全文获取类型
收费全文 | 3644篇 |
免费 | 240篇 |
国内免费 | 649篇 |
专业分类
化学 | 3929篇 |
晶体学 | 117篇 |
力学 | 21篇 |
综合类 | 61篇 |
数学 | 6篇 |
物理学 | 399篇 |
出版年
2024年 | 6篇 |
2023年 | 39篇 |
2022年 | 75篇 |
2021年 | 109篇 |
2020年 | 145篇 |
2019年 | 102篇 |
2018年 | 100篇 |
2017年 | 135篇 |
2016年 | 139篇 |
2015年 | 131篇 |
2014年 | 147篇 |
2013年 | 440篇 |
2012年 | 207篇 |
2011年 | 150篇 |
2010年 | 142篇 |
2009年 | 163篇 |
2008年 | 165篇 |
2007年 | 204篇 |
2006年 | 192篇 |
2005年 | 192篇 |
2004年 | 161篇 |
2003年 | 178篇 |
2002年 | 140篇 |
2001年 | 114篇 |
2000年 | 85篇 |
1999年 | 109篇 |
1998年 | 94篇 |
1997年 | 88篇 |
1996年 | 96篇 |
1995年 | 75篇 |
1994年 | 56篇 |
1993年 | 49篇 |
1992年 | 61篇 |
1991年 | 34篇 |
1990年 | 27篇 |
1989年 | 27篇 |
1988年 | 28篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有4533条查询结果,搜索用时 850 毫秒
81.
Formation at low surfactant concentrations and characterization of mesoporous MCM-41 总被引:2,自引:0,他引:2
At low concentrations of cetyltrimethylammonium bromide,all silica-based mesoporous materials with hexagonal phase have been synthesized via interactions between self-assembled surfactant molecule aggregates and aniomc silicate polymers.The resulting materials are characterized by XRD,FT-IR,solid state 29Si MAS NMR,thermal analysis and N2 adsorption-desorption measurements.After soluble ions are removed,the interactors between surfactant micelles and silicate polymers are reorganized and then form mesostructures 1 he hexagonal framework is sonsistent with amorphous silica gel.The structures of materials depend on the synthesis conditions Hydrothermal process improves the interactions between molecules and increases the degree of framework silicon atom polymerization The.surface area and the mesopore volume of the material prepared at 100℃ increase by 87% and 71 %,respectively,compared with those obtained at room temperature. 相似文献
82.
介孔分子筛MSU-1的合成 总被引:1,自引:0,他引:1
MSU X介孔分子筛具有三维立体交叉排列的蠕虫状孔道结构,有利于客体分子在其孔道内扩散[1]。目前合成MSU X的原料[2 4]TEOS水解速度慢,合成过程较易控制,但价高、易燃、有刺激性。本文采用文献[5 7]法,以水玻璃、A(EO)9为原料,在酸性至近中性的范围里合成了MSU 1介孔分子筛,与TEOS为原料的MSU 1合成进行了比较,考察了pH值和不同类型表面活性剂(脂肪醇聚氧乙烯醚和烷基酚聚氧乙烯醚)对产物结构性质的影响。1 实验部分1 1 试剂和仪器水玻璃(SiO2%≈26、Na2O%≈8),工业级,青岛海洋化工厂生产;脂肪醇聚氧乙烯醚非离子表面活性… 相似文献
83.
Electrical conductance measurements of dilute (<0.1>0.1>–1) aqueous NaCl solutions were made primarily to quantify the degree of ion association which increases with increasing temperature and decreasing solvent density. These measurements were carried out at temperatures from 100 to 600°C and pressures up to 300 MPa with a modified version of the apparatus used previously in the high temperature study in this laboratory. Particular emphasis was placed on conditions close to the critical temperaturelpressure region of water, i.e., at 5° intervals from 370 to 400°C. The results verify previous findings that the limiting equivalent conductance Ao of NaCl increases linearly with decreasing density from 0.75 to 0.3 g-cm–1 and also with increasing temperature from 100 to 350°C. Above 350°C. Ao is virtually temperature independent. The logarithm of the molal association constant as calculated exclusively from the data400°C is represented as a function of temperature (Kelvin) and the logarithm of the density of water (g-cm–3) as follows:
相似文献
84.
85.
86.
The surface pressure vs. mokcular surface area relations for dipalmitoyl phosphatidylcholine (DPPC) insoluble monolayer and sodium deoxycholate (SDC) adsorbed monolayer,L and D1, respectively, were obtained from the analyses of surface tensions measured by the Wilhelmy glass plate. Also, D1 was obtained by a drop-weight method. Next, the surface pressure time course,(t), of the SDC aq. was measured by the Wilhelmy plate before and after DPPC was spread on the liquid surface. At DPPC spreading,(t) jumped to a maximum,, and decreased along an exponential curve. The values of with various surface amounts of DPPC and bulk concentrations of SDC were analyzed using a dual surface-region model. The model enabled the estimation of. For better fitting, modified relations were constructed in place of D1. The exponential decrease of(t) was also observed on the SDC adsorbed monolayer which was rapidly compressed by a moving barrier. The(t) relaxation rate constants of the SDC monolayers which were compressed by DPPC spreading and the moving barrier agreed with each other, suggesting a desorption of SDC from the surface. 相似文献
87.
Yong Zhong DU Fu Qiang HU Hong YUAN Shinzo OMI 《中国化学快报》2006,17(4):553-556
Stable poly(styrene-co-sodium styrene sulfonate) (P(St-NaSS) nanoparticles with broader size distribution were synthesized by thermal emulsion polymerization without any conventional initiators and emulsifiers. The obtained polymer nanoparticles have higher ξ potential, and the particle sizes have broad distribution. The stability of polymer particles originated from the addition of small amounts of ionic comonomer, NaSS, which can act as an emulsifier in somewhat. The monomer conversion could reach up to about 28 wt% in 48 h, and did not increase by further polymerization when higher polymerization temperature (120 ℃) was employed. This polymerization system may be give some further understand for mechanism of emulsion polymerization. 相似文献
88.
89.
Janusz Wasilewski Jan F. Biernat 《Journal of inclusion phenomena and macrocyclic chemistry》1991,10(1):109-118
Lipophilic bis-substituted ester and ether derivatives of benzo-15-crown-5 have been synthesised. The correlation between the structure and potentiometric ion-selectivity has been studied in PVC membrane ion-selective electrodes. An ion-selective potassium sensitive electrode based on 4,5-bis (biphenyloxymethyl)benzo-15-crown-5 exhibited the best electrode properties. The detection limit was loga
K = -5.4; logK
K,Na
ppot = -3.5. The effect of the lipophilicity of neutral carriers upon electrode performance has been also discussed. 相似文献
90.
Usachev N. Ya. Belanova E. P. Krukovsky I. M. Kanaev S. A. Atal"yan O. K. Kazakov A. V. 《Russian Chemical Bulletin》2003,52(9):1940-1949
Thermal transformations in systems formed by interaction of Zn and Na nitrates with Y, X, and A zeolites were studied by TG—DTA technique. Temperature regions of existence of adsorbed water, water of crystallization, and decomposition of NO3
– anion were determined. These intervals depend on the composition, structure, method of preparation, and pre-treatment conditions of zeolite systems. The extent of NO3
– decomposition depends not only on the zinc and sodium content but also on the presence of ammonia involved in NO3
– reduction. The zeolite matrix strongly stabilizes the occluded NO3
– anions. A portion of zinc oxide formed by zinc nitrate decomposition is probably localized inside the zeolite cavities as the [Zn—O—(ZnO)
n
—Zn]2+ particles. The latter compensate charges of the isolated [AlO4]– tetrahedra. 相似文献
|