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11.
Chusaksri S Sutthivaiyakit S Sutthivaiyakit P 《Analytical and bioanalytical chemistry》2006,384(5):1236-1245
A confirmatory method for the determination of organochlorine pesticides (OCPs) and their metabolites (endrin, α-endosulfan,
β-endosulfan, endosulfan sulfate, heptachlor, heptachlor epoxide, 2,4′-DDD, 4,4′-DDD, 2,4′-DDE 4,4′-DDE, 2,4′-DDT, and 4,4′-DDT)
in surface waters using liquid chromatography /APCI/tandem mass spectrometry has been developed. Chromatographic separation
was carried out on a ChromSpher 5 Pesticide column using a gradient elution with mobile phase 1mM ammonium acetate-acetonitrile.
Endrin, α-endosulfan, β-endosulfan , endosulfan sulfate, heptachlor and heptachlor epoxide were determined in the negative
ionization mode, while the rest compounds in positive ionization mode. For the identification of the analytes, two multireaction
monitoring transitions were selected per compounds except for the heptachlor which selected ion monitoring was used. The linearity
of the optimized method ranges after SPE concentration, from 0.009 to 30.60 μgL−1 with correlation coefficients greater than 0.99. The method recovery values varied from 72 to 119 % for the different fortification
levels . The developed method was successfully applied to determine OCPs and their metabolites in surface water samples collected
near paddy fields in growing season of rice, at year 2005 in Pathumthani province, Thailand. Endosulfan sulfate was detected
in five out of seven samples and three of them could be quantitated in the range of 0.31to 0.50 μgL−1. 相似文献
12.
Franziska Hufsky Martin Rempt Florian Rasche Georg Pohnert Sebastian Böcker 《Analytica chimica acta》2012
The automated fragmentation analysis of high resolution EI mass spectra based on a fragmentation tree algorithm is introduced. Fragmentation trees are constructed from EI spectra by automated signal extraction and evaluation. These trees explain relevant fragmentation reactions and assign molecular formulas to fragments. The method enables the identification of the molecular ion and the molecular formula of a metabolite if the molecular ion is present in the spectrum. These identifications are independent of existing library knowledge and, thus, support assignment and structural elucidation of unknown compounds. The method works even if the molecular ion is of very low abundance or hidden under contaminants with higher masses. We apply the algorithm to a selection of 50 derivatized and underivatized metabolites and demonstrate that in 78% of cases the molecular ion can be correctly assigned. The automatically constructed fragmentation trees correspond very well to published mechanisms and allow the assignment of specific relevant fragments and fragmentation pathways even in the most complex EI-spectra in our dataset. This method will be very helpful in the automated analysis of metabolites that are not included in common libraries and it thus has the potential to support the explorative character of metabolomics studies. 相似文献
13.
The use of temporary tethers in facilitating meta photocycloaddition reactions between phenol and allyl alcohol derivatives has been investigated. The merits of silicon, carbonate and methylene acetal tethers were assessed, whilst considering strategies for the preparation of the natural products gymnomitrol and gelsemine. The photoadducts were epoxidised, and then subjected to acid catalysed fragmentation with concomitant cleavage of the tether. Depending on whether water or methanol was used during the fragmentation stage of the methylene tethers, the methylene group was either removed altogether or transformed into a MOM group. 相似文献
14.
Amino acid methyl ester phosphates were synthesized and determined by using positive-ion mode electrospray ionization mass spectrometry(ESIMS) in combination with multistage tandem mass spectrometry. The fragmentation pathways were investigated, and it was observed that most fragment ions contained the phosphoryl group. It was interesting to observe that the fragmentation pathways of the protonated molecule show some differences when compared with those of the sodium ion adduct. The methoxy group of amino acid methyl ester can migrate from the carbonyl group to the phosphoryl group in the sodium ion adduct. 相似文献
15.
JIAO Peng ZHANG Qi-han XU Jia-xi+{**} Key Laboratory of Bioorganic Chemistry Molecular Engineering of Ministry of Education College of Chemistry Molecular Engineering Peking University Beijing China 《高等学校化学研究》2006,(6)
IntroductionN,N′-Bis [1-( hydroxymethyl) alkyl] dicarboxa-mides are important intermediates for the syntheses ofbis-oxazolines, which are a class of the most importantand widely used ligands in catalytic asymmetric reac-tions[1,2]. On determining the str… 相似文献
16.
Yu ZhaoHong-Bin Zhang Ji-Kai LiuJia Su Yan LiZhu-Jun Yao Qin-Shi Zhao 《Tetrahedron letters》2011,52(1):139-142
Two interesting unprecedented fragmentations of 13-oxo-taxyunnansin A (3), initiated by treatment with tBuOK and Red-Al, respectively, have been discovered, optimized and successfully applied to the synthesis of novel abeo-paclitaxel and abeo-docetaxel derivatives. Eight new derivatives of abeo-paclitaxel and abeo-docetaxel possessing the structurally simplified 11 (15→1)-abeo-taxane skeleton with an oxetane ring and π bond conjugate system were accordingly prepared for the further evaluation of anticancer activities. 相似文献
17.
Simultaneous identification and analysis of cassane diterpenoids in Caesalpinia minax Hance by high‐performance liquid chromatography with quadrupole time‐of‐flight mass spectrometry 下载免费PDF全文
Shilong Wu Zhaohua Wu Chaofan Fu Caiyue Wu Jiuzhi Yuan Xiaoyan Xian Huiyuan Gao 《Journal of separation science》2015,38(23):4000-4013
Cassane diterpenoids were successfully and simultaneously identified in Caesalpinia minax Hance by high‐performance liquid chromatography coupled with quadrupole time‐of‐flight tandem mass spectrometry. A total of 59 peaks were detected, and among them 51 compounds, including 41 furanocassane diterpenoids, 10 furanolactone cassane diterpenoids were simultaneously identified and characterized on the basis of the protonated molecule, retention behavior, and fragments in MS2. Ten compounds, including seven novel compounds, were identified or tentatively identified for the first time in C. minax. In a positive ion mode, the fragmentation pathways of cassane diterpenoids were also analyzed for the first time. The relative amounts of the five main diterpenoids (caesalpinin L, caesalpinin F2, bondcellpin C, caesalpinin E, and ξ‐caesalmin) were simultaneously quantified by high‐performance liquid chromatography. Results showed that the newly discovered and known components of C. minax can be used to determine the material basis of bioactivity; this method can also be applied to analyze cassane diterpenoids in herbal medicines from the genus Caesalpinia belonging to the family Fabaceae. 相似文献
18.
选取具有不同结构特征的N-糖链、硫酸软骨素寡糖、人乳寡糖以及海洋来源的壳寡糖、褐藻胶寡糖、卡拉胶寡糖和硫酸岩藻寡糖等,对电喷雾质谱在寡糖的主链序列、分支位点、硫酸基取代位置确定、单糖组成和聚合度分析等方面的应用技术及碎片离子的断裂规律进行了总结.根据相邻同类碎片离子之间的质荷比差值可初步判断寡糖的单糖组成类型;通过与色谱分离技术联用或衍生化方法可提高寡糖的分辨率和离子化效率,并测得寡糖的分子量及聚合度;借助串联质谱及对寡糖还原端的特异性标记,可获得寡糖的还原端残基和部分序列信息;根据寡糖产生的特征碎片离子及其丰度大小可判断残基的特定位置和类型.另外,寡糖的分支通常作为一个整体发生糖苷键断裂或产生D离子,据此可判断分支点的位置;根据硫酸寡糖产生的特异性跨环断裂碎片,可以确定硫酸基的连接位置.这些规律和方法的总结为未知寡糖的结构和序列的分析提供了启发和指导. 相似文献
19.
Gouranga C. Nayak 《Annals of Physics》2010,325(2):514-3898
Factorization theorem plays the central role at high energy colliders to study standard model and beyond standard model physics. The proof of factorization theorem is given by Collins, Soper and Sterman to all orders in perturbation theory by using diagrammatic approach. One might wonder if one can obtain the proof of factorization theorem through symmetry considerations at the lagrangian level. In this paper we provide such a proof. 相似文献
20.
A new configuration for compression-shear soft-recovery experiments is presented. This technique is used to investigate various failure mechanisms during dynamic multiaxial loading of an Al2O3/SiC nanocomposite and TiB2. Velocity profiles of the target surface are measured with a variable sensitivity displacement interferometer, yielding normal and transverse velocity-time histories. A dynamic shear stress of approximately 280 MPa is obtained, in the Al2O3/SiC nanocomposite, for an imposed axial stress of about 3.45 GPa on a 540 m thick sample. This dynamic shear stress is well below the value predicted by elastic wave propagation theory. This could be the result of stress-induced damage and inelasticity in the bulk of the sample or inelasticity on the sample surface due to frictional sliding. To gain further insight into the possible failure mechanisms, an investigation of compression-shear recovery techniques, with simultaneous trapping of longitudinal and lateral release waves, is conducted. 相似文献