全文获取类型
收费全文 | 21795篇 |
免费 | 4128篇 |
国内免费 | 3209篇 |
专业分类
化学 | 15655篇 |
晶体学 | 388篇 |
力学 | 1454篇 |
综合类 | 252篇 |
数学 | 2322篇 |
物理学 | 9061篇 |
出版年
2024年 | 34篇 |
2023年 | 442篇 |
2022年 | 625篇 |
2021年 | 824篇 |
2020年 | 915篇 |
2019年 | 911篇 |
2018年 | 778篇 |
2017年 | 763篇 |
2016年 | 1133篇 |
2015年 | 1118篇 |
2014年 | 1337篇 |
2013年 | 1655篇 |
2012年 | 2126篇 |
2011年 | 2148篇 |
2010年 | 1610篇 |
2009年 | 1552篇 |
2008年 | 1523篇 |
2007年 | 1372篇 |
2006年 | 1361篇 |
2005年 | 1176篇 |
2004年 | 808篇 |
2003年 | 615篇 |
2002年 | 633篇 |
2001年 | 512篇 |
2000年 | 433篇 |
1999年 | 393篇 |
1998年 | 334篇 |
1997年 | 318篇 |
1996年 | 266篇 |
1995年 | 241篇 |
1994年 | 202篇 |
1993年 | 154篇 |
1992年 | 143篇 |
1991年 | 128篇 |
1990年 | 108篇 |
1989年 | 83篇 |
1988年 | 65篇 |
1987年 | 35篇 |
1986年 | 50篇 |
1985年 | 44篇 |
1984年 | 29篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1975年 | 7篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
991.
Li Wei Bin Zhang Yan Zhou Li Qiang Junyan Zhang 《Surface and interface analysis : SIA》2013,45(8):1233-1237
Fluorine‐doped hydrogenated carbon film was grown by chemical vapor deposition technique using CH4 and CF4 as feedstock, with a pulse DC‐bias power supply. The structure of as‐deposited film was characterized by transmission electron microscopy and Raman spectra. The results suggested that the film could be considered as composite thin film with curved graphitic structures embedded in amorphous carbon matrix. The mechanical properties and friction coefficient were tested by TI 950 TriboIndenter and UMT‐2 at humidity of 30%, respectively. The results showed that the film exhibited high hardness (~11.04 GPa), good elasticity recovery(~83%) and ultra‐low coefficient of friction (~0.01). Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
992.
Kang Dai Lei Song Saihua Jiang Bin Yu Wei Yang Richard K.K. Yuen Yuan Hu 《Polymer Degradation and Stability》2013
A novel reactive phosphorus-containing monomer [1-oxo-2,6,7-trioxa-1- phosphabicyclo-[2.2.2]octane-methyl diallyl phosphate, PDAP] was synthesized, and various amounts of PDAP were combined with unsaturated polyester by radical bulk polymerization. The resulting flame-retardant unsaturated polyester resin (FR-UPR) samples were investigated by thermogravimetric analysis (TGA), microscale combustion calorimetry (MCC), and limiting oxygen index (LOI) tests. Due to the relatively high phosphorus content of PDAP (18.2 wt%), incorporation of this monomer into unsaturated polyester resin (UPR) led to a marked decrease in the heat release capacity (HRC), the total heat release (THR), an increase in the LOI and the char yield upon combustion. In order to elaborate the interactions between the UPR and PDAP in degradation, differences between the experimental and theoretical mass losses of a FR-UPR sample were evaluated. Furthermore, thermogravimetry-Fourier transform infrared (TG-FTIR) and real-time Fourier transform infrared (RTIR) spectroscopy were employed to investigate the degradation behavior of UPRs, providing insight into the degradation mechanism. 相似文献
993.
Nadezhda I. Islamova Xi ChenChang-Jun Fan Richard S. AndinoWatson J. Lees 《Polymer Degradation and Stability》2013
Photochromic indolylfulgimides covalently attached to polymers have beneficial properties for optical switching. A 3-indolylfulgide and two 3-indolylfulgimides with one or two polymerizable styrene groups attached on the nitrogen atom(s) were synthesized. Copolymerization with methyl methacrylate (MMA) provided linear copolymers (one styrene group) or a cross-linked copolymer (two styrene groups). The properties of the monomers and copolymers in toluene or as thin films were characterized. The new copolymers were photochromic (reversible Z-to-C isomerization), absorbed visible light, and revealed good thermal and photochemical stability. At room temperature, all copolymer films showed no loss of absorbance after 5 weeks. At 80 °C in either toluene or as films, the Z-forms copolymers were less stable than the C-form copolymers, which showed little or no degradation after 400 h. The degradation rate due to repeated ring-closing – ring opening cycles was less than 3% per 100 cycles. The cross-linked copolymer showed photochemical stability comparable to monomeric fulgides in toluene, <1% per 100 cycles. In general, the properties of the linear and cross-linked copolymers were similar to the corresponding monomers in toluene. In films, the conformations of the Z-form were restricted due to the matrix indicating that the preparation of films from the C-form is advantageous. 相似文献
994.
ZongWen Wang YingWei Fan JinFa Chen Ying Guo WeiHua Wu Ye He LiangJun Xu FengFu Fu 《Electrophoresis》2013,34(15):2177-2184
A novel microfluidic chip‐based fluorescent DNA biosensor, which utilized the electrophoretic driving mode and magnetic beads‐based “sandwich” hybridization strategy, was developed for the sensitive and ultra‐specific detection of single‐base mismatch DNA in this study. In comparison with previous biosensors, the proposed DNA biosensor has much more robust resistibility to the complex matrix of real saliva and serum samples, shorter analysis time, and much higher discrimination ability for the detection of single‐base mismatch. These features, as well as its easiness of fabrication, operation convenience, stability, better reusability, and low cost, make it a promising alternative to the SNPs genotyping/detection in clinical diagnosis. By using the biosensor, we have successfully determined oral cancer‐related DNA in saliva and serum samples without sample labeling and any preseparation or dilution with a detection limit of 5.6 × 10?11 M, a RSD (n = 5) < 5% and a discrimination factor of 3.58–4.54 for one‐base mismatch. 相似文献
995.
Dong‐Jun Yu Jun Hu Yan Huang Hong‐Bin Shen Yong Qi Zhen‐Min Tang Jing‐Yu Yang 《Journal of computational chemistry》2013,34(11):974-985
Understanding the interactions between proteins and ligands is critical for protein function annotations and drug discovery. We report a new sequence‐based template‐free predictor (TargetATPsite) to identify the Adenosine‐5′‐triphosphate (ATP) binding sites with machine‐learning approaches. Two steps are implemented in TargetATPsite: binding residues and pockets predictions, respectively. To predict the binding residues, a novel image sparse representation technique is proposed to encode residue evolution information treated as the input features. An ensemble classifier constructed based on support vector machines (SVM) from multiple random under‐samplings is used as the prediction model, which is effective for dealing with imbalance phenomenon between the positive and negative training samples. Compared with the existing ATP‐specific sequence‐based predictors, TargetATPsite is featured by the second step of possessing the capability of further identifying the binding pockets from the predicted binding residues through a spatial clustering algorithm. Experimental results on three benchmark datasets demonstrate the efficacy of TargetATPsite. © 2013 Wiley Periodicals, Inc. 相似文献
996.
Qing Ye Liang-Fang Zhai Nian-Nian Fan De-Ping Lu 《Journal of Dispersion Science and Technology》2013,34(6):859-869
The poly(methyl methacrylate/butyl acrylate/acrylic acid) [P(MMA/BA/AA)] and poly (styrene/butyl acrylate/acrylic acid) [P(St/BA/AA)] latexes were synthesized using the emulsifier octylphenol polyoxyethylene(10) ether (OP-10) and ammonium sulfate allyloxy nonylphenoxy poly(ethyleneoxy)(10) ether(DNS-86). The optimum amount of OP-10 and DNS-86 was 1.5% and 2.5% respectively. The P(MMA/BA/AA) and P(St/BA/AA) latex containing 1.5% OP-10 or 2.5% DNS-86 were blended pairwise. The performances of latex blends and parent latexes as a function of emulsifiers content in parent latexes were determined. The results indicated that the stability of latex blends is favorable, and particle size distribution was more uniform and thermal stability was improved after blending. 相似文献
997.
Minghuan Shen Xiaohui Xu Yilin Wang Yajun Guo Minghong Fan Guorong Tan 《Journal of Dispersion Science and Technology》2013,34(8):1178-1182
The viscous properties, scanning electronic microscopy (SEM), and water/oil interfacial tension (IFT) of partially hydrolyzed polyacryamide (HPAM) and hydrophobically associating hydrolyzed polyacryamides modified with N‐dodecylacrylamide were studied with the objective of investigating the influence on destabilization of emulsions. As expected, the copolymers exhibit significant viscosity enhancing capacity and three‐dimensional network structures due to intermolecular hydrophobic associations, and also present high interfacial activities as the IFT decrease with increasing polymer concentration. As a result, the existences of copolymers increased both the viscosity of emulsions and the intensity of interfacial film, in which case slow down the diffusion of demulsifier molecules and enhance the stability of emulsions, finally, the separation of water from oil becomes more difficult. 相似文献
998.
Xiaogang Yang Bin Li Haizeng Wang Baorong Hou 《Journal of Dispersion Science and Technology》2013,34(5):672-676
The inhibition effect of cetyl trimethyl ammonium bromide (CTAB) on the corrosion of mild steel in 1.0 mol L?1 hydrochloric acid (HCl) has been studied at different temperatures (25–60°C) by weight loss and potentiodynamic polarization methods. The results reveal that CTAB behaves as an effective inhibitor in 1.0 mol L?1 HCl, and the inhibition efficiency increases with the inhibitor concentration. Polarization curves show that CTAB is a mixed-type inhibitor in hydrochloric acid. The results obtained from weight loss and polarizations are in good agreement. The effect of immersion time on corrosion inhibition has also been examined and is discussed. The adsorption of inhibitor on mild steel surface obeys the Langmuir adsorption isotherm equation. Thermodynamic parameters have been obtained by adsorption theory. The inhibition effect is satisfactorily explained by the parameters. 相似文献
999.
Bin Xie Xue‐Song Feng Chun‐Xiao Zhang Xian‐Cheng Zeng 《Journal of Dispersion Science and Technology》2013,34(6):920-926
Two Schiff base transitional metal complexes bearing morpholine side chains were synthesized and characterized, and were used as a simulative hydrolase in the catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) in this article. A mechanism of PNPP catalytic hydrolysis in the Brij35 micellar solution was proposed and supported by the results of the spectral analysis and the kinetic calculation. The kinetic model of PNPP catalytic hydrolysis was studied. The some kinetic and the thermodynamic constants on the catalytic reaction were calculated. The results of the study show that the metallomicelle made up of the Schiff base transitional metal complexes and Brij35 micelle revealed a good catalytic activity in PNPP catalytic hydrolysis; the rate of the PNPP catalytic hydrolysis is increased following the increase of the pH values in the buffer solution and affected by the polarization action of metal ion of complex. 相似文献
1000.
Zhen Li Bin Dong Fei Geng Ganzuo Li 《Journal of Dispersion Science and Technology》2013,34(8):1066-1071
This article reports a novel preparation of mesoporous silica with series of 1-alky-3-methylimidazolium bromide (CnMIM)Br (n = 12, 14, 16), a kind of amphiphilic room-temperature ionic liquids (RTILs), as a template via a sol-gel nanocasting technique. The pore morphology and structures of these mesoporous silica were characterized by Transmission electron microscopy (TEM). The results show that the RTIL bearing longer alkyl chain is preferred to form the mesoporous silica material with bigger pores. (C16MIM)Br has been chosen to study how the various influencing factors affect the synthesis and structure of the mesoporous silica material, such as the acid concentration, the solling time, the gelling time and the calcination time. N2 adsorption-desorption isotherms measurement was used to characterize the pore size distribution and BET surface area. The results indicate that all of the factors can make an influence on the preparation of the mesoporous silica, which is more sensitive to the concentration of the acid. 相似文献