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741.
F.J. Ciesla 《Icarus》2010,208(1):455-467
Refractory objects such as Calcium, Aluminum-rich Inclusions, Amoeboid Olivine Aggregates, and crystalline silicates, are found in primitive bodies throughout our Solar System. It is believed that these objects formed in the hot, inner solar nebula and were redistributed during the mass and angular momentum transport that took place during its early evolution. The ages of these objects thus offer possible clues about the timing and duration of this transport. Here we study how the dynamics of these refractory objects in the evolving solar nebula affected the age distribution of the grains that were available to be incorporated into planetesimals throughout the Solar System. It is found that while the high temperatures and conditions needed to form these refractory objects may have persisted for millions of years, it is those objects that formed in the first 105 years that dominate (make up over 90%) those that survive throughout most of the nebula. This is due to two effects: (1) the largest numbers of refractory grains are formed at this time period, as the disk is rapidly drained of mass during subsequent evolution and (2) the initially rapid spreading of the disk due to angular momentum transport helps preserve this early generation of grains as opposed to later generations. This implies that most refractory objects found in meteorites and comets formed in the first 105 years after the nebula formed. As these objects contained live 26Al, this constrains the time when short-lived radionuclides were introduced to the Solar System to no later than 105 years after the nebula formed. Further, this implies that the t=0 as defined by meteoritic materials represents at most, the instant when the solar nebula finished accreting significant amounts of materials from its parent molecular cloud. 相似文献
742.
In a set of 16 drop tower experiments the motion of sub-millimeter to millimeter-sized particles under microgravity was observed. Illumination by a halogen lamp induced acceleration of the particles due to photophoresis. Photophoresis on dust-free chondrules, on chondrules, glass spheres and metal spheres covered with SiC dust and on pure SiC dust aggregates was studied. This is the first time that photophoretic motion of millimeter-sized particles has been studied experimentally. The absolute values for the photophoretic force are consistent with theoretical expectations for spherical particles. The strength of the photophoretic force varies for chondrules, dust covered particles and pure dust from low to strong, respectively. The measurements support the idea that photophoresis in the early Solar System can be efficient to transport solid particles outward. 相似文献
743.
简述了基于IBOB和Xilinx System Generator平台的射电望远镜宽带数字频谱仪系统的设计与应用;给出了双路400MHz、2048通道、16IP输出数字频谱仪系统的具体设计方案,并对该数字频谱仪器的性能指标进行了分析和测试,验证了方案的可行性;最后初步讨论了滤波器设备对后端系统的影响。 相似文献
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746.
The Early Cambrian Balang Formation is comprised of mudrock and shale, which was deposited in a shelf environment in the eastern part of Guizhou, south China. The Balang Fauna, which consists of seven phyla, occurs in the middle and upper parts of the Balang Formation. Arthropods are important constituents of the Balang Fauna and include a great number of trilobites, large bivalved arthropods, and newly-discovered well-preserved bradoriid fossils. The bradoriids present include three genera and four species : Comptaluta inflata (Cheng, 1974) emend Hou et al., 2002; Comptaluta kailiensis sp. nov., and Alutella elongeta sp. nov., Aluta sp. This faunal assemblage in the Balang Formation is distinguished from the Tsunyiella Chang, 1964, Songlinella Yin, 1978 and Kunmingella Hou, 1956 assemblage which occurs in the Niutitang and Mingxinsi formations of the Yangtze Platform in middle region of Guizhou and which is earlier than the Balang Formation in age. However, this assemblage resembles the Comptaluta pik, 1968 assemblage from the Early Cambrian Heilinpu Formation in Wuding County, Yuanan Province and from the Ordian Stage of the Cambrian of Australia. The great abundance of Comptaluta pik, 1968 and overall taxonomic diversity of the Comptaluta pik, 1968 assemblage set it distinctly apart from the Alutella Kobayashi et Kato, 1951 and Aluta Hou, 1956 assemblages of the Balang Formation. Alutella Kobayashi et Kato, 1951 and Aluta Hou, 1956 also occur in the Early Cambrian Niutitang Formation of the Yangtze Platform of Guizhou. Individual Bradoriids from the Balang Formation are characterized by large size (3 mm). The discovery of new Bradoriid assemblages not only expands the group’s geographical range and assemblage affinities, but also indicates that Bradoriids migrated eastward from shallow-water to deeper-water environments during the Early Cambrian, indicating that they were capable of life in deeper-water, and adaptation to a new ecological setting. 相似文献
747.
利用钻探、测井及地震资料对辽河盆地东部凹陷驾掌寺—小龙湾地区沙河街组三段上亚段进行了沉积环境和聚煤作用分析,编制了各种单因素图件及古地理图,识别出冲积扇、三角洲平原、三角洲前缘和前三角洲以及滨浅湖等古地理单元。分析认为,研究区物源来自东侧东部斜坡带和西侧中央凸起,并在区内沉积中心—驾掌寺—小龙湾凹陷处汇集,在适宜的气候、缓和的构造背景、适中的沉降幅度、较少的碎屑输入条件下,有一定水体深度的三角洲平原分流间湾沼泽区是成煤的有利地带,巨厚煤层分布于小龙湾地区的小14井、小5井以及小31井一带。 相似文献
748.
CCD����ˮϵͳ�ı궨��������� 总被引:1,自引:0,他引:1
??????????????????????????CCD?????????????????????????????????????? ????????????:????????????CCD???б?????????????????;????????????崫???????б????????????????????????????????????????????ε?????????????????????????÷??????????????????????????????е??????? 相似文献
749.
The Deep Impact mission succeeded in excavating inner materials from the nucleus of Comet 9P/Tempel 1 on 2005 July 04 (at 05:52 UT). Comet 9P/Tempel 1 is one of Jupiter family short period comets, which might originate in the Kuiper belt region in the solar nebula. In order to characterize the comet and to support the mission from the ground-based observatory, optical high-dispersion spectroscopic observations were carried out with the echelle spectrograph (UVES) mounted on the 8-m telescope VLT (UT2) before and after the Deep Impact event. Ortho-to-para abundance ratios (OPRs) of cometary ammonia were determined from the NH2 emission spectra. The OPRs of ammonia on July 3.996 UT and 4.997 UT were derived to be 1.28±0.07 (nuclear spin temperature: Tspin=24±2 K) and 1.26±0.08 (Tspin=25±2 K), respectively. There is no significant change between before and after the impact. Actually, most materials ejected from the impact site could have moved away from the nucleus on July 4.997 UT, about 17 h after the impact. However, a small fraction of the ejected materials might remain in the slit of UVES instrument at that time because an excess of about 20% in the NH2 emission flux is observed above the normal activity level was found [Manfroid, J., Hutsemékers, D., Jehin, E., Cochran, A.L., Arpigny, C., Jackson, W.M., Meech, K.J., Schulz, R., Zucconi, J.-M., 2007. Icarus. This issue]. If the excess of NH2 on July 04.997 UT was produced from icy materials excavated by the Deep Impact, then an upper-limit of the ammonia OPR would be 1.75 (Tspin>17 K) for those materials. On the other hand, the OPR of ammonia produced from the quiescent sources was similar to that of the Oort cloud comets observed so far. This fact may imply that physical conditions where cometary ices formed were similar between Comet 9P/Tempel 1 and the Oort cloud comets. 相似文献
750.
地勘单位的企业化演变,是随着国家体制改革的不断深化而发展的,是一个渐进的过程.概略地分析了地勘单位50年来不同发展阶段的特点及其规律,指出只有认清其发展规律,才能把握住工作的方针和策略,适时地、有步骤地推出改革措施,解决实际问题.论述了生产要素的合理配置,是发展产业经济的关键;适度规模经济、发掘多种资源潜力是发展地勘产业经济的重要措施. 相似文献