全文获取类型
收费全文 | 443篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
化学 | 306篇 |
晶体学 | 20篇 |
力学 | 2篇 |
数学 | 29篇 |
物理学 | 108篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 16篇 |
2021年 | 23篇 |
2020年 | 21篇 |
2019年 | 9篇 |
2018年 | 15篇 |
2017年 | 8篇 |
2016年 | 19篇 |
2015年 | 10篇 |
2014年 | 16篇 |
2013年 | 29篇 |
2012年 | 29篇 |
2011年 | 32篇 |
2010年 | 29篇 |
2009年 | 23篇 |
2008年 | 32篇 |
2007年 | 28篇 |
2006年 | 19篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 6篇 |
1966年 | 2篇 |
1965年 | 4篇 |
1939年 | 1篇 |
排序方式: 共有465条查询结果,搜索用时 15 毫秒
81.
讨论潜伏期和染病期均具有传染性的媒介传染病模型.得到模型基本再生数的表达式,证明了当基本再生数小于1时,无病平衡点是全局渐近稳定的,此时疾病消亡;当基本再生数大于1时,无病平衡点是不稳定的,系统存在全局渐近稳定的地方病平衡点,此时,疾病将在人群中持续存在,数值模拟验证了理论结果. 相似文献
82.
Kazi Zakir Hossain Cristina T. Camagong Takaharu Honjo 《Analytical and bioanalytical chemistry》2001,369(6):543-545
A new method for the quantitative extraction and determination of trace amounts of iridium from hydrochloric acid media has been established based on the formation of an ion-association complex of iridium hexachloro anion IrCl6 2– with dicyclohexyl-18-crown-6 (DC18C6) oxonium cation in chloroform, then determination by inductively coupled plasma atomic emission spectrometry (ICP–AES). The effect of various factors (solvent, acid concentration, crown ether, reagent concentration, shaking time, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of iridium has been investigated. The procedure was used to determine traces of iridium in palladium chloride and rhodium chloride. 相似文献
83.
T. Gamze Ulusoy Ghobadi Amir Ghobadi Merve Demirtas Muhammed Buyuktemiz Kubra N. Ozvural Elif Akhuseyin Yildiz Prof. Emre Erdem Prof. H. Gul Yaglioglu Prof. Engin Durgun Prof. Yavuz Dede Prof. Ekmel Ozbay Prof. Ferdi Karadas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(35):8966-8976
The replacement of traditional ruthenium-based photosensitizers with low-cost and abundant iron analogs is a key step for the advancement of scalable and sustainable dye-sensitized water splitting cells. In this proof-of-concept study, a pyridinium ligand coordinated pentacyanoferrate(II) chromophore is used to construct a cyanide-based CoFe extended bulk framework, in which the iron photosensitizer units are connected to cobalt water oxidation catalytic sites through cyanide linkers. The iron-sensitized photoanode exhibits exceptional stability for at least 5 h at pH 7 and features its photosensitizing ability with an incident photon-to-current conversion capacity up to 500 nm with nanosecond scale excited state lifetime. Ultrafast transient absorption and computational studies reveal that iron and cobalt sites mutually support each other for charge separation via short bridging cyanide groups and for injection to the semiconductor in our proof-of-concept photoelectrochemical device. The reorganization of the excited states due to the mixing of electronic states of metal-based orbitals subsequently tailor the electron transfer cascade during the photoelectrochemical process. This breakthrough in chromophore-catalyst assemblies will spark interest in dye-sensitization with robust bulk systems for photoconversion applications. 相似文献
84.
Ahmed Waqar Chowdhury Z. Z. Kazi S. N. Johan MR. Akram Naveed Oon C. S. Abdelrazek Ali H. 《Journal of Thermal Analysis and Calorimetry》2021,144(4):1517-1534
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers... 相似文献
85.
86.
Murtaza Hasan Ayesha Zafar Maryum Jabbar Tuba Tariq Yasmeen Manzoor Muhammad Mahmood Ahmed Shahbaz Gul Hassan Xugang Shu Nasir Mahmood 《Molecules (Basel, Switzerland)》2022,27(18)
Protein corona composition and precise physiological understanding of differentially expressed proteins are key for identifying disease biomarkers. In this report, we presented a distinctive quantitative proteomics table of molecular cell signaling differentially expressed proteins of corona that formed on iron carbide nanoparticles (NPs). High-performance liquid chromatography/electrospray ionization coupled with ion trap mass analyzer (HPLC/ESI-Orbitrap) and MASCOT helped quantify 142 differentially expressed proteins. Among these proteins, 104 proteins showed upregulated behavior and 38 proteins were downregulated with respect to the control, whereas 48, 32 and 24 proteins were upregulated and 8, 9 and 21 were downregulated CW (control with unmodified NPs), CY (control with modified NPs) and WY (modified and unmodified NPs), respectively. These proteins were further categorized on behalf of their regularity, locality, molecular functionality and molecular masses using gene ontology (GO). A STRING analysis was used to target the specific range of proteins involved in metabolic pathways and molecular processing in different kinds of binding functionalities, such as RNA, DNA, ATP, ADP, GTP, GDP and calcium ion bindings. Thus, this study will help develop efficient protocols for the identification of latent biomarkers in early disease detection using protein fingerprints. 相似文献
87.
A. Hossain A.E. Bolotnikov G.S. Camarda Y. Cui G. Yang K-H. Kim R. Gul L. Xu R.B. James 《Journal of Crystal Growth》2010,312(11):1795-1799
We explored some unique defects in a batch of cadmium zinc telluride (CdZnTe) crystals, along with dislocations and Te-rich decorated features, revealed by chemical etching. We extensively investigated these distinctive imperfections in the crystals to identify their origin, dimensions, and distribution in the bulk material. We estimated that these features ranged from 50 to 500 μm in diameter, and their depth was about ∼300 μm. The density of these features ranged between 2×102 and 1×103 per cm3. We elaborated a model of them and projected their effect on charge collection and spectral response. In addition, we fabricated detectors with these defective crystals and acquired fine details of charge-transport phenomena over the detectors’ volume using a high-spatial resolution (25 μm) X-ray response mapping technique. We related the results to better understand the defects and their influence on the charge-transport properties of the devices. The role of the defects was identified by correlating their signatures with the findings from our theoretical model and our experimental data. 相似文献
88.
Banu KS Chattopadhyay T Banerjee A Bhattacharya S Suresh E Nethaji M Zangrando E Das D 《Inorganic chemistry》2008,47(16):7083-7093
A series of dinuclear copper(II) complexes has been synthesized with the aim to investigate their applicability as potential structure and function models for the active site of catechol oxidase enzyme. They have been characterized by routine physicochemical techniques as well as by X-ray single-crystal structure analysis: [Cu 2(H 2L2 (2))(OH)(H 2O)(NO 3)](NO 3) 3.2H 2O ( 1), [Cu(HL1 (4))(H 2O)(NO 3)] 2(NO 3) 2.2H 2O ( 2), [Cu(L1 (1))(H 2O)(NO 3)] 2 ( 3), [Cu 2(L2 (3))(OH)(H 2O) 2](NO 3) 2, ( 4) and [Cu 2(L2 (1))(N 3) 3] ( 5) [L1 = 2-formyl-4-methyl-6R-iminomethyl-phenolato and L2 = 2,6-bis(R-iminomethyl)-4-methyl-phenolato; for L1 (1) and L2 (1), R = N-propylmorpholine; for L2 (2), R = N-ethylpiperazine; for L2 (3), R = N-ethylpyrrolidine, and for L1 (4), R = N-ethylmorpholine]. Dinuclear 1 and 4 possess two "end-off" compartmental ligands with exogenous mu-hydroxido and endogenous mu-phenoxido groups leading to intermetallic distances of 2.9794(15) and 2.9435(9) A, respectively; 2 and 3 are formed by two tridentate compartmental ligands where the copper centers are connected by endogenous phenoxido bridges with Cu-Cu separations of 3.0213(13) and 3.0152(15) A, respectively; 5 is built by an end-off compartmental ligand having exogenous mu-azido and endogenous mu-phenoxido groups with a Cu-Cu distance of 3.133(2) A (mean of two independent molecules). The catecholase activity of all of the complexes has been investigated in acetonitrile and methanol medium by UV-vis spectrophotometric study using 3,5-di- tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) as substrates. In acetonitrile medium, the conversion of 3,5-DTBC to 3,5-di- tert-butylbenzoquinone (3,5-DTBQ) catalyzed by 1- 5 is observed to proceed via the formation of two enzyme-substrate adducts, ES1 and ES2, detected spectroscopically for the first time. In methanol medium no such enzyme-substrate adduct has been detected, and the 3,5-DTBC to 3,5-DTBQ conversion is observed to be catalyzed by 1- 5 very efficiently. The substrate TCC forms an adduct with 2- 5 without performing further oxidation to TCQ due to the high reduction potential of TCC (in comparison with 3,5-DTBC). But most interestingly, 1 is observed to be effective even in TCC oxidation, a process never reported earlier. Kinetic experiments have been performed to determine initial rate of reactions (3,5-DTBC as substrate, in methanol medium) and the activity sequence is 1 > 5 > 2 = 4 > 3. A treatment on the basis of Michaelis-Menten model has been applied for kinetic study, suggesting that all five complexes exhibit very high turnover number, especially 1, which exhibits turnover number or K cat of 3.24 x 10 (4) (h (-1)), which is approximately 3.5 times higher than the most efficient catalyst reported to date for catecholase activity in methanol medium. 相似文献
89.
Asma Akhtar Tasneem Gul Kazi Hassan Imran Afridi Jameel Ahmed Baig Mohammad Bilal Arain 《应用有机金属化学》2020,34(9):e5784
In the present study an innovative tandem ionic liquid-based dispersive microextraction method using an in-syringe air-assisted vesicle system was developed to determine the ultra-trace levels of lead (PbII) and cadmium (CdII) ions in synthetic sweat extract of branded and nonbranded facial cosmetic products. This method is based on injecting 2-amino-3-sulfhydrylpropanoic acid (l -cysteine) (as an eco-friendly chelating agent), hexafluorophosphate ion [PF6−] (as an ion pair agent) and 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM] [PF6] (as an acceptor phase) into the synthetic sweat extract of facial cosmetic products (branded and nonbranded). The acceleration of the dispersion process was carried out by rapid pressure in the syringe through the back-and-forth movement of plunger. The sediment phase was removed following centrifugation, and then hydrophobic complexes of analyte were back-extracted into HNO3 and finally injected into a flame atomic absorption spectrometer. Several factors were systematically optimized. The validity of the methodology was tested by analyzing spiked known standards of both metals in a real sample. The proposed method was applied to the artificial sweat extracts of face makeup products, indicating how much toxic metals from different cosmetics are directly absorbed into skin. 相似文献
90.
David Barker Anna L. Lehmann Anna Mai Gul S. Khan Eric Ng 《Tetrahedron letters》2008,49(10):1660-1664
A straightforward synthesis of non-symmetrical 3,5-diamidobenzyl amines, ethers and sulfides starting from 3,5-dinitrobenzoic acid is reported. Functionalization of the benzylic position is only achieved after formation of the two amides, otherwise benzylic hydrogenolysis occurs during nitro group reduction. 相似文献