全文获取类型
收费全文 | 1891篇 |
免费 | 202篇 |
国内免费 | 157篇 |
专业分类
化学 | 1023篇 |
晶体学 | 16篇 |
力学 | 38篇 |
综合类 | 9篇 |
数学 | 95篇 |
物理学 | 241篇 |
综合类 | 828篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 38篇 |
2021年 | 42篇 |
2020年 | 50篇 |
2019年 | 53篇 |
2018年 | 43篇 |
2017年 | 60篇 |
2016年 | 85篇 |
2015年 | 78篇 |
2014年 | 81篇 |
2013年 | 111篇 |
2012年 | 101篇 |
2011年 | 104篇 |
2010年 | 105篇 |
2009年 | 119篇 |
2008年 | 109篇 |
2007年 | 135篇 |
2006年 | 107篇 |
2005年 | 100篇 |
2004年 | 89篇 |
2003年 | 68篇 |
2002年 | 72篇 |
2001年 | 50篇 |
2000年 | 57篇 |
1999年 | 46篇 |
1998年 | 41篇 |
1997年 | 49篇 |
1996年 | 36篇 |
1995年 | 32篇 |
1994年 | 30篇 |
1993年 | 26篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2250条查询结果,搜索用时 31 毫秒
41.
Xiao‐Ping Chen Anne Buyle Padias H. K. Hall 《Journal of polymer science. Part A, Polymer chemistry》2002,40(12):1929-1936
A non‐olefinic monomer, methyl 1‐bicyclobutanecarboxylate (MBC), was successfully polymerized by the controlled/“living” atom transfer radical polymerization (ATRP) technique, resulting in a well‐defined homopolymer, PMBC, with only cyclobutane ring units in the polymer chain. An AB block copolymer poly(methyl 1‐bicyclobutanecarboxylate)‐b‐polystyrene (PMBC‐b‐PS), having an all‐ring unit segment, was also synthesized with narrow polydispersity and designed number‐average molecular weight in addition to precise end groups. The 1H NMR spectra, glass‐transition temperature, and thermal stability of PMBC, PMBC‐b‐PS, and PS‐b‐PMBC were investigated. The experimental results showed that the cyclobutane rings in the two block polymers improved their thermal stability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1929–1936, 2002 相似文献
42.
Shape-controlled synthesis of metal nanostructures: the case of silver 总被引:19,自引:0,他引:19
The concept of shape-controlled synthesis is discussed by investigating the growth mechanisms for silver nanocubes, nanowires, and nanospheres produced through a polymer-mediated polyol process. Experimental parameters, such as the concentration of AgNO(3) (the precursor to silver), the molar ratio between poly(vinylpyrrolidone) (PVP, the capping agent) and AgNO(3), and the strength of chemical interaction between PVP and various crystallographic planes of silver, were found to determine the crystallinity of seeds (e.g., single crystal versus decahedral multiply twinned particles). In turn, the crystallinity of a seed and the extent of the PVP coverage on the seed were both instrumental in controlling the morphology of final product. The ability to generate silver nanostructures with well-defined morphologies provides a great opportunity to experimentally and systematically study the relationship between their properties and geometric shapes. 相似文献
43.
"Living"/controlled radical polymerization of styrene was carried out with diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS)/CuCl2/bipyridine (bipy) initiation system at 120℃. The molecular weights of resultant PSt increased with the monomer conversion and the polydispersities were in the range of 1.37 ~ 1.52. A linear ln([M]o/[M])versus time plot was also obtained indicating the constant concentration of growing radicals during the polymerization with this initiation system. End group analysis by 1H-NMR spectroscopic studies showed that the end groups of the polymer obtained is cω-functionalized by a chlorine group from the catalyst and a-functionalized by a (carbethoxy-cyano-phenyl)methyl group from the fragments of the initiator. Having C1 atom at the chain end, the PSt obtained can be used as a macroinitiator to promote a chain-extension reaction with fresh St and block copolymerization reaction with a second monomer, such as methyl methacrylate, in the presence of CuC1/bipy catalyst via a conventional ATRP process. 相似文献
44.
Tao He Ying‐Fang Zou Cai‐Yuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2002,40(20):3367-3378
Comb‐shaped graft copolymers with poly(methyl methacrylate) as a handle were synthesized by the macromonomer technique in two steps. First, polytetrahydrofuran acrylate (A‐PTHF), prepared by the living cationic ring‐opening polymerization of tetrahydrofuran, underwent homopolymerization with 1‐(ethoxycarbonyl)prop‐1‐yl dithiobenzoate as an initiator under 60Co γ irradiation at room temperature; Second, the handle of the comb‐shaped copolymers was prepared by the block copolymerization of methyl methacrylate with P(A‐PTHF) as a macroinitiator under 60Co γ irradiation. The two‐step polymerizations were proved to be controlled with the following evidence: the straight line of ln[M]0/[M] versus the polymerization time, the linear increase in the number‐average molecular weight with the conversion, and the relatively narrow molecular weight distribution. The structures of the P(A‐PTHF) and final comb‐shaped copolymers were characterized by 1H NMR spectroscopy and gel permeation chromatography. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3367–3378, 2002 相似文献
45.
Hydroxypropyl chitosan-graft-carboxymethyl beta-cyclodextrin (HPCH-g-CM beta-CD) was synthesized by grafting CM beta-CD onto HPCH using water soluble 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as the condensing agent. Due to the presence of hydrophobic beta-CD rings onto the HPCH backbone, this polymer can be used as a matrix for controlled drug release. The adsorption of a hydrophobic model drug, ketoprofen, by HPCH-g-CM beta-CD microparticles (using tripolyphosphate as an ionic crosslinking agent) fitted well in the Langmuir isotherm equation. The drug dissolution profile showed that HPCH-g-CM beta-CD microparticles provided a slower release of the entrapped ketoprofen than chitosan, and the release behavior was influenced by the pH value of the medium. These results suggest that beta-CD grafted with chitosan derivatives may become a potential biodegradable delivery system to control the release of hydrophobic drugs with pH-responsive capability. 相似文献
46.
Bianca S. Shemper A. Ersin Acar Lon J. Mathias 《Journal of polymer science. Part A, Polymer chemistry》2002,40(3):334-343
The copper‐catalyzed atom transfer radical polymerization (ATRP) of poly(propylene glycol) methacrylate (PPGM) in solution to produce linear and starlike polymers is reported, using methylethyl ketone as the solvent and a temperature of 80 °C. The ATRP system used was efficient for polymerization of the functionalized monomer without protecting hydroxyl end groups of monomer. The polymerizations were consistent with “living” or controlled processes, as revealed by the linear evolution of molecular weight with conversion. Increasing the [M]0:[I]0 ratio resulted in increasing molecular weights, whereas the polydispersity indices remained low (Mw/Mn < 1.4) even at high conversion. Decreasing the [CuBr]0:[I]0 ratio resulted in lower conversions, slightly larger polydispersities, and decreased molecular weights, likely resulting from a lower initiation efficiency. Polymers were characterized by 1H and 13C NMR; molecular weights of polymers with low degrees of polymerization were estimated by end‐group analysis from 13C NMR spectra obtained using distortionless enhancement by polarization transfer and the gated decoupling techniques. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 334–343, 2002 相似文献
47.
It has been confirmed that, in oxide superconductors, the superconducting transition temperature Tc depends strongly on the oxygen content and oxygen ordering. The microgravimetric method is very useful in the analysis of
oxide superconductors, because it allows investigations in vacuum and controlled environments in classical applications: thermogravimetric
analysis, kinetics and thermodynamics of reaction, determination of oxygen contents in redox reactions, investigations of
the correlation of the deviation from stoichiometry and carrier concentration and also the combined measurement of mass and
additional parameters, e.g. evolved gas analysis, etc. Selected papers are reviewed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
48.
基于受控原动件的机械特性和受控机构二自由度的特点,建立精确实现多点轨迹受控机构的圆拟合优化模型.提出运用广义逆求解补偿运动位移的方法。 相似文献
49.
微乳液法合成纳米二氧化硅粒子 总被引:5,自引:0,他引:5
制备 Triton X- 1 0 0 /正辛醇 /环己烷 /水 (或氨水 )微乳液 ,研究了该微乳液系统稳定相行为与制备条件的关系 .在该微乳液系统稳定的条件下 ,由正硅酸乙酯受控水解反应制备 Si O2 纳米粒子 ,反应后处理简便 ,制得粒子尺度较均一的球形疏松无定型纳米 Si O2 粒子 .Si O2 粒子粒径尺寸可通过调节水与表面活度剂分子数之比 m、水与正硅酸乙酯分子数之比 n控制 .探讨了影响 Si O2 纳米粒子形貌、粒径分布的因素及制备优化条件 相似文献
50.
多步进电机控制算法研究 总被引:6,自引:0,他引:6
采用单台PC机,也就是用单CPU,代替多个CPU控制多个步进电机。根据步进电机工作的特性曲线,计算出单个步进电机运行的时间控制数组,然后把多个步进电机的相对时问控制数组合并成为一个相对时间控制结构数组,利用此一个相对时间控制数组同时对多个步进电机进行控制。 相似文献