全文获取类型
收费全文 | 1999篇 |
免费 | 66篇 |
国内免费 | 16篇 |
专业分类
化学 | 1503篇 |
晶体学 | 16篇 |
力学 | 71篇 |
数学 | 175篇 |
物理学 | 316篇 |
出版年
2024年 | 4篇 |
2023年 | 12篇 |
2022年 | 85篇 |
2021年 | 97篇 |
2020年 | 65篇 |
2019年 | 66篇 |
2018年 | 54篇 |
2017年 | 54篇 |
2016年 | 72篇 |
2015年 | 56篇 |
2014年 | 77篇 |
2013年 | 166篇 |
2012年 | 121篇 |
2011年 | 121篇 |
2010年 | 80篇 |
2009年 | 79篇 |
2008年 | 93篇 |
2007年 | 117篇 |
2006年 | 77篇 |
2005年 | 80篇 |
2004年 | 79篇 |
2003年 | 55篇 |
2002年 | 54篇 |
2001年 | 18篇 |
2000年 | 21篇 |
1999年 | 18篇 |
1998年 | 8篇 |
1997年 | 15篇 |
1996年 | 18篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 19篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有2081条查询结果,搜索用时 31 毫秒
71.
Dr. Saud Asif Ahmed Qiao-Bo Liao Qi Shen Dr. Mirza Muhammad Faran Ashraf Baig Juan Zhou Cai-Feng Shi Dr. Pir Muhammad Dr. Sumaira Hanif Prof. Kai Xi Prof. Xing-Hua Xia Prof. Kang Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(57):12996-13001
Layered/two-dimensional covalent organic frameworks (2D COF) are crystalline porous materials composed of light elements linked by strong covalent bonds. Interlayer force is one of the main factors directing the formation of a stacked layer structure, which plays a vital role in the stability, crystallinity, and porosity of layered COFs. The as-developed new way to modulate the interlayer force of imine-linked 2D TAPB-PDA-COF (TAPB = 1,3,5-tris(4-aminophenyl)benzene, PDA = terephthaldehyde) by only adjusting the pH of the solution. At alkaline and neutral pH, the pore size of the COF decreases from 34 Å due to the turbostratic effect. Under highly acidic conditions (pH 1), TAPB-PDA-COF shows a faster and stronger turbostratic effect, thus causing the 2D structure to exfoliate. This yields bulk quantities of an exfoliated few/single-layer 2D COF, which was well dispersed and displayed a clear Tyndall effect (TE). Furthermore, nanopipette-based electrochemical testing also confirms the slipping of layers with increase towards acidic pH. A model of pH-dependent layer slipping of TAPB-PDA-COF was proposed. This controllable pH-dependent change in the layer structure may open a new door for potential applications in controlled gas adsorption/desorption and drug loading/releasing. 相似文献
72.
I. V. Amirkhanov A. S. Khalil I. Sarkhadov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2013,7(4):711-718
Numerical simulation of the thermal processes occurring in indium phosphide under the action of a heavy gold ion with the energy E 0 = 200 MeV is carried out. The problem is solved taking into account phase transitions of the melting and evaporation types. Numerical studies are carried out on the basis of a modified thermal-peak model and the obtained results are analyzed. 相似文献
73.
Y. M. Khawassek A. M. Masoud M. H. Taha A. E. M. Hussein 《Journal of Radioanalytical and Nuclear Chemistry》2018,315(3):493-502
The present work deals with the adsorption of uranium from a nitric acid waste solution using the cation exchange resin Amberjet 1200 H (AHR) . Batch experiments were performed in order to assess the performance of AHR in uranium adsorption. The influences of pH, contact time, initial uranium concentration and temperature have been enhanced. The physical parameters including the adsorption kinetics, the isotherm models and the thermodynamic data have also been determined to determine the nature of the uranium adsorption by AHR. The studied resin has been agreed with both the pseudo second order reaction and Langmuir isotherm. 相似文献
74.
75.
76.
Gunnar Aksnes Fayez Y. Khalil Piotr J. Majewski 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):157-161
Abstract This study reports rate data of the alkoxide promoted decomposition of triphenyl 3-hydroxypropyl phosphonium chloride, diphenyl di(3-hydroxypropyl)phosphonium chloride, and tetraphenyl phosphonium bromide. Comparison of kinetics, rate constants, and activation parameters of the alkoxide promoted decompositions points to different mechanism as compared to the hydroxyl promoted reaction. The alkoxide reaction is believed to proceed via a hexacovalent intermediate. Reasons for the hexacovalent route are discussed. 相似文献
77.
Taha M. Abdel-Rahman 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1737-1754
A novel method for the synthesis of 1,3,4-thiadiazole and 1,3,4-thiadiazine derivatives bearing a carbazole moiety is described. Carbazole was transformed into carbazole-9-thiocarbohydrazide in two steps. This compound was allowed to react with various electrophiles to yield 1,3,4-thiadiazole derivatives. The reaction with bifunctional electrophiles led to 1,3,4-thiadiazines. 2-(Carbazol-9-yl)-5,6-dihydro-4H-1,3,4-thiadiazin-5-one reacted with piperidine and formaldehyde to yield the 4-(piperidin-1-ylmethyl) derivative. The reaction with aromatic aldehydes led to the corresponding 6-arylidene derivatives, which were transformed into pyrimidino[4,5-e]-1,3,4-thiadiazines and pyrazolo[3,4-e]-1,3,4-thiadiazines by a reaction with guanidine, acetamidine, or phenylhydrazine, respectively. Structures of the products were confirmed by 1H NMR, 13C NMR, IR, and mass spectrometric measurements. Selected examples of products were screened for anticancer activity. 相似文献
78.
Melamine modified polyester amide (MPEA) was synthesized by the reaction of linseed oil fatty amide. The resin was further cured at room temperature by polystyrene co‐maleic anhydride (SMA) in different phr (30–80) to obtain MPEA coatings. The probable structure of MPEA was confirmed by FT‐IR, 1H‐NMR and 13C‐NMR spectroscopic techniques. The physico‐chemical characterization of these resins viz. iodine value, saponification value, refractive index, inherent viscosity were carried out by standard methods. MPEA (40 wt%) solution in ethylene glycol monomethyl ether (EGME) was applied on a mild steel strip of standard sizes to study their physico‐mechanical and chemical resistance properties. It was found that coatings of MPEA with 60 parts per hundred of the resin (phr) of SMA showed the best performance in physico‐mechanical and alkali resistance properties. Thermal stability and curing behavior were studied by Thermo Gravimetric Analyses (TGA) and Differential Scanning Calorimetry (DSC), respectively. 相似文献
79.
Two terthiophenes incorporating the synthon 3,4-(1,2-phenylenedioxy)thiophene (PheDOT) have been developed. Specifically, 2,5-bisthienyl-3,4-(1,2-phenylenedioxy)thiophene (BTh-PheDOT 1) and 2,5-bisethylenedioxythienyl-3,4-(1,2-phenylenedioxy)thiophene (BEDOT-PheDOT 2) were electropolymerized to form electroactive polymer films (P1 and P2) that switched between two highly colored states with the more electron-rich EDOT derivative P2 observed to switch at a lower potential. Additionally, both P1 and P2 displayed moderate to low optical bandgaps of 1.8 and 1.6 eV, respectively. Crystal structures of BTh-PheDOT showed the monomer to be nearly planar with π -stacking observable between monomers. These findings demonstrate the potential of PheDOT as an electroactive synthon for the formation of well-ordered systems. 相似文献
80.
Five new optically active aromatic poly(amide-imide)s (PAIs) 5a–e were prepared from a direct polycondensation reaction of a new diacid of N,N′-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetra carboxylic)-bis-L-isoleucine 3 with various aromatic diamines 4a–e in a medium consisting of triphenyl phosphite (TPP), calcium chloride (CaCl2), pyridine (Py) and N-methyl-2-pyrrolidone (NMP). The polycondensation reaction produced a series of novel poly(amid-imide)s 5a–e in quantitative yields with inherent viscosities of 0.39–0.51 dL/g. The resulting polymers were fully characterized by means of 1H-NMR, FT-IR spectroscopy, elemental analyses, inherent viscosity, solubility test, specific rotation and thermal properties of them were investigated using TGA/DTG and differential scanning calorimeter (DSC). The diacid 4 was synthesized by the condensation reaction of bicyclo[2,2,2]oct-7-ene-2,3,5,6- tetracarboxylic dianhydride 1 with L-isoleucine 2 in acetic acid solution. 相似文献