全文获取类型
收费全文 | 69391篇 |
免费 | 7406篇 |
国内免费 | 13819篇 |
专业分类
化学 | 62054篇 |
晶体学 | 2529篇 |
力学 | 1286篇 |
综合类 | 580篇 |
数学 | 4966篇 |
物理学 | 19201篇 |
出版年
2024年 | 151篇 |
2023年 | 1130篇 |
2022年 | 1862篇 |
2021年 | 2319篇 |
2020年 | 2557篇 |
2019年 | 2350篇 |
2018年 | 1931篇 |
2017年 | 2558篇 |
2016年 | 2634篇 |
2015年 | 2306篇 |
2014年 | 3089篇 |
2013年 | 6236篇 |
2012年 | 4402篇 |
2011年 | 4836篇 |
2010年 | 4121篇 |
2009年 | 4875篇 |
2008年 | 4755篇 |
2007年 | 4807篇 |
2006年 | 4516篇 |
2005年 | 4029篇 |
2004年 | 3785篇 |
2003年 | 3089篇 |
2002年 | 2626篇 |
2001年 | 2148篇 |
2000年 | 2058篇 |
1999年 | 1628篇 |
1998年 | 1396篇 |
1997年 | 1226篇 |
1996年 | 1052篇 |
1995年 | 1018篇 |
1994年 | 941篇 |
1993年 | 765篇 |
1992年 | 666篇 |
1991年 | 506篇 |
1990年 | 339篇 |
1989年 | 310篇 |
1988年 | 263篇 |
1987年 | 175篇 |
1986年 | 146篇 |
1985年 | 155篇 |
1984年 | 121篇 |
1983年 | 53篇 |
1982年 | 94篇 |
1981年 | 122篇 |
1980年 | 97篇 |
1979年 | 93篇 |
1978年 | 66篇 |
1977年 | 71篇 |
1976年 | 42篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
铕掺杂BaPbO3的EXAFS研究 总被引:3,自引:0,他引:3
采用扩展X射线吸收精细结构方法,研究了铕掺杂BaPbO3多晶粉末中Eu,Pb两种原子的近邻结构。Eu的掺杂,导致八面体中金属Pg,Eu的配位数降低。 相似文献
992.
Conditions for the formation of rare earth element (Y, La–Lu) 3-methylglutarates were studied and their quantitative composition
and solubilities in water at 293 K were determined (10–2 mol dm–3). The IR spectra of the prepared complexes with general formula Ln2(C6H8O4)3
nH2O (n=3–8) were recorded and their thermal decomposition in the air were investigated. During heating the hydrated 3-methylglutarates
are dehydrated in one step and next anhydrous complexes decompose to oxides Ln2O3 with intermediate formation Ln2O2CO3 (Y, La, Nd–Gd) or directly to the oxides, Ln2O3, CeO2, Pr6O11 and Tb4O7 (Ce, Pr, Tb–Lu).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
993.
The crystal structure of new compound Ba3BPO7 was determined by ab initio method from high-resolution conventional X-ray powder diffraction data. The Rietveld refinement converged to Rp=5.92%, Rwp=8.87%, Rexp=5.00% with the following details: Hexagonal, space group P63mc, a=5.4898 (1) Å, c=14.7551(1) Å, Z=2. The basic unit of the structure is the [BaO10]-[BO3]-[PO4] polar polyhedra-chain composed of Ba1-B-P-O cluster. These chains, running along c-axis, stack in a HCP mode to build the whole structure with triangular prism channels. The channels are parallel to c-axis too, in which Ba2 and Ba3 are located. 相似文献
994.
995.
A Minor New Flavone from Scutellaria baicalensis Georgi 总被引:1,自引:0,他引:1
A new flavone,6,2′-dihydroxy-5,7,8,6′-tetramethoxyflavone,was isolated from the roots of Scutellaria baicalensis. Its structure was established on the basis of spectral evidences. 相似文献
996.
K. Grob 《Journal of separation science》1978,1(5):263-267
During one year continuous use of on-column injection, the typical advantages described in our first report have fully been confirmed. In addition the analysis of large sample volumes has proved promising. Only minor modifications have been applied to the on-column injector device. Broad evidence has been gathered showing that full separation efficiency of the capillary columns after on-column injection is attained only when cold trapping or the solvent effect, as band shortening mechanisms, are working- While, under the conditions of on-column injection, cold trapping is less efficient than with other injection techniques, the opposite holds true for the solvent effect. Compared with splitless injection, the danger of excessive solvent condensation on the column is increased. A working rule is presented for establishing the optimal chromatographic conditions for handling large sample volumes while ensuring full separation efficiency yet avoiding harm to the column. 相似文献
997.
The interaction of aryldiazonium ions with some Schiff-base complexes of cobalt and ruthenium have been studied. With cobalt, one-electron oxidation of [Co(II)Salen] occurred; with [Co(I)Salen] the corresponding Co(III)-aryl complexes were isolated. In the case of ruthenium oxidation also occurs, [Ru(Salen)(CO)py] gave the corresponding monocation. The results, especially for ruthenium, are in contrast to the stabilisation of both nitrosyl and aryldiazonium adducts in analogous porphyrin complexes. 相似文献
998.
999.
Colin Thomson 《Theoretical chemistry accounts》1973,32(2):93-100
Non-empirical LCAO-MO-SCF calculations on SiF2 using two Gaussian basis sets are reported. The larger basis set gives a calculated geometry in good agreement with experiment. The effect on the energy and population analysis of optimization of the Si 3d exponent was investigated. 3d orbitals are found to be much less important in the bonding than in the isoelectronic molecule SO2. 相似文献
1000.
Journal of Thermal Analysis and Calorimetry - In the ternary system PbO?P2O5?PbCl2, the partial ternary system Pb5Cl2O4?Pb3Cl2O2?Pb10(PO4)6Cl2 was examined by thermal,... 相似文献