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   7966篇
  免费   524篇
  国内免费   863篇
测绘学   1110篇
大气科学   666篇
地球物理   605篇
地质学   1312篇
海洋学   1199篇
天文学   12篇
综合类   817篇
自然地理   3632篇
  2024年   46篇
  2023年   87篇
  2022年   369篇
  2021年   400篇
  2020年   393篇
  2019年   466篇
  2018年   333篇
  2017年   420篇
  2016年   391篇
  2015年   409篇
  2014年   401篇
  2013年   706篇
  2012年   400篇
  2011年   446篇
  2010年   312篇
  2009年   398篇
  2008年   421篇
  2007年   429篇
  2006年   365篇
  2005年   341篇
  2004年   281篇
  2003年   246篇
  2002年   192篇
  2001年   163篇
  2000年   161篇
  1999年   129篇
  1998年   111篇
  1997年   96篇
  1996年   77篇
  1995年   66篇
  1994年   60篇
  1993年   51篇
  1992年   30篇
  1991年   26篇
  1990年   17篇
  1989年   14篇
  1988年   22篇
  1987年   17篇
  1986年   13篇
  1985年   11篇
  1984年   9篇
  1983年   10篇
  1982年   8篇
  1981年   2篇
  1980年   1篇
  1979年   3篇
  1978年   1篇
  1977年   2篇
  1973年   1篇
排序方式: 共有9353条查询结果,搜索用时 15 毫秒
21.
During the last few years, the north‐western part of Romania has been affected by catastrophic floods with most of the watercourses reaching their highest recorded discharges. This study reports the generation of a numerical terrain model and the simulation of a backwater phenomenon at elevation steps according to the volume of water accumulated at the confluence of the Buhai Brook with the Jijia River. The hydrological data are complemented by rainfall data and the careful recording of the flood behaviour during the entire period of its development. The main aim of the study is to identify the causes of the backwater phenomenon and to highlight the material damage inflicted on the town of Dorohoi. At the same time, the study uses cartographic model that was developed to establish which areas are at risk of flooding at various levels of probability. The catastrophic flood began on the Buhai Brook, a slow‐flowing stream that drains the areas to the west of the town of Dorohoi and discharged into the upstream sector of the Jijia confluence. The flood caused two types of backwater waves: one behind the bridges and the houses built on the floodplain and a second that followed the course of the main stem (Jijia) upstream from the confluence, flooding the Ezer Lake, which was created specifically to attenuate such floods. The spillway backwater phenomenon was inter‐basin as it did not occur in a single hydrographic basin. The causes of the catastrophic flash flood and of the inter‐basin backwater overflow are natural but also reflect anthropogenic influence. After the lake filled, the discharge into the Jijia was controlled and the flooding downstream was thus greatly diminished. Though fortuitous, the backwater flooding was important in mitigating the impact of the flood wave from the Jijia River. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
22.
城市基础地理信息系统中大比例尺地形图分幅与编号   总被引:1,自引:0,他引:1  
结合城市基础地理信息系统的特点和要求,在原有的地图分幅与编号方法的基础上,提出了一种新的城市基础地理信息系统的地图分幅与编号方法即数字编码法。详细介绍了该方法的规则、特点及其在计算机上的实现。  相似文献   
23.
李焰  梁美丽 《北京测绘》2021,35(2):222-229
城市开发边界的划定可以在一定程度上引导城市空间的良性扩张。为了研究边界划定的方法,以我国某港口城市作为研究区域,在空间增长模拟的方向进行探索。研究中借助土地适宜性评价和元胞自动机边界工具,构建既符合生态资源环境要求又符合城市发展需要的边界划定,同时,为了实现城市用地健康和动态管控举措,提出了建立健全土地用地管理机制的要求。  相似文献   
24.
25.
26.
Abstract.  Photosynthesis and growth rates in samples of two green seaweeds ( Ulva and Enteromorpha ) were monitored in the laboratory. The macroalgae were collected every 15 days from four coastal embayments in Galicia (NW Spain). Ulva samples were found to be nutritionally limited, particularly in summer. The physiological activity of Enteromorpha did not appear to be as affected by nutrient scarcity, although it may have suffered from phosphorus limitation. The subsistence quotas, critical concentrations and storage capacity for N and P in Ulva were comparable to those obtained by other investigators in similar studies. The trace metals analysed apparently did not negatively affect the macroalgae at the measured concentrations; one explanation is that many of these metals function as essential micronutrients. The complex physiological interactions between metals and nutrients, however, may complicate interpretation of the results.  相似文献   
27.
南海西北部水域斑节对虾资源的调查研究   总被引:2,自引:0,他引:2  
1989-1991年对南海西北部水域进行斑节对虾Penaeusmonodon资源专项调查。结果表明,斑节对虾的密集分布区在海南岛东部和南部海区,其现存资源量为82.6万尾,周年有体长30mm以下的幼虾出现。主要产卵期在9-12月。产卵场在海南岛东部和南部水深30-60m的海区。  相似文献   
28.
本文研究探索了一种快速简单易行的海洋防污剂室内评价筛选方法。将待测防污剂均匀分散于凝胶溶液中,然后均匀涂布到一定面积的玻璃板上,固化得到含防污剂凝胶测试板,将其置于接种有三种分离自舟山以东海域的优势海洋菌种(编号为Y-16,W-1和F-6)的人工加富海水中,连续培养24h后显微镜下可发现凝胶板表面上细菌菌落,将凝胶板表面细菌淋洗、定容,测定其光密度(optical density,OD)值,计算平均抑菌率,得到吡啶硫酮锌(ZPT)为38.87%,吡啶硫酮铜(CPT)为41.24%,三甲基氧化锡(TBTO)为65.19%,N,N-二甲基-3,4-二氯苄胺(DCDMA)为30.88%,敌草隆(Diuron)仅为15.29%,抑菌性大小为TBTOCPTZPTDCDMADiuron。实验结果表明5种受试防污剂的抑菌性大小为TBTOCPTZPTDCDMADiuron。采用绘制OD-t生长曲线法,分别得到5种防污剂对3种海洋细菌的最小抑制浓度(minimum inhibitory concentration,MIC),TBTO对三种菌的MIC均为0.5×10–3mg/mL;CPT对W-1和F-6的MIC为0.97×10–3mg/mL,对Y-16的MIC为1.93×10–3mg/mL;ZPT对W-1和Y-16的MIC为1.91×10–3mg/mL,对F-6的MIC为0.96×10–3mg/mL;DCDMA对W-1和F-6的MIC为8.46×10–3mg/mL,对Y-16的MIC为×10–342.29mg/mL。其中,Diuron对细菌的生长几乎没有抑制作用。其抑菌性与室内短期挂板结果具有一致性,表明经OD-t生长曲线得到的MIC可作为溶剂可溶型防污剂评价的辅助方法。另外,将本文中室内短期挂板方法应用于不同粒径的氧化亚铜的防污评价,也取得了与文献一致的结果。  相似文献   
29.
Neothyris lecticularis (Deshayes, 1839) live mainly south o'f 44°S in waters 90–180 m (extremes 18–384 m) deep where bottom temperatures are always >7°c. Fossil N. “avails” (Hutton, 1886) in the early Pleistocene limestone at Castlepoint (41 °S) are associated with an assemblage of animals generioally the same as the living N. lenticularis assemblage of Foveaux Strait. The granular substrate occupied by the living animals is similar to the matrix of the Castlepoint limestone. Thus the early Pleistocene marine climate in 90–180 m at 43°S may have been about 5°c cooler than it is today; the possible use is mentioned of the presence of the fossil assemblage in studies of palaeoelimates.

Population analysis of living and fossil stocks show a constant bias toward the older age‐groups; this finding is discussed. Various ecological observations are recorded.  相似文献   
30.
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