全文获取类型
收费全文 | 1092篇 |
免费 | 21篇 |
国内免费 | 7篇 |
专业分类
化学 | 829篇 |
晶体学 | 11篇 |
力学 | 40篇 |
数学 | 48篇 |
物理学 | 192篇 |
出版年
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 18篇 |
2018年 | 11篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 16篇 |
2013年 | 69篇 |
2012年 | 52篇 |
2011年 | 51篇 |
2010年 | 43篇 |
2009年 | 41篇 |
2008年 | 68篇 |
2007年 | 62篇 |
2006年 | 53篇 |
2005年 | 60篇 |
2004年 | 48篇 |
2003年 | 47篇 |
2002年 | 57篇 |
2001年 | 18篇 |
2000年 | 14篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 21篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 20篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 10篇 |
1972年 | 11篇 |
1971年 | 7篇 |
1970年 | 6篇 |
1966年 | 7篇 |
排序方式: 共有1120条查询结果,搜索用时 15 毫秒
141.
142.
Katsumi Saitoh Koichiro Sera Tadashi Shirai Tatsuji Sato Matsuo Odaka 《Analytical sciences》2003,19(4):525-528
The purpose of this study is to clarify the chemical characterization of PM2.5 and PM10 in diesel exhaust particles (DEP). Sampling of PM2.5 and PM10 in DEP was carried out in November 1999 using an automobile exhaust testing system at the National Traffic Safety and Environment Laboratory, with a diesel truck (engine type: direct injection, displacement: 7,961 cc, carrying weight: 2,020 kg, equivalent inertia weight: 5,600 kg) placed on a chassis dynamometer. Sampling conditions included idling, constant speed of 40 km/h, M-15 test pattern and 60%-revolution/40%-load of maximum power. Samples were collected on a polycarbonate membrane filter (Nuclepore, pore size: 0.8 microm) using a MiniVol Portable Air Sampler (Airmetrics Co., Inc.). The concentrations of several elemental and ionic species in the PM2.5 and PM10 samples were determined by particle induced X-ray emission (PIXE) and ion chromatography analysis. PIXE analysis of the PM2.5 and PM10 samples revealed 15 elements, of which Na, Mg, Si, S, Cl, Ca, Fe and Zn were found to be the major components. Ionic species were Cl-, NO2-, NO3-, SO4(2-), Na+, NH4+, K+ and Ca2+. Concentrations of elements and ionic species under the sampling condition of 60%-revolution/40%-load were highest in comparison with those of the other sampling conditions. The elemental and ionic species data were compared for PM2.5 and PM10; PM2.5 concentrations were 70% or more of PM10 concentrations for the majority of elements, and concentrations of ionic species in PM2.5 and PM10 were almost identical. 相似文献
143.
Hiroji Oda Yoshitomi Morizawa Koichiro Oshima Hitosi Nozaki 《Tetrahedron letters》1984,25(30):3221-3224
Whereas iododegermylation of (Z)-1-triethylgermyl-1-dodecene gives (Z)-1-iodo-1-dodecene, bromodegermylation proves to give (E)-1-bromo-1-dodecene. Two general procedures for the preparation of vinylgermanes are also described. 相似文献
144.
145.
Koichiro Yonetake Kunio Maruyama Jun-Ichi Sugiyama Toru Masuko Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》1994,32(8):1415-1421
Poly[4-(4-hydroxyphenoxy) benzoic acid] was prepared by the bulk polycondensation of 4-(4-acetoxyphenoxy) benzoic acid. Polycondensation was conducted at 350°C for 3 h under a reduced pressure of 0.1 mmHg and gave a polymer with X?n of 255. The polymer was characterized by elemental analysis, IR spectroscopy, differential scanning calorimetry, and wide-angle X-ray measurement. The crystal/nematic and nematic/isotropic phase transition temperatures of polymer, which depend on the molecular weight, were observed at about 300°C and 410°C, respectively. The polymers with low molecular weights showed nematic textures above 300°C. This nematic/isotropic phase transition temperature is lower than that of poly (4-hydroxybenzoic acid). This thermal behavior of polymer comes from ether units, which increase the flexibility (the rotation or torsion of skeletal bonds) of the polymer chain. © 1994 John Wiley & Sons, Inc. 相似文献
146.
Ei-ichi Nishizawa Leenawaty Limantara Noriyuki Nanjou Hiroyoshi Nagae Tomisaburo Kakuno Yasushi Koyama 《Photochemistry and photobiology》1994,59(2):229-236
The frequency of BChl that was bound to the light-harvesting complex (LHC) of Rhodobacter sphaeroides R26 was found to be 1598 cm-1 , a result which suggests that a pair of BChl molecules form a dimer in the LHC in the T1 state. 相似文献
147.
148.
Three Lennard-Jones binary liquid mixture systems obeying Lorentz-Berthelot rules, but having differing component sizes and energy parameters, have been used to calculate the local fractions of the two components around each type of central particle over the entire composition range from molecular-dynamics data. It is found that well-defined local fractions can be determined even in the case where the size difference between the particles is large. The results obtained are compared with values predicted by the Wilson and NRTL equations. It is confirmed that the NRTL equation gives satisfactory agreement only in the case of mixtures of components having the same size parameters. A new correlation is proposed by a modification of the NRTL equation. This correlation can predict reasonably well local-fraction data for all the Lennard-Jones liquid mixtures studied so far. 相似文献
149.
150.