全文获取类型
收费全文 | 29449篇 |
免费 | 82篇 |
国内免费 | 158篇 |
专业分类
系统科学 | 151篇 |
丛书文集 | 499篇 |
教育与普及 | 42篇 |
理论与方法论 | 113篇 |
现状及发展 | 13685篇 |
研究方法 | 1337篇 |
综合类 | 13462篇 |
自然研究 | 400篇 |
出版年
2013年 | 278篇 |
2012年 | 432篇 |
2011年 | 842篇 |
2010年 | 182篇 |
2008年 | 543篇 |
2007年 | 604篇 |
2006年 | 606篇 |
2005年 | 569篇 |
2004年 | 555篇 |
2003年 | 511篇 |
2002年 | 522篇 |
2001年 | 949篇 |
2000年 | 887篇 |
1999年 | 626篇 |
1992年 | 609篇 |
1991年 | 417篇 |
1990年 | 492篇 |
1989年 | 501篇 |
1988年 | 465篇 |
1987年 | 555篇 |
1986年 | 484篇 |
1985年 | 610篇 |
1984年 | 489篇 |
1983年 | 369篇 |
1982年 | 344篇 |
1981年 | 374篇 |
1980年 | 468篇 |
1979年 | 905篇 |
1978年 | 766篇 |
1977年 | 750篇 |
1976年 | 620篇 |
1975年 | 640篇 |
1974年 | 851篇 |
1973年 | 765篇 |
1972年 | 788篇 |
1971年 | 850篇 |
1970年 | 1081篇 |
1969年 | 822篇 |
1968年 | 827篇 |
1967年 | 804篇 |
1966年 | 687篇 |
1965年 | 475篇 |
1964年 | 159篇 |
1959年 | 250篇 |
1958年 | 442篇 |
1957年 | 294篇 |
1956年 | 263篇 |
1955年 | 247篇 |
1954年 | 240篇 |
1948年 | 164篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
String theorists are certain that they are practicing physicists. Yet, some of their recent critics deny this. This paper argues that this conflict is really about who holds authority in making rational judgment in theoretical physics. At bottom, the conflict centers on the question: who is a proper physicist? To illustrate and understand the differing opinions about proper practice and identity, we discuss different appreciations of epistemic virtues and explanation among string theorists and their critics, and how these have been sourced in accounts of Einstein's biography. Just as Einstein is claimed by both sides, historiography offers examples of both successful and unsuccessful non-empirical science. History of science also teaches that times of conflict are often times of innovation, in which novel scholarly identities may come into being. At the same time, since the contributions of Thomas Kuhn historians have developed a critical attitude towards formal attempts and methodological recipes for epistemic demarcation and justification of scientific practice. These are now, however, being considered in the debate on non-empirical physics. 相似文献
2.
3.
4.
M.Hasegawa 《复旦学报(自然科学版)》2007,(5)
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
5.
6.
7.
8.
9.
10.
P pili in uropathogenic E. coli are composite fibres with distinct fibrillar adhesive tips. 总被引:25,自引:0,他引:25
Escherichia coli is a frequent cause of several common bacterial infections in humans and animals, including urinary tract infections, bacteraemia and bacteria-related diarrhoea and is also the main cause of neonatal meningitis. Microbial attachment to surfaces is a key event in colonization and infection and results mainly from a stereochemical fit between microbial adhesins and complementary receptors on host cells. Bacterial adhesins required for extracellular colonization by Gram-negative bacteria are often minor components of heteropolymeric fibres called pili which must be oriented in an accessible manner in these structures to be able to bind to specific receptor architectures. P pili mediate the binding of uropathogenic E. coli to a digalactoside receptor determinant present in the urinary tract epithelium. We report here that the adhesin is a component of distinct fibrillar structures present at the tips of the pili. These virulence-associated tip fibrillae are thin, flexible polymers composed mostly of repeating subunits of PapE that frequently terminate with the alpha-D-galactopyranosyl-(1-4)-beta-D-galactopyranose or Gal alpha (1-4)Gal binding PapG adhesin. 相似文献