全文获取类型
收费全文 | 3679篇 |
免费 | 508篇 |
国内免费 | 245篇 |
专业分类
化学 | 1176篇 |
晶体学 | 40篇 |
力学 | 1167篇 |
综合类 | 52篇 |
数学 | 614篇 |
物理学 | 1383篇 |
出版年
2024年 | 6篇 |
2023年 | 39篇 |
2022年 | 86篇 |
2021年 | 148篇 |
2020年 | 170篇 |
2019年 | 111篇 |
2018年 | 125篇 |
2017年 | 135篇 |
2016年 | 191篇 |
2015年 | 123篇 |
2014年 | 203篇 |
2013年 | 283篇 |
2012年 | 212篇 |
2011年 | 253篇 |
2010年 | 198篇 |
2009年 | 229篇 |
2008年 | 175篇 |
2007年 | 179篇 |
2006年 | 181篇 |
2005年 | 159篇 |
2004年 | 136篇 |
2003年 | 145篇 |
2002年 | 95篇 |
2001年 | 76篇 |
2000年 | 97篇 |
1999年 | 81篇 |
1998年 | 76篇 |
1997年 | 81篇 |
1996年 | 52篇 |
1995年 | 59篇 |
1994年 | 53篇 |
1993年 | 54篇 |
1992年 | 43篇 |
1991年 | 27篇 |
1990年 | 32篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1971年 | 4篇 |
1969年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有4432条查询结果,搜索用时 15 毫秒
951.
N Reber R Spohr A Wolf H Omichi M Tamada M Yoshida 《Journal of membrane science》1998,140(2):2783-281
Cross-linked poly(N-isopropylacrylamide) (NIPAAm) gel was grafted on the wall of a single ion-track pore in poly(ethylene terephthalate) (PET). The opening and closing of the pore is controlled by temperature and observed by electric conductivity. In the shrunken state of the gel, ions and molecules can penetrate the membrane through the free volume of the pore. In the swollen state, the gel clogs the pore. Using mixtures of polyethylene glycol (PEG) of various molecular weights and 0.1 N potassium chloride, it was demonstrated that the responsive pore acts as a thermally controllable valve preventing the passage of PEG molecules larger than 2 nm. The mean value of the hydrogel mesh size is estimated to be (1.3±0.05) nm. 相似文献
952.
As a potential anticarcinogenic agent, polysaccharides from Cordyceps sinensis have been demonstrated to possess strong antioxidation activity. The aim of the present research was to study the optimal
medium to produce polysaccharides of C. sinensis by using response surface methodology (RSM). The composition of optimized medium for polysaccharide production calculated
from the regression model of RSM was 6.17% sucrose, 0.53% corn steep powder, 0.5% (NH4)2HPO4, and 0.15% KH2PO4 at pH 4.44, with a predicted maximum polysaccharide production of 3.17 g/L. When applying this optimal medium, the maximum
polysaccharide production was 3.05 and 3.21 g/L in a shake flask and a 5-L jar fermentor, respectively. When the pH was controlled
at a higher level such as pH 5.0, both cell growth and polysaccharide production were inhibited. A low pH of 2.85 was required
for maximum production of polysaccharides. 相似文献
953.
Photocatalyst Materials for Water Splitting 总被引:4,自引:0,他引:4
Akihiko Kudo 《Catalysis Surveys from Asia》2003,7(1):31-38
Various photocatalyst materials developed by the group of the present author are described. Alkali and alkaline earth tantalates have arisen as a new group of photocatalyst materials for splitting of water into H2 and O2 under ultraviolet irradiation. They showed activities even without co-catalysts such as Pt, being different from titanate photocatalysts. When NiO co-catalysts were loaded on the tantalate photocatalysts, the photocatalytic activities were markedly increased. Among the tantalates, NiO/NaTaO3 doped with La showed the highest activity. BiVO4, AgNO3, and TiO2 co-doped with Cr and Sb photocatalysts showed high activities for O2 evolution in the presence of a sacrificial reagent (Ag+) under visible light irradiation ( > 420 nm). Pt/SrTiO3 co-doped with Cr and Sb or Ta, Pt/NaInS2, and Pt/AgInZn7S9 photocatalysts showed high activities for H2 evolution from aqueous solutions containing reducing reagents under visible light irradiation. Furthermore, Cu- or Ni-doped ZnS photocatalysts showed H2 evolution activities even without co-catalysts such as Pt. 相似文献
954.
955.
A systematic study of the linear interaction energy (LIE) method and the possible dependence of its parameterization on the force field and system (receptor binding site) is reported. We have calculated the binding free energy for nine different ligands in complex with P450cam using three different force fields (Amber95, Gromos87, and OPLS-AA). The results from these LIE calculations using our earlier parameterization give relative free energies of binding that agree remarkably well with the experimental data. However, the absolute energies are too positive for all three force fields, and it is clear that an additional constant term (gamma) is required in this case. Out of five examined LIE models, the same one emerges as the best for all three force fields, and this, in fact, corresponds to our earlier one apart from the addition of the constant gamma, which is almost identical for the three force fields. Thus, the present free energy calculations clearly indicate that the coefficients of the LIE method are independent of the force field used. Their relation to solvation free energies is also demonstrated. The only free parameter of the best model is gamma, which is found to depend on the hydrophobicity of the binding site. We also attempt to quantify the binding site hydrophobicity of four different proteins which shows that the ordering of gamma's for these sites reflects the fraction of hydrophobic surface area. 相似文献
956.
The ratio of the responses of two different specific detectors to a single compound has, when used in conjunction with the compound's retention index, been investigated as an identification criterion for the compound. The ECD:NPD and ECD:FPD response ratios have been used for the identification of some pesticides. Analyses were performed with a single column – dual parallel detection – personal computer system. The reliability of the detector response ratio (DRR) was demonstrated by the consistency of detector response with time, and the influence of the quantity of analyte and of the chromatographic operating conditions. These factors were selected in the expectation that the technique could be used for routine trace analysis. 相似文献
957.
采用快速动态法制备了具有MFI结构的硅铁沸石分子筛,研究了该分子筛上乙苯脱氢反应的瞬变行为.结合表面吸附态的红外、顺磁结果发现,苯乙烯通过化学活性吸附的乙苯脱氢形成.通过这个模型可满意地解释瞬态曲线和稳态下的动力学行为. 相似文献
958.
Saturation of extrinsic photoconductivity in GaP:N(Zn, Te) diodes could be achieved by excitation with a TEA-CO2-laser. At wavelengths in the 10 m range intensities of several 100 kW/cm2 being near the damage threshold were applied. Carrier lifetimes of 60 ps at 4.2 K and 200 ps at 77 K could be estimated. The only conceivable mechanism explaining these short time constants is the capture of infrared excited holes by ionized shallow acceptors in the highly compensated p-side of the diode. 相似文献
959.
960.
Qing Long JIANG Xiang Kai FU Zhu Jun CHEN Research Institute of Applied Chemistry College of Chemistry Chemical Engineering Southwest University Chongqing Key Laboratory of Applied Chemistry of Chongqing Municipality Chongqing Key Laboratory of Eco-environments in Three Gorges Reservoir Region 《中国化学快报》2006,(11)
A new compound 1-ethyl-1'-(4-vinylbenzyl)-4, 4'-bipyridinium chloride and iodide has been synthesized. The cyclic voltammogram and impedance spectra indicated that a layer of viologen's electrochromic (EC) film could be deposited on conductive ITO glass working electrode. With polyelectrolyte as ionic conduction layer, solid EC devices based on this compound have been assembled and their thickness was about 2.35 mm. When different voltages were added, they showed blue or violet red color. After optimization, its response time was less than 50 ms, the number of redox circulation was over 107 and the color of coloration states could be kept for 3 days. This kind of EC device can meet the demand of electronic ink. 相似文献