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   158篇
  免费   22篇
  国内免费   61篇
测绘学   14篇
大气科学   17篇
地球物理   16篇
地质学   59篇
海洋学   71篇
天文学   12篇
综合类   43篇
自然地理   9篇
  2023年   1篇
  2022年   8篇
  2020年   6篇
  2019年   12篇
  2018年   9篇
  2017年   2篇
  2016年   4篇
  2015年   7篇
  2014年   10篇
  2013年   16篇
  2012年   13篇
  2011年   16篇
  2010年   6篇
  2009年   15篇
  2008年   13篇
  2007年   11篇
  2006年   20篇
  2005年   13篇
  2004年   8篇
  2003年   10篇
  2002年   6篇
  2001年   4篇
  2000年   7篇
  1999年   4篇
  1998年   3篇
  1997年   2篇
  1996年   1篇
  1995年   3篇
  1994年   2篇
  1993年   2篇
  1991年   1篇
  1990年   1篇
  1988年   4篇
  1984年   1篇
排序方式: 共有241条查询结果,搜索用时 15 毫秒
101.
Samples of spiral galaxies from two catalogues of 21 cm line observations and a catalogue of near-infrared observations of nearby galaxies have been used in conjunction with Infrared Astronomical Satellite data to study correlations involving MG, the dynamic mass of the galaxies, the luminosities in theH band (1.6Μm), the blue band and the far infrared bands and the mass of atomic hydrogen, it is found that both the blue and the far-IR luminosities which are indicators of star formation averaged over ∼3 × l09 and ∼107 years respectively, have a linear dependence onM G On the other hand, theH luminosity which is a measure of star formation averaged over the lifetime of galaxies, has a steeper power law dependence onM G. The correlations observed do not have significant dependence on the morophological type of the galaxies There is a poor correlation between the far-infrared luminosity and the mass of atomic hydrogen. The mass of atomic hydrogen has a dependence of the formM G. Because of the decrease in the mean mass for later morphological types and due to differences in power law dependences of luminosities in different bands onM G, the mean value of luminosity-to-mass ratio is a constant for blue and far-IR bands, decreases for theH band and the gas-to-mass ratio increases as morphological type increases.  相似文献   
102.
The well-known shell supernova remnant (SNR) HB3 is part of a feature-rich star-forming region together with the nebulae W3, W4, and W5. We study the HI structure around this SNR using five RATAN-600 drift curves obtained at a wavelength of 21 cm with an angular resolution of 2′ in one coordinate over the radial-velocity range ?183 to +60 km s?1 in a wider region of the sky and with a higher sensitivity than in previous works by other authors. The spatial-kinematic distribution of HI features around the SNR clearly shows two concentric expanding shells of gas that surround the SNR and coincide with it in all three coordinates (α, δ, and V). The outer shell has a radius of 133 pc, a thickness of 24 pc, and an expansion velocity of 48 km s?1. The mass of the gas in it is ≈2.3 × 105M. For the inner shell, these parameters are 78 pc, 36 pc, 24 km s? 1, and 0.9 × 105M, respectively. The inner shell is immediately adjacent to the SNR. Assuming that the outer shell was produced by the stellar wind and the inner shell arose from the shock wave of the SNR proper, we estimated the age of the outer shell, ≈1.7 × 106 yr, and the mechanical luminosity of the stellar wind, 1.5 × 1038 erg s?1. The inner shell has an age of ≈106 yr and corresponds to a total supernova explosion energy of ≈1052 erg.  相似文献   
103.
本文讨论了带有极大值项的一阶中立型差分方程Δ (xn - pnxn-k) +qn maxs∈ [n-l,n] xs=0解的振动性 ,得到了该方程所有解振动的 1个新的充分性条件。特别当 pn =1 ,得到了该方程有非振动解的充分必要条件。  相似文献   
104.
The food selectivity of tethered females of the copepodCalanus helgolandicus was examined by using the colorimetric approach. First, feeding behavior of the copepod did not show any differences between the red-color stained with neutral red and non-stained diets using the diatomCoscinodiscus curvatulus. Then, the copepods were fed a mixtures of two diets, the diatomC. curvatulus, stained with neutral red, and the dinoflagellateGymnodinium sanguineum for 14~60 minutes of feeding duration. The foregut colors of females were examined using a stereo-microscope and a video monitor. The foreguts of animals fed with a high density of diatoms in mixed diets showed a dark red color, whereas those fed with a high density of dinoflagellate in mixed diets were a dark yellow. The results suggest that this species of copepod may not selectively feed either one of the diets used for this study. Their feeding activity may be more likely related to the density of available prey in their environment. Therefore, this quick and easy colorimetric approach could provide very useful information, like the pre-screening procedure before designing and conducting the time-consuming and complex feeding experiments to understand the feeding ecology of copepods.  相似文献   
105.
利用分光光度计比色法测定了温度、pH值和Hg2 等9种金属离子对体长24.2cm±0.7cm仿刺参(Apostichopusjaponicus)消化道中蛋白酶活性的影响。结果表明,蛋白酶的最适温度为40℃,对热不稳定,最适pH为7.2。Hg2 ,Mn2 ,Ag ,Pb2 ,Ba2 ,Ca2 对蛋白酶的活性有抑制作用,抑制作用由强至弱依次为Hg2 >Ag >Mn2 >Pb2 >Ca2 >Ba2 ,其中Hg2 和Ag 与对照差异极显著(P﹤0.01),表现出极强的抑制作用;Cu2 ,Zn2 ,Mg2 则对酶活有一定的促进作用,其促进作用大小依次为Mg2 >Zn2 >Cu2 ,Mg2 与对照差异显著(P﹤0.05)。  相似文献   
106.
鲅鱼(Spanish mackerel)加工后的废弃物富含蛋白质,为了提高蛋白质的利用率并减少环境污染,可以采用微生物发酵的方法酶解这部分蛋白质制取抗氧化活性肽。本实验室已经筛选出一株芽孢杆菌(Bacillus subtilis)Hy-2,以其发酵水产加工废弃物得到了具有较高抗氧化性的产物。为了进一步提高产物的抗氧化性,作者以该株产蛋白酶芽孢杆菌Hy-2为出发菌,采用常压室温等离子体(ARTP)诱变的方法筛选出1株突变菌Hy-23,以鲅鱼加工后的废弃物为原料,接种该突变菌株进行发酵,得到了具有一定抗氧化活性的发酵产物,酶解物总抗氧化活性提高了12.4%。经遗传稳定性测定,该芽孢杆菌突变株在传代8次之后其遗传稳定性仍然良好。  相似文献   
107.
Factures caused by deformation and destruction of bedrocks over coal seams can easily lead to water flooding (inrush) in mines, a threat to safety production. Fractures with high hydraulic conductivity are good watercourses as well as passages for inrush in mines and tunnels. An accurate height prediction of water flowing fractured zones is a key issue in today's mine water prevention and control. The theory of leveraging BP artificial neural network in height prediction of water flowing fractured zones is analysed and app-lied in Qianjiaying Mine as an example in this paper. Per the comparison with traditional calculation results, the BP artificial neural network better reflects the geological condi-tions of the research mine areas and produces more objective, accurate and reasonable results, which can be applied to predict the height of water flowing fractured zones.  相似文献   
108.
将吸附原油的中性氧化铝柱用正己烷、含5%二氯甲烷的正己烷逐步淋洗链状烷烃,用二氯甲烷与正己烷体积比为2∶1的试剂逐步淋洗芳烃,通过分析淋洗过程中所得到的各个产物的色谱检测结果来揭示原油中链状烷烃和芳烃在中性氧化铝层析柱上的解析过程,提出了中性氧化铝作为层析柱吸附剂的结构模型,探讨了原油中链状烷烃、芳烃在中性氧化铝层析柱上的吸附机理,为原油中链状烷烃、芳烃的快速、完全分离提供理论依据。  相似文献   
109.
In 2009, New Zealand's new National-led government abandoned the Carbon Neutral Public Service (CNPS) programme, a Labour-led government initiative intended to help Government achieve carbon neutrality within its core agencies. This short analysis article provides an overview and brief assessment of the CNPS initiative by drawing on the relevant scholarly literature and public documents relating to New Zealand's climate change agenda. It is argued that although the CNPS programme faced a range of challenges it was successful in some respects. Although the Labour-led government was keen to act on climate change mitigation, New Zealand no longer intends to take a lead on carbon neutrality under the National-led government.  相似文献   
110.
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