全文获取类型
收费全文 | 14848篇 |
免费 | 2720篇 |
国内免费 | 3406篇 |
专业分类
测绘学 | 939篇 |
大气科学 | 3040篇 |
地球物理 | 3662篇 |
地质学 | 7401篇 |
海洋学 | 1785篇 |
天文学 | 956篇 |
综合类 | 1410篇 |
自然地理 | 1781篇 |
出版年
2024年 | 27篇 |
2023年 | 200篇 |
2022年 | 583篇 |
2021年 | 640篇 |
2020年 | 562篇 |
2019年 | 687篇 |
2018年 | 717篇 |
2017年 | 719篇 |
2016年 | 813篇 |
2015年 | 705篇 |
2014年 | 818篇 |
2013年 | 843篇 |
2012年 | 781篇 |
2011年 | 805篇 |
2010年 | 894篇 |
2009年 | 793篇 |
2008年 | 828篇 |
2007年 | 765篇 |
2006年 | 548篇 |
2005年 | 579篇 |
2004年 | 461篇 |
2003年 | 462篇 |
2002年 | 459篇 |
2001年 | 546篇 |
2000年 | 495篇 |
1999年 | 705篇 |
1998年 | 607篇 |
1997年 | 577篇 |
1996年 | 547篇 |
1995年 | 466篇 |
1994年 | 382篇 |
1993年 | 372篇 |
1992年 | 323篇 |
1991年 | 232篇 |
1990年 | 194篇 |
1989年 | 160篇 |
1988年 | 168篇 |
1987年 | 81篇 |
1986年 | 75篇 |
1985年 | 58篇 |
1984年 | 43篇 |
1983年 | 28篇 |
1982年 | 44篇 |
1981年 | 38篇 |
1980年 | 26篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1958年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
61.
The pyroxenite xenoliths in the volcanic rocks of Hoh Xil consist of clinopyroxenes and orthopyroxenes. The mineral composition of these pyroxenes is similar to that of mantle xenoliths including peridotite and pyroxenite from China and abroad, and different from that of granulites. The pyroxenes formed at 1101–1400°C (averaging 1250°C) and under 30–60 kb (averaging 46 kb). We deduced that the magma was derived from the mantle at a depth of more than 150 km, which fits in with the geophysical conclusion that the low-velocity layer existed in the mantle under 150 km.
相似文献62.
本文较系统地总结了我国北西部金矿主要类型、矿化特征和金矿时空分布规律,在此基础上划分出4个成矿区、12条成矿带、32条成矿亚带,从而指明了找矿方向,为贯彻“以铀为主,综合找矿,多种经营,搞活地质”的方针,提供了较好的参考资料。 相似文献
63.
Magnetohydrodynamics (MHD) is a fairly recent extension of the field of fluid mechanics. While much remains to be done, it has successfully been applied to the contemporary field of heliospheric space plasma research to evaluate the macroscopic picture of some vital topics via the use of conducting fluid equations and numerical modeling and simulations. Some representative examples from solar and interplanetary physics are described to demonstrate that the continuum approach to global problems (while keeping in mind the assumptions and limitations therein) can be very successful in providing insight and large scale interpretations of otherwise intractable problems in space physics.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988. 相似文献
64.
65.
Trace and RE element geochemistry and genesis have been studied with respect to ferromanganese nodules from the sediments of the Pacific, Atlantic and Indian oceans. 相似文献
66.
Ni Xiang-bin Jiang Yao-tiao Chen Zai-zhang Fang Cheng 《Chinese Astronomy and Astrophysics》1985,9(4):273-277
We propose a new heating mechanism of faculae. We think that the formation of faculae is a result of the Joule dissipation of the Hall current generated by the interaction of the convection field of granules in an active region and the inter-granular magnetic field. For a region to generate effectively Hall current, its characteristic length must be such that the magnetic Reynolds number is less than 1. The equation of energy balance in the facula region is .For five observational models of faculae, we calculated the corresponding velocity fields, and the results are in basic agreement with the observed fields. The present mechanism explains the dependence of the facula brightness on the magnetic and velocity fields, the apparent distribution of the faculae on the solar disk and suggest a possible interpretation of the five structures of faculae. 相似文献
67.
68.
We have investigated numerically how a temperature difference between electrons and protons is produced in a flaring loop by adopting a one-fluid, two-temperature model instead of a single-temperature model. We have treated a case in which flare energy is released in the form of heating of electrons located in the top part of the loop.In this case, a large temperature difference (T
e/T
p 10) appears in the corona in the energy-input phase of the flare. When the material evaporated from the chromosphere fills the corona, the temperature difference in the loop begins to shrink rapidly from below. Eventually, in the loop apex, the proton temperature exceeds the electron temperature mainly due to cooling of the electrons by conduction down the loop and heating of the protons by compression of the ascending material. In the late phase of the flare (t 15 min from the flare onset), the temperature difference becomes less than 2% of the mean temperature of electrons and protons at every point in the loop. 相似文献
69.
The primary occurrence of ruby in the Mogok area, northern Myanmar is exclusively found in marble along with spinel–forsterite-bearing marble and phlogopite–graphite marble. These marble units are enclosed within banded biotite–garnet–sillimanite–oligoclase gneisses. Samples of these marbles collected for C–O stable isotope analysis show two trends of δ13C–δ18O variation resulting most likely from fluid–rock interactions. Ruby-bearing marble and phlogopite–graphite marble follow a trend with coupled C–O depletion, whereas spinel–forsterite-bearing marble follows a δ18O depletion trend with relatively constant δ13C values. Ruby formation might have resulted from CO2-rich fluid–rock interaction, while spinel–forsterite-bearing marble was genetically related to CO2-poor fluid–rock interaction. Both fluids may have arisen from external sources. Based on graphite Raman spectral thermometry, the estimated temperature for phlogopite–graphite marble, and probably ruby-bearing marble, was lower than 607 °C, and for spinel–forsterite-bearing marble, lower than 710 °C. Contrasting C/O diffusion between graphite/ruby/spinel/forsterite and calcite, local variations of isotopic compositions of newly formed minerals as a result of non-pervasive fluid infiltration, and open-system isotopic disturbance during cooling may have affected C-/O-isotopic fractionations between minerals. The estimated high formation temperatures for ruby and spinel/forsterite imply that the parental fluids may have been related to nearby igneous intrusions and/or metamorphic processes. Whether these two types of fluid were genetically related is unclear based on the present data. 相似文献
70.
印度共和国主要矿产资源及其地质特征 总被引:2,自引:0,他引:2
印度共和国是南亚地区矿产资源比较丰富的国家,铁矿探明储量175.7亿吨;铝土矿探明储量26.54亿吨;锰矿探明储量1.35亿吨;铬铁矿储量5900万吨;重晶石储量3000万吨。目前,全印度已开发了89种矿产资源,其中有52种非金属矿产,11种金属矿产,22种稀有金属矿产,4种能源矿产。全国生产矿 相似文献