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   308073篇
  免费   2581篇
  国内免费   1051篇
化学   134417篇
晶体学   3425篇
力学   17529篇
综合类   6篇
数学   67778篇
物理学   88550篇
  2018年   18235篇
  2017年   18889篇
  2016年   10723篇
  2015年   3151篇
  2014年   2321篇
  2013年   6512篇
  2012年   11872篇
  2011年   26528篇
  2010年   15357篇
  2009年   15445篇
  2008年   21188篇
  2007年   26492篇
  2006年   5835篇
  2005年   13541篇
  2004年   9462篇
  2003年   9146篇
  2002年   5791篇
  2001年   4032篇
  2000年   3211篇
  1999年   2298篇
  1998年   2006篇
  1997年   2196篇
  1996年   2243篇
  1995年   2199篇
  1994年   1984篇
  1993年   1935篇
  1992年   2062篇
  1991年   2066篇
  1990年   1959篇
  1989年   1992篇
  1988年   1988篇
  1987年   1935篇
  1986年   1861篇
  1985年   2523篇
  1984年   2686篇
  1983年   2255篇
  1982年   2604篇
  1981年   2384篇
  1980年   2453篇
  1979年   2421篇
  1978年   2562篇
  1977年   2357篇
  1976年   2360篇
  1975年   2267篇
  1974年   2093篇
  1973年   2341篇
  1972年   1420篇
  1971年   1083篇
  1968年   1202篇
  1967年   1185篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Journal of Applied Spectroscopy - With the COVID-19 outbreak, many challenges are posed before the scientific world to curb this pandemic. The diagnostic testing, treatment, and vaccine development...  相似文献   
2.
Faul  Peter F. 《Semigroup Forum》2021,102(3):655-673
Semigroup Forum - It is well known that the set of isomorphism classes of extensions of groups with abelian kernel is characterized by the second cohomology group. In this paper we generalise this...  相似文献   
3.
Jiang  H.  Lei  Z.  Bai  R.  Liu  J.  Guo  Z.  Dong  H.  Feng  W. 《Experimental Mechanics》2021,61(5):867-883
Experimental Mechanics - Ratcheting is an important mechanical behavior of metals and alloys, which is caused by the repeated accumulations of tensile and compressive strain in circle load....  相似文献   
4.
Foundations of Computational Mathematics - We develop some aspects of the homological algebra of persistence modules, in both the one-parameter and multi-parameter settings, considered as either...  相似文献   
5.
Chen  C. Y.  Kao  C. L.  Huang  S. T.  Kuo  C. E.  Song  P. L.  Li  W. J.  Hsu  L. T.  Li  H. T. 《Chemistry of Natural Compounds》2022,58(1):107-109
Chemistry of Natural Compounds -  相似文献   
6.
7.
Chen  R. J.  Chen  W.  Kong  F. L. 《Analysis Mathematica》2022,48(1):19-28

Restricted testing conditions were considered recently. For the maximal operator, Hytönen, Li and Sawyer [8] first obtained parental testing condition. Later, they [9] showed that it suffices to restrict testing to doubling cubes. Chen and Lacey [3] gave a similar restricted testing condition. In our paper, we discuss a version of the latter in the multilinear setting.

  相似文献   
8.
Annals of Operations Research - Selecting a vegetation layer design goes along with determining its future irrigation need. Therefore, it is essential to take a design decision that is minimising...  相似文献   
9.
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   
10.
The new nanocomposites, Pd/C/ZrO2, PdO/ZrO2, and Pd/PdO/ZrO2, were prepared by thermal conversion of Pd@UiO-66-Zr−NH2 (MOF) in nitrogen or air atmosphere. The presence of Pd nanoparticles, uniformly distributed on the ZrO2 or C/ZrO2 matrix, was evidenced by transmission electron microscopy, scanning electron microscopy (SEM), Raman and X-ray Photoelectron Spectroscopy (XPS) methods. All pyrolysed composites retained the shape of the MOF template. They catalyze carbonylative Suzuki coupling under 1 atm CO with an efficiency significantly higher than the original Pd@UiO-66-Zr−NH2. The most active PdO/ZrO2 composite, formed benzophenone with TOF up to 1600 h−1, while by using Pd@UiO-66-Zr−NH2, much lower TOF values, 51–95 h−1, were achieved. After the reaction, PdO/ZrO2 was recovered with the same composition and catalytic activity. Very good results were also obtained in the transfer hydrogenation of benzophenones to alcohols with Pd/C/ZrO2 and PdO/ZrO2 catalysts under microwave irradiation.  相似文献   
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