全文获取类型
收费全文 | 49559篇 |
免费 | 21073篇 |
国内免费 | 46850篇 |
专业分类
测绘学 | 6371篇 |
大气科学 | 22735篇 |
地球物理 | 14822篇 |
地质学 | 43929篇 |
海洋学 | 18425篇 |
天文学 | 969篇 |
综合类 | 5393篇 |
自然地理 | 4838篇 |
出版年
2024年 | 388篇 |
2023年 | 913篇 |
2022年 | 1663篇 |
2021年 | 2250篇 |
2020年 | 2978篇 |
2019年 | 6169篇 |
2018年 | 6211篇 |
2017年 | 5939篇 |
2016年 | 6017篇 |
2015年 | 5713篇 |
2014年 | 5086篇 |
2013年 | 5928篇 |
2012年 | 5975篇 |
2011年 | 5712篇 |
2010年 | 5629篇 |
2009年 | 4932篇 |
2008年 | 4400篇 |
2007年 | 4241篇 |
2006年 | 3929篇 |
2005年 | 3444篇 |
2004年 | 3520篇 |
2003年 | 2989篇 |
2002年 | 2729篇 |
2001年 | 2450篇 |
2000年 | 1981篇 |
1999年 | 1754篇 |
1998年 | 1716篇 |
1997年 | 1761篇 |
1996年 | 1372篇 |
1995年 | 1313篇 |
1994年 | 1186篇 |
1993年 | 1141篇 |
1992年 | 992篇 |
1991年 | 727篇 |
1990年 | 709篇 |
1989年 | 579篇 |
1988年 | 490篇 |
1987年 | 392篇 |
1986年 | 313篇 |
1985年 | 256篇 |
1984年 | 283篇 |
1983年 | 178篇 |
1982年 | 209篇 |
1981年 | 148篇 |
1980年 | 109篇 |
1979年 | 112篇 |
1978年 | 50篇 |
1977年 | 46篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
91.
本文介绍了LZY_(1-1)型光电浊度仪的设计原理,标定方法及使用结果,该仪器用经典法校准后,能快速测量大批量样品的悬浮物含量。 相似文献
92.
You Yuming Hou Min Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Assistant Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1992,(3)
- The data of landsat TM of multi-temporal for Lingdingyang Estuary, Pearl River in China is firstly used with suspended sediment concentration of field measurement to establish a correlative model equation. After the ratio processing of TM data and atmospheric correction, the images of suspended sediment concentration of different temporals are exported from the image processing systems AREIS II and III. These images express the characteristics of suspended sediment distribution, the mode of sediment transport and the extent of dispersion under the actions of tidal current and wind condition of different seasons. 相似文献
93.
Ho Il Yoon Myung Woo Han Byong-Kwon Park Jae-Kyung Oh Soon-Keun Chang 《Marine Geology》1997,140(3-4):265-282
High-resolution (3.5 kHz and multi-channel) seismic profiles and piston cores were collected from Maxwell Bay and its tributary embayment, Marian Cove, in the South Shetland Islands, Antarctica, during the Korea Antarctic Research Program (1992/93 and 1995/96) to elucidate the glaciomarine sedimentation processes and recent glacial history of the area. Seismic data from Maxwell Bay reveal a rugged bay margin and flattened basin floor covered with well-stratified hemipelagic muds. On the base-of-slope, acoustically transparent debris flows occur, indicating downslope resedimentation of glaciomarine sediments. Despite the subpolar and ice-proximal settings of Marian Cove, the seafloor is highly rugged with a thin sediment drape, suggesting that much of the area has been recently eroded by glaciers. Sediment cores from the cove penetrated three distinct fining-upward lithofacies: (1) basal till in the lower part of the core, accumulated just seaward of the grounding line of the tidewater glacier; (2) interlaminated sand and mud in the middle part, deposited in ice-proximal zone by a combination of episodic subglacial meltwater inflow and iceberg dumping; and (3) pebbly mud in the upper part, deposited in ice-distal zone by both surface meltwater plume and ice-rafting from the glacier front. A reconstruction of the glacial history of these areas since the late glacial maximum shows an ice sheet filling Maxwell Bay in late Wisconsin time and grounding of the tidewater glacier in Marian Cove until about 1300 yr BP. 相似文献
94.
95.
养殖对虾病毒性疾病的细菌并发症防治研究 总被引:1,自引:0,他引:1
本文研究报道了发病对虾肝胰腺分离菌物敏感性,采用防台细菌人工感染方法进行药物饲料的筛选,在实验室及养殖池中进行药物饲料的防治效果试验。结果表明,在对虾病毒流行期间,采用药物饲料可有效防止对虾爆发性大量死亡,提高对虾存活率。 相似文献
96.
97.
Relationship between biogeochemical features of biogenic elements and flocculation in the Changjiang Estuary 总被引:1,自引:3,他引:1
RelationshipbetweenbiogeochemicalfeaturesofbiogenicelementsandflocculationintheChangjiangEstuary¥LinYi'an;TangRenyou;LiYan;Do... 相似文献
98.
Samples of O isotopic tracer were mlleMed at Sections P3,P25,PcM-t/2-E and PCM-1/2.w in both the Fast China Sea and the area to the east of the Ryūkyū-gunto during October-November,1991.Analytical results of the δ18O are as follows: (1) In the Kuroshio area,the δ18O isolines are almost parallel to the 200 m isobath.The value of δ18O is negative and reaches minimum mt the main axis of the Kuroshio,and increases on both sides.(2) In the Taiwan Warm Current (TWC) area there is a high δ18O tongue extending to the northeast.(3) In the area near the coast,the distribution of δ18O isoline shows that the Changjiang River runoff diffuses seaward and the land-ocean isotopic effect from the nearshore to the offshore.(4) The values of δ18O are from -1.0×10-3 to -0.5×10-3 in the shelf.(5) There is a low mre of δ18O value(<-1.6×10-3) at the 600 m layer in the Kuroshio area,which is quite in accord with the existence of a low salinity mre (S G 34.30) between the 600 and 800 m layers in the same area.Finally,the mrrelations of the δ18O with the salinity and temperature,the upwelling and so on are discussed. 相似文献
99.
北方劳德藻配子和复大孢子的产生 总被引:8,自引:0,他引:8
于1986年10月在厦门近岸采集北方劳德藻,从培养中观察其有性生殖和光对生殖的影响。结果表明,该藻只有宽度为26-40μm的细胞能形成配子和复大孢子;在光照条件下每昼夜只发生1次性化;雌雄配子以不同发育方式形成,配子发生呈现一定的时间程序;强光照和16h光周期最适于性化。由此得知,引起性化既依赖适当的细胞大小,又依赖光诱导的外部因素;产生两种精子数目是与精原孢囊的体积大小紧密相关;性化与光强度之间 相似文献
100.