全文获取类型
收费全文 | 5502篇 |
免费 | 191篇 |
国内免费 | 14篇 |
专业分类
化学 | 4029篇 |
晶体学 | 51篇 |
力学 | 51篇 |
数学 | 778篇 |
物理学 | 609篇 |
无线电 | 189篇 |
出版年
2021年 | 55篇 |
2020年 | 63篇 |
2019年 | 60篇 |
2018年 | 37篇 |
2017年 | 40篇 |
2016年 | 111篇 |
2015年 | 125篇 |
2014年 | 135篇 |
2013年 | 215篇 |
2012年 | 266篇 |
2011年 | 293篇 |
2010年 | 205篇 |
2009年 | 199篇 |
2008年 | 290篇 |
2007年 | 223篇 |
2006年 | 255篇 |
2005年 | 221篇 |
2004年 | 233篇 |
2003年 | 177篇 |
2002年 | 163篇 |
2001年 | 93篇 |
2000年 | 82篇 |
1999年 | 80篇 |
1998年 | 73篇 |
1997年 | 79篇 |
1996年 | 86篇 |
1995年 | 74篇 |
1994年 | 77篇 |
1993年 | 68篇 |
1992年 | 68篇 |
1991年 | 76篇 |
1990年 | 57篇 |
1989年 | 58篇 |
1988年 | 57篇 |
1987年 | 55篇 |
1986年 | 66篇 |
1985年 | 86篇 |
1984年 | 97篇 |
1983年 | 52篇 |
1982年 | 75篇 |
1981年 | 95篇 |
1980年 | 75篇 |
1979年 | 67篇 |
1978年 | 78篇 |
1977年 | 47篇 |
1976年 | 68篇 |
1975年 | 53篇 |
1973年 | 53篇 |
1971年 | 41篇 |
1970年 | 35篇 |
排序方式: 共有5707条查询结果,搜索用时 0 毫秒
921.
922.
The following investigation deals with injectivity results for general diffeomorphisms as well as for Haar's transformation.
We apply these results to adjoint variational problems introduced by Haar [6]. In particular, we prove a generalization of
Krust's theorem for two-dimensional adjoint extremals.
Received March 20, 1998 / Accepted April 24, 1998 相似文献
923.
Time-resolved FTIR-ATR spectroscopy was used to study the kinetics of the photopolymerization of a diacrylate using a morpholino ketone as photoinitiator. The curing reaction was induced by monochromatic UV radiation with a wavelength of 313 nm. The influence of photoinitiator concentration [PI], light intensity I0, and temperature on the polymerization rate Rp and the double bond conversion was investigated. The dependence of Rp on [PI] and I0, respectively, was found to fit with theoretical predictions very well. In contrast, an increase of the temperature was found to have no effect on Rp. 相似文献
924.
925.
Riadh Neffati Alexander Alexeev Sergey Saunin Jos C. M. Brokken‐Zijp Daan Wouters Stefan Schmatloch Ulrich S. Schubert Joachim Loos 《Macromolecular rapid communications》2003,24(1):113-117
A systematic investigation into the surface properties of siloxane rubber/carbon black (CB) nanocomposites has been performed, using an automated scanning probe microscope. In this way the influence of CB concentration and curing rate of the siloxane rubber matrix on roughness and conductivity of the composites was studied. Decreasing the curing rate while keeping the CB concentration resulted in a decrease in both roughness and surface conductivity, which can be explained by an additional siloxane‐rubber layer formed during curing.
926.
A vinyl substituted 2,2′:6′,2″‐terpyridine and a mixed, bifunctional ruthenium(II)‐terpyridine complex bearing a vinyl and a hydroxymethyl group are utilized as comonomers for radical copolymerization with styrene. The resulting polymers are characterized by means of UV‐vis spectroscopy and gel permeation chromatography, coupled with an in‐line diode array spectrophotometer. 相似文献
927.
928.
929.
930.
Synthesis of Phosphido Chalcogenido Bridged Dirhenium Complexes of the Type Re2(μ‐PCy2)(μ‐ER)(CO)8 (E = S, Se, Te; R = org. Residue) The reaction of Re2(μ‐Br)(μ‐PCy2)(CO)8 with nucleophiles MER (M = Na, Li; E = S, Se, Te; R = org. residue) gives via substitution of the bromido bridge phosphido chalcogenido bridged dirhenium complexes of the general formula Re2(μ‐PCy2)(μ‐ER)(CO)8. The new compounds were characterized by IR, 1H and 13C NMR spectroscopic data and by elemental analyses. In addition the molecular structures for E = S, Se, Te and R = Ph as well as for E = S and R = H, n‐Bu, 2‐pyridyl have been established by single crystal X‐ray analysis. 13C NMR spectra of Re2(μ‐PCy2)(μ‐EPh)(CO)8 (E = S, Se, Te) prove that the sulfur and selenium compounds are at room temperature dynamic molecules due to inversion of the pyramidal chalcogenido bridge. The tellurium compound, however, is rigid on the time scale of 13C NMR spectroscopy. Eventually the reactivity of the SH function of the novel complex Re2(μ‐PCy2)(μ‐SH)(CO)8 was investigated by reaction with Re2(CO)8(MeCN)2. In toluene at 90 °C the novel spirocyclic complex Re2(μ‐PCy2)(CO)8(μ4‐S)Re2(μ‐H)(CO)8 was formed by SH oxidative addition. 相似文献