全文获取类型
收费全文 | 4376篇 |
免费 | 103篇 |
国内免费 | 21篇 |
专业分类
化学 | 3059篇 |
晶体学 | 47篇 |
力学 | 49篇 |
综合类 | 2篇 |
数学 | 243篇 |
物理学 | 1100篇 |
出版年
2023年 | 19篇 |
2021年 | 35篇 |
2020年 | 49篇 |
2019年 | 58篇 |
2018年 | 42篇 |
2017年 | 24篇 |
2016年 | 60篇 |
2015年 | 74篇 |
2014年 | 73篇 |
2013年 | 188篇 |
2012年 | 183篇 |
2011年 | 239篇 |
2010年 | 110篇 |
2009年 | 150篇 |
2008年 | 222篇 |
2007年 | 226篇 |
2006年 | 234篇 |
2005年 | 197篇 |
2004年 | 187篇 |
2003年 | 175篇 |
2002年 | 181篇 |
2001年 | 133篇 |
2000年 | 108篇 |
1999年 | 72篇 |
1998年 | 61篇 |
1997年 | 66篇 |
1996年 | 60篇 |
1995年 | 50篇 |
1994年 | 66篇 |
1993年 | 68篇 |
1992年 | 79篇 |
1991年 | 62篇 |
1990年 | 57篇 |
1989年 | 63篇 |
1988年 | 50篇 |
1987年 | 62篇 |
1986年 | 52篇 |
1985年 | 59篇 |
1984年 | 60篇 |
1983年 | 43篇 |
1982年 | 41篇 |
1981年 | 52篇 |
1980年 | 41篇 |
1979年 | 60篇 |
1978年 | 52篇 |
1977年 | 32篇 |
1976年 | 48篇 |
1975年 | 28篇 |
1974年 | 33篇 |
1973年 | 31篇 |
排序方式: 共有4500条查询结果,搜索用时 15 毫秒
981.
Eiichi?Mine Daisuke?Nagao Yoshio?Kobayashi Mikio?KonnoEmail author 《Journal of Sol-Gel Science and Technology》2005,35(3):197-201
Particle formation in ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) was studied in aqueous solvents that contained ethanol, 1-propanol or 1-butanol. The reactions were performed at a TEOS concentration of 0.2 kmol/m3, a H2O concentration of 5 kmol/m3 and a NH3 concentration of 1 kmol/m3. Average particle size was the largest for 1-butanol and the smallest for ethanol. No specific relation of the average diameter to hydrolysis rate was observed in the reactions. Difference in dielectric constant of the solvent and particle surface potential in the reactions indicated that the magnitudes of interparticle repulsion in the solvents corresponded with the order of the average particle sizes. This suggested that the particle sizes were dominated by the interparticle repulsion. 相似文献
982.
Trimethylselenonium hydroxide is very useful for methylating COOH, SH, aromatic OH, ring NH groups is aromatic heterocycles, etc. 相似文献
983.
The distribution ratio of neodymium(III) in extraction with mono(2-ethylhexyl)-phosphoric acid was determined as a function
of extractant and Nd(III) concentrations, and effect of co-existing DEHPA was studied. A characteristic extraction of a tracer
quantity of Nd(III) was found at an extractant concentration of approximately 0.01 M. Di(2-ethylhexyl)phosphoric acid depresses
the extraction of Nd(III) in MEHPA of a concentration of 0.01M, but enhances it at higher concentrations of MEHPA. Owing to
the high Df values against lanthanides(III) and an excellent radiation stability, the synergistic combination of MEHPA-DEHPA,
preferably at a DEHPA/MEHPA mole ratio of 3, was concluded to be applicable to the isolation of lanthanides (and actinides)
from highly acidic solutions. 相似文献
984.
The structures and reactivities of the complexes between carbenium ions (R(+)) and acetylene or propyne have been investigated with the aid of electron-correlated quantum mechanical calculations (hybrid density functional, perturbation theory, and coupled cluster methods). Depending on the R group, the acetylene/carbenium ion interaction can produce either an "open" 3c-2e structure or the conventional vinyl cation structure. The "open" 3c-2e C-C-C bonding geometry exists as a minimum for R = methyl and primary/secondary/tertiary alkyl, and hence is the most notable. The alignment of three carbon centers is neither bridged nor linear, but L-shaped, and represents a new type of "open" 3c-2e bonding that has so far escaped proper attention. 相似文献
985.
Tajima K Imai Y Nakamura A Koshinuma M 《Advances in colloid and interface science》2000,88(1-2):79-97
The thermal properties of the dispersion of sodium salt of dimyristoylphosphatidylglycerol (NaDMPG) in water have been investigated as functions of incubation temperature and aging time by DSC, XRD, sodium ion activity, pH, zeta-potential, and IR measurements. The DSC charts for NaDMPG dispersions incubated below 30 degrees C showed an endothermic peak at 31.7 degrees C with a small shoulder peak at Tm (gel-liquid crystal transition temperature: 23.5 degrees C). The temperature of 31.7 degrees C coincides with the T* temperature at which a high-order transition in the NaDMPG bilayer assembly has been found to occur in our previous studies. However, no peak was observed for the dispersions incubated above 32 degrees C. These results indicate that thermal properties of NaDMPG bilayers definitely differ below and above the T* temperature. The dispersion which had been once incubated at 40 degrees C for 24 h never showed the endothermic peak at T* even after the further aging at 3 degrees C for 12-day. Namely, the NaDMPG bilayer assembly exhibits an intensive thermohysteresis. The XRD charts for the NaDMPG dispersions incubated at 25 degrees C showed a sharp X-ray diffraction pattern corresponding to the repeat distance of d = 4.75 nm regardless of their aging time, while the dispersions incubated at 40 degrees C had no diffraction peak until 9-day elapsed. After 10-day aging at 40 degrees C, however, a diffraction peak corresponding to d = 5.55 nm clearly appeared. In the DSC measurements for the dispersion incubated at 40 degrees C, a few endothermic peaks began to appear between Tm and T* after approximately 7-day aging. Then, they shifted toward higher temperatures and finally converged into a single peak at 40-42 degrees C after 14-day aging. These XRD and DSC peaks observed after a long period of aging time above T* suggest that conformations of the hydrophilic groups and the hydrocarbon chains in the NaDMPG bilayers take a more tight and closer arrangement very slowly via an intermediate state above T*, and a new gel phase of the bilayers is consequently formed, the transition temperature (T(I) temperature) of which is 40-42 degrees C. A molecular interpretation for such transition processes in the bilayer assembly of NaDMPG dispersions has been proposed on the basis of pH, sodium ion activity, zeta-potential, IR data, etc. 相似文献
986.
987.
Synthesis of methyl α-D-tetronitroside() from D-mannose via methyl α-D-mycaroside() established the D-configuration for tetronitrose(kijanose), a novel nitro sugar which occurs as a component of the antitumor antibiotics tetrocarcins A and B, and kijanimicin. 相似文献
988.
35Cl and 19F relaxation time measurements were carried out on symC6Cl3F3. The analyses of the 19F high-resolution NMR spectra and the 35Cl spin-lattice relaxation time showed that the crystal belongs to a trigonal or a hexagonal crystal system in which the molecules undergo three-fold reorientation about the molecular figure axis with the correlation time τc/s=3.42·10?7 exp(18.2 kJ mol?1/RT). Temperature dependences of the 35Cl NQR frequency and 19F spin-lattice relaxation times are such that only a minor structural change is associated with the phase transition at 296 K. 相似文献
989.
990.
Hiroshi Tsukube Takeo Araki Akira Nakamura Kazuhiro Maruyama 《Journal of polymer science. Part A, Polymer chemistry》1980,18(12):3359-3368
The synthesis and metal ion binding properties of a new class of functional oligomers are described. Oligo[1-(N-phenylthiocarbamoyl)aziridine] (DP ca. 8) and its analogs are prepared by ring-opening oligomerization of the corresponding aziridine monomers in good yields. These oligomers contain sulfur groups capable of binding “soft” metal ions, and the selective binding properties of the novel oligomer for Cu(II) and Hg(II) ions are investigated by liquid-solid adsorption and liquid-liquid extraction experiments. 相似文献