全文获取类型
收费全文 | 3564篇 |
免费 | 395篇 |
国内免费 | 882篇 |
专业分类
测绘学 | 275篇 |
大气科学 | 366篇 |
地球物理 | 1331篇 |
地质学 | 1720篇 |
海洋学 | 469篇 |
天文学 | 130篇 |
综合类 | 201篇 |
自然地理 | 349篇 |
出版年
2024年 | 21篇 |
2023年 | 60篇 |
2022年 | 74篇 |
2021年 | 93篇 |
2020年 | 62篇 |
2019年 | 58篇 |
2018年 | 87篇 |
2017年 | 44篇 |
2016年 | 77篇 |
2015年 | 82篇 |
2014年 | 124篇 |
2013年 | 108篇 |
2012年 | 150篇 |
2011年 | 213篇 |
2010年 | 117篇 |
2009年 | 123篇 |
2008年 | 194篇 |
2007年 | 188篇 |
2006年 | 233篇 |
2005年 | 209篇 |
2004年 | 165篇 |
2003年 | 142篇 |
2002年 | 136篇 |
2001年 | 116篇 |
2000年 | 142篇 |
1999年 | 94篇 |
1998年 | 78篇 |
1997年 | 79篇 |
1996年 | 88篇 |
1995年 | 96篇 |
1994年 | 105篇 |
1993年 | 130篇 |
1992年 | 76篇 |
1991年 | 140篇 |
1990年 | 86篇 |
1989年 | 97篇 |
1988年 | 97篇 |
1987年 | 84篇 |
1986年 | 43篇 |
1985年 | 73篇 |
1984年 | 58篇 |
1983年 | 60篇 |
1982年 | 42篇 |
1981年 | 36篇 |
1980年 | 45篇 |
1973年 | 13篇 |
1964年 | 18篇 |
1959年 | 22篇 |
1958年 | 23篇 |
1957年 | 17篇 |
排序方式: 共有4841条查询结果,搜索用时 15 毫秒
131.
Boitsov S Petrova V Jensen HK Kursheva A Litvinenko I Chen Y Klungsøyr J 《Marine environmental research》2011,71(5):357-368
Subsurface sediments from a pockmark area in South-Western Barents Sea have been earlier found to contain elevated levels of petroleum-related polycyclic aromatic hydrocarbons. This work describes a comprehensive analysis of various biomarkers, including the highly source-specific hopanes, in a 4.5?m long gravity core from the same area, together with subsurface sediment samples from other areas in the region without pockmarks present ("background samples"). A clear difference between the pockmark gravity core and the background sediment cores was found, both with regard to genesis and the level of transformation of organic matter. A number of indicator parameters, such as methylphenanthrene index (MPI-1), point towards a significantly higher maturity of hydrocarbons in the pockmark core throughout its length as compared to the other sampled locations. Higher contents of microbial hopanoids (hopenes) may indicate the former presence of petroleum. These findings confirm the hypothesis of a natural hydrocarbon source in the deeper strata present in the studied location with pockmarks. 相似文献
132.
Female and male individuals of the same species often differ with respect to their susceptibility to toxicant stress. In the present study, sea urchins (Psammechinus miliaris) of both sexes were exposed to high (150 μg L?1) and environmentally relevant (5 μg L?1) concentrations of phenanthrene over 10 days. While food intake was significantly decreased following exposure to 150 μg L?1 phenanthrene, histological indices (lipofuscin accumulation, fibrosis, oocyte atresia), energetic status (energy charge, sum adenylates, AMP/ATP ratio) as well as ascorbate levels in the gonads showed either little or no effect upon phenanthrene exposure. However, most parameters (vitamin C, energy charge, sum adenylates, AMP/ATP ratio, ATP and ADP concentrations, lipofuscin content, fibrosis) significantly differed between male and female animals. This study illustrates the difficulties to identify toxic injury in reproductive tissue as it may be superimposed by gametogenesis and spawning of gametes. 相似文献
133.
密西西比河三角洲是世界上最大的三角洲,包括1.2万km2海岸湿地,是一个重要的生态区.然而,近年来密西西比河三角洲湿地不断流失,从20世纪30年代至90年代,已经流失了3 950 km2,流失速率达65~91 km2/a,对沿岸城市的生态环境和经济发展造成了巨大的负面影响,专家预测,到2050年湿地流失面积将达到1 8... 相似文献
134.
135.
136.
Canesi L Scarpato A Betti M Ciacci C Pruzzo C Gallo G 《Marine environmental research》2002,54(3-5):547-551
The signaling pathways involved in mussel immune defence were investigated utilizing a model of killing of Escherichia coli by Mytilus galloprovincialis hemocytes in a co-culture setting. In particular, the role played by different mitogen activated protein kinases (MAPKs) and by the production of eicosanoids were investigated utilising specific cell permeant, pharmacological enzyme inhibitors. Hemocyte pretreatment with the p38 MAPK inhibitor SB203580 significantly reduced bacterial killing, whereas PD98059 (an inhibitor of ERK--extracellularly regulated kinase--MAPK activation) had no significant effect. Wortmannin also inhibited bacterial killing, indicating a crucial role for PI3-kinase activation in the immune response. Killing of E. coli was also reduced by inhibitors of both PLA2 and cyclooxygenase activities, indicating that eicosanoid production is involved in mediating the response to bacterial challenge. The results demonstrate that bacterial killing by mussel hemocytes is particularly sensitive to inhibitors of the key steps involved in the transduction of bacterial signals into the host cell. Moreover, these data indicate that the hemocyte bactericidal activity can be suitably utilized not only for identifying the signaling pathways involved in the response to bacterial infection, but also as a potential investigative-toxicology model to test drugs and contaminants for their effect on the overall mussel immune defence. 相似文献
137.
Boon JP van Zanden JJ Lewis WE Zegers BN Goksøyr A Arukwe A 《Marine environmental research》2002,54(3-5):719-724
The short-term effects of the commercial PBDE flame retardant mixtures Penta-BDE and cta-BDE on the expression of cytochrome P450 1A (CYP1A), vitellogenin (Vtg) and zona radiata proteins (Zrp) were investigated in juvenile salmon (Salmo salar). For this purpose, groups of fish were dosed twice (oral intake at days I and 4) with 10 and 50 mg/kg body weight of both commercial mixtures. The fishes were sacrificed at day 7 (n = 5 for each group) and 14 (n = 6 for each group), and blood, liver, fillet, and brain were collected. Blanks and positive controls were also part of the experiment. The expressions of Vtg, Zrp, and CYPIA were measured with several techniques (EROD, ELISA, Western, Northern and Slot Blot). The values in the groups of fish treated with Penta-BDE or Octa-BDE did not significantly differ from the reference group for any of the parameters tested. In contrast, the positive control groups treated with estradiol-17beta for Vtg and Zrp expression, and beta-naphthoflavone for CYP1A expression did show a significant response, indicating the potential sensitivity of the fishes for the parameters measured. Since the results of the chemical analyses showed concentrations of a number of PBDE congeners in liver, fillet, and brain that were about three orders of magnitude above those of fish from the North Sea, it is concluded that the short-term toxicity of both commercial PBDE mixtures for these endpoints was low. 相似文献
138.
139.
为适应厦门市经济建设发展的需要,厦门市决定在厦门全岛建设环岛公路。对厦门大学至香山路段,将裁弯取直,在前埔东侧海岸建造路堤和护岸,公路可由厦门大学通过路堤直达香山。路堤和护岸后侧将填海造陆。根据规划要求,今后在填海造陆区将建造国际会议展览中心。为与拟建的国际会展中心建筑相协调,造成优美的景观,因此要求在国际会展中心正前方的海边采用直立式护岸结构。交通部第一航务工程勘察设计院(以下简称一航院)于1997年11月完成本项目的方案设计,参加设计方案评比。经厦门市组织有关专家评审,确定采用一航院提出的消… 相似文献
140.