全文获取类型
收费全文 | 947篇 |
免费 | 35篇 |
国内免费 | 1篇 |
专业分类
化学 | 780篇 |
晶体学 | 5篇 |
力学 | 11篇 |
数学 | 51篇 |
物理学 | 136篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 36篇 |
2021年 | 42篇 |
2020年 | 29篇 |
2019年 | 37篇 |
2018年 | 16篇 |
2017年 | 27篇 |
2016年 | 37篇 |
2015年 | 34篇 |
2014年 | 38篇 |
2013年 | 46篇 |
2012年 | 80篇 |
2011年 | 85篇 |
2010年 | 40篇 |
2009年 | 35篇 |
2008年 | 51篇 |
2007年 | 69篇 |
2006年 | 51篇 |
2005年 | 44篇 |
2004年 | 26篇 |
2003年 | 25篇 |
2002年 | 29篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有983条查询结果,搜索用时 0 毫秒
81.
Fluorescence microscopy offers an important tool for the study of complex biological phenomena such as symbiosis. Here we identify a strategy that adapts the unique differences between the secondary metabolism in host and guest symbiotic species to selectively image endosymbiotic organisms. The method is demonstrated by application to the complex symbiotic relationships in toxic marine dinoflagellates. 相似文献
82.
83.
Carolina Moltó-Puigmartí Ana Isabel Castellote M. Carmen López-Sabater 《Journal of chromatography. A》2009,1216(20):4388-4394
A rapid, highly sensitive and direct Ultra-High-Pressure Liquid Chromatographic method was developed and validated for quantifying δ-, β + γ-, and α-tocopherol in human colostrum and milk. Two reversed-phase chromatographic columns and two detectors (Fluorescence Detector or FD and Photodiode Detector Array or PDA) were used and both methods were independently validated. Two internal standards were selected according to the detector used. Recoveries ranged from 96.71% to 103.55% and the relative standard deviations for the within-day precision were below 6% (PDA) and 3% (FD). Both approaches enabled to achieve low detection limits, on the order of ng (PDA) or pg (FD). Only 300 μL of sample and a chromatographic run of less than 1.6 min were enough to efficiently quantify the isomers in the colostrum and milk of Spanish women. 相似文献
84.
Chun-Sen Liu E. Carolina Sañudo Li-Fen Yan Ze Chang Jun-Jie Wang Tong-Liang Hu 《Transition Metal Chemistry》2009,34(1):51-60
Abstract To explore the influence of the anthracene ring skeleton, with a large conjugated π-system, on the structures and properties
of its complexes, two MnII complexes with anthracene-9-carboxylate ligand were synthesized and structurally characterized: {[Mn(L)2(H2O)2](H2O)}∞ (1) and [Mn2(L)4(phen)2(μ-H2O)](CH3OH) (2) (L = anthracene-9-carboxylate and phen = 1,10-phenanthroline). Complex (1) has a one-dimensional (1D) chain structure that is further assembled to form a two-dimensional (2D) sheet, and then an overall
three-dimensional (3D) network by π···π stacking and/or C–H···π interactions. Complex (2) makes a dinuclear structure by incorporating the chelating phen ligand, which is further interlinked via inter-molecular
π···π stacking and C–H···π interactions to generate a higher-dimensional supramolecular network along the different crystallographic
directions. The results reveal that the bulky anthracene ring skeleton in L, by virtue of intra- and/or inter-molecular π···π
stacking and C–H···π interactions, plays an important role in the formation of complexes (1) and (2). The magnetic properties of (1) and (2) were further investigated. As expected, the very long inter-metallic separations result in weak magnetic coupling, with
the corresponding coupling constant values of J = −10 cm−1 for (1) and J = −2.46 cm−1 for (2).
Graphical abstract The constructions of two new MnII complexes comprising 1D chain (1) and dinuclear subunit (2) structures have been successfully achieved by using a bulky anthracene-9-carboxylic acid (HL), together with incorporating
the chelating 1,10-phenanthroline as a co-ligand for (2). The result reveals that the bulky anthracene ring skeleton of HL, by virtue of intra- and/or inter-molecular π···π stacking
and C–H···π interactions, plays an important role in the formation of the supramolecular architectures of (1) and (2). Moreover, magnetic properties of the complexes have been investigated.
相似文献
85.
Hydrogenation of naphthalene on noble-metal-containing mesoporous MCM-41 aluminosilicates 总被引:2,自引:0,他引:2
S. Albertazzi R. Ganzerla C. Gobbi M. Lenarda M. Mandreoli E. Salatelli P. Savini L. Storaro A. Vaccari 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):261-270
Aromatic saturation of oil fractions is a key process in the refining industry due to increasing demand for cleanest distillates with superior performances. In this study, the behavior of different catalysts containing 1 wt.% of noble-metal inside a mesoporous MCM-41 (Si:Al=20) framework was investigated in the hydrogenation of naphthalene, as preliminary step to investigate bimetallic catalysts. While at atmospheric pressure only Rh and Pd showed a low hydrogenation activity, in the tests performed at 6.0 MPa the catalytic activity grew, exhibiting the following order: Pt>RhPd>>>Ru≈Ir. However, all the catalysts required a large H2 excess, to avoid a decrease in hydrogenation and ring-opening activity, and gave rise to the best performance for a contact time of 6.8 s, favouring at lower values the partial hydrogenation to tetralin and at higher values cracking reactions. Finally, all the catalysts showed low thio-tolerance, with significant deactivation already feeding 100 ppm wt. of dibenzothiophene (DBT), with a partial reversibility only for the Pt-containing catalyst (CAT 3). 相似文献
86.
Synthesis of axinohydantoins 总被引:1,自引:0,他引:1
A short synthesis of the hydantoin-containing marine sponge metabolites axinohydantoins is described. A key feature of the synthesis is a putative biomimetic, intramolecular cyclization of alpha-functionalized imidazolone 5, which affords the tricyclic pyrroloazepinone framework comprising 6. In addition, the conversion of imidazolones to alpha,beta-unsaturated hydantoins is outlined and represents a new approach to these heterocyclic systems. 相似文献
87.
Fernández-Rivas C Méndez M Nieto-Oberhuber C Echavarren AM 《The Journal of organic chemistry》2002,67(15):5197-5201
The intramolecular reaction of allylsilanes and allylstannanes with alkynes proceeds catalytically in the presence of Pt(II), Pd(II), Ru(II), and Au(III) chlorides. Although more limited, AgOTf also catalyzes the cyclization. Usually, PtCl2 as the catalyst in methanol or acetone gives the best results. The reaction proceeds by exo attack of the allyl nucleophile on the alkyne to form five- or six-membered ring carbocycles. The reaction generally proceeds with anti stereoselectivity. However, a terminally substituted trimethylsilyl derivative reacts by a syn-type addition. The intermediate alkenylpalladium complex has been trapped with allyl chloride to form an allylated derivative with an additional carbon-carbon bond. 相似文献
88.
Carolina Pfaff Luis Melo Paulino Betancourt 《Reaction Kinetics and Catalysis Letters》2002,77(2):263-266
Removal of nitrates from drinking water by catalytic hydrogenation over ZSM-5 supported Pt-Cu catalysts was studied. Bimetallics Pt-Cu were prepared by ion exchange of copper on a parent monometallic platinum catalyst. Monometallic platinum catalysts are inactive for nitrate reduction, while Pt-Cu bimetallic catalysts are active for nitrate removal. In the bimetallic catalyst, the role of copper is probably to reduce nitrate according to a redox reaction. The addition of copper to Pt catalysts decreases the production of ammonium ions 相似文献
89.
Carolina Pereira De Souza Margareth Spangler Andrade Bernardo Ruegger Almeida Neves 《Microscopy and microanalysis》2002,8(6):509-517
In this work, effective, yet simple, recycling mechanisms for used scanning probe microscopy (SPM) tips were implemented. Comprising a tip profile characterization methodology and specific cleaning procedures, which decontaminate SPM tips whether the contamination nature is known or not, such routes were optimized during numerous tests with brand new, previously used, and already discarded categories of SPM tips. The results show that if the used tip suffered contamination only, but no physical damages, during its scanning lifetime, it becomes readily available for reutilization after the cleansing process, characterizing a recycling route. On the other hand, if the tip went through wear and breakages during its utilization, it still can be decontaminated, but may not be directly reutilized due to its inadequate physical profile. Nevertheless, the methodology developed in this work may yet be applied as part of a more complex recycling route. 相似文献
90.
The phosphoramidate-like reaction of 1,3-dithiole derived N-(diethoxyphosphinyl)hydrazones with formyl derivatives of 1,3-dithiole affords the longest aza-analogues of extended tetrathiafulvalenes with a polyenic spacer reported to date. Their structural and electrochemical properties are discussed. 相似文献