全文获取类型
收费全文 | 8866篇 |
免费 | 295篇 |
国内免费 | 36篇 |
专业分类
化学 | 5524篇 |
晶体学 | 43篇 |
力学 | 216篇 |
数学 | 1532篇 |
物理学 | 1882篇 |
出版年
2023年 | 55篇 |
2022年 | 57篇 |
2021年 | 82篇 |
2020年 | 151篇 |
2019年 | 128篇 |
2018年 | 90篇 |
2017年 | 95篇 |
2016年 | 221篇 |
2015年 | 209篇 |
2014年 | 254篇 |
2013年 | 407篇 |
2012年 | 470篇 |
2011年 | 584篇 |
2010年 | 294篇 |
2009年 | 294篇 |
2008年 | 513篇 |
2007年 | 524篇 |
2006年 | 490篇 |
2005年 | 443篇 |
2004年 | 402篇 |
2003年 | 277篇 |
2002年 | 279篇 |
2001年 | 185篇 |
2000年 | 152篇 |
1999年 | 106篇 |
1998年 | 94篇 |
1997年 | 108篇 |
1996年 | 81篇 |
1995年 | 103篇 |
1994年 | 81篇 |
1993年 | 75篇 |
1992年 | 90篇 |
1991年 | 77篇 |
1989年 | 53篇 |
1988年 | 64篇 |
1987年 | 60篇 |
1986年 | 62篇 |
1985年 | 85篇 |
1984年 | 91篇 |
1983年 | 84篇 |
1982年 | 96篇 |
1981年 | 87篇 |
1980年 | 93篇 |
1979年 | 79篇 |
1978年 | 84篇 |
1977年 | 91篇 |
1976年 | 58篇 |
1975年 | 66篇 |
1974年 | 70篇 |
1973年 | 81篇 |
排序方式: 共有9197条查询结果,搜索用时 171 毫秒
31.
Örn Helgason Haraldur P. Gunnlaugsson Siguröur Steinthorsson Steen Mørup 《Hyperfine Interactions》1992,70(1-4):981-984
Mössbauer spectroscopy of basalt lava samples, exhibiting reversible thermal magnetization (JS-T) curves with Curie temperatures of about 580°C, has revealed considerable amounts of maghemite (γ-Fe2O3) in many samples. In view of the expected instability, of maghemite at temperatures above 350°C, this reversibility is rather surprising. Here we report Mössbauer studies on heated lava samples, showing high content of maghemite. The samples were kept at 600°C in oxidizing, reducing, and inactive atmospheres, respectively, for different lengths of time, and then analyzed with Mössbauer spectroscopy at room temperature. The Mössbauer spectra showed that maghemite is stable in the oxidizing atmosphere for at least several hours. In the inactive atmosphere a considerable amount of maghemite still exists after two hours heating. In the reducing atmosphere maghemite had transformed to magnetite after only 30 minutes. 相似文献
32.
Lars Eirik Danielsen 《Journal of Combinatorial Theory, Series A》2006,113(7):1351-1367
We consider additive codes over GF(4) that are self-dual with respect to the Hermitian trace inner product. Such codes have a well-known interpretation as quantum codes and correspond to isotropic systems. It has also been shown that these codes can be represented as graphs, and that two codes are equivalent if and only if the corresponding graphs are equivalent with respect to local complementation and graph isomorphism. We use these facts to classify all codes of length up to 12, where previously only all codes of length up to 9 were known. We also classify all extremal Type II codes of length 14. Finally, we find that the smallest Type I and Type II codes with trivial automorphism group have length 9 and 12, respectively. 相似文献
33.
34.
Björn Wängler Carmen Beck Esther Schirrmacher Frank Rösch Michael Eisenhut 《Tetrahedron letters》2006,47(33):5985-5988
The synthesis of tris-allyl-DOTA starting from cyclen and its application in the preparation of DOTA-peptide conjugates is reported. Clinically important conjugates such as DOTA-Tyr3-octreotide (DOTA-TOC), DOTA-Tyr3-octreotate (DOTA-TATE) as well as a DOTA-RGD peptide were synthesized in high yields with Fmoc solid phase peptide synthesis. The final, extremely reliable de-allylation was achieved on solid phase by different methods identifying morpholine/Pd(0) as the most suitable one obtaining all DOTA peptide conjugates in high yields. All DOTA-peptides were purified by reversed phase HPLC and structural identity was proved using MALDI-TOF mass spectrometry. 相似文献
35.
An acoustic pulse propagating on a two-mode fiber can act as a beam splitter in a scanning interferometer. When this device
is employed in white-light interferometry, the effects of distributed coupling and dispersive interferometer arms need to
be considered. A theory suitable for treating acousto-optic interaction of partially coherent light in a moving interaction
region was developed. It was found that differential optical dispersion should be negligible and the acoustic pulse length
short. Also the coherence time should be short but long compared to the intermodal group delay difference over a pulse length.
Experiments with long acoustic pulses were performed, and fairly good agreement with theory was obtained. 相似文献
36.
37.
Steen Mørup 《Hyperfine Interactions》1994,90(1):171-185
Interactions between magnetic nanoparticles can lead to superferromagnetic ordering, i.e. ordering of their magnetic moments at low temperatures. The use of a simple mean field theory, describing the temperature dependence of the order parameter is discussed. This model is found to give excellent fits to experimental results. In systems of particles with pure dipole interactions, the degree of ordering depends critically on the geometrical configuration of the particles. The application of superferromagnetic nanostructures for magnetic refrigeration is also discussed. 相似文献
38.
Martin E. V. Pedersen Lars S. Rishøj Henrik Steffensen Sanshui Xiao Niels Asger Mortensen 《Optical and Quantum Electronics》2007,39(10-11):903-911
Slow-light enhanced optical detection in liquid-infiltrated photonic crystals is theoretically studied. Using a scattering-matrix approach and the Wigner–Smith delay time concept, we show that optical absorbance benefits both from slow-light phenomena as well as a high filling factor of the energy residing in the liquid. Utilizing strongly dispersive photonic crystal structures, we numerically demonstrate how liquid-infiltrated photonic crystals facilitate enhanced light–matter interactions, by potentially up to an order of magnitude. The proposed concept provides strong opportunities for improving existing miniaturized absorbance cells for optical detection in lab-on-a-chip systems. 相似文献
39.
A straightforward process for the encapsulation of HbHNL under low methanol conditions has been developed. By adding a sol, prepared by hydrolysis of TMOS/MTMS at pH 2.8 with continuous removal of methanol, to a stirred solution of the enzyme in a buffer at pH 6.5, at least 65% of the activity of the free enzyme could be recovered after the encapsulation. The aquagels were successfully used in the synthesis of (S)-cyanohydrins. 相似文献
40.