全文获取类型
收费全文 | 11176篇 |
免费 | 540篇 |
国内免费 | 144篇 |
专业分类
化学 | 8069篇 |
晶体学 | 96篇 |
力学 | 528篇 |
综合类 | 3篇 |
数学 | 1326篇 |
物理学 | 1838篇 |
出版年
2024年 | 28篇 |
2023年 | 98篇 |
2022年 | 498篇 |
2021年 | 469篇 |
2020年 | 414篇 |
2019年 | 491篇 |
2018年 | 519篇 |
2017年 | 401篇 |
2016年 | 664篇 |
2015年 | 466篇 |
2014年 | 633篇 |
2013年 | 1172篇 |
2012年 | 864篇 |
2011年 | 831篇 |
2010年 | 600篇 |
2009年 | 495篇 |
2008年 | 536篇 |
2007年 | 463篇 |
2006年 | 319篇 |
2005年 | 328篇 |
2004年 | 196篇 |
2003年 | 197篇 |
2002年 | 165篇 |
2001年 | 86篇 |
2000年 | 55篇 |
1999年 | 65篇 |
1998年 | 41篇 |
1997年 | 52篇 |
1996年 | 48篇 |
1995年 | 35篇 |
1994年 | 40篇 |
1993年 | 20篇 |
1992年 | 37篇 |
1991年 | 34篇 |
1990年 | 30篇 |
1989年 | 36篇 |
1988年 | 33篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 40篇 |
1984年 | 35篇 |
1983年 | 21篇 |
1982年 | 28篇 |
1981年 | 19篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
JPC – Journal of Planar Chromatography – Modern TLC - A water-in-oil microemulsion has been used for the first time as a mobile phase in thin-layer chromatography of amino acids. A new... 相似文献
62.
A. A. Fahad A. W. Ali R. M. Shihab 《Journal of Radioanalytical and Nuclear Chemistry》1989,130(1):195-201
Mobility of137Cs was investigated in columns of calcareous loam and clay soils leached under river water, NH4OAc, KCl, CaCl2, and EDTA. Fractionation of Cs into ten sequential fractions was accomplished in the leached soils as well as in soil samples received carrier-free137Cs and incubated for 60 d. At the end of 90 d of leaching with river water and CaCl2, the bulk of Cs applied (>97%) was found to remain in the upper 1 cm of soil columns. On the other hand, the reduction in Cs concentration was approximately 30% with NH4OAc, 18% with KCl, and 10 to 25% with EDTA. The major soil constituents appeared to be responsible for retaining Cs were clay, silt, and Fe oxides. The leaching consistently increased the magnitude of fractions bound to clay minerals and in most cases decreased the fractions of water soluble, exchangeable, carbonate, and organic matter. 相似文献
63.
The spectral properties of o-aminophenol, catechol, o-nitrophenol, pyrogallol, salicylic acid and gallic acid were investigated in different solvents. The behaviour of hydrogen bonding demonstrated in these systems was discussed. 相似文献
64.
65.
Ali Elriati Karin Achilles Jutta Loose Hans-Hartwig Otto 《Monatshefte für Chemie / Chemical Monthly》2007,76(5):627-634
4-Phenylazetidine-2-one was transformed into 4-phenylazetidine-1-alkanoic acids, which were reacted in the presence of diphenylphosphoroazidate
with amino acid esters and dipeptide esters yielding β-lactam peptides with different spacers between the lactam ring and
the peptide moiety. All structures were established by elementary analyses, HPLC, optical rotation, and spectroscopic data
and all new compounds were tested as inhibitors of PPE using standard procedures. Four compounds exhibited a weak activity compared with the standard inhibitor trifluoroacetyl-l-val-l-tyr-l-val. 相似文献
66.
Syed Mashhood Ali Santosh Kumar Upadhyay Arti Maheshwari 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(3-4):351-355
Desloratadine (DES) is an antihistamine used in the treatment of allergies and chronic urticaria. 1H NMR spectroscopic study of varying ratios of DES and β-Cyclodextrin (β-CD) in D2O suggests the formation of a 1:1 inclusion complex formed by the penetration of Cl-substituted aromatic ring into the β-CD
cavity. The stoichiometry and binding constant of the complex were determined by Scott’s method. 相似文献
67.
Rahman Hosseinzadeh Ali Sharifi Kourosh Tabar-Heydar Farshid Mohsenzadeh 《Monatshefte für Chemie / Chemical Monthly》2002,133(11):1413-1415
Summary. N,N-Dimethylhydrazones of ketones and aldehydes undergo facile cleavage to the corresponding carbonyl compounds upon exposure
to microwaves in water containing a catalytic amount of PdCl2–SnCl2 in high yields.
Corresponding authors. E-mail: rahman@umz.ac.ir
Received December 27, 2001. Accepted (revised) February 6, 2002 相似文献
68.
Marine brown alga Dictyota dichotoma (Dictyotaceae) collected from Karachi coast of Arabian Sea yielded two new (1 and 2) enones (dolastane-diterpenoids) named: dichotenone-A and -B along with an olide (loliolide, 3) as a new source. Their structures have been characterized with the aid of 2D-NMR spectroscopic techniques. 相似文献
69.
Flow injection chemiluminescence determination of hydrazine by oxidation with chlorinated isocyanurates 总被引:1,自引:0,他引:1
A rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of hydrazine based on the CL generated during its reaction with either sodium dichloroisocyanurate (SDCC) or trichloroisocyanuric acid (TCCA) in alkaline medium. The emission intensity is greatly enhanced if dichlorofluorescein (DCF) as sensitizer is present in the reaction medium. The presence of citrate prevents the precipitation of some cations in the reaction medium and also causes an enhancement in emission intensity. The effect of analytical and flow injection variables on these CL systems and determination of hydrazine are discussed. The optimum parameters for the determination of hydrazine were studied and were found to be the following: SDCC and TCCA both 1x10(-3) M; NaOH, 2x10(-1) M; DCF, 5x10(-6) M; citrate, 1x10(-3) M and flow rate, 3.8 ml min(-1). The optimized method yielded 3sigma detection limits of 2x10(-7) and 3x10(-7) M for hydrazine with SDCC and TCCA oxidants, respectively. The method is simple, fast, sensitive, and precise and was applied to the determination of hydrazine in water samples. 相似文献
70.
The oxidation of some xylenols with iodine in aqueous ethanolic solutions in the presence of silver ions as a catalyst was investigated and used for microdetermination of these reductants. The study of these redox reactions and the microdetermination of these phenols were performed by volumetric and spectrophotometric methods. These methods were compared. The spectrophotometric method was more accurate at very low concentrations (60–488 μg). The volumetric methods used silver ions as catalyst. The potentiometric method is more accurate than the visual method. Possible schemes for the course of these redox reactions were suggested. One electron processes for oxidation of xylenols have been indicated. 相似文献