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   1946篇
  免费   322篇
  国内免费   157篇
化学   1576篇
晶体学   17篇
力学   75篇
综合类   12篇
数学   365篇
物理学   380篇
  2024年   1篇
  2023年   11篇
  2022年   43篇
  2021年   83篇
  2020年   113篇
  2019年   80篇
  2018年   49篇
  2017年   59篇
  2016年   112篇
  2015年   110篇
  2014年   155篇
  2013年   173篇
  2012年   120篇
  2011年   133篇
  2010年   122篇
  2009年   118篇
  2008年   97篇
  2007年   107篇
  2006年   96篇
  2005年   94篇
  2004年   77篇
  2003年   67篇
  2002年   63篇
  2001年   36篇
  2000年   44篇
  1999年   31篇
  1998年   32篇
  1997年   28篇
  1996年   35篇
  1995年   15篇
  1994年   30篇
  1993年   17篇
  1992年   11篇
  1991年   13篇
  1990年   5篇
  1989年   7篇
  1988年   7篇
  1987年   11篇
  1986年   3篇
  1985年   4篇
  1984年   7篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1978年   1篇
  1957年   1篇
排序方式: 共有2425条查询结果,搜索用时 156 毫秒
161.
162.
The influence of low-intensity laser radiation (LLR) on the rheological characteristics of human blood has been investigated. The results of the investigation of the blood velocity in the human skin capillaries, the erythrocyte aggregation time, and the spectral width of scattering intensity fluctuations depending on the irradiation time are presented. It has been shown that laser irradiation leads to a decrease in the degree of aggregation of erythrocytes and, accordingly, to an increase in the velocity of blood microcirculation, which can be used for laser therapy and diagnostics and treatment of cardiovascular diseases (CVD). To explain the results obtained, a method of the LLR–biotissue interaction is proposed.  相似文献   
163.
Kim YH  Song SJ  Kim JY 《Ultrasonics》2004,41(10):799-804
The identification of ultrasonic flaw signals is a difficult task in the angle beam ultrasonic testing of welded joints due to the presence of non-relevant signals from the geometric reflectors such as weld-roots and counter-bores. This paper describes a new approach to identify ultrasonic flaw signals in such a problematic situation. A similarity function is defined as the deconvolution of a target signal by a reference signal. The similarity functions for the same type of flaws/references are symmetric bandlimited impulse-like patterns with larger amplitudes while those for different types of flaws/references are asymmetrical broad patterns with relatively smaller amplitudes. Therefore, ultrasonic signals could be identified by the pattern of the similarity function. In the initial experiments, the proposed technique showed great potential for identifying ultrasonic flaw signals in the inspection of weld joints.  相似文献   
164.
We study the composition operators which are similar to an isometry on the classical Hardy space .

  相似文献   

165.
The goal of this article is to develop a new technique to obtain better asymptotic estimates for scalar conservation laws. General convex flux, f″(u)?0, is considered with an assumption . We show that, under suitable conditions on the initial value, its solution converges to an N-wave in L1 norm with the optimal convergence order of O(1/t). The technique we use in this article is to enclose the solution with two rarefaction waves. We also show a uniform convergence order in the sense of graphs. A numerical example of this phenomenon is included.  相似文献   
166.
This review is devoted to stationary discrete time second order processes whose covariance asymptotically behaves like an hyperbolically damped oscillating sequence. We present the two main ways of generating parametric models of this type. Then we gather some results concerning the influence of seasonality on the classical limit theorems. Finally, we present a simulation method which we use to try a semi parametric estimation procedure adapted from the non seasonal situation.  相似文献   
167.
Autophagy is in principle a non-selective degradation system within cells, which is conserved in all eukaryotic cells. Autophagy is usually suppressed at low levels but can be upregulated during periods of nutrient starvation, which facilitates cell survival. In addition to this fundamental role, basal autophagy was recently revealed to be important for constitutive turnover of intracellular proteins and organelles. Autophagy has been considered to be involved also in presentation of endogenous antigens, degradation of invasive bacteria, tumor suppression, cell death and development. This review will discuss the biological significance of autophagy, particularly focusing on its implications in protein metabolism in mammals.  相似文献   
168.
169.
A series of novel derivatives of 4, 5, 6, 7-tetrahydrothieno [3,2-c] pyridine were synthesized and structurally characterized by 1H NMR and MS. Their in vivo anti-platelet aggregation activities were evaluated. A 3D-QSAR was performed using the CoMFA and the CoMSIA. This model provided useful guidelines for novel anti-platelet thienopyridines design.  相似文献   
170.
For stochastic control problems with mixed state-control constraints, we develop a dynamics aggregation method which replaces the stochastic differential or difference equation with a simpler constraint. Solutions of such simplified problems are used to construct a sequence of approximations to the original problem. Convergence properties of the method for both discrete-time and continuous-time models are analyzed in detail.  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