全文获取类型
收费全文 | 257篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
化学 | 165篇 |
晶体学 | 5篇 |
力学 | 6篇 |
数学 | 31篇 |
物理学 | 63篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 37篇 |
2020年 | 15篇 |
2019年 | 14篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 22篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 23篇 |
2012年 | 15篇 |
2011年 | 12篇 |
2010年 | 10篇 |
2009年 | 6篇 |
2008年 | 1篇 |
2007年 | 4篇 |
2006年 | 12篇 |
2005年 | 12篇 |
2004年 | 3篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2000年 | 1篇 |
1995年 | 5篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
排序方式: 共有270条查询结果,搜索用时 421 毫秒
1.
Mousa Z. Al-Noaimi Raid J. Abdel-Jalil Mustafa M. El-Abadelah Salim F. Haddad Younis N. H. Baqi Wolfgang Voelter 《Monatshefte für Chemie / Chemical Monthly》2006,37(12):745-750
In the presence of RuCl3, N-phenylamidrazone underwent oxidative cyclization into 1,4-dihydro-1-phenyl-1,2,4-benzotriazine, the structure of which is
established by spectral and X-ray diffraction data. 相似文献
2.
Some new stabilisers having a chelating polymeric structure were synthesised and characterised, i.e., 8-hydroxyquinoline-formaldehyde chelating resins of Cd, Zn, and Pb. The efficiency of these new stabilisers was studied with respect to PVC. The stabilised PVC samples showed outstanding thermal stability as studied by thermogravimetric techniques, i.e., the percentage of HCl evolved reduced remarkably with increasing polymer decomposition temperature. 相似文献
3.
Phosphine Substituted Chelate Ligands. XVIII. Penta- and Tetracarbonylmetal Complexes of Chromium, Molybdenum, and Tungsten with Secondary and Tertiary Phosphinothioformamide Ligands Mono- and bidentately coordinated phosphinothioformamide complexes are obtained by photochemical substitution of the metal hexacarbonyls M(CO)6 (M ? Cr ( a ), Mo ( b ), W ( c )). The M(CO)5 · THF adducts react with secondary thioamides under exclusion of light to give the P-coordinate pentacarbonyl complexes [(CO)5MPPh2C(S)NHR1] (R1 ? Ph ( 1a – c ), Me ( 2a )). The photoreaction of M(CO)5 · THF with secondary and tertiary thioamides at low temperatures leads to the formation of the P, S-chelate complexes . The corresponding N-silylated complexes 6a – c (R1 ? Me3Si, R2 ? Ph) are obtained by direct photosubstitution of M(CO)6 in cyclohexane solution. The labile bis(thioformamide) complexes [(CO)4M(PPh2C(S)NHMe)2] ( 7a – c , cis-trans isomers) are synthesized in low yields according to the same procedure. The attempted alkylation of the chelate complexes 3a – c remains unsuccessful, whereas the secondary thioformamides react with n-BuLi/CH2Br2 to give the methylene bis(thioformirnidoesters) [Ph2PC(NR1)S]2CH2 (R1 ? Ph (8), Me ( 9 )) in quantitative yields. 相似文献
4.
Supramolecular isomerism in coordination compounds: nanoscale molecular hexagons and chains 总被引:1,自引:0,他引:1
Abourahma H Moulton B Kravtsov V Zaworotko MJ 《Journal of the American Chemical Society》2002,124(34):9990-9991
A nanoscale supramolecular hexagon, 1, and its supramolecular isomeric chain structure, 2, have been prepared from self-assembly of 5-NO2-bdc and Cu(II) cations. The hexagon is neutral and soluble and has outer and inner diameters of 3.1 and 0.8 nm, respectively. 相似文献
5.
Novel highly functionalized benzimidazoles were synthesized in two steps by microwave irradiation: construction of the benzimidazole ring followed by ring closure to the new tricyclic system. 相似文献
6.
Controlled adsorptive accumulation of testosterone, methyltestosterone and progesterone on the static mercury drop electrode provides the basis for direct stripping measurement of these compounds ar nanomolar concentrations. The adsorptive stripping behavior is evaluated with respect to preconcentration time and potential, stripping mode, concentration dependence, drop size and other variables. With 5-min accumulation, peak current enhancements of 45, 18 anal 12 are observed for 5 × 10?8 M testosterone, progesterone and methyltestosterone, respectively, relative to direct pulse voltammetry. Detection limits are 1.6 × 10?10 M for testosterone, 2 × 10?10 M for progesterone and 3.3 × 10?10 M for methyltestosterone with 15-min preconcentration. The relative standard deviation for 8 × 10?8 M progesterone is 3.4% (n=8). Applicability to direct measurements of methyltestosterone in pharmaceutical formulations is assessed. 相似文献
7.
Saify ZS Mushtaq N Khan KM Perveen S Shah ST Abdel-Jalil RJ Fecker M Voelter W 《Chemical & pharmaceutical bulletin》2005,53(1):64-66
A new series of 4-(4'-chlorophenyl)-4-hydroxypiperidine derivatives (2-5), substituted at nitrogen, were synthesized and tested as potential analgesic compounds as well as evaluated for their effect on hypotensive activity. Results showed that all the derivatives exhibit significant analgesic activity in male Wistar rats at a dose of 50 mg/kg of body weight after intramuscular injection, when tested by thermal stimuli (tail flick test). Pethidine was used as reference drug. Compounds 2, 3 and 5 produced reduction in blood pressure in normotensive rat. 相似文献
8.
Coordination Chemistry of Functional Phosphorus Ylides. VII. Pentacarbonylmetal Complexes of Cyanomethylene Triphenylphosphorane, [Ph3P?CH(CN)] · M(CO)5 (M = Cr, Mo, W) The pentacarbonyl complexes [Ph3P?CH(CN)] · M(CO)5 ( 1a –c) are obtained by reaction of the irradiated metal hexacarbonyls M(CO)6 (M = Cr, Mo, W) with cyanomethylene triphenylphosphorane under exclusion of light. The IR and NMR spectra indicate N-coordination of the ligand, that means a nitrile complex. The chromium complex 1a crystallizes triclinic (space group P1 , Z = 2) with the lattice constant a = 1126.5(2), b = 1153.6(3), c = 951.4(3) pm; α = 103.47(3), β = 102.04(3), γ = 84.00(2)°. The linear array of the ligand atoms C7, C6, N forms an angle of 168.1(5)° with the metal-nitrogen bond. Significant bond distances are Cr? N = 206.2(6), N? C6 = 115.3(7), C6? C7 = 137.2(8) and P? C7 = 170.9(5) pm. 相似文献
9.
In this paper, we propose a novel all-optical 2R (re-amplification and re-shaping) regenerator based on inducing nonlinear chirp over a continuous wave probe. The regenerator also performs continuous wave to pulsed wavelength conversion. The chirp is induced in a highly nonlinear fiber by the data modulated pulsed signal that is to be regenerated. Offset filtering is employed at the output of the highly nonlinear fiber to extract the frequencies generated as a result of chirping. The regenerator performance has been evaluated with the help of bit-error-rate plots and eye diagrams at different values of optical signal to noise ratios. Apart from re-shaping and re-amplification, inclusion of the regenerator results in better resilience to amplified spontaneous emission noise. 相似文献
10.
Aftab Aslam Parwaz Khan Anish Khan Abdullah M Asiri Heba A Kashmery 《Russian Journal of Physical Chemistry B, Focus on Physics》2018,12(3):412-421
The oxidation of Rizatriptan by diperiodatoargentate(III) has been studied by spectrophotometry at neutral pH. The kinetics of the reaction of Rizatriptan has been shown to principle of non-complementary oxidation steps. The initial step involves the deprotonated of the diperiodatoargentate(III) with the alkali; this rearranges during the displacement of a ligand to give free periodate and takes up another ligand monoperiodateargentate(III), combines with a substrate to endow with an intermediate complex which decomposes within a slow step to provide the final product in the following step with a first-order rate constant. The main product was identified by spot test, Fourier- transform infrared spectroscopy, Nuclear magnetic resonance and Liquid chromatography-mass spectrometry spectrum. A conceivable mechanism including pre equilibrium of adducts development between the complex and reductant was planned from the kinetics study. The rate conditions got from system can clarify all exploratory phenomena, and the activation parameters alongside rate constants of the rate determining step were ascertained. 相似文献