全文获取类型
收费全文 | 425870篇 |
免费 | 4868篇 |
国内免费 | 2157篇 |
专业分类
化学 | 232437篇 |
晶体学 | 6352篇 |
力学 | 17644篇 |
综合类 | 63篇 |
数学 | 49437篇 |
物理学 | 126962篇 |
出版年
2020年 | 3293篇 |
2019年 | 3673篇 |
2018年 | 4545篇 |
2017年 | 4565篇 |
2016年 | 6923篇 |
2015年 | 4683篇 |
2014年 | 6879篇 |
2013年 | 18647篇 |
2012年 | 14499篇 |
2011年 | 17780篇 |
2010年 | 12163篇 |
2009年 | 11900篇 |
2008年 | 16234篇 |
2007年 | 16542篇 |
2006年 | 15310篇 |
2005年 | 14149篇 |
2004年 | 12639篇 |
2003年 | 11201篇 |
2002年 | 11069篇 |
2001年 | 12384篇 |
2000年 | 9324篇 |
1999年 | 7180篇 |
1998年 | 6022篇 |
1997年 | 5990篇 |
1996年 | 5790篇 |
1995年 | 5292篇 |
1994年 | 5221篇 |
1993年 | 5159篇 |
1992年 | 5605篇 |
1991年 | 5684篇 |
1990年 | 5339篇 |
1989年 | 5280篇 |
1988年 | 5260篇 |
1987年 | 5127篇 |
1986年 | 4991篇 |
1985年 | 6739篇 |
1984年 | 6933篇 |
1983年 | 5733篇 |
1982年 | 6270篇 |
1981年 | 5922篇 |
1980年 | 5682篇 |
1979年 | 5859篇 |
1978年 | 6213篇 |
1977年 | 6136篇 |
1976年 | 6320篇 |
1975年 | 5726篇 |
1974年 | 5906篇 |
1973年 | 6222篇 |
1972年 | 4315篇 |
1971年 | 3412篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ohne Zusammenfassung 相似文献
992.
I. C. McNeill L. Ackerman S. N. Gupta M. Zulfiqar S. Zulfiqar 《Journal of polymer science. Part A, Polymer chemistry》1977,15(10):2381-2392
In the subambient thermal volatilization analysis (TVA) technique, degradation products initially at ?196°C are allowed to warm up to ambient temperature in a controlled manner under vacuum conditions, and volatilization from the sample tube to a trap at ?196°C is monitored by means of a Pirani gauge. The technique is discussed in relation to earlier TVA work in which volatilization from a heated polymer sample was followed. Design and operation of a subambient TVA system are described, and examples of the application of the technique to the study of the degradation products of seven polymers are considered. 相似文献
993.
R.R. Adžić D.N. Simić A.R. Despić D.M. Dražić 《Journal of Electroanalytical Chemistry》1975,65(2):587-601
It was demonstrated that some foreign metal monolayers formed by underpotential deposition have pronounced catalytic effects on the oxidation of formic acid on platinum. The explanation of these effects was sought within the framewor of existing data on the formic acid oxidation and the underpotential deposition. It was found that the catalytic effect of foreign metal monolayers originates in the decrease of hydrogen adsorption thus preventing the formation of the main poisoning species COH. At the same time these experiments confirm the previously postulated mechanism of formation of the poisoning species involving adsorbed hydrogen. 相似文献
994.
995.
Jack A. Zeineh Michael M. Zeineh R. A. Zeineh 《Applied biochemistry and biotechnology》1993,41(3):219-231
The 17″×14″ X-ray film, gels, and blots are widely used in DNA research. However, DNA laser scanners are costly and unaffordable for the majority of surveyed biotech scientists who need it. The high-tech breakthrough analytical personal scanner (PS) presented in this report is an inexpensive 1 lb hand-held scanner priced at 2–4% of the bulky and costly 30–95 lb conventional laser scanners. This PS scanner is affordable from an operation budget and biotechnologists, who originate most science breakthroughs, can acquire it to enhance their speed, accuracy, and productivity. Compared to conventional laser scanners that are currently available only through hard-to-get capital-equipment budgets, the new PS scanner offers improved spatial resolution of 20 μm, higher speed (scan up to 17″×14″ molecular X-ray film in 48 s), 1–32,768 gray levels (16-bits), student routines, versatility, and, most important affordability. Its programs image the film, read DNA sequences automatically, and detect gene mutation. In parallel to the wide laboratory use of PC computers instead of mainframes, this PS scanner might become an integral part of a PC-PS powerful and cost-effective system where the PS performs the digital imaging and the PC acts on the data. 相似文献
996.
997.
Synthesis of 1,7-bis(4′-aminophenylamido)-m-carborane and 1,7-bis(4′-aminophenylcarboxy)-m-carborane
V. V. Korshak L. G. Komarova N. G. Komarova V. V. Vagin G. A. Kats 《Russian Chemical Bulletin》1986,35(12):2554-2555
Conclusion 1,7-Bis(4-aminophenylamido)- and l,7-bis(4-aminophenylcarboxy)-m-carboranes were prepared and characterized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2786–2787, December, 1986. 相似文献
998.
V. M. Lyubchanskaya L. M. Alekseeva V. G. Granik 《Chemistry of Heterocyclic Compounds》1992,28(1):34-39
Previously unknown 3-nitro-6-hydroxyindole derivatives were synthesized by condensation of p-benzoquinone with secondary -nitro enamines.See [1] for Communication 70.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 40–45, January, 1992. 相似文献
999.
S. I. Kozintsev L. I. Basalaeva L. V. Gladkikh N. S. Kozlov 《Chemistry of Heterocyclic Compounds》1988,24(1):19-22
Reaction of furfuryl and tetrahydrofurfuryl alcohols with nitriles over copper oxide catalysts under a hydrogen pressure of 15 atm at a temperature of 230C gives N-alkylfurfuryl- (yield 46–50%) and N-alkyl-tetrahydrofurfurylamines (49–53%), and N-alkylpiperidines (28–41%). A reaction mechanism is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 23–26, January, 1988. 相似文献
1000.