全文获取类型
收费全文 | 3129篇 |
免费 | 142篇 |
国内免费 | 9篇 |
专业分类
化学 | 2259篇 |
晶体学 | 16篇 |
力学 | 54篇 |
数学 | 449篇 |
物理学 | 502篇 |
出版年
2023年 | 28篇 |
2022年 | 22篇 |
2021年 | 52篇 |
2020年 | 63篇 |
2019年 | 68篇 |
2018年 | 37篇 |
2017年 | 34篇 |
2016年 | 89篇 |
2015年 | 113篇 |
2014年 | 116篇 |
2013年 | 179篇 |
2012年 | 230篇 |
2011年 | 225篇 |
2010年 | 128篇 |
2009年 | 123篇 |
2008年 | 155篇 |
2007年 | 167篇 |
2006年 | 177篇 |
2005年 | 153篇 |
2004年 | 177篇 |
2003年 | 130篇 |
2002年 | 101篇 |
2001年 | 59篇 |
2000年 | 40篇 |
1999年 | 44篇 |
1998年 | 49篇 |
1997年 | 46篇 |
1996年 | 32篇 |
1995年 | 45篇 |
1994年 | 45篇 |
1993年 | 26篇 |
1992年 | 33篇 |
1991年 | 26篇 |
1990年 | 15篇 |
1989年 | 22篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 27篇 |
1978年 | 18篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1974年 | 12篇 |
1973年 | 13篇 |
排序方式: 共有3280条查询结果,搜索用时 390 毫秒
131.
132.
Harald Gröger Jens R. Goerlich Reinhard Schmutzler Jürgen Martens 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):253-259
Abstract The synthesis of a cyclic α-amino phosphine oxide and sulfide with an incorporated benzo-thiazine moiety is described. The products can be regarded as analogues of the biologically active thiazolidinylphosphonates, in which several characteristic functional groups have been modified. 相似文献
133.
Oliver Brücher Uwe Bergsträßer Harald Kelm Jens Hartung Marco Greb Ingrid Svoboda Hartmut Fuess 《Tetrahedron》2012,68(34):6968-6980
A cascade, composed of (i) oxovanadium(V)-catalyzed oxidation of bromide by tert-butyl hydroperoxide and (ii) stereoselective 6-endo-bromocyclization, affords 3-bromo-2-aryl-2,6,6-trimethyltetrahydropyrans from styrene-type tertiary alkenols in synthetically useful yields. (E)-Alkenols add the bromo- and the alkoxy substituent anti-selectively across the double bond, indicating a bromonium ion-mechanism for the ring closure. 6-endo-control of the alkenol cyclization thereby arises from the polar effect of the aryl substituent. Two methyl substituents bound to the alkene terminus are not similarly able to favor 6-endo-cyclization, because strain arising from methyl group repulsion, as the bromonium-activated π-bond and the hydroxyl oxygen approach, directs bromocyclization of tertiary prenyl-type substrates toward tetrahydrofuran formation. A hexasubstituted bromotetrahydropyran prepared from the oxidation/bromocyclization cascade served as starting material for synthesis of racemic aplysiapyranoid A, in a sequence of free radical and polar functional group interconversion. 相似文献
134.
Andrew S. Bell Joseph Bradley Jeremy R. Everett Michelle Knight Jens Loesel John Mathias David McLoughlin James Mills Robert E. Sharp Christine Williams Terence P. Wood 《Molecular diversity》2013,17(2):319-335
The screening files of many large companies, including Pfizer, have grown considerably due to internal chemistry efforts, company mergers and acquisitions, external contracted synthesis, or compound purchase schemes. In order to screen the targets of interest in a cost-effective fashion, we devised an easy-to-assemble, plate-based diversity subset (PBDS) that represents almost the entire computed chemical space of the screening file whilst comprising only a fraction of the plates in the collection. In order to create this file, we developed new design principles for the quality assessment of screening plates: the Rule of 40 (Ro40) and a plate selection process that insured excellent coverage of both library chemistry and legacy chemistry space. This paper describes the rationale, design, construction, and performance of the PBDS, that has evolved into the standard paradigm for singleton (one compound per well) high-throughput screening in Pfizer since its introduction in 2006. 相似文献
135.
Andreas Klitgaard Anita Iversen Mikael R. Andersen Thomas O. Larsen Jens Christian Frisvad Kristian Fog Nielsen 《Analytical and bioanalytical chemistry》2014,406(7):1933-1943
In natural-product drug discovery, finding new compounds is the main task, and thus fast dereplication of known compounds is essential. This is usually performed by manual liquid chromatography-ultraviolet (LC-UV) or visible light-mass spectroscopy (Vis-MS) interpretation of detected peaks, often assisted by automated identification of previously identified compounds. We used a 15 min high-performance liquid chromatography–diode array detection (UHPLC–DAD)–high-resolution MS method (electrospray ionization (ESI)+ or ESI?), followed by 10–60 s of automated data analysis for up to 3000 relevant elemental compositions. By overlaying automatically generated extracted-ion chromatograms from detected compounds on the base peak chromatogram, all major potentially novel peaks could be visualized. Peaks corresponding to compounds available as reference standards, previously identified compounds, and major contaminants from solvents, media, filters etc. were labeled to differentiate these from compounds only identified by elemental composition. This enabled fast manual evaluation of both known peaks and potential novel-compound peaks, by manual verification of: the adduct pattern, UV–Vis, retention time compared with log D, co-identified biosynthetic related compounds, and elution order. System performance, including adduct patterns, in-source fragmentation, and ion-cooler bias, was investigated on reference standards, and the overall method was used on extracts of Aspergillus carbonarius and Penicillium melanoconidium, revealing new nitrogen-containing biomarkers for both species. 相似文献
136.
137.
138.
Robert Cichon Dominik Raab Simon Hewera Andrea Lazik-Palm Jens Theysohn Stefan Landgraeber Wojciech Kowalczyk 《PAMM》2016,16(1):77-78
In recent years, femoroacetabular impingement (FAI) has become increasingly common. As published in the literature, FAI is caused by an unphysiological contact between the proximal femur and the acetabular rim, which may lead to pain, limitation of movement, and damage of cartilage. In this paper, patient-specific finite element simulations of the movement of the hip based on gait motion data and MRI segmentation were conducted to check stresses of the acetabulum and femur, and additionally whether a bony contact is present or not. The study's findings show no bony contact between femur and acetabulum, which may lead to the hypothesis that the labrum and its deformation and/or the articular capsule are involved in the mechanism of FAI. In order to verify this hypothesis more simulations including labrum and capsule must be performed. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
139.
140.
Christian K. Frese Dirk Nolting A. F. Maarten Altelaar Jens Griep-Raming Shabaz Mohammed Albert J. R. Heck 《Journal of the American Society for Mass Spectrometry》2013,24(11):1663-1670
Electron transfer dissociation (ETD) is commonly employed in ion traps utilizing rf fields that facilitate efficient electron transfer reactions. Here, we explore performing ETD in the HCD collision cell on an Orbitrap Velos instrument by applying a static DC gradient axially to the rods. This gradient enables simultaneous three dimensional, charge sign independent, trapping of cations and anions, initiating electron transfer reactions in the center of the HCD cell where oppositely charged ions clouds overlap. Here, we evaluate this mode of operation for a number of tryptic peptide populations and the top-down sequence analysis of ubiquitin. Our preliminary data show that performing ETD in the HCD cell provides similar fragmentation as ion trap-ETD but requires further optimization to match performance of ion trap-ETD. 相似文献