全文获取类型
收费全文 | 1900篇 |
免费 | 35篇 |
国内免费 | 6篇 |
专业分类
化学 | 1099篇 |
晶体学 | 73篇 |
力学 | 53篇 |
数学 | 282篇 |
物理学 | 434篇 |
出版年
2022年 | 19篇 |
2021年 | 17篇 |
2020年 | 16篇 |
2019年 | 14篇 |
2018年 | 21篇 |
2017年 | 21篇 |
2016年 | 31篇 |
2015年 | 27篇 |
2014年 | 40篇 |
2013年 | 125篇 |
2012年 | 80篇 |
2011年 | 112篇 |
2010年 | 67篇 |
2009年 | 52篇 |
2008年 | 98篇 |
2007年 | 82篇 |
2006年 | 95篇 |
2005年 | 74篇 |
2004年 | 65篇 |
2003年 | 61篇 |
2002年 | 52篇 |
2001年 | 33篇 |
2000年 | 36篇 |
1999年 | 33篇 |
1998年 | 22篇 |
1997年 | 31篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 23篇 |
1993年 | 31篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 22篇 |
1988年 | 28篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 18篇 |
1984年 | 32篇 |
1983年 | 12篇 |
1982年 | 32篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 27篇 |
1976年 | 23篇 |
1975年 | 22篇 |
1974年 | 21篇 |
1973年 | 18篇 |
排序方式: 共有1941条查询结果,搜索用时 15 毫秒
61.
Aryl/alkyl cyanides were quickly converted into the corresponding esters in the presence of iron(III) chloride in refluxing alcohols with very good yields. 相似文献
62.
Christopher M. Spillmann Jawad Naciri Mu‐San Chen Amritha Srinivasan Banahalli R. Ratna 《Liquid crystals》2013,40(4):373-380
In this report we demonstrate the ability to tune the physical properties of a liquid crystal elastomer (LCE) by varying the amount and type of crosslinking within the elastomer network. LCE films composed of a single mesogenic compound were capable of uniaxial contraction when thermally actuated through the nematic to isotropic phase of the material. We probed the physical properties of the LCE films while varying the amount and concentration of two crosslinking agents and measured actuation strains of 10–35%, elastic moduli of 3–14 MPa, and transition temperatures ranging between 75 and 60°C. The viscous losses of the elastomers and the estimated work capable of being produced by the films were also evaluated. The ability to tune the physical properties of the LCE films allows for a wide range of applications including robotics, microelectromechanical systems (MEMS), shape‐changing membranes, and/or microfluidics. 相似文献
63.
Thermotropic main chain liquid crystalline polyurethanes were prepared from 4-{[4-(6-hydroxyhexyloxy)phenylimino]methyl}benzoic acid 4-{[4-(6-hydroxyhexyloxy)phenylimino]methyl}phenyl ester (mesogenic diol) and 1,6-hexamethylene di-isocyanate. The effects of partial replacement of the mesogenic diol by 20-50 mol% of poly(tetramethylene oxide)glycol (PTMG) of varying molecular mass (M n =650, 1000, 2000) on the liquid crystalline properties were studied. Structural characterization was carried out by FTIR spectroscopy and the molecular mass distribution was determined by GPC. Differential scanning calorimetry and hot stage polarizing optical microscopy were used to study the mesomorphic properties. It was observed that the partial replacement of the mesogenic diol by PTMG of varying molecular masses influenced the phase transitions and the occurrence of mesophase textures. When the molecular mass of PTMG was enhanced, a higher content of mesogenic agent was needed to obtain liquid crystalline properties. 相似文献
64.
Carbon‐Coated LiTi2(PO4)3: An Ideal Insertion Host for Lithium‐Ion and Sodium‐Ion Batteries 下载免费PDF全文
Dr. Vanchiappan Aravindan Dr. Wong Chui Ling Steffen Hartung Nicolas Bucher Prof. Srinivasan Madhavi 《化学:亚洲杂志》2014,9(3):878-882
We report the extraordinary performance of carbon‐coated sodium super ion conductor (NASICON)‐type LiTi2(PO4)3 as an ideal host matrix for reversible insertion of both Li and Na ions. The NASICON‐type compound was prepared by means of a Pechini‐type polymerizable complex method and was subsequently carbon coated. Several characterization techniques such as XRD, thermogravimetric analysis (TGA), field‐emission (FE) SEM, TEM, and Raman analysis were used to study the physicochemical properties. Both guest species underwent a two‐phase insertion mechanism during the charge/discharge process that was clearly evidenced from galvanostatic and cyclic voltammetric studies. Unlike that of Li (≈1.5 moles of Li), Na insertion exhibits better reversibility (≈1.59 moles of Na) while experiencing a slightly higher capacity fade (≈8 % higher than Li) and polarization (780 mV) than Li. However, excellent rate capability profiles were noted for Na insertion relative to its counterpart Li. Overall, the Na insertion properties were found to be superior relative to Li insertion, which makes carbon‐coated NASICON‐type LiTi2(PO4)3 hosts attractive for the development of next‐generation batteries. 相似文献
65.
Woldemedhin M. T. Srinivasan J. Kelly R. G. 《Journal of Solid State Electrochemistry》2021,25(10):2699-2700
Journal of Solid State Electrochemistry - 相似文献
66.
Ahmad R Deng Y Vikram DS Clymer B Srinivasan P Zweier JL Kuppusamy P 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,184(2):236-245
In continuous wave (CW) electron paramagnetic resonance imaging (EPRI), high quality of reconstructed image along with fast and reliable data acquisition is highly desirable for many biological applications. An accurate representation of uniform distribution of projection data is necessary to ensure high reconstruction quality. The current techniques for data acquisition suffer from nonuniformities or local anisotropies in the distribution of projection data and present a poor approximation of a true uniform and isotropic distribution. In this work, we have implemented a technique based on Quasi-Monte Carlo method to acquire projections with more uniform and isotropic distribution of data over a 3D acquisition space. The proposed technique exhibits improvements in the reconstruction quality in terms of both mean-square-error and visual judgment. The effectiveness of the suggested technique is demonstrated using computer simulations and 3D EPRI experiments. The technique is robust and exhibits consistent performance for different object configurations and orientations. 相似文献
67.
Rukmanikrishnan Balasubramanian Ramalingam Srinivasan Kim Sam Soo Lee Jaewoong 《Cellulose (London, England)》2021,28(9):5577-5590
Cellulose - Sustainable food packaging films were developed using a combination of k-Carrageenan (k-C), hydroxyl ethyl cellulose (HEC), silicon dioxide (SiO2), and silver (Ag) nanoparticles. The... 相似文献
68.
Bikshandarkoil R. Srinivasan Kalimuthu Moovendaran S. Natarajan 《Journal of Thermal Analysis and Calorimetry》2014,118(3):1397-1399
The authors of the title paper (J Therm Anal Calorim 2012,110:873–878) report to have grown a dipeptide hydrochloride crystal namely glycyl-l-alanine hydrochloride by the slow evaporation of an aqueous solution containing stoichiometric amounts of l-alanine and glycine and an excess of hydrochloric acid. In this letter, we prove that no such dipeptide hydrochloride can be crystallized simply by mixing two amino acids in aqueous hydrochloric acid. 相似文献
69.
Bal Sydulu Singu Umashankar Male Palaniappan Srinivasan Srinivas Pabba 《Journal of Solid State Electrochemistry》2014,18(7):1995-2003
Polyaniline sulphate salt titanium dioxide composite (PANI-H2SO4·TiO2) was synthesized by chemical in situ polymerization of aniline in the presence of TiO2. The effect of anionic surfactant (sodium lauryl sulphate) in this reaction was also assessed. During the polymerization reaction, sodium lauryl sulphate (SLS) is converted to dodecyl hydrogen sulphate (DHS) in the presence of acidic medium and gets doped onto polyaniline along with sulphuric acid dopant, i.e. formation of polyaniline-sulphate-dodecyl hydrogen sulphate-titanium dioxide composite (PANI-H2SO4-DHS·TiO2). In the PANI-H2SO4-DHS·TiO2 composite, the presence of DHS is confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy-dispersive X-ray analysis (EDAX) and TiO2 is confirmed by XRD and EDAX results. In PANI-H2SO4-DHS·TiO2 system, the nanoparticle of TiO2 (10–20 nm) is uniformly embedded on nanofibres (20–60 nm) of PANI-H2SO4-DHS, and some part of PANI-H2SO4-DHS·TiO2 forms core–shell morphology, wherein TiO2 is in core and PANI-H2SO4-DHS in shell forms. Stability of PANI-H2SO4-DHS increases due to the incorporation of stable TiO2. Utility of PANI-TiO2 composite was carried out in supercapacitor cell system by performing cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopic techniques in 1 M H2SO4 solution. Very low values of solution resistance, charge transfer resistance and time constant are obtained between 0.2 and 0.6 V. Initial specific capacitance values for the cell carried out at low and high current densities are found to be 280 and 205 F g?1, respectively, and after 1,700 charge–discharge cycles, its retention in the specific capacitance values is found to be the same (65–66 %) with coulombic efficiency of 98–100 %. A capacitor can work even at a high discharge rate. The efficiency of oxidizing and doping power increases with the use of a surfactant. Moreover, the use of a long chain surfactant dopant containing polyaniline as an electrode material plays an important role to increase the performance of the supercapacitor by allowing the electrolyte to easily enter and come out from PANI electrodes. 相似文献
70.
Namasivayam Subhapradha Ramachandran Saravanan Pasiyappazham Ramasamy Alagiri Srinivasan Vairamani Shanmugam Annaian Shanmugam 《Applied biochemistry and biotechnology》2014,172(1):9-20
Chitosan has attracted much attention as a biomedical material, owing to its unique biological activities. In this study, hepatoprotective effect of β-chitosan obtained from the gladius of squid Sepioteuthis lessoniana was studied against carbon tetrachloride (CCl4)-induced oxidative stress and liver injury in rats. The rats that received β-chitosan along with the administration of CCl4 showed significantly decreased plasma and tissue alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities and total cholesterol, triglyceride (TG) and free fatty acid (FFA) contents, whereas the treatment with β-chitosan alone markedly increased rat hepatic and circulatory superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) and reduced glutathione (GSH) levels and decreased the malondialdehyde level. Histopathological observations recommended the marked hepatoprotective effect of β-chitosan. The CCl4-induced alterations on circulatory and hepatic antioxidant defence system were normalised by β-chitosan, and it could be concluded that the hepatoprotective effect of chitosan may be due to its antioxidant and antilipidemic property. Therefore, β-chitosan could be considered as antihepatotoxic agent. 相似文献