全文获取类型
收费全文 | 8438篇 |
免费 | 1241篇 |
国内免费 | 825篇 |
专业分类
化学 | 4865篇 |
晶体学 | 56篇 |
力学 | 330篇 |
综合类 | 15篇 |
数学 | 715篇 |
物理学 | 2360篇 |
无线电 | 2163篇 |
出版年
2024年 | 40篇 |
2023年 | 268篇 |
2022年 | 321篇 |
2021年 | 371篇 |
2020年 | 386篇 |
2019年 | 351篇 |
2018年 | 289篇 |
2017年 | 281篇 |
2016年 | 409篇 |
2015年 | 425篇 |
2014年 | 481篇 |
2013年 | 579篇 |
2012年 | 719篇 |
2011年 | 752篇 |
2010年 | 509篇 |
2009年 | 519篇 |
2008年 | 521篇 |
2007年 | 468篇 |
2006年 | 453篇 |
2005年 | 401篇 |
2004年 | 240篇 |
2003年 | 234篇 |
2002年 | 202篇 |
2001年 | 148篇 |
2000年 | 137篇 |
1999年 | 167篇 |
1998年 | 126篇 |
1997年 | 111篇 |
1996年 | 106篇 |
1995年 | 93篇 |
1994年 | 80篇 |
1993年 | 61篇 |
1992年 | 75篇 |
1991年 | 44篇 |
1990年 | 34篇 |
1989年 | 30篇 |
1988年 | 21篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Bo Liu Yi He Chunfeng Duan Na Li Hua Cui 《Journal of photochemistry and photobiology. A, Chemistry》2011,217(1):62-67
It was found that lucigenin alkaline solution could react with hydrazine in the presence of Pt nanoparticles to generate strong chemiluminescence (CL) centered at 480 nm. In order to explore the CL mechanism, UV–visible spectra, X-ray photoelectron spectra studies before and after the CL reaction were carried out. The effects of O2 and superoxide dismutase (SOD) on the CL reaction were examined. The catalytic effect of Pt NPs on the hydrazine–O2 reaction was studied. A possible mechanism is proposed to be due to that Pt NPs catalyzed the reaction between hydrazine and the dissolved oxygen under alkaline conditions to yield hydroperoxide species and superoxide radical anion, which further oxidized lucigenin to produce CL emission. Moreover, the effects of some organic compounds containing hydroxyl (OH), carboxyl (COOH), carbonyl (CO), amino (NH2), or sulfur groups on the lucigenin–hydrazine–Pt NPs CL system were tested. Thiol-containing compounds such as cysteine (Cys), glutathione (GSH), homocysteine (Hcy), and 6-mercaptopurine (6-MP) were observed to greatly enhance the CL intensity. It is suggested that the CL enhancement might be due to the fact that thiol-containing compounds could facilitate the electron transfer process under the catalysis of Pt nanoparticles and accelerate the generation of OH and O2? radicals, leading to the strong CL. 相似文献
992.
Based on zinc blende and wurtzite structures of experimental ZnTe and CdTe nanocrystals, ZnmCdnXy (X = Te, Se and S) clusters were investigated using DFT/B3LYP/LANL2DZ. From analyses of their characters of conformations,
HOMO–LUMO gaps, Raman and absorption spectra, Mulliken charges and WBI (Wiberg Bond Index) values, we have discovered that
ZnmCdnTey, ZnmCdnSey and ZnmCdnSy molecules had similar characters. In this paper, characters of ZnmCdnTey were investigated in detail. First, we have found that HOMO–LUMO gaps, Raman spectra, absorption spectra, bond lengths and
Mulliken charges of doping Zn2CdTe3, ZnCd2Te3, Zn3CdTe4, Zn2Cd2Te4 and ZnCd3Te4 structures were in the scope of corresponding naked ZnTe and CdTe clusters. These characters of doping ZnmCdnTey molecules show that their stabilities are good. Second, comparing with ZnTe structures, the wavelengths of the absorption
peaks of doping ZnmCdnTey clusters shift to red in water environment. Moreover, with increasing of the number of Cd atom, their wavelengths of the
absorption peaks gradually shift to red. This conclusion is consistent with the experimental fact. Third, Raman spectra of
pure ZnTe clusters have higher frequencies than corresponding naked CdTe structures. As for doping molecules, the frequencies
of their Raman spectra gradually shift to low frequencies with increasing of Cd atoms’ number. 相似文献
993.
Zhang Y Zhang H Cui W Chen H 《Journal of the American Society for Mass Spectrometry》2011,22(9):1610-1621
Our previous study showed that selenamide reagents such as ebselen and N-(phenylseleno)phthalimide (NPSP) can be used for selective and rapid derivatization of protein/peptide thiols in high conversion
yield. This paper reports the systematic investigation of MS/MS dissociation behaviors of selenamide-derivatized peptide ions
upon collision induced dissociation (CID) and electron transfer dissociation (ETD). In the positive ion mode, derivatized
peptide ions exhibit tag-dependent CID dissociation pathways. For instance, ebselen-derivatized peptide ions preferentially
undergo Se–S bond cleavage upon CID to produce a characteristic fragment ion, the protonated ebselen (m/z 276), which allows selective identification of thiol peptides from protein digest as well as selective detection of thiol
proteins from protein mixture using precursor ion scan (PIS). In contrast, NPSP-derivatized peptide ions retain their phenylselenenyl
tags during CID, which is useful in sequencing peptides and locating cysteine residues. In the negative ion CID mode, both
types of tags are preferentially lost via the Se–S cleavage, analogous to the S–S bond cleavage during CID of disulfide-containing
peptide anions. In consideration of the convenience in preparing selenamide-derivatized peptides and the similarity of Se–S
of the tag to the S–S bond, we also examined ETD of the derivatized peptide ions to probe the mechanism for electron-based
ion dissociation. Interestingly, facile cleavage of Se–S bond occurs to the peptide ions carrying either protons or alkali
metal ions, while backbone cleavage to form c/z ions is severely inhibited. These results are in agreement with the Utah-Washington mechanism proposed for depicting electron-based
ion dissociation processes. 相似文献
994.
Ding ZG Li MG Ren J Zhao JY Huang R Wang QZ Cui XL Zhu HJ Wen ML 《Organic & biomolecular chemistry》2011,9(8):2771-2776
Phenazinolins A-E (1-5), which possess a carbon skeleton unique to diphenazines (the azabicyclo[3.3.1]nonadienol moiety in 1-3 and the oxabicyclo[3.3.1]nonadienol moiety in 4 and 5), were isolated from tin mine tailings-derived Streptomyces diastaticus YIM DT26, with 1-3 exhibited appreciable cytotoxicity and antibiotic effects. 相似文献
995.
The N-R-quinolinyl-8-amino ligands HL(1-3) (R = 2,6-(i)Pr(2)C(6)H(3) (HL(1)), 2,6-Et(2)C(6)H(3) (HL(2)), 2,6-Me(2)C(6)H(3) (HL(3))) have been prepared, which reacted readily with one equiv. of rare earth metal tris(alkyl)s to afford the corresponding bis(alkyl) complexes L(1)Y(CH(2)SiMe(3))(2)(THF) (1) and L(1-3)Lu(CH(2)SiMe(3))(2)(THF) (2-4) via alkane elimination. Contrastingly, treatment of the in situ generated neodymium tri(alkyl)s with HL(1) afforded a mono(alkyl) neodymium complex (5). Complexes 1, 2 and 5 in combination with aluminium alkyls and organoborates established homogenous ternary systems that exhibited versatile catalytic activities and trans-1,4 selectivities for the polymerization of butadiene, depending on the types of aluminium alkyl, organoborate and rare earth metal used. Furthermore, the trans-1,4 selective copolymerization of butadiene and isoprene was achieved by using the ternary system of 1/AlMe(3)/[Ph(3)C][B(C(6)F(5))(4)]. Both the kinetics of copolymerization and the thermal behavior of the copolymers were investigated. 相似文献
996.
A Pd-catalyzed C4-olefination of oxazoles via C-H bond activation under mild conditions was achieved. The reaction was shown to be general over a range of substrates. New protocols for the divergent transformation of these products to provide functionalized amino alcohol and amino acid derivatives have also been established. 相似文献
997.
A methoxypoly(ethylene glycol)-block-poly(α,L-glutamic acid) (mPEGGA) diblock copolymer is synthesized. Using QCM measurements, it is shown that (CS/mPEGGA)(n) film construction takes place over two build-up stages (exponential-to-linear). UV-vis spectra reveal the regular increase of the multilayer film growth at different molecular weights of mPEGGA. Contact angle and surface morphology investigation prove that the hydrophilicity of CS/mPEGGA multilayer film-modified substrate becomes better and the surface becomes rough. Significantly reduced cell adhesion is observed on the CS/mPEGGA multilayer film coated surface. 相似文献
998.
Highly fluorescent CdTe quantum dots (QDs) stabilized by 3-mercaptopropionic acid were prepared by an aqueous solution approach and used as a fluorescent label to link substance P (SP) in studying the interaction of SP with NK-1 receptor, which was expressed on the AR4-2J cell line. Nonspecific adsorptions of CdTe QDs on the AR4-2J cell membrane were observed, whereas the QD-SP conjugates successfully crossed the cell membrane and entered the cytosol. SP is a neurotransmitter, and neurotransmitter-induced calcium concentration oscillation is a common phenomenon in diverse cells especially of secretory type. Cytosolic calcium concentration responses were studied in the AR4-2J cell line during stimulation with SP and QD-SP conjugates. The oscillations triggered by SP and QD-SP conjugates were dose-dependent and very similar. Such QD-SP conjugates readily internalized into the cytosol as would be expected of an active NK-1 ligand. Therefore QD-SP conjugates could be used successfully to study ligand and NK-1 receptor interactions in live cells. Our research may provide a meaningful reference for congener research. 相似文献
999.
In this paper, a new numerical algorithm is provided to solve nonlinear multi‐point boundary value problems in a very favorable reproducing kernel space, which satisfies all complex boundary conditions. Its reproducing kernel function is discussed in detail. The theorem proves that the approximate solution and its first‐ and second‐order derivatives all converge uniformly. The numerical experiments show that the algorithm is quite accurate and efficient for solving nonlinear multi‐point boundary value problems. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
1000.
An indirect competitive enzyme-linked immunosorbent assay for determination of norfloxacin in waters using a specific polyclonal antibody 总被引:1,自引:0,他引:1
A specific polyclonal anti-norfloxacin antibody was obtained, and a sensitive indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed for determining trace amounts of norfloxacin in various waters. Good linearity was achieved in the range from 0.1 to 10 μg L−1. The average IC50 value was determined to be 2.2 μg L−1 and the limit of detection was 0.016 μg L−1 at a signal-to-noise ratio of 3 in phosphate-buffered saline buffer. Recoveries of norfloxacin at various spiking levels ranged from 74 to 105% in groundwater, surface water, treated and untreated wastewater samples, with relative standard deviations of 3–5%. The assay was applied for determining norfloxacin in municipal wastewater, surface water, and groundwater collected in a metropolis of China. Raw wastewater samples were only submitted to filtration and pH adjustment while the other water samples were pre-concentrated by solid phase extraction prior to the icELISA assay. Good agreement of the results obtained by the icELISA and liquid chromatography tandem mass spectrometry further confirmed the reliability and accuracy of the icELISA for rapid detection of norfloxacin in waters. 相似文献