全文获取类型
收费全文 | 4873篇 |
免费 | 799篇 |
国内免费 | 1236篇 |
专业分类
化学 | 1951篇 |
晶体学 | 47篇 |
力学 | 926篇 |
综合类 | 178篇 |
数学 | 1339篇 |
物理学 | 2467篇 |
出版年
2024年 | 29篇 |
2023年 | 113篇 |
2022年 | 161篇 |
2021年 | 148篇 |
2020年 | 139篇 |
2019年 | 155篇 |
2018年 | 71篇 |
2017年 | 162篇 |
2016年 | 149篇 |
2015年 | 175篇 |
2014年 | 371篇 |
2013年 | 264篇 |
2012年 | 305篇 |
2011年 | 310篇 |
2010年 | 335篇 |
2009年 | 329篇 |
2008年 | 362篇 |
2007年 | 327篇 |
2006年 | 290篇 |
2005年 | 329篇 |
2004年 | 286篇 |
2003年 | 252篇 |
2002年 | 240篇 |
2001年 | 209篇 |
2000年 | 144篇 |
1999年 | 171篇 |
1998年 | 139篇 |
1997年 | 129篇 |
1996年 | 135篇 |
1995年 | 121篇 |
1994年 | 119篇 |
1993年 | 89篇 |
1992年 | 86篇 |
1991年 | 67篇 |
1990年 | 70篇 |
1989年 | 68篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有6908条查询结果,搜索用时 0 毫秒
61.
Yong Zhu Jin-lian Hu Kwok-wing Yeung Hao-jun Fan Ye-qiu 《高分子科学》2006,(2):173-186
SMPU (shape memory polyurethane) non-ionomers and ionomers, synthesized with poly(c-caprolactone) (PCL), 4, 4'-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BDO), dimethylolpropionic acid (DMPA) were measured with cyclic tensile test and strain recovery test. The relations between the structure and shape memory effect of these two series were studied with respect to the ionic group content and the effect of neutralization. The resulting data indicate that, with the introduction of asymmetrical extender, the stress at 100% elongation is decreased for PU non-ionomer and ionomer series, especially lowered sharply for non-ionomer series; the fixation ratio of ionomer series is not affected obviously by the ionic group content; the total recovery ratio of ionomer series is decreased greatly. After sufficient relaxation time for samples stretched beforehand, the switching temperature is raised slightly, whereas the recovery ratio measured with strain recovery test method is lowered with increased DMPA content. The characterization with FT-IR, DSC, DMA elucidated that, the ordered hard domain of the two series is disrupted with the introduction of DMPA which causes more hard segments to dissolve in soft phase; ionic groups on hard segment enhance the cohesion between hard segments especially at high ionic group content and significantly facilitate the phase separation compared with the corresponding non-ionomer at moderate ionic group content. 相似文献
62.
63.
64.
二组分混合物的最小流化特性 总被引:6,自引:0,他引:6
分析且分混合物的3种混合/分离状态及在完全混合时发生连续相转变的极限组成。提出一修养国非等密度体系混合/分离状态的法则与确定混合物空隙率简易可行的随意松散堆积方法。 相似文献
65.
66.
Synthesis and Crystal Structure of the Copper Complex of 7,16-Bis(2-hyd roxy-5-met hylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane 总被引:1,自引:0,他引:1
A lariat crown ether ligand 7,16-bis (2-hydroxy-5-methylbenzyl)- 1,4,10,13-tetraoxa-7,16-diazacyclooctadeeane (L1) has been prepared via one-pot Mannich reaction. Its copper(Ⅱ) complex Cu-L1 was synthesized and characterized by elemental analysis, IR and UV-visible spectroscopy. The crystal structure of the complex has been determined by X-ray diffraction analysis. The result shows that the copper(Ⅱ) ion is six-coordinated by two nitrogen and four oxygen atoms, two from the crown ether and the other two from the deprotonated phenolate anions, forming an elongated octahedral complex. Electrochemical study indicates that the complex undergoes reversible reduction in DMF solution. 相似文献
67.
68.
安力农的极谱测定及其电化学行为 总被引:4,自引:0,他引:4
在pH5.6,0.15mol/L磷酸盐缓冲溶液(PBS)中,得到了安力农的灵敏极谱吸附波,波的二阶导波高在2×10^-8~8×10^-6mol/L范围内与安力农的浓度成直线关系,检测下限为1×10^-8mol/L,测定出电极过程的电子传递系数a=0.43,表面电极反尖速率常数ks=3.3s^-1,安力农在汞电极上的吸附遵从Langmuir等温式,测得其吸附系数β=8.1×10^5。 相似文献
69.
70.
ZHANG Jun SUN Xiao-min CAI Zheng-ting FENG Da-cheng 《高等学校化学研究》2006,22(5):663-664
In the stratosphere,CF3Cl(CFC13)can either photodecompose or react directly with atomic oxygen to generate ozone-depleting agents such as Cl and ClO in the gas phase[1—3].Since the1970s,attention has been focused on the effects of these compounds on the … 相似文献