全文获取类型
收费全文 | 1026篇 |
免费 | 27篇 |
国内免费 | 1篇 |
专业分类
化学 | 671篇 |
晶体学 | 16篇 |
力学 | 24篇 |
数学 | 63篇 |
物理学 | 280篇 |
出版年
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 45篇 |
2012年 | 45篇 |
2011年 | 53篇 |
2010年 | 35篇 |
2009年 | 22篇 |
2008年 | 41篇 |
2007年 | 48篇 |
2006年 | 32篇 |
2005年 | 57篇 |
2004年 | 48篇 |
2003年 | 26篇 |
2002年 | 39篇 |
2001年 | 18篇 |
2000年 | 51篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 18篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 22篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 17篇 |
1975年 | 18篇 |
1974年 | 15篇 |
1973年 | 5篇 |
1923年 | 4篇 |
排序方式: 共有1054条查询结果,搜索用时 0 毫秒
251.
Alley KG Poneti G Aitken JB Hocking RK Moubaraki B Murray KS Abrahams BF Harris HH Sorace L Boskovic C 《Inorganic chemistry》2012,51(7):3944-3946
A dinuclear cobalt complex with cobalt centers bridged by a bis(dioxolene) ligand exhibits a rare two-step valence tautomeric transition. 相似文献
252.
Christian Schröder Inga Köhler Francois L. L. Muller Aleksandr I. Chumakov Ilya Kupenko Rudolf Rüffer Andreas Kappler 《Hyperfine Interactions》2016,237(1):85
Biogeochemistry investigates chemical cycles which influence or are influenced by biological activity. Astrobiology studies the origin, evolution and distribution of life in the universe. The biogeochemical Fe cycle has controlled major nutrient cycles such as the C cycle throughout geological time. Iron sulfide minerals may have provided energy and surfaces for the first pioneer organisms on Earth. Banded iron formations document the evolution of oxygenic photosynthesis. To assess the potential habitability of planets other than Earth one looks for water, an energy source and a C source. On Mars, for example, Fe minerals have provided evidence for the past presence of liquid water on its surface and would provide a viable energy source. Here we present Mössbauer spectroscopy investigations of Fe and C cycle interactions in both ancient and modern environments. Experiments to simulate the diagenesis of banded iron formations indicate that the formation of ferrous minerals depends on the amount of biomass buried with ferric precursors rather than on the atmospheric composition at the time of deposition. Mössbauer spectra further reveal the mutual stabilisation of Fe-organic matter complexes against mineral transformation and decay of organic matter into CO2. This corresponds to observations of a ‘rusty carbon sink’ in modern sediments. The stabilisation of Fe-organic matter complexes may also aid transport of particulate Fe in the water column while having an adverse effect on the bioavailability of Fe. In the modern oxic ocean, Fe is insoluble and particulate Fe represents an important source. Collecting that particulate Fe yields small sample sizes that would pose a challenge for conventional Mössbauer experiments. We demonstrate that the unique properties of the beam used in synchrotron-based Mössbauer applications can be utilized for studying such samples effectively. Reactive Fe species often occur in amorphous or nanoparticulate form in the environment and are therefore difficult to study with standard mineralogical tools. Sequential extraction techniques are commonly used as proxies. We provide an example where Mössbauer spectroscopy can replace sequential extraction techniques where mineralogical information is sought. Where mineral separation is needed, for example in the investigation of Fe or S isotope fractionation, Mössbauer spectroscopy can help to optimize sequential extraction procedures. This can be employed in a large number of investigations of soils and sediments, potentially even for mineral separation to study Fe and S isotope fractionation in samples returned from Mars, which might reveal signatures of biological activity. When looking for the possibility of life outside Earth, Jupiter’s icy moon Europa is one of the most exciting places. It may be just in reach for a Mössbauer spectrometer deployed by a future lander to study the red streak mineral deposits on its surface to look for clues about the composition of the ocean hidden under the moon’s icy surface. 相似文献
253.
R.V. Chopdekar M. Liberati L.F. Kourkoutis B.B. Nelson-Cheeseman A. Doran D.A. Muller 《Journal of magnetism and magnetic materials》2010,322(19):2915-2921
Magnetic order and coupling at the interfaces of highly spin polarized Fe3O4 heterostructures have been determined by surface sensitive and element specific soft X-ray spectroscopy and spectro-microscopy techniques. At ambient temperature, the interface between paramagnetic CoCr2O4 or MnCr2O4 and ferrimagnetic Fe3O4 isostructural bilayers exhibits long range magnetic order of Co, Mn and Cr cations which cannot be explained in terms of the formation of interfacial MnFe2O4 or CoFe2O4. Instead, the ferrimagnetism is induced by the adjacent Fe3O4 layer and is the result of the stabilization of a spinel phase not achievable in bulk form. Magnetism at the interface region is observable up to 500 K, far beyond the chromite bulk Curie temperature of 50-95 K. 相似文献
254.
Alexei?VernitskiEmail author Laila?Tunsi Colette?Ponchel Alexei?Lisitsa 《Semigroup Forum》2018,97(1):75-86
It is known that a knot (link) is rational if and only if its \(\pi \)-orbifold group is dihedral. A semigroup version of this result has been formulated as a conjecture. Working towards proving the conjecture, we describe certain semigroups associated with twist links, clarify how these semigroups are related to dihedral groups and find defining relations of these semigroups. 相似文献
255.
Mari Pretorius D. Bradley G. Williams Andreas Roodt Alfred Muller 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(6):o384-o386
The title compounds, Ph2PCH2N(H)Ph or C25H22NP and Ph2PCH2N(CH3)Ph or C26H24NP, respectively, are isomorphous, with calculated theoretical Tolman angles of 174 and 182°. 相似文献
256.
In this work we study the coupling of a nonlinear renewal equation to an ordinary differential equation. We start with existence and uniqueness issues for the coupled equations and, in particular cases, we study the long-time behaviour. The novelty here is the nonlinearity in the renewal equation. This model arises in the context of atherosclerosis. The renewal part accounts for the inflammatory process: leucocyte recruitment in the arterial wall, differentiation when internalizing low-density lipoprotein (LDL) and death. The ordinary differential equation describes the LDL dynamics in the arterial wall, leucocyte absorption and release in the blood.
相似文献257.
258.
The synthesis of optically active cyclopalladated derivatives containing primary amines and their application as resolving agents of Lewis bases is reviewed. Some other applications such as the determination of the absolute configuration of coordinated chiral phosphines and the synthesis of chiral liquid crystals are also presented. 相似文献
259.
Jansat S Gómez M Philippot K Muller G Guiu E Claver C Castillón S Chaudret B 《Journal of the American Chemical Society》2004,126(6):1592-1593
Palladium nanoparticles (4 nm, fcc) were prepared through decomposition of [Pd2(dba)3] by H2 in the presence of a chiral xylofuranoside diphosphite. These particles catalyze the allylic alkylation of rac-3-acetoxy-1,3-diphenyl-1-propene with dimethyl malonate leading to an almost total conversion of the (R) enantiomer and almost no reaction with the (S). This gives rise to 97% ee for the alkylation product and a kinetic resolution of the substrate recovered with ca. 90% ee. This behavior was compared to that of a molecular catalyst at various dilutions, and the differences between the two systems are discussed. This is the first colloidal system shown to display such a high enantioselectivity besides the well-known Pt/cinchonidine system. 相似文献
260.
Summary A simple and rapid method for the determination of organophosphorus insecticides in serum of poisoned patients is described.
The compounds are extracted with benzene and the extraction residue is gas chromatographed on a glass capillary column with
alkali flame ionisation detection. Concentrations from 2 ng cm−3 can be determined. As an example, results of the analysis of serum samples of three patients, poisoned with parathion and
methylparation, are given. 相似文献