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排序方式: 共有94条查询结果,搜索用时 31 毫秒
1.
VladimirA. Azov Franois Diederich Yoriko Lill Bert Hecht 《Helvetica chimica acta》2003,86(6):2149-2155
We report the synthesis of modified Cram‐type cavitands bearing one or two fluorescent labels for single‐molecule spectroscopic studies of vase? kite conformational switching (Scheme 3). Syntheses were performed by stepwise bridging of the four couples of neighboring H‐bonded OH groups of resorcin[4]arene bowls (Schemes 2 and 3). The new substitution patterns enable the construction of a large variety of future functional architectures. 1H‐NMR Investigations showed that the new partially and differentially bridged cavitands feature temperature‐ and pH‐triggered vase? kite conformational isomerism similar to symmetrical cavitands with four identical quinoxaline bridges (Table). It was discovered that vase? kite switching of cavitands is strongly solvent‐dependent. 相似文献
2.
An analytical methodology has been developed for the UV-spectrophotometric determination of carbaryl in waters after its preconcentration onto a polyether type polyurethane foam followed by on-line elution. The aforementioned strategy offers an easy way for in-field sampling and to improve the analytical sensitivity. Several chemical and flow variables (mass of sorbent, sample flow rate, sample volume and carrier flow rate) were studied to ensure the best performance of the system. Recovery studies, carried out on natural water samples spiked with known amounts of carbaryl at concentration levels between 250 and 500 mug l(-1), provided recovery percentages between 94 and 105%. A detection limit of 12 mug l(-1) was achieved and a variation coefficient of 3.4% was obtained at 0.50 mug ml(-1). 相似文献
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Peter Schramel Anneliese Wolf und Gisela Lill 《Fresenius' Journal of Analytical Chemistry》1984,317(3-4):471-477
Zusammenfassung Indicatoren für lang- und kurzzeitige Umweltbelastungen in verschiedenen geographischen Regionen mit ihren verschiedenartigen Belastungsgraden (z. B. Industrie, Landwirtschaft u. a.) sind weltweit mehr und mehr von Interesse. Die wichtigste Frage dabei ist, wie aussagefähig ein bestimmter Indicator für den Stand der Umweltbelastung betrachtet werden kann.Verschiedene Materialien wie Pflanzen, Tiere (Ganztiere bzw. Organe), Organe des Menschen (z. B. Placenta) und Böden wurden in den letzten Jahren als geeignete Indicatoren diskutiert. In verschiedenen Forschungsprogrammen unserer Arbeitsgruppe sind wir mit diesen Fragestellungen intensiv beschäftigt. Materialien wie menschliche Placenta, verschiedene Tierarten und deren Organe, Pflanzen und Böden wurden dabei untersucht, um geeignete Indicatormaterialien zu finden. An Hand einiger ausgewählter Beispiele soll die Aussagefähigkeit dieser Materialien diskutiert werden, wobei der Schwerpunkt auf die Unterscheidung zwischen normaler biologischer Streuung der Daten und dem Einfluß der Umwelt gelegt werden soll. Etwa 20 Elemente mit essentiellen Spurenelementen wie Cu, Fe, Mn, Zn usw. und toxischen Elementen wie Pb, Cd, Hg, As usw. wurden dabei untersucht.
Herrn Prof. Dr. W. Fresenius zum 70. Geburtstag gewidmet 相似文献
Examinations on the suitability of different types of samples as indicators for heavy metal pollution
Summary Indicators for long- and short-term environmental pollution in different regions with different environmental influences (agriculture, industry, etc.) become world-wide more and more of interest. The main question in this connection is how a substance can give evidence for environmental research.Different materials like human placenta, animals (or some organs of these), plants and soils have been discussed in the last few years for use as indicator substances. The use of bioindicators will be discussed in this paper by means of some examples from the research work of our laboratory. About twenty elements, including nearly all the heavy metals like As, Hg, Cd, Pb, etc. and essential trace elements like Cu, Fe, Mn, Zn, etc. have been investigated in these experiments. Main emphasis is laid on the differentiation between normal biological scattering of data and the environmental influence.
Herrn Prof. Dr. W. Fresenius zum 70. Geburtstag gewidmet 相似文献
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Two flashlamp-pumped, mode-locked and optically coupled dye lasers produce trains of picosecond pulses with definite, but
variable time correlation. One pulsetrain is used to bleach the sample, while the other probes the decay of its transient
transmission. Relaxation times between 15 ps and 1 ns can be monitored by one simultaneous activation of the two lasers. 相似文献
8.
ADOLFO V. T. CARTAXO JOÃO L. REBOLA NATAŠA B. PAVLOVIĆ PEDRO M. A. CHARRUA DANIEL D. T. FONSECA JOSÉ A. P. MORGADO 《Fiber and Integrated Optics》2013,32(3-4):331-352
Abstract This article introduces the main achievements resulting from the DWDM/ODC project. The five areas of research activity within the DWDM/ODC project cover some of the main issues of design and development of dense wavelength division multiplexing systems for transparent optical networks. These issues are: performance assessment with arbitrary optical filtering; performance of signaling formats; dispersion compensation strategies for directly and externally modulated systems in presence of nonlinear transmission-induced degradation; and the impact of noise and crosstalk in the extent of transparent optical networks. All five areas of research activity have contributed significantly to a better understanding of the limitations present in dense wavelength division multiplexing systems. 相似文献
9.
Andreas Jaekel Pascal Lill Stephen Whitelam Barbara Sacc 《Molecules (Basel, Switzerland)》2020,25(23)
Since the pioneering work of Ned Seeman in the early 1980s, the use of the DNA molecule as a construction material experienced a rapid growth and led to the establishment of a new field of science, nowadays called structural DNA nanotechnology. Here, the self-recognition properties of DNA are employed to build micrometer-large molecular objects with nanometer-sized features, thus bridging the nano- to the microscopic world in a programmable fashion. Distinct design strategies and experimental procedures have been developed over the years, enabling the realization of extremely sophisticated structures with a level of control that approaches that of natural macromolecular assemblies. Nevertheless, our understanding of the building process, i.e., what defines the route that goes from the initial mixture of DNA strands to the final intertwined superstructure, is, in some cases, still limited. In this review, we describe the main structural and energetic features of DNA nanoconstructs, from the simple Holliday junction to more complicated DNA architectures, and present the theoretical frameworks that have been formulated until now to explain their self-assembly. Deeper insights into the underlying principles of DNA self-assembly may certainly help us to overcome current experimental challenges and foster the development of original strategies inspired to dissipative and evolutive assembly processes occurring in nature. 相似文献
10.
Biotin carboxylase catalyzes the ATP-dependent carboxylation of biotin and is one component of the multienzyme complex acetyl-CoA carboxylase that catalyzes the first committed step in fatty acid synthesis in all organisms. Biotin carboxylase from Escherichia coli, whose crystal structures with and without ATP bound have been determined, has served as a model system for this component of the acetyl-CoA carboxylase complex. The two crystal structures revealed a large conformational change of one domain relative to the other domains when ATP is bound. Unfortunately, the crystal structure with ATP bound was obtained with an inactive site-directed mutant of the enzyme. As a consequence the structure with ATP bound lacked key structural information such as for the Mg2+ ions and contained altered conformations of key active-site residues. Therefore, nanosecond molecular dynamics studies of the wild-type biotin carboxylase were undertaken to supplant and amend the results of the crystal structures. Specifically, the protein-metal interactions of the two catalytically critical Mg2+ ions bound in the active site are presented along with a reevaluation of the conformations of active-site residues bound to ATP. In addition, the regions of the polypeptide chain that serve as hinges for the large conformational change were identified. The results of the hinge analysis complemented a covariance analysis that identified the individual structural elements of biotin carboxylase that change their conformation in response to ATP binding. 相似文献