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   717篇
  免费   47篇
  国内免费   50篇
化学   172篇
力学   15篇
综合类   11篇
数学   16篇
物理学   78篇
综合类   522篇
  2024年   2篇
  2023年   6篇
  2022年   15篇
  2021年   10篇
  2020年   34篇
  2019年   9篇
  2018年   9篇
  2017年   13篇
  2016年   20篇
  2015年   25篇
  2014年   47篇
  2013年   48篇
  2012年   46篇
  2011年   49篇
  2010年   28篇
  2009年   46篇
  2008年   42篇
  2007年   51篇
  2006年   47篇
  2005年   37篇
  2004年   30篇
  2003年   29篇
  2002年   29篇
  2001年   17篇
  2000年   19篇
  1999年   8篇
  1998年   9篇
  1997年   18篇
  1996年   11篇
  1995年   7篇
  1994年   9篇
  1993年   7篇
  1992年   8篇
  1991年   7篇
  1990年   8篇
  1989年   4篇
  1988年   3篇
  1987年   2篇
  1985年   4篇
  1983年   1篇
排序方式: 共有814条查询结果,搜索用时 9 毫秒
41.
李作明 《力学学报》2003,11(1):111-112
主要阐述了香港作为世界最大集装箱海港的各种优势,同时指出为保持这种优势应注意的一些事项。  相似文献   
42.
We present the results of a re-analysis of a previously published carbon isotope data-set related to coralline sponges in the Caribbean Sea. The original interpretation led to the discrimination between a pre-industrial period, with a signal controlled by solar-induced climatic variations, followed by the industrial era, characterized by a progressive δ13C negative shift due to the massive anthropogenic carbon emissions. Our re-analysis allowed to extract from the raw isotopic data evidence of a solar forcing still visible during the industrial era, with a particular reference to the 88-year Gleissberg periods. These signals are related to slope changes in both the δ13C versus time and the δ13C versus carbon emission curves.  相似文献   
43.
爱迪生珍珠和珈百丽珍珠为近年来相继问世的优质淡水有核珍珠,分别酷似南洋珠和AKOYA珍珠,如何区分白色珍珠、金色珍珠、黑色珍珠及银灰色珍珠的类型和颜色成因,成为目前检测机构棘手的难题。对132颗不同类型的白色系、黄色系、黑色系、灰色系天然呈色珍珠与染色或辐照改色的各类珍珠进行了系统的PL光谱测试分析,结果表明不同类型的珍珠PL光谱有重要鉴别特征,尤其是PL光谱中荧光背景强度(F)与565 nm文石主峰强度(A)比值F/A,可有效区分不同类型白色珍珠以及黑色、金色银灰色珍珠的颜色成因。(1)白色南洋珠F/A值多集中于1附近,白色爱迪生珍珠与白色珈百丽珍珠具有类似的PL光谱与F/A值变化范围,但大部分样品出现631 nm发光峰,F/A值多集中于2;白色AKOYA珍珠的F/A值大于10。(2)金色南洋珠的F/A值多集中于1.6,变化范围较小,染金色南洋珠与染金色爱迪生珍珠F/A值基本都大于4。(3)深灰色体色Tahiti黑珍珠没有特征的发光峰,但随着颜色加深,逐渐出现617 nm处发光峰,黑色体色Tahiti黑珍珠具有稳定的有机卟啉相关的617和650 nm处发光峰;而绝大部分染色、辐照的黑色珍珠样品并未出现明显的荧光背景增强现象,但缺失617和650 nm处发光峰。(4)天然呈色银灰色AKOYA样品F/A值都小于3,而染色和辐照成因的银灰色AKOYA的F/A值都明显高(1.79~144),并且因改色方式不同,存在一定的变化范围。  相似文献   
44.
本文对河北平原旱涝与北太平洋海温距平之间关系进行了研究,发现东太平洋赤道区和黑潮区海温异常分布对河北旱涝影响最为显著。基于统计分析结果,本文提出了北太平洋海温异常对河北平原旱涝影响的可能途径。  相似文献   
45.
46.
This note studies the Radiolarian fossil groups since 1.2 MaBP in ODP leg 184 site 1143, the southern South China Sea (SCS). The result shows that radiolarian abundance experienced a significant variation: before 0.9 MaBP it remained at the extremely low level, but increased with low extent between 0.9–0.65 Ma, which corresponded to the Mid-Pleistocene Transition stage, and it increased rapidly after 0.65 MaBP. During the whole process, the average abundance became higher and higher in each stage, and showed regularly periodic fluctuations. The obvious increase after 0.65 MaBP is inferred to result from the enhanced upwelling in this region, which was induced by the intensified monsoon circulation after the “Mid-Pleistocene Transition”. An outstanding result of the spectral analyses is that a long oscillation of ∼ 0.2 Ma cycle was found in the records of radiolarian abundance and complex diversity, which corresponds well to the result of other paleoceanographic indexes. This probably indicated a special cycle characteristic of paleoecological environment evolution in this area. In addition, all of the radiolarian indexes show an obvious boundary in about 0.47 MaBP, indicating the abrupt variation of the community structure and radiolarian abundance level before and after 0.47 MaBP. So we suppose that there existed a distinct change event of oceanic ecology environment during that period.  相似文献   
47.
Linear sand ridges on the outer shelf of the East China Sea   总被引:3,自引:1,他引:3  
Based on the latest full-coverage high-resolution multi-beam sounding data, the distribution of the linear sand ridges on the outer shelf of the East China Sea (ECS) is studied with quantitative statistical analysis. The study area can be divided into the northeastern part and the southwestern part. Sand ridges in the northeastern area, trending 116°N, show obvious linear character and shrink to the inner shell Sand ridges in the southwestern area, trending 120°N -146°N, tend to have net form. Sand ridges gradually become sand sheets in the center part of study area. Sand ridges are distributed landward to the isobath of 60m, distributed seaward to the water depth of 120 m in the northeast and 150 m in the southwest. Immature sand ridges are observed at water depth of 130-180 m in the southwestern depressions. The acoustic reflection properties of the internal high.angle inclined beddings of the sand ridges are analyzed based on the typical seismic profiles close to the research area. Lithological analysis and dating of 4 boreholes and 12 cores indicate that the widely distributed transgressive sand layer with high content of shell debris which was formed in the early-middle Holocene is the main composition of the linear sand ridges on the outer shelf of the ECS. The dominating factor in formation, developing and burying of the sand ridges is the variation of water depth caused by sealevel change and the rate of sediment supply. In 12400 aBP the cotidal lines of the M2 tidal component were closely perpendicular to the strike-directions of the sand ridges in the study area, and the tidal wave system during 12000-8000 aBP might play a key role in the formation of the linear sand ridges which are widely distributed on the outer shelf of the ECS.  相似文献   
48.
简述了生态脆弱性的概念,从自然和人为干扰两个方面分析了邛海流域的生态脆弱性特征及其成因,并对解决邛海流域的生态脆弱性问题提出了相关的建议。  相似文献   
49.
A VERTICALLY UNIFORM LAYER OF TEMPERATURE(ISOTHERMAL LAYER),SALINITY(ISOHALINE LAYER)AND DENSITY(MIXED LAYER)IS USUALLY FORMED IN THE UPPER OCEAN DUE TO THE WIND STIRRING.UNDERNEATH IS THE LAYER WITH RELATIVELY STRONG VERTICAL GRADIENT AS THE THERMOCLINE,…  相似文献   
50.
本文根据1986—1992年东海北部拖虾调查及虾类资源动态监测调查资料,分析了10种群体数量大、经济价值高的虾类的渔业生物学特性,比较了各群体的体长、体重组成,体长与体重的关系以及繁殖、生长等特点,阐明其规律性及异同关系,为合理利用本海域的虾类资源提供科学依据。  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