全文获取类型
收费全文 | 4943篇 |
免费 | 1099篇 |
国内免费 | 1141篇 |
专业分类
测绘学 | 813篇 |
大气科学 | 337篇 |
地球物理 | 471篇 |
地质学 | 2730篇 |
海洋学 | 167篇 |
天文学 | 17篇 |
综合类 | 1155篇 |
自然地理 | 1493篇 |
出版年
2024年 | 16篇 |
2023年 | 69篇 |
2022年 | 196篇 |
2021年 | 232篇 |
2020年 | 209篇 |
2019年 | 222篇 |
2018年 | 194篇 |
2017年 | 290篇 |
2016年 | 253篇 |
2015年 | 274篇 |
2014年 | 372篇 |
2013年 | 355篇 |
2012年 | 475篇 |
2011年 | 426篇 |
2010年 | 407篇 |
2009年 | 277篇 |
2008年 | 279篇 |
2007年 | 312篇 |
2006年 | 325篇 |
2005年 | 300篇 |
2004年 | 286篇 |
2003年 | 219篇 |
2002年 | 167篇 |
2001年 | 174篇 |
2000年 | 132篇 |
1999年 | 124篇 |
1998年 | 95篇 |
1997年 | 117篇 |
1996年 | 73篇 |
1995年 | 51篇 |
1994年 | 71篇 |
1993年 | 41篇 |
1992年 | 31篇 |
1991年 | 30篇 |
1990年 | 22篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有7183条查询结果,搜索用时 31 毫秒
901.
提高农村地震灾害防御能力,既是推进农村经济社会可持续发展的重要保障,也是维护广大农民群众根本利益的重要举措。在分析宁波市农村地区在地震灾害防御方面存在的主要问题的基础上,提出了加强宁波市农村防震减灾能力建设的对策措施。对其它地区特别是少震弱震区加强农村防震减灾工作具有一定的借鉴和参考意义。 相似文献
902.
Hossein Tavallali Shahram Lalehparvar Abdo‐Reza Nekoei Maryam Ghane Jahromi Khodabakhsh Niknam 《洁净——土壤、空气、水》2012,40(6):640-647
A sensitive, reliable, and environmentally friendly method for simple separation and preconcentration of Ag(I) traces in aqueous samples is presented prior to their flame atomic absorption spectrometric determinations. At pH 7.0, Ag(I) was separated with 2‐(2‐methoxyphenyl)benzimidazole (MPBI) as a new complexing agent and floated after adding sodium dodecyl sulfate (SDS) as a foaming reagent. The floated layer was then dissolved in proper amount of concentrated nitric acid in methanol and introduced to the flame atomic absorption spectrometer (FAAS). The effects of pH, concentration of MPBI, type and amount of surfactant as the floating agent, type and amount of eluting agent, and influence of foreign ions on the recovery of the analyte ion were investigated. Also, using a nonlinear curve fitting method, the formation constant of 1.62 × 106 was obtained for Ag(I)–MPBI complex. The analytical curve was linear in the range of 1.8 × 10?7–1.7 × 10?6 mol/L for determination of Ag(I). The relative standard deviation (RSD; N = 10) corresponding to 0.7 × 10?6 mol/L of Ag(I), the limit of detection (10 blanks), and the enrichment factor were obtained as 1.7%, 2.9 × 10?8 mol/L, and 43.0, respectively. The proposed procedure was then applied successfully for determination of silver ions in different water samples. 相似文献
903.
Chitosan oligosaccharide-Ca complex accelerates the depuration of cadmium from Chlamys ferrari 总被引:1,自引:0,他引:1
This study investigated the effect of a chitosan oligosaccharide-Ca complex (COS-Ca) on the depuration of cadmium (Cd) from Chlamys ferrari. After exposure to 0.5 mg L-1 CdCl2 for 3 or 7 d, the scallops were treated by COS-Ca prior to determina-tion of Cd, calcium (Ca) and zinc (Zn) contents, Cd distribution in organs, malondialdehyde (MDA) content and antioxidant variables. Results showed that COS-Ca reduced Cd content in the viscera of the scallops, with highest Cd depuration rate (47%) observed on day 3. The COS-Ca concentration substantially affected Cd depuration, and the exposure to 8.75 mg L-1 COS-Ca led to significantly higher Cd depuration rate compared with those of lower COS-Ca concentrations (1.75, 3.5, 5.25, and 7.00 mg L-1). Distribution analysis of Cd in scallop organs indicated that COS-Ca significantly reduced Cd content in the kidney throughout the 5-d experiment, as well as in the gill during the early stage of Cd depuration. In addition, COS-Ca treatment decreased glutathione peroxidase (GSH-Px) activity and MDA content while increasing superoxide dismutase (SOD) and catalase (CAT) activities on different days. Our work suggested COS-Ca complex treatment as an effective method for acceleration of Cd depuration from Cd-contaminated bivalves. 相似文献
904.
905.
906.
907.
908.
909.
910.