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   451547篇
  免费   5009篇
  国内免费   1887篇
化学   241236篇
晶体学   6709篇
力学   20280篇
综合类   68篇
数学   53825篇
物理学   136325篇
  2020年   3524篇
  2019年   3793篇
  2018年   5782篇
  2017年   5903篇
  2016年   7745篇
  2015年   4855篇
  2014年   7275篇
  2013年   18181篇
  2012年   14860篇
  2011年   17771篇
  2010年   12592篇
  2009年   12340篇
  2008年   16397篇
  2007年   16675篇
  2006年   15603篇
  2005年   16499篇
  2004年   15103篇
  2003年   12778篇
  2002年   11503篇
  2001年   12512篇
  2000年   9670篇
  1999年   7249篇
  1998年   6258篇
  1997年   6253篇
  1996年   5981篇
  1995年   5422篇
  1994年   5637篇
  1993年   5215篇
  1992年   5890篇
  1991年   5885篇
  1990年   5659篇
  1989年   5517篇
  1988年   5535篇
  1987年   5341篇
  1986年   5206篇
  1985年   6916篇
  1984年   7210篇
  1983年   6054篇
  1982年   6383篇
  1981年   6084篇
  1980年   5912篇
  1979年   6066篇
  1978年   6531篇
  1977年   6456篇
  1976年   6530篇
  1975年   5987篇
  1974年   6187篇
  1973年   6331篇
  1972年   4680篇
  1971年   3846篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Physics of Atomic Nuclei - We have studied the mechanisms influencing production of cumulative pions and protons in the fragmentation of the incident deuterons into cumulative pions and protons...  相似文献   
83.
Journal of Thermal Analysis and Calorimetry - The role of method of synthesis on the size of flakes, dispersion stability and thermophysical properties of aqua based reduced graphene oxide (rGO)...  相似文献   
84.
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   
85.
Journal of Thermal Analysis and Calorimetry - Modeling and computations are performed to study the ND-Co3O4/EG hybrid nanoliquid mixed convective flow past a vertical porous cylinder. The flow...  相似文献   
86.
87.
88.
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   
89.
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   
90.
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