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61.
Jianfei Tang Dejin Wu Guoqing Zhao Ling Chen Chengming Tan 《Astrophysics and Space Science》2014,353(1):131-135
Langmuir waves (LWs), which are believed to play a crucial role in the plasma emission of solar radio bursts, can be excited by streaming instability of energetic electron beams. However, solar hard X-ray observations imply that the energetic flare electrons usually have a power-law energy distribution with a lower energy cutoff. In this paper, we investigate LWs driven by the power-law electrons. The results show that power-law electrons with the steepness cutoff behavior can excite LWs effectively because of the population inversion distribution below the cutoff energy (E c ). The growth rate of LWs increases with the steepness index (δ) and decreases with the power-law index (α). The wave number of the fastest growing LWs (kλ D ), decreases with the characteristic velocity of the power-law electrons ( \(v_{c}=\sqrt{2E_{c}/m_{e}}\) ) and increases with the thermal velocity of ambient electrons (v T ). This can be helpful for us to understand better the physics of LWs and the dynamics of energetic electron beams in space and astrophysical plasmas. 相似文献
62.
G. P. Chernov R. A. Sych Yihua Yan Qijun Fu Chengming Tan Guangli Huang De-Yu Wang Hongao Wu 《Solar physics》2006,237(2):397-418
We present results of the first simultaneous observations of zebra patterns (ZPs) with super-fine spiky structure in the microwave range made at two observatories ~1000 km apart (Beijing and Nanjing, China). The fine structure was recorded by a spectra polarimeter in the 5.2 – 7.6 and 2.8 – 3.6 GHz ranges at the Huairou station and by the spectrometer in the 4.5 – 7.5 GHz range at the Purple Mountain Observatory. Simultaneously, the locations of radio sources were observed by the Siberian Solar Radio Telescope (SSRT) at 5.7 GHz. For a general analysis of the April 10, 2001 event, the Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) data and Transition Region and Coronal Explorer (TRACE) images in EUV 171 Å line were used. The circular polarization degree was very weak for the burst background radio emission and moderate to strong for the fine structure. The polarization sign in all the cases probably corresponds to the extraordinary wave mode. Estimations of the magnetic field values in the whistler model for fine structure agree well with the extrapolated values from magnetic maps. Given the possibility of wave transformation in the perpendicular magnetic field and the spiky structure of the ZP, the whistler wave model appears to be the most appropriate explanation for the zebra stripe phenomenon. 相似文献
63.
空间关系描述的9-交模型 总被引:1,自引:0,他引:1
首先对4元组、9元组描述框架进行了剖析,指明了从4元组向9元组扩展的意义,同时也论述了9元组存在的缺点和不足及其产生的原因。最后,提出用空间实体的势力范围(AV)代替原9元组中的“补”作为空间实体的外部,并结合空间实体的边界(A)、内部(A°),构成新的基于空间实体势力范围的空间关系描述的9-交模型(简称NIV),并对其特点进行了分析。 相似文献
64.
树状河系作为地图骨干要素之一,其简化效果直接决定地图综合的质量。树状河系简化需要考虑其语义、几何、拓扑和结构等多种特征,而现有方法大多只注重了长度、角度和属性等约束性量化指标,致使简化后的空间分布特征容易被破坏。本文首先研究基于树状河系有向拓扑树(DTT)的特征智能识别方法,然后依据Paiva提出的"180°假设"和"锐角假设",从河口出发,自下游向上游建立顾及河流语义、长度、角度约束的树状河系stroke连接,并据此判断树状河系层次关系,最后提出河系整体选取数量确定方法和顾及密度差异的河系分层剔除选取算法,实现树状河系自动化简化。经样本数据测试,验证了该方法的可靠性,同时经实际数据测试,验证了该方法在树状河系简化中的合理性和有效性。 相似文献
65.
太阳射电宽带动态频谱仪1.10~2.06 GHz、2.6~3.8 GHz、5.2~7.6 GHz从2000年~2005年同时在3个频段上观测到复杂型频谱事件(45C爆发:双峰或多峰结构,单频辐射流量小于500 sfu)158个,有139个事件对应高能事件,其中对应X级耀斑3个,对应M级耀斑86个,对应C级耀斑44个。36个爆发对应发生日冕物质抛射(Coronal Mass Ejection,CME)事件,29个事件对应有II型爆发,20个事件对应IV型爆发。在76个事件中显示了丰富的毫秒级精细结构,有尖峰辐射(Spike)、鱼群结构(Fish)、斑马纹结构(Zebra)、纤维结构(Fiber)、漂移脉动结构(DPS)、准周期振荡(QPPS)、M型结构以及II、III型爆发等。举两例说明复杂爆发的观测特征。 相似文献
66.
Electrical conductivity of alkali feldspar solid solutions at high temperatures and high pressures 总被引:1,自引:0,他引:1
Haiying Hu Heping Li Lidong Dai Shuangming Shan Chengming Zhu 《Physics and Chemistry of Minerals》2013,40(1):51-62
The electrical conductivities of alkali feldspar solid solutions ranging in chemical composition from albite (NaAlSi3O8) to K-feldspar (KAlSi3O8) were measured at 1.0 GPa and temperatures of 873–1,173 K in a multi-anvil apparatus. The complex impedance was determined by the AC impedance spectroscopy technique in the frequency range of 0.1–106 Hz. Our experimental results revealed that the electrical conductivities of alkali feldspar solid solutions increase with increasing temperature, and the linear relationship between electrical conductivity and temperature fits the Arrhenius formula. The electrical conductivities of solid solutions increase with the increasing Na content at constant temperature. At 1.0 GPa, the activation enthalpy of solid solution series shows strong dependency on the composition, and there is an abrupt increase from the composition of Or40Ab60 to Or60Ab40, where it reaches a value of 0.96 eV. According to these results in this study, it is proposed that the dominant conduction mechanism in alkali feldspar solid solutions under high temperature and high pressure is ionic conduction. Furthermore, since the activation enthalpy is less than 1.0 eV for the alkali feldspar solid solutions, it is suggested to be a model where Na+ and K+ transport involves an interstitial mechanism for electrical conduction. The change of main charge carriers can be responsible for the abrupt increase in the activation energy for Or60Ab40. All electrical conductivity data were fitted by a general formula in order to show the dependence of activation enthalpy and pre-exponential factor on chemical composition. Combining our experimental results with the effective medium theory, we theoretically calculated the electrical conductivity of alkali feldspar granite, alkali feldspar quartz syenite, and alkali feldspar syenite with different mineral content and variable chemical composition of alkali feldspar at high temperatures at 1.0 GPa, and the calculated results are almost in agreement with previous experimental studies on silicate rocks. 相似文献
67.
首先综述了数字省区地理空间框架的概念,剖析了其构成,即基础地理信息数据体系、目录与交换体系、公共服务体系、政策法规与标准体系和组织运行体系等五部分,在此基础上提炼并归结为基础地理信息数据库和地理信息公共平台两项任务,接下来阐述了它们的建设内容及流程。 相似文献
68.
An analysis of new observations showing fine structures consisting of narrowband fiber bursts as substructures of large-scale
zebra-pattern stripes is carried out. We study four events using spectral observations taken with a newly built spectrometer
located at the Huairou station, China, in the frequency range of 1.1 – 2.0 GHz with extremely high frequency and time resolutions
(5 MHz and 1.25 ms). All the radio events were analyzed by using the available satellite data (SOHO LASCO, EIT, and MDI, TRACE,
and RHESSI). Small-scale fibers always drift to lower frequencies. They may belong to a family of ropelike fibers and can
also be regarded as fine structures of type III bursts and broadband pulsations. The radio emission was moderately or strongly
polarized in the ordinary wave mode. In three main events fiber structure appeared as a forerunner of the entire event. All
four events were small decimeter bursts. We assume that for small-scale fiber bursts the usual mechanism of coalescence of
whistler waves with plasma waves can be applied, and the large-scale zebra pattern can be explained in the conventional double
plasma resonance (DPR) model. The appearance of an uncommon fine structure is connected with the following special features
of the plasma wave excitation in the radio source: Both whistler and plasma wave instabilities are too weak at the very beginning
of the events (i.e., the continuum was absent), and the fine structure is almost invisible. Then, whistlers generated directly at DPR levels
“highlight” the radio emission only from these levels owing to their interaction with plasma waves. 相似文献
69.
应用多个地震活动参数来判定断裂带分段落活动习性的方法,分析安徽省新生代构造变形带不同分段落的现今活动习性及地震危险性。研究结果表明:安徽省新生代构造变形带中存在着9个具有不同现今活动习性的分段落,其中,霍邱-风台、铜陵-宁国、明光-肥东3个段落现今活动习性处于较高应力背景下的相对闭锁状态.应属于有一定应变积累的潜在中强震危险段落:其它6个段落.现今活动习性处于中等或偏低应力背景下,以频繁或稀疏小震滑动为特征.未来复发中强以上地震的可能性较小。 相似文献
70.