全文获取类型
收费全文 | 3950篇 |
免费 | 159篇 |
国内免费 | 30篇 |
专业分类
化学 | 2486篇 |
晶体学 | 17篇 |
力学 | 117篇 |
数学 | 867篇 |
物理学 | 652篇 |
出版年
2023年 | 37篇 |
2022年 | 79篇 |
2021年 | 93篇 |
2020年 | 73篇 |
2019年 | 86篇 |
2018年 | 67篇 |
2017年 | 81篇 |
2016年 | 154篇 |
2015年 | 115篇 |
2014年 | 134篇 |
2013年 | 229篇 |
2012年 | 280篇 |
2011年 | 317篇 |
2010年 | 189篇 |
2009年 | 198篇 |
2008年 | 269篇 |
2007年 | 245篇 |
2006年 | 225篇 |
2005年 | 185篇 |
2004年 | 185篇 |
2003年 | 111篇 |
2002年 | 120篇 |
2001年 | 56篇 |
2000年 | 62篇 |
1999年 | 38篇 |
1998年 | 39篇 |
1997年 | 32篇 |
1996年 | 44篇 |
1995年 | 22篇 |
1994年 | 25篇 |
1993年 | 22篇 |
1992年 | 32篇 |
1991年 | 21篇 |
1990年 | 30篇 |
1989年 | 13篇 |
1988年 | 22篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 23篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1974年 | 7篇 |
1971年 | 6篇 |
1963年 | 5篇 |
排序方式: 共有4139条查询结果,搜索用时 15 毫秒
951.
Laure Laffont Laurence Maurice David Amouroux Patricia Navarro Mathilde Monperrus Jeroen E. Sonke Philippe Behra 《Analytical and bioanalytical chemistry》2013,405(9):3001-3010
We optimized a mercury (Hg) speciation extraction method for human hair in combination with species-specific isotope-dilution analysis by gas chromatography–inductively coupled plasma–mass spectrometry (GC–ICP–MS). The method was validated on human hair reference material RM (IAEA-086), which is recommended for analysis of monomethylmercury (MMHg) and inorganic mercury (IHg). Three reagents, hydrochloric acid (HCl), nitric acid (HNO3), and tetramethylammonium hydroxide (TMAH), and three extraction procedures, at ambient temperature for 12 h, microwave-assisted at 75 °C for 6 min, and oven heated at 80 °C for 2 h were tested. Extraction efficiency, recovery, and potential species transformations were evaluated for each method. The most efficient procedures, with recovery of ~90 % for each species with limited demethylation (<5 %) and methylation (0 %), were HNO3 digestion, irrespective of temperature, and microwave-assisted TMAH extraction. Acidic extraction with HCl induces significant demethylation, with production of artifacts. To correct for potential demethylation artifacts we recommend spiking with isotopically enriched standards before the extraction step. 相似文献
952.
953.
Alfonso Castro Jorge Cossio Carlos Vélez 《Annali di Matematica Pura ed Applicata》2013,192(4):607-619
In this paper, we establish sufficient conditions for an asymptotically linear elliptic boundary value problem to have at least seven solutions. We use the mountain pass theorem, Lyapunov–Schmidt reduction arguments, existence of solutions that change sign exactly once, and bifurcation properties. No symmetry is assumed on the domain or the non-linearity. 相似文献
954.
The Diels-Alder reactivity of 1,2-heteroborines (H4C4B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed. 相似文献
955.
Kieran Griffiths Dr. Christopher W. D. Gallop Dr. Alaa Abdul‐Sada Dr. Alfredo Vargas Dr. Oscar Navarro Dr. George E. Kostakis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6358-6361
Three isoskeletal tetranuclear coordination clusters with general formula [MII2DyIII2L4(EtOH)6](ClO4)2?2 EtOH, (M=Co, 1 ; M=Ni, 2 ) and [NiII2DyIII2L4Cl2(CH3CN)2]?2 CH3CN ( 3 ), have been synthesized and characterized. These air‐stable compounds, and in particular 3 , display efficient homogeneous catalytic behavior in the room‐temperature synthesis of trans‐4,5‐diaminocyclopent‐2‐enones from 2‐furaldehyde and primary or secondary amines under a non‐inert atmosphere. 相似文献
956.
957.
958.
Maria Navarro‐Pascual‐Ahuir Maria J. Lerma‐García Guillermo Ramis‐Ramos Ernesto F. Simó‐Alfonso José M. Herrero‐Martínez 《Electrophoresis》2013,34(6):925-934
In this article, capillary columns constituted by lauryl methacrylate monoliths with embedded silver nanoparticles (AgNPs) were developed and tested. Two incorporation approaches of AgNPs in monoliths were explored. The AgNPs were either photogenerated in situ during polymerization of the monolith by UV irradiation, or incorporated to the polymerization mixture (ex situ). The influence of the AgNP concentration on the morphological and chromatographic properties of the polymer matrix was investigated, and both the in situ and ex situ approaches were comparatively discussed. The morphology of the monoliths was characterized by electron microscopic techniques, and their electrochromatographic performance was also evaluated with test mixtures of neutral compounds (sterols, fatty acid methyl esters, tocopherols, and polyaromatic hydrocarbons). 相似文献
959.