全文获取类型
收费全文 | 1459篇 |
免费 | 31篇 |
国内免费 | 4篇 |
专业分类
化学 | 835篇 |
晶体学 | 10篇 |
力学 | 44篇 |
数学 | 191篇 |
物理学 | 414篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 37篇 |
2021年 | 45篇 |
2020年 | 33篇 |
2019年 | 38篇 |
2018年 | 41篇 |
2017年 | 31篇 |
2016年 | 58篇 |
2015年 | 50篇 |
2014年 | 60篇 |
2013年 | 99篇 |
2012年 | 102篇 |
2011年 | 118篇 |
2010年 | 79篇 |
2009年 | 79篇 |
2008年 | 108篇 |
2007年 | 84篇 |
2006年 | 83篇 |
2005年 | 69篇 |
2004年 | 40篇 |
2003年 | 22篇 |
2002年 | 32篇 |
2001年 | 20篇 |
2000年 | 19篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 21篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 10篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1985年 | 5篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1947年 | 2篇 |
1924年 | 1篇 |
1900年 | 1篇 |
1899年 | 1篇 |
1898年 | 1篇 |
1868年 | 1篇 |
1858年 | 1篇 |
排序方式: 共有1494条查询结果,搜索用时 15 毫秒
1.
Magnetization measurements in the (Dy
x
Y1−x
)Fe2 intermetallic compounds show evidence of blocking of domain wall motion. This effect is a function of concentrationx. The direction of magnetization is also dependent on the Dy concentration. We have used the Mossbauer spectroscopy of57Fe to verify the direction of magnetization in the series as a function ofx and temperature. The results show that this change in easy direction occurs at higher temperatures than those where the blocking
is detected through DC magnetization measurements.
supported by RHAE/SCT. 相似文献
2.
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
3.
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(25):5011-5015
4.
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 Baden A Balamurali V Balderston J Baldin B 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 Carvalho W Casey D 《Physical review letters》1996,76(18):3271-3276
5.
We have established a luminol- and a lucigenin-dependent CL methods to investigate the role of the receptors for Fc portion of IgG (FcgammaR) and/or complement receptors (CR) in mediating the oxidative burst in neutrophils from systemic lupus erythematosus (SLE) patients compared with healthy controls. In the luminol-CL system, all the reactive oxygen species (ROS) are responsible for light production, whereas in the lucigenin-CL system, only the first ROS generated, converts the lucigenin into an unstable intermediate molecule, which also emits light. First, neutrophils from healthy controls and SLE patients were stimulated with different IC opsonized or not with complement from normal human serum (NHS) or SLE serum, in presence of 10(-4) M luminol. This method was able to differentiate the role of the FcgammaR, CR and FcgammaR/CR co-operation in mediating the oxidative burst, as well as show that the oxidative burst mediated by these receptors was reduced in neutrophils from SLE patients. Second, neutrophils from healthy controls and SLE patients were stimulated with different IC, opsonized or not with NHS, in presence of 10(-3) M lucigenin. In this case, the lucigenin-CL system was also able to differentiate the role of FcgammaR and FcgammaR/CR co-operation, as well as show differences among healthy controls and two different groups of SLE patients according to their clinical manifestations. In conclusion, we have established two sensitive CL systems to study the role of FcgammaR and/or CR in stimulating the oxidative burst of neutrophils, which can be applied in monitoring the involvement of these receptors in the immunopathogenesis of SLE. 相似文献
6.
Jos Roberto Berretta Wagner de Rossi Maurício David Martins das Neves Ivan Alves de Almeida Nilson Dias Vieira Junior 《Optics and Lasers in Engineering》2007,45(9):960-966
The technique to weld AISI 304 stainless steel to AISI 420 stainless steel with a pulsed Nd:YAG laser has been investigated. The main objective of this study was to determine the influence of the laser beam position, with respect to the joint, on weld characteristics. Specimens were welded with the laser beam incident on the joint and moved 0.1 and 0.2 mm on either side of the joint. The joints were examined in an optical microscope for cracks, pores and to determine the weld geometry. The microstructure of the weld and the heat affected zones were observed in a scanning electron microscope. An energy dispersive spectrometer, coupled to the scanning electron microscope, was used to determine variations in (weight %) the main chemical elements across the fillet weld. Vickers microhardness testing and tensile testing were carried out to determine the mechanical properties of the weld. The results of the various tests and examinations enabled definition of the best position for the incident laser beam with respect to the joint, for welding together the two stainless steels. 相似文献
7.
A. L. Stepanov C. Marques E. Alves R. C. da Silva M. R. Silva R. A. Ganeev A. I. Ryasnyansky T. Usmanov 《Technical Physics》2006,51(11):1474-1481
Single-crystal Al2O3(0001) and Al2O3(1120) substrates are implanted by 160-keV Au+ ions with doses from 1015 to 1017 cm?2. Some of the implanted samples are air-annealed at 800–1200°C. The properties of the synthesized composite layers are studied by Rutherford backscattering and linear optical reflection measurements, and their nonlinear optical characteristics are examined by RZ-scanning using a picosecond Nd: YAG laser operating at a wavelength of 1064 nm. The Rutherford backscattering spectra indicate that the implanted impurity concentrates near the surface of the Al2O3. The formation of gold nanoparticles in the Al2O3 can be judged from the characteristic optical plasmon resonance band in the reflectance spectra of the samples irradiated to a dose higher than 6.0 × 1016 cm?2. The synthesized particles are shown to be responsible for nonlinear optical refraction in the samples. The nonlinear refractive index, n 2, and the real part of the third-order susceptibility, Rex(3), of the composite layers are determined. 相似文献
8.
Claudianor O. Alves Daniel C. de Morais Filho Giovany M. Figueiredo 《Mathematical Methods in the Applied Sciences》2019,42(14):4862-4875
In this work, we prove the existence of positive solution for the following class of problems where λ>0 and is a potential satisfying some conditions. Using the variational method developed by Szulkin for functionals, which are the sum of a C1 functional with a convex lower semicontinuous functional, we prove that for each large enough λ>0, there exists a positive solution for the problem, and that, as λ→+∞, such solutions converge to a positive solution of the limit problem defined on the domain Ω=int(V?1({0})). 相似文献
9.
Maria Esmeralda C. de Sousa Valria Wanderley-Teixeira lvaro A.C. Teixeira Herbert A.A. de Siqueira Fbio A.B. Santos Luiz C. Alves 《Micron (Oxford, England : 1993)》2009,40(7):743-749
The insect midgut has ultimately been the focus of researches tempting to control insect pests because alterations in the insect gut may affect not only its development, but also physiological events such as nutrient absorption and transformation. The objective of the present work was to describe morphologically, histochemically, and ultrastructurally the larva midgut of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae), a cotton key pest in Brazil. Light and electronic transmission microscopy was used to obtain images from midgut sections of late fourth-instar larvae of A. argillacea. In general, the morphology, histochemistry, and ultrastructure characteristics of A. argillacea midgut follow that described in the literature for other lepidopteran species. However, the results showed a mitochondrial polymorphism and branched microvilli, which suggest an ultrastrucutural and physiological modification possibly associated with a high absorption and secretion activity by the columnar cells of this species. This intense activity may favor a faster response related to the action of ingested microbial agents and/or toxins, and can explain the high susceptibility of A. argillacea to the agents of control such as the toxin of Bacillus thuringiensis. 相似文献
10.
Liane K. Soares Renata G. LaraRaquel G. Jacob Eder J. LenardãoDiego Alves Gelson Perin 《Tetrahedron letters》2014
We present herein our results on the nucleophilic addition of imidazole to a range of arylselanylalkynes by simple heating in DMF without any additives to give (Z)-1-(1-organyl-(2-arylselanyl)vinyl)-1H-imidazoles. The reactions were performed under mild conditions with a range of arylselanylalkynes in good yields and with high regio- and stereoselectivity to give the respective (Z)-arylselanyl alkene as the only isomer. 相似文献