全文获取类型
收费全文 | 1966篇 |
免费 | 269篇 |
国内免费 | 471篇 |
专业分类
测绘学 | 175篇 |
大气科学 | 215篇 |
地球物理 | 409篇 |
地质学 | 1114篇 |
海洋学 | 373篇 |
天文学 | 32篇 |
综合类 | 219篇 |
自然地理 | 169篇 |
出版年
2024年 | 25篇 |
2023年 | 57篇 |
2022年 | 72篇 |
2021年 | 74篇 |
2020年 | 48篇 |
2019年 | 75篇 |
2018年 | 72篇 |
2017年 | 63篇 |
2016年 | 72篇 |
2015年 | 71篇 |
2014年 | 102篇 |
2013年 | 76篇 |
2012年 | 79篇 |
2011年 | 122篇 |
2010年 | 85篇 |
2009年 | 73篇 |
2008年 | 132篇 |
2007年 | 114篇 |
2006年 | 104篇 |
2005年 | 81篇 |
2004年 | 92篇 |
2003年 | 66篇 |
2002年 | 50篇 |
2001年 | 42篇 |
2000年 | 78篇 |
1999年 | 56篇 |
1998年 | 44篇 |
1997年 | 46篇 |
1996年 | 58篇 |
1995年 | 82篇 |
1994年 | 64篇 |
1993年 | 53篇 |
1992年 | 45篇 |
1991年 | 53篇 |
1990年 | 47篇 |
1989年 | 42篇 |
1988年 | 18篇 |
1987年 | 20篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 13篇 |
1978年 | 6篇 |
1976年 | 6篇 |
1964年 | 4篇 |
1959年 | 4篇 |
1958年 | 4篇 |
排序方式: 共有2706条查询结果,搜索用时 15 毫秒
1.
The effects of natural fish oil,DHA oil and soybean lecithin in microparticulate diets on stress tolerance of larval gilthead seabream(Sparus aurata)were investigated after 15 days feeding trials.The tolerance of larval gilthead seabream to various stress factors such as exposure to air(lack of dissolved oxygen),changes in water temperature(low)and salinity(high) were determined.This study showed that microparticulate diet with natural fish oil and soybean lecithin was the most effective for in-creasing the tolerance of larval gilthead seabream to various stresses,and that microparticulate diet with natural fish oil and palmitic acid(16:0)was more effective than microparticulate diet with DHA oil and soybean lecithin. 相似文献
2.
3.
对天区0112-35的UKST物端棱镜底片上的11个类星体候选者进行了光谱观测,证实为类星体,给出了它们的红移值、证认图及光谱图。11个类星体中有6个属于角距小于4角分的3对类星体;1个类星体-星系对。 相似文献
4.
引言农田灌溉是一种最易提高干旱地区农业产量的方法。灌溉农业与旱作农业相比,谷物产量可提高6倍,根块植物产量可提高4—5倍。因此,农田灌溉在渴望得到更多粮食的干旱地区,可以发挥巨大的作用。农田灌溉使这些地区获得高产稳产,同时减轻了干旱和沙漠化的威胁。 相似文献
5.
6.
Farn Parungo Clarence Nagamoto Cecilia M. I. R. Girz Jeff Torgerson Zhou Mingyu 《海洋学报(英文版)》1995,14(2):201-207
ObservationofcloudsandsolarradiationoverthePacificOceanasrelationtoglobalclimate¥FarnParungo;ClarenceNagamoto;CeciliaM.I.R.Gi... 相似文献
7.
北黄海沉积物——水界面反硝化速率及影响因素研究 总被引:4,自引:0,他引:4
探讨近海氮的循环机制,采用乙炔抑制法和现场静态箱法对北黄海夏季局部海域的反硝化速率进行了研究,该海域反硝化速率在2.5~5.8μmol/m2.h之间,平均4.85μmol/m2.h。影响其反硝化速率的主要因素为溶解氧,其次是温度。北黄海的反硝化速率低于珠江口和长江口海域。 相似文献
8.
The influence of salinity on the heat-shock protein response of Potamocorbula amurensis (Bivalvia) 总被引:1,自引:0,他引:1
Werner I 《Marine environmental research》2004,58(2-5):803-807
For biomarkers to be useful in assessing anthropogenic impacts in field studies involving aquatic organisms, they should not be affected by naturally occurring changes in environmental parameters such as salinity. This is especially important in estuarine environments and for relatively unspecific biomarkers like heat-shock proteins (hsps, stress proteins). In this study, the heat-shock protein response was measured in the euryhaline clam, Potamocorbula amurensis, after exposure to a range of salinities reflecting normal and extreme environmental conditions in Northern San Francisco Bay, California. The ability to raise cellular hsp70 levels in response to heat-shock was significantly impaired in P. amurensis collected from a low (0.5 ppt) salinity field site, and after 14 day exposure to low salinity in the laboratory. 相似文献
9.
We studied interactions of nitromusk compounds musk ketone and musk xylene and polycyclic musks Galaxolide trade mark (HHCB), Celestolide trade mark (ADBI), Tetralide trade mark (AHTN), and Traseolide trade mark (AITI) with multixenobiotic resistance (mxr) transporters in gill tissue of the marine mussel Mytilus californianus (Conrad, 1837). A competitive substrate transport test with rhodamine B was used to assay modulation of transport activity by musks. All tested musks inhibited the transport activity in the low microm range as indicated by increased accumulation of rhodamine B in the tissue. Compared to known substrates of mxr transporters, the effective concentration range was similar to quinidine and about 100 times higher than verapamil. Musk ketone and musk xylene also inhibited efflux of rhodamine B from gill tissue which was loaded with the dye and subsequently incubated with these compounds. Synthetic musk compounds are persistent environmental pollutants in aquatic environments with a high potential to bioaccumulate. As potent inhibitors of mxr transporters they may also play a role as chemosensitizers that enable toxic mxr substrates to accumulate in cells of aquatic organisms. 相似文献
10.
In this study male largemouth bass (LMB) were exposed to the naturally occurring androgens, dihydrotestosterone (DHT) or 11-ketotestosterone (11-KT) in order to identify genes that are differentially regulated by these steroid hormones. Using subtractive hybridization on livers of fish treated with DHT against vehicle control, many novel LMB genes were cloned. These genes were added to our gene library and arrayed. Six genes were up-regulated and five were down-regulated by both androgens. But, each androgen also regulated specific genes. One gene that was identified as a potential androgen marker was spermidine-spermine-N(1)-acetyltransferase that was up-regulated by both androgens. Determining which genes are responsive to natural androgens will help to identify biochemical pathways that are impacted. 相似文献