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   78185篇
  免费   6438篇
  国内免费   4927篇
化学   23335篇
晶体学   1807篇
力学   3500篇
综合类   313篇
数学   17461篇
物理学   43134篇
  2023年   150篇
  2021年   299篇
  2020年   609篇
  2019年   909篇
  2018年   865篇
  2017年   564篇
  2016年   413篇
  2015年   386篇
  2014年   1022篇
  2013年   1564篇
  2012年   1113篇
  2011年   1659篇
  2010年   2260篇
  2009年   6766篇
  2008年   7823篇
  2007年   6291篇
  2006年   5746篇
  2005年   3904篇
  2004年   3729篇
  2003年   3944篇
  2002年   4685篇
  2001年   3653篇
  2000年   3466篇
  1999年   3296篇
  1998年   2721篇
  1997年   1891篇
  1996年   1706篇
  1995年   2191篇
  1994年   2129篇
  1993年   1588篇
  1992年   1098篇
  1991年   826篇
  1990年   674篇
  1989年   599篇
  1988年   562篇
  1987年   401篇
  1986年   190篇
  1985年   941篇
  1984年   616篇
  1983年   488篇
  1982年   638篇
  1981年   792篇
  1980年   719篇
  1979年   558篇
  1978年   581篇
  1977年   538篇
  1976年   540篇
  1975年   317篇
  1974年   354篇
  1973年   462篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
51.
In 1994, I. Kan constructed a smooth map on the annulus admitting two physical measures, whose basins are intermingled. In this paper, we prove that Kan's map is C2 robustly topologically mixing.  相似文献   
52.
In this work we obtain positive singular solutions of
{?Δu(y)=u(y)p in yΩt,u=0 on y?Ωt,
where Ωt is a sufficiently small C2,α perturbation of the cone Ω:={xRN:x=rθ,r>0,θS} where S?SN?1 has a smooth nonempty boundary and where p>1 satisfies suitable conditions. By singular solution we mean the solution is singular at the ‘vertex of the perturbed cone’. We also consider some other perturbations of the equation on the unperturbed cone Ω and here we use a different class of function spaces.  相似文献   
53.
54.
Motivated by recent progress in dynamical sampling we prove that every frame which is norm-bounded below can be represented as a finite union of sequences {(Tj)nφj}n=0,j=1,,J for some bounded operators Tj and elements φj in the underlying Hilbert space. The result is optimal, in the sense that it turns out to be problematic to replace the collection of generators φ1,,φJ by a singleton: indeed, for linearly independent frames we prove that we can represent the frame in terms of just one system {Tnφ}n=0, but unfortunately this representation often forces the operator T to be unbounded. Several examples illustrate the connection of the results to typical frames like Gabor frames and wavelet frames, as well as generic constructions in arbitrary separable Hilbert spaces.  相似文献   
55.
56.
57.
In recent years, the fingerprint of high‐performance liquid chromatography has been extensively applied in the identification and quality control of traditional Chinese medicine. It can be a potential protocol for assessing the authenticity, stability and consistency of traditional Chinese medicine and guaranteeing the expected biological activity. In this paper, a method using high‐performance liquid chromatography to identify and control the quality of the extract of Taraxacum mongolicum Hand.‐Mazz. (TME) was established. With this method, the correlation coefficients of the similarity of 10 batches were ≥0.994. The TME displayed a steady proliferative effect in Lactobacillus plantarum. In brief, this study successfully built a reliable, simple and efficient method to control and confirm the quality and the stability of biological activity of the TME.  相似文献   
58.
In this paper we present a-posteriori KAM results for existence of d-dimensional isotropic invariant tori for n-DOF Hamiltonian systems with additional n?d independent first integrals in involution. We carry out a covariant formulation that does not require the use of action-angle variables nor symplectic reduction techniques. The main advantage is that we overcome the curse of dimensionality avoiding the practical shortcomings produced by the use of reduced coordinates, which may cause difficulties and underperformance when quantifying the hypotheses of the KAM theorem in such reduced coordinates. The results include ordinary and (generalized) iso-energetic KAM theorems. The approach is suitable to perform numerical computations and computer assisted proofs.  相似文献   
59.
60.
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