全文获取类型
收费全文 | 18550篇 |
免费 | 4551篇 |
国内免费 | 6432篇 |
专业分类
测绘学 | 3608篇 |
大气科学 | 2682篇 |
地球物理 | 3461篇 |
地质学 | 11769篇 |
海洋学 | 3377篇 |
天文学 | 378篇 |
综合类 | 1512篇 |
自然地理 | 2746篇 |
出版年
2024年 | 108篇 |
2023年 | 435篇 |
2022年 | 1100篇 |
2021年 | 1419篇 |
2020年 | 1114篇 |
2019年 | 1163篇 |
2018年 | 1137篇 |
2017年 | 1115篇 |
2016年 | 1124篇 |
2015年 | 1303篇 |
2014年 | 1262篇 |
2013年 | 1577篇 |
2012年 | 1693篇 |
2011年 | 1687篇 |
2010年 | 1606篇 |
2009年 | 1496篇 |
2008年 | 1609篇 |
2007年 | 1448篇 |
2006年 | 1469篇 |
2005年 | 1168篇 |
2004年 | 925篇 |
2003年 | 634篇 |
2002年 | 697篇 |
2001年 | 668篇 |
2000年 | 509篇 |
1999年 | 322篇 |
1998年 | 124篇 |
1997年 | 95篇 |
1996年 | 89篇 |
1995年 | 53篇 |
1994年 | 58篇 |
1993年 | 45篇 |
1992年 | 55篇 |
1991年 | 32篇 |
1990年 | 33篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 27篇 |
1986年 | 12篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1964年 | 2篇 |
1958年 | 5篇 |
1957年 | 4篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
41.
DunaIiella salina, a halotolerent unicellular green alga, can accurmulate a Iarge amount of β-caroteneunder environmental conditions. The isorners of β-carotene extIacted from D. salina culturedin medium with different nitrate and phosphate concentrations were analysed by HPLC with Alox-Talumins column. At least six isomers were found in different proportions depending on the culture me-dia's nitrate and/or phosphate concentrations. Nitrate and/or phosphae defidency was conducive tothe accumulation of totaI cis isomers but not of al1 trans isomer. lt is sUggeSted that 1 mmol/L KNO_3and 0.1 mmol/L KH_2, PO_4 are favourable for accumulation of total cis β-carotene. 相似文献
42.
1 INTRODUCTIONCompact Symmetric Objects (CSOs) are powerful and compact sources (overall size <1 bpc) with lobe emission on both sides of the central engine. The small size of these sourcesis almost certainly to be attributed to the youth of the sources themselves (ages < 104 yr) andnot due to a dense coallning medium (Readhead 1996). The unification scenario assumes thatCSOs evolve into compact steep spectrum (CSS) sotirces and then into Fanaroff-Riley type 11objects (Fanti 1995). … 相似文献
43.
1995年7月11日—12日,广西地矿厅和河池地区行署首次联合举办矿产资源勘查成果展销会,会址设在河池市,与会代表130余人。展销会提交大会展销的矿产资源勘查成果38项,引资勘查项目38项。经买卖双方三天的洽谈,涉及到的项目25项,会议期间签订矿产资源勘查成果合同协议4项,愈千万元,取得较好的社会经济效益。为地勘资金多渠道来源开辟了新路子,对促进地勘单位地质找矿工作及勘查成果有偿使用发挥了重要作用 相似文献
44.
45.
本文作者首次发现了EXO 2030+375的回旋吸收线迹象.这是迄今唯一一个同时有用回旋吸收线直接测量的磁场数据和用吸积演化方法间接测量的中子星磁矩数据的X射线脉冲星.两种测量方法的结果有很大差别,本文提出了可能导致这种差别的物理机制. 相似文献
46.
低频扩频中伪随机序列产生方法的研究 总被引:2,自引:0,他引:2
伪随机序列的产生是实现BPC低频时码发播台扩展频谱技术升级的一个重要环节。针对BPC低频时码发播台的现有系统,提出了伪随机序列的产生方案,并对其性能作了分析。 相似文献
47.
Three continuous marine fish cell lines of FG (i. e., Hounder Gill) from flounder (Paralichthys olivaceus) gill, SPH (i. e. , Sea Perch Heart) from sea perch (Lateolabrax japonicus) heart and RSBF (i.e., Red Sea Bream Fin) from red sea bream (Pagrosomus major) fin, were characterized by lactate dehydrogenase (LDH) isozyme and morphological analysis. The LDH isozyme patterns of these three cell lines and their corresponding tissues of origin were investigated and compared. The results showed: (1) No difference was found in the LDH isozyme patterns of FG and flounder gill tissue. However, the LDH isozyme patterns of SPH and RSBF were significantly different from their corresponding tissues of origin; (2) LDH isozyme patterns of FG, SPH and RSBF were markedly different from each other and could serve as genetic markers for species identification and detection of cross contamination. Morphological change analysis of these three cell lines in comparison to their original tissues indicated that FG cells still appeared epithelioid without morphological transformation. However, morphological changes were found in SPH and RSBF compared to their original tissues. Therefore, the cellular morphology was still plastic in the relatively stable culture conditions, and it was possible that change of LDH patterns wasrelated to morphological changes of fish cells in vitro. 相似文献
48.
Xiang Shouping 《Astrophysics and Space Science》1985,112(1):83-91
In a two-component Universe which consists of fluid (visible matter) plus collisinless massive neutrino gas (dark matter), the remarkable difference between the developed inhomogeneities in two components could be formed after the decoupling time. Whether the initial perturbation was in which of the two components, the inhomogeneities developed in visible matter are larger than that in neutrinos, especially on smaller scales. The necessary condition for such a situation to arise is only that the density of neutrinos in the Universe is dominant. That means the non-dominant visible component in the Universe is strongly clustered especially on smaller scales, while the distribution of the dominant dark matter (neutrinos) is fairly uniform. 相似文献
49.
50.
报表服务是大地测量信息系统的一项基本功能,但往往会因为格式的微小调整而导致系统的整体重构。首先分析了当前报表生成方法的缺点,提出了基于XML相关技术生成报表的新思路;然后介绍了以XML为基本语法的统一数据交换接口,屏蔽了各种报表数据源的差异;重点讨论了如何运用XSL技术将接口文件变换成通用的HTML,并对报表中的图形信息用SVG进行描述,从而将报表转换成通用浏览器可以识别的信息模型;最后对此技术进行了实践。通过在系统外部更改报表样式文件,能够实现报表服务的个性化,增强系统的扩展性。 相似文献