全文获取类型
收费全文 | 51001篇 |
免费 | 9064篇 |
国内免费 | 11075篇 |
专业分类
测绘学 | 4379篇 |
大气科学 | 5222篇 |
地球物理 | 9960篇 |
地质学 | 31182篇 |
海洋学 | 5428篇 |
天文学 | 2145篇 |
综合类 | 3722篇 |
自然地理 | 9102篇 |
出版年
2024年 | 135篇 |
2023年 | 509篇 |
2022年 | 1350篇 |
2021年 | 1604篇 |
2020年 | 1635篇 |
2019年 | 1791篇 |
2018年 | 1534篇 |
2017年 | 1793篇 |
2016年 | 1916篇 |
2015年 | 2101篇 |
2014年 | 2684篇 |
2013年 | 2695篇 |
2012年 | 2953篇 |
2011年 | 3217篇 |
2010年 | 2790篇 |
2009年 | 3320篇 |
2008年 | 3276篇 |
2007年 | 3608篇 |
2006年 | 3555篇 |
2005年 | 3129篇 |
2004年 | 2945篇 |
2003年 | 2842篇 |
2002年 | 2518篇 |
2001年 | 2268篇 |
2000年 | 2142篇 |
1999年 | 1919篇 |
1998年 | 1655篇 |
1997年 | 1511篇 |
1996年 | 1331篇 |
1995年 | 1146篇 |
1994年 | 1154篇 |
1993年 | 965篇 |
1992年 | 766篇 |
1991年 | 559篇 |
1990年 | 468篇 |
1989年 | 367篇 |
1988年 | 280篇 |
1987年 | 183篇 |
1986年 | 127篇 |
1985年 | 95篇 |
1984年 | 40篇 |
1983年 | 39篇 |
1982年 | 39篇 |
1981年 | 34篇 |
1980年 | 25篇 |
1979年 | 28篇 |
1978年 | 37篇 |
1977年 | 27篇 |
1975年 | 5篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
新地球观 总被引:11,自引:0,他引:11
One of the most important achivements on science in 20th century is the new recognition on the Earth:the Earth,out of the other planets, exhibits very peculiar features because it has an extremely complex and active periphery part (surfacial layers). This periphery part is an open system sustained by inputting solar energe , which is captured , transfered and stored by life. Through the system , cyclings of matters and energe flow are driven and regulated by life activities. This system is self-equilibrated,self-controlled and far away from astrophysical and thermodynamic equilibria mainly because of life and life activities.
Development of human calture influences increasingly on流Earth's periphery system , at last , the natural biosphere that has existed for 3 billion years on the Earth's surface will inavoidably be replaced by so called "noosphere",which is man一reconstructed,man-controlled and unstable system. Thus the fate of the Earth,to a great extent,will be determined by the direction of human calture evolution.
相似文献
Development of human calture influences increasingly on流Earth's periphery system , at last , the natural biosphere that has existed for 3 billion years on the Earth's surface will inavoidably be replaced by so called "noosphere",which is man一reconstructed,man-controlled and unstable system. Thus the fate of the Earth,to a great extent,will be determined by the direction of human calture evolution.
相似文献
992.
地学“开合律”及其在造山带研究中的意义 总被引:14,自引:2,他引:12
“开合律”是地学辩证法基本规律之一。本文概述了它的内容与特点,阐明它在造山带研究中的意义及运用它指导造山带研究的步骤,并根据目前已总结的5种“开”、“合”类型相应地提出了5种造山带类型。 相似文献
993.
黄海北部长山群岛海洋农牧化分区探讨 总被引:7,自引:0,他引:7
本文采用主成分-聚类分析等定量方法,并通过对长山群岛海域的资源、环境、生产条件等的相似性和差异性分析,将其划分为三个海洋农牧化区域,为海水养殖业的合理布局提供科学依据。 相似文献
994.
R. J. Flower 《Journal of Paleolimnology》1991,5(2):175-188
In wind-stressed and unstratified Lough Neagh low aspect ratio sediment traps, which allow for internal resuspension, collected sediment at a rate close to the natural sediment accumulation rate inferred from dated sediment cores. High aspect ratio traps grossly overestimated the natural rate of sediment accumulation as did, but to a lesser extent, burial rate measurements on an artificial stratigraphic marker. The former type of trap deployed over long exposure periods is therefore recommended as providing the best estimate of net downward particle flux in lakes such as Lough Neagh. However, it is emphasized that all sediment trap types, when operated in shallow turbulent lakes, will to a greater or lesser extent be contaminated by secondary or redeposited material and so will not provide a direct measure of primary sedimentation. Use of tube traps in lakes such as Lough Neagh should not, however, be discounted since they can provide a record of the quality of sedimenting material through time. 相似文献
995.
R. Mewe 《Astronomy and Astrophysics Review》1991,3(2):127-168
Summary From the early discovery in 1948 of X-rays from the Solar corona, X-ray spectroscopy has proven to be an invaluable tool in studying hot astrophysical and laboratory plasmas. Because the emission line spectra and continua from optically thin plasmas are fairly well known, high-resolution X-ray spectroscopy has its most obvious application in the measurement of optically thin sources such as the coronae of stars. In particular X-ray observations with theEINSTEIN observatory have demonstrated that soft X-ray emitting coronae are a common feature among stars on the cool side of the Hertzsprung-Russell diagram, with the probable exception of single very cool giant and supergiant stars and A-type dwarfs. Observations with the spectrometers aboardEINSTEIN andEXOSAT have shown that data of even modest spectral resolution (/ = 10–100) permit the identification of coronal material at different temperatures whose existence may relate to a range of possible magnetic loop structures in the hot outer atmospheres of these stars. The higher spectral resolution of the next generation of spectrometers aboard NASA'sAXAF and ESA'sXMM will allow to fully resolve the coronal temperature structure and to enable velocity diagnostics and the determination of coronal densities, from which the loop geometry (i.e. surface filling factors and loop lengths) can be derived. In this paper various diagnostic techniques are reviewed and the spectral results fromEINSTEIN andEXOSAT are discussed. A number of spectral simulations forAXAF andXMM, especially high-resolution iron K-shell, L-shell, and2s-2p spectra in the wavelength regions around 1.9 Å, 10 Å, and 100 Å, respectively, are shown to demonstrate the capabilities for temperature, density, and velocity diagnostics. Finally, iron K-shell spectra are simulated for various types of detectors such as microcalorimeter, Nb-junction, and CCD. 相似文献
996.
Weston Blake Jr. 《Journal of Paleolimnology》1991,6(2):157-166
13C/12C ratios for a number of High Arctic vascular plants (51 determinations), mosses (11), and freshwater algae (11) show considerable variation, particularly among the freshwater algae (range from-6.9 to -36.3). In some cases the stable carbon ratios on modern and fossil materials provide guidance as to whether marine waters formerly occupied a given pond or lake basin. In other cases the 13C values for algae collected along the present-day shore of a pond or lake bear no relation to the values obtained on constituents preserved within the bottom sediments, suggesting that major changes have occurred in the last few thousand years.Geological Survey of Canada Contribution No. 17291. Contribution No. 41 from the Cape Herschel Project. 相似文献
997.
饱和软土压缩试验时,经常出现压缩曲线“反常”、压缩系数“倒大”的现象。它是土的原始结构发生破坏前后的不同压缩性的客观反映。饱和软土的结构力很微弱,唯质量好的原状土才能见到这种“反常”。应从成孔、取样、测试及资料整理等多个环节保证其工程意义。 相似文献
998.
999.
本文讨论了弹性波瞬态传播问题的三维有限元计算方法及当前存在的实际困难.针对要求计算机内存大和计算时间长的问题,采取了改进措施.由于采用了集中质量矩阵和修正的中心差分时间积分显格式相结合的方法,可以使计算机内存和计算时间大为减少;由于采用结点定位法,最适合用于目前发展的并行计算机系统,可使计算速度大大增快;还采用了有效激发震源法,有效激发区是随时间步进的增加而逐步增大,这不仅能节省计算时间,而且使波场的传播过程一目了然,本文计算了由两种介质组成的三维楔形问题,得到若干典型剖面的瞬时波场图及随时间变化的合成地震图. 相似文献
1000.