全文获取类型
收费全文 | 929篇 |
免费 | 37篇 |
国内免费 | 8篇 |
专业分类
化学 | 427篇 |
晶体学 | 14篇 |
力学 | 55篇 |
数学 | 166篇 |
物理学 | 312篇 |
出版年
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2016年 | 22篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 51篇 |
2012年 | 48篇 |
2011年 | 49篇 |
2010年 | 25篇 |
2009年 | 32篇 |
2008年 | 39篇 |
2007年 | 47篇 |
2006年 | 39篇 |
2005年 | 41篇 |
2004年 | 27篇 |
2003年 | 35篇 |
2002年 | 21篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 23篇 |
1998年 | 12篇 |
1997年 | 24篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 28篇 |
1993年 | 19篇 |
1992年 | 27篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有974条查询结果,搜索用时 15 毫秒
881.
We propose and demonstrate an S-band CW dual-wavelength erbium-doped fiber (EDF) dual-ring laser using a compound-ring filter (CRF) with various coupling losses inside the gain cavity. Employing a ring filter combined within the cavity, the fiber laser can lase a dual wavelength without any filter inside the ring loop. The dual-wavelength output exhibits a good performance having optical side-mode suppression ratios (SMSRs) of 31.6 and 31.8 dB and output powers of ?9.6 and ?9.3 dBm at 1505.58 and 1506.43 nm, respectively, when the coupling loss is 30% inside the cavity. In addition, the output stabilities of the dual-wavelength laser have also been analyzed. 相似文献
882.
Chow S Fletcher MT Lambert LK Gallagher OP Moore CJ Cribb BW Allsopp PG Kitching W 《The Journal of organic chemistry》2005,70(5):1808-1827
The major cuticular hydrocarbons from the cane beetle species Antitrogus parvulus are 4,6,8,10,16-penta- and 4,6,8,10,16,18-hexamethyldocosanes, 1 and 2, respectively. Stereoisomers of 2,4,6,8-tetramethylundecanal of established relative stereochemistry were derived from 2,4,6-trimethylphenol and were then coupled with appropriate methyl-substituted phosphoranes 62 and 25 to furnish alkenes, which on reduction provided diastereomers of 1 and 2, respectively. Capillary gas chromatography, mass spectrometry, and high resolution 13C NMR spectroscopy confirmed 1 as either 84a or 84b and 2 as either 15a or 15b. The novelty of these structures and their relative stereochemistry is briefly related to polyketide assembly. 相似文献
883.
The zwitterion effect in proton exchange membranes as synthesised by polymerisation of bicontinuous microemulsions 总被引:2,自引:0,他引:2
Gan LM Chow PY Liu Z Han M Quek CH 《Chemical communications (Cambridge, England)》2005,(35):4459-4461
The bicontinuous microemulsions consisting of a polymerisable zwitterionic surfactant 3-((11-acryloyloxyundecyl)imidazolyl) propyl sulfonate (AIPS) and other monomers can be cross-polymerised to form good proton conductive membranes. 相似文献
884.
We report a successful experimental realization of a photonic-crystal Y splitter operating at lambda~1.6 mum . Our device has a large splitting angle of 120 degrees and a miniature size of ~3 mumx3 mum . Furthermore, the Y-splitter loss is measured to be 0.5-1 dB at lambda=1640-1680 nm, making the Y splitter promising for integrated photonic-circuit applications. These unique properties are attributed to the new guiding principle made possible by the photonic bandgap. 相似文献
885.
A model is proposed to generate solutions for container selection, for the allocation of cargo to containers, and for cargo orientation within a container. The model is in the form of a mixed integer program with the objective of minimizing the total shipping cost. The practical requirements of loading priority and weight distribution along the main dimension of the container are incorporated into the model. A heuristic solution strategy is proposed and used to control the computation time by pre-setting the search increments. Three case examples are presented. The first and third examples show that the proposed model can produce a better solution than the manual schedulers. The second example is taken from the literature and is compared with the solution generated by the proposed model, demonstrating that the practical considerations incorporated into the model do not necessarily lead to increased shipping costs. 相似文献
886.
887.
An abnormal spin-spin coupling of vinylic-allylic protons generated by a constraint of configuration
In a system where a rigid or frozen conformation constrains an allylic proton to orient nearly perpendicular to the plane of the olefinic bond, the allylic spin coupling may become comparable to, or greater than, the vicinal spin coupling. This anomalous situation is demonstrated in three series of compounds: the adducts of diazoalkanes to 1,2-diazepines, 4-piperidinocycloalk-2-en-1-one oximes and heterobicyclo[3,2,0]hept-3,6-dienes, where the NMR spectra have been well established by decoupling experiments. 相似文献
888.
Experimental evidence is presented that moving Bloch-walls decrease the flow stress of nickel single crystals. Via their strain fields, Block-walls interact with dislocations. 相似文献
889.
J. W. Schneider H. Keller W. Odermatt B. Pümpin I. M. Savić H. Simmler S. A. Dodds T. L. Estle R. C. Duvarney K. Chow R. Kadono R. F. Kiefl Q. Li T. M. Riseman H. Zhou R. L. Lichti C. Schwab 《Hyperfine Interactions》1991,64(1-4):543-549
Datailed muon level-crossing resonance measurements of Mu1 and Mu11 centres in single crystals of CuCl are presented. The hyperfine and nuclear hyperfine parameters of the closest two shells
of nuclei are remarkably similar for the two centres, indicating that both are located at the same tetrahedral interstitial
site with four Cu nearest neighbours and six Cl next-nearest neighbours. About 30% of the total unpaired-electron spin density
is located on the muon, about 60% on the four nearest neighbours and the rest on the six next-nearest neighbours, with nothing
observable for any other shell. 相似文献
890.
T. R. Chow 《Mathematische Annalen》1970,188(4):285-303