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91.
内蒙古乌达地区早二叠世早期植物群 总被引:7,自引:2,他引:5
通过对内蒙古乌达地区早二叠世早期山西组植物化石进行研究,共鉴定出植物化石7属11种,即Tingiacarbonica(Schenk)Hale,TpartitaHale,PlagiozamitescfoblongifoliusHale,SphenopterisnoriniHale,SnystroemiSze,StenuisSchenk,PecopterisandersoniHale,PlativenosaHale,Taeniopterissp,Caulopterissp,PterophylumdaihoenseKawasaki。研究结果表明,这些植物化石均为华夏型分子,可以和华夏植物区的一些同期植物群进行对比。根据植物群的总体组成,该区山西组植物群的地质时代属于早二叠世早期,大致相当于阿谢尔期(Aselian)至萨克马尔期(Sakmarian)。 相似文献
92.
Guangzhi Tu 《中国科学D辑(英文版)》1998,41(1):1-13
The new plants documented here, including a representative of the trimerophytesPsilophyton primitiuum sp. nov., a questionable rhyniophyte or trimerophyteHedeia sinica sp. nov., a prelycopodBragwanathia sp. and two species of zosterophyllophytes,Zosterophyllum australianum Lang and Cookson 1930 and2. sp. 1, from the Posongchong Formation of southeastern Yunnan, China, add to the known floral diversity of the Early Devonian
of this region. Two sections of the Posongchong Formation, Changputang section of Wenshan district and Gegu section of Mengzi
district also are introduced. After comparing the plants with those of the coeval flora of Australia and considering the data
of recent paleocontinental reconstructions, the authors suggest that there is a northeastern Gondwana phytogeographic unit
during the early Devonian comprising Australia, South China Block and perhaps Shan-Thai Block. The similarity of the floral
component between Australia and South China is discussed. Because both Australia and South China also have dominant or endemic
taxa, each might be recognized as a subunit, separately characterized byHedeia for Australia andEophyllophyton for South China.
Project supported by the National Natural Science Foundation of China (Grant Nos. 49372075 and 49742004) 相似文献
93.
Ralph A. M. J. Wijers Joshua S. Bloom Jasjeet S. Bagla & Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》1998,294(1):L13-L17
A gamma-ray burst (GRB) releases an amount of energy similar to that of a supernova explosion, which combined with its rapid variability suggests an origin related to neutron stars or black holes. Since these compact stellar remnants form from the most massive stars not long after their birth, GRBs should trace the star formation rate in the Universe; we show that the GRB flux distribution is consistent with this. Because of the strong evolution of the star formation rate with redshift, it follows that the dimmest known bursts have z ∼ 6, much above the value usually quoted and beyond the most distant quasars. This explains the absence of bright galaxies in well-studied GRB error boxes. The increased distances imply a peak luminosity of 8.3 × 1051 erg s−1 and a rate density of 0.025 per million years per galaxy. These values are 20 times higher and 150 times lower, respectively, than are implied by fits with non-evolving GRB rates. This means either that GRBs are caused by a much rarer phenomenon than mergers of binary neutron stars, or that their gamma-ray emission is often invisible to us due to beaming. Precise burst locations from optical transients will discriminate between the various models for GRBs from stellar deaths, because the distance between progenitor birth place and burst varies greatly among them. The dimmest GRBs are then the most distant known objects, and may probe the Universe at an age when the first stars were forming. 相似文献
94.
95.
Bagla 《Monthly notices of the Royal Astronomical Society》1998,297(1):251-254
Recent observations show a large concentration of galaxies at high redshift. At first sight, strong clustering of galaxies at high redshifts seems to be in contradiction with the models of structure formation. In this paper we show that such structures are a manifestation of the strong clustering of rare peaks in the density field. We compute the frequency of occurrence of such large concentrations of galaxies in some models of structure formation. 相似文献
96.
治岭头金银矿及杨梅岗铅锌矿、治岭头黄铁矿均生成在华峰尖火山通道的边缘断裂带内。研究火山构造不但对找矿和成矿预测有重要意义,而且对研究矿床的生成时代、成因类型也有重要意义。治岭头金银矿虽然生成在陈蔡群变质岩的糜棱岩带内,许多研究者认为是变质热液矿床。从矿体的产出部位与火山通道的关系看:应为火山热液矿床,生成时代应为燕山早期。 相似文献
97.
Though entropy production is forbidden in standard FRW Cosmology, Berman and Som presented a simple inflationary model where
entropy production by bulk viscosity, during standard inflation without ad hoc pressure terms can be accommodated with Robertson–Walker’s
metric, so the requirement that the early Universe be anisotropic is not essential in order to have entropy growth during
inflationary phase, as we show. Entropy also grows due to shear viscosity, for the anisotropic case. The intrinsically inflationary
metric that we propose can be thought of as defining a polarized vacuum, and leads directly to the desired effects without
the need of introducing extra pressure terms. 相似文献
98.
依据鲁西地区早前寒武纪花岗质侵入岩普遍具有塑性流变特征和退化变质特征,以及变质作用和变形作用相协调等现象,认为岩体的侵位与变形、变质是同一期构造岩浆作用形成的,是岩浆就位后逐渐冷凝过程中,在持续应力作用下发生的,与后期的地质构造作用无关;固态岩石只能发生脆性变形和局部的脆韧性变形。并从热力场、动力场和化学场的变化趋势对变形、变质作用的制约因素作了简要分析。 相似文献
99.
Formation and early development of tetraspores of Polysiphonia urceolata (Rhodomelaceae, Rhodophyta)
Polysiphonia urceolata is one type of potential commercial red seaweeds used for breeding and cultivation, because of its significant biochemical
and biomedical application. However, the information of breeding and seedling incubation for cultivation is limited, especially
the early development. In this study, tetrasporohyte and gametophyte of P. urceolata were taken as the study materials in Huiquan Bay, Qingdao, China. The cleaned and sterilized tetrasporophytes and gametophytes
were pre-cultured in sterilized seawater, then nurtured at 18°C, 25 μmol photons m−2 s−1 in 12:12 h (light:dark) photoperiod. Continuous observation under microscope showed that the early development consists of
bipolar division stage and seedling stage. In the division stage, tetraspores germinate into bipolar sporelings that further
differentiate into a colorless rhizoidal portion and a lightly pigmented upright shoot. The lightly pigmented rhizoidal cell
develops to a rhizoid and the larger pigmented cell transforms to an erect axis. In the seedling stage, several quasi-protuberances
appear on the erect axis and form juvenile seedlings. The results demonstrate the culture of P. urceolata from tetraspores under laboratory conditions.
Supported by National Key Technology Support Program, Development Program of China (No.2006AA09Z21), National Natural Science
Foundation of China (No. 40618001 and N_CUHK438/06) and Shandong Agricultural Seed Stock Breeding Project 相似文献
100.
S. I. Grachev 《Astrophysics》2007,50(4):515-524
A new method is proposed to account for multiple scattering by electrons in calculations of the correlation functions describing
the angular fluctuations in the cosmic microwave background radiation (CMBR). The apparatus of the theory of radiative transport
with Rayleigh scattering is used. The problem is reduced to solving an integral equation for the vector source function (dependent
only on time), along with differential equations for the other quantities (scalar potentials, baryon velocities, etc.) which
show up in the problem. The quantities which describe the angular fluctuations in the CMBR (in the temperature and in the
polarization) are then calculated by integrating the vector source function along the line of sight. As an illustration, the
correlation functions and power spectra are calculated for the case where the fluctuations are produced by some initial gaussian
perturbations of the CMBR.
__________
Translated from Astrofizika, Vol. 50, No. 4, pp. 621–631 (November 2007). 相似文献