全文获取类型
收费全文 | 355篇 |
免费 | 67篇 |
国内免费 | 109篇 |
专业分类
大气科学 | 4篇 |
地球物理 | 143篇 |
地质学 | 189篇 |
海洋学 | 32篇 |
天文学 | 139篇 |
综合类 | 16篇 |
自然地理 | 8篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 5篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 16篇 |
2015年 | 3篇 |
2014年 | 9篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 16篇 |
2010年 | 17篇 |
2009年 | 18篇 |
2008年 | 24篇 |
2007年 | 29篇 |
2006年 | 22篇 |
2005年 | 27篇 |
2004年 | 20篇 |
2003年 | 26篇 |
2002年 | 15篇 |
2001年 | 24篇 |
2000年 | 55篇 |
1999年 | 65篇 |
1998年 | 30篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有531条查询结果,搜索用时 343 毫秒
401.
Based on the data of the Jiaozbou Bay Ecosystem Dynamic Research,cell volume and surface area of 87 common phytoplankton species in China sea waters were calculated with assignment of the similar geometric form.The cell plasma volume,live weight,carbon mntent and nitrogen content were also calculated with the methods of Mullin et al.(1966),5trathmann(1967),Eppley et al.(1970),arid Taguchi(1976).After comparing these methods,we chose the method of Eppley et al.(1970) as the best method for calculating phytoplankton carbon content in China sea waters. 相似文献
402.
电感耦合等离子体原子发射光谱的若干进展 总被引:16,自引:4,他引:12
综述了近年来电感耦合等离子体原子发射光谱在基础理论研究、进样技术以及广泛的分析应用领域方面的进展,并简介了对仪器装置的改进和研制。引用文献108篇。 相似文献
403.
利用一维自洽的时变极区电离层模型,研究极隙区极光粒子沉降对极区电离层F层电子密度影响的时变过程。假设一维时变电离层模型描述的磁流管中F层等离子体在对流作用下经过极隙区,随对流路径的不同,磁流管在极隙区经历的时间不同,以此考察极光粒子沉降作用下电离层随时间的演化过程。数值计算结果表明,当磁流管在极隙区停留的时间足够长,F层电子密度能显著增大。然而在磁流管经历极隙区实际时间较短的情况下,极隙区极光粒子沉降对F层电子密度的影响并不大。本文还给出了统计对流模型作用下磁流管在经历极隙区时,有沉降粒子作用和没有沉降粒子作用两种情况下,F层等离子体的时间变化过程的差异。 相似文献
404.
报道了HL-2A装置最新的实验结果,讨论并研究了超声分子束的注入位置对分子束在等离子体中的消融和穿透的影响,其中包括电离后的分子束粒子在磁场梯度作用和 E × B 漂移下的加速或减速及由此形成的冷通道效应.研究结果表明,磁场梯度和 E × B 漂移对于超声分子束的加料效果、消融和穿透有着重要的作用.强场侧注入可使电离后的电子和离子更深地进入等离子体芯部.这些研究对于更好地理解超声分子束与等离子体的相互作用和优化设计加料系统有一定作用. 相似文献
405.
406.
Using the reductive perturbation method, we investigate the small amplitude nonlinear acoustic wave in a collisional self-gravitating dusty plasma. The result shows that the small amplitude dust acoustic wave can be expressed by a modified Korteweg-de Vries equation, and the nonlinear wave is instable because of the collisions between the neutral gas molecules and the charged particles. 相似文献
407.
The effects of environmental Na /K ratio on the gill ion-transport enzyme activity,plasma osmolality and growth ofCynoglossus semi/aevis juveniles were investigated.The results showed that,plasma osmolality was similar among flounder adaptedto different Na /K ratios of saline groundwaters (P>0.05),while the growth,gill Na ,K -ATPase and HCO,3'--ATPase activities wereaffected by Na /K ratio significantly (P<0.05).The gill Na ,K -ATPase activity reached its maximum on day 3,then decreasedgradually from day 3 to day 9 and remained constant from day 9 to day 15.The peak values of gill Na ,K -ATPase activity weredetected on day 3 for all Na /K ratios of saline groundwaters,then the enzyme activities descended,and on day 9 the enzyme activi-ties achieved steady state,and the gill HCO,3--ATPase activity increased rapidly and achieved steady state after one day.Duringsteady state,the gill Na ,K -ATPase and HCO,3--ATPase activity of Na /K ratios 20 and 40 treatments were significantly higherthan those in the control group (Na /K ratio 27.5),while there were no significant differences between the Na /K ratio 30 treatmentand the control group; the gill Na ,K -ATPase activity of Na /K ratio 20 and 40 treatments were significantly higher than that forratio 30 treatment,but there were no significant differences of gill HCO3-ATPase activity among these treatments.At the end of the15-day experiment,the weight gain (%) and specific growth rate (SGR) of flounders maintained in seawater were significantly higherthan those in groundwaters; significant differences also occurred among the treatments; Na /K ratio 30 treatment had the highestvalues (33.7% and 1.94 respectively),which were significantly higher than those under Na /K ratios 20 and 40 treatments.There-fore,for the saline groundwater used in this experiment,it is suggested that the Na /K ratio be adjusted to approximately 30,I.e.,asclose to that of natural seawater as possible in the culture of flounder. 相似文献
408.
The effects of environmental Na+/K+ ratio on the gill ion-transport enzyme activity, plasma osmolality and growth of Cynoglossus semilaevis juveniles were investigated. The results showed that, plasma osmolality was similar among flounder adapted to different Na+/K+ ratios of saline groundwaters (P>0.05), while the growth, gill Na+, K+-ATPase and HCO3
−-ATPase activities were affected by Na+/K+ ratio significantly (P<0.05). The gill Na+, K+-ATPase activity reached its maximum on day 3, then decreased gradually from day 3 to day 9 and remained constant from day
9 to day 15. The peak values of gill Na+, K+-ATPase activity were detected on day 3 for all Na+/K+ ratios of saline groundwaters, then the enzyme activities descended, and on day 9 the enzyme activities achieved steady state,
and the gill HCO3
−-ATPase activity increased rapidly and achieved steady state after one day. During steady state, the gill Na+, K+-ATPase and HCO3
−-ATPase activity of Na+/K+ ratios 20 and 40 treatments were significantly higher than those in the control group (Na+/K+ ratio 27.5), while there were no significant differences between the Na+/K+ ratio 30 treatment and the control group; the gill Na+, K+-ATPase activity of Na+/K+ ratio 20 and 40 treatments were significantly higher than that for ratio 30 treatment, but there were no significant differences
of gill HCO3
−-ATPase activity among these treatments. At the end of the 15-day experiment, the weight gain (%) and specific growth rate
(SGR) of flounders maintained in seawater were significantly higher than those in groundwaters; significant differences also
occurred among the treatments; Na+/K+ ratio 30 treatment had the highest values (33.7% and 1.94 respectively), which were significantly higher than those under
Na+/K+ ratios 20 and 40 treatments. Therefore, for the saline groundwater used in this experiment, it is suggested that the Na+/K+ ratio be adjusted to approximately 30, i.e., as close to that of natural seawater as possible in the culture of flounder. 相似文献
409.
为明确海洋生物体中微量元素的含量状况,开发了一种适合海洋生物体中微量元素准确测定的分析方法。研究采用防腐高效溶样罐对GBW08517(海带Saccharina japonica)与GBW08571(贻贝Mytilus coruscus Goyld)2种国内海洋生物标准物质进行2种不同前处理方法的消解实验,然后应用电感耦合等离子质谱仪(ICP-MS)测试了包括稀土元素在内的33个微量元素。实验结果表明,除个别元素外,测试结果均与标准值相符合,且前处理方法1消解的生物样品测试结果更加准确和稳定。使用防腐高效溶样罐优化了生物样品处理的消解方法,能有效去除生物样品中的有机基体,使ICP-MS充分发挥优势。与以往的消解方法相比,在生物消解中效果优于微波消解,前处理方法1还具有易操作、处理效率高、低试剂消耗、安全性强、避免样品污染等优点。 相似文献
410.
采用HClHNO3HF HClO4,HClHNO3HF H2SO4敞口和HClHNO3HFHClO4,HClHNO3HF H2SO4微波消解4种方法溶矿,利用电感耦合等离子体发射光谱(ICPAES)测定,建立了钛铁矿中钾、钠、钙、镁、钡、锶、锌等元素的同时测定方法。对电感耦合等离子体发射光谱仪测定的最佳仪器条件及分析谱线进行了选择,并对钛、铁基体的影响、溶矿提取酸度以及溶矿残渣进行了研究。实验结果表明:采用HClHNO3HF HClO4敞口溶矿,具有检出限低、灵敏度高,操作简便、快速等突出优点。该方法测定值与推荐值基本吻合,分析方法的精密度满足《地质矿产实验室测试质量管理规范》的要求。 相似文献