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21.
Fukuji Higashi Khoji Nakajima Wen Xion Zhang 《Journal of polymer science. Part A, Polymer chemistry》1994,32(4):747-752
It is proposed that depression of the transition temperatures, especially the melting point (Tm), can be achieved by the introduction of a different amide bond structure into the copolyamides of dicarboxylic acids and diamines by copolymerization of aminocarboxylic acids, such as p-aminobenzoic acid. The effect was examined by the amount and distribution of the structure in the copolylamindes. Copolycondensations of PEG3, p-aminobenzoic acid, and diamines with different chain lengths showed that the structural change of the amide bond in the copolymers, especially its distribution, was more important than its total amount in them. Several types of aminocarboxylic acids were briefly examined to study the effect. © 1994 John Wiley & Sons, Inc. 相似文献
22.
Marti E. Kaisersberger E. Emmerich W.-D. 《Journal of Thermal Analysis and Calorimetry》2004,77(3):905-934
The definitions of the temperature resolution, the so-called resolution of DSC instruments given in literature are discussed.
A new definition of the resolution for DSC instruments is presented and outlined. The main characteristic introduced in this
new definition is a minimum between two caloric events as a prerequisite of an existing resolution. Possible candidates of
test substances have been evaluated. The oligomer n-hexatriacontane is revealing an interesting phenomenon, namely a lambda
transition which is in the peak temperature only 2 K lower than the melting temperature of 76°C. The substance was selected
as an ideal test substance for the quantification of the resolution of DSC instruments. The lambda transition is a second
order process which may reach under certain conditions the saturation of the occurring molecular dislocation within 0.2 K,
and after saturation the heat flow rate drops sharply down. Investigations concerning the main characteristics of n-hexatriacontane
in respect to the temperatures of transition (lambda transition and melting), to the involved enthalpies, and to the resolution
factors were performed as functions of the sample mass and the heating rate. The importance of relevant evaluation procedures
increasing the resolution factors of DSC curves are discussed and these procedures are integrated into the testing of the
resolution. The necessity for widening the experimental scope from instruments to evaluation procedures is forced by the existence
of instruments with built-in signal treatments based on electronic devices and software procedures. A comparison with literature
data is outlined for all of the mentioned characteristic values of n-hexatriacontane.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
23.
Hitoshi?MatsukiEmail author Michio?Yamanaka Hiroshi?Kamaya Shoji?Kaneshina Issaku?Ueda 《Colloid and polymer science》2005,283(5):512-520
The dissociation equilibrium between uncharged local anesthetic lidocaine (LC) and charged local anesthetic LC (LCH+) in a surface-adsorbed film was investigated by measuring the surface tension and pH of aqueous solutions of a mixture of hydrochloric acid and LC. The surface tension values decreased slightly with increasing total molality mt at 0X20.5, where X2 is the mole fraction of LC in the mixture, while they decreased rapidly with increasing mt at 0.5<X21. It was shown from the pH measurements that almost all LC molecules were changed into LCH+ ions by protonation at 0X20.5 and both forms coexisted only at 0.5<X21. The quantities of the respective LC and LCH+ transferred from the aqueous solution to the adsorbed film, i.e., their surface densities, were calculated by applying the thermodynamic equations derived to the surface tension and pH data. A greater quantity of LC than LCH+ existed in the adsorbed film at the coexisting composition. The partitioning behavior of LC and LCH+ in the adsorbed film was characterized by three composition regions: (1) slight partitioning of low surface-active LCH+ in the region at 0X20.5, (2) preferential partitioning of LC at 0.5<X2<around 0.7, and (3) negative partitioning of LCH+ at around 0.7X21. The present results clearly indicate that uncharged local anesthetics transfer into hydrophobic environments such as cell membranes more than charged ones. 相似文献
24.
Xi-yan Liu Dong Qiu Mei-li Guo Zhen-zhong Yang 《高分子科学》2005,(5):561-566
Sub-micron sized phenolic epoxy resin waterborne particles were prepared by phase inversion emulsification. Micro-phase separation occurred during the curing process at high temperature. The as-prepared samples possessed one glass transition temperature (Tg) and two exothermal processes during DSC heating scannings. After being thermally treated above the exothermal peak temperature, they possessed two glass transition temperatures with the disappearance of exothermal peaks, whilst a core/shell structure was formed. This was likely related with the outward diffusion of reactive oligomers to the outer layer of particles. 相似文献
25.
Most of the common classes of organic compounds chromatograph normally on Superoxes. There is no tailing or adverse effect from excessively different activity different activity coefficients. Superoxes are therefore universal phases for gas chromatography. This is also expressed by a wide useful temperature range from ~50° to ~300°. High MW Superox-4 has a MAOT about 20° higher than the lower MW Superox-0.1. Several applications illustrating the versatility of Superox phases in (GC)2 are presented. 相似文献
26.
27.
The temperature calibration on cooling of thermal analysis instruments is important for the accurate study of the non-isothermal crystallization kinetics of semi-crystalline polymers. In previous works, a methodology was proposed for performing the calibration on cooling of differential scanning calorimeters (DSCs) with standard metals, and the calibration errors were checked using transitions of high-purity liquid crystals. In this work, alternative, physically meaningful, procedures for carrying out the calibration on cooling are analyzed and validated. The calibration errors are evaluated also with liquid crystalline transitions, when the calibration is performed with standard metals, in a wide temperature range, and when due account is taken for the need of isothermal corrections to the temperature measurements. It is shown that any pair of standard metals may be used to calibrate on cooling, that the calibration errors increase for wider working temperature ranges and that, providing that certain conditions are fulfilled, both calibration procedures yield similar results. 相似文献
28.
The role of rigid unit modes in negative thermal expansion 总被引:1,自引:0,他引:1
J.Z Tao 《Journal of solid state chemistry》2003,173(2):442-448
The rigid unit mode (RUM) model provides a valuable computational method to investigate correlations of transverse thermal motions of atoms important in negative thermal expansion (NTE) materials. We report here detailed RUM calculations of ten framework oxide structures that have been studied for their negative (or ultra low) thermal expansion properties. The results negate any simple and direct correlation between presence or absence of RUMs in a structure and its NTE property. All the structures considered can be viewed as networks of polyhedral connected by corners only. All evidence supports the importance the transverse motion of the atoms at the corners, but NTE does not correlate well with the presence RUMs for the polyhedra. 相似文献
29.
The methacrylate monomer, 2-[(5-methylisoxazol-3-yl)amino]-2-oxo-ethyl methacrylate (IAOEMA), was synthesized by reacting 2-chloro-N-(5-methylisoxazol)acetamide dissolved in acetonitrile with sodium methacrylate in the presence of triethylbenzylammoniumchloride (TEBAC). The free-radical-initiated copolymerization of IAOEMA, with styrene (ST) and methyl methacrylate (MMA) was carried out in dimethylsulphoxide (DMSO) solution at 65 °C using 2,2′-azobisisobutyronitrile (AIBN) as an initiator with different monomer-to-monomer ratios in the feed. The monomer (IAOEMA) and copolymers were characterized by FTIR, 1H- and 13C-NMR spectral studies. The copolymer composition was evaluated by nitrogen content in polymers led to the determination of reactivity ratios. The reactivity ratios of the monomers were determined by the application of Fineman-Ross and Kelen-Tüdös methods. The analysis of reactivity ratios revealed that ST and MMA are more reactive than IAOEMA, and copolymers formed are statisticalle in nature. The molecular weights (Mw and Mn) and polydispersity index of the polymers were determined using gel permeation chromagtography. Glass transition temperatures of the copolymers were found to increase with an increase in the mole fraction of IAOEMA in the copolymers. The apparent thermal decomposition activation energies (Ed) were calculated by Ozawa method using the SETARAM Labsys TGA thermobalance. 相似文献
30.