全文获取类型
收费全文 | 101236篇 |
免费 | 18640篇 |
国内免费 | 11378篇 |
专业分类
化学 | 69665篇 |
晶体学 | 1185篇 |
力学 | 6527篇 |
综合类 | 715篇 |
数学 | 11595篇 |
物理学 | 41567篇 |
出版年
2024年 | 368篇 |
2023年 | 2160篇 |
2022年 | 3589篇 |
2021年 | 3705篇 |
2020年 | 4244篇 |
2019年 | 3898篇 |
2018年 | 3574篇 |
2017年 | 3267篇 |
2016年 | 5073篇 |
2015年 | 4914篇 |
2014年 | 5973篇 |
2013年 | 7595篇 |
2012年 | 9193篇 |
2011年 | 9373篇 |
2010年 | 6295篇 |
2009年 | 6204篇 |
2008年 | 6671篇 |
2007年 | 5872篇 |
2006年 | 5568篇 |
2005年 | 4461篇 |
2004年 | 3532篇 |
2003年 | 2816篇 |
2002年 | 2742篇 |
2001年 | 2385篇 |
2000年 | 1976篇 |
1999年 | 2122篇 |
1998年 | 1784篇 |
1997年 | 1699篇 |
1996年 | 1674篇 |
1995年 | 1415篇 |
1994年 | 1225篇 |
1993年 | 1073篇 |
1992年 | 898篇 |
1991年 | 820篇 |
1990年 | 678篇 |
1989年 | 535篇 |
1988年 | 393篇 |
1987年 | 329篇 |
1986年 | 340篇 |
1985年 | 278篇 |
1984年 | 156篇 |
1983年 | 119篇 |
1982年 | 102篇 |
1981年 | 61篇 |
1980年 | 45篇 |
1979年 | 18篇 |
1974年 | 1篇 |
1957年 | 31篇 |
1936年 | 6篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Dong L Liu YC Tong YH Xiao ZY Zhang JY Lu YM Shen DZ Fan XW 《Journal of colloid and interface science》2005,283(2):380-384
Colloidal ZnO particles with narrow size distribution were prepared via a sol-gel process by base-catalyzed hydrolysis of zinc acetate. The morphology of ordered arrays of the particles was recorded by SEM. SEM also reveals that these uniform particles were composed of tiny ZnO subunits (singlets) sized of several nanometers. The size of the singlets, which is confirmed by X-ray diffraction and UV-vis absorption spectra, increases as the aging time is prolonged. The size-selective formation of colloids by aggregation of nanosized subunits is proposed to consist of two-stage growth by nucleation of nanosized crystalline primary particles and their subsequent aggregation into polycrystalline secondary colloids. The aggregates are all spherical because the internal rearrangement processes are fast enough. The ZnO colloids, i.e., the aggregates, tend to self-assemble into well-ordered hexagonal close-packed structures. Room-temperature photoluminescence was characterized for green and aged ZnO. 相似文献
922.
A strategy for design of bioimprinted proteins with glutathione peroxidase (GPX) activity has been proposed. The proteins imprinted with a glutathione derivative were converted into selenium-containing proteins by chemical modifying the reactive hydroxyl groups of serines followed by sodium hydrogen selenide displacement. These selenium-containing proteins exhibited remarkable GPX activities and the GPX activities of reduction of H2O2 by glutathione (GSH) were found to be 101-817 U μmol−1, which approaches the activity of a selenium-containing catalytic antibody elicited by a hapten similar to our template. The steady state kinetic study for imprinted protein catalysis revealed Michaelis-Menten kinetics for both H2O2 and GSH, e.g. the pesudo-first-order rate constant kcat (H2O2) and the apparent Michaelis constant Km (H2O2) at 1 mM GSH were calculated to be 784 min−1 and 1.24×10−3 M, respectively, and the apparent second-order rate constant kcat (H2O2)/Km (H2O2) was determined to be 6.33×105 (M min)−1. The kinetics and the template inhibition showed that the strategy might be a remarkably efficient one for generating artificial enzyme with GPX activity. 相似文献
923.
Affinity enrichment of plasma membrane for proteomics analysis 总被引:6,自引:0,他引:6
Proteomics analysis of plasma membranes from cells exposed to different extracellular environments is potentially a powerful approach for the identification of membrane-associated proteins responding to these environments. Preparation of high concentration plasma membrane fractions with low contamination from cellular organelles is essential for such studies. Here, we describe an affinity enrichment method, which combines cell surface biotinylation with affinity enrichment by immobilized streptavidin beads, for the isolation of plasma membranes. This method results in a 400-fold enrichment of plasma membrane relative to endoplasmic reticulum, a major contaminant in standard plasma membrane preparations, and dramatically reduces contamination from other cellular organelles. The biotinylation reaction did not interfere with ligand-dependent activation of receptor tyrosine kinases or G-protein coupled receptors, suggesting cell-surface signal transduction machinery remains functional. Membrane fractions prepared by this method should provide excellent starting materials for membrane proteomics analysis such as studies of dynamic trafficking and regulation of signaling molecules or identification of disease-specific membrane markers. 相似文献
924.
Lu Chengxue Yu Xiufang Zhang Honglin 《Journal of Thermal Analysis and Calorimetry》1997,48(2):327-329
The hydrolytic polymerization of Cr3+ at relatively high concentrations was studied by microcalorimetry. The thermal curves were determined with a 2277 thermal activity monitor. From the curves, the identified reaction heats (δrH m σ ), hydrolysis constants (K) and thermodynamic functions (δrS m σ ,δrH m σ ) were calculated at different temperatures. 相似文献
925.
硫酸颜色反应用于荧光法测定利血平研究 总被引:6,自引:1,他引:6
提出了硫酸颜色反应用于利血平的荧光分析新方法。利用血平与浓硫酸反应,生成强荧光物质,所得产物的荧光强度与利血平的浓度在0-0.6μg/mL范围内有良好的线性关系。检测限为0.2ng/mL。本法可直接用于尿液中利血平的定量分析,回收率为82.5%-84.2%。 相似文献
926.
The carbohydrate chains decorating cell membranes and secreted proteins participate in a range of important biological processes. However, their ultimate significance and possible therapeutic potential have not been fully explored due to the lack of economical methods for their production. This study is an example of the use of a genetically engineered bacterial strain in the preparation of diverse oligosaccharides. Based on an ex vivo biosynthetic pathway, an artificial gene cluster was constructed by linking the genes of five associated enzymes on a plasmid vector. This plasmid was inserted into the E. coli NM522 strain to form globotriose-producing cells ('superbug' pLDR20-CKTUF). The specific strain was conveniently applied to the synthesis of globotriose trisaccharide and its derivatives, as potential neutralizers for Shiga toxin. This work demonstrates a novel and economical method for generating ligand diversity for carbohydrate drug development. 相似文献
927.
Xiong C Zhang J Davis P Wang W Ying J Porreca F Hruby VJ 《Chemical communications (Cambridge, England)》2003,(13):1598-1599
Novel constrained beta-turn dipeptide mimetics, 8-phenyl thiaindolizidinone amino acids 3, have been synthesized stereoselectively and incorporated into Leu-enkephalin peptides as a replacement of dipeptide Gly3-Phe4 to afford four individual isomers of Leu-enkephalin analogues 6. 相似文献
928.
Mao-fengZhang Qiao-hongYao Chun-huiHuang Wei-xiaoCao 《高分子科学》2005,(1):27-27
A kind of azo-containing resin (Azo-R) was synthesized by a simple way through the coupling reaction of 2-nitro-N-methyldiphenylamine-4-diazoresin (NDR) with phenol, and a new covalentely attached multilayer film from Azo-R as H-donor and photosensitive diazoresin, diphenylamine-4-diazoresin (DR) as H-acceptor via H-bonding attraction by selfassembly technique has been fabricated. Following the decomposition of diazonium group of DR under exposure to UV light, the H-bonds between the layers of the film convert to covalent bonds and the film becomes very stable toward polar solvents or electrolyte aqueous solutions. Thus the UV-irradiated azo-containing films can be used to measure photocurrent in a conventional three-electrode photoelectrochemical cell using KCl as supporting electrolyte. It was confirmed that the azo-containing multilayer film is responsible for the photocurrent generation. 相似文献
929.
Helseth LE Muruganathan R Zhang Y Fischer TM 《Langmuir : the ACS journal of surfaces and colloids》2005,21(16):7271-7275
We investigate the self-assembly of colloidal particles on microscopic decane droplets in water and show that, by use of paramagnetic colloids, it is possible to assemble ringlike structures that can be controlled with a magnetic field. Moreover, the use of paramagnetic colloids allows us to determine the attractive forces between the colloids located at the three-phase contact line between decane, water, and air. The attractive force is in the femtonewton range and is attributed to capillary interactions due to interface deformations. When the liquid emulsion dries on a glass slide, we observe solid deposits in the form of microscopic rings of varying diameters. 相似文献
930.
Menger FM Zhang H Caran KL Seredyuk VA Apkarian RP 《Journal of the American Chemical Society》2002,124(7):1140-1141
A gemini surfactant is able to promote columnar jointing in vitreous ice where long pillars, often of hexagonal cross section, are formed. This jointing is visible by cryo-high-resolution scanning electron microscopy (cryo-HRSEM), in which colloidal suspensions in bulk water are cooled rapidly in liquid ethane, thereby avoiding the potential artifacts with other types of EM. The jointing is proposed to arise from a new type of colloidal morphology where the surfactant self-assembles into hexagonal columns. Evidence for this mechanism comes from a cryo-HRSEM photo of an ice-free hexagonal "skeleton" composed of surfactant. Cryo-HRSEM, a method that is just beginning to realize its potential, would seem to have a promising future in the discovery of additional and as yet unimagined colloidal structures. 相似文献