全文获取类型
收费全文 | 46066篇 |
免费 | 3309篇 |
国内免费 | 2662篇 |
专业分类
化学 | 22849篇 |
晶体学 | 459篇 |
力学 | 2650篇 |
综合类 | 171篇 |
数学 | 10732篇 |
物理学 | 15176篇 |
出版年
2024年 | 63篇 |
2023年 | 380篇 |
2022年 | 645篇 |
2021年 | 661篇 |
2020年 | 765篇 |
2019年 | 667篇 |
2018年 | 1756篇 |
2017年 | 1952篇 |
2016年 | 1503篇 |
2015年 | 1351篇 |
2014年 | 1459篇 |
2013年 | 1838篇 |
2012年 | 4695篇 |
2011年 | 3917篇 |
2010年 | 2872篇 |
2009年 | 2543篇 |
2008年 | 1702篇 |
2007年 | 1599篇 |
2006年 | 1621篇 |
2005年 | 5262篇 |
2004年 | 4551篇 |
2003年 | 2838篇 |
2002年 | 1029篇 |
2001年 | 747篇 |
2000年 | 476篇 |
1999年 | 618篇 |
1998年 | 422篇 |
1997年 | 360篇 |
1996年 | 379篇 |
1995年 | 325篇 |
1994年 | 314篇 |
1993年 | 221篇 |
1992年 | 358篇 |
1991年 | 307篇 |
1990年 | 267篇 |
1989年 | 219篇 |
1988年 | 204篇 |
1987年 | 122篇 |
1986年 | 101篇 |
1985年 | 79篇 |
1984年 | 59篇 |
1983年 | 52篇 |
1981年 | 36篇 |
1976年 | 79篇 |
1975年 | 37篇 |
1974年 | 40篇 |
1973年 | 48篇 |
1972年 | 39篇 |
1969年 | 37篇 |
1966年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
901.
Xiao Wen Hu Zhi Min Zheng Cai Hong Xu 《中国化学快报》2007,18(11):1351-1352
Three new 1,3-bis(phenylethynyl)disilazanes were synthesized from the reaction of 1,3-dichlorodisilazanes with (phenylethy- nyl)lithium,and characterized by infrared (IR) spectra,nuclear magnetic resonance (NMR) and mass spectrometry (MS). 相似文献
902.
Rafa? Bogel-?ukasik 《Monatshefte für Chemie / Chemical Monthly》2007,2(3):1137-1144
Secondary chiral alcohols are very attractive intermediates in organic synthesis of pharmaceutical and the fine-chemical industries.
The processes employing ionic liquids to obtain enantiomers of secondary alcohols have become sustainable. Furthermore, physico-chemical
properties of ionic liquids opened new possibilities to design “solvent free” processes for the resolution of racemic secondary
alcohols. This review is aimed to highlight some of the most important achievements in resolution of secondary alcohols. 相似文献
903.
本文提出了一种快速、简便、灵敏检测痕量多胺的新方法。用对酞内酰胺苯甲酰氯同多胺进行柱前衍生反应,以反相高效液相色谱定量测定多胺含量。在4~500 pmol范围内有良好的定量线性关系,腐胺、精脒和精胺的检测限均为0.1 pmol。 相似文献
904.
905.
Organic and inorganic anions are analyzed using capillary zone electrophoresis with indirect fluorescence detection. As electrolyte 2,5-dihydroxybenzoic acid is used. By adding Pb2+ to the electrolyte the migration time of SO4(2-) can be selectively influenced and the separation of Cl- and SO4(2-) considerably improved. The fluorescence intensity of 2,5-dihydroxybenzoic acid increases in the presence of Pb2+ up to a concentration of 6*10(-4) mol/L Pb2+. Limits of detection in the lower mumol/L range were obtained. 相似文献
906.
SYNTHESIS OF HYPERBRANCHED CONJUGATIVE POLY(ARYLENEETHYNYLENE)S BY ALKYNE POLYCYCLOTRIMERIZATION 总被引:2,自引:0,他引:2
A series of new hyperbranched poly(aryleneethynylene)s are synthesized by the copolycyclotrimerizations oftetraynes(Ⅰand Ⅱ)with aliphatic monoynes(A-C)catalyzed by tantalum-,niobium-,and cobalt-based catalysts.All thereactions proceed smoothly and soluble polymers of high molecular weights(M_w up to 3.8×10~4)are obtained in high yields(up to 97%). 相似文献
907.
Jian-zhang?Li Bin?Xu Shen-Xin?Li Wei?Zeng Sheng-ying?QinEmail author 《Transition Metal Chemistry》2005,30(6):669-676
Four manganese(III) complexes (MnL1Cl, MnL2Cl, MnL42Cl, MnL52Cl) with a crowned salicylaldimine Schiff base ligand have been synthesized and employed as models to mimic hydrolase in the hydrolysis of p-nitrophenyl picolinate (PNPP). The kinetics and mechanism of catalytic PNPP hydrolysis have been investigated. The kinetic mathematical model of PNPP cleavage catalyzed by these complexes has been proposed. The effects of the ligand structure and crown ether ring in complexes, and the reactive temperature on the rate of catalytic PNPP hydrolysis have been also examined. The results show that compared with the crown-free analogous MnL3Cl and MnL62Cl, the crowned Schiff base manganese(III) complexes, MnL1Cl, MnL2Cl, MnL42Cl and MnL52Cl, exhibit more high catalytic activity, which follow the order: MnL1Cl >MnL2Cl >MnL42Cl >MnL52Cl >MnL3Cl >MnL62Cl; the pseudo-first-order-rate (kobs) for the PNPP hydrolysis catalyzed by the complex MnL1Cl containing three crown ether rings is highest among six complexes and is 1.81 times that of MnL3Cl, 1.49 × 103 times that of spontaneous hydrolysis of PNPP, respectively, at pH = 7.00, [S] = 2.0 × 10−4 mol dm−3. 相似文献
908.
Although the theories and potential applications of intermolecular multiple-quantum coherences (iMQCs) have been under active investigations for over a decade, discussion of iMQC NMR signal formation was mainly confined in the time domain. In this paper, a full line-shape theory was developed to describe iMQC signals in the frequency domain. Relevant features of the line shape, such as peak height, linewidth, and phase, were investigated in detail. Predictions based on the theory agree well with experimental and simulated results. Since radiation-damping effects always couple with iMQCs in highly polarized liquid-state NMR systems, and strongly radiation-damped signals have many spectral characteristics similar to those of iMQCs, a detailed comparison was also made between them from different spectral aspects. With detailed comparison of peak height, linewidth, and phase, this work demonstrates that the iMQC and radiation-damping phenomena result from two completely different physical mechanisms despite that both present similar signal features and coexist in highly polarized liquid-state NMR systems. 相似文献
909.
Based on building emerging engineering education of "energy chemistry", we investigated the state key petro-chemical enterprises according to the industrial development and the demand of professional talents. The research report summarizes, analyzes and discusses the current priority development fields of industry, the talent training status, curriculum structure and education program of the chemistry and chemical engineering in universities. The ideas on emerging engineering education of "energy chemistry" have been proposed, and it will be beneficial to building a novel education program for talents training, which integrates the principle of chemistry, energy conversion and information science, etc. 相似文献
910.
Nanosized aluminum nitride hollow spheres were synthesized by simply heating aluminum nanoparticles in ammonia at 1000 °C. The as-synthesized sphere shells are polycrystalline with cavity diameters ranging from 15 to 100 nm and shell thickness from 5 to 15 nm. The formation mechanism can be explained by the nanoscale Kirkendall effect, which results from the difference in diffusion rates between aluminum and nitrogen. The Al nanoparticles served as both reactant and templates for the hollow sphere formation. The effects of precursor particle size and temperature were also investigated in terms of product morphology. Room temperature cathode luminescence spectrum of the nanosized hollow spheres showed a broad emission band centered at 415 nm, which is originated from oxygen related luminescence centers. The hollow structure survived a 4-h heat treatment at 1200 °C, exhibiting excellent thermal stability. 相似文献