全文获取类型
收费全文 | 194篇 |
免费 | 10篇 |
国内免费 | 24篇 |
专业分类
化学 | 122篇 |
晶体学 | 7篇 |
力学 | 14篇 |
综合类 | 4篇 |
数学 | 41篇 |
物理学 | 40篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 22篇 |
2012年 | 15篇 |
2011年 | 15篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 15篇 |
2007年 | 6篇 |
2006年 | 6篇 |
2005年 | 11篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1972年 | 1篇 |
1968年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有228条查询结果,搜索用时 15 毫秒
51.
可生物降解聚酯P(DHCA-co-LA)的合成与表征 总被引:1,自引:0,他引:1
由3,4-二羟基肉桂酸(DHCA)与D,L-乳酸(LA)经熔融缩聚法得到了新型可生物降解聚酯P(DHCA-co-LA),采用傅立叶变换红外(FTIR),核磁共振(1H-NMR)和凝胶渗透色谱(GPC)对该共聚物的组成与相对分子量进行表征,结果表明其结构明确.改变DHCA与LA单体的配比,得到的P(DHCA-co-LA)的分子量和分子量分布在同一数量级.通过差示扫描量热仪(DSC)、紫外(UV)和荧光光谱研究了共聚物的热性能、紫外与荧光性能,结果表明,P(DHCA-co-LA)有明显的玻璃化转变温度(Tg),随LA的投料比从0增加至50 mol%时,其Tg从132.26℃下降至99.12℃;当LA的投料比为20 mol%时,所得到的聚酯型共聚物溶液呈现最强的荧光强度;在紫外光照下,共聚物可进行环加成反应,但交联度总体较低;紫外光照65 min后,在荧光显微镜下观察到交联颗粒形态稳定、有较强的荧光.X-射线衍射(XRD)测定结果显示,由结晶性DHCA和LA共聚形成的P(DHCA-co-LA)为无定形聚合物,有利于生物降解.共聚物在土壤中的降解实验表明,其降解速度随体系中LA含量的增加而减缓. 相似文献
52.
净室技术与软件能力成熟度模型的融合 总被引:2,自引:0,他引:2
对基于软件能力成熟度模型(CMM)的传统软件开发方法与净室技术进行了比较,阐述了如何将净室技术引入到一个基于CMM 的软件开发框架之中,介绍了从传统方法向净室技术转化的一些方法. 相似文献
53.
Crystal structure and thermal study of the new hydrated cadmium-cerium(III) chloride CeCd4Cl11·13H2O
S. Yahyaoui R.Ben Hassen B. Donadieu A.Ben Salah 《Journal of solid state chemistry》2003,173(2):328-334
The new double-salt CeCd4Cl11·13H2O in the ternary system CeCl3-CdCl2-H2O has been prepared from aqueous solution upon evaporation at 5°C and characterized based on elemental analysis, spectroscopic data, thermal studies and X-ray powder and single-crystal diffraction. CeCd4Cl11·13H2O crystallizes in the monoclinic space group P21 with a=7.667(2), b=17.351(3), c=11.970(2)Å, β=101.61(3)° and Z=2. After refinement of the structure the reliability factor R in the final cycle is 0.064. The structure can be regarded as consisting of endless double chains of CdCl6 and CdOCl5 octahedra and isolated tricapped triangular prisms surrounding the cerium cations. Differential scanning calorimetry showed that the title compound exhibits five endothermic anomalies interpreted from thermogravimetry. A comparison with the structure of SrCd2Cl6·8H2O is proposed. 相似文献
54.
Zied Hassen 《Journal of fluorine chemistry》2003,121(2):177-183
Ten phosphorylated β-hydrazones of structure R2P(O)C(NNHRF)CHR2′ were prepared in 54-91% yield by heating the allenes R2P(O)CHCCR2′ with fluorinated hydrazines H2NNHRF in chloroform or methanol [R=Ph, OCH2C(Me)2CH2O or OCH2C(Me)(Pr)CH2O, R′=H or Me and RF=CH2CF3 or C6F5]. Two cyclohexyl derivatives were prepared similarly from R2P(O)CHCCy. The triphenyl derivatives Ph2P(O)CH2C(NNHCH2CF3)Ph and Ph2P(O)CH2C(NNHC6F5)Ph were made in 91 and 68% yield by heating the ketones Ph2P(O)CH2C(O)Ph with an ethanol solution of the corresponding hydrazines. The stereochemistry of the hydrazones was determined by multinuclear NMR experiments. Compounds with C(NNHRF)Me groups exist as a mixture of Z and E isomers, with the Z form predominating (fluorinated group syn to phosphorus). Those with C(NNHRF)CHMe2, C(NNHRF)Cy or C(NNHRF)Ph groups were formed selectively, the Z isomers being the only products. The results are explained by steric hindrance, the bulkier isopropyl, cyclohexyl or phenyl group disfavouring the E configuration. , , , NMR data, coupling constants and IR data are reported. 相似文献
55.
SrCd2Cl68H2O crystallizes in the space group
and has the unit cell dimensions a = 9.688(2) Å, b = 11.212(2) Å, c = 7.732(3) Å, = 99.85(21)°, = 89.95(22)°, = 75.81(13)°, and Z = 2. After refinement through full-matrix least-squares methods, the reliability factor R in the final cycle is 4.65%. A very persistent occurrence of twinning by pseudosymmetry was observed. The twin element is a twofold axis [001]. The title compound exhibits five endothermic peaks, which have been detected by differential scanning calorimetry and interpreted from thermogravimetry. 相似文献
56.
Hassen Aydi Etienne Sandier 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2009,26(4):1223-1236
We study the vortices of energy minimizers in the London limit for the Ginzburg–Landau model with periodic boundary conditions. For applied fields well below the second critical field we are able to describe the location and number of vortices. Many of the results presented appeared in [H. Aydi, Doctoral Dissertation, Université Paris-XII, 2004], others are new. 相似文献
57.
This paper deals with the converse theory for some aspects offinal-stability, for which a general qualitative theory wasfirst presented by the author in 1970. The theory of final-stabilityis concerned with the behaviour of the trajectories of a systemof differential equations with respect to two arbitrary setsand a finite interval of time. 相似文献
58.
N. Bel Haj Mohamed M. Haouari Z. Zaaboub F. Hassen H. Maaref H. Ben Ouada 《Journal of Physics and Chemistry of Solids》2014
Cadmium sulfide (CdS) nanoparticles were synthesized by a novel wet chemical route with various organic thiol stabilizers. Systematic experimental studies, including X-ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), photoluminescence (PL) spectroscopy, and time-resolved photoluminescence (TRPL), have evidenced that the stability, crystallinity, and optical properties of the CdS nanoparticles are affected by the organic groups which generate significant effects in surface reconstruction. Particle size was evaluated from UV–vis spectroscopy using the effective mass approximation (EMA) method and from XRD patterns based on Scherrer?s formula. The S–H vibrations are not detectable in the infrared (IR) spectra of any of the bound ligands, which are expected for thiols covalently bound to the surface of nanoparticles. PL studies reveal that the emission from the nanostructures is not much influenced by the surface states, indicating a good passivation of the particle?s surface. The time-resolved measurements reveal a biexponential decay behavior. The fast decay component is attributed to the recombination of core states, while the slow decay component of PL is associated with the charge-carrier recombination process with the involvement of surface states. 相似文献
59.
Majdi Abid Hassen Trabelsi Mohamed Taktak Jérôme Antoni Jean Michel Ville Tahar Fakhfakh Mohamed Haddar 《Applied Acoustics》2012,73(10):1022-1028
The current techniques for monitoring and diagnostics of rotating machines to their conditional predictive maintenance mainly are based on vibration monitoring. In this research, experimental and theoretical methods to predict the tonal noise of a faulty fan are developed and validated. These methods can be used on identifying defects of an axial fan based on an acoustic monitoring in situations where it is necessary to operate remotely due to the inaccessibility of the areas of event defects. 相似文献