全文获取类型
收费全文 | 1564篇 |
免费 | 210篇 |
国内免费 | 208篇 |
专业分类
化学 | 1419篇 |
晶体学 | 24篇 |
力学 | 21篇 |
综合类 | 29篇 |
数学 | 20篇 |
物理学 | 469篇 |
出版年
2024年 | 1篇 |
2023年 | 18篇 |
2022年 | 43篇 |
2021年 | 69篇 |
2020年 | 111篇 |
2019年 | 69篇 |
2018年 | 57篇 |
2017年 | 55篇 |
2016年 | 75篇 |
2015年 | 59篇 |
2014年 | 83篇 |
2013年 | 104篇 |
2012年 | 110篇 |
2011年 | 82篇 |
2010年 | 80篇 |
2009年 | 65篇 |
2008年 | 96篇 |
2007年 | 118篇 |
2006年 | 81篇 |
2005年 | 84篇 |
2004年 | 62篇 |
2003年 | 77篇 |
2002年 | 62篇 |
2001年 | 56篇 |
2000年 | 45篇 |
1999年 | 33篇 |
1998年 | 33篇 |
1997年 | 24篇 |
1996年 | 16篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 20篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有1982条查询结果,搜索用时 46 毫秒
1.
2.
ZHANG Tianran YU Huacheng WANG Wenkai BAI Pu JIN Keyan ZHANG Jia-Nan YAN Wenfu 《高等学校化学研究》2022,38(6):1532-1541
It is highly desired yet challenged to find an adsorbent with low cost and excellent performance in the removal of organic dyes from aqueous solution. Here we reported that a layered cationic aluminum oxyhydroxide material hydrothermally synthesized from the low-cost source materials of AlCl3∙6H2O, CaO and H2O, known as JU-111, can meet such criterion in removing methyl orange(MO) and Congo red(CR). JU-111 shows fast adsorption kinetics[especially for CR(15 s)] and high adsorption capacity(MO:>1000 mg/g; CR:>2900 mg/g), surpassing most of the reported adsorbents. Comprehensive characterizations of the adsorption process of MO and CR revealed that both adsorptions were achieved via the anion exchange process. The characteristics of extremely low cost and excellent performance render JU-111 great potential in the practical applications in the removal of anionic dyes. 相似文献
3.
采用简单的水热法合成了六角柱形NaErF_(4)和NaErF_(4)@NaYF_(4)核壳上转换发光材料,利用扫描电镜(SEM)、X射线粉末衍射(XRD)和荧光光谱(PL)等表征对材料的形貌、结构和上转换发光性能进行了研究。结果表明,纯NaErF_(4)样品为六角柱形,边长和厚度均为1μm左右,样品表面光滑。随着NaYF_(4)壳层的包覆,六角相NaErF_(4)周围出现了大量的立方相NaYF_(4)纳米颗粒,得到了NaErF_(4)@NaYF_(4)核壳结构。荧光光谱表明,通过在六角柱形NaErF_(4)表面包覆NaYF_(4)壳层,可以有效增强上转换发光强度,其中,位于527,543,663 nm处的3个发射峰分别对应于Er^(3+)的^(2)H_(11/2)→^(4)I_(15/2)、^(4)S_(3/2)→^(4)I_(15/2)和^(4)F_(9/2)→^(4)I1_(5/2)能级跃迁。随着壳层中Y∶F比例的增加,立方相NaYF_(4)的晶体衍射峰逐渐增强;同时,对应的NaErF_(4)@NaYF_(4)样品发射光谱中红绿比(R/G)逐渐增大,发光颜色也从绿色、经黄绿色逐渐向黄色过渡,实现了多色发光。 相似文献
4.
Amara Venkateswara Rao Basa Ashok Gopireddy Venkata Subbareddy Vatti Chandra Sekhar Gollapudi Venkata Ramanamurthy 《International Journal of Polymer Analysis and Characterization》2019,24(4):346-354
Using aqueous extraction of red sanders powder as a reducing agent, silver and copper bimetallic nanoparticles were in situ generated in cotton fabrics. Silver and copper nanoparticles were also generated separately for comparison. The resulted nanocomposite cotton fabrics (NCFs) were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and antibacterial tests. SEM analysis indicated the generation of more number of nanoparticles when bimetallic source solutions were used. Further, the size range of the generated bimetallic nanoparticles was found to be lower than when individual metal nanoparticles were generated in NCFs. XRD analysis confirmed the in situ generation of silver and copper nanoparticles when equimolar bimetallic salt source solutions were utilized. The NCFs with bimetallic nanoparticles exhibited higher antibacterial activity against both Gram-negative and Gram-positive bacteria and hence can be considered for applications as antibacterial bed and dressing materials. 相似文献
5.
Yu Zhang Dr. Novruz G. Akhmedov Prof. Jeffrey L. Petersen Prof. Carsten Milsmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(12):3042-3052
Luminescent seven-coordinated zirconium and hafnium complexes bearing three mono-anionic 2,2′-pyridylpyrrolide ligands and one chloride were synthesized. Solid-state structures and the dynamic behaviors in solution were probed by X-ray crystallography and variable temperature 1H NMR experiments, respectively. Absorption spectroscopy and time-dependent density functional theory (TD-DFT) calculations supported a hybrid of ligand-to-metal charge transfer (LMCT)/ligand-to-ligand charge transfer (LLCT) for the visible light absorption band. The complexes (MePMPMe)3MCl (M=Zr, Hf, MePMPMe=3,5-dimethyl-2-(2-pyridyl)pyrrolide) are emissive in solution at room temperature upon irradiation with visible light due to a combination of phosphorescence and fluorescence characterized by excited state lifetimes in the μs and low to sub-ns timescale, respectively. Electrochemical experiments revealed that the zirconium complex possesses a reversible redox event under highly reducing condition (−2.29 V vs. Fc+/0). 相似文献
6.
Huili Ma Anqi Lv Lishun Fu Shan Wang Zhongfu An Huifang Shi Wei Huang 《Annalen der Physik》2019,531(7)
Purely organic materials with room‐temperature phosphorescence (RTP) have attracted a growing interest for their potential applications in biological imaging, digital encryption, optoelectronic devices, and so on. To date, many strategies have succeeded in designing efficient organic RTP materials by overcoming the spin‐forbidden transition between singlet and triplet states. However, the underlying mechanisms of RTP still remain ambiguous. Such spin prohibition in phosphorescence are clarified, herein, from the perspective of perturbation theory, helping to understand the intrinsic relationship among various phosphorescence parameters, like phosphorescence efficiency, lifetime, intersystem crossing rate, as well as radiative and nonradiative rates. Taking into consideration the recent progress in organic RTP materials, these factors are further illustrated by a selection of the most relevant molecules. In addition, some novel RTP phenomena are also reviewed, thus providing an excellent guideline to constructing efficient RTP materials. 相似文献
7.
Rebeca P. Medina Angela R. Araujo Raymond J. Andersen Marcos A. Soares Fabio de A. Silva 《Natural product research》2019,33(3):443-446
Endophytic fungi were isolated from red alga Asparagopsis taxiformis - Falkenbergia stage, collected from the Brazilian coast, and were identified as Annulohypoxylon stygium (AT-03) and A. yungensis (AT-06) based on their macro/micromorphological and molecular features. Bioassay-guided fractionation of the EtOAc extract from laboratory cultures of both strains yielded known compounds pyrogallol from A. stygium, (3R)-scytalone and (3R,4R)-4-hydroxy-scytalone from A. yungensis. Pyrogallol was active against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli strains. An inactive fraction from A. stygium afforded two additional compounds, (3R,4R)-3,4,5-trihydroxy-1-tetralone and tyrosol. Optically active compounds had their stereochemistry determined by circular dichroism (CD) spectroscopy. 相似文献
8.
Xiaoyong Chen Zeyu Zhang Jiajie Wu Jiale Wang Aolong Gao 《Particle & Particle Systems Characterization》2021,38(7):2100076
Red fluorescent carbon dots (R-CDs) are special desirable for biochemical analysis due to good biological compatibility and deep penetration; however, they remain as bottlenecks due to difficulties in expanding the sp2 domain, especially those are fused from rigid polycyclic conjugated molecules (RPCMs) with heteroatom substituents due to huge steric hindrance and heteroatom blockage toward graphic lattice. Here, an RPCM with heteroatom substituents, 1,5-diamino-4,8-dihydroxyanthraquinone (DDAQ), based self-doped R-CDs with PL emission at 635 nm is reported. Further investigations reveal that the expanding, hybrid sp2 domain with indanthrone tannin structure from DDAQ is mainly responsible for the obtained red fluorescence of R-CDs. Taking advantage of optical properties, R-CDs are considered to construct a colorimetric/fluorescent dual mode sensing array for quantifying trace levels of Fe3+ and glyphosate based on the static quenching, and a biomarker for cell imaging. The CD-based sensors exhibit outstanding recovery, high selectivity, and sensitivity, also facilitated dual-mode detection with the naked-eye. The R-CDs have low cytotoxicity, good cell membrane penetration for rapid cell entry, and high resolution, demonstrating their potential for biolabeling and bioanalytic applications. 相似文献
9.
《Arabian Journal of Chemistry》2022,15(11):104171
The effectiveness of Congo red (CR) adsorption from aqueous solutions onto MgAl-layered double hydroxide (MgAl-LDH) nanosorbents was examined in this study. MgAl-LDH was synthesized using the hydrothermal method, and physicochemical characterization was performed via powdered X-ray diffraction, high-resolution transmission electron microscopy, Fourier transform infrared analysis, and zeta potential measurements. For optimum adsorption of CR onto the synthesized MgAl-LDH nanosorbent, the adsorption process was employed in batch experiments. Adsorption parameters, such as the adsorbent dosage, solution pH, contact time, and initial adsorbate concentration, vary with the adsorption kinetics and isotherm mechanism. The results of the batch experiments indicated rapid adsorption of CR dye from aqueous solutions onto MgAl-LDH during the first 30 min until equilibrium was achieved at 180 min with a dye concentration of 50 mg/100 mL and MgAl-LDH adsorbent dosage of 0.05 g. The experimental adsorption data fit adequately with the monolayer coverage under the Langmuir isotherm model (R2 = 0.9792), and showed the best fit with the pseudo-second-order kinetic model (R2 = 0.996). The change in zeta potential confirmed the effective adsorption interaction between the positively charged MgAl-LDH and the negatively charged CR molecules with electrostatic interactions. This work is distinguished by the successful hydrothermal preparation of MgAl-LDH in the form of homogenous nanoscale particles (~100 nm). The prepared MgAl-LDH showed a high adsorption capacity toward anionic CR dye with a maximum adsorption capacity of 769.23 mg/g. This capacity is higher than those reported for other adsorbents in previous research. 相似文献
10.
《Journal of Saudi Chemical Society》2022,26(3):101475
This project explains an easy, simple and eco-friendly method to remove some toxic dyes like Brilliant Green and Acid Red from aquatic solution by technique of solid-phase extraction that uses Halloysite nanoclay eco-friendly solid phase as absorbent surface for adsorption of dye. The physical properties of the HNC such as scanning electron microscopy, transmission electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and surface area analysis were studied. The best conditions like pH of the solution, HNC weight, contact shaking time, the temperature of the solution, and ionic strength were investigated for removal effectiveness. The experimental data of the adsorption process showed that HNC can remove most of the dyes within 30 min, with an adsorption capacity of 12.5 mg/g for A.R dye and 13.9 mg/g for B.G dye on HNC solid phase at optimum conditions. The removal process of dyes on HNC was studied kinetically and thermodynamically, and the data confirms that the pseudo-second-order kinetic model was able to describe the adsorption process. Thermodynamic data confirms the process was spontaneous andexothermic in nature for A.R dye, while was spontaneous and endothermic in nature for B.G dye. Finally, the effectiveness of HNC was inspected by removing dyes from three various real samples, and the results showed high performance in removing dyes on HNC for four consecutive cycles. 相似文献