全文获取类型
收费全文 | 28135篇 |
免费 | 4705篇 |
国内免费 | 3486篇 |
专业分类
化学 | 20714篇 |
晶体学 | 399篇 |
力学 | 1663篇 |
综合类 | 263篇 |
数学 | 2893篇 |
物理学 | 10394篇 |
出版年
2024年 | 69篇 |
2023年 | 623篇 |
2022年 | 850篇 |
2021年 | 1022篇 |
2020年 | 1214篇 |
2019年 | 1182篇 |
2018年 | 928篇 |
2017年 | 932篇 |
2016年 | 1322篇 |
2015年 | 1328篇 |
2014年 | 1524篇 |
2013年 | 2014篇 |
2012年 | 2488篇 |
2011年 | 2643篇 |
2010年 | 1788篇 |
2009年 | 1580篇 |
2008年 | 1859篇 |
2007年 | 1723篇 |
2006年 | 1533篇 |
2005年 | 1340篇 |
2004年 | 976篇 |
2003年 | 857篇 |
2002年 | 832篇 |
2001年 | 616篇 |
2000年 | 575篇 |
1999年 | 601篇 |
1998年 | 454篇 |
1997年 | 467篇 |
1996年 | 410篇 |
1995年 | 396篇 |
1994年 | 397篇 |
1993年 | 324篇 |
1992年 | 250篇 |
1991年 | 242篇 |
1990年 | 218篇 |
1989年 | 162篇 |
1988年 | 115篇 |
1987年 | 110篇 |
1986年 | 87篇 |
1985年 | 79篇 |
1984年 | 61篇 |
1983年 | 39篇 |
1982年 | 35篇 |
1981年 | 28篇 |
1980年 | 17篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1959年 | 2篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
941.
A novel one-step protocol for the preparation of porous polyurea material (PPU) through precipitation polymerization of toluene diisocynate (TDI) is presented. The process is based on step polymerization of one singlemonomer, TDI, with water in water-acetonemixed solvent. PPU is obtained without need for any porogen or additives, and no any chemical modification on the outcome polymer is necessary. The morphology, pore size and size distribution of PPU are characterized by scanning electron microscope and BET nitrogen adsorption. Taking acid fuchsine (AF) and Congo Red as dye examples in wastewaters, their adsorption on, desorption from PPU and the reusability of PPU were tested. Experimental conditions for AF adsorption were optimized with regard to pH, adsorption time, AF concentration and amount of PPU. Results demonstrate that the as-prepared PPU is of high performance in dyes adsorption and recycled use. This work presents therefore a novel and attractive candidate for removal of anionic dyes from wastewaters. 相似文献
942.
A convenient and scalable synthesis of l-amino-5-cyanonaphthalene was described. 相似文献
943.
Yunxiang Deng Chaopan Peng Ping Liu Jiang Lu Longmei Zeng Lichang Wang 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):995-1004
Abstract The copolymerization products of α-pinene and styrene were prepared with the compound catalyst system SbCl3/AlCl3 by changing the Sb/Al ratio, feeding monomer ratio, solvent, and polymerization temperature. The compositions of the copolymerization products were quantitatively characterized by the method of the combination of micro-ozonization and thin-layer chromatography in terms of the contents of the homopolymers and the copolymers containing high or low mole fractions of α-pinene, the yields of pure copolymer, and the monomer unit ratios (F 1) of copolymers. The results show that it was easier to obtain the higher yield (up to 80%) of the pure copolymer with the complex catalyst system than with AlCl3 alone. The F 1 values could be controlled between 30 and 56% under the following polymerization conditions: Sb/Al 1/2, α-pinene/styrene 70%, and the conversion of styrene 90%. 相似文献
944.
Dinuclear ytterbium and erbium based bifunction complexes Ln2L2(depma2)Cl2 (1-Ln, Ln = Yb and Er, H2L = N1,N3-bis(salicylideneimino)diethylenetriamine, depma2 = dimerized 9-diethyl-phosphonomethylanthracene) are reported. They undergo thermo-induced consecutive phase transitions, first the dissociation of depma2 ligand forming LnL(depma)Cl (2-Ln) and then the release of chloroethane forming LnL(epma) (3-Ln, epma = 9-ethylphosphonomethylanthrancene). The structural transformations are accompanied with synergetic switch of the luminescence in visible and NIR regions and also magnetic dynamics. 相似文献
945.
946.
Zongxia Guo Yubao Song Ruiying Gong Youbing Mu Yi Jiang Ming Li 《Supramolecular chemistry》2013,25(5-6):383-391
Biomolecule-directed self-assembly of π-conjugated oligomers has attracted great attention in the past decade. In this contribution, two conjugates composed of quaterthiophene and tetrapeptide (Gly-Val-Gly-Val) were synthesised, namely peptide–thiophene–peptide (PTP) and thiophene–peptide–thiophene (TPT), to investigate the influence of peptide content ratio and its location in the molecular structures on the nanostructures and properties of the assemblies. Both conjugates formed organogels consisting of left-handed twisted nanostructures; however, anti-parallel β-sheets were observed in PTP while parallel β-sheets were obtained for TPT, although in both cases oligothiophenes adopted an H-like stacking mode. Obvious solvent-induced supramolecular chirality inversion from the oligothiophene segment was observed for PTP while such phenomenon was not clear for TPT. PTP and TPT gels also showed different stabilities towards temperature increase, as evidenced by variable-temperature circular dichroism study. From the data, it is suggested that the rational design of the location and ratio of peptide plays a key role in constructing materials with determined properties based on peptide–thiophene conjugates. 相似文献
947.
948.
949.
Hou Yu-Ting Wu Fan Yao Jian-Hua Zhu Zhou-Hai Mi Qi-Li Gao Qian Zhou Min Ye Yan-Qing Wang Wei-Guang Yang Guang-Yu Hu Qiu-Fen Guan Ying 《Chemistry of Natural Compounds》2021,57(5):864-868
Chemistry of Natural Compounds - Two new isobenzofuranone derivatives (1 and 2) together with six known compounds (3–8) were isolated from the roots of Phlomis betonicoides, a highly sweet... 相似文献
950.
The precise and real-time sensing of the temperature within the physiological range is of great significance in biology and medicine. Here, a Zn-based metal-organic framework (MOF) named Zn-TCOMA is synthesized with good SHG performance due to its unique structure of the ligand and 3D frameworks. By encapsulating the two-photon fluorescent dye DMASE into the pores of Zn-TCOMA, the composite Zn-TCOMA?DMASE is obtained and simultaneously exhibits SHG response and two-photon fluorescence. Utilizing the intensity ratio between two-photon fluorescence of DMASE and SHG signal of Zn-TCOMA, Zn-TCOMA?DMASE exhibits ratiometric temperature sensing property at physiological temperature region of 20~60 °C with high sensitivity. This MOF thermometer also shows excellent repeatability, good biocompatibility, and high temperature resolution of 0.018 °C, opening a new avenue to develop diverse optical thermometric or thermographic applications in biotechnology or other areas. 相似文献