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   95735篇
  免费   2560篇
  国内免费   1818篇
化学   35836篇
晶体学   970篇
力学   7903篇
综合类   78篇
数学   33488篇
物理学   21838篇
  2024年   221篇
  2023年   434篇
  2022年   695篇
  2021年   763篇
  2020年   861篇
  2019年   813篇
  2018年   10896篇
  2017年   10663篇
  2016年   6893篇
  2015年   1628篇
  2014年   1289篇
  2013年   1512篇
  2012年   5284篇
  2011年   11888篇
  2010年   6580篇
  2009年   6928篇
  2008年   7626篇
  2007年   9639篇
  2006年   1089篇
  2005年   2051篇
  2004年   2056篇
  2003年   2388篇
  2002年   1427篇
  2001年   599篇
  2000年   606篇
  1999年   496篇
  1998年   463篇
  1997年   392篇
  1996年   485篇
  1995年   386篇
  1994年   268篇
  1993年   249篇
  1992年   213篇
  1991年   215篇
  1990年   180篇
  1989年   166篇
  1988年   147篇
  1987年   128篇
  1986年   112篇
  1985年   89篇
  1984年   73篇
  1983年   63篇
  1982年   57篇
  1981年   56篇
  1980年   58篇
  1979年   44篇
  1914年   45篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This paper presents the design and characterization of a prototype compact beta–gamma radioxenon detection system that utilizes a coplanar CdZnTe crystal, an array of SiPMs, and a plastic scintillator. The detector is directly mounted on a custom PCB. The system provides the advantage of room-temperature operation, while being compact, low noise, and with simple readout electronics. Preliminary measurements using 137Cs, 135Xe, and 133/133mXe were conducted to optimize various system parameters to achieve optimal resolution of key photopeaks. The purpose of this research was to explore the potential of these radiation detection elements for use in beta–gamma coincidence applications.  相似文献   
992.
The present paper describes a new analytical method developed for direct determination of boron in steels using radio frequency glow discharge optical emission spectrometer. “Single parameter alternative method” technique has been used to optimize the various experimental conditions of glow discharge plasma such as forward power, gas pressure inside plasma chamber, pre-integration time, and integration time. Different emission lines for boron were studied and inter element interference effect is also discussed in the paper. A complete statistical analysis has been done to validate the developed method. A RSD of less than ±5% is achieved for boron in the range of 0.0010–0.020% in Steels using this method.  相似文献   
993.
Since the introduction of the European Council Directive 2013/51 Euratom in October 2013, the analysis of drinking water has increasingly become the focus of many laboratories in Europe. The activity of tritium, radon and the gross α/β-activity is determined routinely. In order to cope with the increased sample numbers and to reach the necessary detection limits, sensitive measuring devices are required. This work was done with the new Quantulus GCT 6220 to test the sensitivity of this system for drinking water analysis. The results indicate that this instrument is very well suited for this type of analysis and counting times are typically below the required counting times of established systems.  相似文献   
994.
We synthesized liquid scintillators incorporating ZrO2 nanoparticles for application in neutrinoless double beta decay experiments. ZrO2 nanoparticles of less than 10 nm in size were synthesized with sub- and supercritical hydrothermal methods. The Zr concentrations in the liquid scintillators were determined to be up to 1.4 wt% with inductively coupled plasma analysis, and the liquid scintillators were transparent to scintillation. These results indicate that these methods are applicable for the preparation of liquid scintillators for neutrinoless double beta decay experiments.  相似文献   
995.
The purpose of this work was to support the long-term experiments for investigation of rock matrix retention properties at the spent nuclear fuel repository site ONKALO, in Olkiluoto, Western Finland. Towards this end, rock samples were characterised in terms of porosity connected to mineralogy, with emphasis on pore sizes, and fillings. Both filled and unfilled pores were found with unfilled pores being majority in the pegmatitic granite veins of the mostly veined gneiss samples. It was found that the fillings were often connected to local alteration and the alteration caused variation in the range of pore sizes.  相似文献   
996.
The field of therapeutic nuclear medicine is emerging rapidly as choice of treatment in oncology and other cellular malignancies. The growth of this branch of nuclear medicine is greatly facilitated by the introduction of a number of new radiopharmaceuticals and radionuclides. 90Y-radiopharmaceuticals have confirmed their worth in medical and clinical areas in a very short span of time. The 90Y is a radioisotope widely used for therapeutic purposes and considerable perfection has been made to understand the chemistry of 90Y-labeled radiopharmaceuticals. The development of these radiopharmaceuticals can be made favorable by using appropriate buffer, incubation period, optimal pH, specific activity and reaction temperature. In this review, we have discussed the preparation of range of 90Y transporting biological molecules such as antibodies radiolabeled peptides, antigens and microsphere with their clinical applications.  相似文献   
997.
998.
999.
1000.
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