全文获取类型
收费全文 | 104486篇 |
免费 | 9656篇 |
国内免费 | 6181篇 |
专业分类
化学 | 27563篇 |
晶体学 | 519篇 |
力学 | 6444篇 |
综合类 | 1036篇 |
数学 | 19768篇 |
物理学 | 29208篇 |
无线电 | 35785篇 |
出版年
2024年 | 258篇 |
2023年 | 1122篇 |
2022年 | 2005篇 |
2021年 | 2476篇 |
2020年 | 2679篇 |
2019年 | 2134篇 |
2018年 | 1976篇 |
2017年 | 2760篇 |
2016年 | 3464篇 |
2015年 | 3174篇 |
2014年 | 5393篇 |
2013年 | 6617篇 |
2012年 | 5852篇 |
2011年 | 5970篇 |
2010年 | 4654篇 |
2009年 | 5903篇 |
2008年 | 6582篇 |
2007年 | 7152篇 |
2006年 | 6190篇 |
2005年 | 5159篇 |
2004年 | 4586篇 |
2003年 | 4667篇 |
2002年 | 4534篇 |
2001年 | 3456篇 |
2000年 | 3152篇 |
1999年 | 2728篇 |
1998年 | 2474篇 |
1997年 | 1692篇 |
1996年 | 1569篇 |
1995年 | 1493篇 |
1994年 | 1340篇 |
1993年 | 1013篇 |
1992年 | 1021篇 |
1991年 | 753篇 |
1990年 | 623篇 |
1989年 | 455篇 |
1988年 | 426篇 |
1987年 | 363篇 |
1986年 | 314篇 |
1985年 | 300篇 |
1984年 | 287篇 |
1983年 | 184篇 |
1982年 | 221篇 |
1981年 | 219篇 |
1980年 | 159篇 |
1979年 | 176篇 |
1978年 | 147篇 |
1977年 | 132篇 |
1976年 | 84篇 |
1973年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
992.
《Analytical letters》2012,45(4):721-734
Selective hydrolysis of the protein to peptides, their resolution by chromatography and determination of the amino-acid sequence in individual peptides is one method applied to studies of their modifications and mutations in pathological conditions. The purpose of this work is the determination of the green and black tea effect on peptides and their amino acid contents in integral erythrocyte membrane proteins in ethanol intoxicated rats. It was shown that ethanol intoxication causes a decrease in peptides and their amino acid contents in comparison with the control group. The ingestion of green (black) tea with ethanol partially prevents these ethanol-induced changes. 相似文献
993.
《Analytical letters》2012,45(6):673-680
Abstract The methanol soluble amorphous fraction obtained on the CuCl2 induced polymerization of 2,5-dibromo-3-methylthiophene exhibits redox waves on cyclic voltammetric potential polarization for a copper redox couple (for the metal ion incorporated in the polymer matrix) and a redox couple associated with the polymer matrix itself. Furthermore, when used as an electrode for the ferri/ferrocyanide couple in the electrolyte phase it acts as a well behaved electrode surface. Electrodes made from this material show a remarkable stability in aqueous media. 相似文献
994.
《Journal of Coordination Chemistry》2012,65(1):101-106
A Pd(II) complex of the thiosaccharinato (tsac) anion, of stoichiometry Pd(tsac)2·H2O was prepared by interaction of Na2PdCl4 with thiosaccharin in methanol and characterized by infrared and 1H and 13C NMR spectroscopy. These spectral studies confirmed interaction of the metal center with the thiosaccharinate acting as a bidentate ligand through its thiol group and the N-atom. NMR measurements also confirmed that in solution thiosaccharin is mainly present in its thiolate tautomeric form. 相似文献
995.
996.
Uranium extraction using DEHCNPB (butyl-1-[N,N-bis(2-ethylhexyl)carbamoyl]nonyl phosphonic acid, a bifunctional cationic extractant) has been studied to better understand mechanism differences depending on the original acidic solution (phosphoric or sulfuric). Solvent extraction batch experiments were carried out and the organic phases were probed using 31P-NMR. This technique enabled to demonstrate that phosphoric acid is poorly extracted by DEHCNPB ([H3PO4]org < 2mM), using direct quantification in the organic phase by 31P-NMR spectra integration. Moreover, in the presence of uranium in the initial phosphoric acid solution, uranyl extraction by DEHCNPB competes with H3PO4 extraction.Average stoichiometries of U(VI)-DEHCNPB complexes in organic phases were also determined using slope analysis on uranium distribution data. Uranium seems to be extracted from a phosphoric medium by two extractant molecules, whereas more than three DEHCNPB on average would be necessary to extract uranium from a sulfuric medium. Thus, uranium is extracted according to different mechanisms depending on the nature of the initial solution. 相似文献
997.
We propose a form of random forests that is especially suited for functional covariates. The method is based on partitioning the functions' domain in intervals and using the functions' mean values across those intervals as predictors in regression or classification trees. This approach appears to be more intuitive to applied researchers than usual methods for functional data, while also performing very well in terms of prediction accuracy. The intervals are obtained from randomly drawn, exponentially distributed waiting times. We apply our method to data from Raman spectra on boar meat as well as near‐infrared absorption spectra. The predictive performance of the proposed functional random forests is compared with commonly used parametric and nonparametric functional methods and with a nonfunctional random forest using the single measurements of the curve as covariates. Further, we present a functional variable importance measure, yielding information about the relevance of the different parts of the predictor curves. Our variable importance curve is much smoother and hence easier to interpret than the one obtained from nonfunctional random forests. 相似文献
998.
K. Helios H. Maniak M. Sowa W. Zierkiewicz M. Wąsińska-Kałwa M. Giurg 《Journal of Coordination Chemistry》2017,70(20):3471-3487
The first metal complex of Phx-1 ligand, bis(2-amino-4,4α-dihydro-4α,7-dimethyl-3H-phenoxazin-3-one)nitratosilver(I), [Ag(Phx-1)2NO3], has been obtained and investigated by single crystal X-ray diffraction and vibrational spectroscopy methods. The Ag+ is bonded to heterocyclic nitrogen atoms of two organic ligands and one oxygen atom of a nitrate anion. The Phx-1 ligand coordination mode is supported by IR and Raman spectra, interpreted with the help of theoretical DFT studies. The antibacterial activity of the ligand and its Ag(I) complex as well as some reference compounds were screened against Gram-positive and Gram-negative bacteria, applying microdilution procedures. High sensitivity to the studied complex was found for Rhodococcus erythropolis and Bacillus licheniformis strains. Modified Phx-1 ligand preparation procedures are also presented. 相似文献
999.
The shape of the steady-state three-dimensional flow velocity profile established in carrier liquid flowing inside the rectangular cross-sectional channel for field-flow fractionation should be taken into account to optimize the separation. The central parts of this profile in the planes parallel to the main channel walls are flat with almost identical flow velocities which drop down to zero at the side walls. The separated species transported by the flow in the close-to-side walls regions move with lower average velocities compared to the species transported in the central part of the channel and are undesirably broadened. The hydrodynamic splitting of the carrier liquid at the entry of the channel where the sample is injected only into the central part of the channel eliminates the excessive zone broadening. The aspect ratio of the breadth to the thickness of the channel ratio can thus be reduced. The effect of various aspect ratios on the shape of the flow velocity profile is calculated and the results are used to optimize the aspect ratio of microfluidic channels. The experiments carried out by microthermal field-flow fractionation confirmed that the aspect ratio cannot be reduced to a value of 1, proposed by other authors. 相似文献
1000.
Zinc(II) and mercury(II) complexes were prepared by reacting isatin-3-thiosemicarbazone (ISTSCH) with zinc(II) acetate or mercury(II) bromide. The complexes were characterized by IR, Raman, diffuse reflectance, 1H and 13C NMR spectra and elemental analysis. Tetrahedral structures for Zn(ISTSC)2 and Hg(ISTSCH)Br2 are suggested. 相似文献