全文获取类型
收费全文 | 9029篇 |
免费 | 777篇 |
国内免费 | 419篇 |
专业分类
测绘学 | 333篇 |
大气科学 | 1132篇 |
地球物理 | 2871篇 |
地质学 | 3452篇 |
海洋学 | 1033篇 |
天文学 | 671篇 |
综合类 | 273篇 |
自然地理 | 460篇 |
出版年
2023年 | 20篇 |
2022年 | 63篇 |
2021年 | 88篇 |
2020年 | 80篇 |
2019年 | 118篇 |
2018年 | 610篇 |
2017年 | 547篇 |
2016年 | 445篇 |
2015年 | 269篇 |
2014年 | 317篇 |
2013年 | 377篇 |
2012年 | 818篇 |
2011年 | 661篇 |
2010年 | 355篇 |
2009年 | 366篇 |
2008年 | 321篇 |
2007年 | 329篇 |
2006年 | 305篇 |
2005年 | 971篇 |
2004年 | 994篇 |
2003年 | 766篇 |
2002年 | 287篇 |
2001年 | 169篇 |
2000年 | 146篇 |
1999年 | 79篇 |
1998年 | 58篇 |
1997年 | 74篇 |
1996年 | 43篇 |
1995年 | 45篇 |
1994年 | 28篇 |
1993年 | 20篇 |
1992年 | 24篇 |
1991年 | 30篇 |
1990年 | 29篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 28篇 |
1986年 | 18篇 |
1985年 | 18篇 |
1984年 | 30篇 |
1983年 | 33篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 28篇 |
1979年 | 13篇 |
1977年 | 17篇 |
1976年 | 9篇 |
1975年 | 20篇 |
1974年 | 12篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Sunyong Eom Tsutomu Suzuki Myeong-Hun Lee 《International journal of geographical information science》2020,34(5):899-923
ABSTRACT Land-Use Mix (LUM) refers to the strategy of integrating complementary functions within a building or area. While LUM has become a dominant approach in urban planning, its actual benefits and vision for spatial planning remain unclear. To clarify this issue, this study discerns the spatial features of land-use patterns depending on the compatibilities among land-use categories. Accordingly, this study introduces three LUM measures – adjacency, intensity, and proximity – to identify differences in the spatial distribution of land-use categories. Based on these measures, a land-use allocation model is developed to specify spatial patterns satisfying the given compatibilities. This model is tested by applying the concept of the neighborhood unit on a case study of normative land-use patterns subject to specified compatibilities. The results describe spatial features of four compatibility sets, including a set exhibiting a compatibility conflict between the same land-use pair and LUM measures when, for example, a given land-use pair is compatible in terms of intensity but incompatible in terms of proximity. Understanding the spatial features of a normative land-use pattern that satisfies various possible compatibilities will facilitate the incorporation of the LUM approach into local planning guidance and zoning ordinances. 相似文献
3.
4.
5.
6.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
7.
宁波盆地地下揭示的一套包含暗色膏硝质泥岩、泥质白云岩在内的紫红、灰紫色泥岩、棕褐色砂砾岩、细砂岩和玻屑凝灰岩的地层,均称方岩组,内含膏盐并具油色显示。对其时代有早、晚白垩世和早第三纪之认识,笔者从70~90年代地质工作中所获化石分析认为,虽然宁波盆地这一层位含化石不丰,但从分布及数量上比较,相对占优势的应该是孢粉和植物化石,其时代意见也较为一致,指示为早白垩世。 相似文献
8.
9.
Ju. V. Glagolevsky 《Astrophysics》2005,48(2):194-207
Some difficulties in explaining the slow rotation of CP stars are discussed. The most likely hypotheses are (1) a loss of angular momentum involving a magnetic field during “pre-main sequence” evolution and (2) the slow rotation existed from the very start of the creation of these stars. The braking hypothesis is supported by only one property of CP stars— the lower the mass of the star is, the greater the difference between its average rotation velocity vsini and that of normal stars. On the other hand, there is another property— the lower the rotation speeds of CP stars are, the greater their fraction among normal stars. The latter property supports the hypothesis that the lower the initial rotation speed of a star is when it is created, the greater the probability will become chemically peculiar. This property is inherent in chemically peculiar stars both with and without a magnetic field. It is proposed that the cause of the slow rotation of CP stars must be sought in the very earliest phases of their formation, as should the cause of the separation into chemically peculiar magnetic, chemically peculiar nonmagnetic, and normal stars.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 229–245 (May 2005). 相似文献
10.
Seung Ryeol Lee J. Wright Horton Richard J. Walker 《Meteoritics & planetary science》2006,41(6):819-833
Abstract— The osmium isotope ratios and platinum‐group element (PGE) concentrations of impact‐melt rocks in the Chesapeake Bay impact structure were determined. The impact‐melt rocks come from the cored part of a lower‐crater section of suevitic crystalline‐clast breccia in an 823 m scientific test hole over the central uplift at Cape Charles, Virginia. The 187Os/188Os ratios of impact‐melt rocks range from 0.151 to 0.518. The rhenium and platinum‐group element (PGE) concentrations of these rocks are 30–270x higher than concentrations in basement gneiss, and together with the osmium isotopes indicate a substantial meteoritic component in some impact‐melt rocks. Because the PGE abundances in the impact‐melt rocks are dominated by the target materials, interelemental ratios of the impact‐melt rocks are highly variable and nonchondritic. The chemical nature of the projectile for the Chesapeake Bay impact structure cannot be constrained at this time. Model mixing calculations between chondritic and crustal components suggest that most impact‐melt rocks include a bulk meteoritic component of 0.01–0.1% by mass. Several impact‐melt rocks with lowest initial 187Os/188Os ratios and the highest osmium concentrations could have been produced by additions of 0.1%–0.2% of a meteoritic component. In these samples, as much as 70% of the total Os may be of meteoritic origin. At the calculated proportions of a meteoritic component (0.01–0.1% by mass), no mixtures of the investigated target rocks and sediments can reproduce the observed PGE abundances of the impact‐melt rocks, suggesting that other PGE enrichment processes operated along with the meteoritic contamination. Possible explanations are 1) participation of unsampled target materials with high PGE abundances in the impact‐melt rocks, and 2) variable fractionations of PGE during syn‐ to post‐impact events. 相似文献