全文获取类型
收费全文 | 448篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
化学 | 388篇 |
力学 | 5篇 |
数学 | 29篇 |
物理学 | 44篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 4篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 14篇 |
2012年 | 26篇 |
2011年 | 24篇 |
2010年 | 24篇 |
2009年 | 12篇 |
2008年 | 24篇 |
2007年 | 19篇 |
2006年 | 20篇 |
2005年 | 11篇 |
2004年 | 18篇 |
2003年 | 14篇 |
2002年 | 13篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 4篇 |
1996年 | 4篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1990年 | 3篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1975年 | 10篇 |
1956年 | 3篇 |
1939年 | 4篇 |
1936年 | 2篇 |
1935年 | 2篇 |
1933年 | 2篇 |
1930年 | 3篇 |
1929年 | 3篇 |
1928年 | 2篇 |
1926年 | 6篇 |
排序方式: 共有466条查询结果,搜索用时 15 毫秒
401.
402.
403.
The kinetics of the reactions of eleven substituted enamides with benzhydrylium ions (diarylcarbenium ions) were determined in acetonitrile solution. The second-order rate constants follow the correlation log k(2) (20 °C)=s(N)(E+N), which allowed us to derive reactivity parameters N and s(N). With 4.6相似文献
404.
405.
Mahiuddin Baidya Grygoriy Y. Remennikov Dr. Peter Mayer Dr. Herbert Mayr Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(4):1365-1371
TiCl4‐induced Baylis–Hillman reactions of α,β‐unsaturated carbonyl compounds with aldehydes yield the (Z)‐2‐(chloromethyl)vinyl carbonyl compounds 5 , which react with 1,4‐diazabicyclo[2.2.2]octane (DABCO), quinuclidine, and pyridines to give the allylammonium ions 6 . Their combination with less than one equivalent of the potassium salts of stabilized carbanions (e.g. malonate) yields methylene derivatives 8 under kinetically controlled conditions (SN2’ reactions). When more than one equivalent of the carbanions is used, a second SN2’ reaction converts 8 into their thermodynamically more stable allyl isomers 9 . The second‐order rate constants for the reactions of 6 with carbanions have been determined photometrically in DMSO. With these rate constants and the previously reported nucleophile‐specific parameters N and s for the stabilized carbanions, the correlation log k (20 °C)=s(N + E) allowed us to calculate the electrophilicity parameters E for the allylammonium ions 6 (?19<E <?18). The kinetic data indicate the SN2’ reactions to proceed via an addition–elimination mechanism with a rate‐determining addition step. 相似文献
406.
Denegri B Ofial AR Jurić S Streiter A Kronja O Mayr H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(6):1657-1666
The correlation equation log k(25 degrees C) = sf(Nf + Ef), where sf and Nf are nucleofuge-specific parameters referring to leaving group/solvent combinations and Ef are electrofuge-specific parameters referring to the incipient carbocation R+, are used to predict ionization rate constants of alkyl derivatives R--X. We show how to employ the Ef parameters of reference electrofuges and the sf and Nf parameters of reference nucleofuges reported in the preceding article for determining further sf, Nf, and Ef parameters. Since sf is usually close to 1.0, one comes to the semiquantitative rule that at 25 degrees C, compounds R--X for which Nf + Ef>-2 will solvolyze with half-lives of less than a minute, while the solvolysis half-lives will exceed 1 month if Nf + Ef<-6.5. 相似文献
407.
408.
The reactivity-selectivity principle (RSP), once a tenet of organic chemistry, eroded during the 1970s and was more or less abandoned by 1980. Although it has been clear for more than 25 years that a decrease in selectivity with increasing reactivity can only be expected with certainty if diffusion control is approached, the RSP has survived as an intuitively appealing rule. This Minireview shows why selectivity cannot generally decrease with increasing reactivity and highlights the weaknesses of the theoretical foundations of the RSP. 相似文献
409.
410.
Khan AS Mujer CV Alefantis TG Connolly JP Mayr UB Walcher P Lubitz W Delvecchio VG 《Journal of chemical information and modeling》2006,46(1):111-115
The potential devastation resulting from an intentional outbreak caused by biological warfare agents such as Brucella abortus and Bacillus anthracis underscores the need for next generation vaccines. Proteomics, genomics, and systems biology approaches coupled with the bacterial ghost (BG) vaccine delivery strategy offer an ideal approach for developing safer, cost-effective, and efficacious vaccines for human use in a relatively rapid time frame. Critical to any subunit vaccine development strategy is the identification of a pathogen's proteins with the greatest potential of eliciting a protective immune response. These proteins are collectively referred to as the pathogen's immunome. Proteomics provides high-resolution identification of these immunogenic proteins using standard proteomic technologies, Western blots probed with antisera from infected patients, and the pathogen's sequenced and annotated genome. Selected immunoreactive proteins can be then cloned and expressed in nonpathogenic Gram-negative bacteria. Subsequently, a temperature shift or chemical induction process is initiated to induce expression of the PhiX174 E-lysis gene, whose protein product forms an E tunnel between the inner and outer membrane of the bacteria, expelling all intracellular contents. The BG vaccine system is a proven strategy developed for many different pathogens and tested in a complete array of animal models. The BG vaccine system also has great potential for producing multiagent vaccines for protection to multiple species in a single formulation. 相似文献