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   174篇
  免费   23篇
  国内免费   61篇
测绘学   9篇
地球物理   18篇
地质学   35篇
海洋学   147篇
天文学   1篇
综合类   42篇
自然地理   6篇
  2024年   1篇
  2023年   4篇
  2022年   5篇
  2021年   4篇
  2020年   8篇
  2019年   4篇
  2018年   10篇
  2017年   7篇
  2016年   12篇
  2015年   14篇
  2014年   14篇
  2013年   18篇
  2012年   16篇
  2011年   15篇
  2010年   11篇
  2009年   19篇
  2008年   16篇
  2007年   15篇
  2006年   16篇
  2005年   13篇
  2004年   4篇
  2003年   7篇
  2002年   1篇
  2001年   1篇
  2000年   3篇
  1999年   2篇
  1997年   1篇
  1994年   1篇
  1993年   1篇
  1990年   3篇
  1988年   2篇
  1987年   2篇
  1986年   6篇
  1984年   2篇
排序方式: 共有258条查询结果,搜索用时 31 毫秒
81.
The relationship between microsatellite polymorphism and body weight of captive bred Chinese sea cucumber Apostichopus japonicus was investigated in two local populations in Dalian.Among ten loci discovered, nine show changes except for A J07 loci. Seven loci were found highly polymorphic in both populations. For each locus in two populations, the average number of alleles is 6.428 6 and 6.285 7, the average observed heterozygosity at 0.225 7 and 0.245 9, the expected heterozygosity at 0.776 8 and 0.748 8, the polymorphism information content (PIC) at 0.709 2 and 0.674 6, respectively. Further analysis show significant correlation between A. japonicus body weight and occurrence markers AJ02 and AJ04. The findings of the relation may be helpful for molecular breeding,as well as the marker-assisted selection of sea cucumbers.  相似文献   
82.
Ten novel polymorphic microsatellite loci were developed using an enrichment and colony hybridization protocol and characterized for the cuttlefish, Sepiella maindroni. Polymorphism was explored by using 30 individuals from the coastal waters of Zhanjiang, Guangdong province, China, in December 2007. The number of alleles ranged from 5 to 13. The ranges of observed and expected heterozygosity were from 0.578 9 to 1.000 0 and 0.682 8 to 0.925 7, respectively, and the average polymorphic information content (PIC) was 0.778 5. These microsatellite loci will certainly facilitate the detection of the genetic variation and population structure of S. maindroni.  相似文献   
83.
采用相关序列扩增多态性(sequence-reared amplified polymorphism,SRAP)技术分析野生草鱼和家养草鱼,并筛选与草鱼种质退化相关的分子遗传标记。共进行88对引物组合的检测,产生标记数目共计905个。依据标记在群体中出现的频率和变化规律,共筛选出21个可能与种质相关的特异性标记,对这些特异性标记进行测序并将测序结果进行BLAST分析,发现测得片段中有8个片段能在GeneBank中找到同源性较高的序列,而其他片段与数据库中序列的相似性较低。  相似文献   
84.
Error analyses of CHAMP data for recovery of the Earth’s gravity field   总被引:1,自引:0,他引:1  
A preliminary commission error analysis whereby orbit perturbation theory and other techniques are used to assess and predict the recovery of the Earths gravity field from the challenging microsatellite payload (CHAMP) mission is developed and implemented. With CHAMP launched in July 2000, accumulated evidence is now available to quantify the errors in the recovery procedure including the orbital precision from GPS, attitude errors, accelerometer noise and thruster mismatch/misalignment. For the latter, numerical integrations using a variable length single-step Runge–Kutta integrator and a fixed length multi-step method are compared to assess the error associated with assuming that the thruster misalignment can be spread uniformly across a step interval. Error degree variances from simulated studies are compared to results from a recently released CHAMP-based gravity field, EIGEN-1S. It is seen that the orbital positioning, as derived from the onboard GPS receiver, is critical, with accelerometer noise contributing at a lower level. Attitude error, at currently quoted accuracy, is not significant as an error source. AcknowledgementsThe authors would like to thank the UK Natural Environment Research Council (Grant No. NER/A/0000/00612) for financing this study and GFZ for supplying the data and technical support.  相似文献   
85.
The distribution of ring-C monoaromatic and triaromatic steroid hydrocarbons of about fifty crude oils and sediments of various origins and ages were studied in order to test their validity as geochemical source and maturity parameters. Three ratios appeared to be useful maturity parameters, i.e. A/B cis to trans isomers in non-rearranged monoaromatics, mono/triaromatics and shortvs long-chain homologues. Four other variations may be considered as source parameters depending upon lithology or other palaeo-environmental conditions, i.e. rearranged vs non-rearranged monoaromatics, 5β/5α -methyl rearranged monoaromatics, carbon number distribution and occurrence of a yet unknown series of methylated triaromatic steroids. 5α-Methyl rearranged monoaromatics seem to be particularly important in anhydrites from sabkha environments. Recent identification of most aromatic steroid constituents occurring in geological samples confers on this class of compounds an increasing value as correlation parameters in geochemical studies.  相似文献   
86.
Immunological and biochemical techniques were used to investigate organic matter in microbial mats from Solar Lake (Sinai, Egypt). Antibodies, elicited in rabbits against samples taken at different depths from a core of these mats, were used for the detection of immunological determinants preserved in these samples. Special attention was given to an antiserum directed against a top mat fraction (3–10 mm depth) and an antiserum against a fraction from a lower section of the core (380–390 mm depth). Both antisera, tested in a dot-blot immunobinding assay, were found to give positive reactions with organic matter from different depths of the sediment. An immunohistochemical experiment with the antisera points to antigenic determinants on Recent and subfossil sheaths of Microcoleus. In addition, extracts of sediment samples were submitted to electrophoresis in polyacrylamide gels in order to characterize the separated macromolecules by immunological means. The results showed a rapid decrease in the number of antigenic determinants from Recent to subfossil samples. However, even in the deepest layers of the sediment (690–700 mm depth) intact biopolymers were detected.  相似文献   
87.
4种养殖扇贝的群体遗传多样性及特异性AFLP标记研究   总被引:29,自引:2,他引:27  
应用AFLP技术对我国4种主要养殖扇贝进行了遗传分析.虾夷扇贝、海湾扇贝、华贵栉孔扇贝、栉孔扇贝4种养殖扇贝群体中,种内遗传相似度依次分别为0.841 5,0.786 3,0.719 0和0.673 1,香侬氏指数分别为43.52,58.87,80.16和92.83,栉孔扇贝和华贵栉孔扇贝的遗传多样性水平明显高于海湾扇贝和虾夷扇贝;AFLP标记共享位点分布表明,在4种扇贝中栉孔扇贝与华贵栉孔扇贝之间的共享位点最多,同时4种扇贝的种间遗传相似度也以栉孔扇贝和华贵栉孔扇贝之间为最高(0.769 5),海湾扇贝和虾夷扇贝之间为最低(0.662 6),揭示所研究的几种扇贝中栉孔扇贝和华贵栉孔扇贝的遗传关系最近(遗传距离为0.262 1);找到了21个种内特异性AFLP标记和种间共享标记,可用于种质鉴定和分子辅助分类.  相似文献   
88.
在良种选育过程中,为了尽快得到稳定可遗传的优良性状,常采用近交方式进行纯系选育,而近交会导致群体的遗传多样性下降。为了解长牡蛎(Crassostrea gigas)多代近交和自交家系的遗传多样性、遗传结构和生长情况,本实验选用长牡蛎近交4代(F4代)、近交5代(F5代)家系和雌性同体自交1代(自交1代)家系,采用8对多态性高的微卫星序列进行分析,同时对其成体的三个时间点生长数据进行了显著性差异分析。实验结果表明,8对微卫星位点在野生对照组中表现出较高的多态性,F4代、F5代和自交1代3个家系的遗传多样性明显下降,平均等位基因数(Na)由17.00下降到2.00,平均观测杂合度(Ho)由0.538下降到0.449,平均多态信息含量(PIC)由0.826下降到0.297;哈迪-温伯格平衡(HWE)检验结果显示,8个位点在三个家系和野生对照组中均不同程度偏离HWE平衡(P0.0062)。F4代、F5代、自交1代和野生对照的生长性状指标分析表明,和野生对照相比,三个家系生长指标明显提高,对于自交一代而言,与自交实验组亲本选择的偶然性有关。同时,三个家系三个时间点的壳长、壳宽生长性状没有显著性差异(除330日龄壳宽和630日龄壳长),F5代生长性状指标壳高和湿重均大于F4代和自交1代,且差异显著;但F4代和自交1代之间没有显著性差异。通过本研究发现,F5代可以继续用来进行生长性状新品系的选育,自交1代多样性降低程度相当于F5代,但多样性的降低对成体的生长性状影响不明显,仍可以用做相关实验材料。  相似文献   
89.
Ulva species can grow rapidly in nutrient-rich habitats causing green tides and marine fouling. A more complete understanding of the reasons behind these outbreaks is urgently required. Accordingly, this study attempts to use microsatellite markers based expressed sequence tag(EST) to analyze the genetic variation of several Ulva prolifera populations in the South Yellow Sea of China. Two hundred and thirty-eight SSRs were identified from 8 179 unique ESTs(6 203 newly sequenced and 1 976 downloaded from NCBI database) and 37 primer pairs were successfully designed according to the ESTs; 11 pairs were selected to detect the genetic diversity and relationship of 69 attached U. prolifera samples and 13 free-floating samples collected from coastal and off-coast areas of the South Yellow Sea. The results of cross-species transferability showed that six of the 11 EST-SSR primers could give good amplification in other five Ulva species and the average allele number was 4.67. Genetic variation analysis indicated that all 82 U. prolifera samples were clearly divided and most samples collected from the same site clustered together as a group in the dendrogram tree produced by unweighted pair-group mean analysis(UPGMA) method and the cluster results showed some consistency with the geographical origins. In addition, 13 free-floating samples(except HT-001-2) were grouped as a single clade separated from the attached samples.  相似文献   
90.
崔景伟 《沉积学报》2011,29(3):593-598
利用气相色谱-质谱联用仪对采自燕山地区冀北凹陷的中元古界长城系高于庄组(Chg)灰岩和蓟县系洪水庄组(Jxh)泥页岩露头和岩芯中不同赋存状态生物标志物进行了分析.正构烷烃和萜类生物标志物显示从高于庄组(Chg)到洪水庄组(Jxh)生源由浮游类和底栖类为主转变为浮游类为主,而沉积水体的盐度则由高变低.露头样品和相应岩芯中...  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