全文获取类型
收费全文 | 6985篇 |
免费 | 189篇 |
国内免费 | 254篇 |
专业分类
化学 | 3721篇 |
晶体学 | 128篇 |
力学 | 572篇 |
综合类 | 46篇 |
数学 | 1272篇 |
物理学 | 1689篇 |
出版年
2023年 | 46篇 |
2022年 | 188篇 |
2021年 | 185篇 |
2020年 | 164篇 |
2019年 | 168篇 |
2018年 | 157篇 |
2017年 | 155篇 |
2016年 | 183篇 |
2015年 | 145篇 |
2014年 | 155篇 |
2013年 | 274篇 |
2012年 | 167篇 |
2011年 | 144篇 |
2010年 | 137篇 |
2009年 | 184篇 |
2008年 | 223篇 |
2007年 | 191篇 |
2006年 | 182篇 |
2005年 | 321篇 |
2004年 | 525篇 |
2003年 | 421篇 |
2002年 | 369篇 |
2001年 | 303篇 |
2000年 | 232篇 |
1999年 | 184篇 |
1998年 | 150篇 |
1997年 | 145篇 |
1996年 | 206篇 |
1995年 | 164篇 |
1994年 | 203篇 |
1993年 | 155篇 |
1992年 | 139篇 |
1991年 | 78篇 |
1990年 | 69篇 |
1989年 | 63篇 |
1988年 | 55篇 |
1987年 | 72篇 |
1986年 | 53篇 |
1985年 | 40篇 |
1984年 | 41篇 |
1982年 | 41篇 |
1981年 | 37篇 |
1980年 | 46篇 |
1979年 | 61篇 |
1978年 | 48篇 |
1977年 | 50篇 |
1976年 | 37篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 17篇 |
排序方式: 共有7428条查询结果,搜索用时 0 毫秒
1.
2.
The present study was designed to evaluate the contents of different antioxidants compounds and their antioxidant activities in Jalopeno peppers (Capsicum annuum) cultivars (El Dorido, Grande, Tula, Sayula and El Rey) extracts. Free radical scavenging activity of Grande was recorded as high as 87% followed by El Dorido (83%). Results of reducing power (Fe3+ to Fe2+) showed that Grande (0.85%) and El Dorido (0.81%) fruit extract absorbance value were close to synthetic antioxidant BHT (0. 97%) obtained at100 μg/mL. The results showed that total phenolic content of El Dorido and Grande were significantly higher compared to other Jalapeno pepper. Results indicated strong and positive correlation between antioxidant activity and carotenoids content (r = 0.75), vitamin C (r = 0.78) and total capsaicinoids (r = 0.84), respectively. The results of the antioxidant activity assays showed that the El Dorido and Grande had strongest antioxidant activity compared to other peppers cultivars in this study. 相似文献
3.
Ludmila C. Fidale Sarah Köhler Martin H.G. Prechtl Thomas Heinze Omar A. El Seoud 《Cellulose (London, England)》2006,13(5):581-592
The concentrations of water, W, and electrolytes present in solutions of LiCl in N,N-dimethylacetamide, LiCl/DMAc, and of tetrabutylammonium fluoride. x-hydrate in DMSO, TBAF.xW/DMSO can be accurately and expediently determined by three independent methods, UV–vis, FTIR and EMF measurement. The first relies on the use of solvatochromic probes whose spectra are sensitive to solution composition. It is applicable to W/LiCl/DMAc solutions but not to TBAF.xW/DMSO, because the charge-transfer complex bands of the probes are suppressed by strong interactions with the latter electrolyte. Integration of νOH band of water may be employed in order to determine [W], hence [electrolyte] by weight difference. EMF measurement uses ion-selective electrodes in order to determine [electrolyte], hence [W] by weight difference. Results of the latter method were in excellent agreement with those of FTIR. The reason for the failure of Karl Fischer titration is addressed, and the relevance of the results obtained to functionalization of cellulose under homogenous solution conditions is briefly commented on. 相似文献
4.
Longlan Cui Hong Xu Ping He Keiko Sumitomo Yoshinori Yamaguchi Hongchen Gu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5285-5295
A hybrid emulsion polymerization was formulated for synthesizing Fe3O4/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)‐droplets with a diameter of 100–200 nm and styrene (St)‐droplets with a diameter of 3–4 μm, was obtained by mixing Mag‐miniemulsion and St‐macroemulsion. With extremely low surfactants concentration (?critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag‐droplets, as the result of smaller droplet size and larger surface ratio. Both water‐soluble potassium persulfate (KPS) and oil‐soluble 2,2′‐azobis(2‐isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60–200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe3O4/polystyrene latices assembled into well‐ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as‐synthesized Fe3O4/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag‐miniemulsion and St‐macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285–5295, 2007 相似文献
5.
6.
物理实验课程考核、评估体系初探 总被引:4,自引:0,他引:4
对物理实验课程考核、评估方法进行了探讨,提出了物理实验课程考核、评估体系及实施细则.重点介绍了体系中的核心部分——正规的物理实验课程考试. 相似文献
7.
8.
9.
A control volume type numerical methodology for the analysis of steady three‐dimensional rotating flows with heat transfer, in both laminar and turbulent conditions, is implemented and experimentally tested. Non‐axisymmetric momentum and heat transfer phenomena are allowed for. Turbulent transport is alternatively represented through three existing versions of the k–ε model that were adjusted to take into account the turbulence anisotropy promoted by rotation, streamline curvature and thermal buoyancy. Their relative performance is evaluated by comparison of calculated local and global heat balances with those obtained through measurements in a laboratory device. A modified version of the Lam and Bremhorst, low Reynolds number model is seen to give the best results. A preliminary analysis focused on the flow structure and the transfer of heat is reported. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
10.