全文获取类型
收费全文 | 184篇 |
免费 | 17篇 |
国内免费 | 21篇 |
专业分类
化学 | 164篇 |
晶体学 | 11篇 |
力学 | 1篇 |
综合类 | 1篇 |
数学 | 12篇 |
物理学 | 33篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 14篇 |
2012年 | 19篇 |
2011年 | 11篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 13篇 |
2007年 | 10篇 |
2006年 | 12篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1975年 | 1篇 |
1938年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 15 毫秒
81.
A numerical model based on ray optics formulation taking the optical path length into account was described and applied to
numerical investigations on a thermal birefringence compensation scheme proposed and experimentally demonstrated by Q, Lüet al. [Opt. Quantum Electron.28 (1996) 57]. Taking into consideration the thermal lensing effects of laser rods depolarization losses and spatial intensity
profiles of depolarized beams were calculated for the scheme. It was theoretically confirmed that using a polarization rotator
and imaging optics effective compensation for the birefringence in rods is possible for a wide range of pumping power. 相似文献
82.
A fluoroimmunoassay method using unlabeled Terbium chelate isdescribed.The principle is similar to that of fluoroimmunoassay method usinglanthanide chelate as labels.The procedure is simpte because labeling processis unnecessary.The recovery of HSA and albumin in urine is 107% and95% respectively.The standard deviation is tess than 10%. 相似文献
83.
Um JH Kang CD Bae JH Shin GG Kim DW Kim DW Chung BS Kim SH 《Experimental & molecular medicine》2004,36(3):233-242
Tumor hypoxia contributes to the progression of a malignant phenotype and resistance to ionizing radiation and anticancer drug therapy. Many of these effects in hypoxic tumor cells are mediated by expression of specific set of genes whose relation to therapy resistance is poorly understood. In this study, we revealed that DNA-dependent protein kinase (DNA-PK), which plays a crucial role in DNA double strand break repair, would be involved in regulation of hypoxia inducible factor-1 (HIF-1). HIF-1beta-deficient cells showed constitutively reduced expression and DNA-binding activity of Ku, the regulatory subunit of DNA-PK. Under hypoxic condition, the expression and activity of DNA- PK were markedly induced with a concurrent increase in HIF-1alpha expression. Our result also demonstrated that DNA-PK could directly interact with HIF-1, and especially DNA-PKcs, the catalytic subunit of DNA-PK, could be involved in phosphorylation of HIF-1alpha, suggesting the possibility that the enhanced expression of DNA- PK under hypoxic condition might attribute to modulate HIF-1alpha stabilization. Thus, the correlated regulation of DNA-PK with HIF-1 could contribute to therapy resistance in hypoxic tumor cells, and it provides new evidence for developing therapeutic strategies enhancing the efficacy of cancer therapy in hypoxic tumor cells. 相似文献
84.
Second-order rate constants have been measured for the reactions of 2,4-dinitrophenyl X-substituted benzoates (1a-f) with a series of primary amines in 80 mol % H(2)O/20 mol % DMSO at 25.0 +/- 0.1 degrees C. The Br?nsted-type plot for the reactions of 1d with primary amines is biphasic with slopes beta(1) = 0.36 at the high pK(a) region and beta(2) = 0.78 at the low pK(a) region and the curvature center at pK(a) degrees = 9.2, indicating that the reaction proceeds through an addition intermediate with a change in the rate-determining step as the basicity of amines increases. The corresponding Br?nsted-type plot for the reactions with secondary amines is also biphasic with beta(1) = 0.34, beta(2) = 0.74, and pK(a) degrees = 9.1, indicating that the effect of amine nature on the reaction mechanism and pK(a) degrees is insignificant. However, primary amines have been found to be less reactive than isobasic secondary amines. The microscopic rate constants associated with the aminolysis have revealed that the smaller k(1) for the reactions with primary amines is fully responsible for their lower reactivity. The electron-donating substituent in the nonleaving group exhibits a negative deviation from the Hammett plots for the reactions of 1a-f with primary and secondary amines, while the corresponding Yukawa-Tsuno plots are linear. The negative deviation has been ascribed to stabilization of the ground state of the substrate through resonance interaction between the electron-donating substituent and the carbonyl functionality. 相似文献
85.
Pseudo-first-order rate constants (kobs) have been measured spectrophotometrically for reactions of O-4-nitrophenyl thionobenzoate (1) with a series of alicyclic secondary amines in MeCN and H2O at 25.0 +/- 0.1 degrees C. The plot of kobs vs amine concentration exhibits an upward curvature in all cases, indicating that the reactions proceed through two tetrahedral intermediates (a zwitterionic T(+/-) and its deprotonated anionic T-) regardless of the amine basicity and the nature of the reaction medium. However, all the amines investigated have been found to be much less reactive in MeCN than in H2O, although the amines are more basic in the former medium by 7-9 pKa units. 相似文献
86.
Jong Bum Lee Soong Ho Um Jeong-Woo Choi Kee-Kahb Koo 《Colloids and surfaces. B, Biointerfaces》2003,30(4):307-314
The self-assembled ferredoxin monolayer onto the (100) surface of the silicon substrate was prepared and the nonspecifically adsorbed aggregates of ferredoxin on the substrate were successfully eliminated by using a zwitterionic surfactant, 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS). The AFM image of the self-assembled ferredoxin monolayer on the silicon substrate treated with CHAPS clearly shows that the size of ferredoxin clusters is about 20–30 nm, which is on the order of an aggregate of about five ferredoxin molecules, whereas the size of ferredoxin aggregates on the substrate without CHAPS treatment was measured to be about 100–200 nm. Those results offer a useful method for the elimination of the nonspecific adsorption of proteins onto inorganic substrates, which has been a long-term problem in the fabrication of biomolecular electronic devices by the self-assembly technique. 相似文献
87.
Dendritic chelating agents. 1. Cu(II) binding to ethylene diamine core poly(amidoamine) dendrimers in aqueous solutions 总被引:2,自引:0,他引:2
Diallo MS Christie S Swaminathan P Balogh L Shi X Um W Papelis C Goddard WA Johnson JH 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2640-2651
This paper describes an investigation of the uptake of Cu(II) by poly(amidoamine) (PAMAM) dendrimers with an ethylenediamine (EDA) core in aqueous solutions. We use bench scale measurements of proton and metal ion binding to assess the effects of (i) metal ion-dendrimer loading, (ii) dendrimer generation/terminal group chemistry, and (iii) solution pH on the extent of binding of Cu(II) in aqueous solutions of EDA core PAMAM dendrimers with primary amine, succinamic acid, glycidol, and acetamide terminal groups. We employ extended X-ray absorption fine structure (EXAFS) spectroscopy to probe the structures of Cu(II) complexes with Gx-NH2 EDA core PAMAM dendrimers in aqueous solutions at pH 7.0. The overall results of the proton and metal ion binding measurements suggest that the uptake of Cu(II) by EDA core PAMAM dendrimers involves both the dendrimer tertiary amine and terminal groups. However, the extents of protonation of these groups control the ability of the dendrimers to bind Cu(II). Analysis of the EXAFS spectra suggests that Cu(II) forms octahedral complexes involving the tertiary amine groups of Gx-NH2 EDA core PAMAM dendrimers at pH 7.0. The central Cu(II) metal ion of each of these complexes appears to be coordinated to 2-4 dendrimer tertiary amine groups located in the equatorial plane and 2 axial water molecules. Finally, we combine the results of our experiments with literature data to formulate and evaluate a phenomenological model of Cu(II) uptake by Gx-NH2 PAMAM dendrimers in aqueous solutions. At low metal ion-dendrimer loadings, the model provides a good fit of the measured extent of binding of Cu(II) in aqueous solutions of G4-NH2 and G5-NH2 PAMAM dendrimers at pH 7.0. 相似文献
88.
The use of hyphenated LC-NMR and LC-MS techniques for the purpose of directly identifying the major constituents of Belamcanda chinensis was investigated. Reversed-phase isocratic chromatography was performed using an acetonitrile-water solvent system on a C18 column. The NMR spectrum yielded five main peaks, whose analysis revealed them to be 5, 6, 7, 3'-tetrahydroxy-4'-methoxyisoflavone (1), tectorigenin (2), iristectorigenin A (3), irigenin (4), and irisflorentine (5). The identification of these constituents was confirmed by performing LC-ESI-MS experiment. This study shows that hyphenated LC-NMR and LC-MS can be used for the rapid (70 min) identification of the isoflavonoids. 相似文献
89.
为了高效实现Prolog,人们研制了面向Prolog的专用处理机或处理器片子。然而,已有的这类机器大多或者不能支持Prolog数据库操作的实现,或者不能进行快速的数值计算。本文论述了我们设计的一种基于WAM-PLUS模型的顺序推理机GKD-PLM的系统结构。该结构不仅能高速执行Prolog代码,而且支持数据库操作和数值计算。文中在论述GKD-PLM的特点之后,介绍了Prolog处理机SPP的指令系统、数据表示、执行部件的硬件结构、微程序控制器的结构等。并对其性能进行了评估。 相似文献
90.