全文获取类型
收费全文 | 12222篇 |
免费 | 1490篇 |
国内免费 | 697篇 |
专业分类
化学 | 8264篇 |
晶体学 | 123篇 |
力学 | 594篇 |
综合类 | 36篇 |
数学 | 1715篇 |
物理学 | 3677篇 |
出版年
2023年 | 172篇 |
2022年 | 326篇 |
2021年 | 327篇 |
2020年 | 396篇 |
2019年 | 348篇 |
2018年 | 315篇 |
2017年 | 291篇 |
2016年 | 486篇 |
2015年 | 508篇 |
2014年 | 536篇 |
2013年 | 785篇 |
2012年 | 964篇 |
2011年 | 1022篇 |
2010年 | 646篇 |
2009年 | 594篇 |
2008年 | 770篇 |
2007年 | 636篇 |
2006年 | 681篇 |
2005年 | 516篇 |
2004年 | 430篇 |
2003年 | 371篇 |
2002年 | 343篇 |
2001年 | 196篇 |
2000年 | 194篇 |
1999年 | 248篇 |
1998年 | 207篇 |
1997年 | 186篇 |
1996年 | 202篇 |
1995年 | 146篇 |
1994年 | 137篇 |
1993年 | 131篇 |
1992年 | 115篇 |
1991年 | 119篇 |
1990年 | 84篇 |
1989年 | 74篇 |
1988年 | 66篇 |
1987年 | 66篇 |
1986年 | 48篇 |
1985年 | 58篇 |
1984年 | 72篇 |
1983年 | 54篇 |
1982年 | 42篇 |
1981年 | 62篇 |
1980年 | 40篇 |
1979年 | 32篇 |
1978年 | 38篇 |
1977年 | 38篇 |
1976年 | 45篇 |
1975年 | 34篇 |
1974年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Stable, reproducible nanorecording on rotaxane thin films 总被引:3,自引:0,他引:3
Feng M Guo X Lin X He X Ji W Du S Zhang D Zhu D Gao H 《Journal of the American Chemical Society》2005,127(44):15338-15339
Stable, reversible conductance transitions and memory effects were observed in solid-state rotaxane-based Langmuir-Blodgett (LB) thin films. Taking advantage of the switching property, we have achieved reproducible nanometer-scale recording dots on rotaxane LB films via voltage application using a scanning tunneling microscope probe. The stable and easily controlled conductance switching makes the rotaxanes a hopeful candidate for nanorecording. 相似文献
102.
Li J Hong X Li D Zhao K Wang L Wang H Du Z Li J Bai Y Li T 《Chemical communications (Cambridge, England)》2004,(15):1740-1741
Highly luminescent water-soluble CdTe nanorods were prepared with the assistance of the mixed ligand system of cysteine and thioglycolic acid; the aspect ratio and photoluminescence of the CdTe nanorods could be controlled by the refluxing time. 相似文献
103.
在H6TeO6/KOH水溶液中以臭氧为氧化剂,将二价铜化合物氧化成三价铜化合物,并获得一个新的三价铜化合物Ba4K[Cu(H2TeO6)2](OH)4.6H2O;描述了碱性溶液中“Cu(Ⅲ)/Cu(Ⅲ)”循环伏安图。对铜(Ⅲ)化合物,Na4H[H2TeO6)2].17H2O以及相应的铜(Ⅱ)配合物的电子光谱和Cu2pXPS进行了研究,给出了其配位场场强参数和Cu2PXPX的电子结合能。由于价态升高 相似文献
104.
Nitroacetamidine undergoes a useful cyclocondensation with β-diketones to produce substituted 2-amino-3-nitropyridines. Use of an acylpyruvate generates hitherto unreported 2-amino-3-nitropyridine-4-carboxylates. These may be converted easily to functionalized imidazo[4,5-b]pyridines and oxazolo-[5,4-b]pyridines. 相似文献
105.
106.
For an arbitrary poset P, subposets {P
i
: 1ik} form a transitive basis of P if P is the transitive closure of their union. Let u be the minimum size of a covering of P by chains within posets of the basis, s the maximum size of a family of elements with no pair comparable in any basis poset, and a the maximum size of an antichain in P. Define a dense covering to be a collection D of chains within basis posets such that each element belongs to a chain in D within each basis poset and is the top of at least k-1 chains and the bottom of at least k-1 chains in D. Dense coverings generalize ordinary chain coverings of poset. Let d=min {|D|–(k–1)|P|}. For an arbitrary poset and transitive basis, a convenient network model for dense coverings yields the following: Theorem 1: da, with equality iff P has a minimum chain decomposition in which every pair of consecutive elements on each chain are comparable in some basis poset. Theorem 2: usda. Theorem 3: s=d iff s=a. The most interesting special case is where the transitive basis expresses P as the product of two posets, in which case u and s measure the minimum and maximum sizes of unichain coverings and semiantichains. 相似文献
107.
Guan X Lin X Kwok WM Du Y Li YL Zhao C Wang D Phillips DL 《The journal of physical chemistry. A》2005,109(6):1247-1256
Ultraviolet photolysis of low concentrations of CH2I2 in methanol solution found that CH2I2 is converted into dimethoxymethane and some H+ and I- products. Picosecond time-resolved resonance Raman (ps-TR3) experiments observed that the isodiiodomethane (CH2I-I) photoproduct decayed faster as the concentration of methanol increases, suggesting that isodiiodomethane is reacting with methanol. Ab initio calculations indicate isodiiodomethane is able to react with methanol via an O-H insertion/HI elimination to form an iodoether (ICH2-O-CH3) and HI products. The iodoether can then further react via another O-H insertion/HI elimination reaction to form the dimethoxymethane (CH3-O-CH2-O-CH3) observed in the photochemistry experiments. A reaction mechanism consistent with these experimental and theoretical observations is proposed. 相似文献
108.
The ultraviolet photolysis of low concentrations of CH(2)XI (X = Cl, Br, I) were investigated in water and saltwater solutions by photochemistry and picosecond time-resolved resonance Raman spectroscopy. Photolysis in both kinds of solutions formed mostly CH(2)(OH)(2) and HI and HX products. However, photolysis of the CH(2)XI molecules in saltwater resulted in production of some CH(2)XCl products not observed in aqueous solutions without salt present. The appearance of these new products in saltwater solutions is accompanied by a decrease in the amount of CH(2)(OH)(2), HI, and HX products compared to photolysis in aqueous solutions without salt present. The possible implications for photolysis of CH(2)XI and other polyhalomethanes in seawater and other salt aqueous environments compared to nonsaltwater solvated environments is briefly discussed. 相似文献
109.
110.
Hans Zimmer R. Palmer-Sungail Douglas Ho Adel Amer 《Journal of heterocyclic chemistry》1993,30(1):161-167
The reaction pathway towards formation of 4-aroyl-3-hydroxy-2(5H)-furanones 1 from the base catalyzed reaction between an acetophenone, diethyl oxalate and formaldehyde was investigated. If methoxide was used as base, a transesterification was found to occur in the first step, while a side reaction, namely the retro Claisen reaction, was in competition with the desired lactone formation in the second step. The nature of the solvent and the acidic character of 1 as well as the basicity of the aminoarylene were found to have a profound influence on the course of the reaction of 1 with aminoarylenes. 相似文献