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   271篇
  免费   31篇
  国内免费   35篇
测绘学   1篇
大气科学   53篇
地球物理   54篇
地质学   35篇
海洋学   40篇
天文学   129篇
综合类   9篇
自然地理   16篇
  2024年   1篇
  2023年   1篇
  2022年   3篇
  2021年   2篇
  2020年   8篇
  2019年   1篇
  2018年   4篇
  2017年   5篇
  2016年   5篇
  2015年   9篇
  2014年   11篇
  2013年   6篇
  2012年   11篇
  2011年   20篇
  2010年   16篇
  2009年   16篇
  2008年   18篇
  2007年   19篇
  2006年   25篇
  2005年   19篇
  2004年   9篇
  2003年   20篇
  2002年   11篇
  2001年   12篇
  2000年   12篇
  1999年   10篇
  1998年   8篇
  1997年   7篇
  1996年   7篇
  1995年   13篇
  1994年   8篇
  1993年   4篇
  1992年   2篇
  1991年   3篇
  1990年   3篇
  1989年   3篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1980年   1篇
排序方式: 共有337条查询结果,搜索用时 15 毫秒
291.
The microphysical structure, chemical composition and prehistory of aerosol are related to the aerosol optical properties and radiative effect in the UV spectral range. The aim of this work is the statistical mapping of typical aerosol scenarios and adjustment of regional aerosol parameters. The investigation is based on the in situ measurements in Preila (55.55° N, 21.00° E), Lithuania, and the AERONET data from the Gustav Dalen Tower (58 N, 17 E), Sweden.Clustering of multiple characteristics enabled to distinguish three aerosol types for clear-sky periods: 1) clean maritime–continental aerosol; 2) moderately polluted maritime–continental aerosol; 3) polluted continental aerosol. Differences between these types are due to significant differences in aerosol number and volume concentration, effective radius of volume distribution, content of SO4 ions and Black Carbon, as well as different vertical profiles of atmospheric relative humidity. The UV extinction, aerosol optical depth (AOD) and the Ångstrom coefficient α increased with the increasing pollution. The value α = 1.96 was observed in the polluted continental aerosol that has passed over central and eastern Europe and southern Russia. Reduction of the clear-sky UV index against the aerosol-free atmosphere was of 4.5%, 27% and 41% for the aerosol types 1, 2 and 3, respectively.  相似文献   
292.
Degradations of reactive brilliant red X‐3B solution by both conventional UV irradiation and microwave electrodeless UV irradiation were investigated. Degradation processes were studied by UV–VIS spectrophotometry, total organic carbon (TOC), high performance capillary electrophoresis (HPCE), conductivity, pH value, and ion chromatography. The results of color removal (%) and TOC removal (%) showed that the degradation by microwave electrodeless UV irradiation was more effective than by conventional UV irradiation. The results of UV–VIS absorption spectra and HPCE analyses indicated that the degradation of reactive brilliant red X‐3B was occurred at the conjugation system first, the benzene ring and the naphthalene ring later. The reactive brilliant red X‐3B was cleaved into some new small compounds and eventually most of the organic substances were mineralized to CO2 and H2O. The results of the conductivity analysis suggested that the degradation has mainly occurred in the first 40 min of reaction. The pH value of reactive brilliant red X‐3B solution was decreased first and then was increased. The results of inorganic anions analysis hinted that many of the N, Cl, and S elements from reactive brilliant red X‐3B were still attached in organic molecules.  相似文献   
293.
294.
比较分析了2017年南极中山站3种仪器测量地面太阳紫外B(UVB)波段和紫外A(UVA)波段的辐照度。以Brewer光谱仪测值为参考,国产宽波段FSUVB日射表在UVB(波段280~315 nm)的辐照度相对误差为(55±75)%,误差随大气臭氧总量的增加呈上升趋势,但在南极“臭氧洞”期间偏低。Yankee UVB宽波段日射表在UVB(波段280~320 nm)的辐照度相对误差为(-31±22)%;国产宽波段FSUVA日射表在UVA(波段315~400 nm)的辐照度相对误差为(23±5.9)%。太阳天顶角低于80°的晴天以Tropospheric Ultraviolet Visible(TUV)辐射模式计算结果为参考时,FSUVB,Yankee UVB和FSUVA辐照度的平均相对误差分别为(30±37)%,(-22±19)%和(27±6.4)%,而Brewer相对误差未超过3.5%。国产宽波段UV日射表测值偏高,反映出波长较长的杂散光对太阳辐照度测值影响明显。  相似文献   
295.
This research examines the influence of cloud on the cataract effective UV (UVCat) irradiances on a horizontal plane over an extended period of 12months that included the range of cloud conditions, solar zenith angle (SZA) and ozone conditions experienced over that time. The data were collected at five minute intervals. Cloud modification factors were determined from the influence of clouds on the global broadband solar radiation and these were applied to the cloud free cataract effective UV to evaluate the UVCat irradiances on a horizontal plane for all cloud conditions. A comparison of the measured and calculated UVCat irradiances for the 2004 data set in the range of SZA of 70° or less provided an R2 value of 0.85. The data in the first 6months of 2005 for an SZA of 70° or less that were at a different time to that when the technique was developed provided an R2 value of 0.83 for the comparison of the measured and calculated UVCat irradiances.  相似文献   
296.
邻菲啰啉光度法测定高岭土中可溶铁和非可溶铁   总被引:1,自引:1,他引:1  
高岭土中铁的赋存状态和含量影响其白度和增白效果,因此快速准确地测定高岭土中不同种类的铁含量具有实际应用意义。高岭土中自由铁和结构铁定量分析困难,为此本文将高岭土中的铁分为可溶铁和非可溶铁两类。高岭土经盐酸酸溶处理后溶液中的铁含量为可溶铁含量,经氢氧化钠碱熔处理后溶液中的铁含量为总铁含量,非可溶铁含量由总铁含量减去可溶铁含量计算得出。采用邻菲啰啉光度法测定溶液中的铁含量,该方法的相对标准偏差小于5%,加样回收率范围在95%~105%,最低检测含量为1.06μg/g。高岭土中的其他元素对铁的测定均没有干扰。所测得的可溶铁为大部分自由铁和少数结构铁。通过对高岭土中的可溶铁进行定量分析,可得知漂白工艺中可除去的最大铁含量。  相似文献   
297.
The physiological responses of the coral Pocillopora capitata to environmental conditions common in winter and summer were studied in 2007 during February–March (winter) and June–July (summer) at La Boquita reef (Manzanillo, Colima, Mexico). Shallow and deep sampling stations were established at different distances from a small jetty built next to the Juluapan Lagoon. We analyzed superoxide radicals () and lipid peroxidants (TBARS); the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione‐S‐transferase (GST); chlorophyll a (Chl a), zooxanthellae density (ZD); and mycosporine‐like amino acids (MAAs). Our results showed that the , TBARS, CAT, GST, MAAs, and Chl a, levels were significantly higher in summer (P < 0.05); no seasonal difference was found for GPx, GR or ZD. We found significant differences (P < 0.05) in winter only for Chl a and ZD at shallow sites and, in contrast, for at deeper sites. The results of this study indicate that increasing temperature and radiation associated with seasonal changes (from winter to summer), the efficiency of the enzymes GST, CR and GPX, and the production of MAAs together form a powerful mechanism for P. capitata to offset the detrimental effects of environmental change.  相似文献   
298.
冻能松  杨勇 《地球科学》2003,28(3):357-360
在JCXA—733电子探针上采用一种实用的微区紫外一可见阴极荧光的探测方案,可以分析样品表面微区的不可见和可见的荧光.荧光的波长和强度特性与物质的成分、结构、缺陷,物质的形成条件、经历、所处环境条件等密切相关.相对于常规的可见阴极荧光测试技术,探测紫外和红外阴极荧光可以在更宽的波段上获取更多更新的样品内在信息.用此方法对河北唐山石英砂岩及其微小次生加大边进行阴极荧光分析,发现它们具有不同的紫外荧光特征,还有对应波长为287nm的辐射损伤色心,由此可以推测至少有两期胶结作用,且石英碎屑来源复杂.这为分析胶结作用期次和碎屑物物源提供了新的技术方法,对于沉积盆地分析和油气储集具有重要的实用意义.  相似文献   
299.
本文介绍了在阳离子表面活性剂存在下锡[Sn(Ⅳ)]与邻氯苯基荧光酮(O-Cl-PF)胶束增溶显色反应的研究结果,发现在溴化十六烷基三甲基铵(CTMAB)存在下,Sn(Ⅳ)与O-Cl-PF可形成深颜色的络合物,其最大吸收在534nm处,络合物的摩尔吸收系数为1.83×10~5lmol~(-1)·cm~(-1)在0—8μgSn(Ⅳ)/25范围内符合比尔定律,采用等摩尔连续变换法确定了络合物的组成为Sn(Ⅳ):O-Cl-PF=1:4、本文提出了不经分离其伴生元素而快速测定铀矿石中微量Sn(Ⅳ)的新方法,所得结果令人满意。  相似文献   
300.
对于总氮和总磷的测定,国家标准HJ636—2012和GB11893—89规定总氮用碱性过硫酸钾消解,紫外分光光度法测定,总磷用中性过硫酸钾消解,分光光度法测定,两种方法分别取样、消解,分析效率低。本文对国家标准方法进行改进,建立了在一份样品中用过硫酸钾作为氧化剂一次消解,分光光度法联合测定树干茎流液中总氮、总磷含量的方法。样品中的含氮化合物在碱性过硫酸钾溶液中,在高温下氧化分解转化为硝酸盐氮(NO-3-N),其吸光度与总氮浓度成正比;含磷化合物在酸性过硫酸钾溶液中,在高温下氧化分解转化成正磷酸盐(PO3-4-P),其吸光度与正磷酸盐浓度成正比。经实际样品验证,方法精密度(RSD,n=5)为总氮2%,总磷4%,加标回收率为98.0%~104.2%(总氮)和94.0%~107.0%(总磷)。本方法将国家标准方法中配制两条标准系列、两次高压消解改进为配制一条标准系列、一次消解,可以节省50%的样品使用量,且提高了分析效率。由于有机质含量较高时,在本法条件下样品不易消解清亮,影响总氮、总磷的测定,该方法适用于有机质含量较低的树干茎流样品分析。  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