全文获取类型
收费全文 | 580篇 |
免费 | 66篇 |
国内免费 | 113篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 49篇 |
地球物理 | 311篇 |
地质学 | 193篇 |
海洋学 | 104篇 |
天文学 | 2篇 |
综合类 | 24篇 |
自然地理 | 67篇 |
出版年
2023年 | 10篇 |
2022年 | 13篇 |
2021年 | 21篇 |
2020年 | 28篇 |
2019年 | 26篇 |
2018年 | 14篇 |
2017年 | 23篇 |
2016年 | 22篇 |
2015年 | 24篇 |
2014年 | 25篇 |
2013年 | 35篇 |
2012年 | 27篇 |
2011年 | 42篇 |
2010年 | 39篇 |
2009年 | 37篇 |
2008年 | 60篇 |
2007年 | 34篇 |
2006年 | 42篇 |
2005年 | 24篇 |
2004年 | 27篇 |
2003年 | 27篇 |
2002年 | 23篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 14篇 |
1998年 | 27篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 18篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1989年 | 7篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有759条查询结果,搜索用时 468 毫秒
671.
Numerical modeling and experiments are conducted for the South China Sea typhoons Helen (1995) and Willie (1996) with an auto-adaptive mesh model. It is shown that durating the stage of dissipation the typhoons are mainly related with the subtropical high rather than the topography. The high is sensitive to the intensity change of the typhoon so that the former weakens as the latter strengthens and vice versa. Maintaining the typhoon as a main factor, the release of latent heat is in reversed proportion with the subtropical high in terms of the intensity. It is found that the storm tends to be maintained if it moves close to the westerly trough after landfall. 相似文献
672.
本文通过试验,测定了多种材料的阻氡效果。数据表明,即使采用薄铜片阻氡,也难以达到较好地阻氡外逸的目的。文中指出了阻氡的具体途径和最佳的阻氡材料。 相似文献
673.
674.
675.
Joachim Kleiner Hans-Henning Stabel 《Aquatic Sciences - Research Across Boundaries》1989,51(3):181-191
Despite decreasing nutrient loading of Lake Constance over the past few years, annual sedimentation rates of dry matter remained nearly constant at a level of about 1000 gm–2y–1. The phosphorus content in settling material varied between 0.13 and 0.22% of dry weight. Phosphorus was transported to the lake bottom mainly by POM and by coprecipitation with authigenically formed calcite (estimated from results of laboratory studies). Adsorption to sinking particles of allochthonous origin was of minor importance. The effect of a self-cleaning mechanism is discussed with regard to continuously declining contents of dissolved phosphorus in Lake Constance since 1981, due to external sanitation measures in the drainage area. 相似文献
676.
Alberto Barbieri Rosario Mosello 《Aquatic Sciences - Research Across Boundaries》1992,54(3-4):219-237
Chemical studies performed in the last 50 years on the northern and southern basins of Lago di Lugano are reviewed and discussed in relation to the phosphorus and nitrogen loads from the drainage area.Both basins became eutrophic in the fifties as a consequence of the dense population and industrial activity in the drainage area; the effect of these was aggravated by the meromictic condition of the layer below 100 m in the northern basin.The reduction of phosphorus loads in progress since 1976 has resulted in a significant improvement in the chemical and biological condition of the southern basin and the upper 100 m of water in the northern basin. On the other hand, the balance between dissolved oxygen and reducing substances in the northern basin is shifting toward a decrease of the net oxygen concentration, partly as a consequence of the unusually dry conditions of the last three years.A reduction in phosphorus load down to 18 and 22 t a–1 in the northern and southern basins respectively is still necessary in order to reduce the lake phosphorus concentration to 30–35 µg O l–1. 相似文献
677.
华北富磷碱性-偏碱性杂岩的岩浆成分和岩浆熔体结构对岩浆的含磷性和磷的富集起着控制作用。磷的富集作用发生在岩浆起源阶段和岩浆分异作用(岩浆不混溶作用、结晶分异作用)阶段。在这两个阶段的演化过程中,P_2O_5含量及其变化趋势严格受岩浆成分、熔体结构(如NBO/T,M/F)和α_(SiO_2)、μ_(K_2O)控制,表现为P_2O_5含量与SiO_2、K_2O、K_2O+Na_2O及CaO/(MgO+SiO_2)等有密切关系。 相似文献
678.
中国大陆新生代构造应力场的研究 总被引:1,自引:0,他引:1
本文通过断陷盆地的分布特征、震源机制解和地应力测量等方面的资料分析研究,认为新生代以来中国大陆没有统一的构造应力场,或者说现今应力场小于前期应力场;断层活动、地震活动并不意味着应力的不断积累、不断加强,相反是应力的不断释放、不断减弱。 相似文献
679.
Phosphorus Near Edge X-ray Fluorescence Spectroscopy (P-NEXFS) data were collected on phosphorus containing phases including organic and inorganic compounds and minerals. Although phases containing P in the plus five oxidation state P(V) in a tetrahedral PO4 structure have similar primary fluorescence peak positions, the size, shape, and positions of secondary spectral features are diagnostic for different compounds and minerals. In particular, calcium phosphates exhibited a notable post-peak shoulder at 2154.5 eV, while oxidized iron phosphates had a distinctive pre-peak feature at 2148 eV. Polyphosphates have a broad secondary peak located approximately 2 eV higher in energy than a similar feature in phosphate esters and diesters. Compounds containing P(V) in structures other than PO4 tetrahedra such as phosphonates have a primary peak shifted about 1 eV lower than corresponding organo-phosphates. Organo-phosphates with P in the plus three oxidation state P(III) such as phosphines had primary fluorescence peaks shifted still further down in energy (2–3 eV). The substitution of aromatic carbon groups in close proximity to P structures in organic compounds generated both pre- and post-peak features as well as a number of secondary peaks. In addition, X-ray fluorescence mapping of P, Si, Al, Mg, and Na was conducted on a marine sediment sample with sub-micron spatial resolution. Phosphorus was heterogeneously distributed in the sample and not correlated on a broad scale with any other element examined. Much of the P present in the sample was located in small, 0.6–8 μm size, P-rich domains. Several P-rich regions were examined with P-NEXFS using a focused beam with 60 nm resolution and were found to consist of either calcium phosphate or polyphosphate phases. The presence of significant polyphosphate-dominated regions in a marine sediment sample supports the recent observations that such phases can play an important role in marine P cycling. The combination of fluorescence mapping and P-NEXFS data collection on fine particles provides a powerful new tool for environmental phosphorus studies. 相似文献
680.
Lactic acid bacteria (LAB) were encapsulated with alginate, gelatin and trehalose additives by the extrusion method and dried at 4 ℃. The microcapsules were generally spherical and had a wrinkled surface with a size of 1.7 mm ± 0.2 mm. Trehalose as a carbohydrate source in the culture medium could reduce acid production and performed no function in the positive proliferation of LAB. Using trehalose as a carbohydrate source and protective medium simultaneously had a benefit in the protection of LAB cells dur... 相似文献