全文获取类型
收费全文 | 11759篇 |
免费 | 2183篇 |
国内免费 | 2984篇 |
专业分类
测绘学 | 835篇 |
大气科学 | 2277篇 |
地球物理 | 2995篇 |
地质学 | 6339篇 |
海洋学 | 1356篇 |
天文学 | 568篇 |
综合类 | 1092篇 |
自然地理 | 1464篇 |
出版年
2024年 | 77篇 |
2023年 | 230篇 |
2022年 | 544篇 |
2021年 | 655篇 |
2020年 | 563篇 |
2019年 | 653篇 |
2018年 | 704篇 |
2017年 | 624篇 |
2016年 | 757篇 |
2015年 | 607篇 |
2014年 | 765篇 |
2013年 | 696篇 |
2012年 | 711篇 |
2011年 | 745篇 |
2010年 | 743篇 |
2009年 | 660篇 |
2008年 | 627篇 |
2007年 | 625篇 |
2006年 | 500篇 |
2005年 | 403篇 |
2004年 | 363篇 |
2003年 | 367篇 |
2002年 | 374篇 |
2001年 | 362篇 |
2000年 | 366篇 |
1999年 | 438篇 |
1998年 | 369篇 |
1997年 | 362篇 |
1996年 | 305篇 |
1995年 | 264篇 |
1994年 | 302篇 |
1993年 | 234篇 |
1992年 | 180篇 |
1991年 | 137篇 |
1990年 | 112篇 |
1989年 | 86篇 |
1988年 | 104篇 |
1987年 | 50篇 |
1986年 | 45篇 |
1985年 | 43篇 |
1984年 | 36篇 |
1983年 | 33篇 |
1982年 | 35篇 |
1981年 | 28篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1958年 | 8篇 |
1957年 | 3篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
介绍了国内外第一台矿物热敏参数测试仪研制的原理、应用范围和对一些金属矿物、半导体矿物的测试情况以及仪器在浙江、赣南等地区金矿找矿中的初步应用。 相似文献
53.
Arctic sea-ice motion and its relation to pressure field 总被引:5,自引:0,他引:5
Daily Arctic sea-ice motion maps during the winter seasons (December–March) from December 1988 to March 2003 derived from
NSCAT, QuikSCAT, SSM/I, and AMSRE data by a wavelet analysis method have been merged with those derived from buoy data. These
merged sea-ice motion data have been used to study the circulation regimes and winter-to-winter variability of Arctic sea-ice
motion. The relation between sea-ice motion and the pressure field in the Arctic Ocean was also studied by applying Principal
Component Analysis (PCA) to the monthly merged sea-ice motion data and the monthly pressure field data from IABP. The mean
Arctic sea-ice motion map of the 15 winter seasons has two distinct features: the Beaufort Gyre and a cyclonic circulation
system in the Eurasian Basin, which moves ice from the Laptev Sea to Fram Strait. The strengths and sizes of the two features
change from one winter season to another. Seasons with a strong or normal Beaufort Gyre alternate with seasons with a weak
or no Beaufort Gyre every one to three seasons. The principal components of the first two modes of PCA of the monthly sea-ice
motion are closely correlated with their counterparts of the monthly pressure field in the Arctic Ocean. The mode-one components
of these two anomalies alternate between anticyclonic and cyclonic circulation systems. The correlation between Arctic Oscillation
indexes and the principal components of the first mode of PCA of the monthly Arctic sea-ice motion is low but statistically
significant. 相似文献
54.
针对添加伪点加法在抵抗简单功耗分析攻击的同时效率损失过大的问题,为更好兼顾效率与安全,提出一种新的标量乘快速实现算法——随机伪操作法,通过以单片机为核心运算控制芯片的功耗分析平台进行实测分析验证,随机伪操作法不但能够很好抵抗简单功耗分析攻击,而且相对于添加伪点加法运算效率提高30%-50%。 相似文献
55.
56.
西藏冈底斯岩浆岩带西段北侧的林子宗群火山岩含有从板块俯冲机制向大陆碰撞机制转变的丰富信息。将措勤地区典中组火山岩与冈底斯岩浆岩带东段林周盆地的典中组火山岩在同位素地球化学、演化特征方面进行对比,探讨冈底斯岩浆岩带西段与东段在演化过程中的异同性。结果表明,措勤地区典中组火山岩的87Sr/86Sr初始比值变化范围为0.710352~0.713423,具较高的87Sr/86Sr比值;143Nd/144Nd初始比值为0.512293~0.512407,具较低的143Nd/144Nd比值;林周盆地典中组火山岩的87Sr/86Sr初始比值为0.7057~0.7063之间,143Nd/144Nd初始比值范围为0.5125~0.5126。同位素特征显示措勤地区典中组源区物质可能来自于富集Ⅱ型地幔,即源区为俯冲和再循环的大陆地壳物质与地幔岩发生了混合作用的产物,源区受控于冈底斯地壳基底。林周盆地典中组火山岩源区物质可能与富集Ⅰ型地幔有关。 相似文献
57.
深海嗜热异化铁还原菌Caloranaerobacter ferrireducens DY22619T对不同铁氧化物的铁还原特性 总被引:1,自引:0,他引:1
异化铁还原微生物在铁元素的地球化学循环中具有重要意义。深海热液活动是大洋铁元素的重要来源,目前深海热液环境中铁代谢相关微生物研究很少。本文对一株分离自深海热液区的嗜热异化铁还原菌新种Caloranaerobacter ferrireducens DY22619T的铁还原特性进行分析,比较了该菌对无定形羟基氧化铁、无定形铁氧化物和针铁矿3种不同铁氧化物的铁还原速率;并利用透射电镜对矿化产物进行矿物形貌、组成元素和晶型的分析。研究发现该菌生长在指数期至稳定期时,铁还原速率最快,其中对无定形羟基氧化铁和无定形铁氧化物的还原速率较高,达2.82 μmol/h和2.15 μmol/h;透射电镜结果表明,该菌可将3种不同胞外铁氧化物均还原矿化形成颗粒状磁铁矿,由针铁矿矿化形成的磁铁矿少但粒径最大,而由无定形铁氧化物形成的磁铁矿晶面不同于另外两种铁氧化物。结果表明,该菌有很强的铁还原和矿化能力,能厌氧呼吸还原三价铁氧化物,但是铁氧化物的性质对该菌胞外铁还原能力和矿化形成的磁铁矿的性质有重要影响。本研究为认识深海热液环境中异化铁还原菌在铁元素的地球化学循环和生物成矿过程提供了参考。 相似文献
58.
?????????????????????????????????????????????μ?????????????????????????????????????????????????0.05 mm????????0.02 mm?????????????????????????????????÷??????? 相似文献
59.
Agro-meteorological disasters(AMD) have become more frequent with climate warming. In this study, the temporal and spatial changes in the occurrence frequency of major meteorological disasters on wheat production were firstly explored by analyzing the observed records at national agro-meteorological stations(AMS) of China from 1991 to 2009. Furthermore, impact of climate change on AMD was discussed by comparing the warmer decade(2000–2009) with another decade(1991–2000). It was found that drought was the most frequent disaster during the last two decades, with a highest proportion of 79%. And the frequency of AMD increased significantly with climate change. Specifically, the main disasters occurred more frequently in the reproductive period than in the vegetative period. Besides, the spatial changes in the AMD frequency were characterized by region-specific. For example, the wheat cultivation areas located on the Loess Plateau and the middle-lower reaches of the Yellow River suffered mainly from drought. All these results were strongly linked to climate change in China. Therefore, sound adaptation options should be taken based on the latest changes of AMD under global warming to reduce agricultural damages. 相似文献
60.
Little is known about the genome of Pacific white shrimp (Litopenaeus vannamei). To address this, we conducted BAC (bacterial artificial chromosome) end sequencing of L. vannamei. We selected and sequenced 7 812 BAC clones from the BAC library LvHE from the two ends of the inserts by Sanger sequencing. After trimming and quality filtering, 11 279 BAC end sequences (BESs) including 4 609 paired- ends BESs were obtained. The total length of the BESs was 4 340 753 bp, representing 0.18% of the L. vannamei haploid genome. The lengths of the BESs ranged from 100 bp to 660 bp with an average length of 385 bp. Analysis of the BESs indicated that the L. vannamei genome is AT-rich and that the primary repeats patterns were simple sequence repeats (SSRs) and low complexity sequences. Dinucleotide and hexanucleotide repeats were the most common SSR types in the BESs. The most abundant transposable element was gypsy, which may contribute to the generation of the large genome size of L. vannamei. We successfully annotated 4 519 BESs by BLAST searching, including genes involved in immunity and sex determination. Our results provide an important resource for functional gene studies, map construction and integration, and complete genome assembly for this species. 相似文献