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   228246篇
  免费   4699篇
  国内免费   2334篇
化学   120424篇
晶体学   3554篇
力学   9109篇
综合类   72篇
数学   20912篇
物理学   67096篇
综合类   14112篇
  2020年   1872篇
  2018年   1959篇
  2016年   3146篇
  2015年   2619篇
  2014年   3531篇
  2013年   9387篇
  2012年   7148篇
  2011年   8597篇
  2010年   5787篇
  2009年   5719篇
  2008年   7642篇
  2007年   7704篇
  2006年   7315篇
  2005年   6722篇
  2004年   6036篇
  2003年   5377篇
  2002年   5252篇
  2001年   6911篇
  2000年   5410篇
  1999年   4416篇
  1998年   3256篇
  1997年   3234篇
  1996年   3187篇
  1995年   2947篇
  1994年   3016篇
  1993年   2609篇
  1992年   3210篇
  1991年   3052篇
  1990年   3045篇
  1989年   2976篇
  1988年   2897篇
  1987年   2876篇
  1986年   2647篇
  1985年   3487篇
  1984年   3451篇
  1983年   2865篇
  1982年   3011篇
  1981年   2947篇
  1980年   2852篇
  1979年   3095篇
  1978年   3311篇
  1977年   3117篇
  1976年   3022篇
  1975年   2907篇
  1974年   2945篇
  1973年   2820篇
  1972年   1852篇
  1968年   2162篇
  1967年   2385篇
  1966年   2174篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
42.
43.
For the orthosymplectic Lie superalgebra ◂⋅▸OSP(2,2), we choose a set of basis matrices. A linear combination of those basis matrices presents a spatial spectral matrix. The compatible condition of the spatial part and the corresponding temporal parts of the spectral problem leads to a generalized super AKNS (GSAKNS) hierarchy. By making use of the supertrace identity, the obtained GSAKNS hierarchy can be written as the super bi-Hamiltonian structures.  相似文献   
44.
45.

In this paper, we study the Cauchy problem for the Benjamin-Ono-Burgers equation \({\partial _t}u - \epsilon \partial _x^2u + {\cal H}\partial _x^2u + u{u_x} = 0\), where \({\cal H}\) denotes the Hilbert transform operator. We obtain that it is uniformly locally well-posed for small data in the refined Sobolev space \({\tilde H^\sigma }(\mathbb{R})\,\,(\sigma \geqslant 0)\), which is a subspace of L2(ℝ). It is worth noting that the low-frequency part of \({\tilde H^\sigma }(\mathbb{R})\) is scaling critical, and thus the small data is necessary. The high-frequency part of \({\tilde H^\sigma }(\mathbb{R})\) is equal to the Sobolev space Hσ (ℝ) (σ ⩾ 0) and reduces to L2(ℝ). Furthermore, we also obtain its inviscid limit behavior in \({\tilde H^\sigma }(\mathbb{R})\) (σ ⩾ 0).

  相似文献   
46.
Given an n ‐vertex pseudorandom graph G and an n ‐vertex graph H with maximum degree at most two, we wish to find a copy of H in G , that is, an embedding φ : V ( H ) V ( G ) so that φ ( u ) φ ( v ) E ( G ) for all u v E ( H ) . Particular instances of this problem include finding a triangle‐factor and finding a Hamilton cycle in G . Here, we provide a deterministic polynomial time algorithm that finds a given H in any suitably pseudorandom graph G . The pseudorandom graphs we consider are ( p , λ ) ‐bijumbled graphs of minimum degree which is a constant proportion of the average degree, that is, Ω ( p n ) . A ( p , λ ) ‐bijumbled graph is characterised through the discrepancy property: | e ( A , B ) ? p | A | | B | | < λ | A | | B | for any two sets of vertices A and B . Our condition λ = O ( p 2 n / log n ) on bijumbledness is within a log factor from being tight and provides a positive answer to a recent question of Nenadov. We combine novel variants of the absorption‐reservoir method, a powerful tool from extremal graph theory and random graphs. Our approach builds on our previous work, incorporating the work of Nenadov, together with additional ideas and simplifications.  相似文献   
47.
Exosomes are nanovesicles secreted by most cellular types that carry important biochemical compounds throughout the body with different purposes, playing a preponderant role in cellular communication. Because of their structure, physicochemical properties and stability, recent studies are focusing in their use as nanocarriers for different therapeutic compounds for the treatment of different diseases ranging from cancer to Parkinson's disease. However, current bioseparation protocols and methodologies are selected based on the final exosome application or intended use and present both advantages and disadvantages when compared among them. In this context, this review aims to present the most important technologies available for exosome isolation while discussing their advantages and disadvantages and the possibilities of being combined with other strategies. This is critical since the development of novel exosome‐based therapeutic strategies will be constrained to the effectiveness and yield of the selected downstream purification methodologies for which a thorough understanding of the available technological resources is needed.  相似文献   
48.
Ding  Q.  Yao  M.  Wu  Sh.  Zeng  M.  Xue  N.  Wu  D.  Xu  J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the...  相似文献   
49.
Xu  H. J.  Zhang  Q. G.  Debenest  G. 《Transport in Porous Media》2021,140(3):625-627
Transport in Porous Media - The theme of coupling problems for adsorption, absorption and thermochemical transport in porous media is very important for engineering applications. Based on the...  相似文献   
50.
Aliev  A. B.  Shafieva  G. H. 《Differential Equations》2022,58(8):1028-1042
Differential Equations - We study a mixed problem for systems of one-dimensional semilinear hyperbolic equations with variable nonlinearity growth rate and nonlinear boundary conditions. Theorems...  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