全文获取类型
收费全文 | 1142篇 |
免费 | 64篇 |
国内免费 | 3篇 |
专业分类
化学 | 894篇 |
晶体学 | 6篇 |
力学 | 9篇 |
数学 | 81篇 |
物理学 | 219篇 |
出版年
2023年 | 14篇 |
2022年 | 32篇 |
2021年 | 34篇 |
2020年 | 44篇 |
2019年 | 52篇 |
2018年 | 18篇 |
2017年 | 12篇 |
2016年 | 52篇 |
2015年 | 45篇 |
2014年 | 34篇 |
2013年 | 56篇 |
2012年 | 54篇 |
2011年 | 51篇 |
2010年 | 34篇 |
2009年 | 36篇 |
2008年 | 61篇 |
2007年 | 49篇 |
2006年 | 54篇 |
2005年 | 46篇 |
2004年 | 27篇 |
2003年 | 26篇 |
2002年 | 29篇 |
2001年 | 14篇 |
2000年 | 17篇 |
1999年 | 12篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1969年 | 8篇 |
1968年 | 8篇 |
1966年 | 5篇 |
排序方式: 共有1209条查询结果,搜索用时 15 毫秒
91.
[reaction: see text] A new poly(ethylene glycol)-supported porphyrin has been prepared and its ability as a promoter in photooxidation reactions has been studied. The PEG-supported catalyst exhibits high activity, comparable to that of a nonanchored sensitizer, and it is easily removable by filtration from the reaction mixture. The polymer-bound porphyrin has been recycled up to six times with no loss of chemical and stereochemical efficiency. 相似文献
92.
F Ackermann L Walls R van der Meer M Borman 《The Journal of the Operational Research Society》1999,50(3):195-204
Despite undoubtedly being one of the latest fads, Business Process Reengineering (BPR) has provoked much debate about how organisations should be managed if dramatic improvements in performance are to be achieved. This paper takes a multidisciplinary view of BPR and focuses upon a number of the emergent issues. These include the role of strategy making, the promotion of communication and creativity, the role of statistics, and the effective use of performance measurement systems within a learning environment. The paper develops a framework that capitalises on the role of modelling in MS/OR as well as the various disciplines of the authors. As such, the framework draws on recent advances, as well as established thinking, in the areas of strategy development, information systems, quality management and statistical science. More importantly, the framework also provides an iterative approach to BPR enabling organisations to design, implement and monitor progress on an ongoing basis. Emphasis is placed on building effective communications, developing an organisational memory and supporting organisational learning. 相似文献
93.
As part of a continued investigation of the analytical applications of ternary complexes, the systems Ti(IV)/BPR, I), Ti(IV)/BPR/EDTA (II), and Ti(IV)/BPR/NTA (III), where BPR = Bromopyrogallol Red, have been investigated and compared in terms of working concentration range, molar absorptivity, standard deviation, coefficient of variation, calibration sensitivity, limit of detection and of determination. A novel way of summarizing the effects of interferences of a large group of ions (some 47 in all) is presented. The results show that the ternary systems, in particular system II, have a better selectivity than the simple binary system I of titanium with Bromopyrogallol Red. 相似文献
94.
Th. Ackermann 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》1969,81(10):405-405
95.
96.
P. Heitjans B. Bader H. -J. Stöckmann K. Dörr G. Kiese H. Ackermann P. Freiländer W. Müller-Warmuth K. Meise-Gresch 《Hyperfine Interactions》1983,16(1-4):597-600
Nuclear spin-lattice relaxation in Li20·2Si02 glass below 200 K has been studied using the asymmetric Β-decay radiation of polarized8Li (T1/2=0.Bs) nuclei produced by capture of polarized neutrons. Transients of the8Li polarization follow an exp(?√E/T1) law. The dependence of the spin-lattice relaxation rate ⊥¯1 1 on temperature T and magnetic field B can roughly be described by T¯1 1~T/B. The interpretation is based on the assumption that for8Li, contrary to7Li in the same glass, spin-diffusion is absent and that each probe nucleus is coupled by quadrupolar interaction to an individual distribution of nearby centres typical of glasses. The fluctuation of these centres causing relaxation may be induced by either a multi-phonon or a thermally activated motional process. 相似文献
97.
98.
While fluorescence can be clearly observed in resonance-stabilized acyclic anions, its occurrence is insufficient for unambiguous assignment of either ion-pairing type or anion geometry. As in cyclic, aromatic anions, the requirement for contact ion-pairing is less severe in the excited state than in the ground state. The fluorescence lifetimes of acyclic anions are affected more by the associated cation than by the type of ion-pairing. 相似文献
99.
The theory of hopping-impurity-conduction developed byConwell andMott, Pollak etc. is extended by thermodynamic viewpoints. It is shown that the model which is providing simple and independend electron transitions from one donator to another is not adequate except at very low temperatures (<4 °K) and high frequencies (1010 Hz). At lower frequencies coupled transitions must be considered. This transportmechanism is described by a Boltzmann-equation. 相似文献
100.