全文获取类型
收费全文 | 61980篇 |
免费 | 23918篇 |
国内免费 | 45732篇 |
专业分类
测绘学 | 5274篇 |
大气科学 | 25448篇 |
地球物理 | 18549篇 |
地质学 | 48192篇 |
海洋学 | 18389篇 |
天文学 | 2069篇 |
综合类 | 7530篇 |
自然地理 | 6179篇 |
出版年
2024年 | 200篇 |
2023年 | 708篇 |
2022年 | 1916篇 |
2021年 | 2306篇 |
2020年 | 3139篇 |
2019年 | 6509篇 |
2018年 | 6987篇 |
2017年 | 6597篇 |
2016年 | 6909篇 |
2015年 | 6032篇 |
2014年 | 5816篇 |
2013年 | 6416篇 |
2012年 | 6038篇 |
2011年 | 5917篇 |
2010年 | 5855篇 |
2009年 | 5134篇 |
2008年 | 4345篇 |
2007年 | 4295篇 |
2006年 | 3688篇 |
2005年 | 3516篇 |
2004年 | 3486篇 |
2003年 | 3251篇 |
2002年 | 3085篇 |
2001年 | 2887篇 |
2000年 | 2612篇 |
1999年 | 2930篇 |
1998年 | 2653篇 |
1997年 | 2624篇 |
1996年 | 2188篇 |
1995年 | 2031篇 |
1994年 | 1825篇 |
1993年 | 1693篇 |
1992年 | 1408篇 |
1991年 | 1095篇 |
1990年 | 951篇 |
1989年 | 811篇 |
1988年 | 705篇 |
1987年 | 498篇 |
1986年 | 430篇 |
1985年 | 318篇 |
1984年 | 349篇 |
1983年 | 213篇 |
1982年 | 241篇 |
1981年 | 176篇 |
1980年 | 129篇 |
1979年 | 122篇 |
1978年 | 54篇 |
1977年 | 52篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
121.
Vertical drains are usually installed in subsoil consisting of several layers. Due to the complex nature of the problem, over the past decades, the consolidation properties of multi‐layered ground with vertical drains have been analysed mainly by numerical methods. An analytical solution for consolidation of double‐layered ground with vertical drains under quasi‐equal strain condition is presented in this paper. The main steps for the computation procedure are listed. The convergence of the series solution is discussed. The comparisons between the results obtained by the present analytical method and the existing numerical solutions are described by figures. The orthogonal relation for the system of double‐layered ground with vertical drains is proven. Finally, some consolidation properties of double‐layered ground with vertical drains are analysed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
122.
1 IntroductionBacteriaandtheiractivitiesplayanimportantroleintheelementalbiogeochemicalcyclesandenergytransformingintheocean (Zhenetal.1 997) .DortchandPackard(1 989) proposedthatfoodwebsintheeutrophicwatersaredominatedbythebiomassofprimaryproducerswhilefoodwebsintheoligotrophicwatersaredominatedbythebiomassofmicrobes.Heterotrophicbacteriahadbeenshowntoplayanimportantroleinthedecompositionoflarge ,rapidlysinkingorganicparticleswithinandbelowtheeuphot iczone ,andfurthertoaffecttheelementaldyn… 相似文献
123.
124.
Histological study on the ontogeny of the lymphoid organs, kidney, thymus and spleen of Japanese flounder, Paralichthys olivaceus, from hatching to 40 d was carried out. The pronephric kidney duct appeared early in hatching although the primordial haemopoietic
stem cells were observed within a week after hatching. The spleen was first seen after 8d of hatching. The thymus appeared
after 15d, situated near the pronephric kidney. Small lymphoid cells appeared during the later phase of the post-larval stage
in the sequence of thymus, kidney and spleen. During the 40d of observations, there were no distinct inner or outer zones
in thymus and no red or white pulp in spleen. These results suggest that the nonspecific defense immune system plays a very
important role in the early larval stage of Japanese flounder. 相似文献
125.
Brine shrimp (Artemia parthenogenetica) which had ingested three water-insoluble antibacterial drugs i.e. sulfadiazine(SD), oxytetracycline (OTC) and erythromycin
estolate (ERY-Es) were fed toTilapia and Mysis IIIof Penaeus orientalis K. The drug contents in the predators were then determined. After administration of drugs toTilapia and Mysis III, through the bio-encapsulation of the brine shrimp, efficacious therapeutical concentration of OTC and ERY-Es
(but not SD) in the predators could be reached and maintained for more than 8 hours. 相似文献
126.
127.
128.
129.
130.
地壳对海洋潮汐的响应 总被引:2,自引:2,他引:0
应用三维动态有限元方法研究了中国北部地区的地壳对邻近的渤海与黄海海平面变化的响应。虽然此应力场过于微弱不足以引发地震,但发现应力集中的位置及应力场变化较大的位置恰好与某些现代地震的震中一致。这一结果表明研究地壳对广泛分布的载荷的响应对研究区域地震构造是有帮助的。 相似文献