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   83827篇
  免费   1892篇
  国内免费   393篇
化学   44384篇
晶体学   548篇
力学   2317篇
综合类   15篇
数学   19548篇
物理学   19300篇
  2023年   391篇
  2022年   359篇
  2021年   766篇
  2020年   876篇
  2019年   824篇
  2018年   2229篇
  2017年   2332篇
  2016年   2632篇
  2015年   2140篇
  2014年   2089篇
  2013年   4168篇
  2012年   6210篇
  2011年   5555篇
  2010年   3876篇
  2009年   3350篇
  2008年   3506篇
  2007年   3352篇
  2006年   3075篇
  2005年   6701篇
  2004年   5841篇
  2003年   3957篇
  2002年   1993篇
  2001年   1426篇
  2000年   1281篇
  1999年   1009篇
  1998年   753篇
  1997年   644篇
  1996年   771篇
  1995年   548篇
  1994年   650篇
  1993年   558篇
  1992年   719篇
  1991年   614篇
  1990年   644篇
  1989年   537篇
  1988年   517篇
  1987年   435篇
  1986年   415篇
  1985年   565篇
  1984年   525篇
  1983年   409篇
  1982年   420篇
  1981年   430篇
  1980年   343篇
  1979年   341篇
  1978年   356篇
  1977年   337篇
  1976年   393篇
  1974年   323篇
  1973年   340篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
用于机械振动实时监测的光纤光栅有源传感装置   总被引:4,自引:1,他引:3  
把一对中心反射波长分别为1562.11nm和1562.71nm的光纤光栅粘贴在均质、等厚、等腰三角形悬臂梁上下表面作为环形腔光纤激光器端镜,当机械振动激励自由端时,通过观测激光输出脉冲,地施加于自由端的机械振动的频率进行了实时监测;观察两光栅波长漂移量差值的变化,可在0~6.1mm的范围内判断所测振动的振幅。低于100Hz时,实验结果与实际值基本吻合。  相似文献   
83.
84.
85.
Summary This article provides a glimpse of some of the highlights of the joint work of Endre Csáki and Pál Révész since 1979. The topics of this short exploration of the rich stochastic milieu of this inspiring collaboration revolve around Brownian motion, random walks and their long excursions, local times and additive functionals, iterated processes, almost sure local and global central limit theorems, integral functionals of geometric stochastic processes, favourite sites--favourite values and jump sizes for random walk and Brownian motion, random walking in a random scenery, and large void zones and occupation times for coalescing random walks.  相似文献   
86.
Could simple intraannular-arm macrocyclic systems exist in enantiopure stable forms? The effective synthesis of two representative compounds of such a class, their resolution into enantiomers, and experiments justifying their stability toward racemization are presented.  相似文献   
87.
We show the exponential decay of eigenfunctions of second-order geometric many-body type Hamiltonians at non-threshold energies. Moreover, in the case of first-order and small second-order perturbations we show that there are no eigenfunctions with positive energy.  相似文献   
88.
Book rewiev     
Howard Anton and Robert C. Busby, John Wiley & Sons, Inc., 2002.  相似文献   
89.
The aim of this study was to develop novel thermally responsive polymer microspheres with magnetic properties. Dispersion and inverse emulsion copolymerization of N‐isopropylacrylamide (NIPAAm) and N,N′‐methylenebisacrylamide (MBAAm) was investigated in the presence of γ‐Fe2O3 nanoparticles. The resulting microspheres were characterized in terms of morphology, size, polydispersity, iron content, and temperature‐dependent swelling using optical microscopy, transmission electron microscopy, scanning electron microscopy, QELS, and AAS. The effects of several variables, such as the concentration of γ‐Fe2O3, MBAAm crosslinking agent, Span 80 surfactant, 2,2′‐azobis(2‐methyloctanenitrile) (AMON) initiator, and polymerization temperature on the properties of the microspheres were studied. Swelling and thermoresponsive behavior of the microspheres containing γ‐Fe2O3 nanoparticles were also investigated. The microspheres contained about 8 wt % of iron. The presence of magnetic nanoparticles and their concentration changes did not have any significant effect on the temperature sensitivity of the composites. The particles gradually shrink into an increasingly collapsed state when the temperature is raised to 40 °C since the increase in temperature weakens the hydration and PNIPAAm chains gradually become more hydrophobic, which leads to the collapse of the particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5884–5898, 2007  相似文献   
90.
This work deals with As determination in marine sediment using ultrasound for sample preparation. It is shown that As can be quantitatively extracted from marine sediment using 20% (v/v) HCl and sonication. The slurry is centrifuged and the analyte is determined in the supernatant by hydride generation atomic absorption spectrometry (HG AAS). A flow injection (FI) system is employed for hydride generation, with 0.5% (m/v) NaBH(4) used as reducdant and a 20% (v/v) HCl used as sample carrier. The limit of quantification is 1.6 microg g(-1) of As, which is based on 800 microl of sample solution and 0.200 g of sample mass in a volume of 50 mL. Certified and non certified marine sediment samples were analyzed; the results were in accordance with the certified or reference values. Speciation analysis by HPLC-ICP-MS showed that As(V) is the only detectable As species present in the supernatant of the centrifuged sample.  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