全文获取类型
收费全文 | 293篇 |
免费 | 52篇 |
国内免费 | 50篇 |
专业分类
测绘学 | 26篇 |
大气科学 | 15篇 |
地球物理 | 57篇 |
地质学 | 156篇 |
海洋学 | 73篇 |
天文学 | 11篇 |
综合类 | 44篇 |
自然地理 | 13篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 11篇 |
2021年 | 17篇 |
2020年 | 12篇 |
2019年 | 17篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 15篇 |
2014年 | 26篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 21篇 |
2010年 | 19篇 |
2009年 | 20篇 |
2008年 | 11篇 |
2007年 | 6篇 |
2006年 | 12篇 |
2005年 | 15篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 18篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有395条查询结果,搜索用时 15 毫秒
271.
电离层影响下均匀半空间水平谐变电偶极子的电磁响应计算 总被引:3,自引:1,他引:2
空气介质和电离层是电导率不同的分层媒质,当研究由空气层中电流或磁矩激发的电磁场时,地面接收到的电磁波不仅受到空气介质、地下介质的影响,而且还受到电离层的影响。首先,推导出了电磁场一般边值问题,然后,将电离层、空气及地壳视为均匀、线性、各向同性的三层媒质,考虑地壳、空气、电离层的相互耦合,利用分离变量法推导求得了位于地壳表面水平谐变电偶极子的电磁响应表达式,通过这些表达式能够方便地求出电离层影响下均匀半空间空气层中的电磁场场值,同时,为后续的数值计算奠定了理论基础。 相似文献
272.
正Objective Dongsha waters are poorly studied for gas hydrates.Previous multi-channel seismic reflection and Chirp subbottom profiles show that numerous submarine mounds stand up to 100 m high above the seafloor over the continental slope of the SW Dongsha Island in northern margin of the South China Sea(SCS).These mounds are 相似文献
273.
在收集查阅国内外已有研究资料的基础上,对地下水中胶体稳定性、迁移机制以及模拟预测方法进行了详细归纳和总结。研究表明,胶体稳定性主要受自身理化性质和水文地球化学条件的影响,其受控于胶体粒径、形态、电势电位以及地下水的pH、离子强度等条件。胶体在多孔介质中的迁移机制主要表现为胶体沉积和形变阻塞,其中针对胶体稳定性的差异性,胶体沉积过程分别表现为表面封阻和过滤熟化。目前有关胶体在地下水中迁移的模拟技术已发展得日益成熟,但结合多孔介质非均质性和胶体化学性质非均质性的数学模型还需进一步探讨。 相似文献
274.
Flavobacterium columnare causes columnaris disease in freshwater fish. In the present study, the antigenic regions of five outer membrane proteins (OMPs), including zinc metalloprotease, prolyl oligopeptidase, thermolysin, collagenase and chondroitin AC lyase, were bioinformatically analyzed, fused together, and then expressed as a recombinant fusion protein in Escherichia coli. The expressed protein of 95.6 kDa, as estimated by 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was consistent with the molecular weight deduced from the amino acid sequence. The purified recombinant protein was used to vaccinate the grass carp, Ctenopharyngodon idella. Following vaccination of the fish their IgM antibody levels were examined, as was the expression of IgM, IgD and IgZ immunoglobulin genes and other genes such as MHC Iα and MHC IIβ, which are also involved in adaptive immunity. Interleukin genes (IL), including IL-1β, IL-8 and IL-10, and type I and type II interferon (IFN) genes were also examined. At 3 and 4 weeks post-vaccination (wpv), significant increases in IgM antibody levels were observed in the fish vaccinated with the recombinant fusion protein, and an increase in the expression levels of IgM, IgD and IgZ genes was also detected following the vaccinations, thus indicating that an adaptive immune response was induced by the vaccinations. Early increases in the expression levels of IL and IFN genes were also observed in the vaccinated fish. At four wpv, the fish were challenged with F. columnare, and the vaccinated fish showed a good level of protection against this pathogen, with 39% relative percent survival (RPS) compared with the control group. It can be concluded, therefore, that the five OMPs, in the form of a recombinant fusion protein vaccine, induced an immune response in fish and protection against F. columnare. 相似文献
275.
276.
Previous detailed studies of large rhyolite bodies propose that their elemental and isotopic characteristics were largely
acquired in shallow crustal magma chambers. This model explains the common chemical and isotopic zonations of large volumes
of rhyolites as well as the less common chemical and isotopic homogeneity of such bodies. We report an intermediate situation
(the Estérel massif, southeast France) in which chemical variations contrast with Nd-isotope homogeneity. We thus infer that,
in this case, large volumes of rhyolite resided for enough time in shallow magma chambers to develop chemical zonations through
differentiation, but this process was not accompanied by crustal assimilation. The subordinate amount of mafic rocks cropping
out in the Estérel probably evolved from basalt to trachyte through assimilation and fractional crystallization. The relatively
radiogenic Nd-isotope signatures of the rhyolite compared with the Hercynian crust show that it cannot have been generated
by partial melting of exposed basement rocks. Several geological similarities with large rhyolitic provinces could suggest
that the rhyolite was purely mantle derived or, alternatively, generated by partial melting of an ad hoc crustal component.
However, mineralogical, geochemical, and geodynamic connections between the Estérel rhyolite and the hypersolvus anorogenic
granites of Corsica, as well as the extreme Nd-isotope homogeneity of the rhyolite, lead us to propose that the rhyolite was
generated by mixing between mantle-derived magmas and a mafic lower crust. This scenario accounts for the relatively radiogenic
Nd-isotope signatures of the rhyolite compared with the Hercynian crust. The good Nd-isotope homogeneity observed in the rhyolite
implies that the mixing process, which occurred in the deep crust, was complete and provided a shallow magma chamber with
isotopically and probably chemically homogeneous magmas.
Received: 5 December 1997 / Accepted: 16 June 1998 相似文献
277.
转换横波共炮记录单程声波方程正演模拟 总被引:7,自引:1,他引:6
本文分别把分离的纵波和横波方程分裂为各自的两个单向旁轴方程(J.FClear-bout),然后用单程纵波和横波方程,结合相位移加有限差分混合波场延拓法(D.Ristow),在共炮记录叠前深度偏移原理的基础上,借鉴几何地震学的射线法两点问题原理,提出合成转换P—SV波共炮记录的时间一致性原理和逆过程方法,从而推导出精确的转换P—SV波共炮记录正演模拟算法,由于单程延拓波场,可完全解决多次反射波问题。 相似文献
278.
刘品 《中国气象科学研究院年报》2003,(1):27-28
受科技部委托,2003年12月3日中国气象局科技发展司主持对科技部攀登计划专项“海峡两岸及邻近地区暴雨试验研究”项目进行了结题验收。验收专家组一致认为,项目已按计划完成了预期任务,达到了预期目标。 相似文献
279.
刘品 《中国气象科学研究院年报》2004,(1):27-28
通过项目组全体科研人员的共同努力,国家自然科学基金“九五”重大项目“长江三角洲地区低层大气物理化学过程及其与生态系统的相互作用”历时6年,圆满完成。分析了长江三角洲地区大气-生态系统近期变化的动态、大气环境物理化学特征及有关痕量气体源汇分布;进行了水、热与物质(C、N)通量输送与转化的综合观测试验和数值模拟试验,就大气环境变化对典型农业生态系统影 相似文献
280.