首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   18588篇
  免费   3278篇
  国内免费   4270篇
测绘学   1023篇
大气科学   3723篇
地球物理   5201篇
地质学   8949篇
海洋学   2582篇
天文学   793篇
综合类   1753篇
自然地理   2112篇
  2024年   100篇
  2023年   343篇
  2022年   811篇
  2021年   956篇
  2020年   760篇
  2019年   814篇
  2018年   934篇
  2017年   886篇
  2016年   1012篇
  2015年   838篇
  2014年   1016篇
  2013年   1109篇
  2012年   975篇
  2011年   1014篇
  2010年   1076篇
  2009年   1002篇
  2008年   837篇
  2007年   898篇
  2006年   665篇
  2005年   638篇
  2004年   470篇
  2003年   530篇
  2002年   513篇
  2001年   503篇
  2000年   619篇
  1999年   910篇
  1998年   763篇
  1997年   764篇
  1996年   731篇
  1995年   646篇
  1994年   571篇
  1993年   489篇
  1992年   410篇
  1991年   287篇
  1990年   231篇
  1989年   188篇
  1988年   180篇
  1987年   102篇
  1986年   110篇
  1985年   68篇
  1984年   58篇
  1983年   57篇
  1982年   55篇
  1981年   40篇
  1980年   47篇
  1979年   36篇
  1978年   14篇
  1977年   9篇
  1974年   9篇
  1958年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
801.
就主采空区地表塌陷对铁路客运专线的危害性按照《建筑物、水体、铁路及主要井巷煤柱留设与压煤开采规程》及相关规范技术要求,对线路与主采空区之间的安全距离进行了量化评价,之后就小窑采空区场地对高等级铁路稳定性运用浅埋采空平衡拱的理论量化评价。以上两种量化评价的结果是可以保障线路与主采空区之间的安全距离,该小窑采空区顶板不受力,顶板地基稳定性差,最后文中对场地地基稳定性差的线路基础提出处理措施与建议。  相似文献   
802.
城市化是国家社会发展的必然趋势,为了在新一轮城市总体规划中能保证杭州市的大气环境质量,优化不同空间尺度的城市规划,协调城市发展与保护环境的关系,本文利用一个三维非静力区域边界层数值模式,对一些典型天气条件下杭州地区的风场和气温的空间分布特征进行模拟分析,并以此为依据,给出选取化工园区的位置的评估意见。模拟结果表明,化工园区的选址宜考虑在杭州市的西南方向。  相似文献   
803.
We estimated the reproductive success of adult brood fish and the heritability of growth-related traits for large yellow croaker (Larimichthys crocea). We created two independent full-factorial cross groups (1 and 2) by crossing 4 males×4 females and 4 males×3 females, respectively. We measured the body weight (BW), body length (BL), and body height (BH) of 281 individuals from group 1 and 318 individuals from group 2 at 20 months post hatch (harvest age). We also collected a tissue sample from each individual. The parents and offspring were genotyped using six polymorphic microsatellites. Of the 599 offspring, 99.2% were assigned to a single pair of parents. In both groups, some parent pairs produced a large number of offsprings while other pairs did not produce any offspring. The genetic diversity and putative Ne were lower in the offsprings than in the parents in both groups. The heritability estimates at 20-month age were 0.13±0.10 for BW, 0.19±0.13 for BL, and 0.09±0.06 for BH. The genetic and phenotype correlation between BW, BL, and BH was close to 1. The results provide basic information for selective breeding and further genetic characterization of large yellow croaker.  相似文献   
804.
Wang  Tongyu  Zhang  Shuwen  Chen  Fajin  Ma  Yonggui  Jiang  Chen  Yu  Jie 《中国海洋湖沼学报》2021,39(1):14-25
Upper ocean responses to the passage of sequential tropical cyclones over the northwestern South China Sea(SCS) in 2011 were investigated using satellite remote sensing data,Argo reanalysis data,and an array of mooring data.We found that the sea surface low temperature region lasted for more than 38 days and two phytoplankton blooms occurred after the passage of sequential tropical cyclones.The upper ocean cooling reached 2-5℃ with a right-side bias was observed along the typhoon track to about 200 km.The maintenance of low temperature region and the two phytoplankton blooms were mainly driven by upwelling and near-inertial turbulence mixing induced by the sequential tropical cyclones.The first phytoplankton bloom appeared on the 7~(th) day after the passage of the three tropical cyclones,and the chlorophyll-a(chl-a) concentration increased by 226%,which may be mainly driven by typhoons induced upwelling.The second phytoplankton bloom occurred on the 30~(th) day,the chl-a concentration increased by290%.Further analysis suggested that only the typhoons with similar characteristics as Nesat and Nalgae can induce strong near-inertial oscillation(NIO).Strong turbulent mixing associated with the near-inertial baroclinic shear instability lasted for 26 days.The measured mean eddy diffusivity in the upper ocean was above 10~(-4) m~2/s after typhoon Nesat.Enhancement of the turbulent mixing in the upper ocean helped to transport nutrient-rich cold waters from the deep layer to the euphotic layer,and is a maj or mechanism for the long-term maintenance of low temperature region as well as the second phytoplankton bloom.  相似文献   
805.
?о???1996??2005??????????52????С?????????????6????????????????????????????????????????????????????????????P???????NW????300??320???????У??????????????????????????????????????????????????????????????????????????????????仯?????????????????????????????????????NNW????????????總?????????????NWW????EW????  相似文献   
806.
In order to select an optimum extraction method for the target glycoprotein (TGP) from jellyfish (Rhopilema esculentum) oral-arms, a high performance liquid chromatography (HPLC)-assay for the determination of the TGP was developed. Purified target glycoprotein was taken as a standard glycoprotein. The results showed that the calibration curves for peak area plotted against concentration for TGP were linear (r = 0.9984, y = 4.5895x+47.601) over concentrations ranging from 50 to 400 mgL-1. The mean extraction recovery was 97.84% (CV2.60%). The fractions containing TGP were isolated from jellyfish (R. esculentum) oral-arms by four extraction methods: 1) water extraction (WE), 2) phosphate buffer solution (PBS) extraction (PE), 3) ultrasound-assisted water extraction (UA-WE), 4) ultrasound-assisted PBS extraction (UA-PE). The lyophilized extract was dissolved in Milli-Q water and analyzed directly on a short TSK-GEL G4000PWXL (7.8 mm×300 mm) column. Our results indicated that the UA-PE method was the optimum extraction method selected by HPLC.  相似文献   
807.
??????????GPS??????GLONASS???????????????????GPS ???????3?????裬????GPS??GLONASS?????????????Galileo????????????????????????????? ???????????????????????????????????????????棬???????????????λ????е???????????????????????Ч???????????????????????????????????????  相似文献   
808.
We introduce a new code for cosmological simulations, PHo To Ns, which incorporates features for performing massive cosmological simulations on heterogeneous high performance computer(HPC) systems and threads oriented programming. PHo To Ns adopts a hybrid scheme to compute gravitational force, with the conventional Particle-Mesh(PM) algorithm to compute the long-range force,the Tree algorithm to compute the short range force and the direct summation Particle-Particle(PP) algorithm to compute gravity from very close particles. A self-similar space filling a Peano-Hilbert curve is used to decompose the computing domain. Threads programming is advantageously used to more flexibly manage the domain communication, PM calculation and synchronization, as well as Dual Tree Traversal on the CPU+MIC platform. PHo To Ns scales well and efficiency of the PP kernel achieves68.6% of peak performance on MIC and 74.4% on CPU platforms. We also test the accuracy of the code against the much used Gadget-2 in the community and found excellent agreement.  相似文献   
809.
QSO objective prism survey was done for the field centered at 10h40m + 00°00. For the 348 objects selected, we present in this paper their positions,B J magnitudes, spectra, and finding charts. Based on the sample containing 163 QSO candidates with higher reliabilities (F 3), the surface density of QSO candidates withB J 20 is estimated to be about 4.5 per square degree.Work based on UKST plates.  相似文献   
810.
平衡剖面的正演计算及其应用   总被引:5,自引:0,他引:5       下载免费PDF全文
陈伟  曾庆 《地质科学》1993,28(2):117-126
正演运动模型近来已广泛运用于地质剖面的构造演化模拟。作者以Suppe的断层转折褶皱的几何模型为基础,详细阐述了挤压构造区域上盘地层的几何形态变化对应的速度场分布规律及地层长度变化;编制出相应的平衡剖面正演程序,并扩充了正演程序的应用范围。以川东大池干构造为实例,制作出该构造的平衡构造演化剖面。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号