全文获取类型
收费全文 | 14896篇 |
免费 | 3277篇 |
国内免费 | 4854篇 |
专业分类
测绘学 | 2182篇 |
大气科学 | 2131篇 |
地球物理 | 2789篇 |
地质学 | 8873篇 |
海洋学 | 3324篇 |
天文学 | 803篇 |
综合类 | 1106篇 |
自然地理 | 1819篇 |
出版年
2024年 | 115篇 |
2023年 | 299篇 |
2022年 | 769篇 |
2021年 | 1008篇 |
2020年 | 856篇 |
2019年 | 989篇 |
2018年 | 958篇 |
2017年 | 839篇 |
2016年 | 884篇 |
2015年 | 1005篇 |
2014年 | 960篇 |
2013年 | 1253篇 |
2012年 | 1291篇 |
2011年 | 1304篇 |
2010年 | 1277篇 |
2009年 | 1186篇 |
2008年 | 1217篇 |
2007年 | 1142篇 |
2006年 | 1015篇 |
2005年 | 849篇 |
2004年 | 688篇 |
2003年 | 452篇 |
2002年 | 524篇 |
2001年 | 503篇 |
2000年 | 401篇 |
1999年 | 217篇 |
1998年 | 101篇 |
1997年 | 81篇 |
1996年 | 72篇 |
1995年 | 68篇 |
1994年 | 54篇 |
1993年 | 38篇 |
1992年 | 36篇 |
1991年 | 40篇 |
1990年 | 41篇 |
1989年 | 22篇 |
1988年 | 17篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 33篇 |
1984年 | 35篇 |
1983年 | 28篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1978年 | 20篇 |
1976年 | 21篇 |
1975年 | 17篇 |
1974年 | 26篇 |
1972年 | 21篇 |
1971年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
81.
82.
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
83.
This paper presents a numerical model study of the propagation of water waves using the parabolic approximation of the mild-slope equation in the orthogonal coordinate system. Two types of coordinate systems are studied: (a) a general form of orthogonal coordinate system and (b) the conformal system, a special form of orthogonal coordinate system. Two typical examples, namely, expanded breakwaters and a circular channel, are studied to validate the model. First, the examples are studied by use of the general orthogonal coordinates. Then the same examples are computed by use of the confonnal system. The computational results show that the confonnal coordinate system generally gives better predictions than the general orthogonal system. A numerical technique for generating the conformal grid is combined with the numerical model to improve the practicability of the model. The comparison between the result from the numerical grid system and that from the analytical grid system shows that reliable computational results can be obtained by use of the numerical confonnal grid system. 相似文献
84.
85.
6个虾种基因组DNA多态性分析 总被引:2,自引:0,他引:2
采用RAPD方法检测了罗氏沼虾(Macrobrachium rosenbergii)、绿须虾(Aristeus virilis)、长毛对虾(Penaeus penicillatus)、日本对虾(P.japonicus)、斑节对虾(P.monodon)和周氏新对虾(Metapenaeus joyneri)等6个虾种的基因组DNA的多态性。用20个随机引物扩增得到492个DNA片段,根据这些片段的共享度计算出遗传距离并构建系统树。所得结果从DNA水平上反映出虾类在科属种不同分类阶元亲缘关系的远近,并为虾类现行的分类系统提供了分子生物学依据。 相似文献
86.
87.
探讨了windows编程环境下,编绘软件的网络实现方法。通过对WinSock编程方法的讨论,表明了编绘软件电子图板实现网络化编辑的可行性。 相似文献
88.
The gastropod limpet, Cellana grata, is common on moderately exposed to exposed Hong Kong rocky shores. On the basis of the existing literature on trace metal contamination in Hong Kong, four sites were identified, representative of highly polluted (Aberdeen and Lei Yue Mun) and clean (Cape d'Aguilar and Clear Water Bay) conditions. Limpets from the two polluted sites showed similar, but significantly higher body concentrations of copper than limpets from the two clean sites, which were also similar. Non-invasive measurements of cardiac activity of limpets from the four sites showed between site differences in baseline heart rates under standard seawater, irrespective of pollution level. When acutely exposed to water borne copper (2 h, 0.5+/-0.06 SD ppm), however, limpets from clean sites showed a significantly higher increase in inter-beating time (bradycardia) than those from polluted sites. These results highlight the potential use of cardiac activity to assess the exposure of natural populations of limpets to trace metal pollution. 相似文献
89.
An evaluation is made of the effectiveness of the ocean's biological pump in driving the deep-sea excess CO2 from the atmosphere. It is based on sediment-trap data available in the literature and on estimates of present and future inputs of anthropogenic nitrogen and phosphorous. The fraction of annual CO2 production from fossil fuel combustion going into this sink turns out to be insignificant in the total budget of man-made CO2. A discussion is presented on the formation of macroflocs under oceanic conditions, a process that has been believed to be important for the effectiveness of the biological pump. 相似文献
90.