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   2129篇
  免费   99篇
  国内免费   11篇
化学   1143篇
晶体学   17篇
力学   41篇
数学   433篇
物理学   337篇
无线电   268篇
  2024年   6篇
  2023年   32篇
  2022年   82篇
  2021年   95篇
  2020年   80篇
  2019年   103篇
  2018年   96篇
  2017年   74篇
  2016年   163篇
  2015年   87篇
  2014年   105篇
  2013年   144篇
  2012年   151篇
  2011年   143篇
  2010年   85篇
  2009年   70篇
  2008年   85篇
  2007年   78篇
  2006年   75篇
  2005年   67篇
  2004年   42篇
  2003年   29篇
  2002年   25篇
  2001年   15篇
  2000年   16篇
  1999年   10篇
  1998年   16篇
  1997年   10篇
  1996年   16篇
  1995年   9篇
  1994年   14篇
  1993年   10篇
  1992年   11篇
  1991年   11篇
  1990年   11篇
  1989年   10篇
  1988年   14篇
  1987年   6篇
  1986年   8篇
  1985年   16篇
  1984年   12篇
  1982年   13篇
  1981年   16篇
  1980年   14篇
  1979年   17篇
  1978年   5篇
  1977年   5篇
  1974年   5篇
  1973年   4篇
  1972年   5篇
排序方式: 共有2239条查询结果,搜索用时 17 毫秒
141.
Given D a domain in , G an open set in and E a subset of D verifying the harmonic analogue of Local Polynomial Condition of Leja at some point in D. We prove that if f(x, y) is a complex function defined on D × G such that– f(x, ) is harmonic on G for every fixed x E,– f(, y) is harmonic on D for every fixed y G,then f is harmonic in (x, y) on D × G.  相似文献   
142.
We have carried out the study on the isomeric ratios in (γ,p) photonuclear reactions with isotopes 40 92 Zr and 74 183 W in the giant dipole resonance (GDR) region. The targets were irradiated with bremsstrahlungs produced by electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, Russia. Spectra of the irradiated samples were measured with a spectroscopic system consisting of 8192-channel analyzer CANBERRA and high-energy resolution semiconductor detector CANBERRA. The results were discussed and compared with those of other authors. The text was submitted by the authors in English.  相似文献   
143.
To increase battery life in IEEE 802.16e systems, it is essential to efficiently manage energy in mobile stations. The sleep-mode operation in power management helps to increase the life of a station by saving energy consumption. In power management, there are two important performance metrics energy consumption and the response delay of awakening medium access control (MAC) service data unit (SDU). While in a base station (BS) initiation of awakening, the two performance metrics should be simultaneously considered, in a mobile subscriber station (MSS) initiation of awakening, the response delay is not considered because it is self-operational. There performance metrics are affected by the minimum sleep interval (Tmin), the maximum sleep interval (Tmax), and the average interarrival time of awakening MAC SDUs (TI) during sleep-mode operation. Therefore, it is imperative to evaluate the two initiations of awakening depending on TI. To reach a fuller understanding of the performance, this paper shows an analytical mode and simulations results for the standard sleep-mode operation in the IEEE 802.16e MAC.  相似文献   
144.
We present a novel and simple method to measure both the value of the second-order dispersion coefficient and the nonlinear coefficient in optical fibers. This method is based on the higher-order soliton-effect pulse compression phenomenon and is valid for dispersion values greater than 0.5 ps/km/nm. A non-zero dispersion-shifted fiber, a standard single-mode fiber and a highly-dispersive highly-nonlinear fiber have been measured using this method.  相似文献   
145.
Tithonia tagetiflora Desv. (Asteraceae) is a widespread plant in Vietnam, and the species of Tithonia are known as plants containing many biologically active compounds. However, T. tagetiflora's chemical composition remains mostly unknown. Therefore, we now report the structural elucidation of two new sesquiterpene lactones, 8‐angeloyloxy‐2,14‐epoxygermacra‐4,10(1),11(13)‐trien‐6,12‐olide (1) and 6‐angeloyloxy‐1‐hydroxy‐3,4‐epoxygermacra‐9,11(13)‐dien‐8,12‐olide (2), together with three known compounds, including two norisoprenoids, (6S,9S)‐vomifoliol or (6R,9R)‐vomifoliol (3) and (6S,9S)‐roseoside (4), and one glutinane type triterpene, epi‐glutinol (5), from the leaves of T. tagetiflora. Their structures are established by 1D and 2D NMR spectroscopy, as well as ESI‐MS analysis and comparison with literature data. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
146.
Abstract

After a pressure cycle to 30 GPa, benzene transforms to a white solid which can be recovered at ambient. Results obtained from infrared spectroscopy and other physico-chemical methods show that the recovered solid is a highly cross-linked polymer. The molecular structure of benzene is very likely completely altered by the transformation.  相似文献   
147.
148.
The light-oxygen effect consists in a direct excitation of molecular oxygen dissolved in aqueous media of biosystems by the light; it provides the possibility to use lasers for therapeutic purposes. The wavelength of the used light should strictly correspond to the oxygen absorption bands. However, laser therapy also makes use of lasers emitting at 0.89 μm (outside the known oxygen bands), which suggests the action of a new photoreceptor. Here we argue that this mechanism of photoreception is a modification of the light-oxygen effect involving the absorption of photon simultaneously by the oxygen molecule and O-H stretch of the H20 molecule of liquid water.  相似文献   
149.
The seconds living mercury isotopes have been isolated from nuclear reaction products arising in the bombardment of 147Sm target with 40Ar ions at the U-400 cyclotron of JINR-Dubna.  相似文献   
150.
This article shows that finite-dimensional multiplier rules, which are based on the limiting subdifferential, can be proved by Ekeland's variational principle and some basic calculus tools of the generalized differentiation theory introduced by B. S. Mordukhovich. Consequences of a limiting constraint qualification, which yields the normal form of the multiplier rules, stability and calmness of optimization problems, are investigated 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