全文获取类型
收费全文 | 358篇 |
免费 | 11篇 |
国内免费 | 58篇 |
专业分类
化学 | 356篇 |
物理学 | 71篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 15篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 13篇 |
2013年 | 26篇 |
2012年 | 29篇 |
2011年 | 26篇 |
2010年 | 15篇 |
2009年 | 23篇 |
2008年 | 22篇 |
2007年 | 30篇 |
2006年 | 32篇 |
2005年 | 24篇 |
2004年 | 29篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1985年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
排序方式: 共有427条查询结果,搜索用时 390 毫秒
1.
Tomcík P Jencusová P Krajcíková M Bustin D Brescher R 《Analytical and bioanalytical chemistry》2005,383(5):864-868
An interdigitated microelectrode array (IDA) was applied to the determination of formaldehyde released from textiles produced
in industry. The proposed method is based on formaldehyde reaction with hypobromite which is formed in weakly basic media
by control current electrooxidation of bromide on the generator segment of the IDA array. The unreacted hypobromite diffuses
through the gap between individually polarisable IDA segments and it is amperometrically detected on the collector segment
of the IDA. The efficiency of this nonconvective transfer process in the absence of formaldehyde was substantially higher
(78%) in comparison with that when using the rotating ring disc electrode. The influence of the added formaldehyde on the
transfer process can be utilised to develop a simple and sensitive analytical procedure for formaldehyde detection with a
detection limit of 4×10−6 mol dm−3. 相似文献
2.
Flow-injection spectrofluorometric determination of trace amounts of formaldehyde in water after derivatization with acetoacetanilide 总被引:1,自引:0,他引:1
A novel fluorophotometric method for formaldehyde determination in environmental waters was developed: the method does not require any enrichment procedures. A flow-injection analysis method for the spectrofluorometric determination of formaldehyde in waters, which is based on the reaction of formaldehyde with acetoacetanilide and ammonia, is proposed. The proposed method shows a good linearity from 0.50 to 40 × 10−7 M, and the limit of detection (LOD) of 3 × 10−9 M (0.09 ppb) is achievable. The sample throughput is 15 h−1. One of the main advantages in the proposed method is that the reaction can be carried out at room temperature without any heating system. The effect of various interferences possibly present in the real water samples was investigated. Most cations and anions, as well as organic compounds, do not interfere with the determination of formaldehyde in environmental water samples. The proposed method is very simple, rapid, less expensive, and highly sensitive, and can be applied to the environmental water samples, such as rain, tap water and river water, at low concentration levels without any enrichment procedure. 相似文献
3.
对甲醛单分子热反应模拟给出了分子渠道Eckart垒,计算了该渠道在不同温度下的隧道校正因子,研究了分子渠道与游离基渠道间的相互作用,计算了存在反应渠道间相互作用时各渠道的K_(uni)(i)、Ea(i),分子渠道考虑隧道效应,而游离基渠道无隧道效应,计算结果与实验结果一致。 相似文献
4.
工业氨基三甲叉膦酸中副产物的核磁共振分析 总被引:1,自引:0,他引:1
采用多种核磁共振(NMR)技术测定了工业氨基三甲叉膦酸(ATMP)产品中副产物的分子结构,发现该物质为甲氨基二甲叉膦酸(MADMP),它是甲醛歧化反应导致的副产物;给出了可能的反应方程式;测出了MADMP的相对含量,MADMP与ATMP摩尔比约为2。 相似文献
5.
Vnira R. Akhmetova Guzel R. Nadyrgulova Tat'yana V. Tyumkina Mikhail Yu. Antipin Usein M. Dzhemilev 《Tetrahedron》2007,63(47):11702-11709
Cyclocondensation of aliphatic diamines with CH2O and H2S (1:3:2 ratio, 0 °C) was carried out to give thiadiazabicyclanes and dithiadiazabicyclanes (1:6:4 ratio), which were previously difficult to synthesize. Symmetric α,ω-bis-1,3,5-dithiazinanes were synthesized at 80 °C by this reaction. The stereochemistry of thiadiazabicyclanes was assigned by 1H and 13C NMR spectroscopy and by theoretical DFT calculations, and of bis-dithiazinanes by X-ray diffraction study in the solid state. 相似文献
6.
催化光度法测定痕量甲醛 总被引:24,自引:2,他引:24
基于磷酸介质中甲醛催化溴酸钾氧化溴甲酚紫的褪色反应 ,建立了测定痕量甲醛的方法。方法的检出限为 1.0× 10 - 5g·L- 1,线性范围为 0 .0 2 0~ 0 .4 8μg·ml- 1,方法简便 ,用于空气中测定痕量甲醛 ,结果满意。 相似文献
7.
Dimitrios V. Stergiou Spyros C. Karkabounas Panayotis G. Veltsistas Nicholaos P. Evmiridis Athanasios G. Vlessidis 《Mikrochimica acta》2007,158(1-2):59-64
A kinetic-potentiometric method is described for the quantitative assay of formaldehyde (HCHO) in pharmaceutical and industrial
preparations. It is based on the reaction of HCHO with (ethylenediamine)-Cu(II)-sulfate [Cu(CH2NH2)2(H2O)2] · SO4. The changes in potential, resulting from the release of the Cu(II) cations, are monitored with a Cu(II)-ion selective electrode.
The calibration curve for the HCHO is linear in the concentration range 50–250 mg L−1, with a limit of detection of 8.5 mg L−1. The method shows very good reproducibility with an RSD of 2.6% for successive injections (n = 5) of 150 mg L−1 HCHO primary solution, while it is interference free. The method was successfully tested in various industrial and pharmaceutical
preparations. 相似文献
8.
Continuous chemiluminescence determination of formaldehyde in air based on Trautz-Schorigin reaction 总被引:1,自引:0,他引:1
A new continuous method for the determination of formaldehyde in air is described. A cylindrical wet effluent diffusion denuder is used for the collection of formaldehyde from air into a thin film of absorption liquid (distilled-deionized water). Formaldehyde in the denuder concentrate is on-line detected employing a chemiluminescence flow method based on a reaction of formaldehyde and gallic acid with hydrogen peroxide in an alkaline solution. The collection efficiency of formaldehyde is quantitative at the air flow rate of 0.5 L min−1 (absorption liquid flow rate of 336 μL min−1). The limit of detection (S/N = 3) is 0.60 μg m−3 HCHO (0.49 ppb). The calibration graph is linear up to 300 μg m−3 HCHO (244 ppb). The relative standard deviations of chemiluminescence method for 1 × 10−6 and 5 × 10−6 M HCHO are 2.87% and 1.49%, respectively. Acetaldehyde interferes negligible, other compounds do not interfere. The method was employed for formaldehyde measurement in ambient air. The comparison measurement illustrates the good agreement of results obtained by proposed method with those obtained by reference fluorimetric method. 相似文献
9.
Summary The electronically excited states of formaldehyde are examined by means of multiconfigurational second-order perturbation (CASPT2) theory with extended ANO-type basis sets. The calculations comprised five valence excited states plus all singlet 3s, 3p, and 3d members of the Rydberg series converging on the first ionization. The computed vertical excitation energies were found to be within 0.2 eV of the available experimental energies. Full geometry optimization has been performed for five valence excited states. Assuming a planar geometry, the 0-0 transition for the valence1A1( *) state is calculated to appear near 7.9 eV, close to the (n
y
3p) region. This state is, however, not planar and the true adiabatic energy is 7.4 eV, which is 2.3 eV below the corresponding vertical transition. 相似文献
10.
Parameters are developed for a practical application of the empirical van der Waals (vdW) correction infrastructure available in the CPMD density functional theory (DFT) code. The binding energy, geometry, and potential energy surface (PES) are examined for methane, ethane, ethylene, formaldehyde, ammonia, three benzene dimer geometries, and three benzene–water geometries. The vdW corrected results compare favorably with MP2 and CCSD(T) calculations near the complete basis set limits, and with experimental results where they are available. 相似文献