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   6402篇
  免费   1123篇
  国内免费   676篇
化学   4526篇
晶体学   81篇
力学   263篇
综合类   95篇
数学   583篇
物理学   2653篇
  2024年   5篇
  2023年   134篇
  2022年   149篇
  2021年   202篇
  2020年   250篇
  2019年   274篇
  2018年   243篇
  2017年   175篇
  2016年   328篇
  2015年   337篇
  2014年   325篇
  2013年   441篇
  2012年   649篇
  2011年   738篇
  2010年   425篇
  2009年   439篇
  2008年   445篇
  2007年   354篇
  2006年   321篇
  2005年   267篇
  2004年   206篇
  2003年   145篇
  2002年   150篇
  2001年   120篇
  2000年   124篇
  1999年   126篇
  1998年   104篇
  1997年   106篇
  1996年   92篇
  1995年   88篇
  1994年   65篇
  1993年   78篇
  1992年   45篇
  1991年   65篇
  1990年   46篇
  1989年   37篇
  1988年   18篇
  1987年   15篇
  1986年   19篇
  1985年   15篇
  1984年   11篇
  1983年   11篇
  1982年   6篇
  1981年   2篇
  1979年   1篇
  1976年   1篇
  1975年   1篇
  1959年   1篇
  1937年   1篇
  1928年   1篇
排序方式: 共有8201条查询结果,搜索用时 281 毫秒
1.
The European Physical Journal B - Molecular dynamics and Monte Carlo methods are common measurements to study the diffusion coefficients of the fluid particles under restricted conditions. Here,...  相似文献   
2.
Journal of Optimization Theory and Applications - This paper considers an optimal control problem governed by nonlinear fractional-order systems with multiple time-varying delays and subject to...  相似文献   
3.
In this paper, the problem of the uniform stability for a class of fuzzy fractional-order genetic regulatory networks with random discrete delays, distributed delays, and parameter uncertainties is studied. Although there is a portion of literature on using fixed point theorems to study the stability of fractional neural networks, most of them required the fractional order to be in 1 2 , 1 . However, the case of the fractional-order belonging to ( 0 , 1 2 ) has not been discussed. To solve it, this work proposes a novel idea of using fixed point theory to study the stability of fuzzy (0,1) order neural networks, the problem of the uniqueness of the solution of the considered genetic regulatory networks is resolved, and a novel sufficient condition to guarantee the uniform stability of above genetic regulatory networks is also derived. Eventually, an example is given to demonstrate that the obtained result is effective.  相似文献   
4.
We report theoretical studies of electron impact triple differential cross sections of two bio-molecules,pyrimidine and tetrahydrofurfuryl alcohol,in the coplanar asymmetric kinematic conditions with the impact energy of 250 eV and ejected electron energy of 20 eV at three scattering angles of-5°,-10°,and-15°.Present multi-center distorted-wave method well describes the experimental data,which was obtained by performing(e,2e)experiment.The calculations show that the secondary electron produced by the primary impact electron is strongly influenced by the molecular ionic multi-center potential,which must be considered when the low energy electron interacts with DNA analogues.  相似文献   
5.
近年来,机器学习等人工智能技术被应用于蛋白质工程,其在蛋白质结构、功能预测、催化活性等研究中具有独特优势。在未知蛋白质结构的情况下,将蛋白质序列和功能特性与机器学习相结合,基于序列-活性关系(innovative sequence-activity relationship,ISAR)算法,将蛋白质氨基酸序列数字化,用快速傅里叶变换(fast four transform,FFT)进行预处理,再进行偏最小二乘回归建模,可在数据集较少情况下拟合得到最佳模型。通过机器学习对紫色球杆菌视紫红质(gloeobacter violaceus rhodopsin,GR)的突变体蛋白质氨基酸序列与光谱最大吸收波长进行建模,获得了最佳模型。用最佳索引LEVM760106建模得到的确定系数R2 为0.944,均方误差E为11.64。用小波变换进行的预处理,其R2 虽也约为0.944,但E大于11.64,不及FFT进行的预处理。方法较好地解决了蛋白质序列与功能特性之间的数学建模问题,在蛋白质工程中可为预测更优的突变体提供支持。  相似文献   
6.
Zhang  Xia  Dong  Chaoyang  Sun  Yangang  Liu  Binyang  Sun  Lili  Lu  Yongjuan  Yu  Jing  Wei  Yajun  Xu  Yuandong 《Journal of Solid State Electrochemistry》2022,26(2):491-501
Journal of Solid State Electrochemistry - Grapefruit peel carbon (GPC) is prepared from waste grapefruit peel and further used as substrate for in situ construction of MoS2 arrays, forming MoS2/GPC...  相似文献   
7.
Zhou  Lili  Tan  Fei 《Nonlinear dynamics》2019,96(2):869-883
Nonlinear Dynamics - In this paper, we mainly propose a chaotic secure communication scheme which is based on the synchronization of double-layered and multiple complex dynamical networks. Compared...  相似文献   
8.
Han  Jing  Sun  Youhong  Guo  Wei  Deng  Sunhua  Hou  Chuanbin  Qu  Lili  Li  Qiang 《Journal of Thermal Analysis and Calorimetry》2019,135(4):2287-2296
Journal of Thermal Analysis and Calorimetry - In this study, the non-isothermal pyrolysis method was used to investigate the pyrolysis characteristics of oil shale from four areas: namely Nongan,...  相似文献   
9.
The first alkaline-earth metal tin(II) phosphate, BaSn2(PO4)2, has been discovered, which consists of layered structures constructed from strictly alternating [SnO3]4− and [PO4]3− moieties. This compound is expected to have a large birefringence with Δn≈0.071 at 1064 nm, owing to the presence of stereochemically active lone pair metal cations.  相似文献   
10.
Two-dimensional(2D) magnetic materials have been experimentally recognized recently,however,the Curie temperatures(TC) of known 2D systems are quite low.Generally,magnetic systems can be seen as constituent magnetic elements providing spins and the non-magnetic elements providing frameworks to host the magnetic elements.Short bond lengths between the magnetic and non-magnetic elements would be beneficial for strong magnetic interactions and thus high TC.Based on this,we propose to combine the magnetic element Cr and the non-magnetic element boron to design novel 2D magnetic systems.Using our self-developed software package IM2 ODE,we design a series of chromium-boride based 2D magnetic materials.Nine stable magnetic systems are identified.Among them,we find that CrB4-Ⅰ,CrB4-Ⅱ and CrBs-Ⅰ with common structural units [CrB8] are ferromagnetic metals with estimated TC of 270 K,120 K and 110 K,respectively.On the other hand,five CrB3 phases with structural units [Cr2B12] are antiferromagnetic metals.Additionally,we also find one antiferromagnetic semiconductor CrB2-Ⅰ.Our work may open new directions for identifying 2D magnetic systems with high TC.  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