全文获取类型
收费全文 | 1582篇 |
免费 | 44篇 |
国内免费 | 11篇 |
专业分类
化学 | 791篇 |
晶体学 | 9篇 |
力学 | 64篇 |
数学 | 91篇 |
物理学 | 487篇 |
无线电 | 195篇 |
出版年
2023年 | 27篇 |
2022年 | 31篇 |
2021年 | 55篇 |
2020年 | 40篇 |
2019年 | 42篇 |
2018年 | 39篇 |
2017年 | 40篇 |
2016年 | 52篇 |
2015年 | 41篇 |
2014年 | 52篇 |
2013年 | 122篇 |
2012年 | 100篇 |
2011年 | 127篇 |
2010年 | 58篇 |
2009年 | 55篇 |
2008年 | 83篇 |
2007年 | 75篇 |
2006年 | 87篇 |
2005年 | 67篇 |
2004年 | 51篇 |
2003年 | 37篇 |
2002年 | 36篇 |
2001年 | 24篇 |
2000年 | 21篇 |
1999年 | 17篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1969年 | 3篇 |
排序方式: 共有1637条查询结果,搜索用时 296 毫秒
81.
Regioselective opening of the aziridine ring in the carbohydrate-based precursor led to the stereoselective synthesis of N-Boc-O-benzyl-(4S,5S)-5-amino-4-hydroxy-6-phenylhexanoic acid methyl ester, the hydroxyethylene dipeptide isostere moiety of potent HIV-1 protease inhibitor. 相似文献
82.
Recently we reported a convenient method of oxidation of alcohols to carbonyl compounds using chromium(V) reagents.1 Although a variety of reagents are available for effecting this transformation, there are only a few reagents which have been successfully used for the oxidation of aldehydes to carboxyllc adds. Chromic acid, silver oxide and potassium permanganate are commonly employed for this purpose and reactions are performed in protic media under conditions which are not that mild.2 The “non-aqueous” chromium(VI) reagent, pyridinium dichromate, recently reported by Corey3 oxidises alcohols and aldehydes to carboxylic acids in DMF at room temperature. Although Cr(V) species is postulated as an intermediate in all oxidations with Cr(VI), no systematic oxidation studies have been reported with these reagents. This note reports the results of some fruitful investigations on aldehyde → carboxylic acid conversion involving some “non-aqueous” chromium (V) complexes 1, 2, 3 and 5 under anhydrous conditions. 相似文献
83.
Indranil Chakraborty Tanushree Chakraborty Satya P. Moulik 《Colloid and polymer science》2013,291(8):1939-1948
The present study entails interaction between the cationic polymer N,N-dimethylhydroxyethyl cellulose (JR 400) and the double-tailed anionic surfactant Na-bis-2-ethyhexylsulphosuccinate (NaAOT). This oppositely charged polymer and surfactant are expected to cause coacervation and precipitation; hence, we have observed formation of thick solution similar to diluted gel at [JR 400]?~?0.01 and 0.10 %?w/v in aqueous solution. Viscometry, conductometry, tensiometry, and microcalorimetry techniques are used to monitor the interaction process. The results are explained in the light of both intrachain and interchain linking by way of NaAOT reverse micelle formation. Adsorption of NaAOT monomers onto the charged side chains of the polymer shields interchain electrostatic repulsion, leading to the formation of hydrophobic microdomains and microscopic heterogeneity in the solution. The morphologies of the domains depend on the level of addition of NaAOT in the system. The different stages of physiochemical changes that arise in solution have been identified by the use of different techniques, and correlations of the results have been attempted in terms of pragmatic models. 相似文献
84.
This article describes a nutrient‐phytoplankton‐zooplankton system with nutrient recycling in the presence of toxicity. We have studied the dynamical behavior of the system with delayed nutrient recycling in the first part of the article. Uniform persistent of the system is examined. In the second part of the article, we have incorporated diffusion of the plankton population to the system and dynamical behavior of the system is analyzed with instantaneous nutrient recycling. The condition of the diffusion driven instability is obtained. The conditions for the occurrence of Hopf and Turing bifurcation critical line in a spatial domain are derived. Variation of the system with small periodicity of diffusive coefficient has been studied. Stability condition of the plankton system subject to the periodic diffusion coefficient of the zooplankton is derived. It is observed that nutrient‐phytoplankton‐zooplankton interactions are very complex and situation specific. Moreover, we have obtained different exciting results, ranging from stable situation to cyclic oscillatory behavior may occur under different favorable conditions, which may give some insights for predictive management. © 2014 Wiley Periodicals, Inc. Complexity 21: 229–241, 2015 相似文献
85.
Rajesh Chakraborty Sriparna Chatterjee Pabitra Chattopadhyay 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(3):1565-1570
Nanocomposite titanium-phosphate (TiP) of different sizes was synthesized using Triton X-100 (polyethylene glycol-p-isooctylphenyl ether) surfactant. The materials were characterized by FTIR and powdered X-ray diffraction (XRD). The structural and morphological details of the material were obtained by scanning electron microscopy (SEM) and transmission electron microscopy. The SEM study was followed by energy dispersive spectroscopic analysis for elemental analysis of the sample. The important peaks of the XRD spectra were analyzed to determine the probable composition of the material. The average size distribution of the particles was determined by dynamic light scattering method. Ion exchange capacity was measured for different metal ions with sizes of the TiP nanocomposite and size-dependent ion exchange property of the material was investigated thoroughly. The nanomaterial of the smallest size of around 43 nm was employed to separate carrier-free 137mBa from 137Cs in column chromatographic technique using 1.0 M HNO3 as eluting agent at pH 5. 相似文献
86.
Bhaskar Bishayee Biswajit Ruj Santanu Nandi Rishya Prava Chatterjee Aparajita Mallick Prasenjit Chakraborty Jayato Nayak Sankha Chakrabortty 《印度化学会志》2022,99(1):100302
The current investigation involves a continuous adsorption experiment in a packed bed column for the sorptive elucidation of fluoride from contaminated groundwater using an activated soil-clay mixture. Through the combination of naturally accessible laterite soil with silica enriched clay (3:1 ratio), a low-cost Al–Si heterogeneous material has been developed. Following detailed characterization, the developed materials were employed in a long-time column process to achieve a high degree of fluoride separation from real-world groundwater. In a packed bed column investigation, the effect of bed height, initial fluoride concentration, and flow rate on the breakthrough properties of the adsorption system were investigated. By using a non-linear regression equation, three model kinetics, such as the Thomas Model, Adams-Bohart Model, and Yoon-Nelson Model, were fitted to validate the column-based experimental data, by analysing the breakthrough curves profiles, and distinct kinetic parameters. The Bed Depth Service Time Analysis (BDST) model was tested to express the effect of bed height on breakthrough curves, as well as to predict the time for breakthrough, and material depletion under optimal conditions. The Thomas and Yoon-Nelson models were identified to be the most appropriate ones for describing the entire breakthrough curve, whereas the Adams-Bohart model was only utilised to predict the first half of the dynamic process. With correlation coefficients (R2) 0.96, the experimental results were well suited to Thomas, Yoon-Nelson, and Adams-Bohart models. Finally, regeneration assessment was carried out where even after four cycles of operation, regenerated adsorbent showed a rejection efficacy of 78% to fluoride that proves the viability of the material and methodology. 相似文献
87.
Dr. Uttam Chakraborty Patrick Bügel Lorena Fritsch Dr. Florian Weigend Prof. Dr. Matthias Bauer Prof. Dr. Axel Jacobi von Wangelin 《ChemistryOpen》2021,10(2):265-271
The controlled assembly of well-defined planar nanoclusters from molecular precursors is synthetically challenging and often plagued by the predominant formation of 3D-structures and nanoparticles. Herein, we report planar iron hydride nanoclusters from reactions of main group element hydrides with iron(II) bis(hexamethyldisilazide). The structures and properties of isolated Fe4, Fe6, and Fe7 nanoplatelets and calculated intermediates enable an unprecedented insight into the underlying building principle and growth mechanism of iron clusters, metal monolayers, and nanoparticles. 相似文献
88.
The vibrational spectroscopy of lithium dichloride anions microhydrated with one to three water molecules, [LiCl2(H2O)1–3]−, is studied in the OH stretching region (3800–2800 cm−1) using isomer-specific IR/IR double-resonance population labelling experiments. The spectroscopic fingerprints of individual isomers can only be unambiguously assigned after anharmonic effects are considered, but then yield molecular level insight into the onset of salt dissolution in these gas phase model systems. Based on the extent of the observed frequency shifts ΔνOH of the hydrogen-bonded OH stretching oscillators solvent-shared ion pair motifs (<3200 cm−1) can be distinguished from intact-core structures (>3200 cm−1). The characteristic fingerprint of a water molecule trapped directly in-between two ions of opposite charge provides an alternative route to evaluate the extent of ion pairing in aqueous electrolyte solutions. 相似文献
89.
David Terrey Jack James Ivan Tankovski Monika Dalim Michel van Spankeren Arpita Chakraborty Eric Schmitt Aman Paul 《Molecules (Basel, Switzerland)》2021,26(6)
Marine feed ingredients derived from cephalopods (e.g., squid) and crustaceans (e.g., krill) are commercially used to improve the palatability of shrimp diets. Increase in global demand for shrimps has resulted in overfishing of these marine organisms and is a matter of concern. Insect protein hydrolysate could be a sustainable alternative for the possible replacement of these marine feed ingredients. During this study, four formulations: diet A (control: not containing any palatability enhancer), diet B (containing squid meal and krill oil), diet C (containing 1% insect protein hydrolysate), and diet D (containing 2% insect protein hydrolysate) were tested for (1) time required by first subject to begin feeding (time to strike) and (2) palatability in Litopenaeus vannamei. Additionally, the chemical composition of all four diet formulations was also analyzed. Results indicate that all diets had similar crude composition. The major essential amino acids in all diets were leucine and lysine, whereas eicosapentaenoic acid was the major omega-3 fatty acid in all diets. There were no significant differences between the mean time to strike for all the tested formulations. Palatability of tested formulations was found in the following order: diet D > diet C > diet B = diet A (p < 0.05), indicating that addition of squid meal and krill oil has no effect on palatability in comparison to control, whereas inclusion of insect protein hydrolysates significantly improves the palatability of formulations. Palatability enhancement potential of insect protein hydrolysate could be attributed to the high free amino acid content and water solubility in comparison to squid meal. 相似文献
90.
Subhadip Chakraborty Rajib Saha Anupam Karmakar Sanatan Chattopadhyay 《Electroanalysis》2021,33(5):1185-1193
The present work deals with fabrication and characterization of the zinc oxide (ZnO) nanowire based novel two-electrode capacitive biosensors on flexible Polyethylene terephthalate (PET) substrates for accurate estimation of glucose by analyzing the fundamental dielectric nature of the relevant sample. The morphology and crystalline quality of grown nanowires are analyzed by using field-emission scanning electron microscope (FESEM) and X-ray diffractometer (XRD), respectively. Current and capacitance values of the device have been studied for ten different glucose concentrations relevant to the physiological standards. The analytical performance of the devices in terms of enzyme activity, reliability and flexibility has also been evaluated. 相似文献