全文获取类型
收费全文 | 433篇 |
免费 | 27篇 |
国内免费 | 19篇 |
专业分类
化学 | 255篇 |
力学 | 33篇 |
数学 | 109篇 |
物理学 | 82篇 |
出版年
2023年 | 2篇 |
2022年 | 13篇 |
2021年 | 13篇 |
2020年 | 20篇 |
2019年 | 23篇 |
2018年 | 12篇 |
2017年 | 22篇 |
2016年 | 22篇 |
2015年 | 23篇 |
2014年 | 30篇 |
2013年 | 58篇 |
2012年 | 34篇 |
2011年 | 35篇 |
2010年 | 34篇 |
2009年 | 16篇 |
2008年 | 22篇 |
2007年 | 13篇 |
2006年 | 11篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1966年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有479条查询结果,搜索用时 62 毫秒
111.
Summary Statistical procedures to test that a life distribution is exponential against the alternative that it is harmonic new better
than used in expectation (HNBUE) are considered. 相似文献
112.
Shohreh Nafisi Fatemeh Ghoreyshi Kahangi Ebrahim Azizi Nader Zebarjad Heidar-Ali Tajmir-Riahi 《Journal of Molecular Structure》2007,830(1-3):182-187
Zanamivir (ZAN) is the first of a new generation of influenza virus-specific drugs known as neuraminidase inhibitors, which acts by interfering with life cycles of influenza viruses A and B. It prevents the virus spreading infection to other cells by blocking the neuraminidase enzyme present on the surface of the virus. The aim of this study was to examine the stability and structural features of calf thymus DNA and yeast RNA complexes with zanamivir in aqueous solution, using constant DNA or RNA concentration (12.5 mM) and various zanamivir/polynucleotide (P) ratios of 1/20, 1/10, 1/4, and 1/2. FTIR and UV–visible spectroscopy are used to determine the drug external binding modes, the binding constant and the stability of zanamivir–DNA and RNA complexes in aqueous solution. Structural analysis showed major interaction of zanamivir with G-C (major groove) and A-T (minor groove) base pairs and minor perturbations of the backbone PO2 group with overall binding constants of Kzanamivir–DNA = 1.30 × 104 M−1 and Kzanamivir–RNA = 1.38 × 104 M−1. The drug interaction induces a partial B to A-DNA transition, while RNA remains in A-conformation. 相似文献
113.
114.
Robinson DB Persson HH Zeng H Li G Pourmand N Sun S Wang SX 《Langmuir : the ACS journal of surfaces and colloids》2005,21(7):3096-3103
Magnetic MFe2O4 (M = Fe, Co, or Mn) nanoparticles with uniform diameters in the 4-20 nm range and with excellent material properties, reported previously, can be rendered soluble in water or aqueous buffers using a combination of alkylphosphonate surfactants and other surfactants such as ethoxylated fatty alcohols or phospholipids. Surfactant-modified oligonucleotides can be incorporated into the particles' organic shell. The particles can withstand salt concentrations up to 0.3 M, temperatures up to 90 degrees C, and various operations such as concentration to dryness, column or membrane separations, and electrophoresis. The particles can be selectively hybridized to DNA-functionalized gold surfaces with high coverages using a two-story monolayer structure. These particles may find valuable applications involving the magnetic detection of small numbers of biomolecules using spin valves, magnetic tunnel junctions, or other sensors. 相似文献
115.
Slices of T2-weighted and fat-suppressed images were obtained on a clinical scanner with the field strength of 1 T to identify various tissues, internal organs and structural details of a cyprinid fish (Cyprinus carpio). Different parts of pharyngeal and gastro-intestinal organs, liver and spleen were well distinguished. Kidneys were traced and the position of heart and its appendants such as bulbus arteriosus, ventral aorta and branchial arteries were identified. The images were confirmed by the corresponding slices of frozen fish. 相似文献
116.
We obtain an upper bound for the independent domination number of a graph in terms of the domination number and maximum degree. 相似文献
117.
118.
Nader Noshiranzadeh 《合成通讯》2013,43(18):3181-3189
A two‐component condensation reaction between an ortho‐hydroxy aromatic aldehyde and an electron‐poor acetylenic ester efficiently provides fully substituted electron‐poor aryl vinyl ethers and chromenes in a one‐pot reaction in the presence of silica‐gel in solvent‐free conditions. 相似文献
119.
Michael Aalinejad Nader Noroozi Pesyan Nosrat Heidari Hana Batmani Aria Danandeh Asl 《应用有机金属化学》2019,33(6)
Ni@diaza crown ether complex supported on magnetic nanoparticle was provided by grafting technique. The catalytic activity of Fe3O4@diaza crown ether@Ni was explored through one‐pot synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones and it was used as an efficient and recoverably constant nanocatalyst. FT‐IR, SEM, TEM, XRD, BET, ICP, EDS, and TGA techniques were employed to specify the nanocatalyst. This heterogeneous catalyst demonstrated acceptable recyclability and could be used again several times with no considerable loss of its catalytic activity. 相似文献
120.
DABCO (1,4‐diazabicyclo[2.2.2]octane)‐modified magnetite with silica‐MCM‐41 shell (Fe3O4@silica‐MCM‐41@DABCO) as an effective, magnetic and novel heterogeneous reusable nanocatalyst was synthesized and analysed using various techniques. Evaluation of the catalytic activity of this nanocatalyst was performed in the clean synthesis of substituted 2‐aminodihydropyrano[3,2‐b]pyran‐3‐cyano in high yields via in situ reaction of azido kojic acid, malononitrile and various aldehydes. 相似文献