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   141315篇
  免费   11555篇
  国内免费   7801篇
化学   69889篇
晶体学   1560篇
力学   10377篇
综合类   427篇
数学   38945篇
物理学   39473篇
  2024年   139篇
  2023年   1384篇
  2022年   1796篇
  2021年   2456篇
  2020年   2821篇
  2019年   2706篇
  2018年   12169篇
  2017年   11904篇
  2016年   8991篇
  2015年   3994篇
  2014年   4117篇
  2013年   5202篇
  2012年   9699篇
  2011年   16198篇
  2010年   9645篇
  2009年   9757篇
  2008年   10645篇
  2007年   12358篇
  2006年   3703篇
  2005年   4300篇
  2004年   3758篇
  2003年   3771篇
  2002年   2733篇
  2001年   1609篇
  2000年   1509篇
  1999年   1582篇
  1998年   1366篇
  1997年   1261篇
  1996年   1280篇
  1995年   1097篇
  1994年   896篇
  1993年   794篇
  1992年   625篇
  1991年   581篇
  1990年   524篇
  1989年   400篇
  1988年   309篇
  1987年   272篇
  1986年   270篇
  1985年   243篇
  1984年   159篇
  1983年   159篇
  1982年   124篇
  1981年   96篇
  1980年   85篇
  1979年   64篇
  1978年   42篇
  1973年   42篇
  1914年   45篇
  1909年   42篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
11.
Journal of Radioanalytical and Nuclear Chemistry - The simplified 8-oxide system (SiO2-B2O3-Na2O-Al2O3-CaO-TiO2-MoO3-La2O3) has been prepared under two types of cooling methods, and analyzed with...  相似文献   
12.
Sun  Qinqin  Wang  Xiuye  Yang  Guolai  Chen  Ye-Hwa  Ma  Fai 《Nonlinear dynamics》2022,109(3):1629-1650
Nonlinear Dynamics - This paper proposes an optimal parameter design of control scheme for mechanical systems by adopting the Stackelberg game theory. The goal of the control is to drive the...  相似文献   
13.
Xu  Mengtao  Li  Changyou  Sun  Yang  Yang  Tianzhi  Zhang  Hongzhuang  Liu  Zhendong  Liu  Haiyang  Li  Zhenyuan  Zhang  Yimin 《Nonlinear dynamics》2021,105(4):3061-3092
Nonlinear Dynamics - Investigation of the dynamic characteristics of linear guideway is essential for enhancing structural performance of machine tools. However, few mechanical models are...  相似文献   
14.
Jin  Zhuochen  Cao  Nan  Shi  Yang  Wu  Wenchao  Wu  Yingcai 《显形杂志》2021,24(2):349-364
Journal of Visualization - The increasing availability of spatiotemporal data provides unprecedented opportunities for understanding the structure of an urban area in terms of people’s...  相似文献   
15.
Zhan  Yang  Dang  Chuangyin 《Mathematical Programming》2021,190(1-2):585-613
Mathematical Programming - In the general equilibrium with incomplete asset markets (GEI) model, the excess demand functions are typically not continuous at the prices for which the assets have...  相似文献   
16.
International Journal of Theoretical Physics - The Majorana representation, which provides an intuitive way to represent the quantum state by stars on the Bloch sphere, has drawn considerable...  相似文献   
17.
Acridone as a new kind of visible light photocatalyst has been developed to catalyze metal free atom transfer radical polymerization (ATRP). The photocatalyst possess low excited state potential as can undergo an oxidative quenching pathway to initiate ATRP of vinyl monomers. Kinetic study and light on/off reaction demonstrate the “living”/controlled nature of the polymerization by light. Block copolymers can be achieved by using PMMA as macroinitiator to reinitiate polymerization of other vinyl monomers, which shows highly preserved Br chain-end functionality in the synthesized polymers. Moreover, the polymerization can be conducted under air atmosphere as most photocatalysts need anaerobic condition, which may give inspiration of further application of this kind of photocatalyst.  相似文献   
18.
Atopic dermatitis is characterized by leukocyte migration into the skin dermis and typically driven by excessive chemokine production at the site of inflammation. Conventional topical formulations such as gels, creams, and ointments are insufficient for this treatment because of low penetration of drug molecules into the targeted skin tissues. Herein, using a simple, green, sustainable strategy, we have developed novel primary zein nanoparticles embedded in curcumin (Cur) and coated with silk sericin (ZHSCs) for the topical delivery of Cur to penetrate into the dermis and exercise anti-dermatitis effects on the lesion with minimal side-effects. Transdermal delivery experiments and porcine skin fluorescence imaging indicated that ZHSCs facilitate the penetration of Cur across the epidermis layer of skin to reach deep-seated sites. Notably, ZHSCs = 1:0.25 (zein-to-silk sericin mass ratios of 1:0.25) markedly elevated the skin permeability and cumulative turnover of Cur transferred, which were provided a greater than a 3.8-fold increase relative to free Cur. The special nanoparticles of ZHS = 1:0.25 possessed the deepest localization depth and experience a transition of the particle structure and core-shell separation after penetrating into the dermis of skin. In a cell model of dermatitis induced by tumor necrosis factor α/interferon γ co-stimulation, compared with free Cur, Cur-loaded ZHS nanoparticles down-regulated the generation of inflammatory cytokines and chemokines in keratinocytes through suppression of the nuclear translocation of NF-κBp65 and hence exerted an anti-dermatitis effect. This strategy may provide new avenues and direction for the demanding issues of valid topical delivery systems.  相似文献   
19.
在砂土地层中,串囊式充气锚杆的研究还比较少,其承载特性及受力机理尚不明确。本文基于莫尔-库仑模型和Vesic圆孔扩张理论法,分别对圆柱体、球体、组合体、椭球体假设下的串囊式充气锚杆的扩大段进行计算分析。并将计算结果与试验得到的实测值进行对比。结果表明:四种形状假设中椭球体的形状假设理论值与实测值的误差最小,仅为8.35%。通过拟合试验数据,并引入与端阻力和侧摩阻力有关的两个系数对承载力公式进行修正,得到了抗拔承载力的经验公式。  相似文献   
20.
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