首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   260篇
  免费   11篇
化学   188篇
晶体学   3篇
力学   10篇
数学   3篇
物理学   67篇
  2023年   3篇
  2022年   2篇
  2021年   3篇
  2020年   7篇
  2019年   5篇
  2018年   1篇
  2017年   1篇
  2016年   6篇
  2015年   7篇
  2014年   7篇
  2013年   7篇
  2012年   8篇
  2011年   10篇
  2010年   4篇
  2009年   11篇
  2008年   7篇
  2007年   15篇
  2006年   19篇
  2005年   13篇
  2004年   16篇
  2003年   10篇
  2002年   11篇
  2001年   9篇
  2000年   6篇
  1999年   1篇
  1998年   4篇
  1996年   4篇
  1995年   4篇
  1994年   7篇
  1993年   4篇
  1992年   4篇
  1991年   8篇
  1990年   2篇
  1989年   5篇
  1988年   3篇
  1987年   3篇
  1986年   5篇
  1985年   2篇
  1984年   3篇
  1983年   3篇
  1982年   5篇
  1981年   1篇
  1980年   6篇
  1979年   1篇
  1978年   4篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
排序方式: 共有271条查询结果,搜索用时 171 毫秒
101.
102.
We used near infrared (NIR) spectroscopy to evaluate the degree of mixing of blended dry syrup (DS) products whose particle sizes are not specified in the Revised 16th Edition of the Japanese Pharmacopoeia, and also evaluated the degree of mixing when powder products or fine granule products were added to DS products. The data obtained were used to investigate the relationship between the particle size distributions of the products studied and the degree of mixing. We found that the particle size distribution characteristics of the 15 DS products studied can be broadly classified into 5 types. Combinations of frequently prescribed products were selected to represent 4 of the 5 particle size distribution types and were blended with a mortar and pestle. The coefficient of variation (CV) decreased as the percent mass of Asverin? Dry Syrup 2% (Asverin-DS) increased in blends of Periactin? Powder 1% (Periactin) and Asverin-DS, indicating an improved degree of mixing (uniformity). In contrast, in blends of Periactin and Mucodyne? DS 33.3%, mixing a combination at a 1:1 mass ratio 40 times resulted in a CV of 20%. Other mixing frequencies and mass ratios resulted in a CV by 50% to 70%, indicating a very poor degree of mixing (poor uniformity). These results suggest that when combining different DSs, or a DS with a powder or fine granule product, the blending obtained with a mortar and pestle improves as the particle size distributions of the components approach each other and as the ranges of the distributions narrow.  相似文献   
103.
Abstract

KCr5Se8 has a TIV5S8-type structure, containing K ions in one-dimensional tunnels. Deintercalated samples of KxCr5Se8 (0.32 ≤ x ≤ 0.93) were prepared by leaching method using Alc3/FeCl3 aqueous solution. These samples showed a broad peak of magnetic susceptibility at ca. 130 K. 57Fe-Mössbauer spectra of Kx(Cr0.95 57Fe0.05)5Se8 (x = 1.0, 0.49) showed a quadrupole doublet at 300 K. Magnetic sextets appeared at 4.2 K in both samples, indicative of magnetic ordering. The observed isomer shift indicated that the charge of Fe is +3 in both samples. It was proposed that Se2- was partially oxidized by the deintercalation.  相似文献   
104.
A quasielastic neutron scattering and solid-state (2)H NMR spectroscopy study of the polymeric spin-crossover compound {Fe(pyrazine)[Pt(CN)(4)]} shows that the switching of the rotation of a molecular fragment--the pyrazine ligand--occurs in association with the change of spin state. The rotation switching was examined on a wide time scale (10(-13)-10(-3) s) by both techniques, which clearly demonstrated the combination between molecular rotation and spin-crossover transition under external stimuli (temperature and chemical). The pyrazine rings are seen to perform a 4-fold jump motion about the coordinating nitrogen axis in the high-spin state. In the low-spin state, however, the motion is suppressed, while when the system incorporates benzene guest molecules, the movements of the system are even more restricted.  相似文献   
105.
Reaction efficiencies of two organic alkalis, tetramethylammonium hydroxide (TMAH) and trimethylsulfonium hydroxide (TMSH), with lipids during thermally assisted hydrolysis and methylation (THM) were examined focusing on (1) the types of lipids and (2) degree of unsaturation of fatty acid moieties. Different types of lipids such as triglycerides, phospholipids, free fatty acids and cholesteryl esters containing saturated, monounsaturated or polyunsaturated fatty acid (PUFA) residues were subjected to THM-gas chromatography (GC) in the presence of TMAH or TMSH. The obtained results revealed that the THM reaction using TMAH allowed almost quantitative methylation of saturated and monounsaturated fatty acid components independently of the classes of lipids. However, strong alkalinity of TMAH brought about isomerization and/or degradation of PUFA components. In contrast, the use of TMSH was effective to highly sensitive detection of PUFA as well as saturated and monounsaturated fatty acid components contained in triglycerides, phospholipids (phosphatidylcholines) and free fatty acids. On the other hand, TMSH was proved to react hardly with any kind of fatty acid residues in cholesteryl esters due to their steric hindrance.  相似文献   
106.
We develop magnetic metallic contaminant detectors using high-temperature superconducting quantum interference devices (HTS-SQUIDs) for industrial products. Finding ultra-small metallic contaminants is an important issue for manufacturers producing commercial products such as lithium ion batteries. If such contaminants cause damages, the manufacturer of the product suffers a big financial loss due to having to recall the faulty products. Previously, we described a system for finding such ultra-smafi particles in food. In this study, we describe further developments of the system, for the reduction of the effect of the remnant field of the products, and we test the parallel magnetization of the products to generate the remnant field only at both ends of the products. In addition, we use an SQUID gradiometer in place of the magnetometer to reduce the edge effect by measuring the magnetic field gradient. We test the performances of the system and find that tiny iron particles as small as 50 × 50 μm^2 on the electrode of a lithium ion battery could be clearly detected. This detection level is difficult to achieve when using other methods.  相似文献   
107.
While the development of low‐molecular‐weight drugs is saturating, agents for photodynamic therapies (PDTs) may become alternative seeds in pharmaceutical industry. Among them, orally administrative, cancer‐selective, and side effect‐free photosensitizers (PSs) that can be activated by tissue‐penetrative near‐infrared (NIR) lights are strongly demanded. We discovered such a PS from scratch by focusing on a twist‐assisted spin‐orbit charge transfer intersystem crossing (ISC) mechanism in a biphenyl derivative, which was demonstrated by thorough photophysical studies. The unique ISC mechanism enables the PS to be small and slim so as to pass through glucose transporters and exert a PDT effect selectively on a cancer cell line. The smallness will allow for oral administration and fast clearance, which have been agenda of approved PSs with larger molecular weights. We also demonstrated that our PS was able to be activated with an NIR pulse laser through two‐photon excitation.  相似文献   
108.
We have performed precision atomic spectroscopy of trapped radioactive Be isotopes aiming at studies of the charge and magnetization radii of these nuclei especially for a single-neutron halo nucleus 11Be . Some experimental results and the status of the analysis are discussed.  相似文献   
109.
110.
Four monosaccharides (glucose, galactose, mannose and fructose) and one disaccharide (maltose) were subjected to high-performance liquid chromatography with UV or refractive index detection. Various profiles such as broad, tailed and splitted peaks were produced, depending on column temperature and eluent flow-rate because these saccharides underwent isomerization. In contrast, -methylglucoside, a non-converting derivative, always produced a sharp peak. By analyzing these profiles kinetic constants of the isomerization were obtained and compared with the literature data.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号