全文获取类型
收费全文 | 706篇 |
免费 | 20篇 |
专业分类
化学 | 561篇 |
晶体学 | 6篇 |
力学 | 1篇 |
综合类 | 2篇 |
数学 | 62篇 |
物理学 | 94篇 |
出版年
2023年 | 3篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 12篇 |
2013年 | 34篇 |
2012年 | 24篇 |
2011年 | 40篇 |
2010年 | 18篇 |
2009年 | 19篇 |
2008年 | 39篇 |
2007年 | 37篇 |
2006年 | 35篇 |
2005年 | 48篇 |
2004年 | 38篇 |
2003年 | 33篇 |
2002年 | 20篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 16篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1978年 | 15篇 |
1977年 | 7篇 |
1976年 | 19篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 12篇 |
1971年 | 2篇 |
排序方式: 共有726条查询结果,搜索用时 31 毫秒
611.
Chie Hosokawa Suguru N. Kudoh Mariko Suzuki Ai Kiyohara Yoichiroh Hosokawa Kazunori Okano Hiroshi Masuhara Takahisa Taguchi 《Applied Physics A: Materials Science & Processing》2010,101(2):423-428
The surface of a single-crystal germanium wafer was transformed to crystals of germanium fluorides and oxides upon exposure
to a vapor of HF and HNO3 chemical mixture. Structure analysis indicates that the transformation results in a germanate polycrystalline layer consisting
of germanium oxide and ammonium fluogermanate with preferential crystal growth orientation in 〈101〉 direction. Local vibrational
mode analysis confirms the presence of N–H and Ge–F vibrational modes in addition to Ge–O stretching modes. Energy dispersive
studies reveal the presence of hexagonal α-phase GeO2 crystal clusters and ammonium fluogermanates around these clusters in addition to a surface oxide layer. Electronic band
structure as probed by ellipsometry has been associated with the germanium oxide crystals and disorder-induced band tailing
effects at the interface of the germanate layer and the bulk Ge wafer. The acid vapor exposure causes Ge surface to emit yellow
photoluminescence at room temperature. 相似文献
612.
613.
614.
615.
616.
Eiichi Kobayashi Nahoto Hayashi Sadahito Aoshima Junji Furukawa 《Journal of polymer science. Part A, Polymer chemistry》1998,36(11):1707-1716
It was found that poly(butadiene), poly(isoprene), and poly(2,3-dimethylbutadiene) with high cis-1,4 content were obtained with Nd(OCOR)3–(i-Bu)3Al–Et2AlCl catalysts (R = CF3, CCl3, CHCl2, CH2Cl, CH3) in hexane at 50°C [cis-1,4 content: poly(BD), > 98%; poly(IP), ≥ 96%; poly(DMBD), ≥ 94%]. Copolymerization of IP and styrene (St) was carried out at various monomer feed ratios to evaluate the monomer reactivity ratio and cis-1,4 content of the diene unit and then to elucidate the cis-1,4 polymerization mechanism of IP. The cis-1,4 content of the IP unit in the copolymers decreased with increasing St content in the copolymers. The cis-1,4 polymerization was disturbed by incorporating St unit in the copolymers, since the penultimate St unit hardly coordinates to the neodymium metal, resulting in a decrease of the cis-1,4 content in the copolymers. That is, the cis-1,4 polymerization of IP is suggested to be controlled by a back-biting coordination of the penultimate diene unit. On the other hand, in the case of poly(BD-co-IP) and poly(BD-co-DMBD), the cis-1,4 content of the BD, IP, and DMBD units in the copolymers was almost constant (cis: 94–98%), irrespective of the monomer feed ratios and polymerization temperature. Consequently, the penultimate IP and DMBD units favorably control the terminal BD, IP, or DMBD unit to the cis-1,4 configuration through the back-biting coordination. For the monomer reactivity ratios, a clear difference was observed in each system: rBD = 1.22, rIP = 1.14; rBD = 40.9, rDMBD = 0.15. Low polymerizability of DMBD was mainly ascribed to the steric effect of the methyl substituents. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1707–1716, 1998 相似文献
617.
Eiichi Kobayashi Nahoto Hayashi Sadahito Aoshima Junji Furukawa 《Journal of polymer science. Part A, Polymer chemistry》1998,36(2):241-247
Homo- and copolymerizations of butadiene (BD) and styrene (St) with rare-earth metal catalysts, including the most active neodymium (Nd)-based catalysts, have been examined, and the cis-1,4 polymerization mechanism was investigated by the diad analysis of copolymers. Polymerization activity of BD was markedly affected not only by the ligands of the catalysts but also by the central rare-earth metals, whereas that of St was mainly affected by the ligands. In the series of Nd-based catalysts [Nd(OCOR)3:R = CF3, CCl3, CHCl2, CH2Cl, CH3], Nd(OCOCCl3)3 gave a maximum polymerization activity of BD, which decreased with increasing or decreasing the pKa value of the ligands. This tendency was different from that for Gd(OCOR)3 catalysts, where the CF3 derivative led to the highest polymerization activity of BD. For the polymerization of St and its copolymerization with BD, the maximum activities were attained at R = CCl3 for both Nd- and Gd-based catalysts. The copolymerization of BD and St with Nd(OCOCCl3)3 catalyst was also carried out at various monomer feed ratios, to evaluate the monomer reactivity ratios as rBD = 5.66 and rSt = 0.86. The cis-1,4 content in BD unit decreased with increasing St content in copolymers. From the diad analysis of copolymers, it was indicated that Nd(OCOCCl3)3 catalyst controls the cis-1,4 structure of the BD unit by a back-biting coordination of the penultimate BD unit. Furthermore, the long range coordination of polymer chain by the neodymium catalyst was suggested to assist the cis-1,4 polymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 241–247, 1998 相似文献
618.
Eiichi Kaji Toshiya Uozumi Jizhu Jin Tsuneji Sano Kazuo Soga 《Journal of polymer science. Part A, Polymer chemistry》1998,36(15):2735-2740
The Ti(BFA)2Cl2/MgCl2–Al(C2H5)3 catalyst (BFA = 4,4,4-trifluoro-1-phenyl-1,3-butanedione) modified by DIPDMS (diisopropyldimethoxysilane), which had been proved to yield an extremely high isotactic polypropene in high selectivity, was tested for the copolymerization of ethene with propene. The analysis of resulting copolymers by CFC (cross fractionation chromatography) indicated the formation of a small quantity of ethene-rich copolymers as a byproduct, suggesting that the catalyst possesses not only Ti(III) species but a small portion of Ti(II) species. Whereas, the same catalyst without being modified by an external donor selectively yielded propene-rich random copolymers resulting from Ti(III) species in high yields. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2735–2740, 1998 相似文献
619.
Toyoshi Ohashi Eiichi Kobayashi Tomoko Jinbo Junji Furukawa 《Journal of polymer science. Part A, Polymer chemistry》1997,35(9):1621-1625
The crystal structure of 1,4-benzenedithiol (BDT) was determined by the Rietveld method based on the calculation of the atomic coordinates of the BDT molecule using the Molecular Mechanics Program (MMP2). The refined crystal structure of BDT was monoclinic P21/c with dimensions, a = 7.795, b = 7.290, c = 5.955 Å, β = 92.16°, z = 2. The R factor of the refined structure was 0.038. Using above results, the mechanism of solid-state addition polymerization of BDT to 1,4-diethynylbenzene (DEB) was studied. Sublimed BDT piles up onto glass plate substrate and forms the layer structure along with the a axis. An inclination angle of the piled BDT column was 60° toward the substrate surface. DEB crystal structure was also monoclinic P21/c with a = 4.007, b = 6.018; c = 15.340 Å, β = 91.42°, z = 2. Sublimation of equimolar mixture of BDT and DEB gave a crystal having 1 : 1 composition, in which DEB column is situated between the columns of BDT. Relative arrangement of both monomers was suitable for the addition of SH and CCH groups, since the distance between the two groups is 3.3 Å by CERIUS II calculation. Therefore, the addition polymerization of BDT to DEB easily proceeded by UV irradiation and the resulting polymer had a highly layer structure along with the a axis of BDT crystal. Tentatively estimated crystal structure of polymer obtained is monoclinic with a = 7.73, b = 7.30, c = 5.95 Å, β = 92.16°. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1621–1625, 1997 相似文献
620.
Objective: Preoperative performance status is an important factor in thoracic surgery, but little is known about the effect of preoperative physical activity (PA) on the postoperative course. This study investigated the associations between preoperative PA and postoperative complications and clinical outcomes of lung cancer surgery. Methods: This prospective observational study included patients who underwent surgery for lung cancer at a single institution. PA was measured before hospitalization for 5 consecutive days and then after surgery until hospital discharge. The daily step count and time spent performing moderate intensity activity (> 3 metabolic equivalents) were measured with an accelerometer. We examined the correlations between PA and preoperative pulmonary function and physical fitness, and examined the relationship between postoperative complication and PA. Finally, a multivariate analysis was performed with pre-hospital PA as the dependent variable. Results: Forty-two patients were analyzed. Univariate analysis found no correlation between pre-hospital PA and preoperative pulmonary function, but found significant positive correlations between pre-hospital PA and time spent performing moderate intensity activity, in-hospital PA, preoperative 6-minute walk distance, and maximum gait speed (r > 0.5, p < 0.01). The nine patients who developed postoperative complications had significantly lower pre-hospital and postoperative step count than the patients with no complication (p = 0.04). Multiple regression analysis showed that pre-hospital PA was significantly associated with time spent performing moderate intensity activity, maximum gait speed, and postoperative complication. Conclusions: Evaluation of pre-hospital PA is useful in predicting the postoperative course after lung cancer surgery. 相似文献