全文获取类型
收费全文 | 112篇 |
免费 | 0篇 |
专业分类
化学 | 57篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 28篇 |
物理学 | 22篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 7篇 |
2012年 | 9篇 |
2011年 | 8篇 |
2010年 | 2篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 2篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 5篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1959年 | 1篇 |
1955年 | 1篇 |
1936年 | 1篇 |
1923年 | 1篇 |
1922年 | 1篇 |
1918年 | 1篇 |
1912年 | 2篇 |
1891年 | 1篇 |
排序方式: 共有112条查询结果,搜索用时 15 毫秒
21.
We consider two person zero-sum stochastic games. The recursive formula for the valuesvλ (resp.v
n) of the discounted (resp. finitely repeated) version can be written in terms of a single basic operator Φ(α,f) where α is the weight on the present payoff andf the future payoff. We give sufficient conditions in terms of Φ(α,f) and its derivative at 0 for limv
n and limvλ to exist and to be equal.
We apply these results to obtain such convergence properties for absorbing games with compact action spaces and incomplete
information games. 相似文献
22.
23.
Jzsef Reiter Pl Vga Klra Esses-Reiter Lszl Pong Hilda Molnr 《Journal of heterocyclic chemistry》1988,25(6):1751-1755
5-Amino-1,2,4-triazoles reacted with alifatic β-oxo-esters to yield besides the unexpected 1,2,4-triazolo-[1,5-a]-1,3,5-benzotriazepin-5-one derivative 7 either the corresponding esters 5 and 6 or a 1:2 condensation product 8. To the contrary alicyclic and heterocyclic β-oxo-esters formed in the above reaction only derivatives 7. The proposed mechanism of the formation of 7 involving a novel N-carbonylation reaction was proved by the isolation of the by-products and the intermediate of the reaction. Repeating the above reaction with a γ-oxo-ester, namely the ethyl levulinate, derivatives 17 and 18 , respectively, representing two new ring systems were obtained. 相似文献
24.
Tatiane Roquete Amparo Ivanildes Vasconcelos Rodrigues Janaína Brandão Seibert Rafaella Hilda Zaniti Souza Amanda Ribeiro de Oliveira Vivette Appolinário Rodrigues Cabral 《Natural product research》2018,32(16):1951-1954
The crude ethanol extract (CEE) and fractions from branches of Protium spruceanum were subjected to antibacterial and cytotoxicity assays. Compounds of the most active fraction were identified by GC-MS and LC-MS. CEE was active against 19 bacteria and the ethyl acetate fraction (EAF) showed the lowest minimum bactericidal concentration (MBC 0.3–80.0 mg/mL). Through time-kill assay was observed that EAF induced rapid bactericidal effect against Staphylococcus saprophyticus. The cytotoxicity tests against L929 fibroblasts showed great potential of EAF on the treatment of infections caused by five bacteria (MBC < IC50). The results provide in vitro scientific support to the possible application of branches of P. spruceanum as antimicrobial agent that may contribute for treatment of infections. 相似文献
25.
Araujo K Colina M Mazurek R Delgado J Ledo H Gutierrez E Herrera L 《Analytical and bioanalytical chemistry》1996,355(3-4):319-320
The mercury concentrations in wastewater and sewage sludge of a stabilization pond system have been evaluated. The system is built by three parallel facultative ponds followed by two systems of three maturation ponds in series. The samples of wastewater and sludge were digested using nitric acid and placed into a Parr-type bomb for 4 h at 110 degrees C. Mercury was measured by Cold Vapour Atomic Absorption Spectrometry (CV-AAS) at 253.7 nm with sodium tetrahydroborate as reductant. The methodologies were checked with an USEPA quality control sample, a standard reference material from NIST and with another method of mineralization (cold mineralization) showing good results. Concentrations of mercury in wastewater between 1.47 +/- 0.75 microgl(-1) have been found at the entrance of the system and 0.74 +/- 0.0 microgl(-1) at the exit, while in sludge the results were between 0.29 +/- 0.12 microgkg(-1) in the facultative pond and 0.04 +/- 0.02 microgkg(-1) in the second maturation pond (exit). 相似文献
26.
A novel combination of high performance low pressure chromatography with multisyringe flow injection analysis is presented. This system comprises a multisyringe module, three low pressure solenoid valves, a monolithic Chromolith Flash RP-18e column and a diode array spectrophotometer. UV detection is carried out at 250 nm. AutoAnalysis software is used for instrumental control and automated data collection. The results obtained with multisyringe liquid chromatography (MSC) were compared with those obtained with a HPLC system using similar conditions. The chromatographic parameters were calculated from a mixture of anthracene and thiourea using a mobile phase containing acetonitrile-water (60:40) at a flow rate of 2 ml min−1. The proposed MSC system has been successfully applied to the determination of amoxicillin, ampicillin and cephalexin using a mobile phase of sodium acetate buffer (pH 6.2, 0.1 mol l−1)-methanol (90:10) at a flow rate of 2 ml min−1. The low-cost, flexibility and simplicity of MSC should be highlighted. 相似文献
27.
Using video representations of teaching in practice-based professional development programs 总被引:1,自引:0,他引:1
This article explores how video can be used in practice-based professional development (PD) programs to serve as a focal point for teachers’ collaborative exploration of the central activities of teaching. We argue that by choosing video clips, posing substantive questions, and facilitating productive conversations, professional developers can guide teachers to examine central aspects of learning and instruction. We draw primarily from our experiences developing and studying two mathematics PD programs, the Problem-Solving Cycle (PSC) and Learning and Teaching Geometry (LTG). While both programs feature classroom video in a central role, they illustrate different approaches to practice-based PD. The PSC, an adaptive model of PD, provides a framework within which facilitators tailor activities to suit their local context. By contrast, LTG is a highly specified model of PD, which details in advance particular learning goals, design characteristics, and extensive support materials for facilitators. We propose a continuum of video use in PD from highly adaptive to highly specified and consider the affordances and constraints of different approaches exemplified by the PSC and LTG programs. 相似文献
28.
29.
Hilda R. Morales Martín Pérez-Juárez Laura Cuéllar Lourdes Mendoza Héctor Fernández Rosalinda Contreras 《合成通讯》2013,43(13):1213-1219
A new procedure for the high-yield N-monoalkylation of primary aromatic and aliphatic amines is described. 相似文献
30.
The wetting property and evaporation behavior of ethanol-water mixtures of various concentrations on gold surfaces modified with 1-decanethiolate self-assembled monolayers (SAMs) were studied by digital contact angle analysis. It has been shown that the initial contact angle decreases monotonically with increased concentration of ethanol in the mixture. Evaporation studies revealed a general trend with a preliminary increase in contact angle accompanied with a decrease in contact area, then a constant contact angle accompanied with a slower, linear decrease in contact area. At the very beginning of the evaporation process, the contact angles showed a rapid decrease for the microdroplets of a binary mixture with equal volume fractions (i.e., 50% ethanol). Three distinct stages of the evaporation profile for the ethanol-water mixtures were observed, which differ from the inclusive "pinning" and "shrinking" behavior observed for the pure liquid case. Ultimately, the study makes possible the use of an evaporation profile to monitor the change in concentration of a binary system and allows a better understanding of the interactions between liquid microdroplets with solid substrates. 相似文献