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131.
132.
Michal Lutecki Olga Solcova Stephan Werner Cornelia Breitkopf 《Journal of Sol-Gel Science and Technology》2010,53(1):13-20
Thermally stable sulfated zirconia catalysts were synthesized via a new templating procedure and compared with standard zirconia materials prepared by precipitation without templates. Two preparation routes with various amphiphilic systems were employed as structure directing agents: (1) synthesis with hexadecyltrimethylammonium bromide, and (2) combined use of surfactant Brij-56® and triblock-copolymer Pluronic P123®. The formation of materials was characterized by TEM, SEM, X-ray diffraction as well as nitrogen adsorption and mercury intrusion techniques. Different self-assembling properties of the structure directing compounds led to sulfated zirconia materials exhibiting improved morphological and structural properties in terms of thermal stability, specific surface areas, pore diameters and porosity factors. Notably, hierarchical pore structures were obtained for the synthesis route via a combined use of Brij-56® and P123®. Moreover, the morphological features of these materials were evidenced by a significantly improved isomerization activity of n-butane. 相似文献
133.
Robert Ianoş Ioan Lazău Cornelia Păcurariu 《Journal of Thermal Analysis and Calorimetry》2009,97(1):209-214
The reactivity of LiNO3 and Al(NO3)3 with respect to urea and β-alanine was investigated. Experimental results proved that β-alanine is a more suitable fuel for
LiNO3, whereas urea seems to be more adequate for Al(NO3)3. Based on the different metal nitrate/fuel mixture reactivity, nanocrystalline γ-LiAlO2 powders were prepared by solution combustion synthesis using a fuel mixture of urea and β-alanine. This fuel mixture yielded
single-phase nanocrystalline γ-LiAlO2 (32.6 nm) directly from the combustion reaction. The resulted powder had a specific surface area of 3.2 m2/g and no supplementary annealing was required. On the other hand, pure γ-LiAlO2 could not be obtained by using a single fuel (urea, β-alanine) unless annealing at 900 °C for 1 h was performed. 相似文献
134.
135.
Mills NS Llagostera KB Tirla C Gordon SM Carpenetti D 《The Journal of organic chemistry》2006,71(21):7940-7946
Dications of p-substituted 3-phenylindenylidenefluorenes were prepared to examine the response of the resulting indenyl and fluorenyl cationic systems to magnetic measures of antiaromaticity. All measures, (1)H NMR shifts, nucleus independent chemical shifts (NICS(1)(zz)), and magnetic susceptibility exaltation, Lambda, supported the antiaromaticity of the dications 3a-f2+. The 1H NMR shifts and NICS(1)(zz) showed that the indenyl ring system was less antiaromatic than the fluorenyl ring system, contrary to the antiaromaticity of indenyl monocations compared to fluorenyl monocations. The presence of a phenyl substituent in the 3-position was able to stabilize the indenylidene cation through resonance, decreasing its antiaromaticity, but even in the absence of the 3-phenyl substituent, the indenyl system of indenylidenefluorene dications was less antiaromatic than the fluorenyl system. The decreased antiaromaticity of the 3-phenylindenylidenefluorene dications over the unsubstituted indenylidenefluorene dication was supported by (anti)aromatic (de)stabilization energy calculations, ASE. 相似文献
136.
137.
We present a single-resource finite-horizon Markov decision process approach for a firm that seeks to maximize expected revenues by dynamically adjusting the menu of offered products and their prices to be selected from a finite set of alternative values predetermined as a matter of policy. Consumers choose among available products according to an attraction choice model, a special but widely applied class of discrete choice models. 相似文献
138.
139.
Axel R. Fischer Nham Thi Phuong Lan Cornelia Wiedemann Petra Heide Peter Werner Arndt W. Schmidt Gabriele Theumer Hans-Joachim Knölker 《Journal of chromatography. A》2010,1217(17):2950-2955
A new method for determining the endocrine disrupting substance 4-nonylphenol (technical grade = mixture of isomers, 4-NP) from water samples has been developed by using 4-(2,6-dimethylhept-3-yl)phenol (4-sec-NP) as model compound. This branched monoalkylphenol is shown to serve as internal standard (IS) for the determination of technical 4-nonylphenol. To the best of our knowledge, 4-(2,6-dimethylhept-3-yl)phenol (racemic mixture) is a newly synthesized 4-nonylphenol isomer and has not been described elsewhere. Recoveries have been determined by analyzing spiked water samples from distilled water, river water and wastewater. Following acetylation, the compounds were enriched via solid phase extraction (SPE). Analyses of the compounds were performed by capillary column gas chromatography/mass spectrometry (GC/MS), operating in selected ion-monitoring (SIM) mode. The recovery of technical 4-NP using either the newly prepared 4-sec-NP or 4-n-nonylphenol (4-n-NP) as IS have been compared. 4-sec-NP showed slightly better results. However, in the first series of experiments using wastewater, the yields for the derivatization of the two standard compounds were remarkably different. The yield for derivatization of 4-n-NP was approximately 20%, probably due to the difficult matrix of the wastewater. In contrast, the yield for the derivatization of 4-sec-NP was considerably higher (approximately 63%). This problem can be solved by increasing the concentration of the reagent used for derivatization. For better control of the clean-up process, we recommend application of 4-sec-NP as internal standard, at least in water samples with complex matrices (e.g., high content of hydroxylated compounds). 相似文献
140.
Robert H. Crabtree Jennifer A. Loch Karin Gruet Dong-Heon Lee Cornelia Borgmann 《Journal of organometallic chemistry》2000,600(1-2):7-11
In a biomimetic approach to organometallic catalysis, pendant hydrogen-bonding groups are shown to influence the chemistry of ligand binding and activation in an iridium complex. Such groups can bind a substrate by hydrogen bonding and so offer the possibility of a biomimetic approach to catalysis where binding is controlled via molecular recognition. Because catalyst design in this area may be challenging, combinatorial and rapid screening methods may be needed to assay potential catalysts and initial progress on developing these methods for hydrosilation of alkenes and imines is described. Catalysis of aldehyde imination and the origin of pKa changes of bound H2 are discussed. 相似文献