全文获取类型
收费全文 | 57073篇 |
免费 | 5311篇 |
国内免费 | 7028篇 |
专业分类
测绘学 | 2070篇 |
大气科学 | 8580篇 |
地球物理 | 12078篇 |
地质学 | 27804篇 |
海洋学 | 5117篇 |
天文学 | 6171篇 |
综合类 | 3423篇 |
自然地理 | 4169篇 |
出版年
2024年 | 83篇 |
2023年 | 417篇 |
2022年 | 1188篇 |
2021年 | 1385篇 |
2020年 | 1203篇 |
2019年 | 1307篇 |
2018年 | 4875篇 |
2017年 | 4566篇 |
2016年 | 3494篇 |
2015年 | 1480篇 |
2014年 | 1901篇 |
2013年 | 1754篇 |
2012年 | 2810篇 |
2011年 | 4593篇 |
2010年 | 4569篇 |
2009年 | 4647篇 |
2008年 | 3747篇 |
2007年 | 4418篇 |
2006年 | 1407篇 |
2005年 | 1695篇 |
2004年 | 1354篇 |
2003年 | 1431篇 |
2002年 | 1181篇 |
2001年 | 911篇 |
2000年 | 1116篇 |
1999年 | 1525篇 |
1998年 | 1284篇 |
1997年 | 1379篇 |
1996年 | 1152篇 |
1995年 | 1036篇 |
1994年 | 921篇 |
1993年 | 835篇 |
1992年 | 664篇 |
1991年 | 493篇 |
1990年 | 337篇 |
1989年 | 378篇 |
1988年 | 325篇 |
1987年 | 238篇 |
1986年 | 210篇 |
1985年 | 156篇 |
1984年 | 144篇 |
1983年 | 120篇 |
1982年 | 122篇 |
1981年 | 101篇 |
1980年 | 97篇 |
1979年 | 62篇 |
1978年 | 33篇 |
1977年 | 27篇 |
1976年 | 31篇 |
1975年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
The prograde evolution of minerals in metapelites of a Barrovian sequence from the tri-state area (Massachusetts, Connecticut, New York) of the Taconic Range involves assemblages with garnet (Ga), chlorite (Ch), chloritoid (Ct), biotite (Bi) and staurolite (St). Detailed petrologic observations, mineral compositions and chemical zoning in garnet show: (1) garnet high in Mn and Fe but low in Mg is stable with chlorite at grades below those where chloritoid+biotite is found; (2) early formed garnet reacted partially to form Ct+Bi at intermediate grades; (3) at higher grades garnet (with low Mn)+chlorite is again produced, at the expense of chloritoid+biotite, suggesting a reversal in the continuous reaction involving the phases Ga, Ch, Ct and Bi. Thermodynamic modeling of the assemblage Ga+Ch+Ct+Bi±St in the MnKFMASH system reveals: (1) in the MnKFASH system the prograde reaction is Ga+Ch=Ct+Bi whereas in the KFMASH system the prograde reaction is the opposite: Ct+Bi=Ga+Ch; (2) the Ga–Ch–Ct–Bi–St invariant point in the KFMASH system occurs twice, at approximately 6.5 kbar, 545° C and 14.8 kbar, 580° C (although one of them may be metastable in a complex phase system); the appearance of the petrogenetic grid is markedly different from that of Albee, but similar to that of Spear and Cheney; (3) as a consequence, in the KFMASH system, chloritoid+biotite are stable over a wide range of P-T conditions whereas garnet+chlorite assemblages are restricted to a narrow band of P-T conditions; (4) MnO increases the stability field of Ga+Ch relative to both Ct+Bi at low temperatures, and St+Bi at high temperatures; (5) in natural samples the occurrence of Ct+Bi is controlled more by bulk Mg–Fe(-Mn) composition than P-T conditions. Specifically, Ct+Bi is restricted to bulk compositions with Fe/(Mg+Fe+Mn)>0.6. Rocks with Fe/(Mg+Fe+Mn)<0.5 are likely to display only chlorite+biotite at low grade. These observations are consistent with Wang and Spear and Spear and Cheney. 相似文献
162.
《山西地震综合数据处理系统》是遵循《国家地震局数据库技术规范》,以PDP-11/23~+小型机与IBM/PC联机为硬件支撑,以网状型数据库为核心,含前期处理、库管理、数据检索、科学计算、分析会商5个子系统的较大型应用软件系统。具有对数据进行收集、录入、预处理、存储、管理、加工及应用等功能。整个系统通过总控菜单程序实现了异种机间上百个模块的调度,使查询-处理一体化。该系统把地震数据库、日常监测数据处理、专家地震预报系统有机地衔接于一体,可直接服务于地震科研和震情会商。该系统的建设是山西省重大科技攻关项目,也是国家地震局的合同制项目。 相似文献
163.
164.
G. Z. Xie F. K. Liu Y. Y. Zhu J. H. Fan R. W. Lu 《Astrophysics and Space Science》1991,179(2):321-329
It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F
obs = 3 +
F
intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem
v
must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem
v
corr
and logZ have a good correlation. 相似文献
165.
166.
A model of the galactic centre with magnetic monopole has been presented here. The positron can be produced continuously through magnetic monopoles to induce baryon decay (Rubakov catalytic reaction) and a lot of energy can be released as well. The calculation results show that even if the galactic center contains only a few magnetic monopoles (=N
M/NB10–24), this massive object can not collapse into a black hole. This model can explain the observed intensities of the annihilation line and higher energy photons ofE
>511 keV from the galactic centre.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
167.
D. Vandev K. Danov P. Mateev P. Petrov M. Kartalev N. Trendafilov Z. K. Smith M. Dryer 《Astrophysics and Space Science》1986,120(2):211-221
A study is presented of an algorithm, based on the statistical analysis of interplanetary magnetic field data, for the real-time detection of discontinuities in the solar wind. The analysis is based on the application of a sliding or searching algorithm together with a minimum variance treatment. A demonstration is given for a Pioneer data set from 29 August, 1966. This particular data set was chosen because it has been extensively studied (in terms of the fast forward MHD shock wave) by previous groups who utilized the three-dimensional Rankine-Hugoniot shock equations after identifying the shock on a subjective basis. Our procedure differs in that it is perfectly objective because of its searching technique. For this particular data set we identify the original shock with excellent agreement with the earlier studies of its normal vector, as well as an additional shock and tangential discontinuity, neither of which had been identified previously. 相似文献
168.
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
169.
古代西域南道上的若干历史地理问题 总被引:1,自引:0,他引:1
本文探讨塔克拉玛干沙漠南沿、和田以东至若羌间的几个历史地理问题。1,历史时期,塔里木盆地南沿上是否有过一条与北方塔里木河相对应的“南河”?笔者认为是没有的。2,自古以来,和田以东的绿洲数目是在逐期增多或是逐期减少?笔者认为是逐期增多。3,历史时期,和田以东出现过几处绿洲城镇废弃和交通路线改线的现象,笔者就其中的安迪尔、且末、尼雅三地的历史演变作了初步探讨。 相似文献
170.
一万年来白洋淀的扩张与收缩 总被引:5,自引:0,他引:5
本文探讨了一万年来的全新世期间,白洋淀兴起、扩张和收缩的变迁过程,恢复了各个发展阶段的古湖淀范围,论述了相应时期的古环境特征,指出了白洋淀令后的演变趋势。 相似文献