全文获取类型
收费全文 | 8283篇 |
免费 | 1395篇 |
国内免费 | 2858篇 |
专业分类
测绘学 | 280篇 |
大气科学 | 479篇 |
地球物理 | 2054篇 |
地质学 | 6507篇 |
海洋学 | 388篇 |
天文学 | 12篇 |
综合类 | 414篇 |
自然地理 | 2402篇 |
出版年
2024年 | 31篇 |
2023年 | 93篇 |
2022年 | 296篇 |
2021年 | 377篇 |
2020年 | 438篇 |
2019年 | 483篇 |
2018年 | 451篇 |
2017年 | 333篇 |
2016年 | 447篇 |
2015年 | 467篇 |
2014年 | 603篇 |
2013年 | 674篇 |
2012年 | 562篇 |
2011年 | 655篇 |
2010年 | 578篇 |
2009年 | 635篇 |
2008年 | 619篇 |
2007年 | 619篇 |
2006年 | 709篇 |
2005年 | 517篇 |
2004年 | 485篇 |
2003年 | 420篇 |
2002年 | 387篇 |
2001年 | 310篇 |
2000年 | 256篇 |
1999年 | 205篇 |
1998年 | 184篇 |
1997年 | 153篇 |
1996年 | 148篇 |
1995年 | 78篇 |
1994年 | 69篇 |
1993年 | 53篇 |
1992年 | 56篇 |
1991年 | 37篇 |
1990年 | 27篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
长江三角洲晚更新世末期古土壤与古环境 总被引:4,自引:0,他引:4
长江三角洲地区第一暗绿色硬粘土层是上海地区主要建筑持力层之一,也是划分全新统与更新统的标志层,前人已做过大量研究,但尚缺乏古土壤方面的系统研究工作。本文首次从古土壤学的角度系统研究了该层的古土壤特征,通过粒度分析发现有粘粒的生成,微形态研究发现有粘粒及铁锰、碳酸盐等化学组分的迁移与淀积,化学全量分析得出该层的硅铝率为2.80~3.37,说明该层已发生较强的成土作用,可以确认该层为古土壤层,并进一步把该层划分为4个B层、3个A层,亦即该层为复合古土壤层。根据该层的成土特征,将其命名为古潮土 相似文献
32.
根据大量田间试验和调查资料分析,作者提出烟单14号玉米生长过程中,小喇叭口期土壤中全氮、大喇叭口期土壤中速效磷的含量与产量相关密切。并据此建立了产量及构成三因素与土壤养分间的最优相关模型。 相似文献
33.
34.
A Note on Soil Structure Resistance of Natural Marine Deposits 总被引:1,自引:1,他引:1
It has been well documented that natural normally-consolidated marine soils are generally subjected to the effects of soil structure. The interpretation of the resistance of soil structure is an important issue in the theory study and engineering practice of ocean engineering and geotechnical engineering. It is traditionally considered that the resistance of soil structure gradually disappears with increasing stress level when the applied stress is beyond the consolidation yield stress. In this study, however, it is found that this traditional interpretation of the resistance of soil structure can not explain the strength behavior of natural marine deposits with a normally-consolidated stress history A new interpretation of the resistance of soil structure is proposed based on the strength behavior. In the preyield state, the undrained strength of natural marine deposits is composed of two components: one developed by the applied stress and the other developed by the resistance of soil structure. When the applied stress is beyond the consolidation yield stress, the strength behavior is independent of the resistance of soil structure. 相似文献
35.
港口靠船桩工作性状计算的双参数法 总被引:8,自引:0,他引:8
港口靠船桩是承受重复性荷载或多循环荷载的一种横向承载桩。双参数法能较好地描述靠船桩 (单桩、群桩 )的桩土工作性状。用双参数法进行计算时 ,所给的地面条件必须由重复荷载或多循环荷载作用下实测出来。根据现场试桩资料 ,标定桩土参数 ,即k =mx1/n的指数l/n、桩土相对柔度系数α、桩土综合刚度EI等值 ,可以用来设计试桩附近局部地区同类条件下的其它长桩。对于没有进行试桩的某些工程 ,可以联合运用双参数法和p -y曲线法进行桩的分析 相似文献
36.
Petroleum hydrocarbons were investigated in Mytilus edulis and Macoma balthica at six intertidal sites in Port Valdez, Alaska after three to five years of oil terminal operation. Information about the concentrations of total hydrocarbons, unresolved complex mixture, normal alkanes, isoprenoids, olefins, hopanes and polycyclic aromatic hyrocarbons shows that petroleum accumulation in these bivalve mollusks is greatest at the Valdez municipal boat harbor and a crude oil terminal which has been permitted to discharge 170 kg oil day−1. Accumulation two- to ten-fold less were observed at 3 km from the terminal and boat harbor. The temporal trends in petroleum hydrocarbon concentrations in M. edulis and M. balthica reflect the effects of selective retention and depuration of different hydrocarbon classes as well as variation in hydrocarbon sources. It is not clear whether the petroleum concentrations in Port Valdez bivalves had reached steady state by 1982, the final sampling time reported here. 相似文献
37.
The large cylinder is a new-type structure that has been applied to harbor and offshore engineering. An analytic method of the relationship between loads and the structure displacement is developed based on the failure mode of deep embedded large cylinder structures. It can be used to calculate directly the soil resistance and the ultirnate bearing capacity of the structure under usage. A new criterion of the large cylinder structure, which discriminates the deep embedded cylinder from the shallow embedded cylinder, is defined. Model tests prove that the proposed method is feasible for the analysis of deep embedded large cylinder structures. 相似文献
38.
39.
AbstractWith the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing. 相似文献
40.
激光扫描共聚焦显微镜具有成像清晰、获得三维图像、进行多标记观察等优势。本文扼要介绍了激光扫描共聚焦显微镜的原理和特点,着重阐述了激光扫描共聚焦显微镜在海洋动物配子发生;受精过程中细胞内Ca~(2 )变化、肌动蛋白转移和蛋白激酶变化;胚胎和幼体发育的三维成像等研究领域中的应用。并对LSCM在DNA含量、RNA含量等领域的定量、定性前景进行展望。 相似文献