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   318496篇
  免费   4416篇
  国内免费   1234篇
化学   180310篇
晶体学   5037篇
力学   12630篇
综合类   9篇
数学   34144篇
物理学   92016篇
  2016年   4070篇
  2015年   3157篇
  2014年   4219篇
  2013年   13325篇
  2012年   9508篇
  2011年   11991篇
  2010年   7535篇
  2009年   7219篇
  2008年   10874篇
  2007年   10982篇
  2006年   10705篇
  2005年   10010篇
  2004年   8921篇
  2003年   7995篇
  2002年   7762篇
  2001年   8695篇
  2000年   6719篇
  1999年   5477篇
  1998年   4479篇
  1997年   4528篇
  1996年   4516篇
  1995年   4211篇
  1994年   3876篇
  1993年   3693篇
  1992年   4399篇
  1991年   4196篇
  1990年   4026篇
  1989年   4055篇
  1988年   4062篇
  1987年   4026篇
  1986年   3764篇
  1985年   5197篇
  1984年   5308篇
  1983年   4379篇
  1982年   4849篇
  1981年   4665篇
  1980年   4596篇
  1979年   4706篇
  1978年   5015篇
  1977年   4745篇
  1976年   4714篇
  1975年   4477篇
  1974年   4364篇
  1973年   4557篇
  1972年   2844篇
  1971年   2317篇
  1969年   2197篇
  1968年   2789篇
  1967年   3045篇
  1966年   2607篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
41.
42.
43.
44.
In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase‐separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1231–1237  相似文献   
45.
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   
46.
Journal of Thermal Analysis and Calorimetry - Low productivity of single-slope solar still is the main barrier for its worldwide usability. An attempt has been conducted to enhance the distillate...  相似文献   
47.
48.
The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO2 revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO2 co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion.  相似文献   
49.
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   
50.
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