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   102001篇
  免费   18033篇
  国内免费   11400篇
化学   69816篇
晶体学   1185篇
力学   6527篇
综合类   715篇
数学   11594篇
物理学   41597篇
  2024年   368篇
  2023年   2160篇
  2022年   3588篇
  2021年   3886篇
  2020年   4244篇
  2019年   3898篇
  2018年   3574篇
  2017年   3267篇
  2016年   5073篇
  2015年   4914篇
  2014年   5974篇
  2013年   7595篇
  2012年   9193篇
  2011年   9373篇
  2010年   6295篇
  2009年   6204篇
  2008年   6671篇
  2007年   5872篇
  2006年   5568篇
  2005年   4461篇
  2004年   3532篇
  2003年   2816篇
  2002年   2742篇
  2001年   2385篇
  2000年   1976篇
  1999年   2121篇
  1998年   1784篇
  1997年   1699篇
  1996年   1674篇
  1995年   1415篇
  1994年   1225篇
  1993年   1073篇
  1992年   898篇
  1991年   820篇
  1990年   678篇
  1989年   535篇
  1988年   393篇
  1987年   329篇
  1986年   340篇
  1985年   278篇
  1984年   156篇
  1983年   119篇
  1982年   102篇
  1981年   61篇
  1980年   45篇
  1979年   18篇
  1974年   1篇
  1957年   31篇
  1936年   6篇
  1922年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Lipase from Candida rugosa was covalently anchored onto acid-treated multi-walled carbon nanotubes (MWNTs) through a self-catalytic mechanism. A variety of characterization techniques including FTIR, Raman spectroscopy, and XPS were employed to demonstrate the formation of the ester linkage between lipase and MWNTs. The MWNTs-lipase biocomposites showed significantly increased solubility in some common-used organic solvents, such as THF, DMF and chloroform. This study may offer a novel and facile route for covalent modification of carbon nanotubes, and expand the potential utilization of both lipases and MWNTs in the fields of biocatalyst and biosensor.  相似文献   
82.
After having introduced by ion implantation 57Fe to a local concentration of 7 at% into Co6Ag94, we observed it by conversion electron Mössbauer spectroscopy in the as-prepared state and after isochronal annealing. A superferromagnetic state is inferred, which is correlated with the ordering of the magnetic moments on the Fe clusters through chain-like or dendritic Co/Fe linear structures. The magnetic moment disordering temperature lies above 473 K.  相似文献   
83.
In this article, a kind of auxiliary design BSA* for constructing BSAs is introduced and studied. Two powerful recursive constructions on BSAs from 3‐IGDDs and BSA*s are exploited. Finally, the necessary and sufficient conditions for the existence of a BSA(v, 3, λ; α) with α = 2, 3 are established. © 2006 Wiley Periodicals, Inc. J Combin Designs 15: 61–76, 2007  相似文献   
84.
A novel heath monitoring system of the rocket based on fiber optic Bragg gratings is brought forward, its component units and working principle are also described.  相似文献   
85.
For the linear deterministic system with unknown orders and coefficients adaptive controls are given so that the closed-loop system is stabilized and the unknown parameters are consistently estimated. Moreover, if the parameter estimation is ignored, then the system input and output can be reduced to zero with an exponential rate.This project is supported by the National Natural Science Foundation of China.In Commemoration of the 15th Anniversary of the Acta Mathematicae Applicatae Sinica.  相似文献   
86.
This paper discusses a class of second-order derivative nonlinear Schrödinger equations which are used to describe the upper-hybrid oscillation propagation. By establishing a variational problem, applying the potential well argument and the concavity method, we prove that there exists a sharp condition for global existence and blow-up of the solutions to the nonlinear Schrödinger equation. In addition, we also answer the question: how small are the initial data, the global solutions exist?  相似文献   
87.
A Liouville type theorem for polyharmonic elliptic systems   总被引:1,自引:0,他引:1  
In this paper, we consider the polyharmonic system m(−Δ)U=Vq,m(−Δ)V=Up in RN, for m>1, N>2m, with p?1, q?1, but not both equal to 1, where m(−Δ) is the polyharmonic operator. Set α=2m(q+1)/(pq−1), β=2m(p+1)/(pq−1), for α,β∈[(N−2)/2,N−2m), we prove the nonexistence of positive solutions.  相似文献   
88.
In solid immersion lens (SIL) microscopy systems with high numerical aperture (NA), there always exists the aberration produced by Fresnel effects at the interface between SIL and the sample. This aberration may cause the degradation of the image of sample. We design a continuous phase filter and optimize the optical field distribution of SIL system. The numerical results show that when the continuous phase filter is used, the field distribution of SIL system can be optimized, and the focal depth and intensity of transmitted light can be increased. At the same time, the intensity of side-lobe and the resolution are kept almost unchanged.  相似文献   
89.
本文报道了用吸附溶出伏安法测定毗喳酮.以悬汞电极为工作电极,在Na}B,O,-NaOH介质(pH=10)中,毗喳酮产生一尖锐的吸附还原峰,E,二一1. 29V (vs. SCE ),峰电流与毗喳酮浓度在2. 0 X 10-'-8. 0 X 10-smol " L-’范围内呈良好的线性关系.检测限为2. 0 X 10-0mol " L-'(富集90s).本文对毗喳酮在悬汞电极上的电化学行为进行了探讨,对测定毗喳酮的最佳条件进行了详细的选择,利用本法测定了片剂中毗喳酮含量,结果满意.  相似文献   
90.
通过把全息透镜嵌入挡风玻璃,实现全息透镜在车辆中的两种应用,即将具有颜色选择性的窄带全息透镜用于车辆的平视显示,将具有角度选择性的宽带全息透镜用于车辆的阳光防护。  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