全文获取类型
收费全文 | 6323篇 |
免费 | 833篇 |
国内免费 | 1420篇 |
专业分类
测绘学 | 292篇 |
大气科学 | 84篇 |
地球物理 | 408篇 |
地质学 | 4768篇 |
海洋学 | 1718篇 |
天文学 | 4篇 |
综合类 | 588篇 |
自然地理 | 714篇 |
出版年
2024年 | 50篇 |
2023年 | 193篇 |
2022年 | 212篇 |
2021年 | 210篇 |
2020年 | 171篇 |
2019年 | 204篇 |
2018年 | 147篇 |
2017年 | 152篇 |
2016年 | 160篇 |
2015年 | 233篇 |
2014年 | 454篇 |
2013年 | 304篇 |
2012年 | 402篇 |
2011年 | 382篇 |
2010年 | 358篇 |
2009年 | 390篇 |
2008年 | 418篇 |
2007年 | 360篇 |
2006年 | 352篇 |
2005年 | 315篇 |
2004年 | 273篇 |
2003年 | 248篇 |
2002年 | 283篇 |
2001年 | 267篇 |
2000年 | 247篇 |
1999年 | 202篇 |
1998年 | 183篇 |
1997年 | 182篇 |
1996年 | 193篇 |
1995年 | 167篇 |
1994年 | 163篇 |
1993年 | 136篇 |
1992年 | 172篇 |
1991年 | 125篇 |
1990年 | 108篇 |
1989年 | 78篇 |
1988年 | 25篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1946年 | 2篇 |
1944年 | 1篇 |
1941年 | 2篇 |
排序方式: 共有8576条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
辽宁省大石桥-吉洞峪一带出露的主要为古元古代的变质层状岩系,由云母片岩、长英质粒岩和大理类组成。区域上形成一大型北东向的复式向斜构造。复向斜南北两翼变质地层对比问题是辽吉东部辽河岩群研究的主要内容之一。作者根据五年来在大石桥-吉洞峪一带进行1∶5万区调所获得的新资料,从标志层及组合标志层、岩相学特征、主要标志层的岩石化学和稀土地球化学特征、变质作用演化等方面的研究入手,讨论了复向斜两翼变质地层对比的问题。结果表明,辽河岩群构成复向斜南北两翼的变质地层是完全可以对比的,从而进一步证实辽河岩群是一个不可分割的整体 相似文献
995.
LIU Oi-feng Kim Seung-hyun Yun Jong-sup Moon Seong-yong 《中国海洋大学学报(英文版)》2006,5(4):295-299
Changes in the regulatory requirements and the forthcoming Disinfectant/Disinfection By-Products (D/DBP) Rule will require that drinking water treatment facilities be operated to achieve maximum removals of particles and disinfectant tolerant microorganisms as well as natural organic matter (NOM). For drinking water production, the use of membrane filtration processes such as microfiltration and ultrafiltration (MF/UF) alone to satisfy the turbidity, particle and microorganism removal a requirement of the surface water treatment regulation (SWTR) is not enough. MF/UF treatment processes can achieve only nominal (10 percent) removal of disinfection by-products (DBP) precursors (James, et al., 1995). On the other hand, too fast fouling can make the filtration processes more difficult to carry on. To solve these problems, many authors have been interested in installing coagulation pretreatment before membrane filtration to improve membrane performance. However, previous studies reported conflicting results. Some supported the effectiveness of coagulation pretreatment, while others contended that coagulation aggravated membrane performance. This research aims to identify the effects of coagulation pretreatment on membrane filtration through a pilot study using PVDF membrane in combination with analyzing the rationale of coagulation. Another objective of this research was to evaluate the different impacts on membrane performance of using different membrane modules (the submerged module and pressured module). The results showed that coagulation pretreatment greatly improved the membrane performance, extending the filtration time as well as reducing the permeated organic level, and that the submerged module is much more efficient than the pressured module. 相似文献
996.
997.
介绍了“激发学生学习兴趣—优化课堂理论教学—强化实验教学”模式在生物饵料培养课程教学中的探索与实践。提出增强教学的趣味性、改革课程考核方法、合理安排实验课顺序及加强学生实验操作能力的培养等途径改革教学方法。通过问卷对此教学模式进行调查,结果表明生物饵料培养的教学改革取得较好的效果。 相似文献
998.
999.
1000.
In this study, two common pollutants (benzo[a]pyrene and methamidophos) in marine environment were tested by comet assay for their inducement of in vivo genotoxic effect to the blood cells of black porgy ( Acanthopagrus schlegeli). The fish was exposed to 2 μg/L of benzo[a]pyrene (BaP) and methamidophos, and their mixture. The assay was performed on whole blood at 2 h, 5 h, 24 h and 96 h exposure intervals. A significant increase in DNA damage was observed in each treatment with the pollutants. Additive effect of BaP and methamidophos was also found in the experiment. However, the decrease ratios of DNA damage for 5 h and 96 h exposure interals compared with 2 h and 24 h exposure ones, respectively, were noticed. This phenomenon may be explained by the function of repairing process via enzyme cytochrome P450 in the animal. Evidence of the genotoxicity of organophosphorus pesticides (OPs) and polynuclear aromatic hydrocarbons (PAHs) on marine fish are discussed in this paper. 相似文献