全文获取类型
收费全文 | 57397篇 |
免费 | 9602篇 |
国内免费 | 6343篇 |
专业分类
化学 | 39642篇 |
晶体学 | 635篇 |
力学 | 3719篇 |
综合类 | 550篇 |
数学 | 6850篇 |
物理学 | 21946篇 |
出版年
2024年 | 135篇 |
2023年 | 1178篇 |
2022年 | 1765篇 |
2021年 | 1993篇 |
2020年 | 2406篇 |
2019年 | 2265篇 |
2018年 | 1956篇 |
2017年 | 1888篇 |
2016年 | 2729篇 |
2015年 | 2551篇 |
2014年 | 3134篇 |
2013年 | 4152篇 |
2012年 | 5091篇 |
2011年 | 5125篇 |
2010年 | 3565篇 |
2009年 | 3350篇 |
2008年 | 3715篇 |
2007年 | 3302篇 |
2006年 | 3036篇 |
2005年 | 2518篇 |
2004年 | 1935篇 |
2003年 | 1598篇 |
2002年 | 1470篇 |
2001年 | 1260篇 |
2000年 | 1136篇 |
1999年 | 1367篇 |
1998年 | 1111篇 |
1997年 | 997篇 |
1996年 | 998篇 |
1995年 | 889篇 |
1994年 | 777篇 |
1993年 | 716篇 |
1992年 | 594篇 |
1991年 | 521篇 |
1990年 | 512篇 |
1989年 | 371篇 |
1988年 | 275篇 |
1987年 | 220篇 |
1986年 | 200篇 |
1985年 | 166篇 |
1984年 | 103篇 |
1983年 | 95篇 |
1982年 | 91篇 |
1981年 | 43篇 |
1980年 | 20篇 |
1979年 | 7篇 |
1976年 | 1篇 |
1959年 | 3篇 |
1957年 | 10篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
21.
Xiaoxia Yang Hongyan Xie Zhiguang Xu Jiabing Feng Qiwei Fu Haidong Li Yongtang Jia 《Journal of polymer science. Part A, Polymer chemistry》2021,59(9):813-823
An efficient, atom-economic, oxygen-tolerant, and water-tolerant strategy has been established to synthesize cyano-rich polyesters. Four kinds of organic bases, 1,1,3,3-tetramethylguanidine (TMG), 4-dimethylaminopyridine, triethylamine, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were explored for accelerating Michael addition polymerization of malononitrile and 1,4-butandiol diacrylate. TMG can promote the polymerization efficiently under mild conditions to quantitatively afford polyester with high-molecular weight and moderate polydispersity. The comparison of the kinetic studies of TMG and TBD reveals that TMG shows better catalytic performance, while the catalysis of TBD brings about oligomers in spite of the higher efficiency at early age of the polymerization. Moreover, other diacrylate compounds could also be quantitatively polymerized to afford polyesters with high molecular weight. When dimethacrylate is chose as the monomer, the polymerization becomes sluggish. All the afforded polyesters display programmable thermal and mechanical properties that are closely related to their chemical structures. 相似文献
22.
Journal of Thermal Analysis and Calorimetry - In the present work, pyrolysis kinetic mechanism was studied for regenerated cellulosic fiber (RCF) and composite RCF containing silicon/nitrogen flame... 相似文献
23.
Nonlinear Dynamics - Under investigation is a generalized (3 + 1)-dimensional variable- coefficient Kadomtsev– Petviashvili equation in fluid mechanics. Various exact analytical solutions are... 相似文献
24.
25.
26.
Terahertz(THz) wave emission from argon atom in a two-color laser pulses is studied numerically by solving the one-dimensional(1D) time-dependent Schr ¨odinger equation. The THz spectra we obtained include both discontinuous and continuum ones. By using the special basis functions that we previously proposed, our analysis points out that the discontinuous and continuum parts are contributed by bound–bound and continuum–continuum transition of atomic energy levels. Although the atomic wave function is strongly dressed during the interaction with laser fields, our identification for the discontinuous part of the THz wave shows that the transition between highly excited bound states can still be well described by the field-free basis function in the tunneling ionization regime. 相似文献
27.
28.
In the view of substrate availability, atomic efficiency and cost, directly using arenols as coupling partners in cross‐coupling, would be one of the most attractive goals. Up to date, many efforts have been made to activate the C—O bond of phenols with different strategies, for example, through in‐situ formed intermediates, through a catalytic reductive dearomatization‐condensation‐rearomatization sequence or catalytic deoxygenation. In this review, we summarized recent advances in cross‐couplings of arenols as the electrophiles via C—O activation. 相似文献
29.
30.
Yongjie Zhou Yuqi Mei Tian Luo Wenxue Chen Qiuping Zhong Haiming Chen Weijun Chen 《Molecules (Basel, Switzerland)》2021,26(9)
The contribution of rheological properties and viscoelasticity of the interfacial adsorbed layer to the emulsification mechanism of enzymatic modified sugar beet pectin (SBP) was studied. The component content of each enzymatic modified pectin was lower than that of untreated SBP. Protein and ferulic acid decreased from 5.52% and 1.08% to 0.54% and 0.13%, respectively, resulting in a decrease in thermal stability, apparent viscosity, and molecular weight (Mw). The dynamic interfacial rheological properties showed that the interfacial pressure and modulus (E) decreased significantly with the decrease of functional groups (especially proteins), which also led to the bimodal distribution of particle size. These results indicated that the superior emulsification property of SBP is mainly determined by proteins, followed by ferulic acid, and the existence of other functional groups also promotes the emulsification property of SBP. 相似文献