全文获取类型
收费全文 | 143949篇 |
免费 | 26840篇 |
国内免费 | 15293篇 |
专业分类
化学 | 115458篇 |
晶体学 | 1615篇 |
力学 | 7019篇 |
综合类 | 931篇 |
数学 | 16049篇 |
物理学 | 45010篇 |
出版年
2024年 | 274篇 |
2023年 | 2225篇 |
2022年 | 3495篇 |
2021年 | 4141篇 |
2020年 | 5487篇 |
2019年 | 6420篇 |
2018年 | 4799篇 |
2017年 | 4238篇 |
2016年 | 8245篇 |
2015年 | 8269篇 |
2014年 | 9404篇 |
2013年 | 11904篇 |
2012年 | 12645篇 |
2011年 | 12472篇 |
2010年 | 9903篇 |
2009年 | 9618篇 |
2008年 | 9518篇 |
2007年 | 8253篇 |
2006年 | 7634篇 |
2005年 | 6752篇 |
2004年 | 5452篇 |
2003年 | 4570篇 |
2002年 | 5053篇 |
2001年 | 3892篇 |
2000年 | 3548篇 |
1999年 | 2737篇 |
1998年 | 1982篇 |
1997年 | 1789篇 |
1996年 | 1750篇 |
1995年 | 1542篇 |
1994年 | 1383篇 |
1993年 | 1137篇 |
1992年 | 994篇 |
1991年 | 859篇 |
1990年 | 722篇 |
1989年 | 567篇 |
1988年 | 414篇 |
1987年 | 367篇 |
1986年 | 369篇 |
1985年 | 293篇 |
1984年 | 206篇 |
1983年 | 169篇 |
1982年 | 139篇 |
1981年 | 92篇 |
1980年 | 68篇 |
1979年 | 29篇 |
1976年 | 30篇 |
1975年 | 31篇 |
1973年 | 27篇 |
1957年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
The crystallization behavior of miscible syndiotactic polystyrene (sPS) and atactic polystyrene (aPS) blends with different sPS/aPS weight ratios was investigated in supercritical CO2 by using Fourier‐transform infrared spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction. Supercritical CO2 and aPS exhibited different effects on the conformational change of sPS and competed with each other. Increasing the content of amorphous aPS in the blends made its effect on the conformational change of sPS gradually surpass that of supercritical CO2. Supercritical CO2 favored the formation of the helical conformation of sPS in lower temperature range and the all trans planar conformation in higher temperature range, instead of forming the latter one only in higher temperature range in ambient atmosphere. However, increasing aPS content in the blends pushed the range for forming the helical conformation to lower temperature and made the all trans planar conformation dominant in aPS/sPS 25/75 blend after treating in supercritical CO2 above 60 °C. The all trans planar zigzag conformation was more favorable than the helical conformation after mixing aPS in sPS in supercritical CO2. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1755–1764, 2007 相似文献
952.
Kuan‐Wei Lee Hong‐Cheu Lin 《Journal of polymer science. Part A, Polymer chemistry》2007,45(20):4564-4572
A series of new liquid crystalline homopolymers, copolymers, and block copolymers were polymerized from styrene‐macroinitiator ( SMi ) and methacrylates with pendent 4,4′‐bis(biphenyl)fluorene ( M1 ) and biphenyl‐4‐ylfluorene ( M2 ) groups through atom transfer radical polymerization (ATRP). The number‐average molecular weights (Mn) of polymers P1 ‐ P4 were 10,007, 14,852, 6,275, and 10,463 g mol?1 with polydispersity indices values of 1.21, 1.15, 1.31, and 1.22, respectively. All polymers exhibit the nematic phase. The thermal, mesogenic, and photoluminescent properties of all polymers were investigated. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4564–4572, 2007 相似文献
953.
954.
Nathalie Charton Achim Feldermann Alexander Theis Martina H. Stenzel Thomas P. Davis Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2004,42(21):5559-5559
The original article to which this Erratum refers was published in J Polym Sci Part A: Polym Chem (2004) 42(20) 5170–5179. No abstract. 相似文献
955.
956.
A Novel and Efficient Catalytic System for Aerobic Oxidative Coupling of 2-Naphthol Derivatives 总被引:2,自引:0,他引:2
LiCHEN JingBoLAN ZhiHuaMAO XiaoQiYU RuGangXIE 《中国化学快报》2004,15(8):903-906
The paper reported a novel and efficient aerobic oxidative coupling reaction of 2-naphthol derivatives catalyzed by CuCu (Ⅰ or Ⅱ)N-alkylimidazole complexes in excellent yields. The crystal structure of CuCu(Ⅱ)N-methylimidazole complex to be determined by X-Ray. 相似文献
957.
Violetta Patroniak Wanda Radecka‐Paryzek Maciej Kubicki 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(9):o511-o513
The structure of a trifluoromethanesulfonate salt of a nontypical triply protonated linear tetramine, C7H23N43+·3CF3SO3−, with a layered crystal structure is presented. One N atom remains unprotonated. The conformation of the cation is enforced by intra‐ and intermolecular hydrogen bonds. The crystal structure is built of ca 10 Å deep layers, within which cations and anions are hydrogen bonded. Each layer is only weakly bound to its neighbours. This study shows a rare example of an unsymmetrically protonated polyamine and the relation between the lack of protonation, intramolecular hydrogen bonding and the conformation of the cation. 相似文献
958.
介绍了虚拟技术在实验教学改革中的作用与意义,探讨了电子信息系统实验教学改革的新思路与实现措施,并总结了实验教学改革的初步成果. 相似文献
959.
We prove that the renormalized solutions of the Boltzmann equation considered in a bounded domain with different types of (kinetic) boundary conditions converge to the Stokes‐Fourier system with different types of (fluid) boundary conditions when the main free path goes to zero. This extends the work of F. Golse and D. Levermore [9] to the case of a bounded domain. © 2003 Wiley Periodicals, Inc. 相似文献
960.
使用分子图形软件设计出多种CnP-4(n =1~ 7)的结构模型 ,并进行B3LYP密度泛函几何构型优化和振动频率计算 .最稳定的CP-4和C2 P-3 都是平面环状结构 .最稳定的CnP-4(n =3 ,5 ,7)结构在直碳链的一端连接 1个磷原子且另一端是P3 C的四元环的平面结构 .最稳定的CnP-4(n =4,6)结构在直碳链的一端连接 1个磷原子且另一端是P3 的三元环的锄状结构 .直碳链可与平面环的磷原子生成大π键 .大多数构型是由C2 ,C3 ,C4子结构以环状或链状方式组成的 .碳原子与磷原子以交替方式排列的结构数量少、能量高 . 相似文献