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941.
由极地冰芯记录、中纬黄土记录和深海沉积记录的对比可得,15万年以来全球变化的基本框架为:末次间冰期,从距今14万年开始到约12.5万年达鼎盛,可分为五个阶段,即冰芯中三次高温期夹两次低温期;黄土中三层古土壤夹两层黄土;深海沉积中三次高海面夹两次低海面。末次冰期,距今8万年到1万年,可分为三个阶段,早、晚冰段和中间的间冰段。早、晚冰段盛期气候寒冷程度相当,但晚冰段最低温持续期更长,造成海面比早期更低。中间的间冰段,至少可分为7个亚段,即4次暖期(4次弱成土古土壤)夹3次冷期。全新世与末次间冰期对比,总体气候变化较平缓。在上述基本框架中,近几年发现,在末次冰期存在许多短周期、高频快速变化事件。这些事件,温度变化幅度达7℃,变化速率为几年到几十年,对应的环境变化速率可能更快。这些事件的引发机理目前还不清楚,有待进一步研究。  相似文献   
942.
This paper presents a Web-based three-dimensional Geographic Information System (3DGIS) for Wenchuan earthquake disaster assessment. With the help of information technology resources, geoscientists are in a position to learn more about the structure of the earthquake in efficient ways. Due to huge spatial datasets of Wenchuan, China and narrow network bandwidth, general-purpose applications are difficult to transmit and visualize these datasets on the network. The application aims to interactively represent and transfer large spatial objects of Wenchuan County, China, as well as for dynamically rendering them in networking environments. Level-of-detail (LOD) terrain models and vector maps are created, and the server–client architecture is presented. The application provides an effective way for powerful access and manipulation of large-scale Wenchuan datasets.  相似文献   
943.
The chemical composition of the PMMR23 red supergiant located in the Small Magellanic Cloud (SMC) is analyzed. The abundance of 35 chemical elements and the upper limits of abundance for Tl and U are found. The relative abundance of heavy elements is higher by 0.6–1.0 dex with respect to iron peak elements. The spectra of several SMC red supergiants PMMR27, PMMR28, and PMMR144—located in the region where the velocities of stars and interstellar gas are quite high— show the emission components in the wings of the hydrogen line. This emission is not detected for PMMR23. A possibility of interstellar gas accretion on the atmospheres of PMMR23 and other supergiants in Magellanic Clouds is discussed. The analysis is carried out using spectra measured at ESO 3.6 m telescope with the spectral resolving power R = 30000.  相似文献   
944.
Factors affecting mesozooplankton distributions in the northeastern tropical Pacific Ocean were investigated using data obtained along a meridian line (5 degrees -12 degrees N, 131.5 degrees W) in the summers of 1998, 1999, and 2003. The survey periods corresponded to a sharp transition between the 1997-1998 El Ni?o and 1998-1999 La Ni?a events, the 1999 La Ni?a event, and near-normal conditions after the moderate 2002-2003 El Ni?o in the equatorial Pacific. A strong upwelling in the divergence zone from 10.5 degrees to 11 degrees N caused a shoaling of the thermocline depth (approximately 30 m), resulting in increases in nitrate and phytoplankton chlorophyll a (chl-a) concentrations, and, in turn, mesozooplankton abundance during the La Ni?a in 1999. In contrast, in 1998, remnants of El Ni?o characteristics, deeper thermocline depth (60-150 m) and warm surface water (>28 degrees C), led to low concentrations of nitrate, chl-a and low mesozooplankton abundance, except in the convergence zone around 7 degrees N. The thermocline depth and nitrate concentration obtained during the near-normal period in 2003 corresponded to intermediate values as compared to those obtained during El Ni?o and La Ni?a conditions. Interannual changes in the position and strength of ecotones, such as divergence and convergence zones, affected mesozooplankton community structure and cyclopoid-to-calanoid ratios along the 131.5 degrees W meridian line. The clustering pattern of the mesozooplankton community was mostly characterized by calanoid (mainly Clausocalanus sp.) and cyclopoid (mainly Oncaea sp.) copepods, accounting for most of the observed differences among groups during the study period. Cyclopoids and calanoids were more abundant in 1999 than in 1998 or 2003, with a sharp increase to the north, while they were less abundant to the north in 1998 and 2003. The cyclopoid-to-calanoid ratio peaked in the convergence zone in 1998 and the divergence zones in 1999 and 2003, apparently due to the strength and location of the ecotones. Principal component analysis (PCA) with environmental factors and dominant mesozooplankton groups showed that dominant groups were affected by nitrate and chl-a concentrations in 1998, by sigma-t (water density), nitrate and chl-a concentrations in 1999, and by sigma-t, salinity and chl-a concentration (except siphonophores) in 2003. Latitudinal distribution of thermocline depth before and after the 1998/99 La Ni?a event showed a distinct interannual difference. The abundance of mesozooplankton in the divergence zone in 1999 was distinctively higher than abundances found in the convergence and divergence zones in 1998 and 2003, which resulted from the shallow thermocline depth due to an intensified upwelling during the strong 1998-1999 La Ni?a event.  相似文献   
945.
水沙环境中重金属迁移转化模型的两个解析解   总被引:2,自引:0,他引:2  
选取整体模型,将水体中的溶解态(水相)和吸附态(固相)重金属作为整体,开展了水沙环境中重金属迁移转化数学模型的解析解研究.在一定的简化条件下,得出了泥沙单纯沉积和单纯侵蚀两种特定动床条件下一维重金属迁移转化模型的两个解析解.文中成果可用于数学模型的验证和完善.  相似文献   
946.
章丘市确保土地开发整理长期效益   总被引:1,自引:1,他引:0       下载免费PDF全文
章丘市国土资源局以科学发展观为统领,认真贯彻落实国土资源部<土地开发整理若干意见>,进一步加强和改进土地开发整理工作的组织和管理,以实行3个转变为突破口,坚持建设与管护并重,实现了土地开发整理工程的长期效益.2007年4月被山东省国土资源厅评为全省土地开发整理工作先进单位.  相似文献   
947.
根据新一轮国土资源大调查的目标任务,对地质生态调查的内容、方法及成果提交等问题进行了探讨,提出了以人类经济技术活动对地质生态的影响作为主要调查内容,并以地质生态填图和多S技术为主要方法手段的意见。  相似文献   
948.
商河地区为自北向南成明显阶梯状分布的多级构造调节带及多级坡折带,受其构造特征影响,储层特征也表现出明显的规律性。通过对商河地区大量储层物性数据的统计,结合镜下薄片观察发现商河油田具有同一层位,自北向南,商一区、商二区、商三区、商四区储层物性依次变差的特点;而对于同一地区,整体上自上向下随深度增加储层物性逐渐变差;同一层位不同沉积微相的储层具有不同的物性特征,三角洲前缘河口坝砂体储层物性最好,水下分支河道较好,而远砂坝、席状砂砂体储层物性相对较差。经综合研究分析认为储层特征主要受沉积相及成岩作用共同影响,储层成岩作用主要受地层埋深的影响,而由于商河地区的分界大断层主要为同沉积断层,地层厚度和沉积相分布主要受同生断层活动的影响,因此构造作用的同沉积断层是商河地区储层物性的主要控制因素。  相似文献   
949.
The Mekong supports one of the richest inland fisheries in the world, with many of the fish migrating long distance to spawn. Little is known about the fisheries and migration strategies of the Upper Mekong whilst it is supposed that many fish species move between the Lower and Upper Mekong. Most likely, natural fish migration in the river has been altered by dam construction across the mainstream of the Upper Mekong. In this paper, the interconnectivity of fish species between different sections of the Mekong and negative impacts of dams on migratory fish are studied. Of the 162 fish species in the Upper Mekong and the 869 species in the Lower Mekong, 61 species are common. Results show that there is no significant difference at order level between the UM and LM. Similarity coefficients are used to evaluate interconnectivity at species, genus and family levels among four different sections of the Upper Mekong with each other and with the Lower Mekong as a whole. The highest similarity is found between the middle and lower reach of the Upper Mekong at species and genus levels and the middle and upper reach at family level. Of the eight cascade dams, Mengsong Dam in planning is considered as the biggest threat to migratory fish from the Lower Mekong and should be particularly concerned. Supported by National Natural Science Foundation of China (No. 40601096)  相似文献   
950.

The serpentinized peridotites overlying the subducted zones in the Izu-Bonin-Mariana (IBM) arc system have been interpret as the cause of the low-velocity layer identified beneath the IBM froearc, in turn few earthquakes occurred along the plate boundary. Chrysotile, which is a low temperature and highly hydrated phase of serpentine with low frictional strength, has been suggested as the low velocity material in the serpentinized peridotites, besides, brucite is inferred to be likely conducive to stable sliding. However, such idea encounters challenging in our serpentinized peridotites from the southern Mariana forearc, which absent both the above minerals. The presence of talc, which characterized by its weak, low-friction and inherently stable sliding behavior, provides new clue. Here we report the occurrence of talc in serpentinized peridotites collected from the landward trench slope of the southern Mariana forearc. We infer that talc is mainly forming as a result of the reaction of serpentine minerals with silica-saturated fluids released from the subducting slab, and talc also occurs as talc veins sometimes. Due to its unique physical properties, talc may therefore play a significant role in aseismic slip in the IBM subduction zone.

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