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   1387篇
  免费   26篇
  国内免费   5篇
化学   984篇
晶体学   11篇
力学   16篇
数学   54篇
物理学   353篇
  2023年   7篇
  2022年   10篇
  2021年   15篇
  2020年   11篇
  2019年   23篇
  2017年   11篇
  2016年   15篇
  2015年   12篇
  2014年   22篇
  2013年   85篇
  2012年   40篇
  2011年   54篇
  2010年   28篇
  2009年   39篇
  2008年   67篇
  2007年   63篇
  2006年   56篇
  2005年   49篇
  2004年   50篇
  2003年   66篇
  2002年   51篇
  2001年   34篇
  2000年   46篇
  1999年   31篇
  1998年   21篇
  1997年   21篇
  1996年   16篇
  1995年   10篇
  1994年   21篇
  1993年   15篇
  1992年   42篇
  1991年   20篇
  1990年   19篇
  1989年   21篇
  1988年   25篇
  1987年   26篇
  1986年   18篇
  1985年   29篇
  1984年   22篇
  1983年   13篇
  1982年   13篇
  1981年   19篇
  1980年   14篇
  1979年   28篇
  1978年   22篇
  1977年   13篇
  1976年   11篇
  1975年   12篇
  1974年   13篇
  1973年   20篇
排序方式: 共有1418条查询结果,搜索用时 15 毫秒
871.
We consider a heat semigroup with an inverse square potential and prove critical dissipative estimates including the endpoint case. Some application to a nonlinear heat equation with an inverse square potential is also discussed.  相似文献   
872.
873.
We consider the regularity problem under the critical condition to the biharmonic map heat flow from ?4 to a smooth compact Riemannian manifold without boundary. Using Gagliardo‐Nirenberg inequalities and delicate estimates, the Serrin type regularity criterion for the smooth solutions of biharmonic map heat flow is obtained without assuming a smallness condition on the initial energy. Our result improved the results of Lamm in 5 and 6 and generalized the results of Chang, Wang, Yang 1 , Strzelecki 11 and Wang 13 , 14 to non‐stationary case.  相似文献   
874.
Carbohydrate-mediated interactions are involved in various biological processes via specific molecular assembly and recognition. Such interactions are enhanced by multivalent effects of the sugar moieties, and thus supramolecular sugar-assembly, i.e., spontaneous association of glycoamphiphiles, is a promising approach to tailor glycocluster formation. In this study, novel sugar-decorated nanofibers were successfully prepared by self-assembly of low molecular weight hydrogelators composed of azobenzene and disaccharide lactones. Circular dichroism measurement of the as-prepared hydrogels indicated that the azobenzene amphiphile containing a lactose moiety possessed (R)-chirality, while the maltose-azobenzene conjugate exhibited (S)-chirality, even though the cellobiose-conjugated azobenzene existed in an achiral form. This suggests that the chiral orientation of the chromophoric azobenzene depended on both the glycosidic linkages and the steric arrangement of hydroxyl groups in the conjugated carbohydrates. Lectin-binding and cell adhesion assays revealed that the nonreducing ends of the conjugated sugar moieties were exposed on the surfaces of self-assembled nanofibrous hydrogels, allowing them to be effectively recognized by the corresponding lectins. In addition, photoisomerization of azobenzene under ultraviolet irradiation induced the sol-gel transitions of the hydrogels. These results demonstrate that the reversibly transformed fibrous glycohydrogels show potential for application as carbohydrate-decorated scaffolds for cell culture engineering.  相似文献   
875.
Lipid‐membrane‐incorporating C60 and C70 (LMIC60 and LMIC70) were prepared by the fullerene‐exchange reaction from the γ‐cyclodextrin cavity to vesicles (we call this method the “exchange method”). An advantage of this method is that the ratios of [C60]/[lipids] and [C70]/[lipids] can be arbitrarily controlled by adjusting the ratios of the fullerenes and liposome. The maximum ratio (30 mol %) obtained was approximately 14 and 100 times higher than those achieved for LMIC60 and LMIC70, respectively, that were prepared by the classical method, which we call the “premixing method” (dissolving lipids and C60 or C70 in chloroform, followed by concentration and extraction with water). Furthermore, the stabilities and photodynamic activities of the LMIC60 and LMIC70 solutions prepared by the exchange method were shown to be much higher than those prepared by the premixing method. That is, the exchange method was found to be superior to the premixing method as a preparative method of LMIC60 and LMIC70 for applications in photomedical and photomaterials chemistry.  相似文献   
876.
877.
Based on Fourier's law for heat conduction, we investigate the asymmetric heat flow in two segment rods of nonmetallic materials. Specifically, we study the effect of the Kapitza resistance at the boundary of the segments on the thermal rectification. To understand basic features of the rectification, we first develop analytical calculation for the heat currents in an ideal rod of a macroscopic length. Explicitly, this is made by assuming that the thermal conductivity of each constituent has a power-law dependence on temperature and also assuming the continuity of temperature at the boundary. Then, we introduce the temperature jump at the boundary due to the Kapitza resistance and show that this effect on the thermal rectification becomes significant as the length of the rod decreases typically to submillimeters. In particular, we find that the temperature jump yields a finite rectification even when no asymmetry is predicted in the heat currents from the continuity of temperature at the junction. The obtained results have an important implication for the analysis of the thermal rectification of a rod consisting of semiconductors Ge and Si.  相似文献   
878.
Arterial spin labeling (ASL) is a noninvasive technique that can measure cerebral blood flow (CBF). To our knowledge, there is no study that examined regional CBF of multiple sclerosis (MS) patients by using this technique. The present study assessed the relationship between clinical presentations and functional imaging data in MS using pseudocontinuous arterial spin labeling (pCASL). Twenty-seven patients with MS and 24 healthy volunteers underwent magnetic resonance imaging and pCASL to assess CBF. Differences in CBF between the two groups and the relationships of CBF values with the T2-hyperintense volume were evaluated. Compared to the healthy volunteers, reduced CBF was found in the bilateral thalami and right frontal region of the MS patients. The volume of the T2-hyperintense lesion was negatively correlated with regional CBF in some areas, such as both thalami. Our results suggest that demyelinated lesions in MS mainly have a remote effect on the thalamus and that the measurement of CBF using ASL could be an objective marker for monitoring disease activity in MS.  相似文献   
879.
Abstract

Stopping powers of Al, Ti, Cu, Zr, Rh, Ag, Ta and Au for 26 MeV alpha particles have been measured using a surface barrier silicon detector with an accuracy of 0.35%. The stopping powers for alpha particles divided by 4 have been compared with the stopping powers for 6.500 MeV protons of the same velocity. Experimental magnitudes of the Z 3 1 correction which is contained in the Bethe-Bloch stopping formula were extracted using the alpha-proton difference. Using the experimental Z 3 1 corrections thus obtained and the experimental Z 3 1 corrections of the previous paper, parameters of γ and b which appear in the theory of Ashley, Ritchie and Brandt for the Z 3 1 correction have been determined with exactly the same method as the previous paper as γ = 1.336 and b = 1.32. The magnitude of the Z 3 1 correction calculated by the theory of Ashley, Ritchie and Brandt using these parameters have been compared with those obtained by other authors.  相似文献   
880.
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