全文获取类型
收费全文 | 8718篇 |
免费 | 1093篇 |
国内免费 | 569篇 |
专业分类
化学 | 6312篇 |
晶体学 | 45篇 |
力学 | 389篇 |
综合类 | 32篇 |
数学 | 1026篇 |
物理学 | 2576篇 |
出版年
2023年 | 165篇 |
2022年 | 134篇 |
2021年 | 281篇 |
2020年 | 326篇 |
2019年 | 285篇 |
2018年 | 252篇 |
2017年 | 202篇 |
2016年 | 342篇 |
2015年 | 317篇 |
2014年 | 412篇 |
2013年 | 559篇 |
2012年 | 747篇 |
2011年 | 777篇 |
2010年 | 487篇 |
2009年 | 444篇 |
2008年 | 584篇 |
2007年 | 512篇 |
2006年 | 480篇 |
2005年 | 404篇 |
2004年 | 316篇 |
2003年 | 250篇 |
2002年 | 222篇 |
2001年 | 162篇 |
2000年 | 154篇 |
1999年 | 156篇 |
1998年 | 134篇 |
1997年 | 114篇 |
1996年 | 144篇 |
1995年 | 114篇 |
1994年 | 86篇 |
1993年 | 75篇 |
1992年 | 79篇 |
1991年 | 60篇 |
1990年 | 91篇 |
1989年 | 62篇 |
1988年 | 43篇 |
1987年 | 38篇 |
1986年 | 30篇 |
1985年 | 37篇 |
1984年 | 28篇 |
1983年 | 30篇 |
1982年 | 29篇 |
1981年 | 25篇 |
1980年 | 22篇 |
1979年 | 27篇 |
1978年 | 20篇 |
1977年 | 21篇 |
1976年 | 17篇 |
1975年 | 17篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
介绍L波段长脉冲相对论速调管放大器研究中,长脉冲强流相对论电子束(IREB)经过输入腔和中间腔间隙后的脉冲缩短问题.分析了造成束流脉冲缩短的主要机理之一是高频系统的角向非均匀模式与电子束相互作用而使得束流扩散形成的,并经过实验参数的调节,减轻了长脉冲IREB的脉冲缩短问题,得到了较强的基波调制电流.从长脉冲加速器引出500 kV,3.5 kA,1.3 μs的电子束,经过输入腔和两个群聚腔的调制后,得到了2.0 kA的基波调制电流,束流脉冲宽度由0.3 μs增加到1 μs,束流脉冲缩短问题得到明显减轻.
关键词:
相对论速调管放大器
脉冲缩短
高功率微波
长脉冲强流相对论电子束 相似文献
72.
Summary Some stability and convergence theorems of the modified Ishikawa iterative sequences with errors for asymptotically nonexpansive
mapping in the intermediate sense and asymptotically pseudo contractive and uniformly Lipschitzian mappings in Banach spaces
are obtained. 相似文献
73.
Hiroshi Aoki Ken Hosoya Tomohisa Norisuye Nobuo Tanaka Daisuke Tokuda Norio Ishizuka Kazuki Nakanishi 《Journal of polymer science. Part A, Polymer chemistry》2006,44(2):949-958
An investigation was made of the gelation of dimethacrylate‐type crosslinking agents in view of an application for separation media. The study mainly centered on a crosslinking agent, glycerol dimethacrylate (GDMA), which is relatively hydrophilic because of a hydroxyl group in the middle of its structure. The gelation of GDMA was compared with that of other hydrophobic crosslinking agents such as ethylene glycol dimethacrylate and 1,6‐hexanediol dimethacrylate. The diluents used in the study were toluene, toluene with methanol, and cyclohexanol. The gelation was observed in real time with a charge coupled device camera and dynamic light scattering (DLS). Also, the separated dry gels were extensively characterized with scanning electron microscopy, BET (N2 absorption and desorption isotherm), and Fourier transform infrared. DLS analysis showed a stronger molecular interaction of GDMA gelation in toluene, whereas this interaction was much weaker in an alcoholic solvent such as toluene with methanol or cyclohexanol. This indicated that GDMA gelation might proceed through hydrogen bonding as well as a crosslinking reaction of vinyl groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 949–958, 2006 相似文献
74.
Yan Yin Otoo Yamada Shunsuke Hayashi Kazuhiro Tanaka Hidetoshi Kita Ken‐Ichi Okamoto 《Journal of polymer science. Part A, Polymer chemistry》2006,44(12):3751-3762
A series of branched/crosslinked sulfonated polyimide (B/C‐SPI) membranes were prepared and evaluated as proton‐conducting ionomers based on the new concept of in situ crosslinking from sulfonated polyimide (SPI) oligomers and triamine monomers. Chemical branching and crosslinking in SPI oligomers with 1,3,5‐tris(4‐aminophenoxy)benzene as a crosslinker gave the polymer membranes very good water stability and mechanical properties under an accelerated aging treatment in water at 130 °C, despite their high ion‐exchange capacity (2.2–2.6 mequiv g?1). The resulting polymer electrolytes displayed high proton conductivities of 0.2–0.3 S cm?1 at 120 °C in water and reasonably high conductivities of 0.02–0.03 S cm?1 at 50% relative humidity. In a single H2/O2 fuel‐cell system at 90 °C, they exhibited high fuel‐cell performances comparable to those of Nafion 112. The B/C‐SPI membranes also displayed good performances in a direct methanol fuel cell with methanol concentrations as high as 50 wt % that were superior to those of Nafion 112. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3751–3762, 2006 相似文献
75.
Ken‐ichi Shinohara Tasuku Suzuki Takeshi Kitami Shingo Yamaguchi 《Journal of polymer science. Part A, Polymer chemistry》2006,44(2):801-809
We fabricated a micrometer‐long supramolecular chain in which π‐conjugated polyrotaxane was coupled. A new experimental setup was designed and constructed, and the simultaneous direct imaging of the structure and fluorescent function was achieved. Furthermore, we identified the formation of a polymer intertwined network and observed novel fluorescence due to a long‐range interaction via this intertwined network over a distance of 5 μm or more without quenching over 15 min in the near field. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 801–809, 2006 相似文献
76.
77.
78.
Abachi S Derrick M Kooijman P Musgrave B Price LE Repond J Sugano K Blockus D Brabson B Brom J Jung C Ogren H Rust DR Akerlof C Chapman J Errede D Ken MT Meyer DI Neal H Nitz D Thun R Tschirhart R Baringer P Bylsma BG DeBonte R Koltick D Low EH McIlwain RL Miller DH Ng CR Shibata EI 《Physical review D: Particles and fields》1989,40(3):902-905
79.
80.