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   7669篇
  免费   326篇
  国内免费   115篇
化学   5801篇
晶体学   44篇
力学   394篇
数学   765篇
物理学   1106篇
  2024年   16篇
  2023年   60篇
  2022年   284篇
  2021年   369篇
  2020年   379篇
  2019年   382篇
  2018年   389篇
  2017年   371篇
  2016年   501篇
  2015年   356篇
  2014年   474篇
  2013年   872篇
  2012年   647篇
  2011年   568篇
  2010年   368篇
  2009年   349篇
  2008年   352篇
  2007年   306篇
  2006年   209篇
  2005年   176篇
  2004年   119篇
  2003年   117篇
  2002年   97篇
  2001年   33篇
  2000年   17篇
  1999年   27篇
  1998年   19篇
  1997年   21篇
  1996年   23篇
  1995年   10篇
  1994年   14篇
  1993年   10篇
  1992年   14篇
  1991年   12篇
  1990年   9篇
  1989年   9篇
  1988年   5篇
  1987年   14篇
  1986年   5篇
  1985年   12篇
  1984年   13篇
  1982年   14篇
  1981年   8篇
  1980年   14篇
  1979年   8篇
  1978年   9篇
  1977年   5篇
  1976年   5篇
  1973年   3篇
  1971年   3篇
排序方式: 共有8110条查询结果,搜索用时 0 毫秒
71.
Sound quality is among the main factors that influence customers’ preference for choosing good automobile products. It all started more than 10 years ago and grows up so fast due to high competition in the automotive industries. A-weighted noise levels and sound power are usually utilised to measure the noise but they are not adequate to characterise the impact sound inside a car. The most popular approach to determine sound quality of a product is to define an annoyance or specific index, which involves both subjective and objective evaluations. Subjective and objective tests should be studied concurrently in order to determine the sound quality inside a passenger car. This approach is used in this paper to evaluate vehicle comfort index according to most frequently used sound quality metrics, namely; Zwicker loudness, sharpness, roughness and fluctuation strength. As a result researchers of different fields of automotive acoustics investigations can use this index according to the type of road (international road roughness) without any need to perform time-consuming jury tests. The metrics are correlated with jury test results that show which of them and how much has affected the acoustical comfort of the vehicle. The relation between road roughness and vehicle acoustical comfort index is another point of interest in this research.  相似文献   
72.
In this letter we describe the advantages of a dynamic optical interconnection system for parallel information processing applications. The system is based on a liquid crystal television which acts as a binary phase-only spatial light modulator. We describe example algorithms where reconfigurable interconnects would be useful and present results of several interconnection topologies which have been implemented.Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994.  相似文献   
73.
Iron is a crucial element required for the proper functioning of the body. For instance, hemoglobin is the vital component in the blood that delivers oxygen to various parts of the body. The heme protein present in hemoglobin comprises iron in the form of a ferrous state which regulates oxygen delivery. Excess iron in the body is stored as ferritin and would be utilized under iron-deficient conditions. Surprisingly, cancer cells as well as cancer stem cells have elevated ferritin levels suggesting that iron plays a vital role in protecting these cells. However, apart from the cytoprotective role iron also has the potential to induce cell death via ferroptosis which is a non-apoptotic cell death dependent on iron reserves. Apoptosis a caspase-dependent cell death mechanism is effective on cancer cells however little is known about its impact on cancer stem cell death. This paper focuses on the molecular characteristics of apoptosis and ferroptosis and the importance of switching to ferroptosis to target cancer stem cells death thereby preventing cancer relapse. To the best of our knowledge, this is the first review to demonstrate the importance of intracellular iron in regulating the switching of tumor cells and therapy resistant CSCs from apoptosis to ferroptosis.  相似文献   
74.
A simple, inexpensive, environmentally friendly and efficient route for Michael addition of indoles to α,β-unsaturated ketones using pentafluorophenylammonium triflate (PFPAT) as a catalyst is described. Various indole derivatives were synthesized in good to excellent yields. The preparation of PFPAT catalyst from simple and readily available starting materials makes this method more affordable.  相似文献   
75.
76.
The use of aqueous media in palladium‐catalyzed reactions has become popular because water‐based synthetic processes are inherently safer as well as being inexpensive. Moreover, it does not require dry solvents, and the products may easily be isolated by extraction, which greatly facilitates the operation. Thus the use of water in palladium‐catalyzed reactions represents one of the most economically and environmentally viable options for many organic transformations. In this review, recent developments of Sonogashira reaction in water or aqueous media will be disclosed. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
77.
The solventless oxidation of benzaldehydes to carboxylic acids using oxone/wet-alumina under microwave irradiations is described.  相似文献   
78.
Alanine/chlorochromic acid/silica gel is a new and selective reagent for the efficient oxidation of sulfides, thiols, oximes, and alcohols. Oxidation of sulfides is solvent dependent. In chloroform at room temperature sulfoxides are formed as the major products, while in carbon tetrachloride or under solvent-free conditions solfones are produced in good-to-excellent yields.  相似文献   
79.
Poly(4-vinylpyridine) is reported as a green,commercial available and efficient basic recyclable catalyst for the synthesis of chromene derivatives.This catalyst can be easily recovered by simple filtration and recycled up to 5 consecutive runs without any loss of its efficiency.  相似文献   
80.
This paper presents a method for the construction of a graphene paste electrode (GPE) from reduced graphene oxide (RGO). The GPE was successfully used for the determination of medetomidine. The influence of some experimental variables such as pH, supporting electrolyte, scan rate, and possible interferences were studied. Differential pulse voltammetric (DPV) peak currents of medetomidine increased linearly with its concentration in the range from 0.009 to 2.5 µM. The limit of detection (LOD) and limit of quantitation (LOQ) values for the determination of medetomidine were 2.8 and 9.2 nM, respectively. Also, for the first time, the electroreduction behavior of medetomidine was investigated.  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