全文获取类型
收费全文 | 497915篇 |
免费 | 6581篇 |
国内免费 | 2682篇 |
专业分类
化学 | 271131篇 |
晶体学 | 7321篇 |
力学 | 20831篇 |
综合类 | 43篇 |
数学 | 60010篇 |
物理学 | 147842篇 |
出版年
2020年 | 3704篇 |
2019年 | 3934篇 |
2018年 | 4351篇 |
2017年 | 4175篇 |
2016年 | 7400篇 |
2015年 | 5637篇 |
2014年 | 7930篇 |
2013年 | 23121篇 |
2012年 | 17201篇 |
2011年 | 21343篇 |
2010年 | 13624篇 |
2009年 | 13522篇 |
2008年 | 19179篇 |
2007年 | 19416篇 |
2006年 | 18457篇 |
2005年 | 16912篇 |
2004年 | 15179篇 |
2003年 | 13441篇 |
2002年 | 13216篇 |
2001年 | 14775篇 |
2000年 | 11337篇 |
1999年 | 9072篇 |
1998年 | 7431篇 |
1997年 | 7276篇 |
1996年 | 7100篇 |
1995年 | 6536篇 |
1994年 | 6223篇 |
1993年 | 6086篇 |
1992年 | 6724篇 |
1991年 | 6677篇 |
1990年 | 6260篇 |
1989年 | 6093篇 |
1988年 | 6321篇 |
1987年 | 5983篇 |
1986年 | 5774篇 |
1985年 | 8185篇 |
1984年 | 8373篇 |
1983年 | 6858篇 |
1982年 | 7475篇 |
1981年 | 7368篇 |
1980年 | 7118篇 |
1979年 | 7202篇 |
1978年 | 7443篇 |
1977年 | 7286篇 |
1976年 | 7359篇 |
1975年 | 6950篇 |
1974年 | 6911篇 |
1973年 | 7255篇 |
1972年 | 4375篇 |
1971年 | 3298篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Saturated and benzylic organomagnesium compounds are shown to readily undergo addition reactions with the conjugated enynes HCHCH2R′, with R′ = alkyl, OH, OC4H9, NHC25, N(C2H5)2, by refluxing for several hours in benzene or toluene.This reaction leads to both υ-acetylenic compounds (1,2-addition) and β-allenic compounds (1,4-addition). 相似文献
992.
Ohne Zusammenfassung 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.
996.
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
997.
998.
999.
Determination of mercury (II) by substoichiometric extraction with malonic anilide into a mixture of ether and MIBK is reported. The method has been applied in the estimation of the metal in industrial effluents. 相似文献
1000.
J.C. Gramain N. Simonet G. Vermeersch N. Febvay-Garot S. Caplain A. Lablache-Combier 《Tetrahedron》1982,38(4):539-550
Benzophenone is photoreduced by pthalimidines and dihydro isoquinolones. The hydrogen atom α to the nitrogen atom is abstracted and radical coupling leads to adducts. CIDNP studies of these adducts show inversion of polarisation for the adduct on the N-alkyl chain when the nitrogen is bound to a benzylic methylene. This inversion is explained by considering that the radical on the N-alkyl chain derives from the radical on the ring. 相似文献