全文获取类型
收费全文 | 1246篇 |
免费 | 60篇 |
国内免费 | 4篇 |
专业分类
化学 | 907篇 |
晶体学 | 7篇 |
力学 | 27篇 |
数学 | 76篇 |
物理学 | 293篇 |
出版年
2023年 | 11篇 |
2022年 | 5篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 34篇 |
2015年 | 29篇 |
2014年 | 38篇 |
2013年 | 65篇 |
2012年 | 84篇 |
2011年 | 101篇 |
2010年 | 63篇 |
2009年 | 57篇 |
2008年 | 78篇 |
2007年 | 80篇 |
2006年 | 83篇 |
2005年 | 66篇 |
2004年 | 55篇 |
2003年 | 50篇 |
2002年 | 42篇 |
2001年 | 23篇 |
2000年 | 23篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 22篇 |
1995年 | 7篇 |
1994年 | 15篇 |
1993年 | 15篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 4篇 |
排序方式: 共有1310条查询结果,搜索用时 15 毫秒
51.
This paper presents methods of determining the long-term stability of vitamin E emulsion and formation of microemulsions. Several emulsion systems formed by using anionic, zwitterionic and cationic surfactants have been studied in the presence and absence of NaCI. Several conclusions can be drawn: (1) by using UV absorption and particle size measurements, one may be able to predict the long-term stability of an emulsion or the possibility of forming a microemulsion by measuring the initial properties of an emulsion, (2) in order to form a stable vitamin E emulsion or microemulsion, the initial properties of the emulsion should have the following features : (a) the particle size is ≤ 200 nm, (b) the surfactant system has a saturation value ≥ 1 and (c) the surfactant system can dissolve a substantial amount of vitamin E without causing an increase of the emulsion droplet size and (3) the saturation value and the stability of many vitamin E emulsion systems can be increased by adding an optimum amount of NaCI. 相似文献
52.
The structure and action of hydrotropes are discussed using surfactant association structures as a model. The main action of a hydrotrope is to prevent phase separation from an aqueous solution; either by disordering of a lamellar liquid crystal or by preventing the formation of well defined normal and inverse micelles. 相似文献
53.
This work aims at understanding the ethanol effects on the gelation behavior of ethosomes with the consideration of encapsulating a hydrophobic material. Gelation of the empty ethosomes by positively charged water-soluble polymers with and without hydrophobic modification, respectively, was systematically studied first for the effects of solution dielectric constant and gelator concentration on the phase map and rheological property of the mixtures. A comparison of the gelation behavior of empty and α-tocopherol acetate (α-TA)-encapsulated ethosomes sheds light on the possible influence of encapsulated hydrophobic material itself on the interaction between ethosomal lipid bilayers and gelator molecules. The experimental results revealed that ethosomes with an optimized amount of ethanol could result in a reasonable lifetime and encapsulation efficiency of more than 90 %. This is due to the effects of the solution dielectric constant on the formability of liposome and the partition of the hydrophobic material (α-TA) between ethosomal lipid bilayer and bulk phase. Moreover, the phase map and rheological property of the ethosome/polymer mixtures were found to be affected by the configuration of the polymer chain in aqueous ethanol solution. That is, the driving interactions between ethosomal lipid bilayers and gelator molecules were dominated by the hydrophobic material more than the electrostatic association. Finally, inclusion of a hydrophobic material, such as α-TA, in the ethosomes had less influence on the gelation behavior of the ethosomes with water-soluble polymers. 相似文献
54.
B. R. Sheridan G. Poole E. Dowdall C. Chiu 《International journal of environmental analytical chemistry》2013,93(2-4):195-202
Abstract The analysis of PCBs often involves lengthy and expensive cleanup procedures to remove interferences associated with environmental sample matrices. Gel permeation chromatography (GPC) has proven to be a useful tool in removing many of these interferences from environmental samples, especially from difficult matrices such as oils, lipids and sediments. This paper describes the effect of temperature upon the GPC column in separating PCBs from transformer oil and its implication on GC-MS analysis. 相似文献
55.
Liang‐Yun Wang Jia‐Ling Ko Prof. Chien‐Chen Lai Yi‐Hung Liu Prof. Shie‐Ming Peng Prof. Sheng‐Hsien Chiu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(27):8850-8860
Herein, we report a “threading followed by shrinking” approach for the synthesis of rotaxanes by using an “oxygen‐deficient” macrocycle that contained two arylmethyl sulfone units and the dumbbell‐shaped salt bis(3,5‐dimethylbenzyl)ammonium tetrakis(3,5‐trifluoromethylphenyl)borate as the host and guest components, respectively. The extrusion of SO2 from both of the arylmethyl sulfone units of the macrocyclic component in the corresponding [2]pseudorotaxane resulted in a [2]rotaxane that was sufficiently stable to maintain its molecular integrity in CD3SOCD3 at 393 K for at least 5 h. 相似文献
56.
On the Size Evolution of Monolayer‐Protected Gold Clusters during Ligand Place‐Exchange Reactions: The Effect of Solvents 下载免费PDF全文
Dr. Chun‐Ting Kuo Chiu‐Feng Chen Meng‐Wen Gu Man‐Nung Su Jhih‐Fong Huang Dr. Min‐Jie Huang Prof. Chun‐hsien Chen 《化学:亚洲杂志》2014,9(3):844-851
Ligand place‐exchange (LPE) reactions are extensively applied for the post‐functionalization of monolayer‐protected gold clusters (MPCs) by using excessive incoming ligands to displace initial ones. However, the modified MPCs are often enlarged or degraded; this results in ill‐defined size‐dependent properties. The growth of MPCs essentially involves an unprotected surface that is subsequently has gold atoms added or is fused with other gold cores owing to collision. Reported herein is a guideline for the selection of solvents to suppress unwanted MPC growth. Favorable solvents are those with significant affinity to gold or with low solubility for desorbed ligands because these properties retard LPE reactions and minimize the time available for unprotected gold cores. This finding provides a general and convenient approach to regulate the size of functionalized MPCs. 相似文献
57.
Ching-Feng Chiu Hsin-Yi Chang Chun-Yine Huang Chen-Zou Mau Tzu-Ting Kuo Hsiu-Chuan Lee Shih-Yi Huang 《Molecules (Basel, Switzerland)》2021,26(9)
Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease with a 5-year survival rate of <8%. Therefore, finding new treatment strategies against PDAC cells is an imperative issue. Betulinic acid (BA), a plant-derived natural compound, has shown great potential to combat cancer owing to its versatile physiological functions. In this study, we observed the impacts of BA on the cell viability and migratory ability of PDAC cell lines, and screened differentially expressed proteins (DEPs) by an LC-MS/MS-based proteomics analysis. Our results showed that BA significantly inhibited the viability and migratory ability of PDAC cells under a relatively low dosage without affecting normal pancreatic cells. Moreover, a functional analysis revealed that BA-induced downregulation of protein clusters that participate in mitochondrial complex 1 activity and oxidative phosphorylation, which was related to decreased expressions of RNA polymerase mitochondrial (POLRMT) and translational activator of cytochrome c oxidase (TACO1), suggesting that the influence on mitochondrial function explains the effect of BA on PDAC cell growth and migration. In addition, BA also dramatically increased Apolipoprotein A1 (APOA1) expression and decreased NLR family CARD domain-containing protein 4 (NLRC4) expression, which may be involved in the dampening of PDAC migration. Notably, altered expression patterns of APOA1 and NLRC4 indicated a favorable clinical prognosis of PDAC. Based on these findings, we identified potential proteins and pathways regulated by BA from a proteomics perspective, which provides a therapeutic window for PDAC. 相似文献
58.
Shin-Hun Juang Min-Tsang Hsieh Pei-Ling Hsu Ju-Ling Chen Hui-Kang Liu Fong-Pin Liang Sheng-Chu Kuo Chen-Yuan Chiu Shing-Hwa Liu Chen-Hsi Chou Tian-Shung Wu Hsin-Yi Hung 《Molecules (Basel, Switzerland)》2021,26(1)
Constitutive androstane receptor (CAR) activation has found to ameliorate diabetes in animal models. However, no CAR agonists are available clinically. Therefore, a safe and effective CAR activator would be an alternative option. In this study, sixty courmarin derivatives either synthesized or purified from Artemisia capillaris were screened for CAR activation activity. Chemical modifications were on position 5,6,7,8 with mono-, di-, tri-, or tetra-substitutions. Among all the compounds subjected for in vitro CAR activation screening, 6,7-diprenoxycoumarin was the most effective and was selected for further preclinical studies. Chemical modification on the 6 position and unsaturated chains were generally beneficial. Electron-withdrawn groups as well as long unsaturated chains were hazardous to the activity. Mechanism of action studies showed that CAR activation of 6,7-diprenoxycoumarin might be through the inhibition of EGFR signaling and upregulating PP2Ac methylation. To sum up, modification mimicking natural occurring coumarins shed light on CAR studies and the established screening system provides a rapid method for the discovery and development of CAR activators. In addition, one CAR activator, scoparone, did showed anti-diabetes effect in db/db mice without elevation of insulin levels. 相似文献
59.
Po‐Chun Chen Yu‐Chien Chiu Zhi‐Wei Zheng Chun‐Hu Cheng Yung‐Hsien Wu 《固体物理学:研究快报》2016,10(12):919-923
We reported the characteristics of p‐type tin‐oxide (SnO) thin film transistors (TFTs) upon illumination with visible light. Our p‐type TFT device using the SnO film as the active channel layer exhibits high sensitivity toward the blue‐light with a high light/dark read current ratio (Ilight/Idark) of 8.2 × 103 at a very low driven voltage of <3 V. Since sensing of blue‐light radiation is very critical to our eyes, the proposed p‐type SnO TFTs with high sensitivity toward the blue‐light show great potential for future blue‐light detection applications.
60.
Adare A Afanasiev S Aidala C Ajitanand NN Akiba Y Al-Bataineh H Alexander J Al-Jamel A Aoki K Aphecetche L Armendariz R Aronson SH Asai J Atomssa ET Averbeck R Awes TC Azmoun B Babintsev V Baksay G Baksay L Baldisseri A Barish KN Barnes PD Bassalleck B Bathe S Batsouli S Baublis V Bauer F Bazilevsky A Belikov S Bennett R Berdnikov Y Bickley AA Bjorndal MT Boissevain JG Borel H Boyle K Brooks ML Brown DS Bucher D Buesching H Bumazhnov V Bunce G Burward-Hoy JM Butsyk S Campbell S Chai JS Chang BS 《Physical review letters》2007,98(16):162301
Differential measurements of elliptic flow (v2) for Au+Au and Cu+Cu collisions at sqrt[sNN]=200 GeV are used to test and validate predictions from perfect fluid hydrodynamics for scaling of v2 with eccentricity, system size, and transverse kinetic energy (KE T). For KE T identical with mT-m up to approximately 1 GeV the scaling is compatible with hydrodynamic expansion of a thermalized fluid. For large values of KE T mesons and baryons scale separately. Quark number scaling reveals a universal scaling of v2 for both mesons and baryons over the full KE T range for Au+Au. For Au+Au and Cu+Cu the scaling is more pronounced in terms of KE T, rather than transverse momentum. 相似文献