全文获取类型
收费全文 | 987篇 |
免费 | 38篇 |
国内免费 | 6篇 |
专业分类
化学 | 561篇 |
晶体学 | 8篇 |
力学 | 64篇 |
数学 | 192篇 |
物理学 | 206篇 |
出版年
2023年 | 7篇 |
2022年 | 12篇 |
2021年 | 22篇 |
2020年 | 41篇 |
2019年 | 33篇 |
2018年 | 46篇 |
2017年 | 38篇 |
2016年 | 50篇 |
2015年 | 33篇 |
2014年 | 39篇 |
2013年 | 108篇 |
2012年 | 73篇 |
2011年 | 61篇 |
2010年 | 50篇 |
2009年 | 47篇 |
2008年 | 45篇 |
2007年 | 38篇 |
2006年 | 31篇 |
2005年 | 27篇 |
2004年 | 28篇 |
2003年 | 23篇 |
2002年 | 9篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1995年 | 6篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1967年 | 2篇 |
1956年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有1031条查询结果,搜索用时 703 毫秒
51.
Two zinc(II) complexes [Zn(6,6′-dimethyl-2,2′-bipy)Cl2] n (1) and [Zn(6,6′-dimethyl-2,2′-bipy)I2] n (2) are synthesized from the reaction of the 6,6′-dimethyl-2,2′-bipy ligand with ZnCl2 and ZnI2. Zinc(II) oxide nanoparticles are synthesized by the thermolysis of [Zn(6,6′-dimethyl-2,2′-bipy)Cl2] n (1) and [Zn(6,6′-dimethyl-2,2′-bipy)I2] n (2) at two different temperatures. The ZnO nanoparticles are characterized by X-ray diffraction and scanning electron microscopy (SEM). SEM images show the average size of the ZnO nanoparticles produced of 50 nm and 60 nm in compounds 1 and 2 respectively. 相似文献
52.
Highly sensitive FRET-based fluorescence immunoassay for aflatoxin B1 using cadmium telluride quantum dots 总被引:1,自引:0,他引:1
Roya Zekavati Shahabeddin Safi Seyed Jamal Hashemi Tavoos Rahmani-Cherati Meisam Tabatabaei Afshin Mohsenifar Mansour Bayat 《Mikrochimica acta》2013,180(13-14):1217-1223
We report on a competitive immunoassay for the determination of aflatoxin B1 using fluorescence resonance energy transfer (FRET) from anti-aflatoxin B1 antibody (immobilized on the shell of CdTe quantum dots) to Rhodamine 123 (Rho 123-labeled aflatoxin B1 bound to albumin). The highly specific immunoreaction between the antibody against aflatoxin B1 on the QDs and the labeled-aflatoxin B1 brings the Rho 123 fluorophore (acting as the acceptor) and the QDs (acting as the donor) in close spatial proximity and causes FRET to occur upon photoexcitation of the QDs. In the absence of unlabeled aflatoxin B1, the antigen-antibody complex is stable, and strong emission resulting from the FRET from QDs to labeled aflatoxin B1 is observed. In the presence of aflatoxin B1, it will compete with the labeled aflatoxin B1-albumin complex for binding to the antibody-QDs conjugate so that FRET will be increasingly suppressed. The reduction in the fluorescence intensity of the acceptor correlates well with the concentration of aflatoxin B1. The feasibility of the method was established by the detection of aflatoxin B1 in spiked human serum. There is a linear relationship between the increased fluorescence intensity of Rho 123 with increasing concentration of aflatoxin B1 in spike human serum, over the range of 0.1–0.6 μmol·mL?1. The limit of detection is 2?×?10?11 M. This homogeneous competitive detection scheme is simple, rapid and efficient, and does not require excessive washing and separation steps. Figure
A nanobiosensor has been fabricated based on a competitive immunoassay for the determination of aflatoxin B1 using fluorescence resonance energy transfer (FRET). In the presence of aflatoxin B1, it will compete with the labeled aflatoxin B1-albumin complex for binding to the antibody-QDs conjugate so that FRET will be increasingly suppressed. 相似文献
53.
4-Aminoperoxybenzoic acid supported on silica gel was found to be a versatile and efficient oxidant for the oxidation of ketones to esters. 相似文献
54.
The reaction of 2-amino-1-(2-propynyl)pyridinium bromide with various iodobenzenes, catalyzed by Pd-Cu, in the presence of sodium lauryl sulfate as the surfactant and cesium carbonate as the base, in water, leads to the formation of 2-substituted imidazo[1,2-α]pyridines. 相似文献
55.
H. H. Mahmud A. Mansour F. M. Ezz-Eldin 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(1):261-272
Radiation indicator as well as radiation shielding of extremely high dose have been proposed. Three different types of a-SiO2 namely, G1-xerogel, G2-fused and G3-natural silica were monitored by EPR before and after γ-irradiation. The E′-center has been used for EPR radiation characterization of a-SiO2 with assuming that the signal intensity changes with γ-irradiation differently as those of other EPR signals do. Formation and decay of the E′-center are closely related with its precursor, diamagnetic oxygen vacancies. Gamma ray of large dose (500 kGy) creates oxygen vacancies giving up-and-down irradiation effects, which, therefore, might be useful for high dose radiation indicator (G1) and radiation shielding (G2 and G3). 相似文献
56.
Mahmoud Emam Doaa R. Abdel-Haleem Maha M. Salem Lina Jamil M. Abdel-Hafez Rasha R. Abdel Latif Shaimaa Mahmoud Farag Mansour Sobeh Mohamed A. El Raey 《Molecules (Basel, Switzerland)》2021,26(6)
Infections associated with the emergence of multidrug resistance and mosquito-borne diseases have resulted in serious crises associated with high mortality and left behind a huge socioeconomic burden. The chemical investigation of Lavandula coronopifolia aerial parts extract using HPLC–MS/MS led to the tentative identification of 46 compounds belonging to phenolic acids, flavonoids and their glycosides, and biflavonoids. The extract displayed larvicidal activity against Culex pipiens larvae (LC50 = 29.08 µg/mL at 72 h). It significantly inhibited cytochrome P-450 monooxygenase (CYP450), acetylcholinesterase (AChE), and carboxylesterase (CarE) enzymes with the comparable pattern to the control group, which could explain the mode of larvae toxification. The extract also inhibited the biofilm formation of Pseudomonas aeruginosa by 17–38% at different Minimum Inhibitory Concentrations (MICs) (0.5–0.125 mg/mL) while the activity was doubled when combined with ciprofloxacin (ratio = 1:1 v:v). In conclusion, the wild plant, L. coronopifolia, can be considered a promising natural source against resistant bacteria and infectious carriers. 相似文献
57.
Mansour Mohammadpour Farhad Hosseinzadeh-Lotfi Gholam-Reza Jahanshahloo 《The Journal of the Operational Research Society》2015,66(7):1206-1211
Data envelopment analysis (DEA) is a non-parametric approach based on linear programming that has been widely applied for evaluating the relative efficiency of a set of homogeneous decision-making units (DMUs) with multiple inputs and outputs. The original DEA models use positive input and output variables that are measured on a ratio scale, but these models do not apply to the variables in which negative data can appear. However, with the widespread use of interval scale data and undesirable data, the emphasis has been directed towards the simultaneous consideration of the positive and negative data in DEA models. In this paper, using the slacks-based measure, we propose an extended model to evaluate the efficiency of DMUs, even if some variables are measured on an interval scale and some on a ratio scale. Moreover, the extended model allows for the presence of all interval-scale variables, which are capable of taking both negative and positive values. 相似文献
58.
S. Mohammad H. Hashemi Ugljesa Babic Pooria Hadikhani Demetri Psaltis 《Current Opinion in Electrochemistry》2020
Additive manufacturing has established itself as a popular and powerful tool in electrochemistry research and development. In this short review, we focus on the latest results in both 3D printing and electrochemistry communities that could potentially benefit manufacturing in the electrochemical industry. We provide insights from recent and relevant research works and conclude that the likely scenario in the industry is the deployment of a combination of subtractive and additive technologies in order to manufacture high quality and cost-effective electrochemical reactors within reasonable timeframes. 相似文献
59.
Three‐dimensional (3D) printing becomes an attractive technique to fabricate tissue engineering scaffolds through its high control on fabrication and repeatability using the printing parameters. This technique can be combined by the finite element method (FEM), and tissue‐specific scaffolds with desirable morphological and mechanical properties can be designed and manufactured. In this study, the influential 3D printing parameters on the morphological and mechanical properties of polycaprolactone (PCL) filament and scaffold were studied experimentally and numerically. First, the effects of printing parameters and process on the properties of extruded PCL filament were investigated. Then, using FEM, the effects of filament specifications on the overall characteristics of the scaffold were evaluated. Results showed that both the printing process in terms of resting time and remaining time and the printing parameters like pressure, printing speed, and printing path length have influenced the filament properties. In addition, both the filament diameter and elastic modulus had significant effects on the properties of scaffold especially, a 20% increase in the filament diameter caused the scaffold compressive elastic modulus to rise by around 72%. It is concluded that the printing parameters and process must be tuned very well in fabricating scaffolds with the desired morphology and mechanical property. 相似文献
60.