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   45645篇
  免费   166篇
  国内免费   210篇
系统科学   382篇
丛书文集   924篇
教育与普及   87篇
理论与方法论   154篇
现状及发展   20936篇
研究方法   1698篇
综合类   21127篇
自然研究   713篇
  2013年   390篇
  2012年   621篇
  2011年   1348篇
  2010年   295篇
  2008年   773篇
  2007年   856篇
  2006年   876篇
  2005年   849篇
  2004年   829篇
  2003年   795篇
  2002年   728篇
  2001年   1325篇
  2000年   1274篇
  1999年   830篇
  1992年   811篇
  1991年   643篇
  1990年   722篇
  1989年   694篇
  1988年   683篇
  1987年   755篇
  1986年   697篇
  1985年   905篇
  1984年   709篇
  1983年   589篇
  1982年   510篇
  1981年   553篇
  1980年   703篇
  1979年   1394篇
  1978年   1184篇
  1977年   1182篇
  1976年   951篇
  1975年   1007篇
  1974年   1356篇
  1973年   1193篇
  1972年   1246篇
  1971年   1409篇
  1970年   1802篇
  1969年   1369篇
  1968年   1350篇
  1967年   1319篇
  1966年   1155篇
  1965年   827篇
  1964年   267篇
  1959年   471篇
  1958年   770篇
  1957年   553篇
  1956年   496篇
  1955年   443篇
  1954年   474篇
  1948年   321篇
排序方式: 共有10000条查询结果,搜索用时 15 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.
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   
3.
4.
Photon emission of phagocytes in relation to stress and disease.   总被引:1,自引:0,他引:1  
E M Lilius  P Marnila 《Experientia》1992,48(11-12):1082-1091
Phagocytes, the first-line cells of the body's defence mechanisms against invading pathogens, kill microorganisms by means of lysosomal degradative enzymes and highly toxic reactive oxygen intermediates. The reactive oxygen compounds are produced, in a process called the 'respiratory burst', by the NADPH oxidase complex in plasma membranes, and by myeloperoxidase in phagolysosomes after degranulation. These processes generate electronically excited states which, on relaxation, emit photons, giving rise to phagocyte chemiluminescence (CL). This paper describes the conditions for the measurement of CL, and reviews the activity of phagocytes from individuals undergoing stress or disease. The capability of phagocytes to emit photons reflects remarkably well the pathophysiological state of the host. In many cases even the magnitude of the stress, the presence of a pathogen in the body, or the activity of the disease can be estimated. Physiological changes, e.g. in the reproductive cycle, can also be predicted.  相似文献   
5.
6.
7.
8.
9.
1 Results In the coordination system by using complexation with organic ligand, the ff emission of lanthanide(Ⅲ) (Ln(Ⅲ)) is induced the excitation energy transfer form the organic chromophore under the light-irradiation. However, there are not so much number of reports to discuss the energy relaxation mechanism in such complexes with Ln(Ⅲ). Recently, we succeeded firstly to estimate the rate constant of the energy transfer between the ligand and Ln(Ⅲ) in Pr(Ⅲ)-phenanthroline analogs[1]. Here, we will di...  相似文献   
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