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   418670篇
  免费   2364篇
  国内免费   797篇
化学   183372篇
晶体学   6037篇
力学   25735篇
综合类   3篇
数学   78881篇
物理学   127803篇
  2021年   3468篇
  2020年   3788篇
  2019年   4622篇
  2018年   16905篇
  2017年   16860篇
  2016年   14650篇
  2015年   4866篇
  2014年   7929篇
  2013年   14338篇
  2012年   15334篇
  2011年   23664篇
  2010年   16713篇
  2009年   17272篇
  2008年   19425篇
  2007年   21173篇
  2006年   11778篇
  2005年   11217篇
  2004年   11075篇
  2003年   10879篇
  2002年   10155篇
  2001年   9261篇
  2000年   7342篇
  1999年   5437篇
  1998年   5183篇
  1997年   4932篇
  1996年   4489篇
  1995年   3936篇
  1994年   3953篇
  1993年   3975篇
  1992年   4002篇
  1991年   4454篇
  1990年   4359篇
  1989年   4409篇
  1988年   4115篇
  1987年   4127篇
  1986年   3859篇
  1985年   4480篇
  1984年   4791篇
  1983年   4086篇
  1982年   4314篇
  1981年   3939篇
  1980年   3673篇
  1979年   4171篇
  1978年   4349篇
  1977年   4518篇
  1976年   4484篇
  1975年   4227篇
  1974年   4083篇
  1973年   4261篇
  1972年   3563篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.

The problem of the minimax testing of the Poisson process intensity \({\mathbf{s}}\) is considered. For a given intensity \({\mathbf{p}}\) and a set \(\mathcal{Q}\), the minimax testing of the simple hypothesis \(H_{0}: {\mathbf{s}} = {\mathbf{p}}\) against the composite alternative \(H_{1}: {\mathbf{s}} = {\mathbf{q}},\,{\mathbf{q}} \in \mathcal{Q}\) is investigated. The case, when the 1-st kind error probability \(\alpha \) is fixed and we are interested in the minimal possible 2-nd kind error probability \(\beta ({\mathbf{p}},\mathcal{Q})\), is considered. What is the maximal set \(\mathcal{Q}\), which can be replaced by an intensity \({\mathbf{q}} \in \mathcal{Q}\) without any loss of testing performance? In the asymptotic case (\(T\rightarrow \infty \)) that maximal set \(\mathcal{Q}\) is described.

  相似文献   
42.
The biomimetic sol—gel synthesis of silicon—chitosan-containing glycerohydrogels was carried out using silicon tetraglycerolate as a precursor. It was found that chitosan accelerates gel formation in weakly acidic media. In more acidic media, the kinetics of the process changes according to the curve with a maximum, which can be attributed to different mechanisms of silanol condensation before and after the isoelectric point. The investigated silicon—chitosan-containing glycerohydrogels exhibit antibacterial, anti-inflammatory, and wound healing activity. The synthesized hybrid glycerohydrogels are promising materials for biomedical applications.  相似文献   
43.
44.
45.
46.
Davidovich  M. V. 《JETP Letters》2019,109(7):472-477

The elastic moduli of bilayer graphene nanomeshes, i.e., nanomeshes of bilayer graphene, where layers at the edges of “closed” holes are coupled to each other by a continuous network of sp2-hybridized atoms, have been calculated by ab initio methods. Structures with different configurations of holes in layers with AA, AB, and 30° stackings have been studied. It has been shown that the ultimate tensile strength of the nanomeshes under consideration is higher than that of graphene nanostructures and is comparable with the ultimate tensile strength of bilayer graphene and single-layer carbon nanotubes. A possible application of such strong nanomeshes as nanocontainers for hydrogen storage and other compressed gases has been also discussed.

  相似文献   
47.
48.
Optics and Spectroscopy - The transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the...  相似文献   
49.
The accumulated knowledge regarding molecular architectures is based on established, reliable, and accessible analytical tools that provide robust structural and functional information on assemblies. However, both the dynamicity and low population of noncovalently interacting moieties within studied molecular systems limit the efficiency and accuracy of traditional methods. Herein, the use of a saturation transfer-based NMR approach to study the dynamic binding characteristics of an anion to a series of synthetic receptors derived from bambusuril macrocycles is demonstrated. The exchange rates of BF4 are mediated by the side chains on the receptor (100 s−1<kex<5000 s−1), which play a critical role in receptor-anion binding dynamics. The signal amplification obtained with this approach allows for the identification of different types of intermolecular interactions between the receptor and the anion, something that could not have been detected by techniques hitherto used to study molecular assemblies. These findings, which are supported by a computational molecular dynamic study, demonstrate the uniqueness and added value of this NMR method.  相似文献   
50.
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