全文获取类型
收费全文 | 588篇 |
免费 | 31篇 |
专业分类
化学 | 504篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 38篇 |
物理学 | 72篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 15篇 |
2018年 | 9篇 |
2017年 | 3篇 |
2016年 | 21篇 |
2015年 | 19篇 |
2014年 | 25篇 |
2013年 | 28篇 |
2012年 | 43篇 |
2011年 | 50篇 |
2010年 | 42篇 |
2009年 | 26篇 |
2008年 | 49篇 |
2007年 | 41篇 |
2006年 | 29篇 |
2005年 | 38篇 |
2004年 | 31篇 |
2003年 | 28篇 |
2002年 | 12篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有619条查询结果,搜索用时 11 毫秒
81.
Gerrit Gobius du Sart Ivana Vukovic Zorica Vukovic Evgeny Polushkin Panu Hiekkataipale Janne Ruokolainen Katja Loos Gerrit ten Brinke 《Macromolecular rapid communications》2011,32(4):366-370
Supramolecular complexes of a poly(tert‐butoxystyrene)‐block‐polystyrene‐block‐poly(4‐vinylpyridine) triblock copolymers and less than stoichiometric amounts of pentadecylphenol (PDP) are shown to self‐assemble into a core–shell gyroid morphology with the core channels formed by the hydrogen‐bonded P4VP(PDP)complexes. After structure formation, PDP was removed using a simple washing procedure, resulting in well‐ordered nanoporous films that were used as templates for nickel plating.
82.
2H/1H isotope ratios of polyhalogenated compounds were determined by elemental analysis and isotope ratio mass spectrometry (EA-IRMS).
Initial measurements with standard EA-IRMS equipment, which used high-temperature pyrolysis to convert the organic compounds
into hydrogen, did not achieve significant signals for polychlorinated pesticides and related compounds, presumably due to
the formation of HCl instead of hydrogen. To reverse this problematic reaction, a chromium reactor was incorporated into the
element analyzer system, which scavenged Cl, forming chromium chloride and releasing hydrogen again in the form of H2. The optimized system therefore allowed the δ2H values of polyhalogenated compounds to be determined. A quality assurance program was developed based on several parameters.
(i) Each compound was analyzed using a sequence of five injections, where the first measurement was discarded. (ii) Recovery
of H (when calculated relative to acetanilide) had to be >90% for all replicates in a sequence. (iii) All δ-values within
a sequence had to vary by less than 10‰. (iv) Results had to be reproducible on another day with a different sample scheme.
Once this reproducibility had been established, variabilities in the δ2H values of organohalogen standards were investigated using the technique. The highest δ2H value of +75‰ was found for o,p′-DDD, whereas the strongest depletion in deuterium was found for Melipax (–181‰). The most important results for comparable
compounds were as follows. DDT-related compounds gave δ2H values of between +59 and +75‰ (technical DDT, o,p′- and p,p′-DDD) or in the range of approximately −1‰, indicative of the different sources/methods of producing this compound. Four
HCH isomers from the same supplier showed relatively similar hydrogen isotope distributions, whereas two lindane (γ–HCH) standards
from other sources had 39‰ less deuterium. This difference is likely due to different purification steps during the isolation
of pure lindane from the technical HCH mixture. An even greater difference was observed between the δ2H values of Toxaphene (US product dating from 1978) and Melipax (product from the former East Germany, dating from 1979),
which gave δ2H values of –101‰ and –181‰, respectively, meaning that both products were easily distinguished via δ2H-IRMS. Fractioning of hydrogen isotopes in the atmospheric water cycle was suggested as one reason for the different values.
In this theory, the water (which had different δ2H values depending on where it was taken from) was incorporated during the biosynthesis of camphene, which is the natural
product used to produce both products. These results indicate that hydrogen isotope-specific analysis can be a valuable tool
for tracing the origins of a compound in certain cases. 相似文献
83.
We study the efficiency at maximum power, η*, of engines performing finite-time Carnot cycles between a hot and a cold reservoir at temperatures Th and Tc, respectively. For engines reaching Carnot efficiency ηC=1-Tc/Th in the reversible limit (long cycle time, zero dissipation), we find in the limit of low dissipation that η* is bounded from above by ηC/(2-ηC) and from below by ηC/2. These bounds are reached when the ratio of the dissipation during the cold and hot isothermal phases tend, respectively, to zero or infinity. For symmetric dissipation (ratio one) the Curzon-Ahlborn efficiency ηCA=1-√Tc/Th] is recovered. 相似文献
84.
We present the simplest discrete model to date that leads to synchronization of stochastic phase-coupled oscillators. In the mean field limit, the model exhibits a Hopf bifurcation and global oscillatory behavior as coupling crosses a critical value. When coupling between units is strictly local, the model undergoes a continuous phase transition which we characterize numerically using finite-size scaling analysis. In particular, the onset of global synchrony is marked by signatures of the XY universality class, including the appropriate classical exponents beta and nu, a lower critical dimension d(lc) = 2, and an upper critical dimension d(uc) = 4. 相似文献
85.
Fan (in Southeast Asian Bull Math 25, 217–221, 2001) determines the endomorphism type of a finite projective plane. In this note we show that Fan’s result actually characterizes the class of projective planes among the finite bipartite graphs of diameter three. In fact, this will follow from a generalization of Fan’s theorem and its converse to all finite bipartite graphs with diameter d and girth g such that (1) d + 1<g≤2d, and (2) every pair of adjacent edges is contained in a circuit of length g. 相似文献
86.
87.
88.
Enzymatic or In Vivo Installation of Propargyl Groups in Combination with Click Chemistry for the Enrichment and Detection of Methyltransferase Target Sites in RNA 下载免费PDF全文
89.
Schwaighofer A Schroeter T Mika S Hansen K Ter Laak A Lienau P Reichel A Heinrich N Müller KR 《Journal of chemical information and modeling》2008,48(4):785-796
Metabolic stability is an important property of drug molecules that should-optimally-be taken into account early on in the drug design process. Along with numerous medium- or high-throughput assays being implemented in early drug discovery, a prediction tool for this property could be of high value. However, metabolic stability is inherently difficult to predict, and no commercial tools are available for this purpose. In this work, we present a machine learning approach to predicting metabolic stability that is tailored to compounds from the drug development process at Bayer Schering Pharma. For four different in vitro assays, we develop Bayesian classification models to predict the probability of a compound being metabolically stable. The chosen approach implicitly takes the "domain of applicability" into account. The developed models were validated on recent project data at Bayer Schering Pharma, showing that the predictions are highly accurate and the domain of applicability is estimated correctly. Furthermore, we evaluate the modeling method on a set of publicly available data. 相似文献
90.
Heinze K Beckmann M Hempel K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(31):9468-9480
This overview highlights recent progress in the field of selective construction of linear, oligonuclear transition-metal complexes by using solid-phase synthesis procedures. Two general protocols have been identified: formation of coordinative bonds between metal centres and bridging ligands and formation of covalent bonds between preformed kinetically inert transition-metal-containing building blocks in the chain growth step. Currently available suitable building blocks for the second approach are based on ferrocene units, bis(terpyridine)-ruthenium(II) moieties or metal porphyrins. 相似文献