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   1297篇
  免费   32篇
  国内免费   6篇
化学   922篇
晶体学   5篇
力学   25篇
数学   202篇
物理学   181篇
  2023年   9篇
  2022年   31篇
  2021年   34篇
  2020年   29篇
  2019年   22篇
  2018年   32篇
  2017年   20篇
  2016年   50篇
  2015年   28篇
  2014年   40篇
  2013年   71篇
  2012年   57篇
  2011年   67篇
  2010年   43篇
  2009年   37篇
  2008年   64篇
  2007年   48篇
  2006年   42篇
  2005年   41篇
  2004年   35篇
  2003年   42篇
  2002年   34篇
  2001年   16篇
  2000年   11篇
  1999年   7篇
  1998年   11篇
  1997年   18篇
  1996年   17篇
  1995年   8篇
  1994年   7篇
  1993年   15篇
  1992年   10篇
  1991年   11篇
  1990年   7篇
  1987年   8篇
  1985年   7篇
  1984年   11篇
  1983年   8篇
  1981年   11篇
  1979年   8篇
  1976年   7篇
  1972年   6篇
  1918年   8篇
  1907年   6篇
  1905年   6篇
  1901年   11篇
  1895年   6篇
  1894年   6篇
  1888年   6篇
  1885年   9篇
排序方式: 共有1335条查询结果,搜索用时 0 毫秒
121.
Cyclic voltammetry and electron spin resonance (ESR) techniques were used in the investigation of several potential antiprotozoal thiosemicarbazones nitrofurane derivatives. A self-protonation process involving the protonation of the nitro group due to the presence of an acidic proton in the thiosemicarbazone moiety was observed in the first step of a CEE(rev) reduction mechanism of these derivatives. ESR spectra of the free radicals obtained by electrolytic reduction were characterized and analyzed. AM1 methodology was used to obtain the optimized geometries and UB3LYP calculations were performed to obtain the theoretical hyperfine coupling constants. The theoretical study exhibited an unusual assignment of the spin densities showing a free radical centered in the thiosemicarbazone moiety rather than the nitro which are in agreement with the experimental hyperfine pattern.  相似文献   
122.
In this paper, involutions without fixed points on hyperbolic closed Riemann surface are discussed. For an orientable surface X of even genus with an arbitrary Riemannian metric d admitting an involution τ, it is known that min pX d(p, τ(p)) is bounded by a constant which depends on the area of X. The corresponding claim is proved to be false in odd genus, and the optimal constant for hyperbolic Riemann surfaces is calculated in genus 2. The author was supported in part by the Swiss National Science Foundation grants 20-68181.02 and PBEL2-106180.  相似文献   
123.
Trace metals (20 elements) in high-purity chromium, molybdenum and tungsten are collected and preconcentrated by precipitation and adsorption on cellulose collectors. The compound methods allow the application of AAS and ICP-AES as determination methods for the production control of highly pure refractory metals under routine conditions.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria  相似文献   
124.
A method of constructing a family of regular rotating disks as sources of the Kerr metric is discussed. The algebraic type of the energy-momentum tensor is analyzed, and it is found that none of the disks satisfies the dominant energy condition and, in some cases, even the weak energy condition is violated. Therefore, if the constructed family includes the totality of sources for the Kerr metric with a disk-like topology, then any physically satisfactory source will not have a disk structure.  相似文献   
125.
126.
127.
Ohne ZusammenfassungHerrn Prof. M. Bamberger, sage ich für seine freundliche Unterstützung bei Ausführung dieser Arbeit meinen aufrichtigsten Dank.  相似文献   
128.
129.

Background  

Superoxide mediated oxidative stress is a key neuropathologic mechanism in acute central nervous system injuries. We have analyzed the neuroprotective efficacy of the transient overexpression of antioxidant enzyme Cu/Zn Superoxide dismutase (SOD) after excitotoxic injury to the immature rat brain by using a recently constructed modular protein vector for non-viral gene delivery termed NLSCt. For this purpose, animals were injected with the NLSCt vector carrying the Cu/Zn SOD or the control GFP transgenes 2 hours after intracortical N-methyl-D-aspartate (NMDA) administration, and daily functional evaluation was performed. Moreover, 3 days after, lesion volume, neuronal degeneration and nitrotyrosine immunoreactivity were evaluated.  相似文献   
130.
In the last decades, the development of interconnectivity, pervasive systems, citizen sensors, and Big Data technologies allowed us to gather many data from different sources worldwide. This phenomenon has raised privacy concerns around the globe, compelling states to enforce data protection laws. In parallel, privacy-enhancing techniques have emerged to meet regulation requirements allowing companies and researchers to exploit individual data in a privacy-aware way. Thus, data curators need to find the most suitable algorithms to meet a required trade-off between utility and privacy. This crucial task could take a lot of time since there is a lack of benchmarks on privacy techniques. To fill this gap, we compare classical approaches of privacy techniques like Statistical Disclosure Control and Differential Privacy techniques to more recent techniques such as Generative Adversarial Networks and Machine Learning Copies using an entire commercial database in the current effort. The obtained results allow us to show the evolution of privacy techniques and depict new uses of the privacy-aware Machine Learning techniques.  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