全文获取类型
收费全文 | 22727篇 |
免费 | 2173篇 |
国内免费 | 1460篇 |
专业分类
化学 | 16227篇 |
晶体学 | 229篇 |
力学 | 1103篇 |
综合类 | 95篇 |
数学 | 2781篇 |
物理学 | 5925篇 |
出版年
2024年 | 45篇 |
2023年 | 247篇 |
2022年 | 393篇 |
2021年 | 455篇 |
2020年 | 604篇 |
2019年 | 525篇 |
2018年 | 457篇 |
2017年 | 423篇 |
2016年 | 742篇 |
2015年 | 712篇 |
2014年 | 881篇 |
2013年 | 1339篇 |
2012年 | 1666篇 |
2011年 | 1907篇 |
2010年 | 1090篇 |
2009年 | 999篇 |
2008年 | 1429篇 |
2007年 | 1468篇 |
2006年 | 1460篇 |
2005年 | 1388篇 |
2004年 | 1098篇 |
2003年 | 901篇 |
2002年 | 789篇 |
2001年 | 445篇 |
2000年 | 396篇 |
1999年 | 421篇 |
1998年 | 417篇 |
1997年 | 368篇 |
1996年 | 388篇 |
1995年 | 309篇 |
1994年 | 334篇 |
1993年 | 236篇 |
1992年 | 216篇 |
1991年 | 195篇 |
1990年 | 188篇 |
1989年 | 118篇 |
1988年 | 126篇 |
1987年 | 120篇 |
1986年 | 103篇 |
1985年 | 155篇 |
1984年 | 97篇 |
1983年 | 67篇 |
1982年 | 95篇 |
1981年 | 84篇 |
1980年 | 67篇 |
1979年 | 61篇 |
1978年 | 55篇 |
1977年 | 46篇 |
1976年 | 38篇 |
1975年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Jem‐Kun Chen I‐Kuan Lin Fu‐Hsiang Ko Chih‐Feng Huang Kuo‐Shen Chen Chia‐Hao Chan Feng‐Chih Chang 《Journal of Polymer Science.Polymer Physics》2004,42(22):4063-4074
Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma‐polymerization technique with, as the energy source, plasmas of argon, oxygen, or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high‐energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties and morphologies in their surfaces. High‐energy argon atoms provide a thermodynamic factor to initiate the ring‐opening polymerization of BZZ and result in the polymer surface having a grid‐like structure. The ring‐opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma‐polymerization time. By estimating changes in thickness, we found that the PBZZ film synthesized by the oxygen plasma‐polymerization process undergoes the slowest rate of etching in CF4 plasma. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4063–4074, 2004 相似文献
42.
Chunxia Zhao Guowang Xu Xianzhe Shi Jianmei Ma Yan Zhang Shen Lv Qianfeng Weng Qing Yang 《Analytical sciences》2004,20(7):1001-1005
Fluorescent-based single-strand conformation polymorphism (F-SSCP) analysis with capillary electrophoresis (CE) is the most common method for the detection of mutation because of its high sensitivity and resolution. In this study, we prepared an inexpensive linear polyacrylamide (LPA), and successfully applied it to CE-SSCP analysis and tandem CE-SSCP/heteroduplex analysis (HA) of the P53 gene on an ABI capillary genetic analyzer. A comparison of the sieving capabilities of a homemade LPA and commercial polydimethylacrylamide (PDMA) demonstrates that the homemade LPA has a higher resolution, a shorter analysis time, and is more suitable for tandem SSCP/HA than commercial PDMA. To show the usefulness, mutations of P53 gene exon 7 - 8 in 37 tumor samples were investigated by using homemade LPA. The results indicate that 10 mutations were found in 9 of 37 cases; the majority of P53 mutations were missense mutations, and 70% were located in exon 7, which plays an important role in neoplastic progression in human tumorigenesis. 相似文献
43.
建立傅里叶变换步进扫描时间分辨光电导光谱,并研究太阳电池中与转换效率密切相关的少数载流子寿命.实验选取三种典型的硅太阳电池(单晶硅样品1、多晶硅样品2和多晶硅样品3 ),发现其瞬态光电导的上升和衰退曲线可以分别用两个简单的指数函数描述.由于有复合中心的参与,复合过程中少数载流子的寿命比产生过程中的寿命短.为验证实验结果的可靠性,采用了提取样品少数载流子的体寿命和计算其有效扩散长度两种方法.通过与太阳电池暗伏安特性和负载特性研究相结合,进一步分析和讨论了少数载流子寿命与短路电流、开路电压和转换效率的关系.同时探讨了步进扫描时间分辨光谱实验的其他用途.
关键词:
步进扫描
时间分辨
硅太阳电池
瞬态光电导 相似文献
44.
We analyse a model for equilibrium configurations of composite systems of nematic liquid crystal with polymer inclusions, in the presence of an external magnetic field. We assume that the system has a periodic structure, and consider the relaxed problem on the unit length constraint of the nematic director field. The relaxation of the Oseen–Frank energy functional is carried out by including bulk as well as surface energy penalty terms, rendering the problem fully non‐linear. We employ two‐scale convergence methods to obtain effective configurations of the system, as the size of the polymeric inclusions tends to zero. We discuss the minimizers of the effective energies for, both, the constrained as well as the unconstrained models. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
45.
Several 2- and 4-alkylcyclohexadienones were prepared and shown to accept electrons to produce ketyl radical anions that dissociated rapidly at room temperature to release carbon-centered radicals and an aromatic phenoxide type anion. In the PET process with benzyl-substituted cyclohexadienones, initiated with triethylamine, the benzyl radicals dimerised or abstracted an H-atom from solvent. In electrochemical reductions, and in reductions with alkali metals in liquid ammonia, the benzyl radicals were further reduced to anions. 相似文献
46.
47.
48.
49.
本文报道了在Zn0.76Cd0.24Se/ZnSe多量子阱(MQWs)中,用不同的Ar+激光线激发,观察到了共振增强的喇曼散射。首次在室温和77K的条件下,用Ar+的457.9nm谱线激发,观察到分别来自ZnSe垒层和Zn0.76Cd0.24Se阱层的限制纵光学声子模(LO)的喇曼散射,并对上述不同的光学模的起因进行了分析。 相似文献
50.
Andrew Vince 《Graphs and Combinatorics》1993,9(1):75-84
A short graph theoretic proof of the classification of closed surfaces is given. The new proof has the feature that the symmetric canonical graphs for the surfaces do not correspond to the canonical polygons in the usual proof of the classification. 相似文献