全文获取类型
收费全文 | 1377篇 |
免费 | 49篇 |
国内免费 | 8篇 |
专业分类
化学 | 1016篇 |
晶体学 | 34篇 |
力学 | 28篇 |
数学 | 69篇 |
物理学 | 287篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 22篇 |
2021年 | 22篇 |
2020年 | 42篇 |
2019年 | 47篇 |
2018年 | 32篇 |
2017年 | 42篇 |
2016年 | 66篇 |
2015年 | 40篇 |
2014年 | 97篇 |
2013年 | 108篇 |
2012年 | 106篇 |
2011年 | 140篇 |
2010年 | 67篇 |
2009年 | 78篇 |
2008年 | 96篇 |
2007年 | 88篇 |
2006年 | 63篇 |
2005年 | 45篇 |
2004年 | 50篇 |
2003年 | 50篇 |
2002年 | 38篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1434条查询结果,搜索用时 171 毫秒
991.
We report a spectroscopic and microscopic investigation of the synthesis of gold nanoparticles (AuNPs) with average sizes of less than 5 nm. The slow reduction and AuNP formation processes that occur by using 9-borabicyclo[3.3.1]nonane (9-BBN) as a reducing agent enabled a time-dependent investigation based on standard UV-vis spectroscopy and transmission electron microscopy (TEM) analyses. This is in contrast to other borohydride-based syntheses of thiolate monolayer protected AuNPs which form particles very rapidly. We investigated the formation of 1-octadecanethiol (ODT) protected AuNPs with average diameters of 1.5-4.3 nm. By studying the progression of nanoparticle formation over time, we find that the nucleation rate and the growth time, which are interlinked with the amount of ODT and the temperature, influence the size and the size dispersion of the AuNPs. High-resolution TEM (HRTEM) analyses also suggest that the nanoparticles are highly single crystalline throughout the synthesis and appear to be formed by a diffusion-controlled Ostwald-ripening growth mechanism. 相似文献
992.
The effect of poly (acrylic acid) (PAA) adsorption on the electrokinetic behavior of alumina dispersions under high pH conditions was investigated as a function of polymer concentration and molecular weight as well as the presence, concentration and ion type of background electrolyte. Systems of this type are relevant to nuclear waste treatment, in which PAA is known to be an effective rheology modifier. The presence of all but the lowest molecular weight PAA studied (1800) led to decreases in dynamic electrophoretic mobility at low polymer concentrations, attributable to bridging flocculation, as verified by measurements of particle size distribution. Bridging effects increased with polymer molecular weight, and decreased with polymer concentration. Increases in background electrolyte concentration enhanced dynamic electrophoretic mobility as the polymer layers were compressed and bridging was reduced. Such enhancements were reduced as the cation was changed from K(+) to Na(+) to Cs(+). 相似文献
993.
A novel method for the synthesis of a bile acid-based macrocycle has been developed using click chemistry. The 1,2,3-triazolium derivative of the macrocycle shows remarkable selectivity in binding of chloride ion. 相似文献
994.
Rajesh Chakraborty Pabitra Chattopadhyay 《Journal of Radioanalytical and Nuclear Chemistry》2012,294(1):31-35
A new inorganic material, sodium titaniumsilicate has been synthesized, and characterized by physicochemical and spectroscopic tools. The thermal and radiation stability of the compound was checked by TGA technique and a ??-irradiating chamber with a total dose rate of 5?kGy/h. The compound is highly stable towards thermal, chemical and total radiation dose of 64?kGy. The study of the exchange capacity of the material towards different alkali and alkaline earth metal ions showed that the sorption capacities of the alkali metal ions were greater than those of alkaline earth metal ions. The crystalline state of this new inorganic material is very useful as an inorganic ion exchanger to have the carrier free short-lived ??-active daughter product 90Y from the long-lived 90Sr of the radioactive equilibrium mixture. The absorbed daughter was recovered by using 1.0% EDTA solutions at pH 7.0 as eluting agent. The features and trends in elution are encouraging to apply this material as an exchanger in radionuclide generator system. 相似文献
995.
Rajesh H. Panchal D. D. Rao Bipin H. Mehta A. Baburajan Ravindra H. Gaikwad 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(1):401-409
The paper deals with the transfer factors (TF) generated for a few varieties of leafy vegetables (spinach, fenugreek, and
amaranths) consumed by the locals around Tarapur atomic power station environment in India. The soil and leafy vegetable samples
collected from the ambient environment of nuclear site were used for the determination of the TFs and they were compared with
TFs generated from pot experiments under controlled conditions for 137Cs. The activity of 137Cs in soil and each vegetable was determined by gamma spectrometry using HPGe detector (35 and 160% relative efficiency) and
was reported on dry weight basis for both ambient environment and pot samples. The radioactive effluent containing 137Cs (pH ~7) from nuclear power station was used to spike the soil for pot (size 90 cm × 45 cm × 42 cm) experiment. The TFs
obtained for ambient environment and pot experiment were found to be in the range of 0.035–0.592 and 0.0054–0.29, respectively.
It is observed that TFs of ambient environment are in good agreement with those obtained in the pot experiment conducted under
controlled conditions. Further, the observed TF values at Tarapur nuclear site are comparable with the range of typical IAEA
transfer factor values for general leafy vegetation (0.11–2.9) for tropical environment. 相似文献
996.
Rajesh G. Kalkhambkar G. Aridoss Geeta M. Kulkarni R. M. Bapset J. C. Kadakol N. Premkumar Yeon Tae Jeong 《Monatshefte für Chemie / Chemical Monthly》2012,21(9):1075-1086
Abstract
A series of new acrylic acid ethyl esters of quinolinones were synthesized from 4-(bromomethyl)quinolinones and screened for in vitro antimicrobial and in vivo analgesic and anti-inflammatory activities. Most of the compounds with chloro substitution at the C-6 or C-7 position in the quinolinone moiety and a methoxy group in the aryloxy moiety showed potent antibacterial and antifungal activities when compared with non-halogenated quinolinones and the quinolinones bearing a CH3 at the C-8 position. In a pharmacological evaluation, the halogen substitution at the C-6 or C-7 position in quinolinones was found to enhance both analgesic and anti-inflammatory activities of the molecule when compared with a simple unsubstituted (non-halogenated) quinolinone. The structures of all newly synthesized compounds were characterized by elemental analysis, IR, 1H NMR, 13C NMR, and FAB-MS. 相似文献997.
A single, simple and selective method for simultaneous estimation of amiloride and hydrochlorothiazide in human plasma was validated using triamterine and hydrochlorothiazide13C,d2 as internal standard. The compounds were separated on a reverse‐phase column with an isocratic mobile phase consisting of 2 mm ammonium acetate pH 3.0 and acetonitrile (30:70, v/v) and detected by tandem mass spectrometry with positive/negative ion mode. The analytes and internal standards were extracted from plasma using simple solid phase extraction. The ion transitions recorded in multiple reaction monitoring mode were m/z 230.1 → 116.0 for amiloride, m/z 254.1 → 237.1 for internal standard, triamterine in positive mode and m/z 296.1 → 204.9 for hydrochlorothiazide, m/z 299.2 → 205.8 for internal standard, hydrochlorothiazide13C,d2 in negative ion mode. Linearity in plasma was observed over the concentration range 0.1–10 ng/mL for amiloride and 5.0–500.0 ng/mL for hydrochlorothiazide. The mean recovery was 41.1 and 81.5% for amiloride and hydrochlorothiazide respectively. The coefficient of variation of the assay was less than 11.2 and 5.2% for amiloride and hydrochlorothiazide, respectively, and the accuracy was 89.0–98.1 and 96.6–102.9% for amiloride and hydrochlorothiazide, respectively. The validated method can be applied to the pharmacokinetic study of amiloride and hydrochlorothiazide. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
998.
Machhindra Gund S. Mohana Roopan Fazlur-Rahman Nawaz Khan Jong Sung Jin Rajesh Kumar A. Sudheer Kumar 《Research on Chemical Intermediates》2012,38(3-5):1111-1118
An efficient and regioselective O-alkylation of amides with a variety of electrophiles in the presence of silver nanoparticles is reported as part of our recent research on building blocks for synthesis of natural products. The nano-silver catalyst initiates O-alkylation of the amides by heteroalkyl halides. Reaction of equimolar 3-acetyl-6-chloro-4-phenylquinolin-2(1H)-one and 2-chloro-3-(chloromethyl)quinolines in the presence of silver nanoparticles in DMSO solution under reflux condition leads to the formation of 1-{1-[2-chloroquinolin-3-yl)methoxy]-6-chloro-4-phenylquinolin-3-yl}ethanones. 相似文献
999.
A new synthetic route to prepare a series of versatile 2,7-substituted pyrene synthons for the synthesis of pyrene-fused azaacenes is described. By using such synthons, a library of eight pyrene-fused azacenes with different electronic structures and in most cases with enhanced solubility has been synthesized and characterized. 相似文献
1000.
Swaroop PS Raut GN Gonnade RG Verma P Gokhale RS Reddy DS 《Organic & biomolecular chemistry》2012,10(28):5385-5394
First synthesis of diaportheone B, an antituberculosis agent isolated from endophytic fungus Diaporthe sp. P133 is reported using two complementary routes, a one step and a three-step sequence. The absolute configuration of diaportheone B was determined by using X-ray crystal structure analysis of its dibromo derivative. In addition, we have prepared several close analogues of diaportheone B and determined their anti-TB potential using Alamar-blue assay (H(37)Rv). 相似文献