全文获取类型
收费全文 | 2857篇 |
免费 | 245篇 |
国内免费 | 463篇 |
专业分类
化学 | 2855篇 |
晶体学 | 57篇 |
力学 | 15篇 |
综合类 | 44篇 |
数学 | 5篇 |
物理学 | 303篇 |
无线电 | 286篇 |
出版年
2024年 | 12篇 |
2023年 | 71篇 |
2022年 | 71篇 |
2021年 | 98篇 |
2020年 | 132篇 |
2019年 | 109篇 |
2018年 | 97篇 |
2017年 | 133篇 |
2016年 | 129篇 |
2015年 | 119篇 |
2014年 | 112篇 |
2013年 | 324篇 |
2012年 | 155篇 |
2011年 | 124篇 |
2010年 | 112篇 |
2009年 | 124篇 |
2008年 | 125篇 |
2007年 | 144篇 |
2006年 | 139篇 |
2005年 | 147篇 |
2004年 | 126篇 |
2003年 | 124篇 |
2002年 | 100篇 |
2001年 | 72篇 |
2000年 | 54篇 |
1999年 | 76篇 |
1998年 | 68篇 |
1997年 | 70篇 |
1996年 | 65篇 |
1995年 | 53篇 |
1994年 | 43篇 |
1993年 | 28篇 |
1992年 | 39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 | 12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3565条查询结果,搜索用时 15 毫秒
81.
Studies on Sodium Trifluormethanesulfonate – Crystal Structure and Phase Transition of Sodium Trifluormethanesulfonate Monohydrate and Sodium Ion Conductivity of Anhydrous Sodium Trifluormethanesulfonate According to the results of temperature dependent powder diffractometry (Guinier-Simon-technique) sodium trifluormethanesulfonate monohydrate is dimorphous. The phase transition occurs at ?35°C. The room-temperature modification crystallizes monoclinic in space group P21/c with the lattice parameters a = 941.6(5) pm, b = 654.3(2) pm, c = 1062.4(5) pm and β = 107.73(2)°. The crystal structure consists of double layers of trifluormethanesulfonate anions, the lipophilic CF3-groups pointing at each other. Sodium is coordinated by four oxygen atoms from four different anions and by two molecules of crystal water. The resulting polyhedron may be addressed as a distorted octahedron. The low-temperature modification crystallizes orthorhombic in space group Pnma with the lattice parameters a = 645.31(9) pm, b = 538.03(9) pm, c = 1745.3(3) pm. The loss of crystal water occurs at 136°C. Anhydrous sodium trifluormethanesulfonate shows a phase transition at 252°C. The high-temperature modification is a good sodium ionic conductor (σ = 4.1 · 10?1 Ω?1 cm?1 at 250°C). 相似文献
82.
Martina Gudelj Paola urina Lucija Jurko Ante Prki Perica Bokovi 《Molecules (Basel, Switzerland)》2021,26(12)
Micellar systems are colloids with significant properties for pharmaceutical and food applications. They can be used to formulate thermodynamically stable mixtures to solubilize hydrophobic food-related substances. Furthermore, micellar formation is a complex process in which a variety of intermolecular interactions determine the course of formation and most important are the hydrophobic and hydrophilic interactions between surfactant–solvent and solvent–solvent. Glycols are organic compounds that belong to the group of alcohols. Among them, propane-1,2-diol (PG) is a substance commonly used as a food additive or ingredient in many cosmetic and hygiene products. The nature of the additive influences the micellar structure and properties of sodium dodecyl sulfate (SDS). When increasing the mass fraction of propane-1,2-diol in binary mixtures, the c.m.c. values decrease because propane-1,2-diol is a polar solvent, which gives it the ability to form hydrogen bonds, decreasing the cohesivity of water and reducing the dielectric constant of the aqueous phase. The values of are negative in all mixed solvents according to the reduction in solvophobic interactions and increase in electrostatic interaction. With the rising concentration of cosolvent, the equilibrium between cosolvent in bulk solution and in the formed micelles is on the side of micelles, leading to the formation of micelles at a lower concentration with a small change in micellar size. According to the 1H NMR, with the addition of propylene glycol, there is a slight shift of SDS peaks towards lower ppm regions in comparison to the D2O peak. The shift is more evident with the increase in the amount of added propane-1,2-diol in comparison to the NMR spectra of pure SDS. Addition of propane-1,2-diol causes the upfield shift of the protons associated with hydrophilic groups, causing the shielding effect. This signifies that the alcohol is linked with the polar head groups of SDS due to its proximity to the SDS molecules. 相似文献
83.
Yuan Ruan Pei-Pei Yuan Ya-Xin Wei Qi Zhang Li-Yuan Gao Pan-Ying Li Yi Chen Yang Fu Yan-Gang Cao Xiao-Ke Zheng Wei-Sheng Feng 《Molecules (Basel, Switzerland)》2021,26(20)
Lipid deposition in the kidney can cause serious damage to the kidney, and there is an obvious epithelial–mesenchymal transition (EMT) and fibrosis in the late stage. To investigate the interventional effects and mechanisms of phenolic compounds from Mori Cortex on the EMT and fibrosis induced by sodium oleate-induced lipid deposition in renal tubular epithelial cells (NRK-52e cells), and the role played by CD36 in the adjustment process, NRK-52e cells induced by 200 μmol/L sodium oleate were given 10 μmoL/L moracin-P-2″-O-β-d-glucopyranoside (Y-1), moracin-P-3′-O-β-d-glucopyranoside (Y-2), moracin-P-3′-O-α-l-arabinopyranoside (Y-3), and moracin-P-3′-O-[β-glucopyranoside-(1→2)arabinopyranoside] (Y-4), and Oil Red O staining was used to detect lipid deposition. A Western blot was used to detect lipid deposition-related protein CD36, inflammation-related protein (p-NF-κB-P65, NF-κB-P65, IL-1β), oxidative stress-related protein (NOX1, Nrf2, Keap1), EMT-related proteins (CD31, α-SMA), and fibrosis-related proteins (TGF-β, ZEB1, Snail1). A qRT-PCR test detected inflammation, EMT, and fibrosis-related gene mRNA levels. The TNF-α levels were detected by ELISA, and the colorimetric method was used to detects SOD and MDA levels. The ROS was measured by flow cytometry. A high-content imaging analysis system was applied to observe EMT and fibrosis-related proteins. At the same time, the experiment silenced CD36 and compared the difference between before and after drug treatment, then used molecular docking technology to predict the potential binding site of the active compounds with CD36. The research results show that sodium oleate can induce lipid deposition, inflammation, oxidative stress, and fibrosis in NRK-52e cells. Y-1 and Y-2 could significantly ameliorate the damage caused by sodium oleate, and Y-2 had a better ameliorating effect, while there was no significant change in Y-3 or Y-4. The amelioration effect of Y-1 and Y-2 disappeared after silencing CD36. Molecular docking technology showed that the Y-1 and Y-2 had hydrogen bonds to CD36 and that, compared with Y-1, Y-2 requires less binding energy. In summary, moracin-P-2″-O-β-d-glucopyranoside and moracin-P-3′-O-β-d-glucopyranoside from Mori Cortex ameliorated lipid deposition, EMT, and fibrosis induced by sodium oleate in NRK-52e cells through CD36. 相似文献
84.
A selective transformation of clopidogrel hydrogen sulfate (CLP) by reactive halogen species (HOX) generated from peroxymonosulfate (PMS) and sodium halide (NaX) is described. Other sustainable oxidants as well as different solvents have also been investigated. As result of this study, for each sodium salt the reaction conditions were optimized, and four different degradation products were formed. Three products were halogenated at C-2 on the thiophene ring and have concomitant functional transformation, such as N-oxide in the piperidine group. A halogenated endo-iminium product was also observed. With this condition, a fast preparation of known endo-iminium clopidogrel impurity (new counterion) was reported as well. The progress of the reaction was monitored using nuclear magnetic resonance spectroscopy as an analytical tool and all the products were characterized by 1D-, 2D-NMR and HRMS. 相似文献
85.
Usachev N. Ya. Belanova E. P. Krukovsky I. M. Kanaev S. A. Atal"yan O. K. Kazakov A. V. 《Russian Chemical Bulletin》2003,52(9):1940-1949
Thermal transformations in systems formed by interaction of Zn and Na nitrates with Y, X, and A zeolites were studied by TG—DTA technique. Temperature regions of existence of adsorbed water, water of crystallization, and decomposition of NO3
– anion were determined. These intervals depend on the composition, structure, method of preparation, and pre-treatment conditions of zeolite systems. The extent of NO3
– decomposition depends not only on the zinc and sodium content but also on the presence of ammonia involved in NO3
– reduction. The zeolite matrix strongly stabilizes the occluded NO3
– anions. A portion of zinc oxide formed by zinc nitrate decomposition is probably localized inside the zeolite cavities as the [Zn—O—(ZnO)
n
—Zn]2+ particles. The latter compensate charges of the isolated [AlO4]– tetrahedra. 相似文献
86.
Juliane R. Sempionatto Aida Martin Laura García‐Carmona Abbas Barfidokht Jonas F. Kurniawan Jose R. Moreto Guangda Tang Andrew Shin Xiaofeng Liu Alberto Escarpa Joseph Wang 《Electroanalysis》2019,31(2):239-245
A flexible skin‐mounted microfluidic potentiometric device for simultaneous electrochemical monitoring of sodium and potassium in sweat is presented. The wearable device allows efficient natural sweat pumping to the potentiometric detection chamber, containing solid‐contact ion‐selective Na+ and K+ electrodes, during exercise activity. The fabricated microchip electrolyte‐sensing device displays good analytical performance and addresses sweat mixing and carry‐over issues of early epidermal potentiometric sensors. Such soft skin‐worn microchip platform integrates potentiometric measurement, microfluidic technologies with flexible electronics for real‐time wireless data transmission to mobile devices. The new fully integrated microfluidic electrolyte‐detection device paves the way for practical fitness and health monitoring applications. 相似文献
87.
高碱煤含钠矿物沉积层的高温熔融及多相反应过程分析 总被引:1,自引:0,他引:1
采用纯矿物试剂模拟燃用高碱煤时炉内受热面典型的灰沉积层化学组成,利用热机械分析(TMA)、TG-DSC分析、高温煅烧实验结合XRD、SEM-EDS表征方法研究了不同Na2SO4含量灰沉积层的高温熔融过程及矿物间的多相反应机理。结果表明,掺混Na2SO4后沉积层熔化特征温度显著降低,Na2SO4的主要反应途径与掺混比例有关,当掺混比低于20%时,Na2SO4与SiO2、CaO、Al2O3反应主要转变为CaSO4和钠的硅铝酸盐;掺混比大于40%时则主要与CaSO4生成低熔点的钠钙复合硫酸盐。富Na2SO4沉积层颗粒在800℃时开始黏结;900-950℃时,霞石、钠长石等钠的硅铝酸盐发生低温共熔,同时Na2SO4和CaSO4生成的复合硫酸盐开始熔融,逐渐形成液相;1200-1250℃时,镁黄长石与含钙矿物发生强烈共熔,温度超过1300℃后矿物完全熔融成为自由液相。 相似文献
88.
Metal-organic framework MIL-100(Fe) and g-C3N4 heterojunctions (MG-x, x = 5%, 10%, 20%, and 30%, x is the mass fraction of MIL-100(Fe) in the hybrids) were facilely fabricated through ball-milling and annealing, and characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, UV-visible diffuse-reflectance spectrometry, and photoluminescence emission spectrometry. The photocatalytic activities of the series of MG-x heterojunctions toward Cr(VI) reduction and diclofenac sodium degradation were tested upon irradiation with simulated sunlight. The influence of different organic compounds (ethanol, citric acid, oxalic acid, and diclofenac sodium) as hole scavengers and the pH values (2, 3, 4, 6, and 8) on the photocatalytic activities of the series of MG-x heterojunctions was investigated. MG-20% showed superior photocatalytic Cr(VI) reduction and diclofenac sodium degradation performance than did the individual MIL-100(Fe) and g-C3N4 because of the improved separation of photoinduced electron-hole charges, which was clarified via photoluminescence emission and electrochemical data. Moreover, the MG-x exhibited good reusability and stability after several runs. 相似文献
89.
低钠盐及其化验研究 总被引:1,自引:0,他引:1
李京雄 《广东微量元素科学》2003,10(6):60-62
介绍了低钠盐对人体的作用,对低钠盐的定性和定量分析方法进行了研究,包括:低钠盐中镁离子和钾离子的鉴定,用EDTA滴定法测定低钠盐中镁含量和用间接滴定法测定低钠盐中钾含量。 相似文献
90.
水合硫酸氢钠催化合成2-乙氧基萘 总被引:2,自引:0,他引:2
以-水合硫酸氢钠为催化剂,β-萘酚和无水乙醇为原料合成了2-乙氧基萘。优化反应条件为:β-萘酚150mmol,无水乙醇900mmol,催化剂2.0g,回流反应时间5h,产率85.5%。 相似文献