全文获取类型
收费全文 | 10966篇 |
免费 | 1462篇 |
国内免费 | 987篇 |
专业分类
化学 | 2842篇 |
晶体学 | 111篇 |
力学 | 4140篇 |
综合类 | 156篇 |
数学 | 1521篇 |
物理学 | 4645篇 |
出版年
2024年 | 14篇 |
2023年 | 82篇 |
2022年 | 298篇 |
2021年 | 376篇 |
2020年 | 307篇 |
2019年 | 217篇 |
2018年 | 247篇 |
2017年 | 365篇 |
2016年 | 436篇 |
2015年 | 338篇 |
2014年 | 464篇 |
2013年 | 833篇 |
2012年 | 533篇 |
2011年 | 658篇 |
2010年 | 537篇 |
2009年 | 626篇 |
2008年 | 631篇 |
2007年 | 703篇 |
2006年 | 642篇 |
2005年 | 560篇 |
2004年 | 596篇 |
2003年 | 511篇 |
2002年 | 381篇 |
2001年 | 367篇 |
2000年 | 348篇 |
1999年 | 309篇 |
1998年 | 269篇 |
1997年 | 260篇 |
1996年 | 231篇 |
1995年 | 188篇 |
1994年 | 167篇 |
1993年 | 147篇 |
1992年 | 131篇 |
1991年 | 113篇 |
1990年 | 75篇 |
1989年 | 72篇 |
1988年 | 72篇 |
1987年 | 60篇 |
1986年 | 42篇 |
1985年 | 39篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 30篇 |
1981年 | 29篇 |
1980年 | 14篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
M~++BrCN─→MCN~++Br气相反应的从头算研究朱荣顺,戴树珊(云南大学化学系,昆明,650091)关键词气相反应,过渡金属阳离子,溴化氰,从头算,相对论赝势对过渡金属离子与一些小分子的气相反应已有大量的实验和理论研究[1~5],MichelS... 相似文献
122.
Aldehyde-2,4-dinitrophenylhydrazones exist as (E)- and (Z)-geometrical isomers, and adventitious isomerization during sample preparation can cause analytical errors. Purified alkenal-2,4-dinitrophenylhydrazone derivatives comprise only the (E)-isomer. However, partial isomerization to the (Z)-isomer occurs upon addition of acid to attain an equilibrium isomer ratio. The UV-visible spectral properties of the isomers differ; the (Z)-isomer exhibiting a 6-10 nm lower absorption maximum compared to the (E)-isomer. Alkenal-2,4-dinitrophenylhydrazones having a CC double bond at the 2- or 3-position of the alkenal exhibited similar absorption maxima with an equilibrium isomer ratio (0.035) that was much lower than those of other alkenals. The CC double bond at the 3-position migrates to a position of conjugation with the CN double bond during hydrazone synthesis to form a stabilized molecular structure. Alkenal-2,4-dinitrophenylhydrazones having a double bond at the 4-position or greater exhibited a similar absorption maxima equilibrium isomer ratio (0.14) to alkanal-2,4-dinitrophenylhydrazones. The quantitative analysis of carbonyl compounds in air or water using DNPH is usually conducted in the presence of an acid catalyst. Consequently, the solution of the direct extract prepared for HPLC or GC analysis contains both (E)- and (Z)-isomers. 相似文献
123.
124.
依据柱相比的热力学定义和反相液相色谱中溶质的计量置换保留理论(the stoichiometric dispheement heory of solute for retention,SDT-R),对反相液相色谱中固定相和流动相性质、温度对柱相比的影响进行了研究。结果表明:固定相的种类和配基的疏水性对柱相比影响较大,而流动相中有机溶剂的种类,特别是脂肪酸作为置换剂时,对柱相比的影响更大,而柱相比受温度的影响较小。此外,通过用27种小分子溶质对柱相比的测定,其logI和Z良好的线性关系,进一步证明柱相比是一个与溶质性质无关的常数。 相似文献
125.
对130℃下1,3 二烯基 1,1,3,3 四甲基二硅氧烷(DVDS)/苯乙烯(St)的溶液环化共聚合动力学进行了研究.根据低转化率(<10%)的共聚物组成及环状结构比例,通过参数估计方法,求得环化率与竞聚率,分别为r1=0102、r2=348、rc=00210、Kc=381mol/L、K′c=0389mol/L,同时得到它们95%置信概率的联合置信区间及其交互影响的联合置信区间.表明DVDS的反应活性较St低,其非环状结构自由基具有较强的分子内环化反应能力;环的位阻效应使环状结构DVDS自由基的活性低于其非环状结构自由基. 相似文献
126.
XinZHANG DeHuaHE QiJiangZHANG BoQingXU QiMingZHU 《中国化学快报》2003,14(10):1066-1069
Comparatively high CH3OH selectivity (60.0%) and yield (6.7%) were obtained on MoOx/(LaCoO3 Co3O4) catalysts in selective oxidation of methane to methanol using molecular oxygen as oxidant. The interaction between MoOx and La-Co-oxide modified the molecular structure of molybdenum oxide and the ratio of O^-/O^2- on the catalyst surface, which controlled the catalytic performance of MoOx/(LaCoO3 Co3O4) catalysts. 相似文献
127.
Residual stress in the epoxy plate during a rapid cooling process was measured by the layer removal method and calculated by the linear thermoviscoelastic theory considering specific volume relaxation. The relaxations of the tensile modulus and specific volume were measured by an Instron thermomechanical analyzer. When the starting temperature of the cooling process was near the glass transition temperature of the cured epoxy, the residual stress in the epoxy plate was smaller than when the starting temperature was higher than the glass transition temperature. However, the transient stress in the cured epoxy plate was higher when the starting temperature was near the glass transition temperature than when the starting temperature was higher than the glass transition temperature. The quenched epoxy plate was compressed in the direction parallel to the surface and expanded in the thickness direction. 相似文献
128.
The tube model is applied for the treatment of stress-strain measurements on SBR networks. It is shown that this theory allows the separation of crosslink and constraint contributions to the stress-strain behavior and, also, a reliable determination of crosslink densities. The consideration of dynamical contributions is discussed and a special numerical method is developed. 相似文献
129.
130.