全文获取类型
收费全文 | 12079篇 |
免费 | 622篇 |
国内免费 | 3篇 |
专业分类
化学 | 8930篇 |
晶体学 | 70篇 |
力学 | 209篇 |
数学 | 1709篇 |
物理学 | 1786篇 |
出版年
2023年 | 116篇 |
2022年 | 61篇 |
2021年 | 113篇 |
2020年 | 193篇 |
2019年 | 204篇 |
2018年 | 124篇 |
2017年 | 124篇 |
2016年 | 425篇 |
2015年 | 440篇 |
2014年 | 469篇 |
2013年 | 888篇 |
2012年 | 990篇 |
2011年 | 882篇 |
2010年 | 534篇 |
2009年 | 405篇 |
2008年 | 832篇 |
2007年 | 791篇 |
2006年 | 792篇 |
2005年 | 720篇 |
2004年 | 574篇 |
2003年 | 494篇 |
2002年 | 431篇 |
2001年 | 177篇 |
2000年 | 174篇 |
1999年 | 99篇 |
1998年 | 76篇 |
1997年 | 78篇 |
1996年 | 112篇 |
1995年 | 73篇 |
1994年 | 61篇 |
1993年 | 83篇 |
1992年 | 66篇 |
1991年 | 49篇 |
1990年 | 49篇 |
1989年 | 40篇 |
1988年 | 39篇 |
1987年 | 40篇 |
1986年 | 62篇 |
1985年 | 86篇 |
1984年 | 67篇 |
1983年 | 38篇 |
1982年 | 56篇 |
1981年 | 58篇 |
1980年 | 65篇 |
1979年 | 48篇 |
1978年 | 52篇 |
1977年 | 41篇 |
1976年 | 49篇 |
1975年 | 28篇 |
1974年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
951.
Aujard I Baltaze JP Baudin JB Cogné E Ferrage F Jullien L Perez E Prévost V Qian LM Ruel O 《Journal of the American Chemical Society》2001,123(34):8177-8188
Pure organic molecules exhibiting a suitable concave rigid shape are expected to give porous glasses in the solid state. Such a feature opens new opportunities to avoid crystallization and to improve molecular solubility in relation to the high internal energy of these solid phases. To quantitatively explore the latter strategy, a series of rigid tetrahedral conjugated molecules nC and the corresponding models nR have been synthesized. Related to the present purpose, several properties have been investigated using UV absorption, steady-state fluorescence emission, differential scanning calorimetry, (1)H NMR translational self-diffusion, magic angle spinning (13)C NMR, and multiple-beam interferometry experiments. The present tetrahedral crosses are up to 8 orders of magnitude more soluble than the corresponding model compounds after normalization to the same molecular length. In addition, they give concentrated monomeric solutions that can be used to cover surfaces with homogeneous films whose thickness goes down to the nanometer range. Such attractive features make cross-like molecular architectures promising for many applications. 相似文献
952.
953.
Fustero S Navarro A Pina B Soler JG Bartolomé A Asensio A Simón A Bravo P Fronza G Volonterio A Zanda M 《Organic letters》2001,3(17):2621-2624
[reaction: see text]. Hydride reduction of C=N bonds stereocontrolled by intramolecular pi-stacking interactions of 1-naphthylsulfinyl and N-aryl groups, nonoxidative Pummerer rearrangement, and ring-closing metathesis are efficiently combined in a highly stereoselective entry to enantiomerically pure cyclic and acyclic fluorinated beta-amino alcohols and alpha-amino acid derivatives, respectively. 相似文献
954.
Fehr C Dieudonné P Primera J Woignier T Sauvajol JL Anglaret E 《The European physical journal. E, Soft matter》2003,12(Z1):S13-S16
Solid polymorphism of 4-alkyl-4'-cyanobiphenyl (nCB) was studied so far as a function of thermal history. In this paper we show that metastable solid phases of 4-octyl-4'-cyanobiphenyl (8CB) are also formed when the mesogens are confined in porous silica matrices and we study their structure by neutron diffraction and by Raman spectroscopy. Three metastable solid states are identified: one crystalline phase K', two frozen-in smectic-like phases K(s) and K'(s). We discuss the relation between the structure of the metastable solid phases and that of the mesomorph phases. 相似文献
955.
Borrell JI 《Molecular diversity》2003,6(2):73-74
Molecular Diversity - 相似文献
956.
We determine all complete intersection surface germs whose Pythagoras number is 2, and find that they are all embedded in 3 and have the property that every positive semidefinite analytic function germ is a sum of squares of analytic function germs. In addition, we discuss completely these properties for mixed surface germs in 3. Finally, we find in higher embedding dimension three different families with these same properties. Partially supported by DGICYT, BFM2002-04797 and HPRN-CT-2001-00271
Mathematical Subject Classification (2000): 11E25, 14P15.An erratum to this article can be found at 相似文献
957.
Labiche M Orr NA Marqués FM Angélique JC Axelsson L Benoit B Bergmann UC Borge MJ Catford WN Chappell SP Clarke NM Costa G Curtis N D'Arrigo A de Góes Brennand E Dorvaux O Fazio G Freer M Fulton BR Giardina G Grévy S Guillemaud-Mueller D Hanappe F Heusch B Jones KL Jonson B Le Brun C Leenhardt S Lewitowicz M Lopez MJ Markenroth K Mueller AC Nilsson T Ninane A Nyman G de Oliveira F Piqueras I Riisager K Saint Laurent MG Sarazin F Singer SM Sorlin O Stuttgé L 《Physical review letters》2001,86(4):600-603
The two-neutron halo nucleus (14)Be has been investigated in a kinematically complete measurement of the fragments ((12)Be and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large nu(2s(1/2))(2) admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation. 相似文献
958.
959.
A low-coherence reflectometer based on a conventional Michelson interferometer and a novel silicon detector chip with a two-dimensional array of pixels that allows parallel heterodyne detection is presented. We demonstrate acquisition of three-dimensional images with more than 100,000 voxels per scan at a sensitivity of -58 dB and a rate of 6 Hz. 相似文献
960.
We present a new beam-shaping technique with an intracavity optically addressed liquid-crystal spatial light modulator. The Nd:YAG resonator is able to deliver beams with various spatial profiles such as flat-topped super-Gaussian and square-shaped beams. 相似文献