylammonium 4-nitrobenzoate (III), 3-hydroxypropylammonium 4-nitrobenzoate (IV), bis-(2-hydroxyethylammonium) 4-nitrobenzoate (V), morpholinium 4-nitrobenzoate (VI) — containing the same anion but different cations have been studied. The ionic forms of I-VI serve as building blocks of the supramolecular architecture, and in crystals they are held together via ionic N-H···O and O-H···O hydrogen bonds. In the crystal packing the building blocks of I-III are self-assembled via N-H...O, O-H···O and C-H...O hydrogen bonds to form the chains which are further consolidated into two-dimensional layers
by the same type of interactions. In IV-VI the chain-like structures have been generated by building blocks. 相似文献
883.
Manuela Melucci Dr. Massimo Zambianchi Alberto Zanelli Dr. Nadia Camaioni Dr. Massimo Gazzano Dr. Alessandro Bongini Prof. Dr. Giovanna Barbarella Dr. 《Chemphyschem》2007,8(18):2621-2626
A soluble, low‐weight fraction of poly(α‐vinyl,ω‐n‐hexyl‐quaterthiophene), PT4Hex, having n‐hexylquaterthiophenes as side‐chain groups, is prepared by free‐radical polymerization of α‐vinyl,ω‐n‐hexyl‐quaterthiophene and the corresponding properties compared to those of free di‐n‐hexylquaterthiophene (T4Hex). Optical analysis (absorption and emission) and X‐ray diffraction data indicate that in the polyvinyl‐locked architecture the quaterthiophene pendants adopt a cofacial arrangement with a mutual distance close enough for π–π orbitals to overlap (~4 Å). As a consequence of the close chain packing, a shift of the reduction potential of about 0.5 V toward less negative values with respect to free T4Hex, is found for PT4Hex films. Due to its enhanced electron affinity, PT4Hex displays an electron‐acceptor behavior when blended with alkylated and silylated quaterthiophenes acting as donors. 相似文献
884.
Francesco Puoci Francesca Iemma Giuseppe Cirillo Manuela Curcio Ortensia Ilaria Parisi Umile Gianfranco Spizzirri Nevio Picci 《European Polymer Journal》2009,45(6):1634-11734
A new restricted access materials combined to molecularly imprinted polymers (RAM-MIP) with hydrophilic external layer were prepared and their applicability in p-acetaminophenol (AMP) selective recognition and release was evaluated. Glycidilmethacrylate (GMA) was used as pro-hydrophilic co-monomer, and GMA epoxide ring opening with perchloric acid was performed for the hydrophilic modification of polymeric surface. Morphological and hydrophilic properties by scanning electron microscopy and water content measurement were determined and recognition and selectivity properties of RAM-MIP were compared to the unmodified MIP. With RAM-MIP, both hydrophobic non-specific interactions between template or its analogues and polymeric matrices, and bovine serum albumin absorption were drastically reduced. 相似文献
885.
Manuela Meusel 《Tetrahedron letters》2005,46(13):2231-2233
A urea-functionalized polystyrene-resin with a Rink linker was prepared by adaptation of a solution-phase synthesis to solid-phase chemistry. Thereby, a resin-bound acylurea was formed by reacting a Rink-amide resin with trichloroacetyl isocyanate, followed by the thermal removal of the trichloroacetyl group and thus generating the unsubstituted solid-supported urea. 相似文献
886.
Manuela Wallesch Daniel Volz Dr. Daniel M. Zink Dr. Ute Schepers Dr. Martin Nieger Dr. Thomas Baumann Prof. Dr. Stefan Bräse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6578-6590
Easy come, easy go: the great structural diversity of CuI complexes is an ambivalent trait. Apart from the well‐known catalytic properties of CuI, a great number of potent luminescent complexes have been found in the last ten years featuring a plethora of structural motifs. The downside of this variety is the undesired formation of other species upon processing. In here, strategies to avoid this behavior are presented: Only one favorable structural unit often exists for multinuclear CuI complexes with bridging ligands. In addition, these complexes exhibit favorable photophysical properties due to cooperative effects of the metal halide core. Furthermore, we demonstrate the broad range of applications of emitting CuI compounds. 相似文献
887.
Angelo Zinellu Salvatore Sotgia Elisabetta Pisanu Bastianina Scanu Manuela Sanna Maria Franca Usai Roberto Chessa Luca Deiana Ciriaco Carru 《Analytical and bioanalytical chemistry》2010,398(5):1973-1978
The role of neurotransmitter amino acids (NAAs) in the functioning of the nervous system has been the focus of increasingly
intense research over the past several years. Among the various amino acids that have important roles as neurotransmitters,
there are alanine (Ala), glutamic acid (Glu), aspartic acid (Asp), serine (Ser), taurine (Tau) and glycine (Gly). NAAs are
present in plasma, cells and—at trace levels—in all biological fluids, but complex components in biological matrices make
it difficult to determine them in biological samples. We describe a new capillary electrophoresis (CE) method with laser-induced
fluorescence detection by which analytes are resolved in less than 12 minutes in a 18 mmol/L phosphate run buffer at pH 11.6.
The use of elevated temperatures during sample derivatization leads to a drastic reduction in the reaction time, down to 20 min,
compared to the 6–14 h usually described for reactions between FITC and amino acids at room temperature. In order to demonstrate
its wide range of applications, the method was applied to the analysis of NAA in human plasma and in other sample types, such
as red blood cells, urine, cultured cells, cerebrospinal fluid, saliva and vitreous humor, thus avoiding the typical limitations
of other methods, which are normally suitable for use with only one or two matrix types. 相似文献
888.
Manuela Crisan Liliana Halip Paulina Bourosh Sergiu Adrian Chicu Yurii Chumakov 《Chemistry Central journal》2017,11(1):129
Background
Nitroaromatic and chloronitroaromatic compounds have been a subject of great interest in industry and recently in medical-pharmaceutic field. 2-Chloro-4-nitro/2-chloro-5-nitrobenzoic acids and 4-nitrobenzoic acid are promising new agents for the treatment of main infectious killing diseases in the world: immunodeficiency diseases and tuberculosis.Results
New ethanolamine nitro/chloronitrobenzoates were synthesized and characterized by X-ray crystallography, UV–vis, FT-IR and elementary analysis techniques. The toxicity of the compounds prepared and correspondent components was evaluated using Hydractinia echinata as test system. A significant lower toxicity was observed for nitro-derivative compared with chloronitro-derivatives and individual components. Crystallographic studies, together with the chemical reactivity and stability profiles resulted from density functional theory and ab initio molecular orbital calculations, explain the particular behavior of ethanolamine 4-nitrobenzoate in biological test.Conclusions
The experimental and theoretical data reveal the potential of these compounds to contribute to the design of new active pharmaceutical ingredients with lower toxicity.889.
Manuela Merchant Remedios González-Luque Björn O. Roos 《Theoretical chemistry accounts》1996,94(3):143-154
The vertical electronic spectrum of methylenecyclopropene, the prototype of the nonalternant hydrocarbons known as fulvenes, has been studied using multiconfigurational second-order perturbation theory. The calculations comprise three valence states and the 3s, 3p, and 3d members of the Rydberg series converging to the first ionization limit. Vertical excitation energies to three valence states are found at 4.13, 6.12, and 6.82 eV. The second of them corresponds to an excitation from the highest occupied orbital to a * orbital, while the other two are * excitations. The third transition gives rise to the most intense feature in the electronic spectrum. The results are rationalized within the scheme of two interacting double bonds. Comparisons are made between this and the previous theoretical calculations of the electronic spectra of related systems and also between the available experimental data of methylenecyclopropene in solution. 相似文献
890.
Claudia Albertini Marina Naldi Sabrina Petralla Silvia Strocchi Daniela Grifoni Barbara Monti Manuela Bartolini Maria Laura Bolognesi 《Molecules (Basel, Switzerland)》2021,26(4)
Despite Alzheimer’s disease (AD) incidence being projected to increase worldwide, the drugs currently on the market can only mitigate symptoms. Considering the failures of the classical paradigm “one target-one drug-one disease” in delivering effective medications for AD, polypharmacology appears to be a most viable therapeutic strategy. Polypharmacology can involve combinations of multiple drugs and/or single chemical entities modulating multiple targets. Taking inspiration from an ongoing clinical trial, this work aims to convert a promising cromolyn–ibuprofen drug combination into single-molecule “codrugs.” Such codrugs should be able to similarly modulate neuroinflammatory and amyloid pathways, while showing peculiar pros and cons. By exploiting a linking strategy, we designed and synthesized a small set of cromolyn–ibuprofen conjugates (4–6). Preliminary plasma stability and neurotoxicity assays allowed us to select diamide 5 and ethanolamide 6 as promising compounds for further studies. We investigated their immunomodulatory profile in immortalized microglia cells, in vitro anti-aggregating activity towards Aβ42-amyloid self-aggregation, and their cellular neuroprotective effect against Aβ42-induced neurotoxicity. The fact that 6 effectively reduced Aβ-induced neuronal death, prompted its investigation into an in vivo model. Notably, 6 was demonstrated to significantly increase the longevity of Aβ42-expressing Drosophila and to improve fly locomotor performance. 相似文献