首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   195篇
  免费   2篇
  国内免费   3篇
化学   118篇
晶体学   13篇
力学   3篇
数学   10篇
物理学   56篇
  2020年   3篇
  2018年   1篇
  2017年   2篇
  2016年   4篇
  2015年   1篇
  2014年   5篇
  2013年   10篇
  2012年   7篇
  2011年   10篇
  2010年   9篇
  2009年   4篇
  2008年   3篇
  2007年   5篇
  2006年   8篇
  2005年   9篇
  2004年   8篇
  2003年   9篇
  2002年   11篇
  2001年   5篇
  2000年   5篇
  1999年   7篇
  1998年   6篇
  1997年   3篇
  1996年   4篇
  1995年   1篇
  1994年   1篇
  1993年   3篇
  1992年   4篇
  1991年   2篇
  1990年   3篇
  1989年   2篇
  1988年   1篇
  1987年   3篇
  1986年   5篇
  1985年   3篇
  1984年   5篇
  1983年   5篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1979年   4篇
  1978年   2篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
  1969年   1篇
  1965年   1篇
  1961年   1篇
  1886年   1篇
排序方式: 共有200条查询结果,搜索用时 31 毫秒
71.
The interaction-induced light scattering many-body correlation functions and their spectra in a thin argon layer located between two parallel graphite walls have been investigated by molecular dynamics simulation method. The calculations have been performed for three different distances between graphite plates. Our simulations show the increased intensity of the interaction-induced light scattering spectra at low frequencies for argon atoms in confined space, in comparison to the bulk (unconfined) sample. Moreover, we show a substantial dependence of the interaction-induced light scattering correlation functions of argon on the distances between graphite walls, that is, on the density of argon layer. The mean square displacement and related diffusion coefficient of argon atom in the confined space has been also investigated. Moreover, the structural feature of the thin layer has been studied by calculating the argon density profile, perpendicular to the graphite walls. An interesting observation is the development of a fluid phase in the innermost region of the confined argon layer.  相似文献   
72.
Fluorescence correlation spectroscopy (FCS) is a frequently applied technique that allows for the precise and sensitive analysis of molecular diffusion and interactions. However, the potential of FCS for in vitro or ex vivo studies has not been fully realized due in part to artifacts originating from autofluorescence (fluorescence of inherent components and fixative-induced fluorescence). Here, we propose the azadioxatriangulenium (ADOTA) dye as a solution to this problem. The lifetime of the ADOTA probe, about 19.4 ns, is much longer than most components of autofluorescence. Thus, it can be easily separated by time-correlated single-photon counting methods. Here, we demonstrate the suppression of autofluorescence in FCS using ADOTA-labeled hyaluronan macromolecules (HAs) with Rhodamine 123 added to simulate diffusing fluorescent background components. The emission spectrum and decay rate of Rhodamine 123 overlap with the usual sources of autofluorescence, and its diffusion behavior is well known. We show that the contributions from Rhodamine 123 can be eliminated by time gating or by fluorescence lifetime correlation spectroscopy (FLCS). While the pairing of ADOTA and time gating is an effective strategy for the removal of autofluorescence from fluorescence imaging, the loss of photons leads to erroneous concentration values with FCS. On the other hand, FLCS eliminates autofluorescence without such errors. We then show that both time gating and FLCS may be used successfully with ADOTA-labeled HA to detect the presence of hyaluronidase, the overexpression of which has been observed in many types of cancer.  相似文献   
73.
A modification of the point charge model is proposed, taking into account the electronegatives of the metal and ligand atoms. On this basis empirical formulas for the effective ligand (L) charge and its distance with respect to the metal (M) origin have been set up. For a VM valent metal atom, surrounded by NL-nearest ligands at distance R0, the respective relations qeff = vM(?L/?M ? 1)/NR0?L/(?L+ ?M) are obtained. When applied to almost forty lanthanide and actinide non-metallic compounds the model shows reasonable agreement with the experimental data available.  相似文献   
74.
Summary Presented data give some informations of analytical importance as a result of pulse polarographic investigations of Ge(IV) in KCl solutions within pH range 3–12 at Ge concentration from 1×10–4 to 2.5×10–6 M. It was shown that Ge(IV) can be polarographically active in acidic solution but its reduction interferes with hydrogen gas development. The addition ofp-quinone enables the determination of Ge(IV) without this interfering effect.Suggested explanation of the observed changes in polarographic curves dependent on pH and Ge concentration based on the existence of several polarographically active forms.
Elektroanalytische Bemerkungen zur pulspolarographischen Bestimmung von Ge(IV)
Zusammenfassung Unsere Ergebnisse bieten einige Informationen über die pulspolarographische Bestimmung von Ge(IV) in KCl-Lösungen innerhalb pH 3–12 und bei Ge-Konzentrationen zwischen 10–4 und 2,5×10–6 M. Es wurde gezeigt, daß Ge(IV) in saurer Lösung polarographisch aktiv ist, seine Reduktion aber durch Wasserstoff-Entwicklung gestört wird. Der Zusatz vonp-Chinon beseitigt diese Störung. Die Änderung der polarographischen Kurven je nach Ge-Konzentration und pH beruht vermutlich auf der Existenz verschiedener polarographisch aktiver Formen.
  相似文献   
75.
76.
77.
78.
The solvatochromic fluorescent probe 8-anilino-1-naphthalenesulfonate (ANS) has been used to study the hydrophobicity and conformational dynamics of lecithin:cholesterol acyltransferase (LCAT). The ANS to LCAT binding constant was estimated from titrations with ANS, keeping a constant concentration of LCAT (2 microM). Apparent binding constant was found to be dependent on the excitation. For the direct excitation of ANS at 375 nm the binding constant was 4.7 microM(-1) and for UV excitation at 295 nm was 3.2 microM(-1). In the later case, not only ANS but also tryptophan (Trp) residues of LCAT is being excited. Fluorescence spectra and intensity decays show an efficient energy transfer from tryptophan residues to ANS. The apparent distance from Trp donor to ANS acceptor, estimated from the changes in donor lifetime was about 3 nm and depends on the ANS concentration. Steady-state and time-resolved fluorescence emission and anisotropies have been characterized. The lifetime of ANS bound to LCAT was above 16 ns which is characteristic for it being in a hydrophobic environment. The ANS labeled LCAT fluorescence anisotropy decay revealed the correlation time of 42 ns with a weak residual motion of 2.8 ns. These characteristics of ANS labeled LCAT fluorescence show that ANS is an excellent probe to study conformational changes of LCAT protein and its interactions with other macromolecules.  相似文献   
79.
We describe the positive effect of surface plasmon-coupled fluorescence emission (SPCE) on the detection of a signal from a surface immunoassay in highly absorbing or/and scattering samples. A model immunoassay using fluorescently labeled anti-rabbit antibodies that bind to rabbit immunoglobulin on a silver surface was performed, and the signal was detected in the presence of various highly absorbing and/or scattering solutions or suspensions, such as hemoglobin solution, plastic beads, and red blood cells. The results showed that a highly absorbing solution consisting of small molecules (dye, hemoglobin) attenuates the SPCE signal approximately 2-3-fold. In contrast, suspensions with the same absorption containing large particles (large beads, red blood cell suspension) attenuate the SPCE signal only slightly, approximately 5-10%. Also, a suspension of large undyed, highly scattering beads does not reduce the SPCE signal. The effects on the immunoassay signal of the sample background absorption and scattering, the size of the background particles, and the geometry of the experimental set-up are discussed. We believe that SPCE is a promising technique in the development of biosensors utilized for surface-based assays, as well as any assays performed directly in highly absorbing and/or scattering solutions without washing or separation procedures. Figure Red blood cells (unlike hemoglobin) do not attenuate the SPCE fluorescence in surface assays.  相似文献   
80.
In this study, a procedure was developed to determine short-chain alkane monocarboxylic acids (SCMAs) in aqueous samples using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography (GC) coupled with mass spectrometry (MS). A Stabilwax-DA capillary column (30 m × 0.32-mm inner diameter, 0.50-μm film thickness) was used for GC separation and a 60-μm poly(ethylene glycol) fiber was used to isolate SCMAs from water and introduce them into the gas chromatograph. Parameters of HS-SPME, analyte desorption, and GC-MS analysis were selected and an analytical procedure was proposed. Limits of quantitation were on the order of about 0.2 mg L-1. As an example of the application of the procedure, SCAMs were determined in municipal wastewater at different steps of treatment.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号