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   184篇
  免费   10篇
  国内免费   1篇
化学   32篇
力学   4篇
综合类   26篇
数学   32篇
物理学   101篇
  2023年   1篇
  2022年   3篇
  2021年   6篇
  2020年   5篇
  2019年   5篇
  2018年   13篇
  2017年   15篇
  2016年   13篇
  2015年   3篇
  2014年   3篇
  2013年   58篇
  2012年   9篇
  2011年   2篇
  2010年   2篇
  2009年   1篇
  2008年   1篇
  2007年   4篇
  2006年   5篇
  2005年   3篇
  2004年   3篇
  2003年   9篇
  2002年   3篇
  2001年   2篇
  2000年   3篇
  1999年   1篇
  1998年   4篇
  1997年   4篇
  1996年   1篇
  1995年   1篇
  1993年   1篇
  1992年   2篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1987年   3篇
  1986年   1篇
  1972年   1篇
  1959年   1篇
排序方式: 共有195条查询结果,搜索用时 0 毫秒
1.
汤凌 《教学与科技》2007,20(1):24-28
上个世纪70年代以来,绿党在欧洲政坛崛起,这是欧洲社会政治变化的一个新现象。绿党力量的上升乃至绿党政治的出现在某种程度上改变了西欧国家现行的政党格局。研究绿党对于我们了解欧洲政治变化以及绿色思潮与生态政治的影响具有重要意义。  相似文献   
2.
We present the results of a re-analysis of a previously published carbon isotope data-set related to coralline sponges in the Caribbean Sea. The original interpretation led to the discrimination between a pre-industrial period, with a signal controlled by solar-induced climatic variations, followed by the industrial era, characterized by a progressive δ13C negative shift due to the massive anthropogenic carbon emissions. Our re-analysis allowed to extract from the raw isotopic data evidence of a solar forcing still visible during the industrial era, with a particular reference to the 88-year Gleissberg periods. These signals are related to slope changes in both the δ13C versus time and the δ13C versus carbon emission curves.  相似文献   
3.
Land exhibits diverse functions under the combined influence of natural and human forces. A production–living–ecology functional classification system was constructed by integrating land, ecosystem, and landscape functions. The land functional value was calculated by systematically integrating ecosystem service value assessments. The primary and secondary functions, as well as combinations of different land‐use types, were determined using vertical and horizontal comparison methods. The production–living–ecology ranges were then delineated in Puge County, which is a typical mountain county in China. The production–living–ecology functions identified were well connected with the current land‐use types. The “production–living–ecology” space in Puge County showed obvious multifunctionality and agglomeration. The function identification system proposed in this paper integrated multiple methods, overcame the difficulty of direct quantitative identification of land functions. The methods used to map and quantify land function will enhance our ability to understand and model land system changes and adequately inform policies and planning. Summary for Managers
  • The function valuation method constructed in this paper could be used to reflect the multifunctionality and importance of land use and provide guidance and a quantitative basis for regional development planning.
  • The spatial classification results provided in this paper could offer a valuable reference for the land management department to scientifically formulate land use planning.
  • Under the goal of creating a group‐type urban development pattern and constructing an ecological protection pattern in Puge County, the hotspot analysis results of this paper can provide decision‐making tools and alternative spatial plans.
  相似文献   
4.
The detection of explosives and drugs in hard‐to‐reach places is a considerable challenge. We report the development and initial experimental characterization of the air analysis system that includes Field Asymmetric Ion Mobility Spectrometer, array of the semiconductor gas sensors and is installed on multicopter. The system was developed based on the commercially available DJI Matrix 100 platform. For data collection and communication with operator, the special compact computer (Intel Compute Stick) was installed onboard. The total weight of the system was 3.3 kg. The system allows the 15‐minute flight and provides the remote access to the obtained data. The developed system can be effectively used for the detection of impurities in the air, ecology monitoring, detection of chemical warfare agents, and explosives, what is especially important in light of recent terroristic attacks. The capabilities of the system were tested on the several explosives such as trinitrotoluene and nitro powder.  相似文献   
5.
木麻黄质膜离子泵在酸雨条件下对镧的响应   总被引:1,自引:0,他引:1  
研究镧对酸雨(pH为4.5)胁迫下木麻黄幼苗早期生长和质膜离子泵ATP酶活性的影响。结果表明:较低浓度La3+浸种能使幼苗株高、根长、鲜重以及质膜质子泵活性明显增强,在200mg·L-1La3+处理时达到最高增强值,而高浓度的La3+浸种使之表现出抑制效应;幼苗质膜钙泵的活性受La3+抑制。质子泵活性与细胞的伸长生长呈显著正相关关系,镧对质子泵的活化作用有助于促进植物的生长,且适量的镧具有缓解酸雨胁迫下生长的植物细胞质酸化,维持细胞内环境稳定的间接作用。为抗酸雨和促生长,木麻黄经镧浸种8h的最适宜La3+浓度为50~200mg·L-1。  相似文献   
6.
4种鹭的繁殖生态   总被引:6,自引:1,他引:6  
1999-2001年对池鹭、牛背鹭、白鹭、夜鹭混群的迁入状况、繁殖行为、雏鸟生长等进行了观察研究。结果表明:鹭鸟数量逐年增多,种类由2种增加到4种,4种鹭鸟在筑巢、取食和生活习性等方面具有一定的种群协调性。4种鹭鸟的食物组成存在一定差异。夜鹭以蛙类和鱼类为主;白鹭以鱼类和甲壳类为主,另有蛙类和昆虫类;牛背鹭的食物主要由昆虫类和蛙类组成;池鹭以鱼类为主。幼鸟体重生长率与成体体型大小成负相关,比较分析4种鹭鸟体重增长曲线,以池鹭和牛背鹭生长较快。  相似文献   
7.
8.
9.
Angle distributions of the degree and azimuth of polarization of radiation scattered by individual leaves were measured. The polarization characteristics of the reflected radiation were investigated at four radiation wavelengths (460, 550, 680, and 740 nm) and angles of exposure of leaves to light of 60–70°. The experiments were performed with leaves of maples (Acer platonoides) at different stages of vegetation and withering. More than 1000 distributions of the spectral polarization characteristics of the reflected radiation were obtained for maple leaves taken from regions with different ecological conditions during 1993–1995 It was established that the spectral polarization characteristics of the radiation scattered by a leaf markedly change with the state of the leaf. Belarusian State University, 4, F. Skorina Ave., Minsk, 220080, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 107–113, January–February, 1998.  相似文献   
10.
The new C7N aminocyclitol kirkamide ( 1 ) was isolated from leaf nodules of the plant Psychotria kirkii by using a genome‐driven 1H NMR‐guided fractionation approach. The structure and absolute configuration were elucidated by HRMS, NMR, and single‐crystal X‐ray crystallography. An enantioselective total synthesis was developed, which delivered kirkamide ( 1 ) on a gram scale in 11 steps and features a Ferrier carbocyclization and a Pd‐mediated hydroxymethylation. We propose that kirkamide is synthesized by Candidatus Burkholderia kirkii, the obligate leaf symbiont of Psychotria kirkii. Kirkamide ( 1 ) was shown to be toxic to aquatic arthropods and insects, thus suggesting that bacterial secondary metabolites play a protective role in the Psychotria/Burkholderia leaf nodule symbiosis.  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