全文获取类型
收费全文 | 2177篇 |
免费 | 34篇 |
国内免费 | 9篇 |
专业分类
化学 | 1195篇 |
晶体学 | 4篇 |
力学 | 70篇 |
数学 | 272篇 |
物理学 | 679篇 |
出版年
2021年 | 12篇 |
2019年 | 16篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 31篇 |
2015年 | 22篇 |
2014年 | 34篇 |
2013年 | 87篇 |
2012年 | 84篇 |
2011年 | 108篇 |
2010年 | 70篇 |
2009年 | 48篇 |
2008年 | 131篇 |
2007年 | 127篇 |
2006年 | 99篇 |
2005年 | 94篇 |
2004年 | 90篇 |
2003年 | 63篇 |
2002年 | 78篇 |
2001年 | 52篇 |
2000年 | 56篇 |
1999年 | 23篇 |
1998年 | 24篇 |
1997年 | 24篇 |
1996年 | 51篇 |
1995年 | 63篇 |
1994年 | 42篇 |
1993年 | 50篇 |
1992年 | 41篇 |
1991年 | 27篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 21篇 |
1981年 | 32篇 |
1980年 | 22篇 |
1979年 | 23篇 |
1978年 | 25篇 |
1977年 | 23篇 |
1976年 | 29篇 |
1975年 | 25篇 |
1974年 | 17篇 |
1973年 | 21篇 |
1971年 | 14篇 |
1970年 | 12篇 |
排序方式: 共有2220条查询结果,搜索用时 15 毫秒
11.
J. Telser H. -I. Lee E. T. Smith H. Huang P. Brereton M. W. W. Adams R. C. Conover M. K. Johnson B. M. Hoffman 《Applied magnetic resonance》1998,14(2-3):305-321
The hyperthermophilic archaeonPyrococcus furiosus contains a four-Fe ferredoxin (Pf- Fd) that differs from most other 4Fe-Fd’s in that its [Fe4S4] cluster is anchored to protein by only three cysteinyl residues.Pf- Fd also is of interest because in its reduced form, [Fe4S4]+, the cluster exhibits bothS = 1/2 andS = 3/2 spin states. Addition of excess cyanide ion converts the cluster exclusively to anS = 1/2 state (g1 = 2.09, g2 = 1.95, g3 = 1.92), however dialysis restores the EPR signal of native reduced protein indicating that the cluster is not irreversibly altered by cyanide. Both the native protein and protein in the presence of excess cyanide ion (Pf- Fd 4Fe-CN) were investigated here using the techniques of electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. In particular,Pf- Fd 4Fe-CN was investigated using13CN? and C15N? ligands.13C and15N ENDOR indicated that a single cyanide ion bound directly, with the cluster showing an unusually small contact interaction (aiso(13C)~ ?3 MHz, aiso(15N) ~ 0). This is in contrast to cyanide bound to monomeric low-spin Fe(III)-containing proteins such as transferrin and myoglobin, for which the13C hyperfine coupling has a large isotropic component (aiso(13C) ≈ ?30 MHz). This small contact interaction is not due to low spin density of Fe, as57Fe ENDOR of the singly and triply labeledPf- Fd 4FeCN isotopologs, [57FeFe3S4]+ and [Fe57Fe3S4]+, show hyperfine coupling characteristic for [Fe4S4]+ clusters, particularly for the Fe to which cyanide binds. Thus, the low spin density on13C is not due to low spin density on the Fe ion to which it binds. Further theoretical work is needed to explain the contrast between the strong electronic effect of cyanide ion binding with the low spin density on the ligand. 相似文献
12.
13.
M. J. Adams 《Optics & Laser Technology》1972,4(6):273-280
A new family of semiconductor injection lasers with high efficiencies and low threshold currents has recently shown promise for use in a wide range of applications. The heterostructure lasers are described here and the reasons for their improved performance are discussed. 相似文献
14.
For all oddv 3 the complete graph onvK
v
vertices can be decomposed intov – 2 edge disjoint cycles whose lengths are 3, 3, 4, 5,...,v – 1. Also, for all oddv 7,K
v
can be decomposed intov – 3 edge disjoint cycles whose lengths are 3, 4,...,v – 4,v – 2,v – 1,v.
Research supported by Australian Research Council grant A49130102 相似文献
15.
Adams MR Aïd S Anthony PL Averill DA Baker MD Baller BR Banerjee A Bhatti AA Bratzler U Braun HM Breidung H Busza W Carroll TJ Clark HL Conrad JM Davisson R Derado I Dhawan SK Dietrich FS Dougherty W Dreyer T Eckardt V Ecker U Erdmann M Faller F Fang GY Figiel J Finlay RW Gebauer HJ Geesaman DF Griffioen KA Guo RS Haas J Halliwell C Hantke D Hicks KH Hughes VW Jackson HE Jancso G Jansen DM Jin Z Kaufman S Kennedy RD Kinney ER Kirk T Kobrak HG Kotwal AV Kunori S Lancaster S Lord JJ Lubatti HJ 《Physical review letters》1995,74(9):1525-1529
16.
Simon A. Butler Gillian W. Harris David S. Moss Beatrice A. Gorinsky Margaret J. Adams Sheila Gover 《Journal of chemical crystallography》1994,24(1):1-3
We report the estimation of random errors in the refinement of the rigid body displacements of the -helices of the enzyme 6-phosphogluconate dehydrogenase. Least-squares refinement of the TLS parameters of the helices has been carried out using X-ray reflection data of 2.1 Å resolution, resulting in anR-factor of 19.5%. Standard deviations were estimated from the normal matrix. The results show that the translational mean-square displacements of nearly all the helices are significant at this resolution. However the libration parameters are only significant when the helices have at least four turns. Screw-rotation tensor values cannot be determined at this resolution. 相似文献
17.
18.
In a previous paper we studied the Young's and shear modulus of a high-angle twist grain boundary (5) in Cu, using the EAM, and related it to the uniaxial strain derivatives of single crystals. In this paper, we discuss elastic properties of ten additional twist grain boundaries, from 8.8–43.6°. The monolayer Young's modulus at each boundary was calculated and found to be 20–50% higher than the bulk value for all eleven boundaries for both csl and type1 structures. The monolayer shear modulus at each boundary was calculated and found to be 93–98% lower than the bulk value for six grain boundaries with csl structure and found to decrease with increasing twist angle. The critical shear stress was also calculated for eleven boundaries with csl structure and found to roughly decrease with increasing twist angle. 相似文献
19.
Recent measurements of the high-energy charged particle environment with the Radiation Environment Monitor (REM) aboard the Russian Mir space station are presented. Ionizing dose rates in a silicon detector have been measured with two shieldings. The dose is mainly accumulated in two distinct areas, the South Atlantic Anomaly (SAA) and the region of closest approach to the magnetic poles. Whereas the radiation in the South Atlantic Anomaly varied little during 1995, large changes of the daily absorbed doses in the polar regions are observed. A comparison of REM doses with the NASA AP-8 and AE-8 radiation models revealed major differences. AP-8 tends to underestimate the average REM doses, whereas AE-8 overestimates REM doses, and rather describes the worst case. 相似文献
20.
Abachi S Abbott B Abolins M Acharya BS Adam I Adams DL Adams M Ahn S Aihara H Alitti J Álvarez G Alves GA Amidi E Amos N Anderson EW Aronson SH Astur R Avery RE Baarmand MM Baden A Balamurali V Balderston J Baldin B Banerjee S Bantly J Bartlett JF Bazizi K Bendich J Beri SB Bertram I Bezzubov VA Bhat PC Bhatnagar V Bhattacharjee M Bischoff A Biswas N Blazey G Blessing S Bloom P Boehnlein A Bojko NI Borcherding F Borders J Boswell C Brandt A Brock R Bross A Buchholz D Burtovoi VS Butler JM 《Physical review letters》1996,77(4):595-600