首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   346177篇
  免费   20556篇
  国内免费   11403篇
化学   204704篇
晶体学   4792篇
力学   16734篇
综合类   595篇
数学   39177篇
物理学   112134篇
  2022年   4110篇
  2021年   5318篇
  2020年   6093篇
  2019年   6132篇
  2018年   6200篇
  2017年   5966篇
  2016年   9083篇
  2015年   7345篇
  2014年   9680篇
  2013年   17403篇
  2012年   17552篇
  2011年   19947篇
  2010年   13695篇
  2009年   13264篇
  2008年   16064篇
  2007年   15664篇
  2006年   14502篇
  2005年   12859篇
  2004年   10846篇
  2003年   9249篇
  2002年   8948篇
  2001年   9411篇
  2000年   7370篇
  1999年   6218篇
  1998年   5259篇
  1997年   5100篇
  1996年   5239篇
  1995年   4449篇
  1994年   4476篇
  1993年   4034篇
  1992年   4233篇
  1991年   4201篇
  1990年   3821篇
  1989年   3488篇
  1988年   3379篇
  1987年   3207篇
  1986年   3190篇
  1985年   3964篇
  1984年   3990篇
  1983年   3220篇
  1982年   3491篇
  1981年   3220篇
  1980年   2931篇
  1979年   3153篇
  1978年   3340篇
  1977年   3401篇
  1976年   3423篇
  1975年   3102篇
  1974年   3216篇
  1973年   3259篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
Journal of Solid State Electrochemistry - The “shuttle effect” of polysulfides is a serious issue, resulting in a decrease in the life-cycle of lithium-sulfur (Li-S) batteries. To...  相似文献   
93.
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers...  相似文献   
94.
Russian Journal of Organic Chemistry - A green protocol has been developed for the preparation of 2,2′-(arylmethylene)bis(3-hydroxy-5,5-dimethylcyclohex-2-en-1-ones) following the...  相似文献   
95.
96.
97.
98.
Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters.  相似文献   
99.
Human skin is exposed to visible light (VL; 400–700 nm) and long-wavelength ultraviolet A1 (UVA1) radiation (370–400 nm) after the application of organic broad-spectrum sunscreens. The biologic effects of these wavelengths have been demonstrated; however, a dose–response has not been investigated. Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated with 2 light sources (80–480 J cm−2): one comprising VL with less than 0.5% UVA1 (VL+UVA1) and the other pure VL. Skin responses were evaluated for 2 weeks using clinical and spectroscopic assessments. 4-mm punch biopsies were obtained from nonirradiated skin and sites irradiated with 480 J cm−2 of VL+UVA1 and pure VL 24 h after irradiation. Clinical and spectroscopic assessments demonstrated a robust response at VL+UVA1 sites compared with pure VL. Histology findings demonstrated a statistically significant increase in the marker of inflammation (P < 0.05) and proliferation (P < 0.05) at the irradiated sites compared with nonirradiated control. Threshold doses of VL+UVA1 resulting in biologic responses were calculated. Results indicate that approximately 2 h of sun exposure, which equates to VL+UVA1 dose (~400 J cm−2), is capable of inducing inflammation, immediate erythema and delayed tanning. These findings reinforce the need of photoprotection beyond the UV range.  相似文献   
100.
We investigate terahertz radiation(T-rays) from a pentacene organic diode at room temperature. The quantum chemistry calculation for frequency-related Huang–Rhys factor of pentacene is also carried out. The results demonstrate that the T-rays can come from a bending vibration of pentacene skeleton after the energy of pentacene exciton transferring to the vibrational excited state via electron–phonon coupling. Frequency and natural bond orbital analytics of pentacene and its derivatives are performed in order to explain the result and develop new materials to get higher emission. This work provides a new way to produce T-rays with a simple device at room temperature.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号