全文获取类型
收费全文 | 7774篇 |
免费 | 1202篇 |
国内免费 | 1740篇 |
专业分类
测绘学 | 95篇 |
大气科学 | 207篇 |
地球物理 | 920篇 |
地质学 | 5060篇 |
海洋学 | 683篇 |
天文学 | 2152篇 |
综合类 | 346篇 |
自然地理 | 1253篇 |
出版年
2024年 | 39篇 |
2023年 | 111篇 |
2022年 | 326篇 |
2021年 | 346篇 |
2020年 | 318篇 |
2019年 | 348篇 |
2018年 | 302篇 |
2017年 | 294篇 |
2016年 | 282篇 |
2015年 | 345篇 |
2014年 | 354篇 |
2013年 | 406篇 |
2012年 | 391篇 |
2011年 | 381篇 |
2010年 | 336篇 |
2009年 | 585篇 |
2008年 | 477篇 |
2007年 | 520篇 |
2006年 | 586篇 |
2005年 | 435篇 |
2004年 | 432篇 |
2003年 | 476篇 |
2002年 | 385篇 |
2001年 | 319篇 |
2000年 | 317篇 |
1999年 | 268篇 |
1998年 | 297篇 |
1997年 | 199篇 |
1996年 | 161篇 |
1995年 | 135篇 |
1994年 | 149篇 |
1993年 | 93篇 |
1992年 | 90篇 |
1991年 | 51篇 |
1990年 | 47篇 |
1989年 | 29篇 |
1988年 | 23篇 |
1987年 | 23篇 |
1986年 | 11篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
991.
利用美国甚长基线阵,在5GHz和8GHz波段观测致密对称源(CSO)OQ208,由获得的总流量图均显示OQ208是由2个主要的射电结构组成。5GHz波段在该源西南(SW)部分和东北(NE)部分都探测到2个子源。8GHz波段在该源(SW)部分探测到2个子源,而在(NE)部分探测到3个子源。在5GHz波段,根据子源A和D自1993年到2001年间的5个时段VLBI观测成图结果,拟合出它们的分离速度为0.037±0.006mas/a(年)。在8GHz波段,根据1994年到2002年间的9个时段观测数据,获得子源A和C的分离速度为0.046±0.009mas/a。 相似文献
992.
根据化学非均匀恒星的非局部对流理论,计算了质量为0.7-1.15M(?)恒星主序演化模型锂和铍的衰减,并将理论和不同年龄疏散星团锂丰度的观测进行了比较.结果表明,贯穿对流混合能重现温度低于6400 K的晚型主序星锂丰度观测的一般性质.贯穿对流混合可能是晚型矮星锂衰减的一种重要机制. 相似文献
993.
994.
995.
Active galactic nuclei and galaxy interactions 总被引:1,自引:0,他引:1
996.
Jarrod R. Hurley † Christopher A. Tout Onno R. Pols ‡ 《Monthly notices of the Royal Astronomical Society》2002,329(4):897-928
We present a rapid binary-evolution algorithm that enables modelling of even the most complex binary systems. In addition to all aspects of single-star evolution, features such as mass transfer, mass accretion, common-envelope evolution, collisions, supernova kicks and angular momentum loss mechanisms are included. In particular, circularization and synchronization of the orbit by tidal interactions are calculated for convective, radiative and degenerate damping mechanisms. We use this algorithm to study the formation and evolution of various binary systems. We also investigate the effect that tidal friction has on the outcome of binary evolution. Using the rapid binary code, we generate a series of large binary populations and evaluate the formation rate of interesting individual species and events. By comparing the results for populations with and without tidal friction, we quantify the hitherto ignored systematic effect of tides and show that modelling of tidal evolution in binary systems is necessary in order to draw accurate conclusions from population synthesis work. Tidal synchronism is important but, because orbits generally circularize before Roche lobe overflow, the outcome of the interactions of systems with the same semilatus rectum is almost independent of eccentricity. It is not necessary to include a distribution of eccentricities in population synthesis of interacting binaries; however, the initial separations should be distributed according to the observed distribution of semilatera recta rather than periods or semimajor axes. 相似文献
997.
998.
999.
Abstract Syn-metamorphic re-imbrication of the internal part of thrust belts can result in distinct pressure–temperature–time–deformation ( P–T–t–d ) pathways for different structural–metamorphic domains. In the early Proterozoic Cape Smith Thrust Belt (Canada), an external (piggyback-sequence thrusting) domain is characterized by thermal peak metamorphism occurring after deformation. In contrast, thermal peak metamorphism in an internal domain occurred during re-imbrication by out-of-sequence thrusting. The interactions of tectonic and thermal processes have been studied using three methods: (i) qualitative evaluation of the timing between mineral growth and deformation; (ii) analytical P–T paths from growth-zoned garnet porphyroblasts; and (iii) numerical modelling of vertical heat conduction. Derived P–T–t–d pathways suggest that uplift in the external domain resulted in part from erosion and isostatic unloading. In contrast, paths for the internal domain indicate that the out-of-sequence portion of the thrust belt may have experienced faster unroofing relative to the external domain. This is attributed to thickening by out-of-sequence thrusting and possibly to extensional faulting at (now eroded) higher structural levels. Observations on the timing of metamorphism, coupled with numerical modelling, suggest that the thermal peak metamorphism documented in the external domain is a consequence of the emplacement of the out-of-sequence thrusts stack in the internal portion of the thrust belt. 相似文献
1000.
Polyc·lonal antibodies raised against LHC II isolated from SDS-solubilizedBryopsis corticulans thylakiod membranes by SDS-PAGE, were characterised by double immunodiffusion, Rocket immunoelectrophoresis and antigen-antibody
crossed immunoelectro-phoresis assays showed the antibodies had strong cross-reaction with allB. corticulans LHC II components (even with those which were incubated in boiling water) and showed immunological cross-reactivity with
LHC II polypeptides of spinach and the marine green algaCodium fragile. The results suggested that LHC II of different species had similar antigenic determinants and also conservation of amino
acid sequences of the polypeptides during evolution, and that the antibodies could cross react with apoproteins of D2 proteins (which contain P680) fromB. corticulans, spinach andC. fragile, but not with apoproteins of P700 Chl-proteins. Our results indicated some similarities in primary structure between LHC II of different species, and between
LHC II and D2 proteins of marine green algae and spinach. Our finding that D2 and P700 Chl-proteins are not immunologically related suggested that P700 Chl-proteins and D2 proteins pass through independent evolutionary pathways.
Contribution No 1717 from the Institute of Oceanology, Academia Sinica, This subject was supported by the National Science
Foundation of China. 相似文献