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   85766篇
  免费   687篇
  国内免费   378篇
化学   30303篇
晶体学   833篇
力学   6851篇
数学   32949篇
物理学   15895篇
  2023年   76篇
  2022年   53篇
  2021年   76篇
  2020年   136篇
  2019年   160篇
  2018年   10514篇
  2017年   10354篇
  2016年   6347篇
  2015年   1136篇
  2014年   615篇
  2013年   903篇
  2012年   4435篇
  2011年   11143篇
  2010年   5992篇
  2009年   6309篇
  2008年   7186篇
  2007年   9295篇
  2006年   729篇
  2005年   1806篇
  2004年   1933篇
  2003年   2287篇
  2002年   1288篇
  2001年   307篇
  2000年   347篇
  1999年   216篇
  1998年   236篇
  1997年   197篇
  1996年   265篇
  1995年   155篇
  1994年   104篇
  1993年   127篇
  1992年   80篇
  1991年   91篇
  1990年   76篇
  1989年   85篇
  1988年   79篇
  1987年   80篇
  1986年   92篇
  1985年   87篇
  1984年   83篇
  1983年   61篇
  1982年   71篇
  1981年   72篇
  1980年   62篇
  1979年   58篇
  1978年   42篇
  1914年   45篇
  1913年   41篇
  1909年   43篇
  1908年   41篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007  相似文献   
5.
The mechanisms involved in the formation of n‐butanol during the synthesis of butyl acrylate containing latices were investigated. The experimental results showed that neither the hydrolysis of butyl acrylate nor of the ester bond in the butyl acrylate segments of the polymer played a major role in the formation of n‐butanol, which was mainly generated from the polymer backbone, by transfer reactions to polymer chain followed by cyclization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5838–5846, 2007  相似文献   
6.
7.
8.
Structural hierarchy of rock masses and the mechanisms of its formation   总被引:1,自引:0,他引:1  
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed.  相似文献   
9.
Nicholas Nathan tries to resist the current version of the causal argument for sense-data in two ways. First he suggests that, on what he considers to be the correct re-construction of the argument, it equivocates on the sense of proximate cause. Second he defends a form of disjunctivism, by claiming that there might be an extra mechanism involved in producing veridical hallucination, that is not present in perception. I argue that Nathan’s reconstruction of the argument is not the appropriate one, and that, properly interpreted, the argument does not equivocate on proximate cause. Furthermore, I claim that his postulation of a modified mechanism for hallucinations is implausibly ad hoc.  相似文献   
10.
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