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671.
The purpose of this work was the development of a method for the determination of Se compounds in leaves of plants. Water-soluble Se compounds were extracted from samples by water. Enzymatic hydrolysis with the non-specific enzyme protease XIV was used for the release of Se compounds bound to proteins. Separation of Se species was made by ion exchange chromatography, using an anion exchange column for SeIV, SeVI and selenomethionine (SeMet), and a cation exchange column for selenomethylselenocysteine (SeMeSeCys) and selenocystine (SeCys2). Columns were connected “on line” to a hydride generation atomic fluorescence spectrometer (HG-AFS) using a UV lamp between the separation and detection system. The repeatability of the results obtained by the developed method was under 15% (R.S.D.) for all Se species; the detection limit was 2-10 ng Se/g of supernatant. The accuracy was checked by comparison with some literature data for reference materials since there were no suitable certified reference materials available. The method was used for the determination of Se compounds in chicory (Cichorium intybus L.) leaves from plants which were cultivated aeroponically with elevated concentrations of Na2SeO4 for different periods. Se accumulated efficiently in chicory leaves; up to 480 μg/g after 41 days of exposure, mostly (64%) as SeVI, i.e. in the form of Se added. Beside inorganic Se, in the extracts from enzyme hydrolysis we also found SeMet (4.2-8.4%) and SeMeSeCys (<DL−0.7%). Some unidentified peaks were also observed in the chromatograms of plant extracts. 相似文献
672.
Hechun Lin Peter W. de Oliveira Ingrid Grobelsek Aude Haettich Prof. Dr. Dr. h. c. Michael Veith 《无机化学与普通化学杂志》2010,636(11):1947-1954
The solvothermal reactions of Ti(OiPr)4 in alcohol using ionic liquid as additive were investigated. In the presence of [BMIM][Cl], [BMIM][Br], [BMIM][NTf2], [BMIM][SO3Me], [BMIM][SO4Me], or [BMIM][OTf] (BMIM = 1‐Butyl‐3‐methylimidazolium), pure anatase nanoparticles were obtained. The controlled hydrolysis of Ti(OiPr)4 in the presence of ionic liquids to form titanium oxo clusters plays a key role in the formation of anatase nanostructures, and ionic liquids can be repeatedly used to synthesise anatase nanoparticles. However, in the presence of [BMIM][PF6], [BMIM]2[Ti(OH)6] was obtained by an anion exchange reaction. 相似文献
673.
674.
675.
Hans R. Kricheldorf Ingrid Kreiser-Saunders Christian Jürgens Dieter Wolter 《Macromolecular Symposia》1996,103(1):85-102
Polymerizations of lactides via cationic, anionic, and insertion mechanisms are described. The usefulness of these three mechanisms for preparative purposes is evaluated. The polymerization mechanisms initiated by Al-alkoxides or Sn(II)-2-ethylhexanoate are discussed in more detail. Furthermore, the usefulness of 13C NMR spectroscopy for the sequence analysis of copolylactones is demonstrated. Copolyesters of D,L-lactide and ϵ-caprolactone with Tg's around 35°C and high transparency were synthesized. Films of these copolylactones were characterized by various methods and their usefulness as resorbable wound dressing was evaluated. More than 30 patients were successfully treated with this novel wound dressings. 相似文献
676.
Hans R. Kricheldorf Ingrid Kreiser-Saunders Nico Scharnagl 《Macromolecular Symposia》1990,32(1):285-298
Polymerization via anionic mechanisms or insertion mechanisms (pseudoanionic mechanisms) are compared for β-lactones and L-lactide. The following aspects are discussed: initiation and deprotonation of β-lactones, back-biting degradation, stereosequences of poly(β-D,L-butyrolactone), racemization of L-lactide, systematic variation of endgroups including synthesis of macromers. 相似文献
677.
Following quantum counting statistical considerations relations were derived which enable to estimate the error of integral intensity measurements of weak interferences and the minimal detectable volume parts of minority phases as a function of the measuring conditions and of the given error limits, and to optimize the choice of radiation and monochromatization conditions for the X-ray analysis of minority phases. 相似文献
678.
Kyoung Chul Park Prof. Dr. Preecha Kittikhunnatham Dr. Jaewoong Lim Grace C. Thaggard Yuan Liu Dr. Corey R. Martin Dr. Gabrielle A. Leith Donald J. Toler Dr. An T. Ta Dr. Nancy Birkner Dr. Ingrid Lehman-Andino Dr. Alejandra Hernandez-Jimenez Dr. Gregory Morrison Dr. Jake W. Amoroso Prof. Dr. Hans-Conrad zur Loye Dr. Dave P. DiPrete Dr. Mark D. Smith Prof. Dr. Kyle S. Brinkman Prof. Dr. Simon R. Phillpot Prof. Dr. Natalia B. Shustova 《Angewandte Chemie (International ed. in English)》2023,62(5):e202216349
A novel series of heterometallic f-block-frameworks including the first examples of transuranic heterometallic 238U/239Pu-metal–organic frameworks (MOFs) and a novel monometallic 239Pu-analog are reported. In combination with theoretical calculations, we probed the kinetics and thermodynamics of heterometallic actinide(An)-MOF formation and reported the first value of a U-to-Th transmetallation rate. We concluded that formation of uranyl species could be a driving force for solid-state metathesis. Density of states near the Fermi edge, enthalpy of formation, band gap, proton affinity, and thermal/chemical stability were probed as a function of metal ratios. Furthermore, we achieved 97 % of the theoretical maximum capacity for An-integration. These studies shed light on fundamental aspects of actinide chemistry and also foreshadow avenues for the development of emerging classes of An-containing materials, including radioisotope thermoelectric generators or metalloradiopharmaceuticals. 相似文献
679.
Hans R. Kricheldorf Ingrid Kreiser‐Saunders Dirk‐Olaf Damrau 《Macromolecular Symposia》2000,159(1):247-258
Numerous nontoxic (resorbable) salts were prepared from cations and anions belonging to the human metabolism, such as Na, K, Mg, Ca, Zn and Fe in combination with chloride, iodide, hydroxide, carbonate, acetate, stearate, glycolate, L‐lactate, D‐mandelate and various N‐substituted α‐amino acids. All these salts were used as initiators for polymerizations of L‐lactide in bulk at 100–180°C. Furthermore, Grignard reagents, hemin and hematin were included in this study. Zn L‐lactate was found to be the most useful initiator in terms of reactivity, maximum molecular weight of the isolated poly(L‐lactide) and its optical purity. Zn L‐lactate initiated copolymerizations of L‐lactide and glycolid or L‐lactide and ϵ‐caprolactone were also studied. Finally, first studies of the polymerization mechanism of zinc stearate and zin 2‐ethylhexanoate were performed. They suggest that zinc carboxylates combined with an alcohol as coinitiator form reactive zinc alkoxides which are the true initiators at temperatures < 150°C. 相似文献