全文获取类型
收费全文 | 4504篇 |
免费 | 458篇 |
国内免费 | 728篇 |
专业分类
化学 | 2719篇 |
晶体学 | 69篇 |
力学 | 138篇 |
综合类 | 72篇 |
数学 | 1012篇 |
物理学 | 1680篇 |
出版年
2024年 | 6篇 |
2023年 | 37篇 |
2022年 | 76篇 |
2021年 | 78篇 |
2020年 | 100篇 |
2019年 | 113篇 |
2018年 | 112篇 |
2017年 | 136篇 |
2016年 | 156篇 |
2015年 | 107篇 |
2014年 | 175篇 |
2013年 | 306篇 |
2012年 | 267篇 |
2011年 | 269篇 |
2010年 | 211篇 |
2009年 | 286篇 |
2008年 | 302篇 |
2007年 | 324篇 |
2006年 | 268篇 |
2005年 | 263篇 |
2004年 | 222篇 |
2003年 | 212篇 |
2002年 | 166篇 |
2001年 | 161篇 |
2000年 | 142篇 |
1999年 | 137篇 |
1998年 | 119篇 |
1997年 | 107篇 |
1996年 | 107篇 |
1995年 | 99篇 |
1994年 | 88篇 |
1993年 | 51篇 |
1992年 | 78篇 |
1991年 | 61篇 |
1990年 | 53篇 |
1989年 | 49篇 |
1988年 | 38篇 |
1987年 | 32篇 |
1986年 | 32篇 |
1985年 | 22篇 |
1984年 | 19篇 |
1983年 | 10篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有5690条查询结果,搜索用时 0 毫秒
61.
Yasuyuki Takeda Chihiro Takagi 《Journal of inclusion phenomena and macrocyclic chemistry》1994,17(1):93-97
The theory is derived to determine the dimer-formation constant,K
2, of a crown ethermetal salt 111 complex in organic solvents of low dielectric constant by solvent extraction. The theoretical predictions are verified experimentally by extraction of sodium picrate (NaA) with 15-crown-5 (15C5) into carbon tetrachloride. All the experiments were conducted at 25°C. The logK
2 value of the Na(15C5)A complex in carbon tetrachloride has been determined to be 4.05±0.11. Moreover, the partition constant of the complex is calculated. 相似文献
62.
邻-甲氧基苯酚和α-,β-环糊精包合现象的理论与实验研究 总被引:1,自引:0,他引:1
通过紫外可见光谱法考察了水溶液中邻-甲氧基苯酚(o-Mop)和α-与β-环糊精(CD)的分子间相互作用, 利用Hildebrand-Benesi方程给出了两个包合物的稳定常数(Ks). 采用半经验PM3方法研究了α-,β-CD和o-Mop及其类似物苯酚(Phe)、丁香酚(Eug)之间的包络作用, 阐述了这些主客体包合作用过程中体系能量随主客体相对位置改变而变化的细节, 据此推断出主-客体包合物可能的分子结构, 计算了包合物的稳定化能(ΔEs). 研究结果表明, 本文所选主客体体系而言, 当客体和同一种主体分子作用时, 超分子包合物的ΔEs随着客体分子苯环上取代基团数目的增多而增加. 基于PM3方法优化得到的主-客体包合物在真空中的分子结构和通过实验方法在水溶液中测定的结构一致. 相似文献
63.
Mathew D. Penrose 《Journal of statistical physics》1994,77(1-2):3-15
LetG
R
be the graph obtained by joining all sites ofZ
d which are separated by a distance of at mostR. Let (G
R
) denote the connective constant for counting the self-avoiding walks in this graph. Let (G
R
) denote the coprresponding constant for counting the trees embedded inG
R
. Then asR, (G
R
) is asymptotic to the coordination numberk
R ofG
R
, while (G
R
) is asymptotic toek
R. However, ifd is 1 or 2, then (G
R
)-k
R
diverges to –.Dedicated to Oliver Penrose on this occasion of his 65th birthday. 相似文献
64.
The selectivity of a column system, S, defined by equation 28, includes a variation coefficient (β) of plate number with capacity ratio which has a large influence on the peak capacity, as shown in Fig. 18. Some typical chromatograms are given. In order to predict S for a column system from Kovat's Index, equations 40 and 41 are given to calculate the constant of the carbon number rule for squalane at different temperatures or for different stationary phases. The specific retention value of heptane on squalane at different temperatures can be calculated from equation 42. The nonpolarity index, defined by equation 43, was used to calculate the retention value of heptane on various stationary phases. In liquid chromatography, the order of elution may be reversed by changing the composition of the eluent on the same chemically bonded silica (manufactured in China). The linear relations between the log retention values of different kinds of solutes or of a single solute on the silicas of different surface areas when using the same eluent are given. 相似文献
65.
Yi-Lu Sun Ren-Jang Wu Yu-Ching Huang Pi-Guey Su Murthy Chavali Yi-Zhen Chen Chu-Chieh Lin 《Talanta》2007,73(5):857-861
In situ preparation of polypyrrole (Ppy) by photo-polymerization coated on a quartz crystal microbalance (QCM) as a low humidity sensor was reported. Different concentrations of Ppy films say 0 wt.% (as blank), 0.1, 1, and 10 wt.% were investigated to measure humidity concentrations between 14.7 and 5412.5 ppmv. The adsorption/desorption behavior was also examined at humidity concentration 510.2 ppmv. The sensitivities of 0, 0.1 and 1 wt.% Ppy films at 51.5 ppmv were 0.143, 0.219 and 0.427, respectively. For 1 wt.% Ppy, the highest sensitivity was obtained. The slope and correlation coefficients (R2) for 1 wt.% Ppy at the ranges of 14.7–898.6 ppmv were 0.0646 and 0.9909, respectively. A series of molecular simulations have been carried out to calculate bond energy for the water molecule interaction with Ppy, which was found to be 3 kcal/mol indicating the existence of hydrogen bonding during the sorption process. Based on Langmuir isotherm adsorption assumption, for 0.1 and 1 wt.% Ppy films, the association constants were 2606.30 and 5792.98, respectively. This larger association constant for 1 wt.% Ppy film explains higher sensitivity. 相似文献
66.
Predicting the selectivity of imprinted polymers 总被引:2,自引:0,他引:2
Summary Imprinted polymers as stationary phases for HPLC separations have been the subject of extensive investigations in recent years.
In order to aid the rational design of synthetic protocols for the preparation of imprinted polymers, a series of calculations
were made to assess the equilibrium concentration of templatemonomer complexes as a function of association constant (K) for the functional groups involved in the interactions and initial concentrations of reactants. This data was then used
to predict the selectivity of polymers prepared under different reaction conditions and the model was tested using an experimentally
determined value ofK and separation factors taken from the literature. 相似文献
67.
A new pulse sequence is proposed for the determination of scalar coupling correlation in small- and medium-sized organic compounds. The method uses a combination of the double pulsed field gradient spin-echo (DPFGSE) and the selective population transfer (SPT) techniques and is shown to be useful in the analysis of complex spectra with many overlapped signals. The usefulness of this method in the structural elucidation of natural substances is demonstrated using strychnine and digitoxin as examples. 相似文献
68.
69.
N-乙酸基取代四氮杂大环及其镧系配合物的热力学研究 总被引:2,自引:0,他引:2
用pH电位滴定法分别在25±0.1℃,40±0.1℃和80±0.1℃,0.5mol/LKNO3水溶液中测定了H_4L(5,7,12,14-四甲基-1,4,8,11-四氮杂环十四烷-N',n",N"',N""-四乙酸)的逐级质子化常数和焓值。又在40±0.1℃和80±0.1℃条件下测定了H4L与镧系金属离子(La~(3+),Nd~(3+),pr~(3+),Sm~(3+),Eu~(3+),Gd~(3+),Dy~(3+),Yb~(3+))配合物的稳定常数。结果表明:配合物稳定性高。 相似文献
70.
Inorganic-organic hybrids have been synthesized by incorporation of the inorganic component of Ti(OC2H5)4 into the organic polymer of ethyl cellulose. The inorganic-organic hybrids did not dissolve in toluene used as a solvent for the starting materials. The ethanol was formed as a by-product of the alcoholysis condensation reaction between Ti(OC2H5)4 and ethyl cellulose. These results suggest that ethoxy groups of Ti(OC2H5)4 react with hydroxy groups of ethyl cellulose to form cross-linking bonds of –O–Ti–O–. The reaction of Ti(OC2H5)4 with ethyl cellulose was further investigated by Fourier transform infrared (FT-IR) spectroscopy. The FT-IR spectroscopic experiments revealed that the Ti–O bond state of Ti(OC2H5)4 was changed by refluxing a toluene solution of Ti(OC2H5)4 with ethyl cellulose. The inorganic-organic hybrids have an interesting dielectric property; their dielectric constant is higher than that of ethyl cellulose and that of a simple mixture of TiO2 and ethyl cellulose. 相似文献