全文获取类型
收费全文 | 933篇 |
免费 | 26篇 |
国内免费 | 1篇 |
专业分类
化学 | 633篇 |
晶体学 | 6篇 |
力学 | 10篇 |
数学 | 123篇 |
物理学 | 188篇 |
出版年
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 14篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 21篇 |
2015年 | 20篇 |
2014年 | 16篇 |
2013年 | 38篇 |
2012年 | 48篇 |
2011年 | 58篇 |
2010年 | 34篇 |
2009年 | 28篇 |
2008年 | 55篇 |
2007年 | 53篇 |
2006年 | 57篇 |
2005年 | 68篇 |
2004年 | 45篇 |
2003年 | 36篇 |
2002年 | 40篇 |
2001年 | 19篇 |
2000年 | 9篇 |
1999年 | 13篇 |
1998年 | 15篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 8篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1970年 | 6篇 |
排序方式: 共有960条查询结果,搜索用时 93 毫秒
101.
The apparent molar volumes of equimolar concentrations of 18-crown-6-ether (CE) or dibenzo-18-crown-6-ether (B2CE) and MCl (M=Na, K, or Cs) or MI in dilute solutions of anhydrous methanol, acetonitrile and dimethylsulfoxide have been calculated from density data measured at 25°C. After extrapolation to infinite dilution these results together with the apparent molar volumes of the crown ethers and the alkali metal halides were used to calculate the limiting partial molar volume change for the formation of the complexes. By noting that the charge of the complexed cation has been shown to be completely shielded from the solvent, the volume of complexation can be assumed to be a good estimation of the volume change due to electrostriction of the solvent by the cationic charge. The results are compared to the predictions of the Hepler equation.Presented at the Symposium on Electrochemistry and Spectroscopy of Solutions, Honoring Johannes Coetzee, University of Pittsburgh, November 30, 1989.On leave from Rhodes University, Grahamstown, South Africa. 相似文献
102.
Back Cover: CH Activation Generates Period‐Shortening Molecules That Target Cryptochrome in the Mammalian Circadian Clock (Angew. Chem. Int. Ed. 24/2015) 下载免费PDF全文
Tsuyoshi Oshima Dr. Iori Yamanaka Dr. Anupriya Kumar Dr. Junichiro Yamaguchi Dr. Taeko Nishiwaki‐Ohkawa Kei Muto Rika Kawamura Dr. Tsuyoshi Hirota Prof. Dr. Kazuhiro Yagita Prof. Dr. Stephan Irle Prof. Dr. Steve A. Kay Prof. Dr. Takashi Yoshimura Prof. Dr. Kenichiro Itami 《Angewandte Chemie (International ed. in English)》2015,54(24):7200-7200
103.
104.
A cyber-physical system (CPS) is a coupled system integrating computing, networking, and physical processes. Through actuation, cyber-physical systems control the physical processes, usually with feedback loops, where the physical processes affect computing and networking processes, and vice versa. In civil engineering, the most common fields of CPS applications are structural health monitoring (SHM) and structural control. A typical CPS task is the assessment of a structure based on (i) collected measurement data and (ii) a corresponding model. However, for an accurate and precise assessment of a structure, the CPS itself must be modeled and evaluated. In this paper, a conceptual modeling and evaluation approach is proposed, in which each part of a CPS is evaluated individually. In this study, the conceptual approach is presented for modeling and evaluation of CPS in civil engineering. The evaluation is based on an abstract approach allowing a discussion of a principle (i.e. general) model structure of a CPS, identifying critical issues to be studied in more detail in future research. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
105.
This paper proposes a method to improve the reliability of construction schedules by optimizing schedule robustness of construction projects. The schedule robustness is measured by a criterion evaluating the impact of deviations from the initial schedule on the makespan, which arise during the realization phase of a construction project. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
106.
107.
Hamacher K 《Journal of computational chemistry》2011,32(5):810-815
Understanding the stability of the native state and the dynamics of a protein is of great importance for all areas of biomolecular design. The efficient estimation of the influence of individual contacts between amino acids in a protein structure is a first step in the reengineering of a particular protein for technological or pharmacological purposes. At the same time, the functional annotation of molecular evolution can be facilitated by such insight. Here, we use a recently suggested, information theoretical measure in biomolecular design - the Kullback-Leibler-divergence - to quantify and therefore rank residue-residue contacts within proteins according to their overall contribution to the molecular mechanics. We implement this protocol on the basis of a reduced molecular model, which allows us to use a well-known lemma of linear algebra to speed up the computation. The increase in computational performance is around 10(1)- to 10(4)-fold. We applied the method to two proteins to illustrate the protocol and its results. We found that our method can reliably identify key residues in the molecular mechanics and the protein fold in comparison to well-known properties in the serine protease inhibitor. We found significant correlations to experimental results, e.g., dissociation constants and Φ values. 相似文献
108.
Precise dipolar coupling constant distribution analysis in proton multiple-quantum NMR of elastomers
Chassé W López Valentín J Genesky GD Cohen C Saalwächter K 《The Journal of chemical physics》2011,134(4):044907
In this work we present an improved approach for the analysis of (1)H double-quantum nuclear magnetic resonance build-up data, mainly for the determination of residual dipolar coupling constants and distributions thereof in polymer gels and elastomers, yielding information on crosslink density and potential spatial inhomogeneities. We introduce a new generic build-up function, for use as component fitting function in linear superpositions, or as kernel function in fast Tikhonov regularization (ftikreg). As opposed to the previously used inverted Gaussian build-up function based on a second-moment approximation, this method yields faithful coupling constant distributions, as limitations on the fitting limit are now lifted. A robust method for the proper estimation of the error parameter used for the regularization is established, and the approach is demonstrated for different inhomogeneous elastomers with coupling constant distributions. 相似文献
109.
Cyclocarbonylation of α-methylene butyrolactone-containing allene-ynes affords 6,12-guaianolide ring systems. Incorporation of the α-methylene butyrolactone early in a synthetic sequence is rare for reactivity reasons; however, this moiety proves to be beneficial to the allenic Pauson-Khand reaction. The three double bonds and the ketone in the resulting 5-7-5 ring system bear significant differences in their reactivity and are ideally positioned for synthetic application to 6,12-guaianolides and analogs. 相似文献
110.
Swirl-stabilised combustion is one of the most widely used techniques for flame stabilisation, uses ranging from gas turbine
combustors to pulverised coal-fired power stations. In gas turbines, lean premixed systems are of especial importance, giving
the ability to produce low NOx systems coupled with wide stability limits. The common element is the swirl burner, which depends
on the generation of an aerodynamically formed central recirculation zone (CRZ) and which serves to recycle heat and active
chemical species to the root of the flame as well as providing low-velocity regions where the flame speed can match the local
flow velocity. Enhanced mixing in and around the CRZ is another beneficial feature. The structure of the CRZ and hence that
of the associated flames, stabilisation and mixing processes have shown to be extremely complex, three-dimensional and time
dependent. The characteristics of the CRZ depend very strongly on the level of swirl (swirl number), burner configuration,
type of flow expansion, Reynolds number (i.e. flowrate) and equivalence ratio. Although numerical methods have had some success
when compared to experimental results, the models still have difficulties at medium to high swirl levels, with complex geometries
and varied equivalence ratios. This study thus focuses on experimental results obtained to characterise the CRZ formed under
varied combustion conditions with different geometries and some variation of swirl number in a generic swirl burner. CRZ behaviour
has similarities to the equivalent isothermal state, but is strongly dependent on equivalence ratio, with interesting effects
occurring with a high-velocity fuel injector. Partial premixing and combustion cause more substantive changes to the CRZ than
pure diffusive combustion. 相似文献