全文获取类型
收费全文 | 5830篇 |
免费 | 729篇 |
国内免费 | 1058篇 |
专业分类
测绘学 | 1697篇 |
大气科学 | 990篇 |
地球物理 | 1059篇 |
地质学 | 1787篇 |
海洋学 | 630篇 |
天文学 | 568篇 |
综合类 | 418篇 |
自然地理 | 468篇 |
出版年
2024年 | 20篇 |
2023年 | 42篇 |
2022年 | 111篇 |
2021年 | 185篇 |
2020年 | 205篇 |
2019年 | 261篇 |
2018年 | 171篇 |
2017年 | 263篇 |
2016年 | 259篇 |
2015年 | 271篇 |
2014年 | 369篇 |
2013年 | 354篇 |
2012年 | 415篇 |
2011年 | 389篇 |
2010年 | 306篇 |
2009年 | 309篇 |
2008年 | 299篇 |
2007年 | 398篇 |
2006年 | 385篇 |
2005年 | 334篇 |
2004年 | 282篇 |
2003年 | 282篇 |
2002年 | 237篇 |
2001年 | 233篇 |
2000年 | 199篇 |
1999年 | 177篇 |
1998年 | 157篇 |
1997年 | 131篇 |
1996年 | 100篇 |
1995年 | 92篇 |
1994年 | 88篇 |
1993年 | 64篇 |
1992年 | 50篇 |
1991年 | 40篇 |
1990年 | 28篇 |
1989年 | 30篇 |
1988年 | 28篇 |
1987年 | 15篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有7617条查询结果,搜索用时 15 毫秒
41.
42.
43.
利用牙鲆鳃细胞系分离和培养淋巴囊肿病毒 总被引:1,自引:4,他引:1
本文利用牙鲆鳃细胞系进行了养殖牙鲆淋巴囊肿病毒的分离及培养 ,并通过电镜对培养细胞中淋巴囊肿病毒的形态及感染循环进行了初步研究。将病鱼的淋巴囊肿组织无菌滤液接种牙鲆细胞系 ,细胞出现了明显的细胞病变 ( Cytopathic effect,CPE)。电镜观察在培养细胞的胞质中有病毒的包涵体 ,胞质中散在 6角形、5角形或圆形的病毒粒子 ,大小为 10 0~ 140 nm之间。在感染细胞的线粒体中也存在大量的病毒颗粒。 相似文献
44.
An experimental set-up is developed and proved to be effective for laboratory study of an underwater towed system. The experimental technique gives a practical method for monitoring the kinematic and dynamic performance of an underwater towed system in a ship towing tank. Both the theoretical and experimental results in the investigation indicate that the hydrodynamic response of a towed vehicle to the wave induced motion of a towing ship can be significantly reduced by applying a two-part tow method. A comparison of the numerical and experimental results in the investigation demonstrates that the numerical simulation results are close to the experimental data, overall agreement between experimental and theoretical results is satisfactory. The results qualitatively verify the mathematical model of a two-part underwater towed system proposed by Wu and Chwang [Wu, J., Chwang, A.T., 2000. A hydrodynamic model of a two-part underwater towed system. Ocean Engineering 27 (5), 455–472]. 相似文献
45.
46.
The accuracy of the manufacturer’s fall-rate equation for the T-5 Model of expendable bathythermograph (XBT) has been investigated based on about 300 collocated pairs of XBT-CTD (Conductivity-Temperature-Depth profiler) measurements in various climatological regions. We found that the equation systematically overestimates depth by about 5% for the T-5 produced by Tsurumi Seiki, Co. Ltd. (TSK), but almost no bias is associated with the T-5 produced by Sippican, Inc., in USA. The cause of this difference is not clear, because the two manufacturers’ T-5 probes are reported to have identical shape and weight in water. We propose a new fall-rate equation for the TSK T-5: z(t) = 6.54071t - 0.0018691t
2, where z(t) is depth in meters at time, t, in seconds. 相似文献
47.
I. Brandariz P. Castro M. Montes F. Penedo M.E. Sastre de Vicente 《Marine Chemistry》2006,102(3-4):291-299
Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl2 or CaCl2), with binary mixtures of MgCl2 and CaCl2, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl2, while it is increased by the other electrolytes used in this work. 相似文献
48.
Many classes of environmental contaminants affect the reproductive function of animals through interactions with the endocrine system. The primary components affected by endocrine active compounds (EACs) are the steroid receptors and the enzymes responsible for steroidogenesis. This study sought to develop an in vitro model for assessing EAC effects in sea turtles by examining their ability to alter cytochrome P450 aromatase (CYP19) activity. Aromatase is the enzyme responsible for the conversion of testosterone to estradiol. This enzyme is critical in the sexual differentiation of reptiles which demonstrate temperature-dependent sex determination. An immortal testis cell line GST-TS from a green sea turtle was grown in culture at 30 degrees C in RPMI 1640 media. The cells were exposed to three known aromatase inducers; dexamethasone (Dex), 8Br-cyclic AMP, or human chronic gonadotropin (HCG) and one aromatase inhibitor 4-androstenol-dione (4-OHA). In addition, the GST-TS cells were exposed to 0.1-30 microM atrazine and 3-100 microM 4,4'-DDE. The inducing compounds that have been shown to increase aromatase activity in other systems failed to induce aromatase activity in the GST-TS cells, yet exposure to the inhibiting compound, 4-OHA, did result in a significant reduction. Atrazine (0.1, 1.0 and 10 microM) significantly induced aromatase activity following a 24 h exposure, and 4,4'-DDE inhibited the activity but only at cytotoxic concentrations (100 microM). Based on these results, this in vitro model can be useful in examining the endocrine effects of EACs in sea turtles. 相似文献
49.
南黄海表层沉积物中氮的区域地球化学特征 总被引:5,自引:0,他引:5
通过分级浸取分离的方法获得了南黄海表层沉积物不同形态的氮,首次探讨其分布的区域性特征:南黄海表层沉积物中各形态氮在不同测线上均呈现出波状分布。B测线的基本上呈现出中部海域高,两边海域低,而西部海域又略高于东部海域的趋势,D和E测线的基本上呈现出西高、东低的趋势,C测线的则呈现出西低、东高的趋势,F测线的变化趋势比较平缓,从整体上看,SOEF—N和TN的分布呈现出西部海区比东部海区低的趋势。受各测线上沉积物种类差异的影响,自北向南各形态氮的变化幅度逐渐减小,其中SOEF-N在各测线上的变化幅度最大,且自北向南降幅最大。受水动力及沉积物粒度的影响,不同形态氮在黄海槽内各站位沉积物中的含量较高。沉积物中各形态氮在不同测线上的分布还表明,陆源输入对南黄海沉积物中氮测线分布有较小的影响,海洋自生氮对南黄海表层沉积物中氮的形态、含量与分布具有重要影响。 相似文献
50.