全文获取类型
收费全文 | 1310篇 |
免费 | 50篇 |
国内免费 | 3篇 |
专业分类
化学 | 979篇 |
晶体学 | 9篇 |
力学 | 14篇 |
数学 | 173篇 |
物理学 | 188篇 |
出版年
2023年 | 15篇 |
2022年 | 27篇 |
2021年 | 18篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 28篇 |
2015年 | 31篇 |
2014年 | 35篇 |
2013年 | 68篇 |
2012年 | 63篇 |
2011年 | 90篇 |
2010年 | 49篇 |
2009年 | 44篇 |
2008年 | 77篇 |
2007年 | 79篇 |
2006年 | 82篇 |
2005年 | 73篇 |
2004年 | 55篇 |
2003年 | 70篇 |
2002年 | 45篇 |
2001年 | 16篇 |
2000年 | 7篇 |
1999年 | 18篇 |
1998年 | 12篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 20篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 21篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 7篇 |
排序方式: 共有1363条查询结果,搜索用时 660 毫秒
991.
Lukas Medenbach Ines Escher Nicolas Köwitsch Prof. Dr. Marc Armbrüster Dr. Linda Zedler Prof. Dr. Benjamin Dietzek Prof. Dr. Philipp Adelhelm 《Angewandte Chemie (International ed. in English)》2018,57(41):13666-13670
There is currently intense research on sulfur/carbon composite materials as positive electrodes for rechargeable batteries. Such composites are commonly prepared by ball milling or (melt/solution) impregnation to achieve intimate contact between both elements with the hope to improve battery performance. Herein, we report that sulfur shows an unexpected “spillover” effect when in contact with porous carbon materials under ambient conditions. When sulfur and porous carbon are gently mixed in a 1:1 mass ratio, complete surface coverage takes place within just a few days along with the loss of the sulfur bulk properties (crystallinity, melting point, Raman signals). Sulfur spillover also occurs in the presence of a liquid phase. Consequences of this phenomenon are discussed by considering a sodium–sulfur cell with a solid electrolyte membrane. 相似文献
992.
Temperature‐Dependent Atomic Models of Detergent Micelles Refined against Small‐Angle X‐Ray Scattering Data
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Miloš T. Ivanović Linda K. Bruetzel Jan Lipfert Jochen S. Hub 《Angewandte Chemie (International ed. in English)》2018,57(20):5635-5639
Surfactants have found a wide range of industrial and scientific applications. In particular, detergent micelles are used as lipid membrane mimics to solubilize membrane proteins for functional and structural characterization. However, an atomic‐level understanding of surfactants remains limited because many experiments provide only low‐resolution structural information on surfactant aggregates. In this work, small‐angle X‐ray scattering is combined with molecular dynamics simulations to derive fully atomic models of two maltoside micelles at temperatures between 10 °C and 70 °C. The micelles take the shape of general tri‐axial ellipsoids and decrease in size and aggregation number with increasing temperature. Density profiles of hydrophobic groups and water along the three principal axes reveal that the minor micelle axis closely mimics lipid membranes. The results suggest that coupling atomic simulations with low‐resolution data allows the structural characterization of surfactant aggregates. 相似文献
993.
Efficient formulation of the stochastic simulation algorithm for chemically reacting systems 总被引:10,自引:0,他引:10
In this paper we examine the different formulations of Gillespie's stochastic simulation algorithm (SSA) [D. Gillespie, J. Phys. Chem. 81, 2340 (1977)] with respect to computational efficiency, and propose an optimization to improve the efficiency of the direct method. Based on careful timing studies and an analysis of the time-consuming operations, we conclude that for most practical problems the optimized direct method is the most efficient formulation of SSA. This is in contrast to the widely held belief that Gibson and Bruck's next reaction method [M. Gibson and J. Bruck, J. Phys. Chem. A 104, 1876 (2000)] is the best way to implement the SSA for large systems. Our analysis explains the source of the discrepancy. 相似文献
994.
Linda Becerra 《Algebra Universalis》1987,24(1-2):50-59
A Noether lattice satisfying the union condition on primes which is not a domain and in which every nonzero principal element is integrally closed is characterized in terms of its direct summands. It is shown that either: (1) if has no proper nonzero direct summands, then every nonzero principal element of is integrally closed if and only if is a local Noether lattice whose maximal element is principal and has square zero; or (2) if has a proper nonzero direct summand, then every nonzero principal element of is integrally closed if and only if for each minimal direct summandA of, the quotient lattice [0,A] is an integrally closed domain.Presented by R. P. Dilworth. 相似文献
995.
Thermodynamic constants have been determined for hydrogen bonding of phenol to several siloxanes and alkoxysilanes, as well as to Me3SiSCMe3 and Me3SiSSiMe3. Alkoxysilanes are slightly weaker bases toward phenol than the isostructural ethers. Unstrained siloxanes have low values of △H for hydrogen bonding of 3.5–3.9 kcal/mol and are therefore distincatly weaker bases than either alkoxysilanes or ethers. Siloxanes with small SiOSi bond angles show increased basicity. Me3SiSCMe3 (△H 1.9 kcal/mol) and Me3SiSSiMe3 (△ 0.8 kcal/mol) are markedly less basic than dialkyl sulfides. The results are discussed using a molecular orbital model. 相似文献
996.
Stevenson LM Matthias A Banbury L Penman KG Bone KM Leach DL Lehmann RP 《Molecules (Basel, Switzerland)》2005,10(10):1279-1285
Echinacea preparations are widely used herbal medicines for the prevention and treatment of colds and minor infections. There is little evidence for the individual components in Echinacea that contribute to immune regulatory activity. Activity of an ethanolic Echinacea extract and several constituents, including cichoric acid, have been examined using three in vitro measures of macrophage immune function - NF-kappaB, TNF- alpha and nitric oxide (NO). In cultured macrophages, all components except the monoene alkylamide (AA1) decreased lipopolysaccharide (LPS) stimulated NF-kappaB levels. 0.2 microg/ml cichoric acid and 2.0 microg/mL Echinacea Premium Liquid (EPL) and EPL alkylamide fraction (EPL AA) were found to significantly decrease TNF-alpha production under LPS stimulated conditions in macrophages. In macrophages, only the alkylamide mixture isolated from the ethanolic Echinacea extract decreased LPS stimulated NO production. In this study, the mixture of alkylamides in the Echinacea ethanolic liquid extract did not respond in the same manner in the assays as the individual alkylamides investigated. While cichoric acid has been shown to affect NF-kappaB, TNF-alpha and NO levels, it is unlikely to be relevant in the Echinacea alterations of the immune response in vivo due to its non- bioavailability - i.e. no demonstrated absorption across the intestinal barrier and no detectable levels in plasma. These results demonstrate that Echinacea is an effective modulator of macrophage immune responses in vitro. 相似文献
997.
Paterson I Coster MJ Chen DY Aceña JL Bach J Keown LE Trieselmann T 《Organic & biomolecular chemistry》2005,3(13):2420-2430
The fully functionalised C29-C51 southern hemisphere of altohyrtin A/spongistatin 1 , incorporating the E- and F-ring tetrahydropyran rings and the unsaturated side chain, has been synthesised in a highly convergent and stereocontrolled manner. Key steps in the synthesis of this phosphonium salt include four highly diastereoselective, substrate-controlled, boron aldol reactions to establish key C-C bonds and accompanying stereocentres, where the introduction of the chlorodiene side chain and the C47 hydroxyl-bearing centre were realised by exploiting remote stereoinduction from the F-ring tetrahydropyran. 相似文献
998.
Byung-Hwan Um M. Nazmul Karim Linda L. Henk 《Applied biochemistry and biotechnology》2003,105(1-3):115-125
The pretreatment of corn stover with H2SO4 and H3PO4 was investigated. Pretreatments were carried out from 30 to 120 min in a batch reactor at 121°C, with acid concentrations
ranging from 0 to 2% (w/v) at a solid concentration of 5% (w/v). Pretreated corn stover was washed with distilled water until
the filtrate was adjusted to pH 7.0, followed by surfactant swelling of the cellulosic fraction in a 0–10% (w/v) solution
of Tween-80 at room temperature for 12 h. The dilute acid treatment proved to be a very effective method in terms of hemicellulose
recovery and cellulose digetibility. Hemicellulose recovery was 62–90%, and enzymatic digestibility of the cellulose that
remained in the solid was >80% with 2% (w/v) acid. In all cases studied, the performance of H2SO4 pretreatment (hemicellulose recovery and cellulose digestibility) was significantly better than obtained with H3PO4. Enzymatic hydrolysis was more effective using surfactant than without it, producing 10–20% more sugar. Furthermore, digestibility
was investigated as a function of hemicellulose removal. It was found that digestibility was more directly related to hemicellulose
removal than to delignification. 相似文献
999.
This article describes the development and subsequent application of a computer aided method, based on the library search strategy, for the interpretation of laser microprobe mass analysis (LAMMA) spectra. Such a routine is essential whenever huge amounts of spectra are needed to obtain relevant results, as e.g. in environmental research. The main handicap for a straightforward automation is the poor reproducibility of the analytical technique. 相似文献
1000.
Browne WR de Jong JJ Kudernac T Walko M Lucas LN Uchida K van Esch JH Feringa BL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(21):6414-6429
The electro- and spectroelectrochemical properties of dithienylhexahydro- and dithienyhexafluorocyclopentenes are reported. The large effect of variation in the central cyclopentene moieties on the redox properties of the dithienylcyclopentenes is in striking contrast to the minor effect on their photochemical properties. The electronic properties of the oxidised compounds in the +1 and +2 oxidation state are reported, and the possibility of electrochemical cyclisation and cycloreversion were explored by UV/Vis spectroelectrochemistry. The efficiency of electrochemical switching is found to be dependent both on the central cyclopentene unit and on the nature of the substituents at C5 of the thienyl rings. For the hexahydrocyclopentene-based compounds oxidative ring closure of the ring-open form is observed, while for the hexafluorocyclopentene-based compounds oxidative ring opening of the ring-closed form is observed. However, the introduction of electroactive groups such as methoxyphenyl allows oxidative ring closure to occur in the hexafluoro compounds. The effect of electrolyte, solvent and temperature on the spectroelectrochemical properties were examined, and the switching process was found to be sensitive to the donor properties of the solvent/electrolyte system employed. In addition, thermally activated reversible isomerisation of the dicationic closed form was observed. The driving force for electrochemical ring opening and closure appears to be dependent on the relative stabilisation of the dicationic ring-open and ring-closed states. This study provides insight into the factors which determine the direction of cyclisation. 相似文献