全文获取类型
收费全文 | 30860篇 |
免费 | 5495篇 |
国内免费 | 7327篇 |
专业分类
测绘学 | 1363篇 |
大气科学 | 6890篇 |
地球物理 | 7929篇 |
地质学 | 15511篇 |
海洋学 | 3591篇 |
天文学 | 1557篇 |
综合类 | 3404篇 |
自然地理 | 3437篇 |
出版年
2024年 | 129篇 |
2023年 | 556篇 |
2022年 | 1280篇 |
2021年 | 1537篇 |
2020年 | 1300篇 |
2019年 | 1368篇 |
2018年 | 1650篇 |
2017年 | 1526篇 |
2016年 | 1769篇 |
2015年 | 1347篇 |
2014年 | 1873篇 |
2013年 | 1620篇 |
2012年 | 1553篇 |
2011年 | 1609篇 |
2010年 | 1764篇 |
2009年 | 1754篇 |
2008年 | 1512篇 |
2007年 | 1460篇 |
2006年 | 1220篇 |
2005年 | 1118篇 |
2004年 | 881篇 |
2003年 | 893篇 |
2002年 | 887篇 |
2001年 | 848篇 |
2000年 | 1068篇 |
1999年 | 1518篇 |
1998年 | 1267篇 |
1997年 | 1335篇 |
1996年 | 1137篇 |
1995年 | 1041篇 |
1994年 | 932篇 |
1993年 | 809篇 |
1992年 | 656篇 |
1991年 | 480篇 |
1990年 | 332篇 |
1989年 | 367篇 |
1988年 | 304篇 |
1987年 | 205篇 |
1986年 | 171篇 |
1985年 | 125篇 |
1984年 | 102篇 |
1983年 | 81篇 |
1982年 | 79篇 |
1981年 | 55篇 |
1980年 | 50篇 |
1979年 | 34篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1958年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
831.
832.
833.
834.
CMIP5模式对中国近海海表温度的模拟及预估 总被引:2,自引:0,他引:2
基于观测和再分析资料;利用多种指标和方法评估了国际耦合模式比较计划(CMIP5)中21个模式对中国近海海温的月、季节和年际变化模拟能力。多模式集合能够再现气候平均意义下近海海温的空间分布特征;但量值上存在一定的低估。在渤海和黄海;集合平均与观测差别比较明显。在年际尺度上;与观测数据对比;模式模拟海温与Niño3指数相关性较小。中国近海海表面温度在1960-2002年有明显的升高趋势;从2003年开始增温趋缓。评估结果表明;ACCESS1.0、BCC-CSM1.1、HadGEM2-ES、IPSL-CM5A-MR、CMCC-CM、FGOALS-g2、CNRM-CM5-2、INMCM4八个模式对中国近海海温的变化有较好的模拟能力。利用ACCESS1.0、INMCM4、BCC-CSM1.1、IPSL-CM5A-MR、CMCC-CM这5个模式结果对中国近海海温未来的变化进行了预估。在RCP4.5、RCP8.5情景下;未来近100年中国近海海温有明显升高趋势;最优模式多模式集合平均增温分别可达到1.5℃、3.3℃;净热通量变化和平流变化共同促进了东海升温。 相似文献
835.
A new method for the quantification of different redox-species of molybdenum (V and VI) in seawater 总被引:1,自引:0,他引:1
A new method for the direct determination of reduced and oxidized Mo species (Mo (V) and Mo (VI)) in seawater was developed and used for the first time. The method includes the complexation of Mo (V) with tartrate, solid phase extraction of the Mo (V)–tartrate complex by a XAD 7HP resin, followed by elution with acidic acetone. In this study, the eluted Mo (V) was quantified by graphite furnace atomic absorption spectrometry. The detection limit of this protocol was on the order of 0.2 nM. The analytical precision was 10% of ~ 10 nM. This method was successfully applied to the determination of Mo (V) and Mo (VI) in surface and bottom waters at the head of Peconic River Estuary. Total Mo (Mo (V) + Mo (VI)) ranged from 100–120 nM in most bottom saline waters, and 2.5–15 nM for surface fresher waters. Concentrations of Mo (V) in these environments ranged from 0 nM to ~ 15 nM, accounting for 0%–15% of the total dissolved Mo pool. The time series experiments showed that the Mo speciation changed within 1 h after the water collection, and therefore it is strongly suggested that speciation analysis be carried out within the first 15 min. However, since these are the first Mo speciation data in concentration ranges typical of normal marine and coastal waters, additional research may be required to optimize the methodology and further explore Mo cycling mechanisms. 相似文献
836.
碎屑沉积岩的物质组成对其形成的构造背景具有重要的指示作用。通过对临清坳陷东部三叠系碎屑沉积岩样品地球化学主量和微量元素分析表明:三叠系岩石样品主要为成熟度较低的杂砂岩和长石砂岩;碎屑沉积岩的母岩总体上与大陆地壳组成基本一致,原岩以沉积岩和花岗岩为主;临清坳陷东部中生代早—中三叠世处于靠近大陆岛弧的活动大陆边缘构造环境,其动力学机制与早期秦岭洋壳向华北板块俯冲、晚期扬子板块和华北板块碰撞作用有关。研究结果为确定三叠纪时期华北东部南侧的构造环境提供了地球化学方面的证据。 相似文献
837.
Considering the current disadvantages of present offshore wind turbine foundations, a novel anchor foundation with skirt and branches is proposed, called offshore umbrella suction anchor foundation (USAF). A series of experiments and numerical simulations were performed to explore the bearing capacity of the USAF under various kinds of loading modes. The bearing characteristics and the anchor–soil interactions are described in detail for horizontal static loading, horizontal cyclic loading, and an antidrawing (pullout) test in silty soil. In the static loading test, the load–deflection of the anchor under step loading was analyzed and the normalized curve of the load–deflection was obtained to determine the ultimate horizontal bearing capacity of the anchor under normal working conditions. Under horizontal cyclic loading, the relationship between the plastic cumulative deformation and cyclic number was determined. In addition, the responses of USAF were investigated for a low wave frequency and storm surges. In the drawing test, it was found that a “segmentation phenomenon” occurred during the test. Moreover, a method to identify the maximum antidrawing load of USAF was provided based on dynamic mechanics. The numerical results show that the use of anchor branches and skirt can enhance the bearing performance of USAF to a certain degree. However, the anchor branch has a slight positive influence on the bearing performance improvement. The USAF is not only similar to a stiff short pile, but a rotation occurs. The failure envelope under composite loading (V-M) was obtained and the changes associated with changes in the aspect ratio of the internal compartment were clarified. 相似文献
838.
In order to solve unsteady incompressible Navier–Stokes(N–S) equations, a new stabilized finite element method,called the viscous-splitting least square FEM, is proposed. In the model, the N–S equations are split into diffusive and convective parts in each time step. The diffusive part is discretized by the backward difference method in time and discretized by the standard Galerkin method in space. The convective part is a first-order nonlinear equation.After the linearization of the nonlinear part by Newton's method, the convective part is also discretized by the backward difference method in time and discretized by least square scheme in space. C~0-type element can be used for interpolation of the velocity and pressure in the present model. Driven cavity flow and flow past a circular cylinder are conducted to validate the present model. Numerical results agree with previous numerical results, and the model has high accuracy and can be used to simulate problems with complex geometry. 相似文献
839.
The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered soil and the thickness of the top soil layer. The geometric parameters of the anchor and the soil properties (the liquid limit, plastic limit, specific gravity, undrained shear strength, density, and water content) were measured. Based on the energy analysis and present test data, an empirical formula to predict the penetration depth of torpedo anchor in two-layered soil bed was proposed. The proposed formula was extensively validated by laboratory and field data of previous researchers. The results were in good agreement with those obtained for two-layered and single-layered soil bed. Finally, a sensitivity analysis on the parameters in the formula was performed. 相似文献
840.
Acartia bifilosa (Copepoda: Calanoida) is a common species in offing of global waters and it often becomes dominant species in some estuaries. This species develops different strategy according to variation of environment. Despite its ecological role, Acartia bifilosa also has been concerned as live feeds in aquaculture, but study on egg production rate of this species in saturated diet in different temperature and different diet is so far not available. In order to interpret the importance of temperature and diet on natural population variation and also on aquaculture as foods of larval fish, the functional response of reproductive success of Acartia bifilosa was quantified in the laboratory using different temperatures and diets.
Acartia bifilosa was captured in Jiaozhou Bay and acclimated to corresponding temperature for 3~4 days. In order to reduce the effect of large extent temperature range on organism, we captured Acartia bifilosa from March to June and acclimated them to temperature which is adjacent to natural temperature. Daily egg production rate (EPR, eggs female-1day-1) was detected for 11~15 days at 5 different temperatures ranged from 8.0 to 23 °C and all the females was feed on saturated diet all through the experiments. EPR on first day was not calculated in the mean EPR to eliminate the effect of different diets. This result showed that Acartia bifilosa spawned continuously during the experiment days and no obvious regulation was found. EPR was positively correlated with temperature from 8.0 to 23 °C. The highest mean EPR was observed at 23 °C (7.3 eggs female-1day-1), and the lowest value was found at 8 °C (3.8 eggs female-1day-1). The effect of diets on EPR was evaluated at two different temperatures (8.0 °C and 12.5 °C). Same trends were found at the two temperatures: mean EPR fed on Chaetoceros sp. was higher than that fed on Skeletonema costatum, and during the 14-day experiments, EPR was higher for females fed on Skeletonema costatum than chaetoceros sp. in the first few days (3~5 days), but it changed reversely in the subsequent days until the end of the experiments. Hatched eggs were observed in the two experiments at temperature 8°C and 12.5 °C and no diapause eggs were found. The hatching success rate was low at 8°C but reached 93.2% at 12.5 °C.
According to the results in this paper, we detected the comfortable temperature range for EPR, and evaluated the effect of Skeletonema costatum which often brings out red tide in natural waters. These results are beneficial to ecological research for explaining population variation and population recruitment of this species, These data also can be used in Acartia bifilosa aquaculture. 相似文献