全文获取类型
收费全文 | 1792篇 |
免费 | 41篇 |
国内免费 | 1篇 |
专业分类
化学 | 1409篇 |
晶体学 | 10篇 |
力学 | 11篇 |
数学 | 99篇 |
物理学 | 305篇 |
出版年
2022年 | 12篇 |
2021年 | 13篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2018年 | 20篇 |
2017年 | 19篇 |
2016年 | 23篇 |
2015年 | 24篇 |
2014年 | 43篇 |
2013年 | 81篇 |
2012年 | 77篇 |
2011年 | 125篇 |
2010年 | 55篇 |
2009年 | 64篇 |
2008年 | 99篇 |
2007年 | 105篇 |
2006年 | 95篇 |
2005年 | 90篇 |
2004年 | 88篇 |
2003年 | 87篇 |
2002年 | 77篇 |
2001年 | 36篇 |
2000年 | 27篇 |
1999年 | 23篇 |
1998年 | 11篇 |
1997年 | 32篇 |
1996年 | 18篇 |
1995年 | 14篇 |
1994年 | 22篇 |
1993年 | 32篇 |
1992年 | 27篇 |
1991年 | 16篇 |
1990年 | 25篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 33篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 28篇 |
1979年 | 26篇 |
1978年 | 18篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1974年 | 11篇 |
1972年 | 9篇 |
1966年 | 8篇 |
排序方式: 共有1834条查询结果,搜索用时 953 毫秒
991.
992.
Hiromichi Kataura Yoshinori Kumazawa Noriaki Kojima Yutaka Maniwa Ikurou Umezu Shinichi Masubuchi 《Molecular Crystals and Liquid Crystals》2013,570(1):757-762
Abstract We have measured Raman spectra of bromine doped single-walled carbon nanotubes (SWNTs) using various laser lines to clarify the electronic states of the doped SWNT. In the case of evacuated sample after full doping, two breathing mode peaks were observed simultaneously by visible laser excitations. We assigned the higher frequency peak to the doped SWNT bundles, and the other peak to the undoped portions in the sample. Intensity ratio between them decreased with decreasing excitation energy, and in the infrared region, the breathing mode band of the doped bundle was not observed. These results can be explained by a simple rigid band model. 相似文献
993.
Aqueous phenolphthalein solution under sonication was investigated for use as a chemical dosimeter. The fading time of aqueous phenolphthalein solution under sonication depended on the concentration of phenolphthalein and the pH values of solutions. The fading time was correlated to the ultrasonic intensity in a reaction vessel that is estimated on the basis of decomposition of porphyrin. The relation between the fading time and the ultrasonic intensity for different frequencies is expressed by a single curve. From these results, it is indicated that aqueous solutions of phenolphthalein is useful for simple quantification of ultrasonic intensity for practical use, and one can regard it as one of the ultrasonic intensity indicators. 相似文献
994.
Kiyoshi Nomura Souichirou Taya Atsushi Okazawa Norimichi Kojima 《Hyperfine Interactions》2014,226(1-3):161-169
Mg oxides doped with 1 % 57Fe were prepared by a sol-gel method, and annealed at various temperatures. Nano-size Mg oxides were characterized by Mössbauer spectrometry, magnetization and XRD measurements. The crystalline size of MgO increases with increase of annealing temperature. Samples annealed at 600 °C and 800 °C gave only doublet peaks of paramagnetic Fe3+ in Mössbauer spectra although Fe3+ doping into MgO induced a distorted structure and showed weak ferromagnetism. It is considered that the magnetic property is due to defect induced magnetism by doping Fe3+ into MgO. For a sample heated at 1000 °C, it is found from low temperature Mössbauer spectra that Fe3+ species are located at the core and shell of fine MgFe2O4 grains and diluted in MgO matrix. 相似文献
995.
A. Okazawa J. Yoshida N. Kida I. Kashima W. Murata M. Enomoto N. Kojima 《Hyperfine Interactions》2014,226(1-3):351-357
We have investigated magnetic properties in a series of photoresponsive dithiooxalato (dto)-bridged iron mixed-valence complexes, (SP-R)[FeIIFeIII(dto)3] (SP-R = R-substituted pyridospiropyran cation; R = Me, Et, and Pr; abbreviated as 1 Me, 1 Et, and 1 Pr, respectively). As for our previous reports, 1 Me and 1 Et show two-step succeeding ferromagnetic transitions at T C?=?25 & 8 K and 22 & 5 K, respectively. However, 1 Et has no hysteresis in the magnetic susceptibility, while 1 Me undergoes the charge transfer phase transition with thermal hysteresis around 75 K. To elucidate the two-step transitions of them, we measured 57Fe Mössbauer spectra of 1 Et. The spectra of FeII (S?=?2) and FeIII (S?=?1/2) in the HTP were observed in the magnetically ordered state as well as the paramagnetic state, and revealed that only HTP exists in a temperature range up to 5 K. The result is consistent with that of 1 Pr, where one ferromagnetic phase transition occurs at T C?=?10 K. 57Fe Mössbauer spectroscopy is useful to clarify the origin of the succeeding magnetic transition for these systems. 相似文献
996.
Associated with some properties of weighted composition operators on the spaces of bounded harmonic and analytic functions on the open unit disk $\mathbb{D}$ , we obtain conditions in terms of behavior of weight functions and analytic self-maps on the interior $\mathbb{D}$ and on the boundary $\partial \mathbb{D}$ respectively. We give direct proofs of the equivalence of these interior and boundary conditions. Furthermore we give another proof of the estimate for the essential norm of the difference of weighted composition operators. 相似文献
997.
998.
Atsushi OkazawaKei Fujiwara Ryo WatanabeNorimichi Kojima Shunsuke YoshiiHiroyuki Nojiri Takayuki Ishida 《Polyhedron》2011,30(18):3121-3126
Heterometallic polymeric coordination compounds [{Ln(hfac)2(CH3OH)}2{Cu(dmg)(Hdmg)}2]n (abbreviated as [Ln2Cu2]n) involving light lanthanoid ions, Pr, Nd, Sm, and Eu, were synthesized, where H2dmg and Hhfac stand for dimethylglyoxime and 1,1,1,5,5,5-hexafluoropentane-2,4-dione, respectively. The X-ray crystallographic analysis shows that their structures are isomorphous to those of the known heavy lanthanoid analogs. The exchange couplings were evaluated by high-frequency electron paramagnetic resonance and pulsed-field magnetization studies, giving ferromagnetic exchange parameters: JPr-Cu/kB = 0.039(1) K, JNd-Cu/kB = 0.38(1) K, JSm-Cu/kB = 0.95(2) K, and no interaction between Eu and Cu ions. A significant trend is found in the order of the periodic table. The ferro- and antiferromagnetic 4f-3d couplings were characterized for the light and heavy lanthanoid derivatives, respectively. The magnitude of JLn-Cu decreases with a decrease of the 4f-spin portion, i.e., the number of unpaired electrons, whether the coupling is ferro- or antiferromagnetic. 相似文献
999.
Chonticha SuttibutYoshihito Kohari Ko IgarashiHiroto Nakano Masafumi HiramaChigusa Seki Haruo MatsuyamaNobuhiro Takano Yuko OkuyamaKenichi Osone Mitsuhiro TakeshitaEunsang Kwon 《Tetrahedron letters》2011,52(37):4745-4748
An easily prepared chiral amino alcohol catalyst was found to provide an efficient synthetic intermediate of oseltamivir with excellent chemical yield and enantioselectivity (up to 98% yield and up to 98% ee) in enantioselective Diels-Alder reactions of 1,2-dihydropylidines with acroleins. 相似文献
1000.
Hajime Seito Tatsuya Ichikawa Hiroaki Hanaya Yoshishige Sato Hirohisa Kaneko Yasuyuki Haruyama Hiroshi Watanabe Takuji Kojima 《Radiation Physics and Chemistry》2009,78(11):961-965
Characteristics of clear PMMA dosimeter (Radix W) were studied for electron irradiation and compared with the response for gamma irradiation. The dose–response curves were nearly linear up to 30 kGy and become sublinear at higher doses. The radiation-induced absorbance was reduced with 6% within 4 h after irradiation. Dose comparisons were performed for 2, 3, 4 and 5 MeV electron irradiation using cellulose triacetate dosimeter (CTA) (FTR-125) and Radix W dosimeters which were independently calibrated for 2 MeV electrons and 60Co gamma-rays using calorimeter and ionizing chamber, respectively. The doses estimated by CTA and Radix W were different by about 20%. The magnitude of this difference was, however, independent of electron energy. 相似文献