全文获取类型
收费全文 | 238501篇 |
免费 | 1958篇 |
国内免费 | 680篇 |
专业分类
化学 | 102311篇 |
晶体学 | 3340篇 |
力学 | 9287篇 |
综合类 | 5篇 |
数学 | 22470篇 |
物理学 | 69004篇 |
无线电 | 34722篇 |
出版年
2021年 | 1847篇 |
2020年 | 2014篇 |
2019年 | 2270篇 |
2018年 | 2998篇 |
2017年 | 2870篇 |
2016年 | 4163篇 |
2015年 | 2427篇 |
2014年 | 3986篇 |
2013年 | 9719篇 |
2012年 | 7671篇 |
2011年 | 9194篇 |
2010年 | 6613篇 |
2009年 | 6837篇 |
2008年 | 9133篇 |
2007年 | 9598篇 |
2006年 | 9287篇 |
2005年 | 8427篇 |
2004年 | 7830篇 |
2003年 | 7044篇 |
2002年 | 6725篇 |
2001年 | 7706篇 |
2000年 | 6209篇 |
1999年 | 4986篇 |
1998年 | 4168篇 |
1997年 | 4169篇 |
1996年 | 3839篇 |
1995年 | 3646篇 |
1994年 | 3492篇 |
1993年 | 3326篇 |
1992年 | 3687篇 |
1991年 | 3598篇 |
1990年 | 3484篇 |
1989年 | 3209篇 |
1988年 | 3127篇 |
1987年 | 2851篇 |
1986年 | 2636篇 |
1985年 | 3337篇 |
1984年 | 3563篇 |
1983年 | 2938篇 |
1982年 | 3091篇 |
1981年 | 3052篇 |
1980年 | 2909篇 |
1979年 | 2964篇 |
1978年 | 3048篇 |
1977年 | 3051篇 |
1976年 | 3073篇 |
1975年 | 2879篇 |
1974年 | 2854篇 |
1973年 | 3010篇 |
1972年 | 1937篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
882.
A. Zh. Zhakaeva T. Yu. Orlova V. I. Zdanovich V. N. Setkina D. N. Kursanov 《Russian Chemical Bulletin》1977,26(1):202-203
Conclusions The pyridinium cyclopentadienylidechromium(molybdenum) tricarbonyl complexes were synthesized and a study was made of their IR, NMR, and mass spectra.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 227–228, January, 1977.The authors express their gratitude to N. I. Vasyukova and G. A. Panosyan for taking the mass and NMR spectra. 相似文献
883.
Ohne Zusammenfassung 相似文献
884.
R.R. Adžić D.N. Simić A.R. Despić D.M. Dražić 《Journal of Electroanalytical Chemistry》1975,65(2):587-601
It was demonstrated that some foreign metal monolayers formed by underpotential deposition have pronounced catalytic effects on the oxidation of formic acid on platinum. The explanation of these effects was sought within the framewor of existing data on the formic acid oxidation and the underpotential deposition. It was found that the catalytic effect of foreign metal monolayers originates in the decrease of hydrogen adsorption thus preventing the formation of the main poisoning species COH. At the same time these experiments confirm the previously postulated mechanism of formation of the poisoning species involving adsorbed hydrogen. 相似文献
885.
886.
About the Fluorescence Thermochromism of Acetonitrile Copper Iodide with Dibenzo-18-Crown-6 Copper iodide reacts in actonitrile solution with dibenzo-18-crown-6 to form a compound,(CuJ)4(CH3CN)4(db-18-c-6), which fluoresces yellow at 298K, but pink at 77 K. It decomposes at 55.3°C. (5 Torr) by lost of acetonitrile and a heterogeneous mixture of copper iodide and polyether results. In absence of dibenzo-18-crown-6, copper iodide forms with acetonitrile a heterogeneous mixture of copper iodide and polyether results. In absence of dibenzo-18-crown-6, copper iodide forms with acetonitrile a solvate CuJ. CH3CN. It also shows fluorescence thermochromism (yellow at 298 K, but green at 77 k) but decomposes at 0°C and 760 Torr. The luminescences pectra of the macrocyclic polyether complex at 298 K is redshifted. This probably results from intersection between the crown and the acetonitrile copper iodide. 相似文献
887.
888.
Crystals of 1,6-8, 13-bis-oxido-[14]-annulene are monoclinic, a = 9,29, b = 9,74, c = 11,46 Å, β = 90,0°, space group P 21/c, with 4 molecules in the unit cell. The structure has been solved by direct methods and refined by full-matrix least-squares analysis of three-dimensional intensity data. The cis-configuration of the two oxygen bridges is confirmed, and the observed molecular parameters are in full accord with the aromatic properties of the molecule. 相似文献
889.
Serber Z Ledwidge R Miller SM Dötsch V 《Journal of the American Chemical Society》2001,123(37):8895-8901
Our recently developed in-cell NMR procedure now enables one to observe protein conformations inside living cells. Optimization of the technique demonstrates that distinguishing the signals produced by a single protein species depends critically on protein overexpression levels and the correlation time in the cytoplasm. Less relevant is the selective incorporation of (15)N. Poorly expressed proteins, insoluble proteins, and proteins that cannot tumble freely due to associations within the cell cannot yet be observed. We show in-cell NMR spectra of bacterial NmerA and human calmodulin and discuss limitations of the technique as well as prospects for future applications. 相似文献
890.
A paradox was observed in a previous study of the electrophoresis of linear DNA fragments in agarose gels (D. L. Holmes and N. C. Stellwagen, Electrophoresis 1990, 11, 5-15). The pore size of the agarose matrix was more accurately determined if the root-mean-square radius of gyration was used to measure DNA macromolecular size. However, the Ogston equations were obeyed and other gel parameters such as the apparent fiber radius and fiber volume appeared to be better described if the geometric mean radius was used to measure DNA size. This paradox can be resolved if relative mobilities (with respect to the smallest DNA molecule in the data set) are used to construct the Ferguson plots, instead of absolute mobilities. Using relative mobilities and the root-mean-square radius of gyration, the Ogston equations are obeyed and the pore size of the matrix is consistent with values determined by other methods. 相似文献