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   1984篇
  免费   79篇
  国内免费   7篇
化学   1505篇
晶体学   41篇
力学   11篇
综合类   1篇
数学   109篇
物理学   403篇
  2023年   11篇
  2022年   19篇
  2021年   24篇
  2020年   30篇
  2019年   32篇
  2018年   23篇
  2017年   11篇
  2016年   47篇
  2015年   48篇
  2014年   58篇
  2013年   118篇
  2012年   99篇
  2011年   120篇
  2010年   58篇
  2009年   69篇
  2008年   78篇
  2007年   94篇
  2006年   99篇
  2005年   89篇
  2004年   73篇
  2003年   74篇
  2002年   56篇
  2001年   49篇
  2000年   54篇
  1999年   32篇
  1998年   18篇
  1997年   20篇
  1996年   37篇
  1995年   29篇
  1994年   18篇
  1993年   17篇
  1992年   35篇
  1991年   25篇
  1990年   26篇
  1989年   21篇
  1988年   37篇
  1987年   19篇
  1986年   20篇
  1985年   26篇
  1984年   20篇
  1983年   21篇
  1982年   18篇
  1981年   25篇
  1980年   17篇
  1979年   30篇
  1978年   16篇
  1977年   13篇
  1975年   11篇
  1974年   11篇
  1973年   21篇
排序方式: 共有2070条查询结果,搜索用时 0 毫秒
91.
π‐Stacked polymers, which consist of layered π‐electron systems in a polymer, can be expected to be used in molecular electronic devices. However, the construction of a stable π‐stacked structure in a polymer is considerably challenging because it requires sophisticated designs and precise synthetic methods. Herein, we present a novel π‐stacked architecture based on poly(quinolylene‐2,3‐methylene) bearing alanine derivatives as the side chain, obtained through the living cyclo‐copolymerization of an o‐allenylaryl isocyanide. In the resulting polymer, the neighboring quinoline rings of the main chain form a layered structure with π–π interactions, which is stabilized by intramolecular hydrogen bonds. The vicinal quinoline units form two independent helices and the whole molecule is a twisted‐tape structure. This structure is established on the basis of UV/CD spectra, theoretical calculations, and atomic‐force microscopy.  相似文献   
92.
93.
Transport in Porous Media - A concise and accurate prediction method is required for membrane permeability in chemical engineering and biological fields. As a preliminary study on this topic, we...  相似文献   
94.
Objective: This study aimed to clarify the effects of pre- and postoperative physical function on the 6-minute walking distance (6MWD) in patients with peripheral arterial disease (PAD). Method: Forty-two elderly patients with PAD who were hospitalized for revascularization and able to walk independently were included in the study. The 6MWD, ankle brachial index (ABI), weight-bearing index (WBI), gait, and intermittent claudication distance (ICD) were measured before and after the surgery, and skeletal muscle index was measured only before surgery. Analyses were performed by comparing the pre- and postoperative values of each factor using a paired t-test. In addition, multiple regression analysis was performed with 6MWD as the dependent variable before and after surgery. Results: Postoperatively, pain disappeared in 22 patients, and ABI, ICD, 6MWD, and stride length improved significantly. ICD and stride length were extracted as factors related to 6MWD before and after surgery, and ABI, WBI, and stride length were extracted as factors related to 6MWD after surgery. Conclusion: The improvement of intermittent claudication associated with revascularization suggests a stronger influence of functional aspects on postoperative 6MWD.  相似文献   
95.
Recently, there has been a strong demand for technologies that use hydrogen as an energy carrier, instead of fossil fuels. Hence, new and effective hydrogen storage technologies are attracting increasing attention. Formic acid (FA) is considered an effective liquid chemical for hydrogen storage because it is easier to handle than solid or gaseous materials. This review presents recent advances in research into the development of homogeneous catalysts, primarily focusing on hydrogen generation by FA dehydrogenation. Notably, this review will aid in the development of useful catalysts, thereby accelerating the transition to a hydrogen-based society.  相似文献   
96.
97.
98.
99.
In this paper, we investigate a delayed HIV infection model that considers the homeostatic proliferation of CD4+ T cells. The existence and stability of uninfected equilibrium and infected equilibria(smaller and larger ones) are studied by analyzing the characteristic equation of the system. The intracellular delay does not affect the stability of uninfected equilibrium, but it can change the stability of larger positive equilibrium and Hopf bifurcation appears inducing stable limit c...  相似文献   
100.
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