全文获取类型
收费全文 | 379篇 |
免费 | 22篇 |
专业分类
化学 | 347篇 |
晶体学 | 3篇 |
数学 | 20篇 |
物理学 | 31篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 15篇 |
2021年 | 11篇 |
2020年 | 17篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 19篇 |
2014年 | 14篇 |
2013年 | 24篇 |
2012年 | 32篇 |
2011年 | 42篇 |
2010年 | 25篇 |
2009年 | 31篇 |
2008年 | 28篇 |
2007年 | 24篇 |
2006年 | 13篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 2篇 |
排序方式: 共有401条查询结果,搜索用时 0 毫秒
1.
Flávio A. Pavan Yoshitaka Gushikem Celso C. Moro Tania M. Costa Edilson V. Benvenutti 《Colloid and polymer science》2003,281(2):173-177
Anilinepropylsilica xerogel was obtained by using an appropriate organosilane and tetraethyl orthosilicate as precursor reagents. The gelation was carried out using HF and NaF as catalysts. The presence of Na+ (when NaF was used) resulted in a decrease in the final organic content of the materials. This effect was interpreted as an inhibition of the organosilane polycondensation possibly due to the Na+ interaction with the SiO- groups of the hydrolyzed organosilane. The presence of Na+ also results in morphological changes in the xerogels. 相似文献
2.
The use of high-throughput techniques allowed the rapid identification of new catalysts for the enantioselective reduction of imines using polymethylhydrosiloxane (PMHS) as a reducing agent. By a simple modification of the chiral ligand structure that came out of the screening, the enantioselectivity of the reduction was increased from 40% ee to 60% ee. 相似文献
3.
The unique advantages of quantum dot (QD) bioconjugates have motivated their application in biological assays. However, physical characterization of bioconjugated QDs after surface modification has often been overlooked. Here, biotinylated antibodies (biotin-IgG) were attached to commercial streptavidin-conjugated quantum dots (strep-QDs) at different stoichiometric ratios, and these QD bioconjugates were characterized with atomic force microscopy and discontinuous sodium dodecyl sulfate agarose gel electrophoresis (SDS-AGE). The results from these complementary analytical techniques showed that the molar ratio determined the relative sizes, molecular weights and morphologies of the QD bioconjugates. Additionally, the novel discontinuous SDS-AGE analysis confirmed specific binding between biotin-IgG and strep-QDs. Researchers who design QD bioconjugates for cell-based assays should consider stoichiometry-dependent differences in the physical properties of their QD bioconjugates. 相似文献
4.
Fermo P Gilardoni S Jauni Simarro T Bolzacchini E Lasagni M Gianelle V Pozzoli L Perrone G Librando V 《Annali di chimica》2003,93(4):389-396
The carbonaceous component in the Milan urban particulate matter, i.e. the two components black carbon (BC) and organic carbon (OC), has been measured by means of a thermogravimetric analyzer combined with an infrared spectrophotometer (TGA/FT-IR). While black carbon may be considered a primary pollutant, organic carbon includes both primary emissions and secondary organic aerosols. Since carbonaceous aerosol (including a small quantity of inorganic carbon, too) makes up roughly from 25% to 50% of the average annual PM 2.5 mass concentration, a deeper understanding of this component is required. The TGA/FT-IR technique, employed for the first time to our knowledge for the quantification of the particulate matter carbonaceous component, allows, thought the results here presented are preliminary, to assess the two components BC and OC in a simple way especially if compared with the methods reported in the literature. The total carbon (TC) determinations performed by TGA/FT-IR on Milan urban particulate matter are in good agreement with the results obtained by a total organic carbon (TOC) analyzer operating directly on the solid sample. 相似文献
5.
6.
Ireland T Tappe K Grossheimann G Knochel P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(4):843-852
A new family of ferrocenylphosphane ligands has been prepared. Their flexible synthesis allows many structural modifications. The asymmetric induction of these ligands was examined in the hydrogenation of functionalized C=C, C=O, and C=N bonds. The enantioselectivity of the reaction was strongly dependent on the substituent R at the position alpha to the ferrocene moiety. In many cases, both enantiomeric beta-hydroxyesters of the reduction product can be obtained by simply replacing a dimethylamino group in the ligand with a methyl group. 相似文献
7.
Pavan FA Lucho AM Gonçalves RS Costa TM Benvenutti EV 《Journal of colloid and interface science》2003,263(2):688-691
The metal ion adsorption properties of the microporous hybrid anilinepropylsilica xerogel were studied using divalent copper, zinc, and cadmium ions in aqueous solutions in concentrations ranging from 10(-4) up to 5x10(-3) moll(-1). At low concentrations the surface of the solid phase presents selectivity for Cu (II), even in competitive conditions. This preferential sorption ability for copper in relation to zinc and cadmium ions was interpreted by considering the xerogel morphology. 相似文献
8.
Huygens A Huyghe D Bormans G Verbruggen A Kamuhabwa AR Roskams T de Witte PA 《Photochemistry and photobiology》2003,78(6):607-614
The aim of this study was to investigate the in vitro cellular accumulation, distribution and photocytotoxic effect of hypericin in two-dimensional (2-D) and three-dimensional (3-D) cultured RT-112 transitional cell carcinoma cells of the bladder. In addition, two iodinated derivatives of hypericin were incorporated to investigate whether these analogs, with their increased lipophilicity and heavy-atom effect, display a different biological behavior and optimized photodynamic effect. The results indicate that hypericin and mono-iodohypericin behave similarly in terms of cellular accumulation, spheroidal distribution and photocytotoxic effect. In contrast, di-iodohypericin concentrated to a higher extent in monolayers and spheroids, but the accumulation was restricted to the outermost part of the spheroid. An inverse correlation therefore seems to exist between the extent of cellular uptake under 2-D conditions and the penetration of the compounds in multicellular systems. Moreover, a less pronounced photocytotoxic effect was observed for di-iodohypericin in both 2-D and 3-D cell culture systems. It can be concluded that iodinated derivatives of hypericin do not show an increased cytotoxic effect upon irradiation in either monolayers or spheroids. Moreover, this study shows that when new photosensitizers are preclinically developed, the use of 3-D cell aggregates is critical for a correct evaluation of their efficacy. 相似文献
9.
Bel'nikevich N. G. Bobrova N. V. Bronnikov S. V. Kalyuzhnaya L. M. Budtova T. V. 《Russian Journal of Applied Chemistry》2004,77(2):313-318
Mixed solutions of chitosan and polymers with different chain rigidities (polyvinyl alcohol and methyl cellulose) in 2% acetic acid, at various component ratios, were studied viscometrically. The compatibility of the components in solutions and in the solid phase was assessed, and the mechanical characteristics of films prepared from these blends were determined. 相似文献
10.
Jesús M. Ruiz Gonzalez Marcos Loroo Tania Crdova Gabriel Chuchani 《Journal of Molecular Structure》2005,732(1-3):55-61
Møller-Plesset MP2/6-31G method was used to examine the gas-phase elimination of 2-substituted alkyl ethyl N,N-dimethylcarbamates. The results of these calculations support a concerted non-synchronous six-membered cyclic transition state mechanism for carbamates containing a Cβ–H bond at the alkyl side of the ester. These substrates produce the N,N-dimethylcarbamic acid and the corresponding olefin. The unstable intermediate, N,N-dimethylcarbamic acid, rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO2 gas. Correlation of the logarithm of theoretical rate coefficients against original Taft's σ* values gave an approximate straight line (ρ*=−1.39, r=0.9558 at 360 °C). In addition to this fact, when log krel is plotted against the theoretical log krel for 2-substituted ethyl N,N-dimethylcarbamates a reasonable straight line (r=0.9919 at 360 °C) is obtained, suggesting similar mechanism. 相似文献