全文获取类型
收费全文 | 3013篇 |
免费 | 265篇 |
国内免费 | 191篇 |
专业分类
化学 | 2079篇 |
晶体学 | 6篇 |
力学 | 208篇 |
综合类 | 72篇 |
数学 | 254篇 |
物理学 | 850篇 |
出版年
2024年 | 4篇 |
2023年 | 46篇 |
2022年 | 136篇 |
2021年 | 140篇 |
2020年 | 127篇 |
2019年 | 97篇 |
2018年 | 80篇 |
2017年 | 161篇 |
2016年 | 203篇 |
2015年 | 169篇 |
2014年 | 164篇 |
2013年 | 276篇 |
2012年 | 169篇 |
2011年 | 150篇 |
2010年 | 155篇 |
2009年 | 114篇 |
2008年 | 138篇 |
2007年 | 149篇 |
2006年 | 169篇 |
2005年 | 107篇 |
2004年 | 112篇 |
2003年 | 94篇 |
2002年 | 92篇 |
2001年 | 43篇 |
2000年 | 51篇 |
1999年 | 47篇 |
1998年 | 39篇 |
1997年 | 37篇 |
1996年 | 41篇 |
1995年 | 24篇 |
1994年 | 32篇 |
1993年 | 18篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有3469条查询结果,搜索用时 62 毫秒
71.
72.
The dynamics of gel isoelectric focusing were studied by using amphoteric low-molecular-mass colored substances (isoelectric point markers). The polyacrylamide gel in slab format was in direct contact with the electrodes. In addition to isoelectric focusing with a pH gradient composed of synthetic carrier ampholytes, pH gradients created by simple buffers of acetic acid, 2-(N-morpholino)ethanesulfonic acid, histidine and N,N,N',N'-tetramethylethylenediamine were applied. The progress of the electrofocusing process was monitored by a charge-coupled device camera and video recording. The gradient profile and dynamics were approximated from the positions of isoelectric point markers, which were focused both on boundaries between individual zones of simple buffers and within the zones themselves. The obtained animated records enabled the observation of the entire real focusing run within fractions of a minute, which is useful both for the understanding and optimization of the focusing. 相似文献
73.
Summary Ten heterocyclic aromatic amines (HAA) (1)–(10) were analyzed in commercially available meat products and fish. After sample preparation by Extrelut treatment and subsequent
solid phase extraction applying propylsulphonic and C18 silica cartridges, HPLC-ESI-MS-MS using selected reaction monitoring (SRM) and d3-PhIP and d3-MeIQx as internal and external standards, respectively, revealed the widely distributed presence of PhIP (8) and MeIQx (4), ranging from 0.1 to 5.3 ng g−1 and 0.1 to 5.2 ng g−1, respectively. Lower amounts were found for 4,8-DiMeIQx (5) and 7,8-DiMeIQx (6), ranging from 0.2 to 2.0 ng g−1 and 0.1 to 0.2 ng g−1, respectively. The other HAA under study, i.e. IQ, MeIQ, 4,7,8-TriMeIQx, Glu-P-1, and Glu-P-2 were not determinable under
the experimental conditions used (determination limit 0.1 ng g−1). 相似文献
74.
75.
A simple optical method for quantitative comparison of the effectiveness of epoxy cure accelerators, used for speeding up the crosslinking process of epoxy resins with cyclic anhydrides, is described. Fluorescent molecular probes and a miniature fiber optic spectrometer have been applied for measurement of the cure kinetics of a model epoxy resin/anhydride composition in the presence of various cure accelerators. A quantitative index of accelerator performance has been determined for several of the most common accelerators. 相似文献
76.
Dr. Mahnaz Najafi Dr. Sara Abednatanzi Abbas Yousefi Prof. Mehrorang Ghaedi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(72):17999-18014
Photocatalysis has been known as one of the promising technologies due to its eco-friendly nature. However, the potential application of many photocatalysts is limited owing to their large bandgaps and inefficient use of the solar spectrum. One strategy to overcome this problem is to combine the advantages of heteroatom-containing supports with active metal centers to accurately adjust the structural parameters. Metal nanoparticles (MNPs) and single atom catalysts (SACs) are excellent candidates due to their distinctive coordination environment which enhances photocatalytic activity. Metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and carbon nitride (g-C3N4) have shown great potential as catalyst support for SACs and MNPs. The numerous combinations of organic linkers with various heteroatoms and metal ions provide unique structural characteristics to achieve advanced materials. This review describes the recent advancement of the modified MOFs, COFs and g-C3N4 with SACs and NPs for enhanced photocatalytic applications with emphasis on environmental remediation. 相似文献
77.
Abstract The various methods for determining the mode of occurrence of trace metals in sediments and soils have a long history which dates back to the determinations of the availability of metals for plant nutrition performed earlier. Various methods have been developed in the 70′s and 80′s dealing with both single and sequential extraction schemes. Although some schemes received wide acceptance, none of them developed into a commonly accepted procedure. As a result, the information obtained was site-specific and the interpretation of the results scientist-specific. The workshop on single and sequential extraction in sediments and soils held at Sitges 相似文献
78.
G. A. Eiceman A. P. Snyder D. A. Blyth 《International journal of environmental analytical chemistry》2013,93(3):415-425
Abstract Automated, continuous monitoring of organic vapors in air under three field designs for plume drift was demonstrated using a hand-held ion mobility spectrometer (IMS) in characterizing IMS behavior as a point sensor. In one field study, the IMS was placed 50cm from a 9m2 grass plot contaminated with methylsalicylate and response to airborne vapors was recorded during a 13hr period of atmospheric turbulence to illustrate susceptibility of point sensors to wind direction. A similar study under near-quiescent atmospheric conditions was made using dimethylsulfoxide. In a third study, the plume from a point source of dipropyleneglycolmonomethylether was interrogated over a 25m × 12m grid downwind with windspeeds of 6–18km h?. Laboratory studies were used to measure instrumental response times and influences from potentially interfering atmospheric organic pollutants. 相似文献
79.
Sébastien Gagné 《Biomedical chromatography : BMC》2013,27(5):664-668
A novel method for the biological monitoring of benzene‐exposed workers has been developed through ultra‐performance liquid chromatography coupled to tandem mass spectrometry. The method uses trans,trans‐muconic acid in urine as the benzene‐exposure biomarker. The method was developed using a triple quadrupole mass spectrometer with enough sensitivity to facilitate diluting and injecting the urine samples directly, rather than performing a solid‐phase extraction procedure as is common in the available protocols. Moreover, compared with a conventional high‐pressure liquid chromatography system, the separation power provided by the ultra‐performance liquid chromatography system allows a 10‐fold reduction in run time. The method was adjusted to a dynamic range of between 198.9 and 4916.7 µg/L to cover the biological exposure index of trans,trans‐muconic acid in urine. Also, the method demonstrated intra‐day and inter‐day precision at 98%, and accuracy within an acceptable range of 101 ± 8%. The method has been used to quantify various types of urine samples, such as workers' urine and inter‐laboratory proficiency tests. Depending on the sample, the quantified levels ranged from less than the limit of quantitation to 3836.7 µg/L. No levels exceeding the calibration range were detected in the urine of workers, and the reported concentrations in urine for the proficiency tests were, as expected, based on known values. Moreover, the new method using sample dilution and faster chromatographic run was more effective, facilitating fast communication of results, as needed, to decision‐makers. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
80.
F. Deyhimi F. Mermoud F. O. Gülaçlar A. Buchs 《International journal of environmental analytical chemistry》2013,93(1-2):75-85
Abstract The use of classical urea inclusion techniques for the separation of straight chain hydrocarbons from branched and cyclic compounds is satisfactory when applied to mixtures in the milligram to gram ranges, but leads to low separation efficiencies when quantities in the microgram to milligram range are involved. In this study, a modified inclusion technique using an urea-packed milli-bore column and a catalytic eluent is described. Examples of its use for the separation of mixtures of linear and cyclic hydrocarbons from 30μg up to a few milligrams are given. The versatility of this technique for the analyses of low amounts of environmental samples is described, and an application to the hydrocarbon fraction of surface sediment from lake Leman (Switzerland) is presented. 相似文献