全文获取类型
收费全文 | 78篇 |
免费 | 8篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 27篇 |
地球物理 | 15篇 |
地质学 | 33篇 |
海洋学 | 8篇 |
天文学 | 6篇 |
综合类 | 3篇 |
自然地理 | 5篇 |
出版年
2022年 | 6篇 |
2021年 | 1篇 |
2019年 | 2篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 1篇 |
2011年 | 7篇 |
2010年 | 2篇 |
2009年 | 7篇 |
2008年 | 4篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有99条查询结果,搜索用时 171 毫秒
91.
钻石与合成立方氧化锆外观相似,在没有鉴定仪器的条件下,使用10倍放大镜和肉眼观察颜色、光泽、色散、瑕疵、加工工艺、腰围等,辅以透字试验、亲油性实验、称重、测量直径等简单方法即可将钻石与合成立方氧化锆快速鉴别。 相似文献
92.
区域矿产资源经济综合评价是矿产普查与勘探学科和地质经济学科中十分重要的新分支.本文侧重讨论了区域矿产资源经济综合评价中的评价指标体系的构造、评价指标效果值的确定、综合评价方法和计算机评价系统的建立等问题. 相似文献
93.
设计了三条路线合成了席夫碱冠醚2,3:10,11-二苯并-1,12,15-三氧杂-5,8-二氧-2,3:4,5:8,9:10,11-十七环四烯(DTDC),并通过红外、紫外、伏安法等手段对产品的性状进行了表征。结果表明,设计的路线都是可行的,且具有简便、产物纯度高等优点。 相似文献
94.
95.
The P21/mC2/m displacive phase transition in the synthetic end-member amphibole Na NaMg Mg5 Si8 O22 (OH)2 has been studied by monitoring changes in unit-cell parameters and the intensities of superlattice reflections at 25–400 °C. This amphibole allows investigation of the effects of compositional variations at the A- and B-group sites upon the transition. Polynomial fitting of a 24 Landau potential to the evolution of the order parameter with T yielded a T
c of 257 ± 3 °C, and Landau coefficients compatible with a second-order transition. Structure refinement of single-crystal data collected at 25, 140, 270 and 370 °C allowed modelling of the structural changes as a function of T and symmetry. Crystal-chemical analysis suggests that differences in T
c in cummingtonites and in the crystal of this work depend mainly upon the relations between the aggregate ionic radii of the B- and C-group cations.
Electronic Supplementary Material: of Table 5 is available in the online version of this article at http://dx.doi.org/10.1007/s00269-003-0348-9 相似文献
96.
设计了一种基于正交调制原理的数字频率特性测试仪,系统用稳态响应法测量电路的频率特性.单片机作为主控芯片,完成系统的总体控制及数字信号处理;使用集成的直接数字频率合成芯片输出全频率范围内的正弦波.系统对待测电路的输入信号及其输出响应采样,经数字信号处理后,获得电路的幅频特性和相频特性.设计的测试仪测某RLC网络,中心频率的相对误差小于0.2%,有载品质因数相对误差小于1.25%,最大电压增益大于-1 dB.频率特性测试仪输入输出阻抗均为50 Ω,幅频误差绝对值小于0.5 dB,相频误差绝对值小于3°,测试仪能满足微机械谐振传感器特征参数测试需求. 相似文献
97.
时间尺度是通过综合众多精密时钟得到的。时间尺度的计算目前主要采用类ALGOS算法 ,这类算法的缺点是权值没有准确反映精密时钟噪声参数以及不能使五种噪声分量同时达到优化综合和不能形成实时的时间尺度。从精密时钟综合的优化算法原理出发 ,探讨了精密时钟噪声参数的估计、精密时钟噪声中噪声分量的分解等问题的解决方法 ,并由此提出了较优化的时间尺度算法 (精密时钟综合算法 ) ,还提出了对现有算法的改进意见。 相似文献
98.
Naphthalenesulfonates and their condensates with formaldehyde (SNFC) are widely used in industrial processes, e.g. as plasticizers for concrete or as tanning agents. Based on their high aqueous solubility these compounds are expected to be eliminated incompletely in mechanical-biological treatment plants and to end up in the aquatic environment. Due to the lack of reference compounds the identification and quantification of these condensates in the aquatic environment was impossible in the past. This paper describes the synthesis of several condensates of 2-naphthalenesulfonate with formaldehyde. With the synthesized products as reference compounds it was possible for the first time to detect and quantify some sulfonated naphthalene-formaldehyde condensates in the aquatic environment. For this purpose characteristic peaks in the HPLC screening of wastewater and river water samples were compared with the corresponding peaks of a technical SNFC product. Three out of several paths on which these compounds enter the aquatic environment were identified. The identified compounds in the analyzed wastewater samples have concentrations between 0.14 and 110 μg/L. 相似文献
99.
Long-term global emission scenarios enable the analysis of future climate change, impacts, and response strategies by providing insight into possible future developments and linking these different climate research elements. Such scenarios play a crucial role in the climate change literature informing the Intergovernmental Panel on Climate Change’s (IPCC) Assessment Reports (ARs) and support policymakers. This article reviews the evolution of emission scenarios, since 1990, by focusing on scenario critiques and responses as published in the literature. We focus on the issues raised in the critiques and the possible impact on scenario development. The critique (280) focuses on four areas: 1) key scenario assumptions (40%), 2) the emissions range covered by the scenarios and missing scenarios (25%), 3) methodological issues (24%), and 4) the policy relevance and handling of uncertainty (11%). Scenario critiques have become increasingly influential since 2000. Some areas of critique have decreased or become less prominent (probability, development process, convergence assumptions, and economic metrics). Other areas have become more dominant over time (e.g., policy relevance & implications of scenarios, transparency, Negative Emissions Technologies (NETs) assumptions, missing scenarios). Several changes have been made in developing scenarios and their content that respond to the critique. 相似文献