全文获取类型
收费全文 | 1092篇 |
免费 | 42篇 |
专业分类
化学 | 787篇 |
晶体学 | 8篇 |
力学 | 34篇 |
数学 | 83篇 |
物理学 | 222篇 |
出版年
2023年 | 8篇 |
2022年 | 24篇 |
2021年 | 22篇 |
2020年 | 15篇 |
2019年 | 23篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 26篇 |
2014年 | 46篇 |
2013年 | 43篇 |
2012年 | 68篇 |
2011年 | 88篇 |
2010年 | 51篇 |
2009年 | 71篇 |
2008年 | 87篇 |
2007年 | 69篇 |
2006年 | 67篇 |
2005年 | 46篇 |
2004年 | 30篇 |
2003年 | 27篇 |
2002年 | 26篇 |
2001年 | 19篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 19篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1974年 | 12篇 |
1973年 | 12篇 |
1964年 | 2篇 |
排序方式: 共有1134条查询结果,搜索用时 15 毫秒
31.
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 Electron-withdrawn groups as well as long unsaturated chains were hazardous to the activity.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
32.
Kai‐Hsuan Hsieh Chih‐Ying Hsu I‐Ju Hung Chih‐Ling Yeh Yau‐Hung Chen Chien‐Chung Cheng 《中国化学会会志》2021,68(1):34-38
Liposomes composed of cell‐penetrating peptide derivatives increased transport across the cell membrane. Conjugating rhodamine to a cell‐penetrating peptide increased the toxicity of rhodamine in E. coli and zebrafish embryos. A similar total protein inhibition pattern with different intensities, indicating that the interaction pathways of the rho‐KTTKS‐CONH2 monomer and liposomes were the same. It suggests that the rho‐KTTKS‐CONH2 liposomes showed higher toxicity because better transport across the cell membrane increased the effective concentration inside cells. The staining of zebrafish embryos using rho‐KTTKS‐CONH2 liposomes showed a longer retention time, suggesting that it can penetrate deeper tissues or organs in zebrafish. 相似文献
33.
Shang-Hao Liu Yen-Pin Yu Yu-Chi Lin Sheng-Yi Weng Tung-Feng Hsieh Hung-Yi Hou 《Journal of Thermal Analysis and Calorimetry》2014,116(3):1361-1367
Azo compounds are widely used in dyes, pigments, blowing agents, and initiators. Unfortunately, these compounds contain the bivalent –N–N– composition which might be cleavaged readily even under high ambient temperature. The self-accelerating decomposition might cause a runaway reaction and lead to a fire or explosion when the cooling system fails or other upsets occur. To investigate the thermal stability parameters of 2,2′-azobis(isobutyronitrile) with thermal hazard and mechanism, differential scanning calorimetry and thermal activity monitor III were applied with non-isothermal method and isothermal method to obtain onset temperature (T 0), maximum temperature (T max), and heat of decomposition (ΔH d). Thermal stability parameters play a pivotal role in thermal analysis, leading particularly to complex evaluation of the inherently safer design during preparation, processing, transport, or storage. The results provide sufficient thermokinetic parameters for process safety in terms of proactive loss prevention program. 相似文献
34.
Molecular Engineering of Push–Pull Porphyrin Dyes for Highly Efficient Dye‐Sensitized Solar Cells: The Role of Benzene Spacers 下载免费PDF全文
Shaik M. Zakeeruddin Shu‐Nung Chang Chi‐Hung Hsieh Chen‐Yu Yeh Michael Grätzel 《Angewandte Chemie (International ed. in English)》2014,53(11):2973-2977
Porphyrins have drawn much attention as sensitizers owing to the large absorption coefficients of their Soret and Q bands in the visible region. In a donor and acceptor zinc porphyrin we applied a new strategy of introducing 2,1,3‐benzothiadiazole (BTD) as a π‐conjugated linker between the anchoring group and the porphyrin chromophore to broaden the absorption spectra to fill the valley between the Soret and Q bands. With this novel approach, we observed 12.75 % power‐conversion efficiency under simulated one‐sun illumination (AM1.5G, 100 mW cm?2). In this study, we showed the importance of introducing the phenyl group as a spacer between the BTD and the zinc porphyrin in achieving high power‐conversion efficiencies. Time‐resolved fluorescence, transient‐photocurrent‐decay, and transient‐photovoltage‐decay measurements were employed to determine the electron‐injection dynamics and the lifetime of the photogenerated charge carriers. 相似文献
35.
Stereoelectronic Basis for the Kinetic Resolution of N‐Heterocycles with Chiral Acylating Reagents 下载免费PDF全文
Sheng‐Ying Hsieh Benedikt Wanner Dr. Philip Wheeler Prof. Dr. André M. Beauchemin Prof. Dr. Tomislav Rovis Prof. Dr. Jeffrey W. Bode 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(24):7228-7231
The kinetic resolution of N‐heterocycles with chiral acylating agents reveals a previously unrecognized stereoelectronic effect in amine acylation. Combined with a new achiral hydroxamate, this effect makes possible the resolution of various N‐heterocycles by using easily prepared reagents. A transition‐state model to rationalize the stereochemical outcome of this kinetic resolution is also proposed. 相似文献
36.
We report on the fabrication of a surface‐enhanced Raman scattering (SERS) platform, comprised of a three‐dimensional (3D) porous eggshell membrane (ESM) scaffold decorated with Ag nanoparticles (NPs). Both native and treated ESM were used, where the treated ESM pore size and fiber crossing density was controlled by timed exposure to hydrogen peroxide (H2O2). Ag NPs were synthesized in situ by reduction of silver nitrate with ascorbic acid. Our results demonstrate that H2O2‐treated Ag‐ESM provides a more densely packed 3D network of active material, which leads to consistently higher SERS enhancement than untreated Ag‐ESM substrates. 相似文献
37.
38.
We described a simple and quick miniaturized sequencing gel system for DNA analysis. Two major modifications were made to the previously reported miniaturized DNA sequencing gel system to achieve high-resolution hydroxyl radical cleavage analysis: including formamide in the miniaturized gel and providing uniform heating during electrophoresis. Our method enables one to reduce the cost for chemicals and to significantly reduce electrophoresis time. Furthermore, minimal gel handling simplifies the entire process. We show that the resolution of DNA fragments obtained by hydroxyl radical cleavage for the miniaturized gel is similar to that of a large conventional sequencing gel. 相似文献
39.
Hweiyan Tsai Hsiao-Ching Hu Chih-Chung Hsieh Yi-Hsuan Lu Chien-Hong Chen Chwan-Bor Fuh 《中国化学会会志》2020,67(1):152-159
Chloramphenicol (CAP) is a veterinary antibiotic that has been banned due to its severe side effects in humans. Through the application of manure, veterinary antibiotics can enter the soil, where they can be taken up by crops and vegetables and pose a potential health hazard to humans. Thus, it is highly desirable to develop a rapid and sensitive tool for on-site detection of CAP to ensure food safety and to control the abuse of antibiotics. To this end, nitrogen-doped graphene quantum dots (N-GQDs) were successfully prepared via microwave-assisted synthesis using citric acid and urea as carbon and nitrogen sources, respectively. Analytical results suggested that the interaction between N-GQDs and CAP could occurs via π-π stacking, which quenched N-GQD fluorescence. CAP spiked into chicken feed could be rapidly extracted with ethanol and quantified based on N-GQD fluorescence quenching without further separation. This method showed good recovery (97–102.6%), a low detection limit (1.8 ppm), and was not affected by interference from florfenicol, and thiamphenicol, legal substitute antibiotics. This method has excellent potential for determination of CAP in livestock feed and soil. 相似文献
40.
In this work we demonstrated a facile method for the fabrication of C18 coordination polymer gel in a capillary, called stage-frit, which was efficiently applied to pack sub-2 μm C18 beads into the capillary by a high pressure bomb for the online separation of proteolytic peptides. The back pressure of the column with 10 cm × 75 μm i.d. is regularly lower than 170 bar at a flow rate of 300 nl/min, which could be operated on a common nanoLC system instead of nanoUPLC system due to the good permeability, low back pressure and high mechanical stress of the frit that will totally reduce the cost for the purchase of instrument. The stage-frit allows long-term continuous flow of the solvent and no significant beads loss or pressure instability was observed during the period. The repeatability of retention time for fifteen BSA tryptic peaks was found to be less than 1.08% (RSD) in six time nanoLC-ESI-MS/MS experiments. The average full width at half maximum (FWHM) of peptide peaks is 5.87 s. The sub-2 μm stage-frit nanoLC column showed better sensitivity than the commercial available for large scale proteomic analysis of total tissue proteins from human spleen. The number of identified peptides is approximately 0.4-fold and 0.2-fold higher than that obtained by utilizing commercial columns packed with 3 μm and 1.8 μm C18 materials, respectively. In the field of analytical chemistry, particularly the use of nanoLC systems, stage-frit nanoLC column offers a great potential for the separation of complex mixtures. 相似文献