全文获取类型
收费全文 | 357篇 |
免费 | 17篇 |
国内免费 | 2篇 |
专业分类
化学 | 213篇 |
晶体学 | 3篇 |
力学 | 5篇 |
数学 | 97篇 |
物理学 | 58篇 |
出版年
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 25篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 26篇 |
2012年 | 25篇 |
2011年 | 22篇 |
2010年 | 14篇 |
2009年 | 16篇 |
2008年 | 28篇 |
2007年 | 28篇 |
2006年 | 15篇 |
2005年 | 7篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 16篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1994年 | 6篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1914年 | 4篇 |
排序方式: 共有376条查询结果,搜索用时 62 毫秒
101.
102.
103.
Soybean isoflavones possess hormonal and nonhormonal properties that may reduce the risk of coronary heart disease, osteoporosis, and certain cancers, and alleviate hot flashes in menopausal women. Among the various cancers whose risk may be reduced by isoflavones, there is particular interest in prostate cancer. Eleven trials have examined the effects of isoflavones on serum prostate-specific antigen (PSA) levels. The dose of isoflavones in these trials from supplements or soy protein ranged from 60 to 900 mg/day (typical Japanese intake is 30-50 mg/day), subject number/group ranged from 8 to 62, and study duration from 20 days to 1 year. Isoflavones did not affect serum PSA in healthy subjects. In contrast, in 4 of 8 trials involving prostate cancer patients, isoflavones significantly favorably affected PSA although in no studies was there an absolute decrease in PSA concentrations. The mechanism by which isoflavones affect PSA could not be determined from the existing research, although hormonal changes do not seem to be a factor. The clinical evidence is sufficiently encouraging to justify considering additional Phase II and III clinical trials investigating the efficacy of soy isoflavones in different populations of prostate cancer patients alone and in combination with other treatments. 相似文献
104.
105.
Elmastaş M Turkekul I Oztürk L Gülçin I Isildak O Aboul-Enein HY 《Combinatorial chemistry & high throughput screening》2006,9(6):443-448
The ethanol extracts of Morchella vulgaris (EEMV) and Morchella esculanta (EEME) were analysed for their antioxidant activities in different systems including reducing power, free radical scavenging, superoxide anion radical scavenging, total antioxidant activity, and metal chelating activity. EEMV and EEME had similar reducing power, free radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, and metal chelating activity at concentrations of 50, 100, and 150 microg/mL. These various antioxidant activities were compared to standard antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and alpha-tocopherol. The percent inhibition of different concentrations of EEMV on peroxidation in the linoleic acid system was 85 and 87 % respectively, which was greater than that of 100 and 250 microg/mL of alpha-tocopherol (50 and 77%, respectively) and similar to 250 microg/mL of BHA (85, 87%, respectively). The percent inhibition of different concentrations of EEME on peroxidation in the linoleic acid system was 80 and 87 % respectively, which was greater than that of 100 and 250 microg/mL of alpha-tocopherol (50, 77%) and similar to 250 microg/mL BHA (87%). On the other hand, the percent inhibition of 100 and 250 microg/mL of BHT was 97 and 99%, respectively. In addition, the total phenolic compounds in EEMV and EEME were determined as gallic acid equivalents. 相似文献
106.
Applications of fractional complex transform and $\left( \frac{G^{\prime }}{G}\right) $-expansion method for time-fractional differential equations 下载免费PDF全文
Ahmet Bekir Ozkan Guner Omer Unsal Mohammad Mirzazadeh 《Journal of Applied Analysis & Computation》2016,6(1):131-144
In this paper, the fractional complex transform and the $\left( \frac{G^{\prime }}{G}\right) $-expansion method are employed to solve the time-fractional modfied Korteweg-de Vries equation (fmKdV),Sharma-Tasso-Olver, Fitzhugh-Nagumo equations, where $G$ satisfies a second order linear ordinary differential equation. Exact solutions are expressed
in terms of hyperbolic, trigonometric and rational functions. These solutions may be useful and desirable to explain some nonlinear physical phenomena in genuinely nonlinear fractional calculus. 相似文献
107.
108.
The existence of the weak limit as n of the uniform measure on rooted triangulations of the sphere with n vertices is proved. Some properties of the limit are studied. In particular, the limit is a probability measure on random triangulations of the plane. 相似文献
109.
Pauliukaite R Metelka R Svancara I Królicka A Bobrowski A Vytras K Norkus E Kalcher K 《Analytical and bioanalytical chemistry》2002,374(6):1155-1158
Carbon paste electrodes bulk-modified with Bi(2)O(3)were used for the determination of Cd(II) and Pb(II). The best composition was 1% (wt%) Bi(2)O(3) in the paste. The measurements were made by differential pulse voltammetry in the potential range from -1.2 V to -0.3 V. The peak potential of the reoxidation of Cd is -0.85 V, and of Pb -0.60 V vs. SCE. The lowest concentration that could be determined was 5 microg L(-1) of both metals (preconcentration time 240 s), the relative standard deviation was 3.5%-5.0% (four determinations). The correlation coefficient ( r(2)) of the calibration curves was 0.9966 (for Cd) and 0.9971 (for Pb). The Bi(2)O(3)-modified electrode could be used for the analysis of drinking water, mineral water and urine. 相似文献
110.
Bobrowski M Liwo A Ołdziej S Jeziorek D Ossowski T 《Journal of computational chemistry》2002,23(11):1076-1089
In this article we report our study of two possible mechanisms of photooxidation of hydroxyaromatic compounds, involving the intermediacy of zwitterionic peroxa intermediates or 1,4-endoperoxides. To study the pathway of the first of them, as yet unexplored by theoretical methods, a simpler system composed of 1,3-butadiene-1-ol and singlet ((1)Delta(g)) dioxygen was considered first, for which calculations were carried out at the CASSCF/MCQDPT2 ab initio level, mostly with the 6-31G* basis set. The cumulative activation barrier to this reaction was found to be 20 kcal/mol and corresponded to a proton transfer (from the hydroxy oxygen atom to the attached oxygen molecule) in the cyclic zwitterionic peroxacyclopenta-3-ene-2-ol intermediate. This intermediate and the proton-transfer transition state were found to have a closed-shell character, which enabled us to estimate the corresponding activation barrier for the phenol-dioxygen system by carrying out optimization at the RHF level and single-point calculations at the MP2, CASSCF, and MCQDPT2 levels of theory. The energy barrier to the reaction was estimated to at least about 40 kcal/mol, rendering this mechanism for the phenol-oxygen system unlikely for nonpolar solvents. Similarly, calculations of the barrier to proton transfer from the 1,4-endoperoxide of phenol to its hydroperoxide were found to exceed 60 kcal/mol, eliminating such a mechanism too, which leaves only the earlier postulated mechanisms involving an initial charge or hydrogen-atom transfer to dioxygen as probable. 相似文献