全文获取类型
收费全文 | 243篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
化学 | 156篇 |
晶体学 | 3篇 |
力学 | 23篇 |
数学 | 44篇 |
物理学 | 30篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 14篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 25篇 |
2012年 | 11篇 |
2011年 | 23篇 |
2010年 | 13篇 |
2009年 | 17篇 |
2008年 | 10篇 |
2007年 | 14篇 |
2006年 | 6篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有256条查询结果,搜索用时 15 毫秒
51.
Dumitru Vieru Corina Fetecau Muhammad Athar Constantin Fetecau 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2009,60(2):334-343
The unsteady flow of a viscoelastic fluid with the fractional Maxwell model, induced by a constantly accelerating plate between
two side walls perpendicular to the plate, is investigated by means of the integral transforms. Exact solutions for the velocity
field are presented under integral and series forms in terms of the derivatives of generalized Mittag–Leffler functions. The
corresponding solutions for Maxwell fluids are obtained as limiting cases for β → 1. In the absence of the side walls, all
solutions that have been determined reduce to those corresponding to the motion over an infinite plate.
相似文献
52.
Danciu C Soica C Csanyi E Ambrus R Feflea S Peev C Dehelean C 《Chemistry Central journal》2012,6(1):58
ABSTRACT: BACKGROUND: The isoflavonoid genistein represents the major active compound from soybean, the vegetalproduct from Glycine max (Fabaceae). The aim of this study is to prove that genistein wasincorporated in two semisynthetic cyclodextrins, beta-cyclodextrin derivatives:hydroxypropyl-beta-cyclodextrin and randomly-methylated-beta-cyclodextrin as well as to compare the anti-inflammatory activity of genistein with that of genistein incorporated inthese two types of semisynthetic cyclodextrins. RESULTS: The animal studies were conducted on 8-week old C57BL/6 J female mice. Inflammation wasinduced in both ears of each mouse by topical application of 10 micrograms 12-Otetradecanoylphorbol-3-acetate dissolved in 0.1 ml solvent (acetone : dimethylsulfoxide in amolar ratio 9:1). Thirty minutes later treatment was applied. The inflammatory reaction wascorrelated with increased values in ear thickness. Treatment with genistein and genisteinincorporated in the two cyclodextrins led to decreased values for ear thickness. Better antiinflammatoryaction was found for the complexes of genistein. Both haematoxylin-eosinanalysis and CD45 marker expression are in agreement with these findings. CONCLUSIONS: Results allow concluding that genistein is an active anti-inflammatory phytocompound andits complexation with hydrophilic beta-cyclodextrin derivatives leads to a stronger antiinflammatoryactivity. 相似文献
53.
L de Lichtervelde CE Antal AE Boitano Y Wang P Krastel F Petersen AC Newton MP Cooke PG Schultz 《Chemistry & biology》2012,19(8):994-1000
To identify small molecules that selectively control hematopoietic stem cell differentiation, we performed an unbiased screen using primary human CD34(+) cells. We identified a plant-derived natural product, euphohelioscopin A, capable of selectively differentiating CD34(+) cells down the granulocyte/monocytic lineage. Euphohelioscopin A also inhibits proliferation and induces differentiation of the myeloid leukemia cell lines THP-1 and HL-60. Mechanistic studies revealed that euphohelioscopin A is an activator of protein kinase C (PKC), and that the promonocytic effects of this natural product are mediated by PKC activation. In addition to shedding insights into normal hematopoiesis, this work may ultimately facilitate the application of stem cell therapies to a host of myeloid dysfunctions. 相似文献
54.
Developing accurate models to simulate the interaction between pneumatic tires and unprepared terrain is a demanding task. Such tire–terrain contact models are often used to analyze the mobility of a wheeled vehicle on a given type of soil, or to predict the vehicle performance under specified operational conditions (as related to the vehicle and tires, as well as to the running support). Due to the complex nature of the interaction between a tire and off-road environment, one usually needs to make simplifying assumptions when modeling such an interaction. It is often assumed that the tire–terrain interaction can be captured using a deterministic approach, which means that one assumes fixed values for several vehicle or tire parameters, and expects exact responses from the system. While this is rarely the case in real life, it is nevertheless a necessary step in the modeling process of a deterministic framework. In reality, the external excitations affecting the system, as well as the values of the vehicle and terrain parameters, do not have fixed values, but vary in time or space. Thus, although a deterministic model may capture the response of the system given one set of deterministic values for the system parameters, inputs, etc., this is in fact only one possible realization of the multitude of responses that could occur in reality. The goal of our study is to develop a mathematically sound methodology to improve the prediction of the tire–snow interaction by considering the variability of snow depth and snow density, which will lead to a significantly better understanding and a more realistic representation of tire–snow interaction. We constructed stochastic snow models using a polynomial chaos approach developed at Virginia Tech, to account for the variability of snow depth and of snow density. The stochastic tire–snow models developed are based on the extension of two representative deterministic tire–snow interaction models developed at the University of Alaska, including the pressure–stress deterministic model and the hybrid (on-road extended for off-road) deterministic model. Case studies of a select combination of uncertainties were conducted to quantify the uncertainties of the interfacial forces, sinkage, entry angle, and the friction ellipses as a function of wheel load, longitudinal slip, and slip angle. The simulation results of the stochastic pressure–stress model and the stochastic hybrid model are compared and analyzed to identify the most convenient tire design stage for which they are more suitable. The computational efficiency of the two models is also discussed. 相似文献
55.
Cristina Stere Mihaela‐Corina Iovu Horia Iovu Adrian Boborodea Dan Sorin Vasilescu Simon James Read 《先进技术聚合物》2001,12(5):300-305
The polymerization of ?‐caprolactone initiated by two catalyst systems was studied: (1) carbazole‐potassium in the presence of 18‐crown‐6 ether and (2) NdCl3/TBP/TIBA (neodymiumtrichloride/tri‐n‐butyl‐phosphate/triisobutylaluminium) at the molar ratio 1/3/1. For both initiator systems conversion/time plots were determined and the polymers were characterized by IR, GPC and by 1H‐ and 13C?NMR spectroscopy. Polyesters with the highest molecular weight (M n?44 000 g/mol) were obtained for the polymerizations initiated by the carbazole‐potassium/18‐crown‐6 ether system. The features of the polymerization initiated by the carbazole‐potassium/18‐crown‐6 ether system are discussed on the basis of a simple scheme. The nature of this polymerization is non‐living. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
56.
Ion Grosu Loïc Toupet Gerard Plé Sorin Mager Eugen Mesaros Andreea Varga Elena Bogdan 《Monatshefte für Chemie / Chemical Monthly》2000,131(3):277-286
Summary. The synthesis and stereochemistry of new dibrominated spiro-1,3-dioxane derivatives are reported. Investigations by means
of NMR methods and single crystal X-ray diffraction for two compounds revealed the high regio- and diastereoselectivity of
the bromination reaction of some new spiro-1,3-dioxanes and the asymmetric induction of the chiral carbon atom located in
the spiro skeleton.
Received July 13, 1999. Accepted October 21, 1999 相似文献
57.
Raluca Maria Pop Ioana Corina Bocsan Anca Dana Buzoianu Veronica Sanda Chedea Sonia Ancua Socaci Michela Pecoraro Ada Popolo 《Molecules (Basel, Switzerland)》2020,25(22)
Natural products black cumin—Nigella sativa (N. sativa) and wild garlic—Allium ursinum (AU) are known for their potential role in reducing cardiovascular risk factors, including antracycline chemotherapy. Therefore, this study investigates the effect of N. sativa and AU water and methanolic extracts in a cellular model of doxorubicin (doxo)-induced cardiotoxicity. The extracts were characterized using Ultraviolet-visible (UV-VIS) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, Liquid Chromatography coupled with Mass Spectrometry (LC-MS) and Gas Chromatography coupled with Mass Spectrometry (GC-MS) techniques. Antioxidant activity was evaluated on H9c2 cells. Cytosolic and mitochondrial reactive oxygen species (ROS) release was evaluated using 2′,7′-dichlorofluorescin-diacetate (DHCF-DA) and mitochondria-targeted superoxide indicator (MitoSOX red), respectively. Mitochondrial membrane depolarization was evaluated by flow cytometry. LC-MS analysis identified 12 and 10 phenolic compounds in NSS and AU extracts, respectively, with flavonols as predominant compounds. FT-IR analysis identified the presence of carbohydrates, amino acids and lipids in both plants. GC-MS identified the sulfur compounds in the AU water extract. N. sativa seeds (NSS) methanolic extract had the highest antioxidant activity reducing both intracellular and mitochondrial ROS release. All extracts (excepting AU methanolic extract) preserved H9c2 cells viability. None of the investigated plants affected the mitochondrial membrane depolarization. N. sativa and AU are important sources of bioactive compounds with increased antioxidant activities, requiring different extraction solvents to obtain the pharmacological effects. 相似文献
58.
Dr. Dulce M. Morales Dr. Stefan Barwe Dr. Eugeniu Vasile Prof. Dr. Corina Andronescu Prof. Dr. Wolfgang Schuhmann 《Chemphyschem》2019,20(22):3030-3036
Earth-abundant transition-metal-based catalysts are attractive for alkaline water electrolysis. However, their catalytic properties are often limited by their poor electrical conductivity. Here, we present a strategy for enhancing the electrical conductivity of NiFe layered double hydroxide (LDH) in order to further improve its properties as an electrocatalyst for the oxygen evolution reaction (OER) in alkaline media. We show that NiFe LDH containing metal tetrasulfonate phthalocyanine in the interlayers between the NiFe oxide galleries can be coupled with graphene during liquid-phase exfoliation by taking advantage of their π-π stacking capabilities. A substantial enhancement in the electrocatalytic activity of NiFe LDH with respect to the OER was observed. Moreover, the activity and selectivity of the catalyst materials towards the oxygen reduction reaction were investigated, demonstrating that both the metal hydroxide layer and the interlayer species contribute to the electrocatalytic performance of the composite material. 相似文献
59.
60.
Corina J. van As-Brooks Florien J. Koopmans-van Beinum Louis C.W. Pols Frans J.M. Hilgers 《Journal of voice》2006,20(3):355-368
SUMMARY: Because of the aperiodicity of many tracheoesophageal voices, acoustic analysis of the tracheoesophageal voice is less straightforward than that of the normal voice. This study presents the development and testing of an acoustic signal typing system based on visual inspection of a narrow-band spectrogram that can be used by researchers for classification of voice quality in tracheoesophageal speech. In addition to this classification system, a selection of acoustic measures [median fundamental frequency, standard deviation of fundamental frequency, jitter, percentage of voiced (%Voiced), harmonics-to-noise ratio (HNR), glottal-to-noise excitation (GNE) ratio, and band energy difference (BED)] was computed to provide more insight into the acoustic components of tracheoesophageal voice quality. For clinical relevance, relationships between the acoustic signal types and an overall judgment of the voice were investigated as well. Results showed that the four acoustic signal types form a good basis for performing more acoustic analyses and give a good impression of the overall quality of the voice. 相似文献