全文获取类型
收费全文 | 469篇 |
免费 | 33篇 |
国内免费 | 5篇 |
专业分类
化学 | 362篇 |
力学 | 14篇 |
数学 | 36篇 |
物理学 | 95篇 |
出版年
2023年 | 6篇 |
2022年 | 16篇 |
2021年 | 17篇 |
2020年 | 30篇 |
2019年 | 34篇 |
2018年 | 36篇 |
2017年 | 36篇 |
2016年 | 43篇 |
2015年 | 26篇 |
2014年 | 33篇 |
2013年 | 57篇 |
2012年 | 33篇 |
2011年 | 24篇 |
2010年 | 18篇 |
2009年 | 11篇 |
2008年 | 21篇 |
2007年 | 20篇 |
2006年 | 10篇 |
2005年 | 2篇 |
2004年 | 7篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有507条查询结果,搜索用时 78 毫秒
41.
Elham Kanaani 《合成通讯》2017,47(14):1326-1331
A series of novel dihydroquinoline derivatives were synthesized using malononitrile, 2-aminobenzoic acid, and benzaldehydes in the presence of a catalytic amount of acetic acid, without the use of any additional cocatalyst, under solvent-free conditions. The reaction is characterized by high efficiency, easy workup, simple purification of the products, and availability of catalyst. 相似文献
42.
We studied the DFT (B3LYP) and HF at 6-31+G/6-31+G∗∗ levels of theory in order to throw light on the conformation, structure, intramolecular hydrogen bond network, as well as proton and nitrogen NMR (GIAO method) of a series of model primary amides in the gas phase and/or in solution (chloroform, methanol, water, dimethyl sulfoxide, and heptane). In this manner, it was possible to show that the amidic group of these model compounds acts as the H-bond donor and interacts with two different H-bond acceptors, thus stabilizing the C8 pseudocycle. The study was conducted to gain a better understanding of the conformation (both experimentally and theoretically) adopted by hydrazino acetamides (model compounds for aza-β3-peptides). In the light of this, we were able to explain why aza-β3-peptides develop a different H-bond network in comparison to their isosteric β3-peptide analogues (an extension of the β-peptide concept). 相似文献
43.
44.
45.
46.
Synthesis,Electrochemical and Luminescence Studies of Nickel and Vanadium Complexes Containing Tetradentate Schiff Base Ligand with N2O2 Donor Atoms
下载免费PDF全文
![点击此处可从《中国化学会会志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A symmetrical tetradentate Schiff base ligand was derived by the condensation of ortho‐vanillin and thiourea in 2:1 molar ratio and adjusted pH. Nickel and vanadyl complexes were obtained using the template method by the reaction of ortho‐vanillin and thiourea with Ni(OAc)2. 4H2O and VO(acac)2 (2:1:1 molar ratio) in absolute ethanol and adjusted pH. The Schiff base ligand and its complexes have been characterized by FT‐IR, 1H NMR, UV/Vis, elemental analysis and conductometry measurements. In nickel and also vanadyl complexes the ligands were coordinated to the metals via the imine N and enolic O atoms. The complexes have been found to possess 1:1 metal to ligand stoichiometry and the molar conductance data revealed that the metal complexes were non‐electrolytes. The nickel and vanadyl complexes exhibited tetrahedral and square pyramidal coordination geometry, respectively. The emission spectra of the ligand and its complexes were studied in DMSO. Electrochemical properties of the ligand and its complexes were also investigated in the DMF solvent at the 150 mVs‐1 scan rate. The ligand and its complexes showed irreversible processes at this scan rate. 相似文献
47.
Mehrorang Ghaedi Gholamreza Karimipour Elham Alambarkat Arash Asfaram Morteza Montazerozohori Sahar Izadpanah 《International journal of environmental analytical chemistry》2015,95(11):1030-1041
The development of a solid-phase extraction (SPE) procedure for the pre-concentration of trace amounts of Pb2+ ion on 2-furan-2-yl-1-furan-2-ylmethyl-1H-benzoimidazole loaded on activated carbon modified with silver nanoparticles (L-AC-Ag-NP) was presented. The metal ion retained on the sorbent was quantitatively determined via complexation with the ligand. The complexed metal ion was efficiently eluted using 10 mL of 4 mol L?1 sulphuric acid in 10 w/v% acetone. The influences of the analytical parameters, including pH, amounts of the ligand and the solid phase, eluent conditions and sample volume, on the recoveries of the metal ion were optimised. Using the optimised parameters, the linear response of the SPE method for Pb2+ ion were in the ranges of 0.2–160 µg L?1, and the detection limit for Pb2+ ion was 0.034 µg L?1. The proposed method exhibits a pre-concentration factor (PF) of 80 and an enhancement factor of 30 for Pb2+ ion. The presented results demonstrate the successful application of the proposed method for the determination of Pb2+ ion in some real samples with high recoveries (>93%) and reasonable relative standard deviation (RSD < 2%). 相似文献
48.
Zeinab Ansari-Asl Tahereh Sedaghat Abbas Tarassoli Hossein Motamedi Elham Hoveizi 《Phosphorus, sulfur, and silicon and the related elements》2017,192(5):538-543
Three new water-soluble organotin complexes R2Sn(5-BrSalGT)Cl [R = Ph, Me] and Ph2Sn(2-OHNaphGT)Cl have been synthesized by the reaction of R2SnCl2 (R = Ph or Me) with Schiff bases derived from condensation of Girard-T reagent with 5-bromosalicylaldehyde and 2-naphthaldehyde, (5-BrH2SalGT)Cl (1) and (2-OHH2NaphGT)Cl (2). The synthesized compounds have been investigated by elemental analysis, conductometric measurements, IR, 1H NMR, and 119Sn NMR spectroscopy. These data show that the deporotonated ligand is coordinated to Sn(IV) via ONO atoms and six-coordinate zwitterionic complexes are formed. The ligands and their complexes were investigated for their in vitro toxicity against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. The results show remarkable antibacterial activity against the studied bacteria. All complexes exhibit more inhibitory effects than the parent ligand. The anticancer activity of all compounds were also performed on HN5 cell line and (2-OHH2NaphGT)Cl with concentration of 1 mg mL?1 was found to show higher anticancer activity than other compounds. 相似文献
49.
50.
Elham Masoudipour Soheila Kashanian Abbas Hemati Azandaryani Kobra Omidfar Elham Bazyar 《Cellulose (London, England)》2017,24(10):4217-4234
Storage conditions seem to be important in the long-term stability of nanoparticles (NPs). This work studies the effects of surfactants and storage container on particle size distribution and zeta potential during long-term storage of acid hydrolyzed potato starch NPs. The NPs were prepared from potato starch using acid hydrolysis and high-intensity ultrasonication. During the ultrasonic treatment, the surfactants were added dropwise to the solutions to reduce the size and stabilize the formed NPs. Particle size distribution, zeta potential, and FE-SEM were used to characterize the ensuing NPs. Additionally, a 5-month stability study was performed to evaluate the maintenance of potato starch NPs over time at different storage conditions. Then, NPs from corn starch were produced by the same procedure and were used for preparing pH-responsive nanocarriers containing NaHCO3 for delivery of an anti-cancer drug, FTY720. These NPs were able to release the drug at pH 5.0 because of CO2 generated from NaHCO3 in acidic pH and released from the NPs by the production of pores, which accelerate drug release. 相似文献