全文获取类型
收费全文 | 8479篇 |
免费 | 1667篇 |
国内免费 | 1990篇 |
专业分类
测绘学 | 604篇 |
大气科学 | 1412篇 |
地球物理 | 2123篇 |
地质学 | 4431篇 |
海洋学 | 1062篇 |
天文学 | 561篇 |
综合类 | 807篇 |
自然地理 | 1136篇 |
出版年
2024年 | 41篇 |
2023年 | 143篇 |
2022年 | 440篇 |
2021年 | 487篇 |
2020年 | 413篇 |
2019年 | 525篇 |
2018年 | 477篇 |
2017年 | 494篇 |
2016年 | 497篇 |
2015年 | 467篇 |
2014年 | 496篇 |
2013年 | 510篇 |
2012年 | 498篇 |
2011年 | 509篇 |
2010年 | 483篇 |
2009年 | 466篇 |
2008年 | 491篇 |
2007年 | 448篇 |
2006年 | 326篇 |
2005年 | 315篇 |
2004年 | 283篇 |
2003年 | 273篇 |
2002年 | 293篇 |
2001年 | 332篇 |
2000年 | 290篇 |
1999年 | 301篇 |
1998年 | 249篇 |
1997年 | 265篇 |
1996年 | 208篇 |
1995年 | 196篇 |
1994年 | 162篇 |
1993年 | 135篇 |
1992年 | 144篇 |
1991年 | 77篇 |
1990年 | 73篇 |
1989年 | 66篇 |
1988年 | 57篇 |
1987年 | 27篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 26篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
21.
在太阳活动区的物理研究中,特别是在二维动力学光谱分析中,迫切需要相应活动区的磁图资料。本文介绍了在太阳光谱仪的入射狭缝后安装一种新型偏振器进行活动区二维磁场观测的新方法。这种方法不仅能获得日面上任一点的磁场强度,且可快速获得活动区的纵向场磁图。除此之外,还可利用多条谱线的同时观测,获得有关磁力线管结构等方面的资料。 相似文献
22.
随着河南区域化探扫面工作的结束,异常评价是摆在我们面前的当务之急。近年来,随着地质工作的不断深入,我们在异常评价程序及方法上作了一些探索,下面以桐柏县固庙—新集1:20万金银异常评价方法及效果为例,重点加以讨论。 相似文献
23.
本矿床是我国金红石矿床重要的成因及工业类型,为具有特定化学成分的岩石在特定变质条件下形成的。本文通过对大量数据的处理,查明了化学成分与成矿的关系:高Al2O3、MgO、Fe2O3+FeO、K2O、P2O5、H2O+、MnO,低SiO2、CaO、Na2O、CO2、S等,利于钛富集;高TiO2、MgO、P2O5、S,低SiO2、CaO、K2O、Al2O3、Fe2O3/FeO,利于金红石形成;高Sc、Zr、Ni、Zn及La/Yb,低Y、Nb、Th、Cd、Ba、Be、ΣREE,利于金红石纯度提高。对研究矿床成因及寻找新的同类矿床等有重要意义 相似文献
24.
介绍一种自行设计和加工的直接雾化石墨炉进样装置的结构、工作原理和操作方法。该装置由微机控制与石墨炉加热程序同步工作,可以实现自动控制和自动测量。对雾化进样石墨炉分析的仪器参数和实验条件进行了研究和选择。结果表明,该装置与石墨炉结合具有自动化程度高、重现性好、样品利用率高和分析速度快等特点。 相似文献
25.
Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and are capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase. 相似文献
26.
Four bromophenols were isolated from the extract of marine red alga,Rhodomela confervoides by column chromatography and HPLC methods. By means of spectroscopic methods inclding IR, MS, 1D, and 2D-NMR techniques,
their structures were elucidated as (1) 3-bromo-4,5-dihydroxy benzoic acid methyl ester; (2) bis (2,3-dibromo-4,5-dihydroxybenzyl)
ether; (3) 3,4-dibromo-5-(methoxymethyl)-1,2-benzenediol and (4) 3-bromo-4,5-dihydroxy-benzaldehyde. Compound 1 was first
isolated from the algae in nature, and 1, 4 were found to have selective cytotoxic activities against KB, Bel 7402 and A549
cells, 2 showed powerful antibacterial activities againstStaphylococcus aurens andPseudomonas aeruginosa.
Supported by National “863” Program (No. 2004AA625030, 2001AA620503), Quingdao marine sciences project (No. 04-2-NN-26) and
Key Knowledge Innovative Project of the Chinese Academy of Sciences (KZCX3-SW-215). 相似文献
27.
There are more than 600 Cenozoic volcanic cones and craters with abeut 50 000 km2of lava flows in northeast China, which formed many volcanic clusters and shown the features of the continental rift - type volcanoes. Most volcanic activities in this area, especially in the east part of Songliao graben, were usually controlled by rifts and faults with the main direction of NE / NNE in parallel and become younger from the central graben towards its both sides, especially to the east continental margin. It is revealed that the volcanism occurred in northeast China was as strong as that occurred in Japan during the Miocene and the Quaternary. The Quaternary basalt that is usually distributed along river valley is called "valley basalt"while Neogene basalt usually distributed in the top of mounts is called "high position basalt". These volcanoes and volcanic rocks are usually composed of alkaline basalts with ultramafic inclusions, except Changbaishan volcano that is built by trachyte and pantellerite. 相似文献
28.
29.
1IntroductionOne of the key factors related to basin geody-namics is deep process controlling formation and evolution of sedimentary basin. Depth and tempera-ture of asthenosphere,existence of mantle plume,occurrence of mantle melting,and amounts of melts under depressurization during thinning of lithosphere are controlling factors influenced formation and characteristics of extensional basin directly (Li,1994). Rifting is probably governed by frictional forces exerted on the base of litho… 相似文献
30.