全文获取类型
收费全文 | 2105篇 |
免费 | 145篇 |
国内免费 | 8篇 |
专业分类
化学 | 1760篇 |
晶体学 | 20篇 |
力学 | 20篇 |
数学 | 92篇 |
物理学 | 366篇 |
出版年
2023年 | 28篇 |
2022年 | 30篇 |
2021年 | 39篇 |
2020年 | 66篇 |
2019年 | 73篇 |
2018年 | 49篇 |
2017年 | 33篇 |
2016年 | 107篇 |
2015年 | 93篇 |
2014年 | 87篇 |
2013年 | 117篇 |
2012年 | 193篇 |
2011年 | 221篇 |
2010年 | 85篇 |
2009年 | 69篇 |
2008年 | 144篇 |
2007年 | 123篇 |
2006年 | 106篇 |
2005年 | 104篇 |
2004年 | 86篇 |
2003年 | 57篇 |
2002年 | 52篇 |
2001年 | 29篇 |
2000年 | 19篇 |
1999年 | 10篇 |
1998年 | 13篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 15篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 23篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1981年 | 5篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有2258条查询结果,搜索用时 15 毫秒
121.
A novel self-oscillating polymer was prepared by utilizing the Belousov-Zhabotinsky (BZ) reaction. In this study, a sulfonic acid group was newly introduced as a pH-control site into the copolymer of N-isopropylacrylamide, and the ruthenium complex was introduced as a catalyst site. By introducing the pH-control site, we succeed in causing the soluble-insoluble self-oscillation of the polymer solution under acid-free conditions in which only two BZ substrates, malonic acid and sodium bromate, were present as added agents. The self-oscillating behavior was remarkably influenced by the temperature and polymer concentration, which reflects the intermolecular aggregative capacity of the polymer chains in the reduced state to change the lower critical solution temperature. This achievement of self-oscillation of polymer chains under acid-free conditions may lead to their practical use as novel biomimetic materials under biological conditions. 相似文献
122.
Preparation of Sr2CeO4:Eu3+,Dy3+ white luminescence phosphor particles and thin films by using an emulsion liquid membrane system 总被引:3,自引:0,他引:3
Sr(2)CeO(4) and Sr(2)CeO(4):Eu(3+),Dy(3+) phosphor particles and thin films were prepared by using an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system, containing VA-10 (2-methyl-2-ethylheptanoic acid) as extractant (cation carrier). A two-step extraction enabled efficient extraction for Sr(3+) and rare earth ions, and the resulting precursor metal oxalate particles produced in the internal water phase of the ELM system were about 60 nm in diameter. Calcination of the oxalate particles in air gave submicrometer-sized Sr(2)CeO(4) and Sr(2)CeO(4):Eu(3+),Dy(3+) particles, which showed blue and white luminescence, respectively, by UV excitation. Blue and white luminescence phosphor thin films were also prepared by soaking alumina substrates into the W/O emulsion containing precursor oxalate particles, followed by calcination in air. 相似文献
123.
Dr. Ayumi Hirano‐Iwata Yutaka Ishinari Dr. Hideaki Yamamoto Prof. Michio Niwano 《化学:亚洲杂志》2015,10(6):1266-1274
Ion channel proteins provide gated pores that allow ions to passively flow across cell membranes. Owing to their crucial roles in regulating transmembrane ion flow, ion channel proteins have attracted the attention of pharmaceutical investigators as drug targets for use in the studies of both therapeutics and side effects. In this review, we discuss the current technologies that are used in the formation of ion channel‐integrated bilayer lipid membranes (BLMs) in microfabricated devices as a potential platform for next‐generation drug screening systems. Advances in BLM fabrication methodology have allowed the preparation of BLMs in sophisticated formats, such as microfluidic, automated, and/or array systems, which can be combined with channel current recordings. A much more critical step is the integration of the target channels into BLMs. Current technologies for the functional reconstitution of ion channel proteins are presented and discussed. Finally, the remaining issues of the BLM‐based methods for recording ion channel activities and their potential applications as drug screening systems are discussed. 相似文献
124.
The infinite dilution activity coefficients of exactly athermal fluids were calculated by Monte Carlo simulation with hard-core models. The hard-core models used in this work were hard-sphere and hard-spherocylinder models. The Widom test particle method was adopted to calculate the residual chemical potentials of solutes in pure solvent and in pure solute solutions. The infinite dilution activity coefficients of solutes were obtained from the residual chemical potentials of solutes. The infinite dilution activity coefficients calculated by Monte Carlo simulation were compared with those of athermal terms in activity coefficient equations. Staverman–Guggenheim equation overestimates the activity coefficients. The deviations of activity coefficients increase with increasing the hard-core volume of solute. Flory–Huggins equation based on molar volume gives good results for the hard-spherocylinder systems. Elbro-FV equation gives good results for both the hard-sphere and hard-spherocylinder systems. 相似文献
125.
Yusuke Imai Atsushi Terahara Keitaro Matsui Nobuhiko Ueno 《European Polymer Journal》2009,45(3):630-3519
Transparent organic-inorganic nanocomposites were successfully synthesized from sulfonic acid-modified poly(bisphenol A carbonate) (SPC) and TiO2 or ZrO2 nanoparticles. The dispersibility of nanoparticles was significantly improved by both the surface treatment of nanoparticles with phosphoric acid 2-ethylhexyl esters (PAEH) and the introduction of a sulfonic acid moiety into the PC chain. It was found that in some cases, crystallization of the matrix caused a reduction in transparency. Efficient dispersion of nanoparticles and the absence of crystallization resulted in highly transparent nanocomposites with up to 42 wt% TiO2 and 50 wt% ZrO2 nanoparticles. The refractive indices of the nanocomposites based on SPC increased with the increasing amount of nanoparticles. Theoretical equation based on Maxwell-Garnett effective medium theory provided reasonably close estimation of the refractive indices to the experimentally observed values. The prepared nanocomposites had lower thermal stability than the host matrix polymers. 相似文献
126.
An 8-endo selective Friedel-Crafts cyclization of vinyloxirane 8 with Co2(CO)6-complexed benzeneacetylene was found to give poly-functional eight-membered cyclic compound 9 in high yields. 相似文献
127.
Kiyoshi Tanaka Yasuhiro Yamamoto Hiroto Obara Satoru Iwata 《Supramolecular chemistry》2013,25(4):347-352
5,15- cis -bis(Ureidophenyl)porphyrins have significant recognizing ability for p -benzoquinones through four-point hydrogen bonding. Although an unusual temperature-dependence of the complexation is observed with bis( N '-phenylureidophenyl) porphyrin, bis( N '-ethylureidophenyl)porphyrin shows a satisfactorily linear van't Hoff plot and recognizes an electron-rich p -benzoquinone such as tetramethyl- p -benzoquinone more effectively, which is ascribed to the large enthalpy change in the complex. 相似文献
128.
Fullerene epoxides, C??O(n), having epoxide groups directly attached to the fullerene cage, constitute an interesting class of fullerene derivatives. In particular, the chemical transformations of fullerene epoxides are expected to play an important role in the development of functionalized fullerenes. This is because such transformations can readily afford a variety of mono- or polyfunctionalized fullerene derivatives while conserving the epoxy ring arrangement on the fullerene surface, as seen in representative regioisomeric fullerene polyepoxides. The first part of this review addresses the synthesis and structural characterization of fullerene epoxides. The formation of fullerene epoxides through different oxidation reactions is then explored. Adequate characterization of the isolated fullerene epoxides was achieved by concerted use of NMR and LC-MS techniques. The second part of this review addresses the substitution of fullerene epoxides in the presence of a Lewis acid catalyst. Most major substitution products have been isolated as pure compounds and their structures established through spectroscopic methods. The correlation between the structure of the substitution product and the oxygenation pattern of the starting materials allows elucidation of the mechanistic features of this transformation. This approach promises to lead to rigorous regioselective production of various fullerene derivatives for a wide range of applications. 相似文献
129.
Thomas TD Püttner R Fukuzawa H Prümper G Ueda K Kukk E Sankari R Harries J Tamenori Y Tanaka T Hoshino M Tanaka H 《The Journal of chemical physics》2007,127(24):244309
The boron 1s photoelectron spectrum of (11)BF(3) has been measured at a photon energy of 400 eV and a resolution of about 55 meV. The pronounced vibrational structure seen in the spectrum has been analyzed to give the harmonic and anharmonic vibrational frequencies of the symmetric stretching mode, 128.1 and 0.15 meV, as well as the change in equilibrium BF bond length upon ionization, -5.83 pm. A similar change in bond length has been observed for PF(3) and SiF(4), but a much smaller change for CF(4). Theoretical calculations for BF(3) that include the effects of electron correlation give results that are in reasonable accord with the experimental values. The Lorentzian (lifetime) width of the boron 1s core hole in BF(3) is found to be 72 meV, comparable to the value of 77 meV that has been reported for CF(4). 相似文献
130.
Kiyoshi Tanaka Tohru Kurushima Satoru Iwata Syunsuke Shimada 《Journal of heterocyclic chemistry》2007,44(2):303-307
2‐(3,4,5,6‐Tetrafluoro‐2‐hydroxyphenyl)imidazo[1,2‐a]pyridine ( 1 ) emits long wavelength light around 540 nm both in polar and in nonpolar solvents. Zn2+ perchlorate in acetonitrile causes the intermediate wavelength emission around 430 nm, which is ascribed to the species where the imidazole nitrogen atom and the phenolate oxygen atom bridge Zn2+. In the presence of Hg2+ and Al3+ perchlorates, short wavelength emission around 370 nm is strongly increased and this fluorescent enhancement is attributable not to the coordination of Hg2+ and Al3+ to 1 but to the formation of the salt of perchloric acid of 1 . 相似文献