全文获取类型
收费全文 | 1176篇 |
免费 | 162篇 |
国内免费 | 235篇 |
专业分类
测绘学 | 80篇 |
大气科学 | 82篇 |
地球物理 | 161篇 |
地质学 | 694篇 |
海洋学 | 149篇 |
天文学 | 2篇 |
综合类 | 106篇 |
自然地理 | 299篇 |
出版年
2024年 | 10篇 |
2023年 | 22篇 |
2022年 | 70篇 |
2021年 | 80篇 |
2020年 | 75篇 |
2019年 | 65篇 |
2018年 | 41篇 |
2017年 | 62篇 |
2016年 | 49篇 |
2015年 | 58篇 |
2014年 | 81篇 |
2013年 | 65篇 |
2012年 | 67篇 |
2011年 | 85篇 |
2010年 | 74篇 |
2009年 | 71篇 |
2008年 | 67篇 |
2007年 | 61篇 |
2006年 | 43篇 |
2005年 | 43篇 |
2004年 | 42篇 |
2003年 | 46篇 |
2002年 | 28篇 |
2001年 | 29篇 |
2000年 | 28篇 |
1999年 | 23篇 |
1998年 | 22篇 |
1997年 | 25篇 |
1996年 | 26篇 |
1995年 | 20篇 |
1994年 | 20篇 |
1993年 | 17篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1573条查询结果,搜索用时 578 毫秒
941.
海洋功能区划控制体系研究 总被引:2,自引:0,他引:2
合理利用海域、改善海洋环境质量和降低海洋开发利用活动负外部性,都需要通过加强海洋开发利用活动的控制来实现,而海洋功能区划是控制和管理开发利用活动的重要手段和工具。从文本控制、图则控制、指标控制、海域使用全过程控制四个方面构建了海洋功能区划控制体系,其中文本控制由目标、原则和文本条款组成;图则控制由图则边界、用海类型和管理要求组成;指标控制由规模控制、结构控制、利用方式控制、海域使用强度和效率控制、环境控制指标构成;海域使用全过程控制由建设期、运行期和结束后构成。通过构建海洋功能区划控制体系,有助于区划目标 相似文献
942.
探讨了海域使用结构形成机制,海域使用结构是受海洋资源结构约束,受消费结构引导,通过海洋产业落实到海域空间:分析了海域使用结构现状和变化趋势,结果显示渔业用海呈下降趋势,工业用海呈上升趋势;并以各类海洋功能区为基础,构建了海域使用结构优化模型,为海域使用结构调整提供定量化技术依据. 相似文献
943.
Giant red sea cucumber (Parastichopus californicus) is an under-utilized species due to its high tendency to autolysis.The aim of this study was to evaluate the functional properties of collagen hydrolysates from this species.The degree of hydrolysis (DH),amino acid composition,SDS-PAGE,emulsion activity index (EAI),emulsion stability index (ESI),foam expansion (FE),and foam stability (FS) of hydrolysates were investigated.The effects of pH on the EAI,ESI FE and FS of hydrolysates were also inves-tigated.The results indicated that the β and α1 chains of the collagen were effectively hydrolyzed by trypsin at 50℃ with an En-zyme/Substrate (E/S) ration of 1:20 (w:w).The DH of collagen was up to 17.3% after 3 h hydrolysis with trypsin.The hydrolysates had a molecular weight distribution of 1.1 17 kDa,and were abundant in glycine (Gly),proline (Pro),glutamic acid (Glu),alanine (Ala) and hydroxyproline (Hyp) residues.The hydrolysates were fractionated into three fractions (< 3 kDa,3 10 kDa,and > 10 kDa),and the fraction of 3 10 kDa exhibited a higher EAI value than the fraction of > 10 kDa (P<0.05).The fraction of > 10 kDa had higher FE and FS values than other fractions (P<0.05).The pH had an important effect on the EAI,ESI,FE and FS.All the fractions showed undesirable emulsion and forming properties at pH 4.0.Under pH 7.0 and pH 10.0,the 3 10 kDa fraction showed higher EAI value and the fraction of > 10 kDa showed higher FE value,respectively.They are hoped to be utilized as functional ingredients in food and nutraceutical industries. 相似文献
944.
945.
Shin Ozawa Masaaki Miyahara Eiji Ohtani Makoto Kimura Yoshinori Ito 《Polar Science》2011,4(4):550-557
Yamato 984028 (Y984028) is a newly identified lherzolitic shergottite, recovered from the Yamato Mountains, Antarctica, in 1999. As part of a consortium study, we conducted petrographic observations of Y984028 and its melt vein in order to investigate its shock metamorphism. The rock displays the typical non-poikilitic texture of lherzolitic shergottite, characterized by a framework of olivine, minor pyroxene (pigeonite and augite), and interstitial maskelynite. Shock metamorphic features include irregular fractures in olivine and pyroxene, shock-induced twin-lamellae in pyroxene, and the complete conversion of plagioclase to maskelynite, features consistent with those found in other lherzolitic shergottites. The melt vein is composed of coarse mineral fragments (mainly olivine) entrained in a matrix of fine-grained euhedral olivine (with several modes of compositional zoning) and interstitial glassy material. Some coarse olivine fragments consist of an assemblage of fine-grained euhedral to subhedral olivine crystals, suggesting shock-induced fragmentation, recrystallization, and/or a process of sintering. The implication is that the fine-grained olivine crystals in the matrix of the melt vein represent complicated crystallization environments and histories. 相似文献
946.
The oxidation of surface functional groups on biochar increases its reactivity and may contribute to the cation exchange capacity of soil. In this study, two Eucalyptus wood biochars, produced at 450 °C (B450) and 550 °C (B550), were incubated separately in each of the four contrasting soils for up to 2 years at 20 °C, 40 °C and 60 °C. Carbon functional groups of the light fraction (< 1.8 g/cm3) of the control and biochar amended soils (fresh and aged for 1 and 2 years at 20 °C, 40 °C and 60 °C) were investigated using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). The spectra of biochar and light fractions of the control and biochar amended soils showed two distinct peaks at ∼285.1 eV and 288.5 eV, which were attributed to the C1s-π1CC transitions of aromatic C and C1s-π1CO transitions of carboxylic C, carboxyamide C and carbonyl C. The proportion of aromatic C was substantially greater in the light fraction of the biochar amended soils than the corresponding light fraction of the control soils. Also, the proportion of aromatic C was much higher in the light fraction of the B550 amended soils than in the corresponding B450 amended soils. Neither NEXAFS nor XPS results show any consistent change in the proportion of aromatic C of biochar amended soils after 1 year ageing. However, XPS analysis of hand-picked biochar samples showed an increase in the proportion of carboxyl groups after ageing for 2 years, with an average value of 8.9% in the 2 year aged samples compared with 3.0% in the original biochar and 6.4% in the control soil. Our data suggest that much longer ageing time will be needed for the development of a significant amount of carboxyl groups on biochar surfaces. 相似文献
947.
原生晕垂向分带模型找矿法及其在铀矿勘查中的应用 总被引:1,自引:0,他引:1
原生晕指示元素垂向分带模型找矿法是通过发现、研究矿床原生晕指示元素垂向分带规律、建立指示元素垂向分带模型进行找矿的地球化学勘查方法。找矿实践表明,该方法可用于攻深找盲、推断矿体剥蚀程度、追踪矿体延伸方向,其找矿效果明显。有关该方法分带序列计算方法、分带模型以及在铀矿床(体)预测应用等方面已取得了较大进展。在分带序列计算方法方面,我国化探工作者提出的广义衬值法、浓集重心法,计算过程简单,值得推广。近年来该方法的重要研发成果——构造地球化学原生叠加晕评价技术在铀矿地质领域得到了广泛应用,可大大减小工作程度较高地区的化探工作量、降低勘查费用、缩短勘查周期,从而有效提升铀矿资源勘查的水平和能力。因此,该方法应用于铀矿勘查,其前景非常广阔。 相似文献
948.
949.
沈诚 《地质灾害与环境保护》2014,(3):25-29
对关岭县地质灾害进行系统调查和分析,根据灾害危害程度将全区划分为高易发区、中易发区和低易发区,并分别评价。提出有针对性的防治规划,并建立监测网络预警系统。 相似文献
950.
明确国土空间生态修复分区是有序实施国土整治与生态修复的前提与基础。重庆市是长江上游生态屏障的最后一道关口,在国家生态安全格局中的战略地位突出。本文以重庆市为例,探讨基于适应性循环模型的国土空间生态修复分区研究框架,构建评价指标体系诊断国土空间系统潜力、连通度和韧性3维属性的时空演变趋势,识别县域单元所处适应性循环阶段,划定国土空间生态修复分区,并明确基于分区的生态修复策略。结果表明:① 2000—2020年重庆市国土空间系统3维属性整体呈现东高西低的空间特征。当前各县域单元大多处于重组阶段、开发阶段和协调开发阶段,少部分处于保护阶段,尚未进入释放阶段。② 重庆市国土空间生态修复分区包含4个大区和9个亚区。总体而言,生态修复区应关注建成区的系统性生态修复工程,加强环境综合改良与治理力度;生态提升区应逐步提高生态保护修复工程的实施标准,优化各类生态要素的协调度,提升综合生态效益;生态控制区应限制国土空间开发强度,降低人类活动干扰的负面影响;生态保育区应优化自然生态系统功能,加强生态保护区管理与生态问题治理。 相似文献