全文获取类型
收费全文 | 2615篇 |
免费 | 178篇 |
国内免费 | 457篇 |
专业分类
化学 | 2836篇 |
晶体学 | 57篇 |
力学 | 14篇 |
综合类 | 44篇 |
数学 | 5篇 |
物理学 | 294篇 |
出版年
2024年 | 4篇 |
2023年 | 36篇 |
2022年 | 56篇 |
2021年 | 80篇 |
2020年 | 95篇 |
2019年 | 80篇 |
2018年 | 78篇 |
2017年 | 109篇 |
2016年 | 109篇 |
2015年 | 100篇 |
2014年 | 106篇 |
2013年 | 315篇 |
2012年 | 148篇 |
2011年 | 114篇 |
2010年 | 105篇 |
2009年 | 115篇 |
2008年 | 120篇 |
2007年 | 138篇 |
2006年 | 131篇 |
2005年 | 143篇 |
2004年 | 122篇 |
2003年 | 121篇 |
2002年 | 99篇 |
2001年 | 71篇 |
2000年 | 52篇 |
1999年 | 75篇 |
1998年 | 66篇 |
1997年 | 69篇 |
1996年 | 63篇 |
1995年 | 52篇 |
1994年 | 43篇 |
1993年 | 28篇 |
1992年 | 38篇 |
1991年 | 18篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 19篇 |
1987年 | 11篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有3250条查询结果,搜索用时 960 毫秒
991.
Kabir-ud-Din Nahid Parveen Andleeb Z. Naqvi 《Journal of Dispersion Science and Technology》2013,34(10):1500-1505
It is well known that, like surfactants aggregating at a certain concentration (called critical micelle concentration, CMC), hydrotropes also have minimum hydrotrope concentration (MHC). However, unlike surfactant CMC, this MHC value is usually very high, thereby reducing their application. In this paper we report the results of conductivity and viscosity measurements with a well known hydrotrope sodium salicylate (NaSal) solutions in presence and absence of additives (propanol, PrOH; butanol, BuOH; pentanol, PeOH and tetrabutylammonium bromide, Bu4NBr). We have found that MHC value of NaSal decreases in presence of additives. Alcohols increase the hydrophobic interactions and decrease the MHC while Bu4NBr, in addition to ameliorating the hydrophobic interactions, reduces the charge on head groups and MHC decreases more steeply in its presence. Increased solubility of riboflavin in NaSal containing the above additives corroborates the results. 相似文献
992.
Benjarat Tepsongkroh Pitchaon Maisuthisakul Withida Chantrapornchai 《Journal of Dispersion Science and Technology》2013,34(8):1126-1133
The influence of polyglycerol polyricinoleate (PGPR) and biopolymers (gelatin and sodium alginate) on the stabilization of water-in-oil (W/O) emulsions was investigated to improve the encapsulation efficiency (EE) of water-in-oil-in-water (W/O/W) emulsions containing mango seed kernel extract (MSKE). The physical properties and EE of the emulsions were found to depend more strongly on PGPR than on biopolymers. High EE values of MSKE were obtained when W/O emulsions stabilized by 4–8 wt% PGPR were incorporated with 1–5 wt% gelatin, or by 6–8 wt% PGPR incorporated with 0.5–1.5 wt% sodium alginate in the inner aqueous phase. 相似文献
993.
M. Vinceković D. Jurašin V. Tomašić M. Bujan 《Journal of Dispersion Science and Technology》2013,34(8):1099-1111
The interactions of alkylammonium chlorides (the number of carbon atom per chain was either 12, 14, or 16) with sodium cholate have been investigated by a combination of techniques including light and electron microscopy, surface tension, conductivity, light scattering, and microelectrophoretic measurements. The phase behavior has strongly depended on the molar ratio and actual concentration of oppositely charged surfactants. The change in the composition of the aggregates leads to a shape transformation from globular to elongated micelles to open and/or closed bilayers (vesicles) and precipitation. The length of micelles has been found to decrease dramatically with the concentration shift to the micellar regions of either surfactant. Upon a moderate excess of one surfactant, the mean hydrodynamic diameter of aggregates increases and wormlike micelles and/or open and closed bilayers are formed. Microscopic observations of alkylammonium cholates (novel catanionic surfactants precipitated in and/or close to equimolar region) have shown the presence of a variety of morphologies including twisted ribbons, tubules and bundles of tubules. 相似文献
994.
A combination of alumina/methanesulfonic acid (AMA) and sodium nitrite was used as an effective nitrosating agent for the nitrosation of secondary amines under mild and heterogeneous conditions in good to excellent yields. 相似文献
995.
Abstract Abstract:?A number of 4‐aryloxymethyl pyrano[3,2‐c][1]benzopyran‐5‐(2H)‐ones 3(a–f) were prepared by refluxing 4‐chloromethyl pyrano[3,2‐c][1]benzopyran‐5‐(2H)‐ones 1(a,b) with o‐bromophenols 2(a–c) in acetone in the presence of anhydrous potassium carbonate and sodium iodide in 70–80% yield. Compounds 3(a–f) were then subjected to radical cyclization by refluxing with tri‐n‐butyltin chloride, sodium cyanoborohydride, and azobisisobutyronitrile (AIBN) in dry benzene for 4–5 h to give a cis‐diastereomeric mixture of [6,6]pyranopyran derivatives in 80–85% yield. 相似文献
996.
A novel and efficient method for the synthesis of alkylsulfanylisothiazoles and alkylsulfanylthiophenes using sodium α‐cyanoketene dithiolates as starting components is described. 相似文献
997.
A simple, mild, efficient, and expedient greener dethioacetalization protocol employing a catalytic amount of nontoxic ammonium iodide (10 mol%) in combination with 30% hydrogen peroxide as terminal oxidizer is revealed. The reagent accomplished facile deprotection of 1,3-dithianes and dithiolanes of activated aromatic substrates in an aqueous medium in the presence of sodium dodecylsulfate (SDS) at room temperature under virtually neutral conditions. Deactivated and sterically encumbered substrates, which are otherwise reluctant to cleave under aqueous micellar conditions, were expeditiously cleaved in good to excellent yields in acetic acid. The method is tolerant, with several acid-sensitive protecting groups, such as tert-butyldiphenylsilyl (TBDPS) ether, aryl acetate, NHBoc, and NHBn, and with further oxidation of oxidation-prone activated benzaldehydes and furyl aldehydes. A tentative mechanism of hypoiodous acid–mediated catalytic cleavage is proposed.
998.
Acylferrocenes 2a–c reacted with ortho-aminoarylaldehydes 1a–e via the Friedländer condensation reaction to afford the corresponding ferrocenylquinolines 3a–o in moderate yields in the presence of sodium ethoxide (30 mmol%) under mild reaction conditions. Under the same reaction conditions, 1,1′-diacetylferrocene 2d and 1,1′-dipropionylferrocene 2e reacted with ortho-aminoaldehydes 1a–e to afford the corresponding 1,1′-bis(substituted quinolin-2-yl)ferrocene derivatives 3p–t. The structures of compounds 3a–t were determined and characterized by infrared, 1H NMR, mass spectrometry, and elemental analysis. The crystal structures of 3e and 3q were determined by x-ray crystallography. 相似文献
999.
Adil Amin Aijaz Ahmad Dar Mohsin Ahmad Bhat Musarat Jan Nuzhat Rehman Mohammad Amin Mir 《Journal of Dispersion Science and Technology》2013,34(3):406-414
The present study deals with the interaction of sodium alkanoates viz. sodium acetate, sodium propionate, sodium butanoate, sodium hexanoate and sodium benzoate on the micellization of dodecylbenzyldimethylammonium chloride using conductometeric and flourscence quenching experiments carried out at 25°C. The analysis has been made through study of variation of critical micelle concentration (cmc), degree of counterion binding (β), aggregation number (N), and micropolarity with the concentration of these hydrophobic salts. The differentiation between the effects of hydrophobic and inorganic salts was made by comparing the above results with the influence of NaCl on cmc, β, and N. 相似文献
1000.
Marina Tavares Gregolin Bruna Galdorfini Chiari Helena M. Ribeiro 《Journal of Dispersion Science and Technology》2013,34(6):820-825
Rheological characteristics of gels were studied, with the focus on their use as a cosmetic base. Some ideal characteristics can be predicted by the rheological characterization, such as the performance, with easy application and without dripping or forming lumps and bubbles. Moreover, it is possible to detect signs of physical instability. The gels were prepared with sodium carboxymethyl cellulose 3% and 5%, with Carbopol 940 (INCI: Carbomer) and with Carbopol Ultrez (INCI: Acrylates/C10-30 alkyl acrylate crosspolymer). The tests performed were yield stress, stress sweep and creep and recovery. The gel with 3% of sodium carboxymethyl cellulose presented the most appropriated behavior and can be indicated as the most suitable cosmetic base. 相似文献