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   26250篇
  免费   72篇
  国内免费   71篇
系统科学   235篇
丛书文集   507篇
教育与普及   51篇
理论与方法论   61篇
现状及发展   11280篇
研究方法   1006篇
综合类   12855篇
自然研究   398篇
  2013年   162篇
  2012年   349篇
  2011年   750篇
  2010年   119篇
  2008年   382篇
  2007年   452篇
  2006年   468篇
  2005年   456篇
  2004年   469篇
  2003年   443篇
  2002年   374篇
  2001年   828篇
  2000年   792篇
  1999年   483篇
  1992年   483篇
  1991年   416篇
  1990年   448篇
  1989年   370篇
  1988年   414篇
  1987年   424篇
  1986年   381篇
  1985年   549篇
  1984年   417篇
  1983年   360篇
  1982年   280篇
  1981年   299篇
  1980年   385篇
  1979年   815篇
  1978年   691篇
  1977年   637篇
  1976年   560篇
  1975年   631篇
  1974年   777篇
  1973年   668篇
  1972年   695篇
  1971年   821篇
  1970年   1094篇
  1969年   844篇
  1968年   750篇
  1967年   761篇
  1966年   714篇
  1965年   524篇
  1964年   147篇
  1959年   300篇
  1958年   460篇
  1957年   344篇
  1956年   302篇
  1955年   268篇
  1954年   299篇
  1948年   202篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
1.
This is a contribution towards a history and philosophy of modeling in its early stages in electromagnetism. In 1873, James Clerk Maxwell (1831–1879) hinted at the methodology of modeling at the end of his Treatise on Electricity and Magnetism. We focus on Maxwell's impact on physicists who immediately followed him, specifically Oliver Lodge (1851–1940) and George Francis FitzGerald (1851–1901). We begin with the role that the scientific concept of model played in the late nineteenth century, as assessed by Ludwig Boltzmann (1844–1906). We then discuss the role of hypothesis as a methodology, the appeal to (dynamical) illustration, and the way Maxwell applied model and working model in his studies of electromagnetism. We show that for Maxwell these key terms were kept distinct, but Lodge did not maintain these distinctions and, in this regard, FitzGerald followed Lodge. Notwithstanding Lodge's influence, Fitzgerald modified Maxwell's theory based on the mechanical model he designed, thereby implicitly taking the first step towards modeling. This methodology consists in drawing consequences from the (mechanical) model to the (electrodynamic) theory and modifying the latter in light of the functioning of the former. At the core of our argument is the thesis that it was a methodological novelty to move from the concept of model to the methodology of modeling. The introduction of modeling as a new methodology into physics in the late nineteenth century was a major event which deserves proper recognition.  相似文献   
2.
Areas of the Knysna estuarine bay in the Western Cape are dominated by three endemic South African truncatelloid microgastropods, temporarily known as ‘Hydrobiaknysnaensis (Krauss), ‘Assimineacapensis (Sowerby) and ‘Assimineaglobulus Connolly. Although first described 80–170 years ago and present in abundance (up to 100,000 m?2), they remain surrounded by confusion and still await taxonomic assignment, largely because they appear most atypical members of their groups by virtue of anatomy and/or biogeography and/or habitat. This study contributes in-life perspectives to morphological and phylogenetic analyses known to be on-going. At Knysna, they are syntopic: at least two occurring in >85% and all three in >40% of individual 0.0026 m2 samples from their region of dominance. Nevertheless, they tend to greater abundance in divergent microhabitats; ‘A.’ globulus dominating higher tidal levels, and ‘A.’ capensis and ‘Hydrobia’ lower ones; the former especially unvegetated sediment, the latter, if anything, seagrass. Interspecific feeding interactions appear unlikely to be responsible for these patterns, other evidence suggesting that all are maintained below carrying capacity. Field biology of ‘H.’ knysnaensis generally appears equivalent to that of northern-hemisphere intertidal hydrobiids and that of ‘A.’ globulus is typically assimineid, albeit at atypically low shore height. Unlike assimineids, however, ‘A.’ capensis is truly aquatic. The success of these truncatelloids in unusual circumstances may be consequent on the absence from South Africa of other microgastropod groups that fill their niches elsewhere in the southern hemisphere.  相似文献   
3.
4.
5.
6.
The shrink proofing on wool with treatment of protease named Argaenzyme STL was studied. The various pretreating auxiliaries, different parameters for protease treating process and the effect of stabilizer were discussed in detail. The varieties of some properties before and after protease treatment were also investigated.  相似文献   
7.
西文期刊回溯建库中几个重要项目的著录   总被引:4,自引:0,他引:4  
在实践的基础上,从期刊的出版日期、出版周期、卷、期、年、月及其他标识、ISSN、增刊、出版者以及期刊的历史发展等方面对西文期刊机读目录的标准化著录问题进行了探讨。  相似文献   
8.
9.
10.
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