全文获取类型
收费全文 | 1091篇 |
免费 | 29篇 |
国内免费 | 2篇 |
专业分类
化学 | 756篇 |
晶体学 | 9篇 |
力学 | 29篇 |
数学 | 40篇 |
物理学 | 288篇 |
出版年
2021年 | 9篇 |
2020年 | 24篇 |
2019年 | 15篇 |
2018年 | 6篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 14篇 |
2014年 | 16篇 |
2013年 | 34篇 |
2012年 | 45篇 |
2011年 | 58篇 |
2010年 | 31篇 |
2009年 | 26篇 |
2008年 | 56篇 |
2007年 | 61篇 |
2006年 | 57篇 |
2005年 | 60篇 |
2004年 | 64篇 |
2003年 | 42篇 |
2002年 | 38篇 |
2001年 | 44篇 |
2000年 | 27篇 |
1999年 | 22篇 |
1998年 | 12篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 17篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1976年 | 12篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1969年 | 7篇 |
1967年 | 6篇 |
排序方式: 共有1122条查询结果,搜索用时 375 毫秒
121.
Ohyanagi T Nagahori N Shimawaki K Hinou H Yamashita T Sasaki A Jin T Iwanaga T Kinjo M Nishimura S 《Journal of the American Chemical Society》2011,133(32):12507-12517
Glycans are expected to be one of the potential signal molecules for controlling drug targeting/delivery or long-term circulation of biopharmaceuticals. However, the effect of the carbohydrates of artificially glycosylated derivatives on in vivo dynamic distribution profiles after intravenous injection of model animals remains unclear due to the lack of standardized methodology and a suitable platform. We report herein an efficient and versatile method for the preparation of multifunctional quantum dots (QDs) displaying common synthetic glycosides with excellent solubility and long-term stability in aqueous solution without loss of quantum yields. Combined use of an aminooxy-terminated thiol derivative, 11,11'-dithio bis[undec-11-yl 12-(aminooxyacetyl)amino hexa(ethyleneglycol)], and a phosphorylcholine derivative, 11-mercaptoundecylphosphorylcholine, provided QDs with novel functions for the chemical ligation of ketone-functionalized compounds and the prevention of nonspecific protein adsorption concurrently. In vivo near-infrared (NIR) fluorescence imaging of phosphorylcholine self-assembled monolayer (SAM)-coated QDs displaying various simple sugars (glyco-PC-QDs) after administration into the tail vein of the mouse revealed that distinct long-term delocalization over 2 h can be achieved in cases of QDs modified with α-sialic acid residue (Neu5Ac-PC-QDs) and control PC-QDs, while QDs bearing other common sugars, such as α-glucose (Glc-PC-QDs), α-mannose (Man-PC-QDs), α-fucose (Fuc-PC-QDs), lactose (Lac-PC-QDs), β-glucuronic acid (GlcA-PC-QDs), N-acetyl-β-D-glucosamine (GlcNAc-PC-QDs), and N-acetyl-β-D-galactosamine (GalNAc-PC-QDs) residues, accumulated rapidly (5-10 min) in the liver. Sequential enzymatic modifications of GlcNAc-PC-QDs gave Galβ1,4GlcNAc-PC-QDs (LacNAc-PC-QDs), Galβ1,4(Fucα1,3)GlcNAc-PC-QDs (Le(x)-PC-QDs), Neu5Acα2,3Galβ1,4GlcNAc-PC-QDs (sialyl LacNAc-PC-QDs), and Neu5Acα2,3Galβ1,4(Fucα1,3)GlcNAc-PC-QDs (sialyl Le(x)-PC-QDs) in quantitative yield as monitored by direct matrix-assisted laser desorption ionization time-of-flight mass spectrometry analyses. Live animal imaging uncovered for the first time that Le(x)-PC-QDs also distributed rapidly in the liver after intravenous injection and almost quenched over 1 h in similar profiles to those of LacNAc-PC-QDs and Lac-PC-QDs. On the other hand, sialyl LacNAc-PC-QDs and sialyl Le(x)-PC-QDs were still retained stably in the whole body after 2 h, while they showed significantly different in vivo dynamics in the tissue distribution, suggesting that structure/sequence of the neighboring sugar residues in the individual sialyl oligosaccharides might influence the final organ-specific distribution. The present results clearly visualize the evidence of an essential role of the terminal sialic acid residue(s) for achieving prolonged in vivo lifetime and biodistribution of various glyco-PC-QDs as a novel class of functional platforms for nanomaterial-based drug targeting/delivery. A standardized protocol using multifunctional PC-QDs should facilitate live animal imaging of ligand-displayed QDs using versatile NIR fluorescence photometry without influence of size-dependent accumulation/excretion pathway for nanoparticles (e.g., viruses) >10 nm in hydrodynamic diameter by the liver. 相似文献
122.
Urea compounds are useful anion sensors due to their hydrogen-bonding capabilities. We investigated the emissive properties of complexes consisting of urea-anthracene (nPUA, n = 1, 2) host compounds and acetate anions held as guests through intermolecular hydrogen bonding. The kinetics of a new emission band formed by conformational changes in the excited singlet state were revealed. The new band is thought to arise from a charge-transfer interaction between the anthracene and urea moieties after intermolecular hydrogen-bond reconfiguration in the excited state, with rate constants of 2.4 × 10(9) and 4.0 × 10(7) s(-1) for 1PUA and 2PUA, respectively. 相似文献
123.
124.
Role of base in the formation of silver nanoparticles synthesized using sodium acrylate as a dual reducing and encapsulating agent 总被引:1,自引:0,他引:1
Nishimura S Mott D Takagaki A Maenosono S Ebitani K 《Physical chemistry chemical physics : PCCP》2011,13(20):9335-9343
The formation mechanism of Ag nanoparticles (NPs) synthesized with a wet-chemical reduction method using sodium acrylate as a dual reducing and capping agent was investigated with various analytical techniques. The time course of the state of the reaction solution was investigated using UV-vis and XAFS spectroscopies which showed that the NP formation rate increased with increasing concentration of sodium hydroxide (NaOH). The detailed kinetic analyses reveal that both the reduction rate of Ag ions and the nucleation rate of Ag NPs are dramatically increased with increasing NaOH concentration. XANES analyses imply that another reaction pathway via alternative Ag(+) species, such as Ag(OH)(x), was developed in the presence of NaOH. Consequently, NaOH is found to play an important role not only in creating specific intermediates in the reduction of Ag(+) to Ag(0), but also in accelerating the reduction and nucleation rates by enhancing the oxidation of sodium acrylate, thereby increasing the rate of formation of the Ag NPs. 相似文献
125.
126.
Masayuki Nishimura 《Journal of Optical and Fiber Communications Reports》2005,2(2):115-139
In order to meet the requirements necessary for advanced optical fiber transmission schemes that enable larger transmission capacity, higher efficiency and/or lower transmission costs per bit, optical fiber technologies are still evolving toward ultimate performance. Recent developmental activities have realized a number of improved performance optical fibers, such as ultra-low loss or ultra-low nonlinearity fibers and various types of dispersion-modified fibers. Fiber-based dispersion compensators or dispersion compensating fibers have also become one of the most essential optical components that support high-speed large capacity optical transmission. Very recently, the dispersion compensating fibers have further evolved into dispersion-managed optical transmission lines, which are now being actually deployed in transoceanic submarine optical cable networks. 相似文献
127.
We propose, in this paper, a unified method of generating a regularized integral equation in the double layer potential approach for 3D anisotropic elastodynamics. Our regularization preserves the causality in the time-domain. The method is based on a special decomposition of the hypersingular kernel which appears in the integral representation of the stress tensor. 相似文献
128.
Yukihiro Okada Manabu Mizutani Fuyuhiko Ishii Jun Nishimura 《Tetrahedron letters》1997,38(52):5347-9016
The modification of title compounds to chiral receptors and their characterization are reported. The two synthetic methods were developed. The racemates obtained could be resolved to each stable enantiomer by a chiral HPLC column. Chiral calixarenes were designed as the receptors with planar chirality. The (−)-receptor strongly forms 1:1 complex with (R)-(+)--phenylethylammonium picrate. 相似文献
129.
Yuzuru Hayashi Rieko Matsuda Katsutoshi Ito Waka Nishimura Kazuhiro Imai Masako Maeda 《Analytical sciences》2005,21(2):167-169
This paper theoretically derives a general rule that while the slope of the semi-logarithmic plot (Y vs. log X) of a calibration curve varies depending on analyte concentration, X, the slope takes a specific value at the detection limit (L(D)). This rule holds good irrespective of the shape of the calibration curve (linear or non-linear) and in this paper, is applied to competitive ELISA (enzyme linked immunosorbent assay). The following relationship is deduced: slope of log-dose B/B0 at L(D) = [relative standard deviation (RSD) of blank responses] / 0.13. The L(D) obtained from the above-mentioned slope corresponds to the dose at which the RSD of dose estimates is 0.3 (= 30%). A commercial kit for 17alpha-hydroxyprogesterone is taken as an example. 相似文献
130.
Yoshio Tanigawa Kazuaki Nishimura Akihiko Kawasaki Shun-Ichi Murahashi 《Tetrahedron letters》1982,23(52):5549-5552
Allyl diethyl phosphates (1) can be easily substituted with malonates and amines in the presence of palladium(O) catalyst. Synthetic utility of the reaction is demonstrated by the sequential amination-amination and alkylation-amination of (Z)-4-acetoxybut-2-enyl diethyl phosphate (1b) with high regio- and stereoselectivity. 相似文献