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   288458篇
  免费   1510篇
  国内免费   449篇
化学   131268篇
晶体学   4480篇
力学   16790篇
综合类   10篇
数学   44851篇
物理学   93018篇
  2020年   2016篇
  2019年   2573篇
  2018年   11121篇
  2017年   11770篇
  2016年   8379篇
  2015年   3035篇
  2014年   4404篇
  2013年   8706篇
  2012年   10652篇
  2011年   18997篇
  2010年   12601篇
  2009年   12959篇
  2008年   16983篇
  2007年   20114篇
  2006年   6889篇
  2005年   11487篇
  2004年   8487篇
  2003年   8259篇
  2002年   6507篇
  2001年   5771篇
  2000年   4476篇
  1999年   3175篇
  1998年   2740篇
  1997年   2778篇
  1996年   2720篇
  1995年   2322篇
  1994年   2421篇
  1993年   2322篇
  1992年   2596篇
  1991年   2726篇
  1990年   2638篇
  1989年   2706篇
  1988年   2625篇
  1987年   2648篇
  1986年   2501篇
  1985年   3132篇
  1984年   3222篇
  1983年   2697篇
  1982年   2659篇
  1981年   2623篇
  1980年   2425篇
  1979年   2822篇
  1978年   2795篇
  1977年   2903篇
  1976年   2936篇
  1975年   2720篇
  1974年   2657篇
  1973年   2809篇
  1972年   2126篇
  1971年   1979篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
Russian Journal of Organic Chemistry - Binder-free iron- and nickel-containing micro-, meso-, and macroporous zeolites FeHY and NiHY were found to effectively catalyze Knoevenagel condensation of...  相似文献   
62.
Russian Journal of General Chemistry - Some new fluoro-heterocyclic compounds containing thiazole and pyridine moities have been synthesized and studied for their antiproliferative activity....  相似文献   
63.
64.
65.
Journal of Applied and Industrial Mathematics - We consider the optimization of the short wave phased antenna arrays as a quadratic programming problem. The penalty function method and the gradient...  相似文献   
66.
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   
67.
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   
68.
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   
69.
70.
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