全文获取类型
收费全文 | 2137篇 |
免费 | 58篇 |
国内免费 | 80篇 |
专业分类
测绘学 | 82篇 |
大气科学 | 232篇 |
地球物理 | 433篇 |
地质学 | 750篇 |
海洋学 | 145篇 |
天文学 | 475篇 |
综合类 | 9篇 |
自然地理 | 149篇 |
出版年
2023年 | 21篇 |
2022年 | 20篇 |
2021年 | 10篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 68篇 |
2017年 | 59篇 |
2016年 | 101篇 |
2015年 | 64篇 |
2014年 | 75篇 |
2013年 | 122篇 |
2012年 | 90篇 |
2011年 | 115篇 |
2010年 | 100篇 |
2009年 | 157篇 |
2008年 | 117篇 |
2007年 | 108篇 |
2006年 | 101篇 |
2005年 | 84篇 |
2004年 | 86篇 |
2003年 | 96篇 |
2002年 | 63篇 |
2001年 | 82篇 |
2000年 | 64篇 |
1999年 | 48篇 |
1998年 | 56篇 |
1997年 | 47篇 |
1996年 | 50篇 |
1995年 | 30篇 |
1994年 | 43篇 |
1993年 | 27篇 |
1992年 | 28篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1921年 | 1篇 |
1915年 | 1篇 |
排序方式: 共有2275条查询结果,搜索用时 15 毫秒
151.
Two existing mass-consistent models, COMPLEX and NOABL, were tested in three regions in the UK: Devon, the Northern Pennines and Shetland. In order to solve problems arising with both models, a number of modifications were made, leading to the development of a new model, MC-3. First, the entire wind field was scaled down (or up) by a certain percentage to make the wind predictions at the predictor stations as close to the observed values as possible. Second, modifications to the non-divergent process used in COMPLEX were made. Site roughness-length and anemometer height corrections were also made. The new model worked well in terms of mean wind speed predictions, and gave a significant improvement over the predictions of COMPLEX and NOABL. 相似文献
152.
The total inversion algorithm and some elements of Mathematical Information Theory are used in the treatment of travel-time data belonging to a seismic refraction experiment from the southern segment (Sardinia Channel) of the European Geotraverse Project. The inversion algorithm allows us to improve a preliminary propagating model obtained by means of usual trial and error procedure and to quantify the resolution degree of parameters defining the crust and upper mantle of such a model. Concepts related to Mathematical Information Theory detect some seismic profiles of the refraction experiment which give the most homogeneous coverage of the model in terms of number of trajectories crossing it. Finally, the efficiency of the inversion procedure is quantified and the uncertainties regarding knowledge of different parts of the model are also evaluated. 相似文献
153.
This paper addresses some fundamentally contradictory conclusions drawn by Tso and Ying1 and the authors2 regarding the additional seismic ductility demand in asymmetric building structures and the adequacy of certain code torsional provisions. It also clarifies a number of issues arising from the different approaches employed in the two studies. The Mexico 76 and 87 code torsional provisions are taken as examples. Results show that the structural element at the stiff edge is the more critical and that the Mexico 76 code torsional provisions (among others) are inadequate, substantially underestimating the strength demand of this element. On the other hand, the Mexico 87 code torsional provisions are found to be over-conservative. Recommendations are also given for improving the form and effectiveness of these code torsional provisions. 相似文献
154.
Summary A principal component analysis (PCA) based on a network including 179 pluviometric gauges is attempted in order to describe the main patterns governing precipitation in Catalonia (NE Spain). This PCA procedure is applied to the interstation covariance matrix and component loadings are then deduced from it and extensively interpreted. PCA results are used immediately after in a Davis and Kalkstein clustering process, leading to a rainfall division. The homogeneity of the different groups obtained is tested by means of the analysis of their spatial and temporal within-group variances.With 8 Figures 相似文献
155.
156.
The toxicity of marine sediments in Victoria Harbour, Hong Kong 总被引:4,自引:0,他引:4
When the toxicity of marine sediment in Hong Kong was evaluated, it was found that the seven sediments collected within Victoria Harbour were severely contaminated with heavy metals, at concentrations many times higher than those in sediments collected from outside the harbour. The highest metal content was recorded in site VS14 (located near the airport runway and the industrialized area), with copper, zinc, lead and chromium values of 3789, 610, 138 and 601 mg kg−1 dry wt, respectively. This site also had the greatest alkaline phosphatase activities (15 fluorescent intensity unit g−1 wet wt), the largest number of total coliforms (910 CFU g−1 wet wt) and sulphate-reducing bacteria (8.5 × 104 cells g−1 wet wt), implying that site VS14 was also contaminated with organic matter and nutrients. Sediment bioassays, Microtox and algal tests, demonstrated that sediment elutriates obtained from site VS14 were of greatest toxicity. The EC10 value in Microtox tests was 17% elutriate, and the 96-h IC50 values using Skeletonema costatum and Dunaliella tertiolecta were 40 and 79% elutriate, respectively. No toxic effects were found in sediment samples collected from the control site outside Victoria Harbour. Significant correlations were found between the results of the algal toxicity test (using S. costatum) and the coliform count and metal content of the sediments. The Microtox test was less sensitive than the algal bioassay, and no sediment elutriate, even from the site mostly contaminated by heavy metals, caused more than 50% inhibition of the light-emitting activity of the bacteria. In this study, S. costatum (the diatom) provided a more sensitive and reliable test species than D. tertiolecta (the flagellate) in differentiating the toxicity of marine sediments. 相似文献
157.
158.
K. Nishiizumi J.R. Arnold D. Elmore X. Ma D. Newman H.E. Gove 《Earth and Planetary Science Letters》1983,62(3):407-417
Cosmic-ray-produced53Mn (t1/2 = 3.7 × 106years) has been measured in twenty Antarctic meteorites by neutron activation analysis.36Cl (t1/2 = 3.0 × 105years) has been measured in fourteen of these objects by tandem accelerator mass spectrometry. Cosmic ray exposure ages and terrestrial ages of the meteorites are calculated from these results and from rare gases.14C (t1/2 = 5740years) and26Al (t1/2 = 7.2 × 105years) data. The terrestrial ages range from 3 × 104 to 5 × 105 years. Many of the L3 Allan Hills chrondrites seem to be a single fall based on these results. In addition,10Be (t1/2 = 1.6 × 106years) and36Cl have been measured in six Antarctic ice samples. The first measurements of10Be/36Cl ratios in the ice core samples demonstrate a new dating method for ice. 相似文献
159.
The incidence of power station emissions in the composition of the atmospheric aerosols in an urban-industrial area is presented in this study. The Iberdrola (Spanish electrical company) thermoelectric power station is located at Castellon's industrial estate along the Spanish Mediterranean coast. Due to the fact that there are other polluting industries in this region, the present study is also helpful to investigate potential tracers to discriminate the origin and source of particular pollution events. The analysis of air particulate samples, collected on cellulose membrane filters, was carried out by means of the following instrumentation: (1) mineralogical analysis by X-ray diffraction (XRD), (2) morphological study by scanning electron microscopy (SEM/EDX), and (3) chemical analysis by inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS), to carry out quantitative chemical analyses of both major and trace elements. This analysis has allowed the authors to find marker elements, V and Zn, for the power station emissions. 相似文献
160.
Centrifuge Modeling of Rock Slopes Susceptible to Block Toppling 总被引:2,自引:0,他引:2
Summary This paper presents the results of centrifuge tests that were aimed at validating the Goodman-Bray method for rock slope toppling
analysis. The Goodman-Bray method was extended by the authors to accommodate non-persistent basal planes of rock columns.
Two gypsum column models, with and without anchors were used to represent the failure modes. Measured critical centrifuge
accelerations were in agreement with the results obtained from numerical modeling. A background of the toppling slope failures
associated with a large hydropower project in China instigated the need for the centrifuge study. The centrifuge model tests
used an artificial rock. The observed failure mode did not follow a straight failure plane as proposed by Goodman and Bray.
The failures revealed a bi-planar slip surface with a deep-seated portion near the toe of the slope. The outcomes of the centrifuge
tests illustrated the need to search for the critical failure surface when performing a toppling analysis. The search technique
is similar to that usually performed in a conventional sliding analysis. 相似文献