全文获取类型
收费全文 | 1042篇 |
免费 | 27篇 |
国内免费 | 2篇 |
专业分类
化学 | 536篇 |
晶体学 | 3篇 |
力学 | 16篇 |
数学 | 39篇 |
物理学 | 299篇 |
无线电 | 178篇 |
出版年
2021年 | 7篇 |
2018年 | 8篇 |
2016年 | 18篇 |
2015年 | 14篇 |
2014年 | 15篇 |
2013年 | 27篇 |
2012年 | 41篇 |
2011年 | 64篇 |
2010年 | 31篇 |
2009年 | 29篇 |
2008年 | 45篇 |
2007年 | 49篇 |
2006年 | 57篇 |
2005年 | 56篇 |
2004年 | 48篇 |
2003年 | 38篇 |
2002年 | 30篇 |
2001年 | 33篇 |
2000年 | 28篇 |
1999年 | 20篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 16篇 |
1994年 | 15篇 |
1993年 | 26篇 |
1992年 | 22篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 19篇 |
1981年 | 9篇 |
1980年 | 19篇 |
1979年 | 15篇 |
1978年 | 21篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1973年 | 15篇 |
1972年 | 14篇 |
1971年 | 6篇 |
1970年 | 6篇 |
1968年 | 6篇 |
排序方式: 共有1071条查询结果,搜索用时 15 毫秒
71.
A. Berndtsson R. Nyholm R. Nilsson J. Hedman C. Nordling 《Journal of Electron Spectroscopy and Related Phenomena》1978,13(2):131-139
The applicability of the F Kα X-ray line (hv = 676 eV) from potassium fluoride for the excitation of electron spectra is demonstrated. Relative photoionization cross-sections in Au and gaseous Hg have been measured. The F Kα radiation from KF, RbF and CsF has been studied. The Ba Mζ line (hv = 602 eV) is found to be too broad for use in ESCA, even when emitted from metallic barium. 相似文献
72.
H.C. Christensen G. Nilsson K.-Å. Thuomas T. Reitberger 《Chemical physics letters》1973,22(3):533-536
A 5 Me V proton accelerator has been used for pulse radiolysis of organic gases. The transient spectra obtained from the alkanes methane, ethane, propane, n-butane and neopentane have tentatively been assigned to alkyl radicals. Some methodological aspects of this new technique are discussed. 相似文献
73.
Continuous separation of lipid particles from erythrocytes by means of laminar flow and acoustic standing wave forces 总被引:1,自引:0,他引:1
Improved continuous acoustic particle separation (separation efficiency close to 100%) and separation of erythrocytes (red blood cells) from lipid microemboli in whole blood is reported. 相似文献
74.
Niedermaier O Scheit H Bildstein V Boie H Fitting J von Hahn R Köck F Lauer M Pal UK Podlech H Repnow R Schwalm D Alvarez C Ames F Bollen G Emhofer S Habs D Kester O Lutter R Rudolph K Pasini M Thirolf PG Wolf BH Eberth J Gersch G Hess H Reiter P Thelen O Warr N Weisshaar D Aksouh F Van den Bergh P Van Duppen P Huyse M Ivanov O Mayet P Van de Walle J Aystö J Butler PA Cederkäll J Delahaye P Fynbo HO Fraile LM Forstner O Franchoo S Köster U Nilsson T Oinonen M Sieber T Wenander F Pantea M 《Physical review letters》2005,94(17):172501
We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient gamma spectrometer MINIBALL. Using 30Mg ions accelerated to an energy of 2.25 MeV/u together with a thin (nat)Ni target, Coulomb excitation of the first excited 2+ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation gamma-ray yields the B(E2;0(+)gs-->2(+)1) value of 30Mg was determined to be 241(31)e2 fm4. Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope 30Mg resides outside the "island of inversion." 相似文献
75.
Single-mode plane-polarized ytterbium-doped large-core fiber laser with 633-W continuous-wave output power 总被引:3,自引:0,他引:3
Jeong Y Nilsson J Sahu JK Soh DB Dupriez P Codemard CA Baek S Payne DN Horley R Alvarez-Chavez JA Turner PW 《Optics letters》2005,30(9):955-957
We demonstrate a cladding-pumped single-mode plane-polarized ytterbium-doped fiber laser generating 633 W of continuous-wave output power at 1.1 microm with 67% slope efficiency and a polarization extinction ratio better than 16 dB. The laser is end pumped through both fiber ends and shows no evidence of roll-over, even at the highest output power, which is limited only by the available pump power. 相似文献
76.
Single-frequency, single-mode, plane-polarized ytterbium-doped fiber master oscillator power amplifier source with 264 W of output power 总被引:10,自引:0,他引:10
Jeong Y Nilsson J Sahu JK Soh DB Alegria C Dupriez P Codemard CA Payne DN Horley R Hickey LM Wanzcyk L Chryssou CE Alvarez-Chavez JA Turner PW 《Optics letters》2005,30(5):459-461
We present a single-frequency, single-mode, plane-polarized ytterbium-doped all-fiber master oscillator power amplifier source at 1060 nm generating 264 W of continuous-wave output power. The final-stage amplifier operated with a high gain of 19 dB and a high conversion efficiency of 68%. There was no evidence of rollover from stimulated Brillouin scattering even at the highest output power, and the maximum output was limited only by the available pump power. 相似文献
77.
Nikitin A Ogasawara H Mann D Denecke R Zhang Z Dai H Cho K Nilsson A 《Physical review letters》2005,95(22):225507
Towards the development of a useful mechanism for hydrogen storage, we have studied the hydrogenation of single-walled carbon nanotubes with atomic hydrogen using core-level photoelectron spectroscopy and x-ray absorption spectroscopy. We find that atomic hydrogen creates C-H bonds with the carbon atoms in the nanotube walls, and such C-H bonds can be completely broken by heating to 600 degrees C. We demonstrate approximately 65 +/- 15 at % hydrogenation of carbon atoms in the single-walled carbon nanotubes, which is equivalent to 5.1 +/- 1.2 wt % hydrogen capacity. We also show that the hydrogenation is a reversible process. 相似文献
78.
Andappan MM Nilsson P von Schenck H Larhed M 《The Journal of organic chemistry》2004,69(16):5212-5218
Arylations of electron-rich heteroatom-substituted olefins were performed with arylboronic acids. This appears to constitute the first example of palladium(II)-catalyzed internal Heck arylations. The novel protocol exploits oxygen gas for environmentally benign reoxidation and a stable 1,10-phenanthroline bidentate ligand to promote the palladium(II) regeneration and to control the regioselectivity. Internal arylation is strongly favored with electron-rich arylboronic acids. DFT calculations support a charge-driven selectivity rationale, where phenyls substituted with electron-donating groups prefer the electron-poor alpha-carbon of the olefin. Experiments, verified by calculations, confirm the cationic nature of the catalytic route. This Heck methodology provides a facile and mild access to functionalized enamides. Controlled microwave heating and increased oxygen pressure were used to further reduce the reaction time to 1 h. 相似文献
79.
Herein we report a rapid, palladium-catalyzed terminal diarylation of the chelating olefin N,N-dimethyl(2-ethenyloxy)ethanamine under noninert conditions utilizing controlled microwave heating as a convenient energy source. Among the aryl bromides examined, both electron-rich and electron-poor substrates were demonstrated to furnish useful yields after only 10-120 min of directed microwave heating at 160-200 degrees C. The good terminal regioselectivity suggests that the precatalyst (Herrmann's palladacycle) serves as a source of weakly coordinated palladium(0) in the investigated high-temperature Heck process. 相似文献
80.
Orrling K Nilsson P Gullberg M Larhed M 《Chemical communications (Cambridge, England)》2004,(7):790-791
This communication describes the development of a controlled microwave methodology for rapid milliliter-scale PCR. 相似文献