全文获取类型
收费全文 | 5045篇 |
免费 | 15篇 |
国内免费 | 22篇 |
专业分类
系统科学 | 12篇 |
丛书文集 | 18篇 |
教育与普及 | 4篇 |
理论与方法论 | 2篇 |
现状及发展 | 2210篇 |
研究方法 | 262篇 |
综合类 | 2546篇 |
自然研究 | 28篇 |
出版年
2013年 | 52篇 |
2012年 | 100篇 |
2011年 | 118篇 |
2010年 | 26篇 |
2008年 | 88篇 |
2007年 | 111篇 |
2006年 | 99篇 |
2005年 | 98篇 |
2004年 | 119篇 |
2003年 | 80篇 |
2002年 | 89篇 |
2001年 | 181篇 |
2000年 | 150篇 |
1999年 | 118篇 |
1992年 | 112篇 |
1991年 | 72篇 |
1990年 | 75篇 |
1989年 | 66篇 |
1988年 | 70篇 |
1987年 | 78篇 |
1986年 | 56篇 |
1985年 | 96篇 |
1984年 | 91篇 |
1983年 | 79篇 |
1982年 | 62篇 |
1981年 | 54篇 |
1980年 | 68篇 |
1979年 | 174篇 |
1978年 | 141篇 |
1977年 | 111篇 |
1976年 | 116篇 |
1975年 | 123篇 |
1974年 | 147篇 |
1973年 | 119篇 |
1972年 | 123篇 |
1971年 | 149篇 |
1970年 | 198篇 |
1969年 | 142篇 |
1968年 | 151篇 |
1967年 | 127篇 |
1966年 | 137篇 |
1965年 | 104篇 |
1964年 | 39篇 |
1959年 | 39篇 |
1958年 | 68篇 |
1957年 | 47篇 |
1956年 | 38篇 |
1955年 | 36篇 |
1954年 | 46篇 |
1948年 | 28篇 |
排序方式: 共有5082条查询结果,搜索用时 0 毫秒
1.
2.
Summary Immunohistochemistry revealed an Ig-A-like substance on the luminal surface of the pineal follicles and in the parafollicular layer. This substance was observed around 1 week of age and disappeared by 8 weeks at the time when the transformation of the follicular pattern leads to an adult-type pineal tissue. 相似文献
3.
4.
5.
The antifungal activity of two drimane sesquiterpene dialdehydes, polygodial (1) and warburganal (2), alone and in combination with several other substances, was examined against three fungi,Candida albicans, Saccharomyces cerevisiae andPityrosporum ovale employing a broth dilution method. Anethole significantly synergized the activity of the two sesquiterpenoids againstC. albicans andS. cerevisiae however, it had only an, additive effect againstP. ovale. By contrast, two antioxidants, ascorbic acid (vitamin C) and BHA (butylated hydroxyanisole), noticeably enhanced the activity of the sesquiterpenoids againstP. ovale, but had no, effect againstC. albicans andS. cerevisiae. 相似文献
6.
6-Trichloromethyl-9-methylpurine (1) rearranges to 6-dichloromethyl-9-methyl-8-oxopurine (2) in aqueous mild acidic solution. The rearrangement is rationalized in terms of a reaction involving protonation, covalent hydration, prototropic equilibrium and/or a hydride transfer. An alternative mechanism involving a "positive' halogen compound and hypochlorous acid as an intermediary is also proposed. Compound 1 condenses with 4,5-diaminopyrimidine to give the purine-pyrimidine Schiff base pair 4. 相似文献
7.
Pineal gland changes of rats exposed to heat 总被引:1,自引:0,他引:1
8.
I. Grattan-Guinness 《Archive for History of Exact Sciences》1970,6(5):372-400
Summary In this paper I discuss the development of mathematical analysis during the second and third decades of the nineteenth century; and in particular I assert that the well-known correspondence of new ideas to be found in the writings of Bolzano and Cauchy is not a coincidence, but that Cauchy had read one particular paper of Bolzano and drew on its results without acknowledgement. The reasons for this conjecture involve not only the texts in question but also the state of development of mathematical analysis itself, Cauchy both as personality and as mathematician, and the rivalries which were prevalent in Paris at that time. 相似文献
9.
10.
MDMethodinSolvingMultipleCriteriaDecisionProblemsArisingfromInvestmentSystemsDUWenzhong;CIJianhua(EconomicInformationCenterof... 相似文献