全文获取类型
收费全文 | 3121篇 |
免费 | 122篇 |
国内免费 | 7篇 |
专业分类
化学 | 2574篇 |
晶体学 | 8篇 |
力学 | 47篇 |
数学 | 311篇 |
物理学 | 310篇 |
出版年
2024年 | 2篇 |
2023年 | 27篇 |
2022年 | 113篇 |
2021年 | 132篇 |
2020年 | 87篇 |
2019年 | 89篇 |
2018年 | 64篇 |
2017年 | 27篇 |
2016年 | 110篇 |
2015年 | 101篇 |
2014年 | 129篇 |
2013年 | 196篇 |
2012年 | 227篇 |
2011年 | 265篇 |
2010年 | 167篇 |
2009年 | 158篇 |
2008年 | 233篇 |
2007年 | 177篇 |
2006年 | 169篇 |
2005年 | 175篇 |
2004年 | 139篇 |
2003年 | 107篇 |
2002年 | 98篇 |
2001年 | 34篇 |
2000年 | 27篇 |
1999年 | 16篇 |
1998年 | 14篇 |
1997年 | 23篇 |
1996年 | 21篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1967年 | 1篇 |
1937年 | 1篇 |
1932年 | 1篇 |
1915年 | 1篇 |
排序方式: 共有3250条查询结果,搜索用时 15 毫秒
991.
Silvestro A. Ruffolo Mauro F. La Russa Piergiorgio Aloise Cristina M. Belfiore Andrea Macchia Antonino Pezzino Gino M. Crisci 《Applied Physics A: Materials Science & Processing》2014,114(3):753-758
Salt crystallisation process is one of the most powerful weathering agents in stone materials, especially in the coastal areas, where sea-spray transports large amount of salts on the stone surface. The consolidation of such degraded stone material represents a critical issue in the field of restoration of cultural heritage. In this paper, the nanolime consolidation behaviour in limestone degraded by salt crystallization has been assessed. For this purpose, a stone material taken from a Sicilian historical quarry and widely used in the eastern Sicilian Baroque architecture has been artificially degraded by the salt crystallization test. Then degraded samples have been treated with NanoRestore®, a suspension of nanolime in isopropyl alcohol. To evaluate the consolidating effectiveness, the peeling test and point load test were performed. Moreover, mercury intrusion porosimetry has been executed to evaluate the variations induced by treatment, while colorimetric measurements have been aimed to assess aesthetical issues. 相似文献
992.
We characterize the zero–Hopf bifurcation at the singular points of a parameter codimension four hyperchaotic Lorenz system. Using averaging theory, we find sufficient conditions so that at the bifurcation points two periodic solutions emerge and describe the stability of these orbits. 相似文献
993.
994.
H.K. Hall Jr. Kenneth ChildersTrevor Centeno-Hall Cristina ContrerasBrian Mazel Hari MenonVan Nguyen Jeffrey RobertsonRobert Bates 《Tetrahedron letters》2012,53(35):4725-4726
Seven MIRC reactions of methyl dichloroacetate with alkenes containing electron-withdrawing groups were used to make 1-chlorocyclopropanecarboxylates. 相似文献
995.
Adriana Cristina Cherri Marcos Nereu Arenales Horacio Hideki Yanasse Kelly Cristina Poldi Andréa Carla Gonçalves Vianna 《European Journal of Operational Research》2014
In this article, we review published studies that consider the solution of the one-dimensional cutting stock problem (1DCSP) with the possibility of using leftovers to meet future demands, if long enough. The one-dimensional cutting stock problem with usable leftovers (1DCSPUL) is a problem frequently encountered in practical settings but often, it is not dealt with in an explicit manner. For each work reviewed, we present the application, the mathematical model if one is proposed and comments on the computational results obtained. The approaches are organized into three classes: heuristics, item-oriented, or cutting pattern-oriented. 相似文献
996.
The asymmetric logistic peak is tested as a new function for the parametric signal fitting (PSF) of highly asymmetric electrochemical signals in non-bilinear datasets, such as those obtained in linear sweep voltammetry (LSV) or in the presence of irreversible electrochemical processes. This new multivariate curve resolution strategy (PSF-ALPA) is successfully applied to LS voltammograms measured for the Cd(II)-glutathione system with a hanging mercury drop electrode, where Cd(II) is reversibly reduced, and to differential pulse voltammograms (DPV) measured at a glassy carbon electrode, where Cd(II) reduction becomes irreversible. Matrix augmentation by using LS voltammograms measured at different scan rates provides good results and encourages the development of ALPA methodology for third order data. 相似文献
997.
Aufartová J Mahugo-Santana C Sosa-Ferrera Z Santana-Rodríguez JJ Nováková L Solich P 《Analytica chimica acta》2011,704(1-2):33-46
Residues of steroid hormones have become a cause for concern because they can affect the biological activity of non-target organisms. Steroid hormones are a potential risk for wildlife and humans through the consumption of contaminated food or water. Their determination requires extraction and clean-up steps, prior to detection, to reach low concentration levels. In recent years, a great effort has been made to develop new analytical methodologies, such as microextraction techniques, that reduce environmental pollution. Researchers have modified old methods to incorporate procedures that use less-hazardous chemicals or that use smaller amounts of them. They are able to do direct analysis using miniaturised equipment and reduced amounts of solvents and wastes. These accomplishments are the main objectives of green analytical chemistry. In this overview, we focus on microextraction techniques for the determination of steroid hormones in biological (e.g., human urine, human serum, fish, shrimp and prawn tissue and milk) and environmental (e.g., wastewaters, surface waters, tap waters, river waters, sewage sludges, marine sediments and river sediments) samples. We comment on the most recent applications in sorptive-microextraction modes, such as solid phase microextraction (SPME) with molecularly imprinted polymers (MIPs), in-tube solid-phase microextraction (IT-SPME), stir-bar sorptive extraction (SBSE) and microextraction in packed sorbent (MEPS). We also describe liquid-phase microextraction (LPME) approaches reported in the literature that are applied to the determination of steroid hormones. 相似文献
998.
Daiane Cristina Sass Vladimir Constantino Gomes Heleno Jader da Silva Barbosa Gustavo Oliveira Morais Fernando Batista Da Costa Mauricio Gomes Constantino 《Tetrahedron letters》2013,54(7):625-627
The conversion of a germacranolide structure (tagitinin C) into a furanoheliangolide one (diversifolin) was achieved by hydride conjugate addition using Stryker’s reagent. 相似文献
999.
Marina Prigol Cristina W. Nogueira Gilson Zeni Maria Rosário Bronze Luís Constantino 《Applied biochemistry and biotechnology》2013,169(3):885-893
The objective of the present study was to evaluate the physicochemical and biochemical profiling of diphenyl diselenide (PhSe)2, a selenoorganic compound with biological activity. Experimental protocols were established for chemical stability in isotonic phosphate buffer (PBS) pH 7.4 and in simulated gastric and intestinal fluids, biological stability (bovine serum albumin (BSA) and plasma), solubility in PBS pH 7.4, distribution coefficient (Log D) in octanol/PBS, and determination of free (PhSe)2 concentrations in BSA and plasma by using liquid chromatography with ultraviolet detection and tandem mass spectrometry. (PhSe)2 was found to be chemically stable and not susceptible to degradation in plasma. The aqueous solubility was 0.98?±?0.072 μM and the Log D in octanol/PBS system was found to be 3.13. The percentage of unbound fractions of (PhSe)2 obtained by equilibrium dialysis from BSA and plasma incubated with 100 μM (PhSe)2 were 0.69?±?0.12 and 0.44?±?0.09 %, respectively. The findings indicated that (PhSe)2 presents chemical and biological stability. Though, the compound showed low aqueous solubility, high Log D value and high binding to plasmatic protein. These data contribute to the knowledge of the toxicokinetic properties of (PhSe)2 and further explain its low bioavailability in experimental models. 相似文献
1000.
Dan Donescu Raluca Somoghi Catalin Ilie Spataru Doina Manaila-Maximean Denis Mihaela Panaitescu Eugeniu Vasile Cristina L. Nistor 《Colloid and polymer science》2013,291(10):2345-2358
The work describes a study for preparing polystyrene (PSt) and polymethyl methacrylate (PMMA) latex, containing magnetite (Fe3O4), covalently bounded to the polymeric chains. The magnetite was functionalized with various alkoxysilanes containing double bonds: vinyltriethoxysilane (VTES), methacryloyl propyl trimethoxysilane (MPTS) and vinyldimethylethoxysilane (VMe2TES). The ferrite-silane composite forms higher average size particles with MPTS than with VTES. Ferrite functionalized with VMe2TES forms stable latexes with both PSt and PMMA polymers. PSt forms also stable latexes with ferrite functionalized with VTES but unstable with ferrite functionalized with MPTS. 相似文献