全文获取类型
收费全文 | 7858篇 |
免费 | 213篇 |
国内免费 | 24篇 |
专业分类
化学 | 5868篇 |
晶体学 | 38篇 |
力学 | 71篇 |
数学 | 1137篇 |
物理学 | 981篇 |
出版年
2020年 | 77篇 |
2019年 | 74篇 |
2016年 | 154篇 |
2015年 | 153篇 |
2014年 | 122篇 |
2013年 | 270篇 |
2012年 | 259篇 |
2011年 | 343篇 |
2010年 | 190篇 |
2009年 | 198篇 |
2008年 | 315篇 |
2007年 | 319篇 |
2006年 | 290篇 |
2005年 | 315篇 |
2004年 | 300篇 |
2003年 | 247篇 |
2002年 | 210篇 |
2001年 | 114篇 |
2000年 | 109篇 |
1999年 | 117篇 |
1998年 | 115篇 |
1997年 | 129篇 |
1996年 | 113篇 |
1995年 | 118篇 |
1994年 | 109篇 |
1993年 | 121篇 |
1992年 | 106篇 |
1991年 | 110篇 |
1990年 | 83篇 |
1989年 | 113篇 |
1988年 | 117篇 |
1987年 | 113篇 |
1986年 | 113篇 |
1985年 | 141篇 |
1984年 | 105篇 |
1983年 | 101篇 |
1982年 | 112篇 |
1981年 | 98篇 |
1980年 | 108篇 |
1979年 | 101篇 |
1978年 | 88篇 |
1977年 | 85篇 |
1976年 | 85篇 |
1974年 | 98篇 |
1973年 | 87篇 |
1971年 | 77篇 |
1961年 | 141篇 |
1960年 | 195篇 |
1959年 | 102篇 |
1958年 | 115篇 |
排序方式: 共有8095条查询结果,搜索用时 359 毫秒
1.
2.
Mechanistic Aspects of a Highly Active Dinuclear Zinc Catalyst for the Co‐polymerization of Epoxides and CO2 下载免费PDF全文
Stefan Kissling Peter T. Altenbuchner Dr. Maximilian W. Lehenmeier Dr. Eberhardt Herdtweck Dr. Peter Deglmann Dr. Uwe B. Seemann Prof. Dr. Bernhard Rieger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8148-8157
The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO2 revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO2 co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion. 相似文献
3.
Pu Duan Bo Zhi Luke Coburn Christy L. Haynes Klaus Schmidt-Rohr 《Magnetic resonance in chemistry : MRC》2020,58(11):1130-1138
The composition of fluorescent polymer nanoparticles, commonly referred to as carbon dots, synthesized by microwave-assisted reaction of citric acid and ethylenediamine was investigated by 13C, 13C{1H}, 1H─13C, 13C{14N}, and 15N solid-state nuclear magnetic resonance (NMR) experiments. 13C NMR with spectral editing provided no evidence for significant condensed aromatic or diamondoid carbon phases. 15N NMR showed that the nanoparticle matrix has been polymerized by amide and some imide formation. Five small, resolved 13C NMR peaks, including an unusual ═CH signal at 84 ppm (1H chemical shift of 5.8 ppm) and ═CN2 at 155 ppm, and two distinctive 15N NMR resonances near 80 and 160 ppm proved the presence of 5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridine-7-carboxylic acid (IPCA) or its derivatives. This molecular fluorophore with conjugated double bonds, formed by a double cyclization reaction of citric acid and ethylenediamine as first shown by Y. Song, B. Yang, and coworkers in 2015, accounts for the fluorescence of the carbon dots. Cross-peaks in a 1H─13C HETCOR spectrum with brief 1H spin diffusion proved that IPCA is finely dispersed in the polyamide matrix. From quantitative 13C and 15N NMR spectra, a high concentration (18 ± 2 wt%) of IPCA in the carbon dots was determined. A pronounced gradient in 13C chemical-shift perturbations and peak widths, with the broadest lines near the COO group of IPCA, indicated at least partial transformation of the carboxylic acid of IPCA by amide or ester formation. 相似文献
4.
5.
Let R be a discrete nonsingular equivalence relation on a standard probability space , and let V be an ergodic strongly asymptotically central automorphism of R. We prove that every V-invariant cocycle with values in a Polish group G takes values in an abelian subgroup of G.
The hypotheses of this result are satisfied, for example, if A is a finite set, a closed, shift-invariant subset, V is the shift, μ a shift-invariant and ergodic probability measure on X, the two-sided tail-equivalence relation on X, a shift-invariant subrelation which is μ-nonsingular, and a shift-invariant cocycle. 相似文献
6.
7.
8.
9.
JPC – Journal of Planar Chromatography – Modern TLC - This paper reports the efficiency of the C30 phase for HPLC and TLC separation of a mixture of tocopherol homologs and... 相似文献
10.
Simplicial complexes X provide commutative rings A(X) via the Stanley- Reisner construction. We calculated the cotangent cohomology, i.e., T1 and T2 of A(X) in terms of X. These modules provide information about the deformation theory of the algebro geometric objects assigned to X. 相似文献