全文获取类型
收费全文 | 860篇 |
免费 | 44篇 |
国内免费 | 10篇 |
专业分类
化学 | 621篇 |
晶体学 | 5篇 |
力学 | 25篇 |
数学 | 138篇 |
物理学 | 125篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 13篇 |
2019年 | 35篇 |
2018年 | 14篇 |
2017年 | 8篇 |
2016年 | 27篇 |
2015年 | 35篇 |
2014年 | 37篇 |
2013年 | 60篇 |
2012年 | 71篇 |
2011年 | 59篇 |
2010年 | 34篇 |
2009年 | 38篇 |
2008年 | 60篇 |
2007年 | 54篇 |
2006年 | 45篇 |
2005年 | 36篇 |
2004年 | 39篇 |
2003年 | 38篇 |
2002年 | 29篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1968年 | 2篇 |
1966年 | 4篇 |
排序方式: 共有914条查询结果,搜索用时 15 毫秒
71.
A simple and fast method was developed to determine non-UV active compounds directly without derivatization. The usefulness of the method was demonstrated by detecting the major components in aminoglycoside antibiotic mixtures using capillary zone electrophoresis with potential gradient detection. Under optimized separation conditions (0.2 mM cetyltrimethylammonium bromide (CTAB), 1 mM ammonium citrate, pH 3.5), gentamicin was separated into three major peaks (C1, C1a, and C2+C2a) within 15 min. This method showed better sensitivity than other capillary electrophoresis (CE) methods for determining underivatized gentamicin. The linear range was from 10 to 500 ppm. Because of its good repeatability and simplicity, this new method could be a good alternative for the current assays given by US Pharmacopoeia and European Pharmacopoeia. 相似文献
72.
A portable chip-CE system with potential gradient detection (PGD) was developed and applied to the determinations of alkali metals and alkaloids. The separation efficiency appeared to be satisfactory and nonaqueous capillary electrophoresis (NACE) proved to be applicable to PGD or conductivity detection. The power supplies, separation and detection were built on a device of 3 kg in weight. A branch channel near the end of the separation channel was designed to perform PGD and make the application of relatively high field strength possible. The study is the first report on the application of PGD on the microchip platform. The design of the chip-CE system shows several advantages, such as simplicity, miniaturization and wide applicability. 相似文献
73.
Bis(peroxo)vanadium(V) complexes are widely investigated as anticancer agents. They exert their antitumor and cyctotoxic effects through inhibition of tyrosine phosphatases and DNA cleavage, respectively. The latter process remains poorly understood. The mechanism of DNA cleavage by NH(4)[(phen)V(O)(eta(2)-O(2))(2)] (phen = 1,10-phenanthroline) was investigated. Kinetic studies on DNA cleavage revealed that the complex is a single-strand nicking agent with no specificity. EPR experiments using 2,2,6,6-tetramethyl-4-piperidone (TMP) and 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO) as spin-traps for singlet oxygen and hydroxyl radical, respectively, implicated hydroxyl radical production upon photodecomposition of bis(peroxo)vanadium(V). This was corroborated by benzoate inhibition of DNA strand scission and stoichiometric oxidation of 2-propanol to acetone upon irradiation of bis(peroxo)vanadium(V) phenanthroline. High-resolution polyacrylamide gel analysis of the vanadium cleavage reaction and [Fe(II)EDTA](2)(-)/H(2)O(2) resulted in comigration of "ladder" pattern bands, which superimposed when both reactions were run on the same lane. These findings identify hydroxyl radical produced from the photooxidation of the peroxo ligand on vanadium as the active species in DNA cleavage. 相似文献
74.
Sam I. Ahonkhai
Andreas N
llePeter Behr
Horst Heydtmann 《Journal of photochemistry and photobiology. A, Chemistry》1994,80(1-3):389-392Experimental results are presented of a Fourier transform IR product study at 298 K of the reaction system CFO+O2 at oxygen pressures between 3 and 250 mbar. Pulsed photolysis of oxalyl fluoride (CFO)2 or formyl fluoride (CHFO) at 193 nm was used to produce CFO. As stable products we detected bis-fluoroformyl peroxide, carbonyl fluoride and carbon dioxide. The yields of the peroxide and of CF2O were measured as a function of [O2]/[precursor] and are discussed qualitatively. 相似文献
75.
A study on the determination of the antibiotic tobramycin by CE with capacitively coupled contactless conductivity detection is presented. This method enabled the direct quantification of the non-UV-absorbing species without incurring the disadvantages of the indirect approaches which would be needed for optical detection. The separation of tobramycin from inorganic cations present in serum samples was achieved by optimizing the composition of the acetic acid buffer. Field-amplified sample stacking was employed to enhance the sensitivity of the method and a detection limit of 50 microg/L (S/N = 3) was reached. The RSDs obtained for migration time and peak area using kanamycin B as internal standard were typically 0.12 and 4%, respectively. The newly developed method was validated by measuring the concentration of tobramycin in serum standards containing typical therapeutic concentrations of 2 and 10 mg/L. The recoveries were 96 and 97% for the two concentrations, respectively. 相似文献
76.
77.
From the stem bark of Albizzia julibrissin DURAZZ (Leguminosae), two new phenolic glycosides (albibrissinosides A and B) were isolated. Their structures were determined by spectroscopic analysis. The albibrissinoside B was found to be a radical scavenger on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. 相似文献
78.
We apply a variational wave function capable of describing qualitatively and quantitatively the so-called "resonating valence bond" (RVB) in realistic materials, by improving standard ab initio calculations by means of quantum Monte Carlo methods. In this framework we clearly identify the Kekulé and Dewar contributions to the chemical bond of the benzene molecule and establish the corresponding RVB energy of these structures (?0.01 eV/atom). We apply this method to unveil the nature of the chemical bond in undoped graphene, providing an estimate of the RVB energy gain, and show that this picture remains only within a small "resonance length" of a few atomic units. 相似文献
79.
It was demonstrated that separation of DNA fragments by a CE-contactless conductivity detection system (CE-CCD) could be enhanced with multiple-wall carbon nanotubes (MWCNs) as buffer additive. For HaeIII digest of PhiX174 DNA, optimized MWCN concentration was obtained when the MWCN was above its threshold concentration, at which MWCN could form a network in the buffer as pseudostationary phase to provide additional interaction sites. In the case of larger DNA, MWCN near or below its threshold concentration was enough to provide great improvement of the resolution, which was shown by the separation of the 2-Log DNA ladder. Furthermore, the buffer containing MWCN could provide a more stable baseline in the CE-CCD system, owing to less fluctuation of its conductivity. Compared with CE-UV, CE-CCD with MWCN could provide lower LODs as well as better resolution. 相似文献
80.