全文获取类型
收费全文 | 1019篇 |
免费 | 43篇 |
国内免费 | 5篇 |
专业分类
化学 | 703篇 |
晶体学 | 30篇 |
力学 | 25篇 |
数学 | 74篇 |
物理学 | 235篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 37篇 |
2021年 | 46篇 |
2020年 | 32篇 |
2019年 | 44篇 |
2018年 | 35篇 |
2017年 | 19篇 |
2016年 | 51篇 |
2015年 | 37篇 |
2014年 | 49篇 |
2013年 | 96篇 |
2012年 | 87篇 |
2011年 | 77篇 |
2010年 | 57篇 |
2009年 | 37篇 |
2008年 | 54篇 |
2007年 | 47篇 |
2006年 | 38篇 |
2005年 | 28篇 |
2004年 | 32篇 |
2003年 | 20篇 |
2002年 | 19篇 |
2001年 | 5篇 |
2000年 | 15篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有1067条查询结果,搜索用时 15 毫秒
61.
Mahmoud Sunjuk Mousa Al-Noaimi Ghassan Abu Sheikha Ekkehard Lindner Bassam El-Eswed Kamal Sweidan 《Polyhedron》2009
Water-soluble functionalized bis(phosphine) ligands L (a–h) of the general formula CH2(CH2PR2)2, where for a: R = (CH2)6OH; b–g: R = (CH2)nP(O)(OEt)2, n = 2–6 and n = 8; h: R = (CH2)3NH2 ( Scheme 1), have been prepared photochemically by hydrophosphination of the corresponding 1-alkenes with H2P(CH2)3PH2. Water-soluble palladium complexes cis-[Pd(L)(OAc)2] (1–8) were obtained by the reaction of Pd(OAc)2 with the ligands a–h in a 1:1 mixture of dichloromethane:acetonitrile. The water-soluble phosphine ligands and their palladium complexes were characterized by IR, 1H and 31P NMR. A crystallographic study of complex 1 shows that the Pd(II) ion has a square planar coordination sphere in which the acetate ligands and the diphosphine ligand deviate by less than 0.12 Å from ideal planar. 相似文献
62.
Yousaf Raffia bintay Bakar Shahzad Abu Mazhar Muhammad Mansoor Muhammad Adil Iqbal Mudassir 《Russian Journal of Applied Chemistry》2022,95(1):37-45
Russian Journal of Applied Chemistry - Owing to high stability, metal oxide-based ceramic thin films are of great interest for photocatalytic oxidation of water. Therefore, the current research is... 相似文献
63.
64.
65.
S.Abu el Ata-Doss 《Journal of Mathematical Analysis and Applications》1979,72(1):106-113
Control systems governed by linear parabolic evolution partial differential equations in the case of quadratic cost functions are considered. Sensitivity of the performance of the optimal systems to small parameter variations is studied. It is proved that the cost function sensitivity is the same if the optimal control is implemented in open-loop form or in feedbeck form. 相似文献
66.
Abu T. Khan Parijat Sharma Richard R. Schmidt 《Journal of carbohydrate chemistry》2013,32(9):1353-1367
Abstract Reaction of the 4-C-lithiomethyl intermediates, obtained from 4-deoxy-4-C-iodomethylglucopyranosides 5a,b, with open-chain glucose derivative 8 afforded 4-deoxy-4-C-heptitylglucopyranosides 9a,b. Mesylation of the newly generated hydroxy group and then desilylation gave 11a,b which were subjected to ring closure under basic conditions. Surprisingly, no C-bridged cellobiosides 12a,b (or, alternatively the corresponding maltosides) were obtained as major products; with loss of one benzyl alcohol residue the furanosides 13a,b were preferentially formed. Their generation and structural assignment is discussed. 相似文献
67.
68.
Mohd Rushdi Abu Bakar Zoltan Kalman Nagy Christopher David Rielly 《Journal of Thermal Analysis and Calorimetry》2010,99(2):609-619
A combination of differential scanning calorimetry and hot-stage microscopy with image analysis has been used to investigate
the polymorphism of sulfathiazole. The use of light intensity profiles obtained from the HSM images, as an alternative way
to present results of the HSM analysis, was found to be useful in describing and verifying thermal events. The approach provides
a unique insight into the polymorphic transformations and thermal behaviour exhibited by this compound. The results of the
experiments show that sulfathiazole tends to crystallise as mixtures of polymorphs, even though the literature methods for
producing pure polymorph were followed. 相似文献
69.
The complexes [Zn(phenylacetato)2(2-aminopyridin)2] (3), [Zn(phenylacetato)2(1,10-phenanthroline)]·H2O (4), and [Zn(phenylacetato)2(2,9-dimethyl-1,10-phenanthroline)]·0.5 H2O (5) were prepared and characterized by IR-, UV–Visible, 1H and 13C NMR spectroscopy, and single crystal X-ray diffraction. BNPP hydrolysis of the complexes and their parent nitrogen ligands showed that the hydrolysis rate of bis-(4-nitrophenyl) phosphate (BNPP) was 1.7 × 105 L mol?1 s?1 for 3, 3.1 × 105 L mol?1 s?1 for 4 and 4.3 × 104 L mol?1 s?1 for 5. Antibacterial activities show the effect of complexation on activity against Gram-positive (S. epidermidis, S. aureus, E. faecalis, M. luteus and B. subtilis) and Gram-negative (K. pneumonia, E. coli, P. mirabilis and P. aeruginosa) bacteria using the agar well diffusion method. Complex 4 showed good activity against G? bacteria except P. aeruginosa, and against G+ bacteria except E. ferabis. Complex 5 showed no activity against G? bacteria, low activity against M. luteus and B. subtilis bacteria and high activity against S. epidemidis and S. aureus. Complex 3 did not show any activity against G? or G+ bacteria. 相似文献
70.
Kinetics of oxidation of L ‐cysteine by CoIII and FeIII complexes based on α‐ and γ‐diimine Schiff base ligands were studied in aqueous solution. Pairs of trans and cis isomers of the metal complexes were used in the studies. Kinetic measurements were performed at 25 °C and constant pH and ionic strength under pseudo‐first order condition, in which the concentration of cysteine was around two orders of magnitude greater than that of the metal complex. The observed rate constant was obtained by following the change in absorbance of the reaction mixture with time at a predetermined wavelength. The overall rate constant and order of the reaction with respect to cysteine and metal complex were determined. For both metal ions studied, the oxidation rate constant for the trans isomer was higher than that for the cis isomer. This was attributed to the contribution of the steric factor and the trans effect. The effects of substituents and the nature of the metal ion on the reaction rate are discussed. 相似文献