全文获取类型
收费全文 | 1859篇 |
免费 | 97篇 |
国内免费 | 12篇 |
专业分类
化学 | 1306篇 |
晶体学 | 9篇 |
力学 | 41篇 |
综合类 | 1篇 |
数学 | 233篇 |
物理学 | 378篇 |
出版年
2023年 | 16篇 |
2022年 | 25篇 |
2021年 | 48篇 |
2020年 | 63篇 |
2019年 | 54篇 |
2018年 | 33篇 |
2017年 | 35篇 |
2016年 | 72篇 |
2015年 | 74篇 |
2014年 | 60篇 |
2013年 | 116篇 |
2012年 | 95篇 |
2011年 | 126篇 |
2010年 | 49篇 |
2009年 | 54篇 |
2008年 | 92篇 |
2007年 | 72篇 |
2006年 | 80篇 |
2005年 | 65篇 |
2004年 | 80篇 |
2003年 | 57篇 |
2002年 | 44篇 |
2001年 | 18篇 |
2000年 | 18篇 |
1999年 | 17篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 12篇 |
1994年 | 21篇 |
1993年 | 24篇 |
1992年 | 28篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 19篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1975年 | 13篇 |
1974年 | 12篇 |
1973年 | 15篇 |
排序方式: 共有1968条查询结果,搜索用时 13 毫秒
51.
Valkovska DS Shearman GC Bain CD Darton RC Eastoe J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(11):4436-4445
A quantitative model for the kinetics of adsorption of ionic surfactants to an expanding liquid surface is presented for surfactant concentrations below and above the critical micelle concentration (cmc). For surfactant concentrations below the cmc, the electrostatic double layer is accounted for explicitly in the adsorption isotherm. An overflowing cylinder (OFC) was used to create nonequilibrium liquid surfaces under steady-state conditions. Experimental measurements of the surface excess for solutions of cationic surfactants CH3(CH2)n-1N+(CH3)3 Br- (CnTAB, n = 12, 14, 16) and the anionic fluorocarbon surfactant sodium bis(1H,1H-nonafluoropentyl)-2-sulfosuccinate (di-CF4) in the OFC are in excellent agreement with the theoretical predictions for diffusion-controlled adsorption for all concentrations studied below the cmc. For surfactant concentrations above cmc, the diffusion ofmicelles and monomers are handled separately under the assumption of fast micellar breakdown. This simplified model gives excellent agreement for the system C14TAB + 0.1 M NaBr above the cmc. Agreement between theory and experiment for C16TAB + 0.1 M NaBr is less good. A plausible explanation for the discrepancy is that micellar breakdown is no longer fast on the time scale of the OFC (ca. 0.1 s). 相似文献
52.
Julian Tyson 《Trends in analytical chemistry : TRAC》1985,4(7):IV-V
Professional scientific societies are becoming increasingly aware of the public image of their members' activities. The Analytical Division of the Royal Society of Chemistry, through the activities of its Honorary Publicity Secretary, is making a conscious effort to inform young people about the activities of analytical chemists and to interest them in the profession of analytical chemistry. 相似文献
53.
54.
55.
The compounds P2O3F4 and K2P2O5F2 have been studied by vibrational spectroscopy. From the shifts of the symmetric vibration of the terminal PO bonds it appears that the molecular structure contracts as the number of PO (bridged) and/or PF bonds increases. The changes occur at the expense of PO terminal bonds. In these tetrahedral phosphorus (V) compounds the PO (bridged) and PF bonding have a similar role, and the same phenomenon occurs in sulfur VI oxide fluoride compounds. 相似文献
56.
A slurry sampling method has been developed for the determination of Pb in marine plankton by ETAAS using a freshwater plankton certified reference material (CRM 414). Slurries were prepared in 1–3% m/v range with 1% v/v HNO3 by ultrasonic agitation for 5 min. The effects of several chemical modifiers, including Ir(NO3)2, Mg(NO3)2, Pd(NO3)2, Pd(NO3)2 + Mg(NO3)2, and Mg(NO3)2 + NH4H2PO4, were investigated for the stabilization of Pb during thermal pretreatment. Lead in slurries was effectively stabilized up to 1000 °C with Ir, Pd and Pd + Mg modifiers among which Pd + Mg provided the best results with complete atomization at 1850 °C. Firings in the presence of Ir were, problematic due to ash formation inside the atomizer. Water, dilute HNO3 and HF were examined as suspension medium. Dilute HNO3 (1–2% v/v) proved to be advantageous over water as it afforded extraction of Pb from plankton almost quantitatively in 5 min agitation. Hydrofluoric acid was the least suitable medium. Increasing HF concentration up to 5% v/v resulted in inaccuracy and substantial background absorption. Fast-heating furnace method provided comparable accuracy and precision to that of conventional-heating in slurries of CRM 414. Detection limits and characteristic masses were, respectively, 0.49 μg L− 1 and 32 pg for the conventional method and 0.62 μg L− 1 and 37 pg for the fast-heating method. However, fast-heating approach suffered from distorted peaks at high temperatures and incomplete pyrolysis of matrix at lower temperatures. Analysis of marine plankton samples for Pb was performed by using the conventional furnace program. The results showed a high correlation with those obtained by solution ICP-MS. Differences were statistically insignificant within 95% confidence interval. 相似文献
57.
Kocher N Henn J Gostevskii B Kost D Kalikhman I Engels B Stalke D 《Journal of the American Chemical Society》2004,126(17):5563-5568
The concept of hypervalency in molecules, which hold more than eight valence electrons at the central atom, still is a topic of constant debate. There is general interest in silicon compounds with more than four substituents at the central silicon atom. The dispute, whether this silicon is hypervalent or highly coordinated, is enlightened by the first experimental charge density determination and subsequent topological analysis of three different highly polar Si-E (E = N, O, F) bonds in a hexacoordinated compound. The experiment reveals predominantly ionic bonding and much less covalent contribution than commonly anticipated. For comparison gas-phase ab initio calculations were performed on this compound. The results of the theoretical calculations underline the findings of the experiment. 相似文献
58.
Denning MS Watts ID Moussa SM Durand P Rosseinsky MJ Tanigaki K 《Journal of the American Chemical Society》2002,124(19):5570-5580
The high symmetry and resulting electronic degeneracy of the C(60)(3)(-) anion is viewed as the key molecular feature in the high superconducting transition temperatures of fulleride and oxidized fullerene systems. The experimental evaluation of this hypothesis requires the synthesis of face-centered cubic (fcc) trivalent fulleride anion salts derived from higher fullerenes such as C(70), which have thus far proved elusive with only stable A(1)C(70), A(4)C(70), and A(6)C(70) phases known. In this paper, we report the synthesis of fcc A(3)C(70) phases stabilized by size-matching the tetrahedral site with the sodium cation. The structures are strongly dependent on the cooling protocol due to the existence of metastable partially or completely orientationally disordered phases. EPR data indicate that the phases are metallic but not superconducting. The densities of states at the Fermi level appear too low to give superconductivity at above 5 K, consistent with recent observations that four electrons per C(70) anion are required for superconductivity. Size-matching on both the octahedral and tetrahedral sites is required for A(3)C(70) stability - K(2)CsC(70) is only stable at elevated temperature and Na(2)C(70) is unstable, the composition corresponding to C(70) and a sodium-rich trigonal phase. 相似文献
59.
Reactivite et distribution moleculaire dans les copolycondensats lineaires-I: Reactivite intrinseque
The effect of unequal intrinsic reactivity of functional groups on the molecular distribution in a linear step polymerization system is studied. In an R(A)2/R′(B)2 copolycondensate, the dependence of the polydispersity index on the relative reactivities of the two A-functional groups, at different extents of reaction, is examined in detail. 相似文献
60.
Rotureau E Leonard M Dellacherie E Durand A 《Journal of colloid and interface science》2004,279(1):68-77
Ionic amphiphilic dextran derivatives were synthesized by the attachment of sodium sulfopropyl and phenoxy groups on the native polysaccharide. A family of dextran derivatives was thus obtained with varying hydrophobic content and charge density in the polymer chains. The surface-active properties of polymers were studied at the air-water and dodecane-water interfaces using dynamic surface/interfacial tension measurements. The adsorption was shown to begin in a diffusion-limited regime at low polymer concentrations, that is to say, with the diffusion of macromolecules in the bulk solution. In contrast, at long times the interfacial adsorption is limited by interfacial phenomena: adsorption kinetics or transfer into the adsorbed layer. A semiempirical equation developed by Filippov was shown to correctly fit the experimental curves over the whole time range. The presence of ionic groups in the chains strongly lowers the adsorption kinetics. This effect can be interpreted by electrostatic interactions between the free molecules and the already adsorbed ones. The adsorption kinetics at air-water and oil-water interfaces are compared. 相似文献