首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5865篇
  免费   897篇
  国内免费   964篇
测绘学   451篇
大气科学   847篇
地球物理   1256篇
地质学   2628篇
海洋学   1000篇
天文学   34篇
综合类   312篇
自然地理   1198篇
  2024年   47篇
  2023年   138篇
  2022年   226篇
  2021年   281篇
  2020年   258篇
  2019年   314篇
  2018年   229篇
  2017年   292篇
  2016年   306篇
  2015年   271篇
  2014年   460篇
  2013年   465篇
  2012年   401篇
  2011年   381篇
  2010年   369篇
  2009年   394篇
  2008年   378篇
  2007年   374篇
  2006年   371篇
  2005年   285篇
  2004年   257篇
  2003年   194篇
  2002年   211篇
  2001年   132篇
  2000年   121篇
  1999年   98篇
  1998年   104篇
  1997年   64篇
  1996年   68篇
  1995年   42篇
  1994年   47篇
  1993年   39篇
  1992年   44篇
  1991年   11篇
  1990年   7篇
  1989年   6篇
  1988年   5篇
  1987年   6篇
  1986年   9篇
  1985年   6篇
  1984年   5篇
  1983年   4篇
  1982年   1篇
  1980年   1篇
  1978年   3篇
  1977年   1篇
排序方式: 共有7726条查询结果,搜索用时 9 毫秒
41.
42.
43.
鲫鱼(Carassius auratus)在微冻保鲜过程中的质量变化   总被引:2,自引:0,他引:2  
该文研究鲫鱼 ( Carassius auratus)在微冻 ( - 3℃ )保鲜过程中的质量变化规律。以感官评价、细菌总数、T- VBN值、p H值、ATPase活性、K值等作为质量指标。实验结果表明 ,微冻可以明显抑制细菌总数的增长 ,维持较低的 T- VBN和 K值。但是 ,微冻条件下鲫鱼的 ATPase活性下降速度较快  相似文献   
44.
45.
We describe industry funded contributions to the assessment of the SNA1 snapper (Pagrus auratus) fishery during the 1990s and discuss the advantages and disadvantages of industry funded research. We also provide background on the history of fisheries management in New Zealand, on the current assessment and management processes, and on the SNA1 snapper fishery. In the SNA1 fishery, the contributions of industry and the cooperation with Government scientists has resulted in high quality assessments. In our opinion, the advantages of industry funded research out weigh the disadvantages and suggest that industry funded assessments are highly desirable and should be an integral part of any management system.  相似文献   
46.
47.
48.
A risk assessment of Tributyltin (TBT) in Tokyo Bay was conducted using the Margin of Exposure (MOE) method at the species level using the Japanese short-neck clam, Ruditapes philippinarum. The assessment endpoint was defined to protect R. philippinarum in Tokyo Bay from TBT (growth effects). A No Observed Effect Concentration (NOEC) for this species with respect to growth reduction induced by TBT was estimated from experimental results published in the scientific literature. Sources of TBT in this study were assumed to be commercial vessels in harbors and navigation routes. Concentrations of TBT in Tokyo Bay were estimated using a three-dimensional hydrodynamic model, an ecosystem model and a chemical fate model. MOEs for this species were estimated for the years 1990, 2000, and 2007. Estimated MOEs for R. philippinarum for 1990, 2000, and 2007 were approximately 1–3, 10, and 100, respectively, indicating a declining temporal trend in the probability of adverse growth effects.A simplified software package called RAMTB was developed by incorporating the chemical fate model and the databases of seasonal flow fields and distributions of organic substances (phytoplankton and detritus) in Tokyo Bay, simulated by the hydrodynamic and ecological model, respectively.  相似文献   
49.
European brackish water seas (Baltic Sea, Black Sea and Sea of Azov, Caspian Sea) are subject to intense invasion of non-indigenous species (NIS). In these seas, salinity is the most important range limiting factor and native species seem to reach a minimum species richness at intermediate salinities. This trend, revealed by Remane in 1934 and later on confirmed by many other scientists, was compared to the salinity range of already established NIS in the European brackish water seas. It turned out that most NIS are well adapted to the salinities holding lowest native species richness, already in their native area, and that NIS richness maximum in brackish water seas occurs in the salinity intervals of native species richness minimum. A predictable pattern in the salinity range of NIS can be used as a tool in initial risk assessment of future invasions in brackish water seas, especially when mapping highly potential donor and recipient areas. A product of empty niches, suitable environmental conditions, and availability of proper vectors might be the most effective predictor for the invasibility of brackish water areas.  相似文献   
50.
南四湖湖内浅槽工程施工对水环境的影响及控制措施   总被引:1,自引:0,他引:1  
南四湖湖内工程是沂沭泗河洪水东调南下续建工程的单项工程,工程区位于山东省省级自然保护区内;挖泥船施工将对湖内水环境产生一定影响。本文从排泥场回水污染物、生产废水和生活污水三个方面阐述了工程施工对水环境的影响程度,并且提出了相应的控制措施。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号