全文获取类型
收费全文 | 2636篇 |
免费 | 241篇 |
国内免费 | 649篇 |
专业分类
测绘学 | 232篇 |
大气科学 | 225篇 |
地球物理 | 868篇 |
地质学 | 1174篇 |
海洋学 | 335篇 |
天文学 | 103篇 |
综合类 | 376篇 |
自然地理 | 213篇 |
出版年
2024年 | 12篇 |
2023年 | 35篇 |
2022年 | 25篇 |
2021年 | 38篇 |
2020年 | 33篇 |
2019年 | 33篇 |
2018年 | 55篇 |
2017年 | 36篇 |
2016年 | 47篇 |
2015年 | 44篇 |
2014年 | 100篇 |
2013年 | 64篇 |
2012年 | 118篇 |
2011年 | 158篇 |
2010年 | 87篇 |
2009年 | 99篇 |
2008年 | 140篇 |
2007年 | 150篇 |
2006年 | 160篇 |
2005年 | 152篇 |
2004年 | 139篇 |
2003年 | 146篇 |
2002年 | 142篇 |
2001年 | 140篇 |
2000年 | 147篇 |
1999年 | 78篇 |
1998年 | 57篇 |
1997年 | 109篇 |
1996年 | 52篇 |
1995年 | 68篇 |
1994年 | 70篇 |
1993年 | 81篇 |
1992年 | 63篇 |
1991年 | 86篇 |
1990年 | 69篇 |
1989年 | 79篇 |
1988年 | 55篇 |
1987年 | 37篇 |
1986年 | 32篇 |
1985年 | 51篇 |
1984年 | 39篇 |
1983年 | 25篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1980年 | 31篇 |
1979年 | 12篇 |
1959年 | 5篇 |
1947年 | 7篇 |
1939年 | 7篇 |
1926年 | 5篇 |
排序方式: 共有3526条查询结果,搜索用时 15 毫秒
51.
The data of SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), installed on SeaStar, has been used to generate SSC (suspended sediment concentration) of complex and turbid coastal waters in China. In view of the problems of the SeaDAS (SeaWiFS Data Analysis System) algorithm applied to China coastal waters, a new atmospheric correction algorithm is discussed, developed, and used for the SSC of East China coastal waters. The advantages of the new algorithm are described through the comparison of the restdts from different algorithms. 相似文献
52.
Many classes of environmental contaminants affect the reproductive function of animals through interactions with the endocrine system. The primary components affected by endocrine active compounds (EACs) are the steroid receptors and the enzymes responsible for steroidogenesis. This study sought to develop an in vitro model for assessing EAC effects in sea turtles by examining their ability to alter cytochrome P450 aromatase (CYP19) activity. Aromatase is the enzyme responsible for the conversion of testosterone to estradiol. This enzyme is critical in the sexual differentiation of reptiles which demonstrate temperature-dependent sex determination. An immortal testis cell line GST-TS from a green sea turtle was grown in culture at 30 degrees C in RPMI 1640 media. The cells were exposed to three known aromatase inducers; dexamethasone (Dex), 8Br-cyclic AMP, or human chronic gonadotropin (HCG) and one aromatase inhibitor 4-androstenol-dione (4-OHA). In addition, the GST-TS cells were exposed to 0.1-30 microM atrazine and 3-100 microM 4,4'-DDE. The inducing compounds that have been shown to increase aromatase activity in other systems failed to induce aromatase activity in the GST-TS cells, yet exposure to the inhibiting compound, 4-OHA, did result in a significant reduction. Atrazine (0.1, 1.0 and 10 microM) significantly induced aromatase activity following a 24 h exposure, and 4,4'-DDE inhibited the activity but only at cytotoxic concentrations (100 microM). Based on these results, this in vitro model can be useful in examining the endocrine effects of EACs in sea turtles. 相似文献
53.
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
54.
55.
本文采用黄海(35°N以北,124°E以西)断面调查资料,对海域表层盐度年变化进行谐波分析,讨论了年波与半年波位相与振幅在海区的分 布不同水系消长及运动的关系。 相似文献
56.
电阻率测深是利用岩(矿)石电阻率的差异,保持观测点不动,而不断改变电极距进行观测的一种方法。随着供电电极距AB的增大,电流分布范围加深变宽,此时视电阻率ρ_s值即反映了该测点周围更宽范围内电性不均匀的情况。根据ρ_s值的变化情况,可定量地求出某些电性层的厚度和埋藏深度。作者曾将此方法应用到探测第四纪含气层,推算含气层的储存条件,发现其结果与钻探资料对比符合较好,证明此法有实际使用价值。 相似文献
57.
58.
Man-made defence structures (e.g., breakwaters, jetties) are becoming common features of marine coastal landscapes all around the world. The ecology of assemblages of species associated with such artificial structures is, however, poorly known. In this study, we evaluated the density and size of fish predators of echinoids (i.e., Diplodus sargus, Diplodus vulgaris, Sparus aurata), and the density of sea urchins (i.e., Paracentrotus lividus) at defence structures (i.e., breakwaters) inside and outside the marine protected area of Miramare (northern Adriatic Sea) in order to: (1) assess possible differences in fish predator density and size between protected and fished breakwaters; (2) assess whether fish predation may have the potential to affect sea urchin density in artificial rocky habitats. Surveys were carried out at four random times over a period of two years. Total density, and density of medium- and large-sized individuals of the three predatory fishes were generally greater at the protected than at the fished breakwaters, whereas no differences were detected in the density of small-sized individuals. Density of the sea urchin P. lividus did not show any difference between protected and fished breakwaters. The results of this study suggest that: (1) protection may significantly affect predatory fishes in artificial rocky habitats; (2) differences in predatory fish density, and size may be unrelated with the density of the sea urchin P. lividus; (3) protected artificial structures such as breakwaters, originally planned for other purposes, could represent a potential tool for fish population recovery and enhancement of local fisheries. 相似文献
59.
60.
新疆与哈萨克斯坦寒武纪磷块岩资源 总被引:1,自引:0,他引:1
新疆和哈萨克斯坦寒武纪均为主要的磷矿成矿时代之一,但所形成的磷块岩资源量差别巨大.新疆寒武纪磷块岩矿层薄、矿石质量差、储量很少,哈萨克斯坦小卡拉套山寒武纪磷块岩矿层厚度大、矿石质量好、储量巨大.从实施“走出去”战略出发,邻国小卡拉套地区丰富的磷矿资源对于弥补新疆磷矿资源的严重不足具有重要意义. 相似文献