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41.
Growth strata are used to determine the kinematics of synsedimentary structures such as faults. Classical methods of analysis such as thickness versus throw plot consider that the available space created by fault slip in the hanging wall of faults is instantaneously filled up by sediments. This has lead many previous works to identify a cyclic activity for growth faults. Here we perform a careful analysis of the variation of strata thicknesses on each side of a very well documented normal growth fault in the Niger delta. We show that these thickness variations are induced by the alternation of sedimentary processes during continuous fault slip. Suspended-load processes induce either uniform or slightly variable thickness of a large majority of mudstone layers. Bedload processes result in a preferential thickening of sand layers in the hanging wall. These high quality data thus provide strong grounds for doubting the polycyclic growth diagnosed for some faults at the scale of sedimentary cycles and supports the notion that fault displacement rates can be very well behaved. Our study emphasizes the important conclusion that stable fault growth, and related displacement rates, can appear to be punctuated when viewed at the scale of sedimentary cycles. It follows that care should be taken when attempting to derive displacement rates on temporal scales equivalent to those of alternating sedimentological cycles.  相似文献   
42.
A replicated mesocosm experiment was carried out to evaluate differential effects of feeding conditions for larval Northeast Arctic (NA) cod and Norwegian coastal (NC) cod. The two populations were (1) reared together with a 6-day older NA cohort (mixed) in high (HC) and low prey concentration (LC; 2000 and 200 prey/L initially), and (2) reared separately in HC treatments (non-mixed) to be able to evaluate both the effect of feeding conditions and possible effects of size interaction within mesocosms. The larvae were fed natural zooplankton, and the two stocks were identified in the mixed mesocosms by otolith marking. NA larvae hatched at a larger size, had higher growth rates, and survived better than NC larvae in both mixed and non-mixed mesocosms in the HC treatment. The second cohort clearly survived better in the non-mixed than in the mixed mesocosms, indicating the presence of an interaction effect before cannibalism could occur. We found a significant higher weight-at-length between NC and NA larvae (<12 mm), which was bigger than the effect difference due to feeding conditions. Furthermore, a positive relation between survival and initial growth within mesocosms was found. We suggest that lower growth at early larval stages was accompanied by lower survival, and suggest that this was further enhanced when larvae interacted with older and larger larvae.  相似文献   
43.
Concern about future anthropogenic warming has lead to demands for information on what might happen to fish and fisheries under various climate-change scenarios. One suggestion has been to use past events as a proxy for what will happen in the future. In this paper a comparison between the responses of Atlantic cod (Gadus morhua) to two major warm periods in the North Atlantic during the 20th century is carried out to determine how reliable the past might be as a predictor of the future. The first warm period began during the 1920s, remained relatively warm through the 1960s, and was limited primarily to the northern regions (>60°N). The second warm period, which again covered the northern regions but also extended farther south (30°N), began in the 1990s and has continued into the present century. During the earlier warm period, the most northern of the cod stocks (West Greenland, Icelandic, and Northeast Arctic cod in the Barents Sea) increased in abundance, individual growth was high, recruitment was strong, and their distribution spread northward. Available plankton data suggest that these cod responses were driven by bottom-up processes. Fishing pressure increased during this period of high cod abundance and the northern cod stocks began to decline, as early as the 1950s in the Barents Sea but during the 1960s elsewhere. Individual growth declined as temperatures cooled and the cod distributions retracted southward. During the warming in the 1990s, the spawning stock biomass of cod in the Barents Sea again increased, recruitment rose, and the stock spread northward, but the individual growth did not improve significantly. Cod off West Greenland also have shown signs of improving recruitment and increasing biomass, albeit they are still very low in comparison to the earlier warming period. The abundance of Icelandic cod, on the other hand, has remained low through the recent warm period and spawning stock biomass and total biomass are at levels near the lowest on record. The different responses of cod to the two warm events, in particular the reduced cod production during the recent warm period, are attributed to the effects of intense fishing pressure and possibly related ecosystem changes. The implications of the results of the comparisons on the development of cod scenarios under future climate change are addressed.  相似文献   
44.
广东地区河流阶地和冲积扇沉积物中砂岩砾石风化晕随时间增厚。风化晕生长速度呈指数衰减,并拟合于下列公式:T 1485D4.13这里T=时间,以年表示,D=沉积物表部约50块砾石风化晕厚度的加权平均值,以毫米表示。利用风化晕厚度确定出广东地区河流第一和第二级阶地分别为1000—13300年和8600—26500年,肇庆盆地北部山前地带第Ⅰ和第Ⅱ级冲积扇分别为51500年和24400年。同时,在构造地貌变形分析的基础上,估算出本区三条主要北东向断裂带在晚更新世—中全新世的垂直断层作用速度为0.6—1.6毫米/年,中全新世甚或晚更新世晚期以来的活动速度极小  相似文献   
45.
晶体生长机理   总被引:3,自引:0,他引:3  
李武  高世扬 《盐湖研究》1994,2(3):76-80
从扩散控制,成核控制,位错控制和综合控制等几个方面阐述了自溶液中生长晶体的晶体生长机理.  相似文献   
46.
Effects of global warming on animal distribution and performance become visible in many marine ecosystems. The present study was designed to develop a concept for a cause and effect understanding with respect to temperature changes and to explain ecological findings based on physiological processes. The concept is based on a wide comparison of invertebrate and fish species with a special focus on recent data obtained in two model species of fish. These fish species are both characterized by northern and southern distribution limits in the North Atlantic: eelpout (Zoarces viviparus), as a typical non-migrating inhabitant of the coastal zone and the cod (Gadus morhua), as a typical inhabitant of the continental shelf with a high importance for fisheries.Mathematical modelling demonstrates a clear significant correlation between climate induced temperature fluctuations and the recruitment of cod stocks. Growth performance in cod is optimal at temperatures close to 10°C, regardless of the population investigated in a latitudinal cline. However, temperature specific growth rates decrease at higher latitudes. Also, fecundity is less in White Sea than in North and Baltic Sea cod or eelpout populations. These findings suggest that a cold-induced shift in energy budget occurs which is unfavorable for growth performance and fecundity. Thermal tolerance limits shift depending on latitude and are characterized by oxygen limitation at both low or high temperatures. Oxygen supply to tissues is optimized at low temperature by a shift in hemoglobin isoforms and oxygen binding properties to lower affinities and higher unloading potential. Protective stimulation of heat shock protein synthesis was not observed.According to a recent model of thermal tolerance the downward shift of tolerance limits during cold adaptation is associated with rising mitochondrial densities and, thus, aerobic capacity and performance in the cold, especially in eurythermal species. At the same time the costs of mitochondrial maintenance reflected by mitochondrial proton leakage should rise leaving a lower energy fraction for growth and reproduction. The preliminary conclusion can be drawn that warming will cause a northern shift of distribution limits for both species with a rise in growth performance and fecundity larger than expected from the Q10 effect in the north and lower growth or even extinction of the species in the south. Such a shift may heavily affect fishing activities in the North Sea.  相似文献   
47.
耕作制度的改变,为棉铃虫种群数量上升提供了良好的食物源和生态环境;大面积使用化学农药,不仅削弱了天敌的控害作用,也提高了棉铃虫的抗药性;气候变暖,适宜于棉铃虫数量上升。因此,棉铃虫种群增加,棉花、玉米、小麦、豆类、瓜菜等受害也明显加重。要控制棉铃虫的发生程度,首先要防治棉田外一代幼虫和卵,减少一代种群数量;对二代棉铃虫,宜有选择地使用化学农药和生物农药进行防治,并充分发挥天敌的自然控制力,以减少种群数量;三代、四代棉铃虫主要危害作物繁殖器官,直接影响作物的产量和品质,以物理诱杀和玉米诱集带集中诱杀为主,既可控制其危害,又对其天敌无负面影响;五代棉铃虫虽对当年作物产量影响不大,但其种群数量直接影响下一年一代发生量,因此应及时喷施病毒类等生物性药剂,降低其越冬种群,同时也保护自然天敌安全越冬。  相似文献   
48.
通过试验研究,探讨主要气象因子在唐河县的变化规律和对金花梨生长发育的影响,研究金花梨在遭受灾害性天气影响时,采取相应的技术措施,确保金花梨的高产、稳产。  相似文献   
49.
通过腹腔注射药物、尾静脉取血、放射免疫测定激素含量等方法研究L-多巴等几种药物对草鱼鱼种生长激素分泌的影响,发现腹腔注射L-多巴、阿朴吗啡可以显著提高草鱼鱼种血清生长激素水平,而腹腔注射多巴胺、去甲肾上腺素、肾上腺素和6-羟多巴则可明显降低草鱼鱼种血清生长激素水平。说明儿茶酚胺类参与了草鱼鱼种生长激素的分泌调节,L-多巴或其代谢物是通过中枢神经系统促进草鱼鱼种生长激素分泌的,而多巴胺、去甲肾上腺素和肾上腺素则是在脑垂体水平上抑制草鱼鱼种生长激素的分泌。  相似文献   
50.
取体长为11mm的斑节对虾苗和刀额新对虾苗体长为6.1mm,经暂养数天后,分别在不同盐度的水中进行试验。结果表明,这两种虾苗适应低盐度十分广泛。刀额新对虾苗可比斑节对虾苗适应更低的盐度。斑节对虾苗在从盐度23.18直接降至盐度6.21时,成活率仍可达70%。当虾苗饲养在盐度18.54时,直接放水至海水盐度5.1,成活率为85%。当虾苗在从盐度25.13逐渐淡化到盐度1时,成活率仍有20%~40%。但是,考虑到体重的增重率,虾苗最佳饲养盐度为13.8。刀额新对虾苗从盐度23.18的海水直接放入盐度2以下的海水中,成活率仍有56.7%~63.3%。如果逐渐淡化海水,可在盐度<2时正常生长。在盐度8.96左右饲养,其体重增重率最佳。上述这两种虾适于河口低盐度地区养殖。在有条件的养成场适当降低盐度,有利其生长。  相似文献   
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