全文获取类型
收费全文 | 1632篇 |
免费 | 308篇 |
国内免费 | 143篇 |
专业分类
化学 | 1026篇 |
晶体学 | 9篇 |
力学 | 86篇 |
综合类 | 28篇 |
数学 | 221篇 |
物理学 | 713篇 |
出版年
2024年 | 4篇 |
2023年 | 32篇 |
2022年 | 44篇 |
2021年 | 45篇 |
2020年 | 61篇 |
2019年 | 65篇 |
2018年 | 54篇 |
2017年 | 36篇 |
2016年 | 70篇 |
2015年 | 66篇 |
2014年 | 81篇 |
2013年 | 108篇 |
2012年 | 129篇 |
2011年 | 146篇 |
2010年 | 86篇 |
2009年 | 91篇 |
2008年 | 84篇 |
2007年 | 92篇 |
2006年 | 93篇 |
2005年 | 78篇 |
2004年 | 76篇 |
2003年 | 49篇 |
2002年 | 49篇 |
2001年 | 27篇 |
2000年 | 27篇 |
1999年 | 40篇 |
1998年 | 35篇 |
1997年 | 25篇 |
1996年 | 37篇 |
1995年 | 29篇 |
1994年 | 27篇 |
1993年 | 26篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1973年 | 4篇 |
1930年 | 1篇 |
排序方式: 共有2083条查询结果,搜索用时 15 毫秒
221.
The chaotic dynamics of the softening-spring Duffing system with multi-frequency external periodic forces is studied. It is found that the mechanism for chaos is the transverse heteroclinic tori. The Poincare map, the stable and the unstable manifolds of the system under two incommensurate periodic forces were set up on a two-dimensional torus. Utilizing a global perturbation technique of Melnikov the criterion for the transverse interaction of the stable and the unstable manifolds was given. The system under more but finite incommensurate periodic forces was also studied. The Melnikov‘s global perturbation technique was therefore generalized to higher dimensional systems. The region in parameter space where chaotic dynamics may occur was given. It was also demonstrated that increasing the number of forcing frequencies will increase the area in parameter space where chaotic behavior can occur. 相似文献
222.
Tan G Lou Z Jing J Li W Zhu Z Zhao L Zhang G Chai Y 《Biomedical chromatography : BMC》2011,25(12):1343-1351
Aconite roots are popularly used in herbal medicines in China. Many cases of accidental and intentional intoxication with this plant have been reported; some of these are fatal because the toxicity of aconitum is very high. It is thus important to detect and identify aconitum alkaloids in biofluids. In this work, an improved method employing LC-TOFMS with multivariate data analysis was developed for screening and analysis of major aconitum alkaloids and their metabolites in rat urine following oral administration of aconite roots extract. Thirty-four signals highlighted by multivariate statistical analyses including 24 parent components and 10 metabolites were screened out and further identified by adjustment of the fragmentor voltage to produce structure-relevant fragment ions. It is helpful for studying aconite roots in toxicology, pharmacology and forensic medicine. This work also confirmed that the metabolomic approach provides effective tools for screening multiple absorbed and metabolic components of Chinese herbal medicines in vivo. 相似文献
223.
Yan Jie Bao Jun Jun Li Yi Ting Wang Lei Yu Lei Lou Wei Ji Du Zi Qiang Zhu Hui Peng Jian Zhong Zhu 《中国化学快报》2011,22(7):843-846
Toxicities of CdSe and CdSe/CdS quantum dots(QDs) synthesized by ultrasound-assisted methods were investigated in vitro and in vivo.Five human cell lines were used to assess the cytotoxicity of as-prepared CdSe and CdSe/CdS by assays of MTT viability,red blood cell hemolysis,flow cytometry,and fluorescence imaging.The results show that these QDs may be cytotoxic by their influence in S and G2 phases in cell cycles.The cytotoxicity of QDs depends on both the physicochemical properties and related to target cells. 相似文献
224.
Louërat F Tye H Napier S Garrigou M Whittaker M Gros PC 《Organic & biomolecular chemistry》2011,9(6):1768-1773
The concomitant use of silver oxide and catalytic amount of TBAF allowed the efficient and chemoselective coupling of readily available 4-chloro- and 4-methyl-2-trimethyl-silyl-pyridines with heteroaromatic and aromatic halides. Based on control experiments, a mechanism involving the formation of a pyridylsilver intermediate and TBAF recycling is postulated. 相似文献
225.
Lou Z Huang B Wang P Wang Z Qin X Zhang X Cheng H Zheng Z Dai Y 《Dalton transactions (Cambridge, England : 2003)》2011,40(16):4104-4110
The near-spherical AgCl micro-crystals were prepared by an ionic liquids-assisted hydrothermal method. The influence of ionic liquids (C(x)MimCl x = 4, 8, 12, 16) on (001) facet growth of AgCl was studied systemically. The composition of the as-prepared samples was characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and FTIR spectra. The morphological structures were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Based on experimental data and the classical crystal growth theory, a plausible growth mechanism of the near-spherical AgCl was proposed. The plasmonic photocatalyst Ag@AgCl prepared from the near-spherical AgCl showed higher activity than that of cubic morphologies. 相似文献
226.
Zou X Liu D Zhong L Yang B Lou Y Hu B Yin Y 《Analytical and bioanalytical chemistry》2011,401(4):1251-1261
In this study, we describe a method for highly specific enrichment of phosphopeptides with multifunctional chitosan–glycidyl
methacrylate (GMA)–iminodiacetic acid (IDA)–Fe (III) nanospheres for direct analysis by matrix-assisted laser desorption–ionization
mass spectrometry (MALDI-MS). This is the first time that chitosan has been used to create nanospheres support material for
selective enrichment of phosphopeptides by modification with GMA, derivatization with IDA, and loading with Fe (III) ions.
Chitosan-GMA-IDA-Fe (III) nanospheres with a diameter of 20 to 100 nm have multifunctional chemical moieties which confer
unique properties, good dispersibility in highly acidic binding buffers, as well as good biocompatibility and chemical stability
which improves their specific interaction with phosphopeptides using various types of acid binding buffers. The process of
enrichment is very simple, quick, efficient, and specific. Its high specificity and efficiency for purification of phosphopeptides
is reflected in the very low and substoichiometric amounts of phosphopeptides which can be detected, in quantities as low
as 1:3,000 M ratios. Compared with other state-of the-art technologies such as the use of conventional Fe3+-IMAC and TiO2, these chitosan nanosphere techniques show superior specificity and sensitivity. Moreover, the resultant chitosan-GMA-IDA-Fe3+ nanosphere-absorbed phosphopeptides can be either directly analyzed by MALDI-TOF MS analysis or eluted and further analyzed
by nano-LC-MS/MS. 相似文献
227.
Bendong Lou 《Journal of Differential Equations》2011,251(6):1447-1474
Consider the parabolic equation
(E) 相似文献
228.
In this paper, a new iterative algorithm involving nonexpansive mapping in Hilbert space is proposed and proved to be strongly
convergent to a point which is simultaneously a fixed point of a nonexpansive mapping and a solution of an equilibrium problem.
The results of the paper extend previous results, see, for instance, Takahashi and Takahashi (J Math Anal Appl 331:506–515,
2007), and other results in this field. Moreover, this algorithm is applied to find zeros of a maximal monotone operator and
solve an optimization problem. 相似文献
229.
Multilayers of myoglobin (Mb) with ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([EMIM]BF4) was assembled on carbon ionic liquid electrode (CILE) based on the electrostatic attraction between the negatively charged Mb and the positively charged imidazolium ion of IL. The CILE was fabricated with 1‐ethyl‐3‐methylimidazolium ethylsulfate ([EMIM]EtOSO3) as the modifier, which exhibited imidazolium ion on the electrode surface. Then Mb molecules were assembled on the surface of CILE step‐by‐step to get a {IL/Mb}n multilayer film modified electrode. UV‐Vis adsorption and FT‐IR spectra indicated that Mb remained its native structure in the IL matrix. In deaerated phosphate buffer solution (pH 7.0) a pair of well‐defined quasi‐reversible redox peaks appeared with the apparent formal potential (E0′) as ‐0.212 V (vs. SCE), which was the characteristic of Mb heme Fe(III)/Fe(II) redox couples. The results indicated that the direct electron transfer of Mb was realized on the modified electrode. The {IL/Mb}n/CILE displayed excellent electrocatalytic ability to the trichloroacetic acid reduction in the concentration range from 2.0 to 22.0 mmol/L with the detection limit of 0.6 mmol/L (3σ). The proposed method provides a new platform to fabricate the third generation biosensor based on the self‐assembly of redox protein with ILs. 相似文献
230.
A novel water-soluble heptaplatin analogue, cis-[(4R,5R)-4,5-bis-(aminomethyl)-2-isopropyl-1,3-dioxolane](3-hydroxy-1,1-cyclobutanedicarboxylato)platinum(II), has been synthesized and biologically evaluated. The complex shows more activity and less toxicity than its parent drug heptaplatin, exhibiting the great potential for further development. 相似文献