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   39925篇
  免费   6608篇
  国内免费   4730篇
化学   20878篇
晶体学   467篇
力学   1546篇
综合类   223篇
数学   3016篇
物理学   10553篇
无线电   14580篇
  2024年   202篇
  2023年   1090篇
  2022年   1430篇
  2021年   1885篇
  2020年   1833篇
  2019年   1672篇
  2018年   1478篇
  2017年   1481篇
  2016年   1898篇
  2015年   2155篇
  2014年   2421篇
  2013年   3206篇
  2012年   3620篇
  2011年   3606篇
  2010年   2661篇
  2009年   2625篇
  2008年   2864篇
  2007年   2412篇
  2006年   2195篇
  2005年   1844篇
  2004年   1364篇
  2003年   1053篇
  2002年   969篇
  2001年   758篇
  2000年   679篇
  1999年   635篇
  1998年   446篇
  1997年   357篇
  1996年   400篇
  1995年   316篇
  1994年   289篇
  1993年   241篇
  1992年   200篇
  1991年   183篇
  1990年   150篇
  1989年   118篇
  1988年   91篇
  1987年   69篇
  1986年   71篇
  1985年   67篇
  1984年   46篇
  1983年   26篇
  1982年   21篇
  1981年   24篇
  1980年   11篇
  1979年   11篇
  1976年   12篇
  1975年   14篇
  1971年   7篇
  1957年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes.  相似文献   
3.
4.
5.
The Pd‐catalyzed polycondensation of 4‐octylaniline with various dibromoarylenes was carried out under microwave heating. Microwave heating led to a decrease in the reaction time and an increase in the molecular weight of the polymers as compared to conventional heating. Microwave heating also allowed the catalyst loading to be reduced to 1 mol %, yielding polymerization results that were comparable to those under conventional heating and 5 mol % catalyst. Investigations regarding field‐effect transistors and organic photovoltaic cells using the obtained poly(arylamine) with azobenzene units revealed that increasing the molecular weight of the polymer led to improved device performance, including hole mobility and power conversion efficiency. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 536–542  相似文献   
6.
7.
8.
9.
Zhenju antihypertensive compound (ZJAHC) is a combined Chinese–Western medicine formula including clonidine (CLO), hydrochlorothiazide (HCT), rutin, Chrysanthemum indicum extract and pearl powder. Compared with CLO preparations, ZJAHC shows improved activities and decreased adverse effects. It is believed that the side effects of CLO are caused by its high peak plasma concentration. Hence, study of the influence of ZJAHC on the pharmacokinetic behaviors of clonidine seems essential. In present study, the plasma concentrations of CLO were determined with a liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method. The MS/MS transitions monitored for clonidine and internal standard were 230.2 → 213.1 and 152.2 → 110.2, respectively. The analyte was quantified in a single run within 3 min. The pharmacokinetic study showed that the area under the plasma concentration–time curve of CLO in ZJAHC (60 µg/kg CLO) was similar to that of CLO‐HCT‐high (120 µg/kg CLO) but the peak concentration was much lower than that in CLO‐HCT‐high. ZJAHC could enhance the bioavailability without greatly increasing peak concentration of clonidine. This comprehensive effect of enhancing the bioavailability and avoiding the high peak plasma concentration for CLO might mainly result from the co‐contribution of Western medicine and traditional Chinese medicine (TCM), while the effect of TCM was stronger than that of Western medicine. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
10.
移动通信系统中功率控制研究   总被引:2,自引:0,他引:2  
李蕾 《信息技术》2006,30(11):83-85
在阐述功率控制在移动通信系统中的发展过程的基础上,着重研究了WCDMA系统的功率控制,最后对功率控制未来的研究方向做了简要的分析。  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