全文获取类型
收费全文 | 1243篇 |
免费 | 27篇 |
国内免费 | 8篇 |
专业分类
化学 | 898篇 |
晶体学 | 3篇 |
力学 | 26篇 |
数学 | 178篇 |
物理学 | 173篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 21篇 |
2020年 | 23篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 40篇 |
2015年 | 40篇 |
2014年 | 27篇 |
2013年 | 59篇 |
2012年 | 88篇 |
2011年 | 87篇 |
2010年 | 60篇 |
2009年 | 58篇 |
2008年 | 80篇 |
2007年 | 77篇 |
2006年 | 79篇 |
2005年 | 67篇 |
2004年 | 69篇 |
2003年 | 50篇 |
2002年 | 42篇 |
2001年 | 32篇 |
2000年 | 37篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 18篇 |
1995年 | 12篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有1278条查询结果,搜索用时 0 毫秒
61.
Alvaro M Corma A Das D Fornés V García H 《Chemical communications (Cambridge, England)》2004,(8):956-957
Preparation of hybrid organic-inorganic MCM-41 and SBA-15 silicas functionalized with perfluoroalkylsulfonic acid groups has been achieved in a single step by reacting the mesoporous silicas with 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethane sulfonic acid beta-sultone; the catalysts showed higher activity than commercial Nafion-silica composite for the esterification of long chain fatty acids with ethanol. 相似文献
62.
Brenno Santos Leite Melissa Tatiana Andreuccetti Sibele Augusta Ferreira Leite José Vicente Hallak d’Angelo 《Journal of Thermal Analysis and Calorimetry》2013,112(3):1539-1544
As a consequence of the continuous increase in the production rate of pulp and paper mills around the world, a great quantity of black liquor, a by-product of the wood digestion process, is produced. This by-product has a great potential as biomass, but needs to be concentrated to higher solids content to be burned as fuel in a recovery boiler. This is necessary to make the pulping process economically feasible, incinerating black liquor to produce high pressure steam, recycling inorganic chemicals to the process. The greater the solids content in black liquor, the better the combustion process in the boiler. Nevertheless, concentration of solids in black liquor above 75 mass/%, causes scaling formation on the heat transfer surfaces of evaporators and concentrators, due to the precipitation of sodium salts, reducing the overall efficiency of this equipment. The aim of this work is to evaluate the use of thermal analyses techniques, TG and DSC, as alternative methods to estimate solids content in eucalyptus black liquor samples since this information is essential to understand scaling formation process, allowing actions to reduce this industrial problem. Traditional techniques applied to determine solids content use gravimetric methods, which are simple, fine, but take a lot of time to be executed. Thermal analyses have proved to be very accurate and have the advantage to be faster than the traditional techniques. On the other hand, the cost-benefit relationship of the traditional technique is much greater and the final decision which one should be used depends on the conditions available. 相似文献
63.
64.
Alkyl substituted chromium Fischer carbene complexes react with 1,1-diphenylallene in the presence of rhodium(I) catalysts (10 mol%) to yield highly substituted dienyl indenone derivatives. In this process a catalytic chromium(0)-rhodium(I) exchange occurs, four new C-C bonds are created, and four-components (two allenes, the carbene ligand and one CO ligand) are joined in a chemo- and regioselective manner. 相似文献
65.
José Vicente Prof. Dr. José‐Antonio Abad Dr. María‐José López‐Sáez Dr. Peter G. Jones Prof. Dr. Delia Bautista Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(2):661-676
Complexes [Pd(C6H3XH‐2‐R′‐5)Y(N^N)] (X=O, NH; Y=Br, I; R′=H, NO2; N^N=N,N,N′,N′‐tetramethylethylenediamine (tmeda), 2,2′‐bipyridine (bpy), 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine (dtbbpy)) react with RN?C?E (E=NR, S) or RC≡N (R=alkyl, aryl, NR′′2) and TlOTf (OTf=CF3SO3) to give, respectively, 1) products of the insertion of the C?E group into the C? Pd bond, protonation of the N atom, and coordination of X to Pd, [Pd{κ2‐X,E‐(XC6H3{EC(NHR)}‐2‐R′‐4)}(N^N)]OTf or [Pd(κ2‐X,N‐{ZC6H3(NH?CR)‐2‐R′‐4})(N^N)]OTf, or products of the coordination of carbodiimides and OH addition, [Pd{κ2‐C,N‐(C6H4{OC(NR)}NHR‐2)}(bpy)]OTf; or 2) products of the insertion of the C≡N group to Pd and N‐protonation, [Pd(κ2‐X,N‐{XC6H3(NH?CR)‐2‐R′‐4})(N^N)]OTf. 相似文献
66.
67.
Marthyna P. Souza Miguel A. Cerqueira Bartolomeu W. S. Souza José A. Teixeira Ana L. F. Porto António A. Vicente Maria G. Carneiro-da-Cunha 《Chemical Papers》2010,64(4):475-481
Policaju-based coatings were applied on “Tommy Atkins” mangoes and the effects of four different treatments on mango shelf-life were evaluated under storage condition at 4°C and 82 % of relative humidity over 28 days. The surface tension of mangoes was found to be 29.04 mN m−1; the dispersive and polar components were 27.57 mN m−1 and 1.47 mN m−1, respectively, and the critical surface tension was 22.7 mN m−1. A significantly lower mass loss was observed in all mangoes treated with Policaju-based coatings. For all applied treatments, no significant variation in the total soluble solids and pH was detected over the experimental storage time. The results show that Policaju-based coatings have a positive effect on the shelf-life extension of mangoes at low storage temperatures (4°C). 相似文献
68.
69.
Raquel Múrtula M. Adela Yáñez Elena Soria Vicente Catalán 《Accreditation and quality assurance》2010,15(4):217-221
The standard methodology used for the detection of bacteria in environmental samples and food is primarily based on bacterial growth on specific culture media and confirmation by biochemical and/or immunological tests of all presumptive colonies. However, this methodology presents a number of drawbacks, such as low sensitivity and specificity, and the long time needed to obtain results. For this reason, the implementation of molecular methods in diagnostic laboratories has increased over the past several years. Nevertheless, most of these newer methods have not been included in current legislation, and, in most of cases, they have not yet been normalized. In this sense, the availability of appropriate reference materials (RMs) can help to overcome these deficiencies. The aim of this study was to develop and validate, following ISO Guide 34, a new RM, in a tablet format, for the quantification of Legionella pneumophila and Salmonella spp. by quantitative PCR (qPCR). This new RM can be used as a work reference sample in internal quality control, in the organization of proficiency testing schemes (PTS), as well as for the validation of molecular methods based on qPCR. 相似文献
70.
Mateos E Cebolla VL Membrado L Piera E Caballero MA 《Journal of chromatographic science》2007,45(8):524-530
Gel permeation chromatography with differential refractometry is used to obtain molecular weight distributions (MWD) of poly-(epsilon-caprolactams). Elution is carried out using an m-cresolchlorobenzene mixture (50:50, v/v) at 50 degrees C. MW values are obtained by a Hamielec-based calibration method, using broad-MWD poly-(epsilon-caprolactam) standards with the same chemical nature and similar MWD to the samples. Relative errors for the number-average MW (Mn) using this calibration method range from 0.4% (in the low polyamide MW range) to 20% (in the high polyamide MW range). These values are much lower than those obtained from narrow-MWD polystyrene calibration, which range from 39% to 78%. Similar values have been obtained for the other usual average MW parameters. The ability to obtain repeatability parameters for a given confidence interval and the utilization of statistical criteria for chromatogram rejection allow this method to be used in quality control for MWD of poly-(epsilon-caprolactams). Thus, production variables are related to polyamide-6 behavior in its ulterior treatment. Typical relative standard deviation percentages (for n=6) of a polyamide sample range from 1.9% (for Mn) to 3.3% (for M(z+1)). 相似文献