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   714553篇
  免费   22806篇
  国内免费   2610篇
化学   398828篇
晶体学   9604篇
力学   34125篇
综合类   78篇
数学   92933篇
物理学   204401篇
  2021年   8209篇
  2020年   10567篇
  2019年   9379篇
  2018年   11906篇
  2017年   10497篇
  2016年   18806篇
  2015年   12805篇
  2014年   17092篇
  2013年   34476篇
  2012年   26824篇
  2011年   29643篇
  2010年   23949篇
  2009年   23579篇
  2008年   27850篇
  2007年   27530篇
  2006年   24791篇
  2005年   22239篇
  2004年   20330篇
  2003年   18094篇
  2002年   17925篇
  2001年   18881篇
  2000年   14622篇
  1999年   11250篇
  1998年   9655篇
  1997年   9530篇
  1996年   9075篇
  1995年   8185篇
  1994年   8205篇
  1993年   7996篇
  1992年   8429篇
  1991年   8780篇
  1990年   8334篇
  1989年   8220篇
  1988年   8026篇
  1987年   7732篇
  1986年   7484篇
  1985年   9702篇
  1984年   10069篇
  1983年   8458篇
  1982年   8902篇
  1981年   8358篇
  1980年   7965篇
  1979年   8475篇
  1978年   8851篇
  1977年   8861篇
  1976年   8887篇
  1975年   8524篇
  1974年   8437篇
  1973年   8606篇
  1972年   6500篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
Mathematical Notes - Subspaces of the space of analytic functions on a convex domain in the complex plane that are invariant with respect to the differentiation operator are studied. The problem of...  相似文献   
42.
In the periodic table the position of each atom follows the ‘aufbau’ principle of the individual electron shells. The resulting intrinsic periodicity of atomic properties determines the overall behavior of atoms in two-dimensional (2D) bonding and structure formation. Insight into the type and strength of bonding is the key in the discovery of innovative 2D materials. The primary features of 2D bonding and the ensuing monolayer structures of the main-group II–VI elements result from the number of valence electrons and the change of atom size, which determine the type of hybridization. The results reveal the tight connection between strength of bonding and bond length in 2D networks. The predictive power of the periodic table reveals general rules of bonding, the bonding-structure relationship, and allows an assessment of published data of 2D materials.  相似文献   
43.
The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well.  相似文献   
44.
The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF3). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF3, by cyanostar macrocycles that are size-complementary to the inorganic BF4 progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R−BF3 anions.  相似文献   
45.
Russian Physics Journal - The temperature dependences of the linear dielectric permittivity ε′ and the third harmonic coefficient γ3ω for nanocomposites obtained by embedding a...  相似文献   
46.
Central European Journal of Operations Research - Sustainability practice within supply chains remains in an early development phase. Enterprises still need tools that support the integration of...  相似文献   
47.
Nonlinear Dynamics - Given a data-set of Ribonucleic acid (RNA) sequences we can infer the phylogenetics of the samples and tackle the information for scientific purposes. Based on current data and...  相似文献   
48.

We show that near periodic rivet chains that connect two Kirchhoff plates and are modeled by point Sobolev transmission conditions, Rayleigh waves arise, propagate along the chains, and decay exponentially in the orthogonal direction. Under additional geometric conditions we discover the standing (periodic) waves that carry no energy.

  相似文献   
49.
Osipov  A. A. 《JETP Letters》2021,113(6):413-417
JETP Letters - The result of removing heavy particles with different mass from the theory spectrum can be described at low energy by the effective action, which is an asymptotic series in inverse...  相似文献   
50.
Optics and Spectroscopy - The current–voltage characteristics and photocurrent of “monolithic” diode optical pairs optically coupled by a substrate made of InAs common for them...  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