全文获取类型
收费全文 | 203875篇 |
免费 | 1955篇 |
国内免费 | 592篇 |
专业分类
化学 | 102304篇 |
晶体学 | 3340篇 |
力学 | 9290篇 |
综合类 | 5篇 |
数学 | 22481篇 |
物理学 | 69002篇 |
出版年
2021年 | 1655篇 |
2020年 | 1797篇 |
2019年 | 1998篇 |
2018年 | 2699篇 |
2017年 | 2601篇 |
2016年 | 3765篇 |
2015年 | 2304篇 |
2014年 | 3613篇 |
2013年 | 9085篇 |
2012年 | 7239篇 |
2011年 | 8734篇 |
2010年 | 6042篇 |
2009年 | 5910篇 |
2008年 | 7913篇 |
2007年 | 8080篇 |
2006年 | 7722篇 |
2005年 | 6890篇 |
2004年 | 6426篇 |
2003年 | 5650篇 |
2002年 | 5491篇 |
2001年 | 6426篇 |
2000年 | 4932篇 |
1999年 | 3794篇 |
1998年 | 3039篇 |
1997年 | 3045篇 |
1996年 | 2791篇 |
1995年 | 2613篇 |
1994年 | 2462篇 |
1993年 | 2337篇 |
1992年 | 2691篇 |
1991年 | 2671篇 |
1990年 | 2600篇 |
1989年 | 2396篇 |
1988年 | 2449篇 |
1987年 | 2448篇 |
1986年 | 2279篇 |
1985年 | 2960篇 |
1984年 | 3215篇 |
1983年 | 2631篇 |
1982年 | 2801篇 |
1981年 | 2771篇 |
1980年 | 2637篇 |
1979年 | 2727篇 |
1978年 | 2821篇 |
1977年 | 2819篇 |
1976年 | 2886篇 |
1975年 | 2670篇 |
1974年 | 2644篇 |
1973年 | 2776篇 |
1972年 | 1763篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
252.
We review data on methods for synthesis, chemical and pharmacological properties of pyrido[1,2-a)pyrimidines.Scientific-Research Institute of Pharmacology of the Russian Academy of Medical Sciences, All-Union Science Center for Biologically Active Substances, Staraya Kupavna, 124432. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 579–596, May, 1994. Original article submitted March 3, 1994. 相似文献
253.
254.
255.
256.
Mössbauer spectroscopy was used to investigate the reactions of microbes with iron minerals in aqueous solutions and as components of rocks in banded iron formations and granite. A microbial biofilm that formed on a wall of an excavated granite vault in a deep underground laboratory initiated this research. At the aerobic face of the biofilm, iron was found in a form of ferrihydrite; in the anaerobic face against the rock, iron was found as very small siderite particles. Laboratory incubations of the biofilm microbial consortium showed different mineral species could be formed. When the microbial consortium from the biofilm was incubated with magnetite grains, up to about 10% of the iron was altered in three weeks to hematite. The ability of the consortium to precipitate iron both as Fe2+ and Fe3+ in close proximity may have a bearing on the deposition of banded iron formations. These reactions could also be important in microbially induced corrosion. 相似文献
257.
In the nineteenth century, field theory brilliantly resolveda number of questions that had taxed mathematicians for centuries;for example, The circle cannot be squared by straightedge and compass, and solving polynomial equations by radicalsis not always possible. These successes have continued to beheld up as superb examples of the power of mathematical thought,and are demonstrated at an undergraduate level. The purposeof this article is to provide another such natural example whichleads to a concrete realisation of the free group on 2 generators. 相似文献
258.
V. D. Dyachenko S. G. Krivokolysko Yu. A. Sharanin V. P. Litvinov 《Chemistry of Heterocyclic Compounds》1997,33(7):793-798
Ammonium 6-amino-4-aryl-3,5-dicyano-1,4-dihydropyridine-2-thiolates were synthesized by recyclization of 4-aryl-2,6-diamino-3,5-dicyano-4H-thiopyranes in the presence of organic bases. On acidification of the products, the corresponding substituted 3,4-dihydropyridine-2(1H)-thiones were obtained which were used in the synthesis of 2-alkylthio-1,4-dihydropyridines, bis-(pyridyl-2)disulfides and thieno[2,3-b]pyridines.Deceased.T. G. Shevchenko Lugansk State Pedagogical Institute, Lugansk 348011. N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 909–914, July, 1997. 相似文献
259.
260.
Summary It is shown that the outer automorphism group of a Coxeter groupW of finite rank is finite if the Coxeter graph contains no infinite bonds. A key step in the proof is to show that if the
group is irreducible andΠ
1 andΠ
2 any two bases of the root system ofW, thenΠ
2 = ±ωΠ
1 for some ω εW. The proof of this latter fact employs some properties of the dominance order on the root system introduced by Brink and
Howlett.
This article was processed by the author using the Springer-Verlag TEX PJour1g macro package 1991. 相似文献