全文获取类型
收费全文 | 60802篇 |
免费 | 7052篇 |
国内免费 | 12007篇 |
专业分类
化学 | 51724篇 |
晶体学 | 2350篇 |
力学 | 2483篇 |
综合类 | 530篇 |
数学 | 4026篇 |
物理学 | 18748篇 |
出版年
2024年 | 124篇 |
2023年 | 986篇 |
2022年 | 1188篇 |
2021年 | 2007篇 |
2020年 | 2166篇 |
2019年 | 1943篇 |
2018年 | 1647篇 |
2017年 | 2154篇 |
2016年 | 2359篇 |
2015年 | 2004篇 |
2014年 | 2655篇 |
2013年 | 5597篇 |
2012年 | 3844篇 |
2011年 | 4335篇 |
2010年 | 3668篇 |
2009年 | 4341篇 |
2008年 | 4190篇 |
2007年 | 4324篇 |
2006年 | 4160篇 |
2005年 | 3607篇 |
2004年 | 3397篇 |
2003年 | 2843篇 |
2002年 | 2405篇 |
2001年 | 1958篇 |
2000年 | 1807篇 |
1999年 | 1484篇 |
1998年 | 1245篇 |
1997年 | 1112篇 |
1996年 | 925篇 |
1995年 | 935篇 |
1994年 | 847篇 |
1993年 | 644篇 |
1992年 | 618篇 |
1991年 | 444篇 |
1990年 | 309篇 |
1989年 | 259篇 |
1988年 | 233篇 |
1987年 | 165篇 |
1986年 | 118篇 |
1985年 | 130篇 |
1984年 | 109篇 |
1983年 | 43篇 |
1982年 | 74篇 |
1981年 | 100篇 |
1980年 | 69篇 |
1979年 | 71篇 |
1978年 | 46篇 |
1977年 | 54篇 |
1976年 | 32篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
991.
992.
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
993.
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
994.
995.
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
996.
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
997.
通过电化学途径和化学途径在YBa_2Cu_3O_7超导体表面制备了导电高分子聚吡咯膜,用以保护超导体不受环境作用的影响,实验结果发现电化学过程能破坏YBa_2Cu_O_7的超导性,而采用化学法制备的聚吡咯和聚氯乙烯混和材料包覆在YBa_2Cu_3O_7表面后,超导体不仅保持原有超导性,而且有很好的保护超导体免遭环境中酸和水作用的能力。 相似文献
998.
The novel coordination polymer [Pr(BYBA)3(H2O)2]·[Pr(BYBA)3(H2O)] (BYBAH=2-benzoylbenzoic acid) was yielded by hydrothermal synthesis,determined by single-crystal X-ray diffraction,and characterized by FT-IR and UV-Vis spectra. The crystal crystallizes in the triclinic system,space group P1 with a=9.112(3),b=14.644(5),c=27.076(11),α=84.223(3),β= 87.816(4),γ=88.902(4)o,V=3592(2)3,C84H60O21Pr2,Mr=1687.14,Z=2,F(000)=1700,Dc= 1.560 g/cm3,μ=1.419 mm-1,the final R=0.0485 and wR=0.1258 for 13035 observed reflections with I > 2σ(I). The compound contains two different building units,[Pr2(BYBA)6(H2O)4] and [Pr2(BYBA)6(H2O)2]. It is noticeable that [Pr2(BYBA)6(H2O)4] is an isolated binuclear building block,in which the Pr3+ ion centers are both located in an eight-coordinated environment. However,in [Pr2(BYBA)6(H2O)2] the Pr3+ ion centers are located in a nine-coordinated environment and connected by BYBA ligands to form 1D chains. 相似文献
999.
S. Tamai J. Kamada T. Ono T. Kuroki K. Goto A. Yamaguchi 《Journal of polymer science. Part A, Polymer chemistry》2002,40(3):423-428
Polyimide containing an indan unit and alkyl moiety with a high molecular weight was prepared from 5,7‐diamino‐1,1,4,6‐tetramethylindan and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride. This polyimide was amorphous and soluble in common organic solvents, such as tetrahydrofuran, chloroform, and cyclopentanone. Thermogravimetry of the polyimide showed good thermal stability, indicating that a 10% weight loss of the polyimide was observed at 500 °C in nitrogen. The glass‐transition temperature of the polyimide was not observed by DSC measurement between room temperature and 400 °C at a heating rate of 10 °C/min (Apparatus: DSC3100 MAC Science Co., Ltd.). Transparency of the polyimide at 365 nm was 80%. The polyimide acted as a photosensitive resist of negative type by UV radiation. The resist had a sensitivity of 31 mJ/cm2 and a contrast of 2.3 when it was developed with cyclopentanone at room temperature. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 423–428, 2002 相似文献
1000.
由原位缩聚制备了刚性高分子聚酰亚胺(PI)和柔性基体聚N-乙烯吡咯烷附(PVP)的分子复合物,并由实验证明了中间体聚酰胺酸(PA)和聚乙烯吡咯烷酮大分子之间存在的酸一碱相互作用.这种相互作用促进了混容性,使聚酰亚胺能以分子水平或接近分子水平分散在聚毗咯烷酮的基体之中.聚酰亚胺/聚N-乙烯吡咯烷团分子复合物的薄膜呈透明性,在整个组成范围内只有一个Tg,显示单相行为。当PI含量<20%时,SEM相片呈现均相形貌,看不到PI微晶.广角X-ray衍射图表明PI特征结晶峰消失,和无定形的PVP完全混容.当PI含量>40%,SEM显示有均匀分布的、棒状PI微晶存在.通过分子复合,即使PI含量为10%,聚N-乙烯吡咯烷酮不再溶于乙醇,耐热性也有提高. 相似文献