全文获取类型
收费全文 | 18393篇 |
免费 | 2613篇 |
国内免费 | 2258篇 |
专业分类
化学 | 9901篇 |
晶体学 | 176篇 |
力学 | 842篇 |
综合类 | 140篇 |
数学 | 1742篇 |
物理学 | 4957篇 |
无线电 | 5506篇 |
出版年
2024年 | 88篇 |
2023年 | 320篇 |
2022年 | 514篇 |
2021年 | 672篇 |
2020年 | 615篇 |
2019年 | 613篇 |
2018年 | 559篇 |
2017年 | 537篇 |
2016年 | 714篇 |
2015年 | 829篇 |
2014年 | 1033篇 |
2013年 | 1249篇 |
2012年 | 1456篇 |
2011年 | 1619篇 |
2010年 | 1191篇 |
2009年 | 1252篇 |
2008年 | 1395篇 |
2007年 | 1213篇 |
2006年 | 1103篇 |
2005年 | 901篇 |
2004年 | 661篇 |
2003年 | 540篇 |
2002年 | 611篇 |
2001年 | 484篇 |
2000年 | 429篇 |
1999年 | 418篇 |
1998年 | 313篇 |
1997年 | 291篇 |
1996年 | 307篇 |
1995年 | 261篇 |
1994年 | 186篇 |
1993年 | 149篇 |
1992年 | 142篇 |
1991年 | 115篇 |
1990年 | 99篇 |
1989年 | 77篇 |
1988年 | 51篇 |
1987年 | 47篇 |
1986年 | 49篇 |
1985年 | 35篇 |
1984年 | 23篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1968年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
Metal selenites and tellurites are a class of very important compounds. In this paper, the structures and properties of metal selenites or tellurites combining with transition-metal (TM) ions with the d (0) electronic configuration or tetrahedral MO 4 building blocks of post-transition main-group elements were reviewed. Most compounds in the alkali or alkaline-earth-d (0) TM-Se (IV) (or Te (IV))-O systems exhibit extended anionic architectures composed of distorted octahedra of (d (0)) TM cations and tellurite or selenite groups. The distortion of the octahedron is always away from the lone-pair cation, and some of them exhibit excellent second-order nonlinear optical properties due to the adductive effects of two types of bond polarizations. Because of the high coordination number of Ln (III) ions, most of compounds in the Ln-d (0) TM-Se (IV) (or Te (IV))-O systems are not second-harmonic-generation active; however, they are able to emit strong luminescence in the visible or near-IR region; also in most cases, the d (0) TM cations are in tetrahedral geometry and are well separated from selenite or tellurite groups. It is also interesting to note that the selenite group is normally "isolated", whereas the TeO x ( x = 3-5) can be polymerized into a variety of discrete polynuclear anionic clusters or extended architectures via Te-O-Te bridges. 相似文献
222.
Fang J Shan XQ Wen B Lin JM Lu XC Liu XD Owens G 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):10929-10935
The sorption and desorption of phenanthrene by three engineered nanoparticles including nanosize zerovalent iron (NZVI), copper (NZVC), and silicon dioxide (NSiO2) were investigated. The sorption of phenanthrene onto NSiO2 was linear and reversible due to the hydrophilic properties of NSiO2. In comparison, sorption of phenanthrene onto NZVI and NZVC was nonlinear and irreversible, which was potentially due to the existence of significantly heterogeneous surface energy distribution patterns detected by a standard molecular probe technique. Naphthalene exerted significant competitive sorption with phenanthrene for NZVI and NZVC, and the isotherm of phenanthrene changed from being significantly nonlinear to nearly linear when naphthalene was simultaneously absorbed. A surface adsorption mechanism was proposed to explain the observed sorption and competition of phenanthrene on both NZVI and NZVC. In contrast, no competition was observed for sorption onto NSiO2. The sorption of phenanthrene on all three nanoparticles significantly decreased with increasing pH. The sorption irreversibility of phenanthrene on NZVI and NZVC were significantly enhanced with decreasing pH. A pH-dependent hydrophobic effect and dipole interactions between the charged surface (electron acceptors) and phenanthrene with electron-rich pi systems (electron donors) were proposed to explain the observed pH-dependent sorption. 相似文献
223.
224.
Feifan Li Xinyang Mu Xueqing Tang Ge Song Hongzhao Sun Xiuling Zha Peiyan Sun Jianhui Fang Dongmei Hu Shan Cong Zhigang Zhao 《Angewandte Chemie (International ed. in English)》2023,62(12):e202218055
Non-metallic materials have emerged as a new family of active substrates for surface-enhanced Raman scattering (SERS), with unique advantages over their metal counterparts. However, owing to their inefficient interaction with the incident wavelength, the Raman enhancement achieved with non-metallic materials is considerably lower with respect to the metallic ones. Herein, we propose colourful semiconductor-based SERS substrates for the first time by utilizing a Fabry-Pérot cavity, which realize a large freedom in manipulating light. Owing to the delicate adjustment of the absorption in terms of both frequency and intensity, resonant absorption can be achieved with a variety of non-metal SERS substrates, with the sensitivity further enhanced by ≈100 times. As a typical example, by introducing a Fabry-Pérot-type substrate fabricated with SiO2/Si, a rather low detection limit of 10−16 M for the SARS-CoV-2S protein is achieved on SnS2. This study provides a realistic strategy for increasing SERS sensitivity when semiconductors are employed as SERS substrates. 相似文献
225.
Weidong Shang Sheng‐Nan Su Rong Shi Ze‐Dong Mou Guo‐Qiang Yu Xia Zhang Dawen Niu 《Angewandte Chemie (International ed. in English)》2021,60(1):385-390
We here report glycosyl sulfoxides appended with an aryl iodide moiety as readily available, air and moisture stable precursors to glycosyl radicals. These glycosyl sulfoxides could be converted to glycosyl radicals by way of a rapid and efficient intramolecular radical substitution event. The use of this type of precursors enabled the synthesis of various complex C‐linked glycoconjugates under mild conditions. This reaction could be performed in aqueous media and is amenable to the synthesis of glycopeptidomimetics and carbohydrate‐DNA conjugates. 相似文献
226.
Wenbo Huang Liqiao Shi Manli Liu Zhigang Zhang Fang Liu Tong Long Shaohua Wen Daye Huang Kaimei Wang Ronghua Zhou Wei Fang Hongtao Hu Shaoyong Ke 《Molecules (Basel, Switzerland)》2022,27(5)
Primary arylsulfonamide functional groups feature prominently in diverse pharmaceuticals. However, natural arylsulfonamides are relatively infrequent. In this work, two novel arylsulfonamide natural products were first synthesized, and then a series of novel molecules derived from natural arylsulfonamides were designed and synthesized, and their in vitro cytotoxic activities against A875, HepG2, and MARC145 cell lines were systematically evaluated. The results indicate that some of these arylsulfonamide derivatives exhibit significantly good cytotoxic activity against the tested cell lines compared with the control 5-fluorouracil (5-FU), such as compounds 10l, 10p, 10q, and 10r. In particular, the potential molecule 10q, containing a carbazole moiety, exhibited the highest inhibitory activity against all tested cell lines, with IC50 values of 4.19 ± 0.78, 3.55 ± 0.63, and 2.95 ± 0.78 μg/mL, respectively. This will offer the potential to discover novel drug-like compounds from the sparsely populated area of natural products that can lead to effective anticancer agents. 相似文献
227.
二价铜、锌离子对盐酸巴马亭与牛血清白蛋白结合反应光谱的影响研究 总被引:9,自引:0,他引:9
The binding of Palmatine hydrochloride to bovine serum albumin (BSA) was studied, in the presence of Cu2+ and Zn2+, with fluorescence spectrum and ultra-violet spectrum. The results show that Cu2+ and Zn2+ don′t influence the first binding constant of Palmatine to BSA and the binding site of it to BSA. But Cu2+ has the fluorescence quenching effect on sensitive fluorescence of medicine binding to BSA. 相似文献
228.
Wang F Wen-Chen Z Lv H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,71(2):513-515
The optical spectra and EPR spectra (characterized by the spin-Hamiltonian parameters g(//), g(perpendicular), A(//) and A(perpendicular)) for the molecular ion VO2+ in LiKSO4 crystals are calculated from two microscopic theory methods, one of which is the complete diagonalization (of energy matrix) method (CDM) and the other is the perturbation theory method (PTM). The calculated three optical absorption bands and four spin-Hamiltonian parameters from the two methods are not only close to each other, but also in reasonable agreement with the experimental values. It appears that both theoretical methods are effective in the explanation of optical and EPR spectra for 3d1 ions in crystals. The negative signs of hyperfine structure constants A(//) and A(perpendicular) for VO2+ in LiKSO4 crystals are also suggested from the calculations. 相似文献
229.
Qing Zhang Huifang Wang Guosong Sun Kelin Huang Weiping Fang Yiquan Yang 《天然气化学杂志》2008,17(4):355-358
Activated carbon-supported Ni catalysts for vapor phase carbonylation of ethanol to propionic acid in the presence of ethyl iodide as promoter were investigated. Under optimum reaction conditions, the conversions of carbon monoxide and ethanol were measured to be 81.4% and 98.4%, respectively, while the selectivity for propionic acid was found to be 98.65%. The catalyst was stable within 48 h on stream. XRD and XPS methods were used to characterize the structures and surface properties of the fresh and tested catalysts. The characterization results indicated that aggregation of nickel particles and formation of nickel iodide on the catalyst surface should be responsible for the deactivation of the catalysts. 相似文献
230.
The sofid-state ECL behavior of a water-insoluble bis-cyclometalated (pq)2Ir(N-phMA) complex is presented, in which pq is a 2-phenylquinoline anion and N-phMA is N-phenyl methacrylamide, a monoanionic bidentate ligand. The MWNTs/(pq)2Ir(N-phMA) film, MWNTs/Ru(bpy)32+ film and (pq)2Ir(N-phMA) directly modified glassy carbon electrode were fabricated; only the MWNTs/(pq)2Ir(N-phMA) film can produce steady ECL in the presence of tri-n-propylamine as a coreactant. 相似文献