全文获取类型
收费全文 | 4087篇 |
免费 | 157篇 |
国内免费 | 23篇 |
专业分类
化学 | 2764篇 |
晶体学 | 34篇 |
力学 | 155篇 |
综合类 | 1篇 |
数学 | 399篇 |
物理学 | 914篇 |
出版年
2024年 | 16篇 |
2023年 | 27篇 |
2022年 | 185篇 |
2021年 | 194篇 |
2020年 | 144篇 |
2019年 | 133篇 |
2018年 | 161篇 |
2017年 | 113篇 |
2016年 | 159篇 |
2015年 | 154篇 |
2014年 | 159篇 |
2013年 | 307篇 |
2012年 | 251篇 |
2011年 | 280篇 |
2010年 | 157篇 |
2009年 | 140篇 |
2008年 | 148篇 |
2007年 | 169篇 |
2006年 | 127篇 |
2005年 | 133篇 |
2004年 | 84篇 |
2003年 | 78篇 |
2002年 | 70篇 |
2001年 | 71篇 |
2000年 | 53篇 |
1999年 | 58篇 |
1998年 | 27篇 |
1997年 | 27篇 |
1996年 | 43篇 |
1995年 | 40篇 |
1994年 | 27篇 |
1993年 | 31篇 |
1992年 | 33篇 |
1991年 | 40篇 |
1990年 | 19篇 |
1989年 | 20篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 38篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1978年 | 27篇 |
1977年 | 27篇 |
1976年 | 18篇 |
1968年 | 10篇 |
排序方式: 共有4267条查询结果,搜索用时 15 毫秒
991.
A simple and rapid spectrophotometric method has been investigated for the determination of furosemide. The method is based upon simple diazotization reaction. The absorbance was measured at 480 nm. The method is optimized for acidity, amount of reagents required and heating time. The range of linearity was 0.4–10 μg mL?1 of furosemide with molar absorptivity of 1.0 × 104 l mol?1 cm?1. Standard deviation, coefficient of variance, limit of detection and limit of quantification were calculated using authentic standard of furosemide and were found to ± 0.0013,12.7%, 0.16 ppm and 0.52 ppm, respectively. The method was applied to various pharmaceutical preparations containing furosemide. The results of the investigated method for furosemide were compared with available official literature method. The results obtained by the proposed method agree well with the standard established method. 相似文献
992.
Heather Davis Walter Skrzypek Arshad Khan 《Journal of polymer science. Part A, Polymer chemistry》1994,32(12):2267-2274
The iodine binding capacity (IBC) of amylopectin (AP, from potatoes) is determined to be around 0.38% (w/w) of the total AP in the solution. The mass of iodine bound comprises about 13.6% of the mass of AP involved with the complex, suggesting that with every four iodine atoms bound there are 23 anhydroglucose residues (AGU). Since our previous study indicates that four iodine atoms within the helix of 11 AGUs form a chromophore unit in the API complex, only 48% of the AGUs (11 out of 23) in the AP molecule are directly involved with the iodine. The heat of reaction for the API complex formation is determined to be around ?47 kJ/mol of I–I units bound and is significantly lower in magnitude than that of the amylose-iodine (AI) complex [Biopolymers, 31 , 57 (1991)]. A possible mechanism has been proposed for the formation of AI and API complexes with fixed compositions. © 1994 John Wiley & Sons, Inc. 相似文献
993.
Illicium verum Hook. f. is used as an herbal tea to treat colic pain in infants. Reports suggest that Star anise herbal tea may be adulterated with Illicium anisatum Linn. A short and rapid method using microscopy and gas chromatography (GC) was developed to detect I. anisatum Linn., an adulterant in the powdered mixture of I. verum. Anatomical differences in the epicarp cells of I. verum and I. anisatum fruits were clearly defined as examined under fluorescent microscopy and scanning electron microscopy. A GC method was developed for quick identification of possible I. anisatum adulteration with I. verum. 相似文献
994.
A highly oxygenated, novel pentacyclic bis-oxa-bridged compound 8 was synthesized with remarkable efficiency starting from readily available tetrachloro-5,5-dimethoxyclopentadiene and 1,4-cyclohexadiene in three steps. The ruthenium-catalyzed oxidation of 2:1 bis-adduct 1 followed by a one-pot transformation of the resulting bis-alpha-diketone 3 furnished (after esterification) the title compound in an overall yield of 29.1%. The versatility of this simple method was further demonstrated with other norbornyl alpha-diketones to obtain the corresponding strained oxa-bridged derivatives. 相似文献
995.
The role of anion-exchange resin beads in the initiation of reactions of tertiary amines with 2,4-dinitrophenylhydrazine has been explored. This reagent has been used for the selective detection and determination of aliphatic amines. Radiochemical studies have been performed to show that the coloured species is adsorbed but not exchanged on ion-exchange beads. A model for the interaction is proposed. 相似文献
996.
V. Lange M. A. Khan U. Eichmann W. Sandner 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,18(4):319-324
We report on the spectroscopy of highly excited strontium ions after resonant multistep laser excitation. The states observed belonged to then s (26≦n≦79),n d (25≦n≦83),n f (28≦n≦86) andn g (30≦n≦81) series of Sr+. A least squares fit has been applied to determine the quantum defects and their linear energy dependence in each series, together with the ionisation limit of Sr+. The analysis of our data lead to a revised value for this ionisation limit of 88 965.18±0.02 cm?1, with respect to the ground state of the Sr+ ion. Analysis of the non core-penetratingn g states yielded experimental values for the dipole and quadrupole polarizability of Sr++, which are in satisfactory agreement with previous calculations. 相似文献
997.
Atul N. Jadhav Chidananda Swamy Rumalla Bharathi Avula Ikhlas A. Khan 《Chromatographia》2007,66(9-10):797-800
Naturally occurring 20-hydroxyecdysone is an important anabolic ecdysteroid. A simple thin-layer chromatography method to quantitate 20-hydroxyecdysone in methanolic extract of the whole plant material of Sida rhombifolia L. was developed. This method was successfully applied for quantitative evaluation of dietary supplements. The separation was achieved on glass TLC plates coated with silica gel 60F254, using chloroform: methanol (8:2 v/v) as developing solvent. Densitometric evaluation of 20-hydroxyecdysone was performed at 250 nm in reflectance/absorbance mode. The calibration was in the range of 200–1,000 ng spot?1 and correlation coefficient for the calibration curve was >0.999. In addition, for six different Sida species unique fingerprints were obtained on the HPTLC plate. 相似文献
998.
M. M. Taqui Khan Debabrata Chatterjee H. C. Bajaj 《Reaction Kinetics and Catalysis Letters》1993,49(1):81-85
Selective oxidation of cyclohexane to cyclohexanone was carried out in a RuCl3-pyridine-acetic acid-KHSO5 mixture. This system yields 2.8% of cyclohexanone (based on oxone concentration) under the conditions employed. Mechanistic postulate for the oxidation reaction involves the formation of a carbene intermediate (Ru=C) prior to the ketone formation. 相似文献
999.
1000.
The disappearance of collective flow effects in heavy ion collisions is investigated using a microscopic optical model formalism for estimating collision momentum transfers. Phenomenological expressions for the balance energy are obtained which agree very well with measurements for various experimental collision pairs and with results obtained from Boltzmann-Uehling-Uhlenbeck simulations. 相似文献