全文获取类型
收费全文 | 4922篇 |
免费 | 230篇 |
国内免费 | 25篇 |
专业分类
化学 | 3308篇 |
晶体学 | 21篇 |
力学 | 106篇 |
数学 | 711篇 |
物理学 | 1031篇 |
出版年
2023年 | 48篇 |
2022年 | 66篇 |
2021年 | 99篇 |
2020年 | 137篇 |
2019年 | 134篇 |
2018年 | 92篇 |
2017年 | 75篇 |
2016年 | 225篇 |
2015年 | 162篇 |
2014年 | 197篇 |
2013年 | 274篇 |
2012年 | 390篇 |
2011年 | 496篇 |
2010年 | 234篇 |
2009年 | 149篇 |
2008年 | 322篇 |
2007年 | 326篇 |
2006年 | 299篇 |
2005年 | 281篇 |
2004年 | 200篇 |
2003年 | 129篇 |
2002年 | 115篇 |
2001年 | 50篇 |
2000年 | 34篇 |
1999年 | 36篇 |
1998年 | 24篇 |
1997年 | 27篇 |
1996年 | 43篇 |
1995年 | 43篇 |
1994年 | 44篇 |
1993年 | 34篇 |
1992年 | 30篇 |
1991年 | 19篇 |
1989年 | 12篇 |
1987年 | 9篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1973年 | 33篇 |
1970年 | 9篇 |
排序方式: 共有5177条查询结果,搜索用时 15 毫秒
71.
72.
O'Driscoll BM Ruggles JL Gentle IR 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6246-6251
Langmuir and Langmuir-Blodgett (LB) films of a cationic amphiphilic porphyrin mixed with n-alkanes octadecane and hexatriacontane were prepared and characterized, to examine the influence of the alkanes on film structure and stability. While the structure present in these films was controlled primarily by the porphyrin, the addition of the alkanes resulted in significant changes to both the phase behavior of the Langmuir films and the molecular arrangement of the LB films. These changes, as well as the observed chain length effects, are explained in terms of the intermolecular interactions present in the films. 相似文献
73.
74.
Shape-controlled synthesis of metal nanostructures: the case of silver 总被引:19,自引:0,他引:19
The concept of shape-controlled synthesis is discussed by investigating the growth mechanisms for silver nanocubes, nanowires, and nanospheres produced through a polymer-mediated polyol process. Experimental parameters, such as the concentration of AgNO(3) (the precursor to silver), the molar ratio between poly(vinylpyrrolidone) (PVP, the capping agent) and AgNO(3), and the strength of chemical interaction between PVP and various crystallographic planes of silver, were found to determine the crystallinity of seeds (e.g., single crystal versus decahedral multiply twinned particles). In turn, the crystallinity of a seed and the extent of the PVP coverage on the seed were both instrumental in controlling the morphology of final product. The ability to generate silver nanostructures with well-defined morphologies provides a great opportunity to experimentally and systematically study the relationship between their properties and geometric shapes. 相似文献
75.
Benjamin Scharf 《Chemical physics letters》1983,96(1):89-92
Prominent progressions of non-totally symmetric modes may ensue in non-linear molecules in electronic transitions involving degenerate states in the absence of Jahn-Teller distortions. In the presence of Jahn-Teller interactions prominent non-Jahn-Teller progressions may result. 相似文献
76.
Population balance equations (PBEs) for reversible aggregation-fragmentation processes are important to particle agglomeration and dissolution, polymerization and degradation, liquid droplet coalescence and breakup, and floc coagulation and disintegration. Moment solutions provide convenient solutions to the PBEs, including steady state and similarity solutions, but may not be feasible for complex forms of size-dependent rate coefficients and stoichiometric kernels. Numeric solutions are thus necessary not only for applications, but also for the study of the mathematics of PBEs. Here we propose a numerical method to solve PBEs and compare the results to moment solutions. The numeric results are consistent with known steady state and asymptotic long-time similarity solutions and show how processes can be approximated by self-similar formulations. 相似文献
77.
Jun Liu Kelton A. Schleyer Tyrel L. Bryan Changjian Xie Gustavo Seabra Yongmei Xu Arjun Kafle Chao Cui Ying Wang Kunlun Yin Benjamin Fetrow Paul K. P. Henderson Peter Z. Fatland Jian Liu Chenglong Li Hua Guo Lina Cui 《Chemical science》2021,12(1):239
Heparanase (HPA) is a critical enzyme involved in the remodeling of the extracellular matrix (ECM), and its elevated expression has been linked with diseases such as various types of cancer and inflammation. The detection of heparanase enzymatic activity holds tremendous value in the study of the cellular microenvironment, and search of molecular therapeutics targeting heparanase, however, no structurally defined probes are available for the detection of heparanase activity. Here we present the development of the first ultrasensitive fluorogenic small-molecule probe for heparanase enzymatic activity via tuning the electronic effect of the substrate. The probe exhibits a 756-fold fluorescence turn-on response in the presence of human heparanase, allowing one-step detection of heparanase activity in real-time with a picomolar detection limit. The high sensitivity and robustness of the probe are exemplified in a high-throughput screening assay for heparanase inhibitors.Heparanase, a critical enzyme involved in the remodeling of the extracellular matrix, activates a disaccharide probe HADP to give a strong fluorescence signal. 相似文献
78.
Antonio Fernández-Ramos Benjamin A. Ellingson Rubén Meana-Pañeda Jorge M. C. Marques Donald G. Truhlar 《Theoretical chemistry accounts》2007,118(4):813-826
This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them
to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational
symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i)
if the reaction is symmetric, (ii) if reactants and/or transition states are chiral, (iii) if the reaction has multiple conformers
for reactants and/or transition states and, (iv) if there is an internal rotation of part of the molecular system. All these
four situations are treated systematically and analyzed in detail in the present article. We also include a large number of
examples to clarify some complicated situations, and in the last section we discuss an example involving an achiral diasteroisomer. 相似文献
79.
The thermodynamics and dynamics of a model S(N)1 reaction: t-BuCl --> t-Bu+ + Cl- is studied at the water liquid/vapor interface using molecular-dynamics computer simulations. The empirical valence bond approach is used to couple two diabatic states, covalent and ionic, in the electronically adiabatic limit. Umbrella sampling calculations are used to calculate the potential of mean force along the reaction coordinate (defined as the t-Bu to Cl distance) in bulk water and in several locations at the interface. We find a significant increase of the dissociation barrier height and of the reaction free energy at the interface relative to the bulk. This is shown to be due to the reduced polarity of the interface. Reactive flux correlation function calculations show significant deviation of the rate constant from the transition-state theory: The transmission coefficients range from 0.49 in the bulk to 0.05 above the Gibbs surface. The low transmission coefficient at the interface despite the lower friction is shown to be due to slow vibrational relaxation. 相似文献
80.
Judit Sipos Benjamin Podnyi Istvn Hermecz Levente Pusztay Gbor Tth Lszl Szilgyi 《Journal of heterocyclic chemistry》1989,26(4):1061-1068
Ethyl 4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylates 1–4 , their piperidine ring homologues 5–6 and their 2-oxo isomers 7–9 were reacted with benzaldehyde. At low temperature, kinetically stable addition products were formed. Thermodynamically stable condensation products were obtained at higher temperature, which were also formed when the addition products were refluxed in benzene. The 9-benzyl derivatives were prepared by the hydrogenation of the condensation products over Pd/C. The stereochemical features of the new compounds were determined via 1H and 13C nmr chemical shift and coupling constant analysis and NOE measurements. 相似文献