全文获取类型
收费全文 | 2060篇 |
免费 | 136篇 |
国内免费 | 11篇 |
专业分类
化学 | 1346篇 |
晶体学 | 8篇 |
力学 | 45篇 |
数学 | 112篇 |
物理学 | 221篇 |
无线电 | 475篇 |
出版年
2024年 | 3篇 |
2023年 | 15篇 |
2022年 | 24篇 |
2021年 | 49篇 |
2020年 | 60篇 |
2019年 | 58篇 |
2018年 | 21篇 |
2017年 | 40篇 |
2016年 | 100篇 |
2015年 | 71篇 |
2014年 | 114篇 |
2013年 | 156篇 |
2012年 | 166篇 |
2011年 | 179篇 |
2010年 | 98篇 |
2009年 | 101篇 |
2008年 | 149篇 |
2007年 | 123篇 |
2006年 | 96篇 |
2005年 | 95篇 |
2004年 | 78篇 |
2003年 | 80篇 |
2002年 | 93篇 |
2001年 | 27篇 |
2000年 | 33篇 |
1999年 | 25篇 |
1998年 | 19篇 |
1997年 | 21篇 |
1996年 | 19篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1974年 | 3篇 |
1971年 | 4篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有2207条查询结果,搜索用时 9 毫秒
91.
Yoon Yeol Yoon Kil Yong Lee Kyung Seok Ko 《Journal of Radioanalytical and Nuclear Chemistry》2010,284(3):591-595
The contents of H-3 and C-14 in groundwater and surface waters around low and medium-level atomic waste repository site in Korea were determined. The concentrations of C-14 were in the range 0.186–0.287 Bq/L. The H-3 concentration of the groundwaters and surface waters were <0.06–5.75 and 1.22–4.74 Bq/L. The average H-3 contents of west, north and south direction were 1.18 ± 0.12, 1.11 ± 0.78 and 2.85 ± 2.66. H-3 and C-14 concentrations in the south direction were relatively higher than west and north direction samples. The surface waters sampled from catchment were four times higher than average H-3 concentration in precipitation. The concentrations of H-3 and C-14 within 5 km area samples were much higher than other samples. 相似文献
92.
A rapid, specific and sensitive multiresidue method based on dispersive solid phase extraction sample preparation and gas chromatography with the mass spectrometric detection for the analysis of 234 pesticides in Korean herbs (Acanthopanax senticosus, Morus alba L., Hovenia dulcis) has been developed. Method recoveries were found to be between 62 and 119% with relative standard deviation lower than 21% for all compounds in the concentration range of 0.05 to 0.400 mg kg? 1. Limits of quantification of most compounds are below 0.050 mg kg? 1. The data demonstrate that this method was successfully used for analysis of 234 pesticides in Korean herbs. 相似文献
93.
A simple reversed‐phase high performance liquid chromatography (RP‐HPLC) method was developed to determine the level of caffeine and theophylline in human plasma samples. The sample clean‐up step involved the on‐line solid‐phase extraction (SPE) of the analytes from plasma samples into a weak cation monolithic column using a column switching system. Separation was performed on a C18 column (5 µm, 150 mm×4.6 mm) with ultraviolet detection at 274 nm. The mobile phase consisted of methanol‐water (32/68, V/V) under isocratic conditions at a flow rate of 0.6 mL·min−1. The measured concentration of caffeine and theophylline showed a good linear relationship over the concentrations range, 0.1–80.0 µg·mL−1. The absolute recoveries ranged from 77.10% to 85.39%, and the inter‐day and intra‐day relative standard deviations (RSD) were all less than 5%. This method avoids a tedious pretreatment and provides an economic, repeatable and effective method for assaying trace drugs in biological samples. 相似文献
94.
Shin A Kang D Choi JY Lee KM Park SK Noh DY Ahn SH Yoo KY 《Experimental & molecular medicine》2007,39(3):361-366
Cytochrome P450 1A1 (CYP1A1) is involved in the 2-hydroxylation of estrogen, the hormone that plays a critical role in the etiology of breast carcinoma. We evaluated the associations between two CYP1A1 polymorphisms [MspI (rs4646903); Ile462Val (rs1048943)] and breast cancer in a multicenter case-control study of 513 breast cancer cases and 447 controls in Korea. Women carrying the T allele of the CYP1A1 MspI polymorphism were found to have a 1.72-fold (95% CI 1.11-2.68) greater risk of developing breast cancer. No association was found between any CYP1A1 Ile462Val polymorphism and breast cancer. Haplotype analysis of the two loci showed that the CA haplotype was associated with the lowest risk of breast cancer, and CA/CA diplotypes were associated with a lower risk of breast cancer [OR=0.28 (0.13-0.61)] than others/others diplotypes. Moreover, this reduced risk was more pronounced among women with a lower body mass index (BMI) [OR=0.18 (0.06-0.58)] or with a shorter lifetime exposure to estrogen [OR=0.23 (0.07-0.81)]. The results obtained suggest that the CYP1A1 MspI polymorphisms could affect susceptibility to breast cancer. 相似文献
95.
A Conductive Hybridization Matrix of RuO2 Two‐Dimensional Nanosheets: A Hybrid‐Type Photocatalyst 下载免费PDF全文
Jang Mee Lee Eun Kyung Mok Seul Lee Dr. Nam‐Suk Lee Dr. Lamjed Debbichi Prof. Hyungjun Kim Prof. Seong‐Ju Hwang 《Angewandte Chemie (International ed. in English)》2016,55(30):8546-8550
A universal methodology to efficiently improve the photocatalyst performance of semiconductors was developed by employing exfoliated RuO2 two‐dimensional nanosheets as a conducting hybridization matrix. The hybridization with a RuO2 nanosheet is easily achieved by crystal growth or electrostatically derived anchoring of semiconductor nanocrystals on the RuO2 nanosheet. An enhanced chemical interaction of inorganic semiconductor with hydrophilic RuO2 nanosheet is fairly effective in optimizing their photocatalytic activity and photostability by the enhancement of charge separation and charge mobility. The RuO2‐containing nanohybrids show much better photocatalyst functionalities than do the graphene‐containing ones. The present study clearly demonstrates that hydrophilic RuO2 nanosheets are superior hybridization matrices, over the widely used hydrophobic graphene nanosheets, for exploring new efficient hybrid‐type photocatalysts. 相似文献
96.
Jikun Li Xinxin Feng Wei Zhu Nikita Oskolkov Tianhui Zhou Boo Kyung Kim Noman Baig Prof. Michael T. McMahon Prof. Eric Oldfield 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(1):264-271
Diamagnetic chemical exchange saturation transfer (CEST) contrast agents offer an alternative to Gd3+‐based contrast agents for MRI. They are characterized by containing protons that can rapidly exchange with water and it is advantageous to have these protons resonate in a spectral window that is far removed from water. Herein, we report the first results of DFT calculations of the 1H nuclear magnetic shieldings in 41 CEST agents, finding that the experimental shifts can be well predicted (R2=0.882). We tested a subset of compounds with the best MRI properties for toxicity and for activity as uncouplers, then obtained mice kidney CEST MRI images for three of the most promising leads finding 16 (2,4‐dihydroxybenzoic acid) to be one of the most promising CEST MRI contrast agents to date. Overall, the results are of interest since they show that 1H NMR shifts for CEST agents—charged species—can be well predicted, and that several leads have low toxicity and yield good in vivo MR images. 相似文献
97.
Cost‐Effective,High‐Performance Porous‐Organic‐Polymer Conductors Functionalized with Sulfonic Acid Groups by Direct Postsynthetic Substitution 下载免费PDF全文
Dong Won Kang Kwang Soo Lim Kyung Jin Lee Jong Hyeon Lee Dr. Woo Ram Lee Jeong Hwa Song Kyu Hyun Yeom Dr. Jin Young Kim Prof. Chang Seop Hong 《Angewandte Chemie (International ed. in English)》2016,55(52):16123-16126
We demonstrate the facile microwave‐assisted synthesis of a porous organic framework 1 and the sulfonated solid ( 1S ) through postsubstitution. Remarkably, the conductivity of 1S showed an approximately 300‐fold enhancement at 30 °C as compared to that of 1 , and reached 7.72×10?2 S cm?1 at 80 °C and 90 % relative humidity. The superprotonic conductivity exceeds that observed for any conductive porous organic polymer reported to date. This material, which is cost‐effective and scalable for mass production, also revealed long‐term performance over more than 3 months without conductivity decay. 相似文献
98.
Benkoski JJ Bowles SE Korth BD Jones RL Douglas JF Karim A Pyun J 《Journal of the American Chemical Society》2007,129(19):6291-6297
The assembly and direct imaging of ferromagnetic nanoparticles into one-dimensional mesostructures (1-D) are reported. Polymer-coated ferromagnetic colloids (19 nm, 24 nm) were assembled at a crosslinkable oil-water interface under both magnetic field induced and zero-field conditions and permanently fixed into 1-D mesoscopic polymer chains (1-9 mum) in a process referred to as Fossilized Liquid Assembly (FLA). In the FLA process, nanoparticle chains were fixed at the oil interface through photopolymerization, enabling direct visualization of organized mesostructures using atomic force microscopy. Using the FLA methodology, we systematically investigated different conditions and demonstrated that dispersed ferromagnetic colloids possess sufficient dipolar interactions to organize into mesoscopic assemblies. Application of an external magnetic field during assembly enabled the formation of micron-sized chains which were aligned in the direction of the applied field. This universal methodology is an attractive alternative technique to cryogenic transmission electron microscopy (cryo-TEM) for the visualization of nanoparticle assembly in dispersed organic media. 相似文献
99.
Lee WG Bang H Yun H Lee J Park J Kim JK Chung S Cho K Chung C Han DC Chang JK 《Lab on a chip》2007,7(4):516-519
This paper presents a novel method for an on-chip erythrocyte deformability test under optical pressure, especially to enhance the level of sensitivity with respect to the detection of cancerous diseases. To demonstrate the performance and sensitivity of the combined method, we introduce the concept of transit velocity, a modified elongation index, and shape recovery time of individual erythrocytes in a strictly confined region (2 microm deep, 4 microm wide, and 100 microm long). Finally, we investigate a synergy or convergence effect due to the combination of these parameters for in situ detection of cancerous diseases under optical pressure. 相似文献
100.
The rate constant hydrolysis of α-(p-nitrophenyl)cinnamonitrile(NCPN) and its derivatives have been determined at various pH, and the rate equation which can
be applied over a wide pH range is obtained. On the basis of the rate equation, hydrolysis product, general base, and substituent
effects, a plausible mechanism of hydrolysis has been proposed: At pH < 4.0, the hydrolysis was initiated by the addition
of water to β-carbon of the carbon-carbon double bond. At pH > 8.5, the addition of hydroxide ion to the double bond was rate
controlling. In the range of pH 4.0–8.5, these two reactions occurred competitively.
Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 5, pp. 670–676.
This article was submitted by the authors in English. 相似文献