全文获取类型
收费全文 | 6971篇 |
免费 | 632篇 |
国内免费 | 1312篇 |
专业分类
化学 | 5902篇 |
晶体学 | 52篇 |
力学 | 127篇 |
综合类 | 11篇 |
数学 | 44篇 |
物理学 | 2779篇 |
出版年
2024年 | 7篇 |
2023年 | 202篇 |
2022年 | 219篇 |
2021年 | 275篇 |
2020年 | 364篇 |
2019年 | 262篇 |
2018年 | 241篇 |
2017年 | 307篇 |
2016年 | 387篇 |
2015年 | 363篇 |
2014年 | 381篇 |
2013年 | 553篇 |
2012年 | 466篇 |
2011年 | 587篇 |
2010年 | 442篇 |
2009年 | 574篇 |
2008年 | 526篇 |
2007年 | 535篇 |
2006年 | 447篇 |
2005年 | 365篇 |
2004年 | 288篇 |
2003年 | 205篇 |
2002年 | 115篇 |
2001年 | 124篇 |
2000年 | 121篇 |
1999年 | 63篇 |
1998年 | 99篇 |
1997年 | 94篇 |
1996年 | 57篇 |
1995年 | 41篇 |
1994年 | 30篇 |
1993年 | 28篇 |
1992年 | 34篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有8915条查询结果,搜索用时 15 毫秒
1.
Approximately every 100 years, as witnessed in the last two centuries, we are facing an influenza pandemic, necessitating the need to combat a novel virus strain. As a result of the new coronavirus (severe acute respiratory syndrome coronavirus type 2 [SARS-CoV-2] outbreak in January 2020, many clinical studies are being carried out with the aim of combating or eradicating the disease altogether. However, so far, developing coronavirus disease 2019 (COVID-19) detection kits or vaccines has remained elusive. In this regard, the development of antiviral nanomaterials by surface engineering with enhanced specificity might prove valuable to combat this novel virus. Quantum dots (QDs) are multifaceted agents with the ability to fight against/inhibit the activity of COVID-19 virus. This article exclusively discusses the potential role of QDs as biosensors and antiviral agents for attenuation of viral infection. 相似文献
2.
The behaviors of ferromagnetic transition metals of the first period: Fe, Co and Ni are examined within density functional theory calculations in two dimensional carbon extended networks using model structure LiC6. Around geometry optimized structures, the energy-volume equations of states considering non magnetic and spin polarized configurations established ferromagnetic ground states with magnetizations –reduced with respect to the metals’– of 2 μB for FeC6 and 1 μB for CoC6 while no magnetic solution could be identified for NiC6. In the D6h point group of the P6/mmm space group lm decomposition of the d states results with increasing energy into doublet state E1g with d(x2-y2) and d(xy); singlet state A1g d(z2) and doublet state E2g d(xz) and d(yz) lying on EF and responsible of the onset of magnetic moments. This was mirrored via molecular orbital approach with a construct of Fe embedded between two extended carbon networks thus validating the model structure proposed for TC6 compounds. The 100% polarization in one spin channel allows proposing potential uses in spintronics applications. 相似文献
3.
In this study, we investigated an alternative method for the chemical CO2 reduction reaction in which power ultrasound (488 kHz ultrasonic plate transducer) was applied to CO2-saturated (up to 3%) pure water, NaCl and synthetic seawater solutions. Under ultrasonic conditions, the converted CO2 products were found to be mainly CH4, C2H4 and C2H6 including large amount of CO which was subsequently converted into CH4. We have found that introducing molecular H2 plays a crucial role in the CO2 conversion process and that increasing hydrogen concentration increased the yields of hydrocarbons. However, it was observed that at higher hydrogen concentrations, the overall conversion decreased since hydrogen, a diatomic gas, is known to decrease cavitational activity in liquids. It was also found that 1.0 M NaCl solutions saturated with 2% CO2 + 98% H2 led to maximum hydrocarbon yields (close to 5%) and increasing the salt concentrations further decreased the yield of hydrocarbons due to the combined physical and chemical effects of ultrasound. It was shown that CO2 present in a synthetic industrial flue gas (86.74% N2, 13% CO2, 0.2% O2 and 600 ppm of CO) could be converted into hydrocarbons through this method by diluting the flue gas with hydrogen. Moreover, it was observed that in addition to pure water, synthetic seawater can also be used as an ultrasonicating media for the sonochemical process where the presence of NaCl improves the yields of hydrocarbons by ca. 40%. We have also shown that by using low frequency high-power ultrasound in the absence of catalysts, it is possible to carry out the conversion process at ambient conditions i.e., at room temperature and pressure. We are postulating that each cavitation bubble formed during ultrasonication act as a “micro-reactor” where the so-called Sabatier reaction - - takes place upon collapse of the bubble. We are naming this novel approach as the “Islam-Pollet-Hihn process”. 相似文献
4.
Non-noble bifunctional electrocatalysts with robust activity and stability toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are greatly significant but challenging for Zn-air batteries. Here, in situ confinement of FeNx active sites in high porosity carbon framework (FeNx/CMCC) derived from chelate of carboxymethylcellulose (CMC) and iron ions were synthesized. Particularly, construction of FeNx within porous carbon framework accelerates the electron transfer and the sufficient utilization of active centers, and then expedites the reaction kinetics of ORR and OER. As expected, the optimized FeNx/CMCC exhibits superior ORR activity with a larger half-wave potential of 0.869 V. The rechargeable Zn-air battery delivers a higher power density of 99.6 mW/cm2 and a special capacity of 781.9 mA h/gZn at 10 mA/cm2, together with excellent durability of over 335 h. Remarkably, the as-assembled solid-state battery exhibits a higher open circuit voltage (OCV) of 1.5 V, a special capacity of 709.7 mA h/gZn, as well as prolonged cycling stability (90 h). Moreover, the flexible solid-state battery displays negligible loss of electrochemical performance under various bending angles, illustrating its potential application in flexible electronic devices. 相似文献
5.
Ke Xu Evan T. Vickers Longshi Rao Dr. Sarah A. Lindley A'Lester C. Allen Prof. Binbin Luo Prof. Xueming Li Prof. Jin Zhong Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(19):5014-5021
CH3NH3PbBr3 perovskite quantum dots (PQDs) are synthesized by using four different linear alkyl phosphonic acids (PAs) in conjunction with (3-aminopropyl)triethoxysilane (APTES) as capping ligands. The resultant PQDs are characterized by means of XRD, TEM, Raman spectroscopy, FTIR spectroscopy, UV/Vis, photoluminescence (PL), time-resolved PL, and X-ray photoelectron spectroscopy (XPS). PA chain length is shown to control the PQD size (ca. 2.9–4.2 nm) and excitonic absorption band positions (λ=488–525 nm), with shorter chain lengths corresponding to smaller sizes and bluer absorptions. All samples show a high PL quantum yield (ca. 46–83 %) and high PL stability; this is indicative of a low density of band gap trap states and effective surface passivation. Stability is higher for smaller PQDs; this is attributed to better passivation due to better solubility and less steric hindrance of the shorter PA ligands. Based on the FTIR, Raman, and XPS results, it is proposed that Pb2+ and CH3NH3+ surface defects are passivated by R−PO32− or R−PO2(OH)−, whereas Br− surface defects are passivated by R−NH3+ moieties. This study establishes the combination of PA and APTES ligands as a highly effective dual passivation system for the synergistic passivation of multiple surface defects of PQDs through primarily ionic bonding. 相似文献
6.
In this work, the interfacial mass balance relations combined with the non-parametric kinetic (NPK) analysis results were used for evaluating the thermo-chemical ablation process and oxidation mechanism of carbon aerogels with various porous structure. It was found that the two-parameter model of Nomen–Sempereis was able to describe the kinetics of the oxidation reaction and to reveal the structure-dependent contribution of two main processes with chemical and physical nature. The porosity of the carbon aerogel, rather than the other microstructural features, was realized more effective on the rate of ablation. 相似文献
7.
A. Bande 《Molecular physics》2019,117(15-16):2014-2028
ABSTRACTRecently, highly accurate multi-configuration time-dependent Hartree electron dynamics calculations demonstrated the efficient long-range energy transfer inter-Coulombic decay (ICD) process to happen in charged semiconductor quantum dot (QD) pairs. ICD is initiated by intraband photoexcitation of one of the QDs and leads to electron emission from the other within a duration of about 150 ps. On the same time scale electronically excited states are reported to relax due to the coupling of electrons to acoustic phonons. Likewise, phonons promote ionisation. Here, the QDs' acoustic breathing mode is implemented in a frozen-phonon approach. A detailed comparison of the phonon effects on electron relaxation and emission as well as on the full ICD process is presented, which supports the previous empirical finding of ICD being the dominant decay channel in paired QDs. In addition the relative importance of phonon–phonon, phonon–electron and electron–electron interaction is analysed. 相似文献
8.
The carbon composite materials have been a research hotspot in the fields of catalysis, energy conversion and so on, because of their features of large structure and morphology variety, good chemical and electrochemical stability, and high electronic conductivity, large specific surface area and rich active sites. This paper summarizes some research progress of carbon composite materials, including assembly methodologies, their structure regulation, properties, and related applications. Moreover, the current challenges and the prospects of these materials are also discussed. 相似文献
9.
Farah Noun John Manioudakis Rafik Naccache 《Particle & Particle Systems Characterization》2020,37(8):2000119
Carbon dots possess versatile optical properties that have prompted their investigation in applications including photocatalysis, photovoltaics, imaging, and drug delivery, among others. However, the preparation of these nanodots is accompanied by the formation of fluorophores and intermediates, which can be difficult to separate. In the absence of thorough purification protocols, the reported optical properties are often heterogeneous, which hinders understanding of their physicochemical and optical properties and concrete application development. Here, two hydrophilic carbon dot systems starting with citric acid and diethylenetriamine are prepared. The impact of purification, including dialysis, ultrafiltration, and organic washes, on the properties of the dots is demonstrated. It is shown that monitoring the purification endpoint using near-infrared, fluorescence, and absorbance spectroscopies is possible. Moreover, it is demonstrated that fluorescence quantum yields can be a reliable tool to determine the purification endpoint. This work shows that even carbon dots derived from the same chemical precursors can have different purification profiles and purification requirements. However, the developed approach can be used to determine the proper purification procedure and endpoint for any carbon dot system regardless of the starting materials. Finally, it is envisioned that this work can be easily extended toward the purification of other hydrophilic nanomaterials. 相似文献
10.