全文获取类型
收费全文 | 167篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 144篇 |
数学 | 16篇 |
物理学 | 15篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 22篇 |
2012年 | 3篇 |
2011年 | 13篇 |
2010年 | 11篇 |
2009年 | 3篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1997年 | 3篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1981年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有175条查询结果,搜索用时 46 毫秒
51.
Felicia Seichter Andreas Wilk Katharina Wörle Seong-Soo Kim Josef A. Vogt Ulrich Wachter Peter Radermacher Boris Mizaikoff 《Analytical and bioanalytical chemistry》2013,405(14):4945-4951
The 12CO2/13CO2 isotope ratio is a well-known marker in breath for a variety of biochemical processes and enables monitoring, e.g., of the glucose metabolism during sepsis. Using animal models—here, at a mouse intensive care unit—the simultaneous determination of 12CO2 and 13CO2 within small volumes of mouse breath was enabled by coupling a novel low-volume hollow waveguide gas cell to a compact Fourier transform infrared spectrometer combined with multivariate data evaluation based on partial least squares regression along with optimized data preprocessing routines. 相似文献
52.
Martina C. Meinke Felicia Syring Sabine Schanzer Stefan F. Haag Rüdiger Graf Manuela Loch Ingo Gersonde Norbert Groth Frank Pflücker Jürgen Lademann 《Photochemistry and photobiology》2013,89(5):1079-1084
Modern sunscreens are well suited to provide sufficient protection in the UV range because the filter substances absorb or scatter UV radiation. Although up to 50% of radicals are formed in the visible and infrared spectral range during solar radiation protection strategies are not provided in this range. Previous investigations of commercially available products have shown that in addition to physical filters, antioxidants (AO) are necessary to provide protective effects in the infrared range by neutralizing already formed radicals. In this study, the efficacy of filter substances and AO to reduce radical formation in both spectral ranges was investigated after UV/VIS or IR irradiation. Optical properties and radical protection were determined for the investigated creams. It was found that organic UV filters lower radical formation in the UV/VIS range to 35% compared to untreated skin, independent of the presence of AO. Further reduction to 14% was reached by addition of 2% physical filters, whereas physical filters alone were ineffective in the UV/VIS range due to the low concentration. In contrast, this filter type reduced radical formation in the IR range significantly to 65%; similar effects were aroused after application of AO. Sunscreens which contain organic UV filters, physical filters and AO ensure protection in the complete solar spectrum. 相似文献
53.
Thomas Sch?nherr Edwin Weber Gerd Rheinwald Wilhelm Seichter 《Journal of inclusion phenomena and macrocyclic chemistry》2005,51(1):93-96
A new onium salt host molecule 1 featuring a spiro-type ammonium backbone was synthesized and shown to form a crystalline inclusion compound with chloroform, 1 · chloroform (1:2), the crystal structure of which is reported. The host molecular interactions including C–H···Br, Cl···Cl and aromatic stacking contacts are typical of the packing structure. 相似文献
54.
Alicia Dickenstein Laura Felicia Matusevich Timur Sadykov 《Advances in Mathematics》2005,196(1):78-123
We undertake the study of bivariate Horn systems for generic parameters. We prove that these hypergeometric systems are holonomic, and we provide an explicit formula for their holonomic rank as well as bases of their spaces of complex holomorphic solutions. We also obtain analogous results for the generalized hypergeometric systems arising from lattices of any rank. 相似文献
55.
We report a method for obtaining highly reproducible surface-enhanced Raman spectroscopy (SERS) of single and double-stranded thiolated DNA oligomers. Following a protocol that relaxes the DNA into an extended conformation, SERS spectra of DNA oligonucleotides are found to be extremely similar, strongly dominated by the Stokes modes of adenine. A spectral correlation function analysis useful for assessing reproducibility and for quantifying the highly complex changes corresponding to modifications in molecular conformation of the adsorbate molecules is introduced. This approach is used to monitor the interaction of DNA with cisplatin, a chemotherapy agent in widespread use. 相似文献
56.
Borodi G Bratu I Dragan F Peschar R Helmholdt RB Hernanz A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,70(5):1041-1048
Inclusion complexes of atenolol with beta-cyclodextrin (beta-CD) in aqueous solution have been investigated with (1)H NMR and UV-vis spectroscopy. The stoichiometry of this inclusion complex was established to be equimolar (1:1) and its stability constant was determined by UV-vis spectroscopy. The crystal structure of the beta-CD-atenolol (1:1) inclusion compound has been solved from synchrotron powder diffraction data using direct-space search techniques. The crystal structure model and (1)H NMR data are in good agreement and, with support of Hyperchem MM+ molecular dynamics results, suggest which protons are likely to be involved in the inclusion process that leads to the supramolecular architecture of this guest-host complex. 相似文献
57.
Ricci C Nyadong L Yang F Fernandez FM Brown CD Newton PN Kazarian SG 《Analytica chimica acta》2008,623(2):178-186
Pharmaceutical counterfeiting has become a significant public health problem worldwide and new, rapid, user-friendly, reliable and inexpensive methods for drug quality screening are needed. This work illustrates the chemical characterization of genuine and fake artesunate antimalarial tablets by portable Raman spectroscopy and validation by FT-Raman spectroscopy and ambient mass spectrometry. The applicability of a compact and robust portable Raman spectrometer (TruScan™) for the in situ chemical identification of counterfeit tablets is reported. 相似文献
58.
Vagner Irina Varlam Carmen Faurescu Ionut Faurescu Denisa Bucura Felicia 《Journal of Radioanalytical and Nuclear Chemistry》2017,314(2):709-713
Natural essential oil sample obtained from basil (Ocinum basilicum), and ethanol sample obtained from wine were measured to determine 14C specific activity, using two different sample preparation methods, and liquid scintillation counting method. The paper describes the use of two preparation methods, direct measurement method and CO2 absorption method, and the results obtained for this comparative study. Depending on carbon content of the sample and bubbling time, different correction factors of carbon mass trapped in liquid scintillation cocktail were established for CO2 absorption method.
相似文献59.
We investigate the solution space of hypergeometric systemsof differential equations in the sense of Gelfand, Graev,Kapranov and Zelevinski. For any integer d 2, we constructa matrix A(d) d x 2d and a parameter vector ß(d)such that the holonomic rank of the A-hypergeometric systemHA(d)(ß(d)) exceeds the simplicial volume vol(A(d))by at least d 1. The largest previously known gap betweenrank and volume was 2. Our construction gives evidence to the general observation thatrank jumps seem to go hand in hand with the existence of multipleLaurent (or Puiseux) polynomial solutions. 相似文献
60.
Yang Hsia Eric Gnesa Simon Tang Felicia Jeffery Paul Geurts Liang Zhao Andreas Franz Craig Vierra 《Applied Physics A: Materials Science & Processing》2011,105(2):301-309
The diversity in function and mechanical behavior of spider silks, and the ability to produce these silks recombinantly, have
tremendous potential in creating a new class of biomimetic materials. Here we investigate the structural and mechanical properties
of pyriform silks from the golden orb-weaver, Nephila clavipes. Nanoscale indentation measurements using atomic force microscopy on natural pyriform silk suggests that this biomaterial
has high toughness that may be suitable for dissipating high amounts of mechanical energy. We also observed the occurrence
of highly organized nanocrystals within the pyriform silk fibers that may contribute to the remarkable energy dissipation
capability of these silks. It has been demonstrated that poly-(Gly–Ala) and poly-Ala stretches within the internal block repeat
modules of dragline silk fibroins form nanocrystals, and these nanocrystalline structures may be responsible for the high
extensibility of the dragline silks. In contrast, amino acid sequence analysis shows that PySp2 does not contain the same
motifs. In the absence of poly-(Gly–Ala) and poly-Ala repeats, we hypothesized that PySp2 contains new protein motifs sufficient
to polymerize into functional structures. To investigate the functional contributions of these novel motifs during pyriform
fiber formation, we expressed different recombinant PySp2 fibroins with various segments spanning its block repeat units.
We demonstrate that PySp2 recombinant proteins with the Pro-rich sub-block domain (PXP motifs, where X= sub-set of the amino acids A, L, or R) and/or the Ser + Gln + Ala-rich sub-block domain (QQSSVAQS motifs) are sufficient
for artificial fiber formation. Moreover, we show that recombinant PySp2 proteins that contain a single block repeat unit
can self-assemble into foam-like nanostructures. Collectively, our findings support the use of PySp2 recombinant proteins
for a wide range of biomimetic materials with morphologies ranging from fibers to porous structures. 相似文献