全文获取类型
收费全文 | 4041篇 |
免费 | 166篇 |
国内免费 | 18篇 |
专业分类
化学 | 2815篇 |
晶体学 | 40篇 |
力学 | 95篇 |
数学 | 333篇 |
物理学 | 942篇 |
出版年
2024年 | 5篇 |
2023年 | 21篇 |
2022年 | 72篇 |
2021年 | 93篇 |
2020年 | 79篇 |
2019年 | 69篇 |
2018年 | 59篇 |
2017年 | 46篇 |
2016年 | 121篇 |
2015年 | 114篇 |
2014年 | 141篇 |
2013年 | 229篇 |
2012年 | 318篇 |
2011年 | 348篇 |
2010年 | 181篇 |
2009年 | 171篇 |
2008年 | 266篇 |
2007年 | 248篇 |
2006年 | 229篇 |
2005年 | 217篇 |
2004年 | 169篇 |
2003年 | 152篇 |
2002年 | 137篇 |
2001年 | 88篇 |
2000年 | 90篇 |
1999年 | 74篇 |
1998年 | 59篇 |
1997年 | 33篇 |
1996年 | 49篇 |
1995年 | 45篇 |
1994年 | 48篇 |
1993年 | 44篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 29篇 |
1989年 | 21篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有4225条查询结果,搜索用时 15 毫秒
991.
Chien-Hsin Yang Shyh-Jiun Liu Chia-Chin Chang Li-Ying Lin 《Journal of Electroanalytical Chemistry》2006,590(2):161-172
Electrochemical copolymerization of 3-trimethoxysilanyl-propyl-N-aniline (TMSPA) with 2,5-dimethoxyaniline (DMA) was performed in 1 M HCl aqueous solution for different feed ratios of TMSPA using cyclic voltammetry. The deposition rate of TMSPA–DMA copolymer is higher than that of PTMSPA but lower than that of PDMA. (TMSPA-co-DMA) film was deposited using electrochemical polymerization as conducting film on indium tin oxide (ITO) electrode and used as an electrode in an electrochromic device. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) was spin-coated on ITO as the other electrode. Carboxyl-terminated- butadiene-acrylonitrile (CTBN) blended with LiClO4 was used as solid polymer electrolyte. A total solid electrochromic device was assembled as follows: ITO|P(TMSPA-co-DMA)LiClO4-CTBNPEDOT:PSS|ITO. The columbic efficiency of the devices reached to 104% for P(TMSPA-co-DMA) film with TMSPA feed ratio of 0.25. The optical contrast (ΔT, %) of the single electrode and the device were determined by UV–vis spectroelectrochemical studies. The stability of ΔT was improved during color switching from +1.5 to −1.5 V (vs. PEDOT) for this device. The device was pale yellow at −1.5 V and blue at +1.5 V. 相似文献
992.
Kim JS Kim HJ Kim HM Kim SH Lee JW Kim SK Cho BR 《The Journal of organic chemistry》2006,71(21):8016-8022
1,3-Alternate calix[4]arene-based fluorescent chemosensors bearing two-photon absorbing chromophores have been synthesized, and their sensing behaviors toward metal ions were investigated via absorption band shifts as well as one- and two-photon fluorescence changes. Free ligands absorb the light at 461 nm and weakly emit their fluorescence at 600 nm when excited by UV-vis radiation at 461 nm, but no two-photon excited fluorescence is emitted by excitation at 780 nm. Addition of an Al(3+) or Pb(2+) ion to a solution of the ligand causes a blue-shifted absorption and enhanced fluorescence due to a declined resonance energy transfer (RET) upon excitation by one- and two-photon processes. Addition of a Pb(2+) ion to a solution of 1.K(+) results in a higher fluorescence intensity than the original 1.Pb(2+) complex regardless of one- or two-photon excitation, due to the allosteric effect induced by the complexation of K(+) with a crown loop. 相似文献
993.
Perylenetetracarboxylic diimide derivatives bearing 2- or 4-peripheral pyrrole pendants could be efficiently crosslinked to form an insoluble film either by electropolymerization or visible light induced oxidative photopolymerization of the pyrrole units. 相似文献
994.
Sessler JL Cho DG Stepień M Lynch V Waluk J Yoon ZS Kim D 《Journal of the American Chemical Society》2006,128(39):12640-12641
The synthesis of an inverted, methoxylated sapphyrin derivative is described. This system, wherein inversion of pyrrolic nitrogen atoms is configurationally enforced via the use of a 3,3'-bipyrrolic precursor, displays what is best described as "weak aromaticity" as judged from its spectroscopic features and supporting theoretical calculations. 相似文献
995.
Cho H Felmy AR Craciun R Keenum JP Shah N Dixon DA 《Journal of the American Chemical Society》2006,128(7):2324-2335
Evidence for nine new solution state silicate oligomers has been discovered by (29)Si NMR homonuclear correlation experiments of (29)Si-enriched samples. In addition to enhancing signal sensitivity, the isotopic enrichment increases the probability of the (29)Si-(29)Si two-bond scalar couplings that are necessary for the observation of internuclear correlations in 2-D experiments. The proposed assignments are validated by comparisons of experimental and simulated cross-peaks obtained with high digital resolution. The internuclear connectivity indicated by the NMR data suggests that several of these oligomers can have multiple stereoisomers, including conformers and/or diastereomers. The stabilities of these oligomers and their possible stereoisomers have been investigated by electronic structure calculations. 相似文献
996.
We introduce a novel and versatile approach for preparing self-assembled nanoporous multilayered films with tunable optical properties. Protonated polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and anionic polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films. BCM film growth is governed by electrostatic and hydrogen-bonding interactions between the opposite BCMs. Both film porosity and film thickness are dependent upon the charge density of the micelles, with the porosity of the film controlled by the solution pH and the molecular weight (M(w)) of the constituents. PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films prepared at pH 4 (for PS(7K)-b-P4VP(28K)) and pH 6 (for PS(2K)-b-PAA(8K)) are highly nanoporous and antireflective. In contrast, PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films assembled at pH 4/4 show a relatively dense surface morphology due to the decreased charge density of PS(2K)-b-PAA(8K). Films formed from BCMs with increased PS block and decreased hydrophilic block (P4VP or PAA) size (e.g., PS(36K)-b-P4VP(12K)/PS(16K)-b-PAA(4K) at pH 4/4) were also nanoporous. This is attributed to a decrease in interdigitation between the adjacent corona shells of the low M(w) BCMs, thus creating more void space between the micelles. Multilayer films with antireflective and photochromic properties were obtained by incorporating a water-insoluble photochromic dye (spiropyran) into the hydrophobic PS core of the BCMs assembled in the films. The optical properties of these films can be modulated by UV irradiation to selectively and reversibly control the transmission of light. Light transmission of higher than 99% was observed with accompanying photochromism in the (PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K)) multilayer films assembled at pH 4/6. Our approach highlights the potential to incorporate a range of materials, ranging from conventional hydrophilic materials with specific interactions to hydrophobic compounds, into the assembled BCMs to yield multifunctional nanoporous films. 相似文献
997.
The synthesis of a new series of 2,3-diindol-3'yl quinoxalines (DIQ), as well as a comparison of their anion recognition properties to those of our previously reported pyrrole based sensors, 2,3-dipyrrol-2'yl quinoxalines, is reported. To the best of our knowledge, this new DIQ system represents the first example of a free-standing indole-based small molecule receptor for which evidence of anion binding is available both in solution and in the solid-state. It also provides one of the few structurally characterized neutral receptor-dihydrogen phosphate complexes. This work thus serves to demonstrate the utility of indoles as an anion recognition motif. 相似文献
998.
Ragupathi G Koide F Livingston PO Cho YS Endo A Wan Q Spassova MK Keding SJ Allen J Ouerfelli O Wilson RM Danishefsky SJ 《Journal of the American Chemical Society》2006,128(8):2715-2725
Several novel, fully synthetic, carbohydrate-based antitumor vaccines have been assembled. Each construct consists of multiple cancer-related antigens displayed on a single polypeptide backbone. Recent advances in synthetic methodology have allowed for the incorporation of a complex oligosaccharide terminating in a sialic acid residue (i.e., GM2) as one of the carbohydrate antigens. Details of the vaccine synthesis as well as the results of preliminary immunological investigations are described herein. 相似文献
999.
Carrying out density functional theory calculations of four DNA bases, base derivatives, Watson-Crick (WC) base pairs, and multiple-layer base pair stacks, we studied vibrational dynamics of delocalized modes with frequency ranging from 1400 to 1800 cm(-1). These modes have been found to be highly sensitive to structure fluctuation and base pair conformation of DNA. By identifying eight fundamental basis modes, it is shown that the normal modes of base pairs and multilayer base pair stacks can be described by linear combinations of these vibrational basis modes. By using the Hessian matrix reconstruction method, vibrational coupling constants between the basis modes are determined for WC base pairs and multilayer systems and are found to be most strongly affected by the hydrogen bonding interaction between bases. It is also found that the propeller twist and buckle motions do not strongly affect vibrational couplings and basis mode frequencies. Numerically simulated IR spectra of guanine-cytosine and adenine-thymine bases pairs as well as of multilayer base pair stacks are presented and described in terms of coupled basis modes. It turns out that, due to the small interlayer base-base vibrational interactions, the IR absorption spectrum of multilayer base pair system does not strongly depend on the number of base pairs. 相似文献
1000.
[Structure: see text] Binding of fluoride anion as well as carboxylic acid tetraalkylammonium salts by macrocyclic compounds of different size was studied by NMR in DMSO-d6. It has been found that at least a 15-membered ring is necessary for successful recognition of fluoride. Larger macrocycles obtained in a [2+2] cyclization were shown to bind dicarboxylic acid salts. Effects of binding topicity are discussed. 相似文献