全文获取类型
收费全文 | 2225篇 |
免费 | 316篇 |
国内免费 | 369篇 |
专业分类
化学 | 1854篇 |
晶体学 | 13篇 |
力学 | 245篇 |
综合类 | 32篇 |
数学 | 155篇 |
物理学 | 611篇 |
出版年
2024年 | 2篇 |
2023年 | 36篇 |
2022年 | 63篇 |
2021年 | 134篇 |
2020年 | 122篇 |
2019年 | 93篇 |
2018年 | 85篇 |
2017年 | 76篇 |
2016年 | 109篇 |
2015年 | 90篇 |
2014年 | 96篇 |
2013年 | 154篇 |
2012年 | 110篇 |
2011年 | 130篇 |
2010年 | 107篇 |
2009年 | 103篇 |
2008年 | 103篇 |
2007年 | 123篇 |
2006年 | 116篇 |
2005年 | 113篇 |
2004年 | 123篇 |
2003年 | 104篇 |
2002年 | 90篇 |
2001年 | 80篇 |
2000年 | 87篇 |
1999年 | 69篇 |
1998年 | 63篇 |
1997年 | 39篇 |
1996年 | 44篇 |
1995年 | 32篇 |
1994年 | 33篇 |
1993年 | 43篇 |
1992年 | 21篇 |
1991年 | 24篇 |
1990年 | 20篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1966年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有2910条查询结果,搜索用时 15 毫秒
31.
32.
《Macromolecular rapid communications》2017,38(17)
Involving supramolecular chemistry in self‐assembling block copolymer systems enables design of complex macromolecular architectures that, in turn, could lead to complex phase behavior. It is an elegant route, as complicated and sensitive synthesis techniques can be avoided. Highly grafted double‐comb diblock copolymers based on symmetric double hydrogen bond accepting poly(4‐vinylpyridine)‐block‐poly(N‐acryloylpiperidine) diblock copolymers and donating 3‐nonadecylphenol amphiphiles are realized and studied systematically by changing the molecular weight of the copolymer. Double perpendicular lamellae‐in‐lamellae are formed in all complexes, independent of the copolymer molecular weight. Temperature‐resolved measurements demonstrate that the supramolecular nature and ability to crystallize are responsible for the formation of such multiblock‐like structures. Because of these driving forces and severe plasticization of the complexes in the liquid crystalline state, this supramolecular approach can be useful for steering self‐assembly of both low‐ and high‐molecular‐weight block copolymer systems. 相似文献
33.
34.
作为一种无金属的新型半导体材料,g-C_3N_4因具有稳定的物理化学性质及合适的能带结构而引起人们的关注.理论上g-C_3N_4完全满足水分解的电势条件.然而研究发现,g-C_3N_4材料本身的光催化性能并不好,这主要是由于半导体材料被光激发后生成的自由电子和空穴还没来得及到达材料表面参与反应,就在材料体相内发生复合,导致电子参与有效光催化制氢反应的几率大大降低.同时还发现,将少量的贵金属,如Pt,Au,Pd作助催化剂修饰在该半导体表面,其光催化性能明显提高.但由于这些贵金属储量非常稀少,价格昂贵,导致它们的使用受到一定限制.而Ag作为一种价格远低于Pt,Au,Pd的贵金属,也得到了广泛的研究.研究表明,金属Ag储存电子的能力很好,因此可以有效地将半导体上生成的光生电子快速转移到Ag上面去,从而达到电子空穴快速分离的目的.但是在光催化制氢过程中,Ag吸附H~+的能力较弱,致使电子与H~+反应的诱导力较弱,使得Ag释放电子的能力较差.因此可以通过提高Ag表面对H~+的吸附强度,以加速Ag的电子释放,通过表面修饰来提高Ag助剂的光催化活性.研究发现,Ag纳米粒子表面与含硫化合物之间存在很强的亲和力.硫氰根离子(SCN~–)具有很强的电负性,容易吸附溶液中H~+离子,并且也易吸附在Ag纳米粒子的表面.因此可以利用Ag与SCN~–的作用来增强Ag释放电子的能力.本文采用光还原法将Ag沉积在g-C_3N_4半导体材料表面,然后通过在制氢牺牲剂中加入KSCN溶液,利用SCN~-与Ag的亲和力来提高光生电子参与光催化反应的效率.结果表明,在SCN~-存在的情况下,g-C_3N_4/Ag的光催化制氢性能显著提高.当制氢溶液中SCN~–浓度为0.3 mmol L~(–1)时,材料的光催化制氢性能达最大,为3.89μmol h~(–1),比g-C_3N_4/Ag性能提高5.5倍.基于少量的SCN~–就能明显提高g-C_3N_4/Ag材料的光催化性能,我们提出了一个可能性的作用机理:金属银和SCN~-协同作用,即银纳米粒子作为光生电子的捕获和传输的一种有效的电子传递介质,而选择性吸附在银表面的SCN~-作为界面活性位点有效地吸附溶液中的质子以促进产氢反应,二者协同作用,加速了g-C_3N_4-Ag–SCN~-三物种界面之间电荷的传输、分离及界面催化反应速率,有效抑制了g-C_3N_4主体材料光生电子和空穴的复合,因而g-C_3N_4/Ag–SCN复合材料的光催化制氢性能提高.考虑到其成本低、效率高,SCN~–助催化剂有很大的潜力广泛应用于制备高性能的银修饰光催化材料. 相似文献
35.
Composition assessment of ferric oxide by accurate peak fitting of the Fe 2p photoemission spectrum 下载免费PDF全文
M. Bravo Sanchez J. A. Huerta‐Ruelas D. Cabrera‐German A. Herrera‐Gomez 《Surface and interface analysis : SIA》2017,49(4):253-260
A quantitative study of the surface composition of ferric oxide employing photoemission spectra is presented. It was possible to accurately reproduce the expected composition (Fe2.00±0.05O3) by modeling the background as a combination of Shirley‐type (Shirley–Vegh–Salvi–Castle) and slope backgrounds through the active approach. The line‐shape employed to fit apparent peak asymmetries was the double‐Lorentzian. It was possible to resolve a previously unreported satellite located at ~729 eV. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
36.
Vadim Baigildin Galina Pankova Tatyana Evseeva Nikolay Lavrov Irina Shirokova Gleb Vaganov 《Journal of Dispersion Science and Technology》2017,38(11):1570-1577
The present article investigates the influence of dispersion medium on the aggregate stability of cross-linked poly-(methyl methacrylate) particles on the surface layer of which aliphatic amino groups are localized. It is shown that particle size depends on the ionic strength of dispersion medium. The research determines the optimal content of cross-linked agent, ethylene glycol dimetharylate that results in the formation of cationic particles being stable in saline. Particle modification is performed by bovine serum albumin and luminophore fluorescein 5(6)-isothiocyanate. Protein sorption is observed not to influence luminescent properties of the particles. It is also determined that due to the aggregate stability of particles obtained from 5?wt% of ethylene glycol dimethacrylate in saline, the monodispersity and the absence of inversion of zeta potential in wide pH range is retained, such particles may be considered as perspective carriers of biologically active substances. 相似文献
37.
Dr. Joshua Britton Prof. Dr. Timothy F. Jamison 《Angewandte Chemie (International ed. in English)》2017,56(30):8823-8827
A rapid and modular continuous flow synthesis of highly functionalized fluorinated pyrazoles and pyrazolines has been developed. Flowing fluorinated amines through sequential reactor coils mediates diazoalkane formation and [3+2] cycloaddition to generate more than 30 azoles in a telescoped fashion. Pyrazole cores are then sequentially modified through additional reactor modules performing N-alkylation and arylation, deprotection, and amidation to install broad molecular diversity in short order. Continuous flow synthesis enables the safe handling of diazoalkanes at elevated temperatures, and the use of aryl alkyne dipolarphiles under catalyst-free conditions. This assembly-line synthesis provides a flexible approach for the synthesis of agrochemicals and pharmaceuticals, as demonstrated by a four-step, telescoped synthesis of measles therapeutic, AS-136A, in a total residence time of 31.7 min (1.76 g h−1). 相似文献
38.
《Journal of mass spectrometry : JMS》2017,52(11):728-738
2‐Mercaptopyridine N ‐oxide (pyrithione, PTOH) along with several transition metal ions forms coordination compounds displaying notable biological activities. Gas‐phase complexes formed between pyrithione and manganese (II), cobalt (II), nickel (II), copper (II), and zinc (II) were investigated by infusion in the electrospray source of a quadrupole‐time of flight mass spectrometer. Remarkably, positive ion mode spectra displayed the singly charged metal adduct ion [C10H8MN2O2S2]2+ ([M(PTO)2]+• or [M(DPTO)]+•), where DPTO is dipyrithione, 2,2′‐dithiobis(pyridine N ‐oxide), among the most abundant peaks, implying a change in the oxidation state of whether the metal ion or the ligands. In addition, doubly charged ions were recognized as metal adduct ions containing DPTO ligands, [M(DPTO)n]2+. Generation of [M(PTO)2]+• / [M(DPTO)]+• could be traced by CID of [M(DPTO)2]2+, by observation of the sequential losses of a charged (PTO+) and a radical (PTO•) deprotonated pyrithione ligand. The fragmentation pathways of [M(PTO)2]+• / [M(DPTO)]+• were compared among the different metal ions, and some common features were noticed. Density functional theory (DFT) calculations were employed to study the structures of the observed adduct ions, and especially, to decide in the adduct ion [M(PTO)2]+• / [M(DPTO)]+• whether the ligands are 2 deprotonated pyrithiones or a single dipyrithione as well as the oxidation state of the metal ion in the complex. Characterization of gas‐phase pyrithione metal ion complexes becomes important, especially taking into account the presence of a redox‐active ligand in the complexes, because redox state changes that produce new species can have a marked effect on the overall toxicological/biological response elicited by the metal system. 相似文献
39.
Surface silanol structures, acid properties, and tungsten dispersion of the sol-gel-derived 7W/SiO2–xAl2O3 (x = 0.2–23 wt%) were investigated by means of 29Si, 27Al, and 1H MAS NMR, NH3-TPD, in-situ NH3-IR spectroscopy, XRD, and Raman spectroscopy. The surface silanol structure changed upon Al and tungsten loadings; however, loading of 1 wt% Al2O3 appeared to be the threshold for preserving the Si(OH)Al with isolated bridge after impregnation of 7 wt% W. The 7W/SiO2–1Al2O3 (1 wt% Al2O3) was also found to exhibit the lowest ratio of Bronsted to Lewis acid with the highest amount of Lewis acid sites and the best catalyst performances in propene self-metathesis at 550 °C in terms of both propene conversion and ethylene/butene selectivity. Despite its low tungsten dispersion, the metathesis activity was correlated well with the higher amount of tungsten carbene species, which were formed on the catalysts containing higher isolated bridge silanol and the presence of higher Lewis acid sites. 相似文献
40.