全文获取类型
收费全文 | 6367篇 |
免费 | 214篇 |
国内免费 | 44篇 |
专业分类
化学 | 4431篇 |
晶体学 | 41篇 |
力学 | 170篇 |
数学 | 1179篇 |
物理学 | 804篇 |
出版年
2024年 | 10篇 |
2023年 | 47篇 |
2022年 | 137篇 |
2021年 | 173篇 |
2020年 | 116篇 |
2019年 | 135篇 |
2018年 | 123篇 |
2017年 | 102篇 |
2016年 | 233篇 |
2015年 | 199篇 |
2014年 | 222篇 |
2013年 | 396篇 |
2012年 | 437篇 |
2011年 | 506篇 |
2010年 | 313篇 |
2009年 | 320篇 |
2008年 | 405篇 |
2007年 | 409篇 |
2006年 | 379篇 |
2005年 | 360篇 |
2004年 | 264篇 |
2003年 | 192篇 |
2002年 | 192篇 |
2001年 | 81篇 |
2000年 | 67篇 |
1999年 | 57篇 |
1998年 | 45篇 |
1997年 | 48篇 |
1996年 | 74篇 |
1995年 | 48篇 |
1994年 | 41篇 |
1993年 | 37篇 |
1992年 | 46篇 |
1991年 | 34篇 |
1990年 | 21篇 |
1989年 | 32篇 |
1988年 | 25篇 |
1987年 | 22篇 |
1986年 | 25篇 |
1985年 | 38篇 |
1984年 | 26篇 |
1983年 | 23篇 |
1982年 | 30篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 17篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1975年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有6625条查询结果,搜索用时 15 毫秒
1.
Chemical versus Electrochemical Synthesis of Carbon Nano‐onion/Polypyrrole Composites for Supercapacitor Electrodes 下载免费PDF全文
Olena Mykhailiv Monika Imierska Martyna Petelczyc Prof. Dr. Luis Echegoyen Dr. Marta E. Plonska‐Brzezinska 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5783-5793
The development of high‐surface‐area carbon electrodes with a defined pore size distribution and the incorporation of pseudo‐active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano‐onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission‐ and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800 F g?1 for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300 F g?1 for the CNOs/Ppy bilayer (electrochemical deposition). 相似文献
2.
Biodistribution study of free and microencapsulated 6‐methylcoumarin in Wistar rats by HPLC 下载免费PDF全文
Aura Rocío Hernández Luis Fernando Ospina Diana Marcela Aragón 《Biomedical chromatography : BMC》2015,29(2):176-181
A sensitive, specific and reproducible HPLC method has been developed and validated for the quantitative determination of 6‐methylcoumarin (6MC) in plasma and other tissues in Wistar rats. A C18 column was used with UV detection at 321 nm and a gradient system consisting of methanol‐deionized water was used as mobile phase. The retention time for 6MC was 14.921 min and no interfering peaks were observed for any of the matrices. Linear relationships (r2 > 0.997) were obtained between the peak height ratios and the corresponding biological sample concentrations over the range 0.4–12.8 µg/mL. Precision and accuracy were evaluated; the coefficient of variation and the relative error for all of the organs were <2 and 7%, respectively. The limit of quantitation was 0.20 µg/mL for the heart and 0.30 µg/mL for the other tissues evaluated. This HPLC method was successfully used in the determination of 6MC in the biodistribution study after administration of 200 mg/kg of both 6MC‐free and 6MC‐loaded polymeric microparticles. In this study, extensive 6MC was found, in both free and microencapsulated forms, in all the organs tested. The 6MC‐free showed a range of between 1.7 and 11.5 µg/g, while the microencapsulated 6MC showed concentrations of between 6.35 and 17.7 µg/g, suggesting that 6MC improved absorption rate. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
Functional Carbazole Liquid‐Crystal Block Codendrimers with Optical and Electronic Properties 下载免费PDF全文
Ismael Gracia Beatriz Feringán Prof. José Luis Serrano Dr. Roberto Termine Dr. Attilio Golemme Dr. Ana Omenat Prof. Joaquín Barberá 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(3):1359-1369
The synthesis and characterisation of a family of block codendrimers consisting of highly versatile mesogenic and carbazole‐containing 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) dendrons are reported. The liquid‐crystal behaviour was investigated by means of differential scanning calorimetry, polarised‐light optical microscopy and X‐ray diffraction. Depending on the chemical structure of the constituent dendrons, the codendrimers show lamellar or columnar mesophases. On the basis of the experimental results, models both at the molecular level and in the mesophase are proposed. The physical properties of the block codendrimers derived from the presence of the carbazole moiety in their structure were investigated: photoluminescence in solution and in the mesophase, electrochemical behaviour and hole transport. Electrodeposition of carbazole dendrons afforded a globular supramolecular conformation in which the mesogenic molecular side plays a key role. 相似文献
4.
5.
6.
Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons 下载免费PDF全文
Dr. François Riobé Rózsa Szűcs Dr. Pierre‐Antoine Bouit Dr. Denis Tondelier Bernard Geffroy Fátima Aparicio Julia Buendía Prof. Luis Sánchez Prof. Régis Réau Prof. László Nyulászi Prof. Muriel Hissler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6547-6556
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs). 相似文献
7.
8.
Rhodium catalysts have been prepared on palygorskite and montmorillonite (clay) supports by reduction with hydrogen (1 atmosphere) at room temperature of a cationic organometallic rhodium compound anchored to the support. The activity of these catalysts for the hydrogenation of liquid-phase 1-hexene remains constant with increase of prehydrogenation time and with re-use for several runs. No rhodium leaching is observed. 相似文献
9.
A sequential injection methodology for the spectrophotometric determination of calcium, magnesium and alkalinity in water samples is proposed. A single manifold is used for the determination of the three analytes, and the same protocol sequence allows the sequential determination of calcium and magnesium (the sum corresponds to the water hardness). The determination of both metals is based on their reaction with cresolphtalein complexone; mutual interference is minimized by using 8-hydroxyquinoline for the determination of calcium and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) for the determination of magnesium. Alkalinity determination is based on a reaction with acetic acid, and corresponding color change of Bromcresol Green. Working ranges of 0.5 - 5 mg dm(-3) for Ca, 0.5 - 10 mg dm(-3) for Mg, and 10 - 100 mg HCO3- dm(-3), for alkalinity have been achieved. The results for water samples were comparable to those of the reference methods and to a certified reference water sample. RSDs lower than 5% were obtained, a low reagent consumption and a reduced volume of effluent have been accomplished. The determination rate for calcium and magnesium is 80 h(-1), corresponding to 40 h(-1) per element, while 65 determinations of alkalinity per hour could be carried out. 相似文献
10.
Luis L. Bonilla 《Journal of statistical physics》1987,46(3-4):659-678
A nonlinear Fokker-Planck equation is derived to describe the cooperative behavior of general stochastic systems interacting via mean-field couplings, in the limit of an infinite number of such systems. Disordered systems are also considered. In the weak-noise limit; a general result yields the possibility of having bifurcations from stationary solutions of the nonlinear Fokker-Planck equation into stable time-dependent solutions. The latter are interpreted as non-equilibrium probability distributions (states), and the bifurcations to them as nonequilibrium phase transitions. In the thermodynamic limit, results for three models are given for illustrative purposes. A model of self-synchronization of nonlinear oscillators presents a Hopf bifurcation to a time-periodic probability density, which can be analyzed for any value of the noise. The effects of disorder are illustrated by a simplified version of the Sompolinsky-Zippelius model of spin-glasses. Finally, results for the Fukuyama-Lee-Fisher model of charge-density waves are given. A singular perturbation analysis shows that the depinning transition is a bifurcation problem modified by the disorder noise due to impurities. Far from the bifurcation point, the CDW is either pinned or free, obeying (to leading order) the Grüner-Zawadowki-Chaikin equation. Near the bifurcation, the disorder noise drastically modifies the pattern, giving a quenched average of the CDW current which is constant. Critical exponents are found to depend on the noise, and they are larger than Fisher's values for the two probability distributions considered. 相似文献