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   1047篇
  免费   206篇
  国内免费   310篇
测绘学   51篇
大气科学   347篇
地球物理   258篇
地质学   510篇
海洋学   97篇
天文学   29篇
综合类   131篇
自然地理   140篇
  2024年   7篇
  2023年   13篇
  2022年   64篇
  2021年   54篇
  2020年   58篇
  2019年   76篇
  2018年   75篇
  2017年   85篇
  2016年   91篇
  2015年   58篇
  2014年   85篇
  2013年   44篇
  2012年   65篇
  2011年   62篇
  2010年   57篇
  2009年   60篇
  2008年   36篇
  2007年   53篇
  2006年   41篇
  2005年   50篇
  2004年   32篇
  2003年   26篇
  2002年   27篇
  2001年   21篇
  2000年   30篇
  1999年   68篇
  1998年   43篇
  1997年   31篇
  1996年   30篇
  1995年   21篇
  1994年   22篇
  1993年   20篇
  1992年   18篇
  1991年   10篇
  1990年   9篇
  1989年   8篇
  1988年   4篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1980年   1篇
  1958年   1篇
排序方式: 共有1563条查询结果,搜索用时 27 毫秒
991.
详细介绍了自1993年开始以来《中日亚洲季风机制合作研究计划》在青藏高原上观测研究的一些基本情况。包括三个部分:观测仪器的特点、观测环境的气候特征和观测项目(要素);观测资料的特点;部分观测资料的初步分析结果介绍  相似文献   
992.
A theoretical investigation has been made on the head-on collision of cylindrical and spherical electron-acoustic solitary waves in a non-Maxwellian plasma composed of stationary ions, cold fluid electrons, and superthermal electrons obeying κ velocity distribution. By using the extended Poincaré-Lighthill-Kuo perturbation method, the effects of plasma parameters, especially the superthermal effect on the interaction of colliding solitary waves are studied. It is found that there are both positive and negative colliding phase shifts for each colliding wave in its traveling direction. Also, it is shown that the solitary waves received the largest colliding phase shifts in spherical geometry, followed by the cylindrical and planar geometries.  相似文献   
993.
????????????????????????????в??????????????????У??????????????о??????????????????????仯??????????????????????????????в??????????????仯??????????£??????????????????????????????????????????????????ζ????????????????????????????????????????????ж???????????????????- ??????????????????????????????????????????????????????????  相似文献   
994.
In order to find out whether long interspersed elements (LINEs) existed in macro-algae ge- nomes or not, we tested the LINE homologues in representative families (species): Gracilaria (G. eucheumoides Harv., G. tenuistipitata Chang et Xia, and G. textorii (Sur) De-Toni), Laminaria (L. longis- sima Miyabe and L. japonica Aresch.), and Ulva (U. lactuca L. and U. pertusa Kjellm.) during 2004 to 2005. Polymerase Chain Reaction (PCR) was carried out with degenerate oligonucleotide primers de- signed from LINEs of rice homologues and Cin4 of maize. Cloning and nucleotide sequencing of the PCR products revealed that 4 clones that derived from 3 species of Gracilaria have LINE homologues. The nucleotide sequences of the 4 LINE homologues diverged greatly, but the amino acid sequences deduced from them were relatively conserved. The endonuclease regions of the LINE homologues greatly di- verged from that of other plants, but they had closer phylogenetic relationship to Zepp elements in Chlor- ella sp., which indicated that sequence divergence by vertical transmission has been a major influence on the evolution of algal LINEs.  相似文献   
995.
A series of reference materials are proposed for intercomparison and quality control purposes during the quantification of lignin oxidation products (LOP) from diverse environmental matrices. These materials are all easily accessible and certified for diverse organic constituents (NIST and IHSS). They represent a suite of natural environmental matrices (from solids to aqueous) and are characterized by a wide range of organic carbon and lignin concentrations with abundant proportions of all major LOP. The variability of LOP concentrations and signatures for all these materials averages 3–5% and does not exceed 10%. Using these standards, a new quantification method was developed and validated for the determination of low-level CuO oxidation products using capillary gas chromatography–tandem mass spectrometry (GC/MS–MS). Tandem mass spectrometry provides both the high sensitivity and selectivity required for the identification and quantification of trace levels of dissolved lignin. The method is particularly useful for removing interference from co-eluting isotopes generated from the DOM matrix and during glucose amendment procedures of low-carbon samples. Such glucose amendment is not necessary, however, when the CuO to organic carbon weight-to-weight ratio can be kept at a value < 200–300.  相似文献   
996.
??????????????GRACE?????????????仯????????????????????????о???2003~2005?????????????仯?????????????????GRACE????????????????????????????????仯?????????????????????Σ?GRACE??????????????????????????仯??  相似文献   
997.

The moisture transport history to the south of the Tibetan Plateau was modeled using the meteorological data provided by NCEP in this paper, and the modeled results were compared with the measured δ18O in the south of the Tibetan Plateau. The relation between δ18O in precipitation in the south of the Tibetan Plateau and moisture trajectories was discussed. The results show that the extremely low δ18O in precipitation in the south of the Tibetan Plateau is always related to the moisture from the low-level sea surface evaporation. The long-distance transport of moisture also contributes to low δ18O in precipitation probably due to the rainout process during moisture transport. It is also found that low δ18O in precipitation is also related with deep layer transport of moisture, and with intensive condensation in the upper layers of the atmosphere, resulting in low δ18O because of depletion of heavy isotopes in deep condensation. However, high δ18O in precipitation whether in monsoon period or not is always companied with moisture coming from the upper layers, and the moisture is from northern or western sides of the plateau. The interpretation of the modeled results is in agreement with the isotope fractionation processes.

  相似文献   
998.
固体潮观测数据在进行各种分析之前,需进行平滑处理以便消除各种突跳及错误数据。常用的平滑方法有Lecolazet数字滤波法和Nakai方法。本文讨论了各种方法的特点及存在问题。为了经济、快速而又有效地平滑数据,提出如下建议:对于高精度的观测数据,通常使用数字滤波法处理即可;在少数情况下,数据中出现连续错数,这时可取卅天为时间间隔,在上述滤波法平滑的基础上,分段对数据进行调和分析,如果某几段调和分析的误差较大,那末再进一步对这些数据段用Nakai法进行平滑处理。  相似文献   
999.
为提高测震数据流服务器的性能及安全性,提出了采用LVS服务器集群技术构建测震数据流服务器集群的方案,通过选用恰当的IP负载均衡技术及连接调度技术,较好的克服了单台服务器性能瓶颈问题,同时增强了地震数据流服务器系统的容错性及可靠性。  相似文献   
1000.
和田地震台阵勘址测量与数据分析   总被引:1,自引:1,他引:0  
介绍了新疆和田地震台阵候选台址现场勘址测量及后续数据处理分析等内容,为确定台阵的最终台址和子台布局提供了可靠的数据基础。  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