全文获取类型
收费全文 | 126篇 |
免费 | 22篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 35篇 |
地球物理 | 9篇 |
地质学 | 38篇 |
海洋学 | 31篇 |
综合类 | 18篇 |
自然地理 | 35篇 |
出版年
2024年 | 1篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 7篇 |
2012年 | 6篇 |
2011年 | 11篇 |
2010年 | 4篇 |
2009年 | 11篇 |
2008年 | 11篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 9篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有169条查询结果,搜索用时 15 毫秒
131.
新疆森林资源动态分析 总被引:6,自引:0,他引:6
1 M ethod ofsurvey and analysis1.1 Survey area and dataThe survey area am ounted to 1.647 m illion km 2,covering the w hole territory of X injiang.TheLandsat TM im age data obtained from rem ote sensing in w hole X injiang during the periods1995-1996 and … 相似文献
132.
新变种矿物—含锗锡硫钒铜矿 总被引:3,自引:0,他引:3
含锗锡硫钒铜矿是硫钒铜矿的含锗锡变种。它产于四川省白玉县呷村银多金属矿床中,反光显微镜下为淡柠檬黄色,形态呈正方形、长方形及不规则状。粒度一般为0.01—0.1mm,最大为0.3mm。显微硬度Hv=137.8kg/mm2,相当于HM=3.49。反射率:589nm 31.54%。主要化学成分为:Cu 52.29—54.71%,S 30.59—32.49%,V 5.70—6.50%,Ge 4.3—6%,Sn2.43—3.56%,还含微量Zn、Fe、As、Sb、Bi等。简化式为:Cu3(V,Ge,Sn)S4。矿物为等轴晶系,ao=10.66,V=1211.36,空间群为P43m,Z=8。 相似文献
133.
大容量气枪震源主动探测技术系统及试验研究 总被引:13,自引:8,他引:13
针对地下介质动态变化监测研究中的信噪比、震源可重复性和波速精确测量等关键问题,利用大容量气枪震源,构建了一套高性能的主动探测技术系统,该系统包括气枪震源激发和信号接收,并在河北、云南和新疆等地的内陆水库和人工水体等不同激发环境,开展了探索性试验研究。试验结果表明:①气枪震源激发频率低,能量强,具有高度的可重复性、可通过叠加提高信噪比、探测距离大、绿色环保等特征,是一种理想的低频震源;②该探测技术系统操作简单,易控制,自动化程度高,探测精度高,能观测到固体潮引起的连续变化,可应用于区域尺度地下介质动态变化监测和开展4D 地震学研究;③气枪震源激发产生的信号震相丰富,有较强的S波,为研究地壳介质特性、应力分布及其动态变化等提供了新的技术路线。 相似文献
134.
??????-????????20????90?????????????????????????????????????????????????????????????Bruns?????Stokes????????????????????????????????????仯???о????????????仯???????????????????????????????????????????????????????仯?????????????з????????????????????????????????6?????????????????????????????????????????λ???й?? 相似文献
135.
136.
超大穗小麦在山东引种的气候适应性 总被引:2,自引:0,他引:2
利用山东省和陕西省中部45个气象台站建站至1990年的气象资料,采用欧氏距离的计算方法,并按照各气候要素不同的权重系数进行修正,求出综合相似距。 相似文献
137.
Sexual traits plasticity of the potentially invasive limpet Bostrycapulus odites (Gastropoda: Calyptraeidae) within its natural distribution in South America 下载免费PDF全文
Maximiliano Cledón Jesús Darío Nuñez Emiliano Hernán Ocampo Julia D. Sigwart 《Marine Ecology》2016,37(2):433-441
The slipper limpet Bostrycapulus odites has recently been reported as an introduced species on the Spanish Mediterranean coast. Another species in the family Calyptraeidae, Crepidula fornicata, is a problematic invasive species in the Northeast Atlantic, which makes the closely related Bostrycapulus introduction a matter of concern. Information on the biology of B. odites in its natural environment can facilitate predictions on where the species could find favourable conditions for settlement and expansion. Size and sex were recorded for individuals in four populations over 2600 km of the Southwestern Atlantic shoreline, in Argentina and Brazil, covering the whole native latitudinal range of this widely distributed species. Animals were collected by hand in the intertidal or by SCUBA in subtidal locations; specimens were examined to determine shell length, sex, and the presence and number of brooded egg capsules in females. Mean shell length for the whole population did not differ significantly among populations. However, this species experiences sequential hermaphroditism (protandrism), and the size at sexual maturity (minimum male size) increased significantly with latitude. The fecundity of females at all sites increased with size, and the number of brooded egg capsules as well as the average size of capsules was larger in bigger individual females; however, mean fecundity varied among sites independent of mean female body size. This limpet species modifies its reproductive traits with local conditions, and sexual characters develop earlier in more temperate localities. 相似文献
138.
Breeding practice for Undaria pinnatifida (Harvey) Suringar requires the screening of a large number of offspring from gametophyte crossings to obtain an elite variety for large-scale cultivation. To better understand the genetic relationships of different gametophyte cultures isolated from different sources, 20 microsatellite loci were screened and 53 gametophyte clone cultures analyzed for U. pinnatifida isolated from wild sporophytes in Vladivostok, Russia and from cultivated sporophytes from Dalian and Qingdao, China. One locus was abandoned because of poor amplification. At the sex-linked locus of Up-AC-2A8, 3 alleles were detected in 25 female gametophyte clones, with sizes ranging from 307 to 316 bp. At other loci, 3 to 7 alleles were detected with an average of 4.5 alleles per locus. The average number of alleles at each locus was 1.3 and 3.7 for Russian and Chinese gametophyte clones, respectively. The average gene diversity for Russian, Chinese, and for the combined total of gametophyte clones was 0.1, 0.4, and 0.5, respectively. Russian gametophyte clones had unique alleles at 7 out of the 19 loci. In cluster analysis, Russian and Chinese gametophyte clones were separated into two different groups according to genetic distance. Overall, high genetic diversity was detected in gametophyte clones isolated from the two countries. These gametophyte cultures were believed to be appropriate parental materials for conducting breeding programs in the future. 相似文献
139.
通过对云南省玉溪市2001~2004年引种番茄椒田间试验观测数据及当地同期气象资料的对比分析,结果表明云南省玉溪市可有选择性露地引种番茄椒,但需要安排好适宜的播种期和移植期才利于提高单位面积产量。这一结果对指导玉溪市引种、推广番茄椒品种有积极地参考作用。 相似文献
140.
Introduced species may outcompete or hybridize with native species, resulting in the loss of native biodiversity or even alteration of ecosystem processes. In this study, we reported an alien distromatic Ulva species, which was found in an embayment(Holly Pond) connected with Long Island Sound, USA. The morphological and anatomical observations in combination with molecular data were used for its identification to species. Anatomy of collected specimens showed that the cell shape in rhizoidal and basal regions was round and the marginal teeth along the basal and median region were not found. These characteristics were primarily identical to the diagnostic characteristics of Ulva laetevirens Areschoug(Chlorophyta). The plastid-encoding tufA and nucleus-encoding ITS1 were used for its molecular identification. Phylogenetic analysis for the tufA gene placed the specimens from Holly Pond in a well-supported clade along with published sequences of U. laetevirens identified early without any sequence divergence. In ITS tree, the sample also formed well-supported clades with the sequences of U. laetevirens with an estimated sequence divergence among the taxa in these clades as low as 1%. These findings confirmed the morpho-anatomical conclusion. Native to Australia, this species was reported in several countries along the Mediterranean coast after the late of 1990 s. This is the first time that U. laetevirens is found in the northeast coast of United States and the second record for Atlantic North America. 相似文献