全文获取类型
收费全文 | 867篇 |
免费 | 26篇 |
国内免费 | 7篇 |
专业分类
化学 | 552篇 |
晶体学 | 7篇 |
力学 | 24篇 |
数学 | 134篇 |
物理学 | 183篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2016年 | 21篇 |
2015年 | 9篇 |
2014年 | 19篇 |
2013年 | 19篇 |
2012年 | 36篇 |
2011年 | 45篇 |
2010年 | 23篇 |
2009年 | 17篇 |
2008年 | 43篇 |
2007年 | 37篇 |
2006年 | 47篇 |
2005年 | 48篇 |
2004年 | 39篇 |
2003年 | 31篇 |
2002年 | 30篇 |
2001年 | 18篇 |
2000年 | 44篇 |
1999年 | 30篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 10篇 |
1969年 | 6篇 |
1959年 | 5篇 |
排序方式: 共有900条查询结果,搜索用时 15 毫秒
41.
We discuss the process $$e^ + e^ - \to Q\bar Q \to 3gluons \to 3jets$$ with attention to the kinematics and observability of the jets. We also show how to check the gluon spin through jet or hadron angular distributions. Gluon flavor can be checked by looking for quantum number correlations between opposite jets. We predict that correlations exist off resonance for \(e^ + e^ - \to q\bar q\) , but not on resonance for \(Q\bar Q \to 3g\) . 相似文献
42.
A procedure for the selective deprotection of p-methoxybenzyl ethers using catalytic amounts of DDQ and of sodium nitrite, with oxygen as the terminal oxidant, is reported. 相似文献
43.
Polyethersulfone has been shown to be miscible with phenoxy resin. Cast films were found to be clear and show a single, composition-dependent glass transition-Blends were found to phase separate on heating with a lower critical solution temperature around 185°C. The heat of mixing of low molecular weight analogs was small and negative, suggesting a favorable interaction between the polymers. Phase diagrams were simulated using the equation-of-state theory of Flory and co-workers and were found to agree closely with the observed behavior. The water vapor sorption of the blends was investigated, and this also suggested a weak favorable interaction between the polymers. 相似文献
44.
45.
Influence theory is a foundational theory of physics that is not based on traditional empirically defined concepts, such as positions in space and time, mass, energy, or momentum. Instead, the aim is to derive these concepts, and their empirically determined relationships, from a more primitive model. It is postulated that there exist things, which are call particles, that influence one another in a discrete and directed fashion resulting in a partially ordered set of influence events. The problem of consistent quantification of the influence events is considered. Observers are modeled as particle chains (observer chains) as if an observer were able to track a particle and quantify the influence events that the particle experiences. From these quantified influence events, consistent quantification of the universe of events based on the observer chains is studied. Herein, the kinematics and dynamics of particles from the perspective of influence theory are both reviewed and further developed. 相似文献
46.
Wenjun Yang Bo Ling Bowen Hu Haolin Yin Prof. Dr. Jianyou Mao Prof. Dr. Patrick J. Walsh 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(1):167-172
An umpolung 1,4-addition of aryl iodides to enals promoted by cooperative (terpy)Pd/NHC catalysis was developed that generates various bioactive β,β-diaryl propanoate derivatives. This system is not only the first reported palladium-catalyzed arylation of NHC-bound homoenolates but also expands the scope of NHC-induced umpolung transformations. A diverse array of functional groups such as esters, nitriles, alcohols, and heterocycles are tolerated under the mild conditions. This method also circumvents the use of moisture-sensitive organometallic reagents. 相似文献
47.
The syntheses of boronates derived from the reaction of dioxaborolanes and dioxaborinanes with either organolithium or organomagnesium reagents are investigated along with their subsequent use in the palladium cross coupling reaction. The intrinsic stability of these cyclic esters contributes to their facile reaction with both lithium and magnesium nucleophiles at mild and safe conditions. We have found that many of the reactions proceed at room temperature which is a significant improvement over the traditional routes which require cryogenic temperatures. The scope of these reactions and their practical application to large scale process synthesis is described. 相似文献
48.
When poly(ethylene terephthalate) was quenched from above Tg and then heated, it exhibited a step increase in thickness in the glass transition region at every rate tested. When the polymer was cooled more slowly than it was heated, a higher Tg and a slightly larger step increase in thickness were observed as the cooling rate was reduced. These experimental results appear to be adequately interpreted on the basis of the normal structural changes that occur in a glass as its thermal history is varied. Two observations, however, were not easily included in this view. First, the polymer, on cooling from above Tg, exhibited an abnormally high expansion coefficient over much of the range of temperature in which it exists as a fluid. Second, the polymer exhibited a step increase in thickness when it was heated at the same rate at which it had previously been cooled. 相似文献
49.
Nusrah Hussain Gustavo Frensch Jiadi Zhang Patrick J. Walsh 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(14):3767-3771
The combination of aryl bromides, allylbenzene, base and a palladium catalyst usually results in a Heck reaction. Herein we combine these same reagents, but override the Heck pathway by employing a strong base. In the presence of LiN(SiMe3)2, allylbenzene derivatives undergo reversible deprotonation. Transmetalation of the resulting allyllithium intermediate to LPdAr(Br) and reductive elimination provide the 1,1‐diarylprop‐2‐enes, which are not accessible by the Heck reaction. The regioselectivity in this deprotonative cross‐coupling process is catalyst‐controlled and very high. 相似文献
50.
Kirsty McKay Tara L. Salter Andrew Bowfield James L. Walsh Ian S. Gilmore James W. Bradley 《Journal of the American Society for Mass Spectrometry》2014,25(9):1528-1537
Plasma-based desorption/ionization sources are an important ionization technique for ambient surface analysis mass spectrometry. In this paper, we compare and contrast three competing plasma based desorption/ionization sources: a radio-frequency (rf) plasma needle, a dielectric barrier plasma jet, and a low-temperature plasma probe. The ambient composition of the three sources and their effectiveness at analyzing a range of pharmaceuticals and polymers were assessed. Results show that the background mass spectrum of each source was dominated by air species, with the rf needle producing a richer ion spectrum consisting mainly of ionized water clusters. It was also seen that each source produced different ion fragments of the analytes under investigation: this is thought to be due to different substrate heating, different ion transport mechanisms, and different electric field orientations. The rf needle was found to fragment the analytes least and as a result it was able to detect larger polymer ions than the other sources. Figure
? 相似文献