全文获取类型
收费全文 | 7566篇 |
免费 | 1154篇 |
国内免费 | 765篇 |
专业分类
化学 | 4952篇 |
晶体学 | 74篇 |
力学 | 463篇 |
综合类 | 46篇 |
数学 | 770篇 |
物理学 | 3180篇 |
出版年
2024年 | 28篇 |
2023年 | 157篇 |
2022年 | 214篇 |
2021年 | 210篇 |
2020年 | 274篇 |
2019年 | 234篇 |
2018年 | 218篇 |
2017年 | 208篇 |
2016年 | 320篇 |
2015年 | 312篇 |
2014年 | 392篇 |
2013年 | 537篇 |
2012年 | 576篇 |
2011年 | 626篇 |
2010年 | 428篇 |
2009年 | 429篇 |
2008年 | 456篇 |
2007年 | 391篇 |
2006年 | 391篇 |
2005年 | 360篇 |
2004年 | 291篇 |
2003年 | 214篇 |
2002年 | 234篇 |
2001年 | 183篇 |
2000年 | 178篇 |
1999年 | 187篇 |
1998年 | 145篇 |
1997年 | 147篇 |
1996年 | 169篇 |
1995年 | 120篇 |
1994年 | 126篇 |
1993年 | 112篇 |
1992年 | 109篇 |
1991年 | 84篇 |
1990年 | 66篇 |
1989年 | 77篇 |
1988年 | 53篇 |
1987年 | 48篇 |
1986年 | 38篇 |
1985年 | 34篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有9485条查询结果,搜索用时 15 毫秒
101.
102.
Gu Ping TANG Zhi Yu WANG 《中国化学快报》2006,17(1):113-116
The work described the synthesis and evaluation of PEI-g-comb-PEG-transferrin as a potential system for gene therapy in vitro. The MW of PEG was 10KDa, and PEI was 2KDa. Its structure was identified by NMR, FT-IR and TGA spectroscopy. MTT assay found that at concentration up to 4000 n mol/L of the polymer, cell viability was over 85%. The bio-character of polymer/DNA complex was characterized by agarose gel electrophoresis, ethidium bromide exclusion and zeta-potential assay. The polymer could retardate DNA at N/P ratio 3.0-3.5 (mol/mol). The particle size of the polymer/DNA complex was less than 300 nm. Transfection efficiency of the complex was studied in COS7 and NT2 cell lines. 相似文献
103.
The polymer bound Schiff‐base ligand (PS‐SalGlu) has been prepared from polystyrene bound salicylaldehyde and glutamic acid, and its complex (PS‐SalGlu‐Co) has also been synthesized. The polymer ligand and its complex were characterized by infrared spectroscopy, small area X‐ray photoelectron spectroscopy, and inductively coupled plasma‐atomic emission spectro (ICP‐AFS). In the presence of the complex, cyclohexene can be effectively oxidized by molecular oxygen without reductant. The long‐chain linear aliphatic olefins, such as 1‐octene, 1‐decene, 1‐dodecene and 1‐tetradecene, can be directly oxidized by molecular oxygen catalyzed by PS‐SalGlu‐Co, which affords the 1,2‐epoxy alkane. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
104.
Calpains are unique calcium-dependent thiol proteases that have been proposed to participate in a number of physiological processes including signal transduction and protein turnover in skeletal muscle. Calpains exist in two major forms. Interestingly, the two forms of protease show no significant difference in their action on various substrates. The only demonstrable difference in their activity involves the concentration of calcium required for activation. Both mu- and m-calpains typically achieve half maximal activation at 50 microM and 0.7 mM calcium, respectively. The focus of this study was to examine the action of both forms of calpain on casein substrates and assess whether any differences could be observed in the resulting peptide finger print using capillary electrophoresis. Purified mu- and m-calpain were incubated for various lengths of time with Oregon Green labeled alphas- and beta-casein. The reactions were stopped with sodium dodecyl sulfate (SDS) and products separated by capillary electrophoresis in micellar electrokinetic capillary chromatography (MEKC) mode using laser-induced fluorescence (LIF) detection. Comparison of the electropherograms showed no difference in the peptide profile for either enzyme. However, it was found that beta-casein was hydrolyzed more extensively than alphas-casein, by both enzymes. Capillary electrophoresis was found to be a very sensitive technique for detection of calpain activity. Using beta-casein as substrate, the CE approach was able to detect 2-3 ng of calpain activity. The results also suggest that capillary electrophoresis is a useful tool for proteolytic investigations of protein structure. 相似文献
105.
表面活性剂在非极性溶剂中形成的反胶束在催化反应、光化学、蛋白质苹取分离等方面有着广泛的应用问.这些应用与反胶束的性质有着密切的关系,而增溶水后的反胶束其形状和大小都会发生很大的变化.增溶不同水量的反胶束的微极性、酸碱性、微勤度等已有不少文献报导[2-5].一些不溶于非极性溶剂而溶于水的物质可以溶解在非极性溶剂中的反胶束核心水团中,这个现象被称为二次增溶.其中,电解质的二次增溶对于研究配体转换反应。酶催化反应问及改变反胶束内部的微环境有着十分重要的作用,Aebi和Weibush回首先研究了有水存在时N。CI在A… 相似文献
106.
107.
本文通过红外光谱(FT-IR)测量数据和预测数据,计算与研究了十九种长链正烷基脂肪酸(简称脂肪酸或碳酸)的碳链骨架振动能量。结果显示出脂肪酸的碳链骨架振动能量随碳数增加呈阶梯状关系,而且脂肪酸的碳链骨架振动能量∑E出现奇偶数更迭规律。此结果可用来解释脂肪酸的熔点或熔化热呈现奇偶数更迭现象。 相似文献
108.
A palladium-catalyzed silicon-aryl carbon bond formation on solid-phase is reported. A phenylalanine silane resin was prepared directly from protected iodo-substituted phenylalanine with butyl diethylsilane polystyrene in one step. A rapid and high-yield solid-phase synthesis of sansalvamide A peptide was achieved from the phenylalanine silane resin. [reaction: see text] 相似文献
109.
Peng CY Nam WJ Fonash SJ Gu B Sen A Strawhecker K Natarajan S Foley HC Kim SH 《Journal of the American Chemical Society》2003,125(31):9298-9299
We describe the use of hard etching methods to create nanodimensional channels and their use as templates for the formation of polymer filament arrays with precise dimensional and orientational control in a single integrated step. The procedure is general as illustrated by the radical, coordination, and photochemical polymerizations that were performed in these nanochannels. The nanochannel templates (20 nm high, 20-200 nm wide, and 100 mum long) were fabricated by the combined use of electron-beam lithography and a sacrificial metal line etching technique. Radical polymerization of acrylates, metal-catalyzed polymerization of norbornene, and photochemical polymerization of 1,4-diiodothiophene were carried out in these nanochannels. The polymers grown follow the dimensions and orientation of the channels, and the polymer filaments can be released without breaking. The approach opens up the possibility of just-in-place manufacturing and processing of patterns and devices from nanostructured polymers using well-established polymer chemistry. 相似文献
110.
P. Jing R. -N. Fu R. -J. Dai J. -L. Ge J. -L. Gu Z. Huang Y. Chen 《Chromatographia》1996,43(9-10):546-550