全文获取类型
收费全文 | 9821篇 |
免费 | 261篇 |
国内免费 | 20篇 |
专业分类
化学 | 5831篇 |
晶体学 | 162篇 |
力学 | 267篇 |
数学 | 733篇 |
物理学 | 3109篇 |
出版年
2023年 | 94篇 |
2022年 | 212篇 |
2021年 | 161篇 |
2020年 | 177篇 |
2019年 | 243篇 |
2018年 | 207篇 |
2017年 | 232篇 |
2016年 | 317篇 |
2015年 | 213篇 |
2014年 | 400篇 |
2013年 | 781篇 |
2012年 | 548篇 |
2011年 | 655篇 |
2010年 | 417篇 |
2009年 | 405篇 |
2008年 | 460篇 |
2007年 | 440篇 |
2006年 | 335篇 |
2005年 | 281篇 |
2004年 | 229篇 |
2003年 | 163篇 |
2002年 | 183篇 |
2001年 | 117篇 |
2000年 | 125篇 |
1999年 | 86篇 |
1998年 | 56篇 |
1997年 | 56篇 |
1996年 | 92篇 |
1995年 | 104篇 |
1994年 | 98篇 |
1993年 | 93篇 |
1992年 | 120篇 |
1991年 | 86篇 |
1990年 | 79篇 |
1989年 | 92篇 |
1988年 | 87篇 |
1987年 | 90篇 |
1986年 | 74篇 |
1985年 | 104篇 |
1984年 | 119篇 |
1983年 | 82篇 |
1982年 | 98篇 |
1981年 | 97篇 |
1980年 | 102篇 |
1979年 | 90篇 |
1978年 | 102篇 |
1977年 | 84篇 |
1976年 | 56篇 |
1975年 | 61篇 |
1974年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Imprinted silica nanoparticles coated with N‐propylsilylmorpholine‐4‐carboxamide for the determination of m‐cresol in synthetic and real samples
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Manisha Ghai Priyanka Narula Varinder Kaur Raghubir Singh 《Journal of separation science》2015,38(19):3442-3449
m‐Cresol‐imprinted silica nanoparticles coated with N‐propylsilylmorpholine‐4‐carboxamide have been developed that contain specific pockets for the selective uptake of m‐cresol. Silica nanoparticles were synthesized by a sol–gel process followed by functionalization of their surface with N‐propylsilylmorpholine‐4‐carboxamide. The formation of m‐cresol‐imprinted silica nanoparticles was confirmed by UV‐Vis spectrophotometry, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. Electron microscopic studies revealed the formation of monodispersed imprinted silica nanoparticles with spherical shape and an average size of 83 nm. The developed nanoparticles were filled in a syringe and used for the extraction of m‐cresol from aqueous samples followed by quantification using high‐performance liquid chromatography with diode array detection. Various adsorption experiments showed that developed m‐cresol‐imprinted silica nanoparticles exhibited a high adsorption capacity and selectivity and offered a fast kinetics for rebinding m‐cresol. The chromatographic quantification was achieved using mobile phase consisting of acetonitrile/water (70:30 v/v) at an isocratic flow rate of 1.0 mL/min using a reversed‐phase C18 column and detection at λmax = 275 nm. The limits of detection and quantification were 1.86 and 22.32 ng/mL, respectively, for the developed method. The percent recoveries ranged from 96.66–103.33% in the spiked samples. This combination of this nanotechnique with molecular imprinting was proved as a reliable, sensitive and selective method for determining the target from synthetic and real samples. 相似文献
992.
Anuj Kumar Yuvraj Singh Negi Veena Choudhary Nishi Kant Bhardwaj 《International Journal of Polymer Analysis and Characterization》2017,22(2):139-151
Cellulose nanocrystal-reinforced poly(vinyl alcohol)/silica glass hybrid scaffolds were fabricated using the freeze-drying method. In this study, we develop molecular-level-based hybrid scaffolds with possible bioactivity behavior by adding silica sol–gel. The results showed a highly porous structure and a significant improvement in mechanical performance (stiffness) of hybrid scaffolds with an increased content of cellulose nanocrystals followed by the addition of silica-based bioactive glass. In vitro cell study with MC3T3-E1 cells on hybrid scaffolds for 1 and 3 days revealed good cell adhesion and growth. Thus, the obtained hybrid scaffold may be a competitive candidate for bone tissue engineering applications. 相似文献
993.
C. F. Mok F. Muhamad N. A. Abu Osman Ramesh Singh 《International Journal of Polymer Analysis and Characterization》2017,22(4):294-304
Poly(vinyl alcohol)-α-chitin composite films reinforced by oil palm empty fruit bunch fiber-derived nanocellulose were prepared by casting technique. Fourier transform infrared spectroscopy analysis revealed partial miscibility between chitin and poly(vinyl alcohol) through hydrogen bonding, as supported by differential scanning calorimetry and field emission scanning electron microscopy. Tensile strength of the poly(vinyl alcohol)/chitin films increased with α-chitin content varied from 10 to 30?wt%, which was from 29.06 to 39.27?MPa. With the addition of 1?wt% nanocellulose, a maximum improvement of 57.64 and 50.66% in terms of tensile strength and Young’s modulus was achieved, respectively. 相似文献
994.
995.
996.
Arjun K. Mishra Nidhi Singh Pragati Agnihotri Shikha Mishra Saurabh P. Singh Bala K. Kolli Kwang Poo Chang Amogh A. Sahasrabuddhe M. I. Siddiqi J. Venkatesh Pratap 《Journal of computer-aided molecular design》2017,31(6):547-562
Nucleoside diphosphate kinases (NDKs) are ubiquitous enzymes that catalyze the transfer of the γ-phosphate moiety from an NTP donor to an NDP acceptor, crucial for maintaining the cellular level of nucleoside triphosphates (NTPs). The inability of trypanosomatids to synthesize purines de novo and their dependence on the salvage pathway makes NDK an attractive target to develop drugs for the diseases they cause. Here we report the discovery of novel inhibitors for Leishmania NDK based on the structural and functional characterization of purified recombinant NDK from Leishmania amazonensis. Recombinant LaNDK possesses auto-phosphorylation, phosphotransferase and kinase activities with Histidine 117 playing an essential role. LaNDK crystals were grown by hanging drop vapour diffusion method in a solution containing 18% PEG-MME 500, 100 mM Bis-Tris propane pH 6.0 and 50 mM MgCl2. It belongs to the hexagonal space group P6322 with unit cell parameters a?=?b?=?115.18, c?=?62.18 Å and α?=?β?=?90°, γ?=?120°. The structure solved by molecular replacement methods was refined to crystallographic R-factor and Rfree values of 22.54 and 26.52%, respectively. Molecular docking and dynamics simulation-based virtual screening identified putative binding compounds. Protein inhibition studies of selected hits identified five inhibitors effective at micromolar concentrations. One of the compounds showed ~45% inhibition of Leishmania promastigotes proliferation. Analysis of inhibitor-NDK complexes reveals the mode of their binding, facilitating design of new compounds for optimization of activities as drugs against leishmaniasis. 相似文献
997.
Abhay Nanda Srivastva Netra Pal Singh Chandra Kiran Shriwastaw 《Research on Chemical Intermediates》2017,43(10):5453-5465
Reaction between hydrazine derivative ligands (HrzE) or (HrzB) and chromium salt in 1:2 (metal:ligand) molar ratio yielded monometallic trivalent coordination compounds with general formula [Cr(HrzE)2X2]X and [Cr(HrzB)2X2]X, where (HrzE) = hydrazine carboxylic acid ethyl ester, (HrzB) = hydrazine carboxylic acid tert-butyl ester, and X = Cl?, Br? or F?. Elemental analysis, conductivity measurements, magnetic moment measurements, and various spectroscopic techniques, viz. infrared, ultraviolet–visible, and electrospray ionization mass spectrometry, were applied to illustrate the structure and composition of the coordination compounds. Analytic and conductivity results were consistent with 1:1 electrolytic behavior and the proposed formulas of the coordination compounds. Electronic absorption data and magnetic moment parameters indicated octahedral geometry surrounding the metal ion in the coordination compounds. The in vitro antimicrobial behavior of the ligands and coordination compounds was screened using four bacterial strains (Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Salmonella typhi) and two fungal strains (Candida parapsilosis and Saccharomyces cerevisiae). The results indicated improved activity of the coordination compounds compared with the free ligands against the studied bacteria and fungi. 相似文献
998.
Sun Zhipeng Singh Ambrish Xu Xihua Chen Songsong Liu Wanying Lin Yuanhua 《Research on Chemical Intermediates》2017,43(11):6719-6736
Research on Chemical Intermediates - Pomelo peel extract (PPE) has been evaluated as a corrosion inhibitor for N80 steel in 3.5% NaCl saturated with CO2 solution using weight loss measurements,... 相似文献
999.
Santosh Ramdas Borkar Naveen Bokolia Indrapal Singh Aidhen Inshad Ali Khan 《Tetrahedron: Asymmetry》2017,28(1):186-195
A series of threo- and erythro-configured open-chain trihydroxy ketones was synthesized starting from l- and d-ascorbic acid respectively as the starting material, through the use of Grignard reactions for the requisite CC bond formations. The lipophilic ketones were screened against Mycobacteriumtuberculosis for anti-proliferative activity. The lipophilic ketones with tetradecyl alkyl side chains were found to be moderately active against cell proliferation. 相似文献
1000.
A tri-armed-pyrene-linked molecular receptor, 5 has been designed, synthesised and evaluated for ionic recognition. It has been observed that the synthesised molecular receptor can recognise mercury and cyanide ions through a change in colour, UV–Vis and fluorescence intensity. The binding stoichiometry of the receptor and these ionic species has been found to be 1:1 through Job’s plots, Benesi–Hildebrand plots and isothermal titration calorimetry (ITC). 相似文献