全文获取类型
收费全文 | 9344篇 |
免费 | 1483篇 |
国内免费 | 1290篇 |
专业分类
化学 | 7199篇 |
晶体学 | 151篇 |
力学 | 497篇 |
综合类 | 77篇 |
数学 | 923篇 |
物理学 | 3270篇 |
出版年
2024年 | 54篇 |
2023年 | 208篇 |
2022年 | 390篇 |
2021年 | 398篇 |
2020年 | 475篇 |
2019年 | 480篇 |
2018年 | 347篇 |
2017年 | 385篇 |
2016年 | 449篇 |
2015年 | 486篇 |
2014年 | 544篇 |
2013年 | 732篇 |
2012年 | 809篇 |
2011年 | 849篇 |
2010年 | 599篇 |
2009年 | 525篇 |
2008年 | 620篇 |
2007年 | 510篇 |
2006年 | 451篇 |
2005年 | 384篇 |
2004年 | 281篇 |
2003年 | 250篇 |
2002年 | 284篇 |
2001年 | 200篇 |
2000年 | 175篇 |
1999年 | 147篇 |
1998年 | 113篇 |
1997年 | 108篇 |
1996年 | 111篇 |
1995年 | 111篇 |
1994年 | 105篇 |
1993年 | 88篇 |
1992年 | 60篇 |
1991年 | 52篇 |
1990年 | 48篇 |
1989年 | 53篇 |
1988年 | 30篇 |
1987年 | 35篇 |
1986年 | 30篇 |
1985年 | 46篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 5篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
Beatty KE Xie F Wang Q Tirrell DA 《Journal of the American Chemical Society》2005,127(41):14150-14151
We describe fluorescence labeling of newly synthesized proteins in Escherichia coli cells by means of Cu(I)-catalyzed cycloaddition between alkynyl amino acid side chains and the fluorogenic dye 3-azido-7-hydroxycoumarin. The method involves co-translational labeling of proteins by the non-natural amino acids homopropargylglycine (Hpg) or ethynylphenylalanine (Eth) followed by treatment with the dye. As a demonstration, the model protein barstar was expressed and treated overnight with Cu(I) and 3-azido-7-hydroxycoumarin. Examination of treated cells by confocal microscopy revealed that strong fluorescence enhancement was observed only for alkynyl-barstar treated with Cu(I) and the reactive dye. The cellular fluorescence was punctate, and gel electrophoresis confirmed that labeled barstar was localized in inclusion bodies. Other proteins showed little fluorescence. Examination of treated cells by fluorimetry demonstrated that cultures supplemented with Eth or Hpg showed an 8- to 14-fold enhancement in fluorescence intensity after labeling. Addition of a protein synthesis inhibitor reduced the emission intensity to levels slightly above background, confirming selective labeling of newly synthesized proteins in the bacterial cell. 相似文献
143.
Yang Q Xu ZK Hu MX Li JJ Wu J 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10717-10723
Cell surface carbohydrates, usually binding with other biomacromolecules (such as lipids and proteins), are involved in numerous biological functions, including cellular recognition, adhesion, cell growth regulation, and inflammation. Synthetic carbohydrate-based polymers, so-called glycopolymers, are emerging as important well-defined tools for investigating carbohydrate-based biological processes and for simulating various functions of carbohydrates. In this study, a novel two-step sequence for the generation of a glycopolymer layer tethered on a polypropylene microporous membrane is described. First, a UV-induced graft polymerization of 2-aminoethyl methacrylate hydrochloride (AEMA) was carried out on the membrane to generate an amino-functionalized surface, and the effects of polymerization factors (monomer/initiator concentration and UV irradiation time) on the grafting density were studied. Second, sugar moieties were bound with the grafted functional layer to form glycopolymer by the reaction between the amino groups on the membrane surface and carbohydrate lactones. Chemical analysis by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy combined with surface morphology observation by scanning electron microscopy confirmed the graft polymerization of AEMA and the formation of glycopolymer. The decreases of water contact angle and protein adsorption on the membrane revealed the enhancement of hydrophilicity and protein resistance due to the typical characteristics of the glycopolymer tethered on the surface. These results indicated that the novel sequence reported in this work is a facile process to form glycopolymer-modified surfaces. 相似文献
144.
Jun Dai Liqiang Xu Zengli Fang Daopeng Sheng Qingfeng Guo Zeyu Ren Kang Wang Yitai Qian 《Chemical physics letters》2007,440(4-6):253-258
Straight boron nitride nanotubes (BNNTs) with pure hexagonal phase were conveniently prepared by heating the mixture of Mg(BO2)2 · H2O, NH4Cl, NaN3 and Mg powder in an autoclave at 600 °C for 20–60 h. These BNNTs had diameters mainly ranging 30–300 nm and lengths up to 5 μm, and a majority of them had at least one closed end. Besides the traditional end tips, additional cone-like tips were frequently found to be attached on the BNNTs. The effects of temperature, reactants and the possible mechanism of the catalytic formation of the BNNTs are discussed. 相似文献
145.
Reactions of bis(trifluoromethyl)nitroxyl with a number of methyl- and trifluoromethyl- substituted arsines and stibines at room temperature lead to the formation of pentavalent arsenic and antimony derivatives, namely (CH3)3?n(CF3)nM[ON(CF3)2]2 (M = As, n = 0, 1, 2; M = Sb, n = 0, 1). The derivatives yield bis(trifluoromethyl)- hydroxylamine and the corresponding dichlorides on treatment with hydrogen chloride. A free radical mechanism is proposed for the oxidative addition reactions. 相似文献
146.
Polymer-stabilized noble metal colloids were efficiently immobilized on silica by the addition of organic acids under mild conditions. The function of organic acids in the immobilization was studied by infrared spectroscopy. Transmission electron micrographs indicate that the immobilized colloids have a controlled particle size and size distribution. They serve as catalysts in the hydrogenation of cyclohexene and cyclopentadiene, the results of which show that this new type of immobilized colloid has high selectivity and good stability. 相似文献
147.
IntroductionItiswellknownthatyttriumcanbeusedinmanyfields ,suchasmetallurgy ,ceramics ,lasersandelectron ics ,especiallyinfluorescentmaterialswhoseneedforhighpurityyttriumoxideisincreasing .InChina ,there sourceofyttriumisrich ,andthehighpureyttriumisbe ingo… 相似文献
148.
149.
S.H. LiuX.F. Qian J. YinL. Hong X.L. WangZ.K. Zhu 《Journal of solid state chemistry》2002,168(1):259-262
Ag2S nanoparticles in hyperbranched polyurethane matrix were prepared through the in situ reaction with thioacetamide as the sulfur source at room temperature. Transmission electron microscopic analysis revealed a uniform spherical shape for Ag2S nanoparticles, with an average size of about 4-10 nm and a narrow size distribution. X-ray powder diffraction and UV-vis spectroscopy were also used to characterize the obtained nanoparticles 相似文献
150.
QianWANG XuXU 《中国化学快报》2003,14(12):1278-1280
The mixtures of two polymers, poly (N,N-dimethylacrylamide) (PDMA) and polyvinylpyrrolidone (PVP) were synthesized and used as the separation medium for double-stranded and single-stranded DNA fragments by capillary electrophoresis with UV detector. On optimal conditions, 2%w/v PDMA 2%w/v PVP can be used to separate the doublet 123/124bp in pBR322/Hae Ⅲ Markers. 相似文献