全文获取类型
收费全文 | 959篇 |
免费 | 14篇 |
国内免费 | 8篇 |
专业分类
化学 | 503篇 |
晶体学 | 9篇 |
力学 | 27篇 |
数学 | 118篇 |
物理学 | 196篇 |
无线电 | 128篇 |
出版年
2021年 | 11篇 |
2018年 | 9篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 44篇 |
2011年 | 46篇 |
2010年 | 21篇 |
2009年 | 24篇 |
2008年 | 45篇 |
2007年 | 52篇 |
2006年 | 53篇 |
2005年 | 33篇 |
2004年 | 37篇 |
2003年 | 24篇 |
2002年 | 23篇 |
2001年 | 32篇 |
2000年 | 23篇 |
1999年 | 14篇 |
1998年 | 7篇 |
1997年 | 25篇 |
1996年 | 21篇 |
1995年 | 13篇 |
1994年 | 21篇 |
1993年 | 18篇 |
1992年 | 13篇 |
1991年 | 21篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 16篇 |
1975年 | 11篇 |
1974年 | 15篇 |
1973年 | 7篇 |
1972年 | 8篇 |
1971年 | 6篇 |
1970年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有981条查询结果,搜索用时 296 毫秒
71.
The Kawasaki identity (KI) and the Jarzynski equality (JE) are important nonequilibrium relations. Both of these relations take the form of an ensemble average of an exponential function and can exhibit convergence problems when the average of the exponent differs greatly from the log of the average of the exponential function. In this work, we re-express these relations so that only selected regions need to be evaluated in an attempt to avoid these convergence issues. In the context of measuring free energies, we compare our method to the JE and the literature standard approach, the maximum likelihood estimator (MLE), and show that in a system with asymmetric work distributions it can perform as well as the MLE. For the KI, we derive an analog to the MLE to compare with our relation and show that these two new relations improve on the KI and are complimentary to each other. 相似文献
72.
Benjamin M. Gray Andrew L. Hector William Levason Gillian Reid Michael Webster Wenjian Zhang Marek Jura 《Polyhedron》2010
The reaction of o-C6H4(AsMe2)2 with VCl4 in anhydrous CCl4 produces orange eight-coordinate [VCl4{o-C6H4(AsMe2)2}2], whilst in CH2Cl2 the product is the brown, six-coordinate [VCl4{o-C6H4(AsMe2)2}]. In dilute CH2Cl2 solution slow decomposition occurs to form the VIII complex [V2Cl6{o-C6H4(AsMe2)2}2]. Six-coordination is also found in [VCl4{MeC(CH2AsMe2)3}] and [VCl4{Et3As)2]. Hydrolysis of these complexes occurs readily to form vanadyl (VO2+) species, pure samples of which are obtained by reaction of [VOCl2(thf)2(H2O)] with the arsines to form green [VOCl2{o-C6H4(AsMe2)2}], [VOCl2{MeC(CH2AsMe2)3}(H2O)] and [VOCl2(Et3As)2]. Green [VOCl2(o-C6H4(PMe2)2}] is formed from [VOCl2(thf)2(H2O)] and the ligand. The [VOCl2{o-C6H4(PMe2)2}] decomposes in thf solution open to air to form the diphosphine dioxide complex [VO{o-C6H4(P(O)Me2)2}2(H2O)]Cl2, but in contrast, the products formed from similar treatment of [VCl4{o-C6H4(AsMe2)2}x] or [VOCl2{o-C6H4(AsMe2)2}] contain the novel arsenic(V) cation [o-C6H4(AsMe2Cl)(μ-O)(AsMe2)]+. X-ray crystal structures are reported for [V2Cl6{o-C6H4(AsMe2)2}2], [VO(H2O){o-C6H4(P(O)Me2)2}2]Cl2, [o-C6H4(AsMe2Cl)(μ-O)(AsMe2)]Cl·[VO(H2O)3Cl2] and powder neutron diffraction data for [VCl4{o-C6H4(AsMe2)2}2]. 相似文献
73.
Syed R. Haider Helen J. Reid Barry L. Sharp 《Analytical and bioanalytical chemistry》2010,397(2):655-664
This study describes a modification to tricine sodium dodecyl sulphate polyacrylamide gel electrophoresis to make it more
effective for the separation of low molecular mass proteins and for coupling with inductively coupled plasma mass spectrometry
(ICP-MS). The modified method employs low-percentage polyacrylamide gels (7–10%) (w/v) and low reagent concentrations that
provide efficient separations, good quantitation and low matrix levels that are compatible with ICP-MS. Using phosphopeptides
as a model system, and offline analysis, we obtained recoveries of 73% (w/v) in a 9% gel compared with 55% in a conventional
16% gel. Online coupling was achieved by modification of a standard commercially available gel electroelution apparatus and
casting of the gel into a 7.3-cm-long tube. Online separation of a digest of β-casein was demonstrated with recovery of the
mono- and tetraphosphopeptides, which were identified by comparison with peptide standards. A mass balance study with the
standards yielded recoveries of 95% for tetraphosphopeptides and 48% for monophosphopeptides. The factors affecting the separations
and recoveries are discussed in detail. The detection limits for 10-μL samples of the mono- and tetraphosphopeptides were
0.7 μM (7 pmol) and 0.2 μM (2 pmol) respectively. 相似文献
74.
Xiao Zhou Yali Lu Wenjing Wang Babak Borhan Gavin E. Reid 《Journal of the American Society for Mass Spectrometry》2010,21(8):1339-1351
Protein surface accessible residues play an important role in protein folding, protein-protein interactions and protein-ligand
binding. However, a common problem associated with the use of selective chemical labeling methods for mapping protein solvent
accessible residues is that when a complicated peptide mixture resulting from a large protein or protein complex is analyzed,
the modified peptides may be difficult to identify and characterize amongst the largely unmodified peptide population (i.e.,
the ‘needle in a haystack’ problem). To address this challenge, we describe here the development of a strategy involving the
synthesis and application of a novel ‘fixed charge’ sulfonium ion containing lysine-specific protein modification reagent,
S,S′-dimethylthiobutanoylhydroxysuccinimide ester (DMBNHS), coupled with capillary HPLC-ESI-MS, automated CID-MS/MS, and data-dependant
neutral loss mode MS3 in an ion trap mass spectrometer, to map the surface accessible lysine residues in a small model protein, cellular retinoic
acid binding protein II (CRABP II). After reaction with different reagent:protein ratios and digestion with Glu-C, modified
peptides are selectively identified and the number of modifications within each peptide are determined by CID-MS/MS, via the
exclusive neutral loss(es) of dimethylsulfide, independently of the amino acid composition and precursor ion charge state
(i.e., proton mobility) of the peptide. The observation of these characteristic neutral losses are then used to automatically
‘trigger’ the acquisition of an MS3 spectrum to allow the peptide sequence and the site(s) of modification to be characterized. Using this approach, the experimentally
determined relative solvent accessibilities of the lysine residues were found to show good agreement with the known solution
structure of CRABP II. 相似文献
75.
We present here a study of the phase behavior of mixed component NaNO(3)-Na(2)SO(4) (SNS) droplets with NaNO(3) to Na(2)SO(4) molar ratios of 1:1, 3:1, and 10:1, comparing observations with thermodynamic predictions. Measurements are made by Fourier transform infrared attenuated total reflection and micro-Raman spectroscopy for SNS droplets deposited on ZnSe and quartz substrates, respectively. The conventional deliquescence/efflorescence hysteresis in phase behavior is observed. On drying, heterogeneous crystallization leads to phase behavior that is consistent with bulk solution thermodynamics, with the formation of the mixed salt NaNO(3)·Na(2)SO(4)·H(2)O, Na(2)SO(4) (s), and NaNO(3) (s) all observed to form at relative humidities that coincide with predictions by the aerosol inorganics model. However, conditioning of the droplet at high relative humidity prior to drying is observed to lead to quantitative differences between the fractions of different salts formed. When substrate effects do not influence the crystallization process, supersaturated solutions are formed, and this leads to the observation of contact ion pairs. Such measurements of the phase behavior of mixed component droplets are important for testing the reliability of thermodynamic models. 相似文献
76.
Blanchard F Golde D Su FH Razzari L Sharma G Morandotti R Ozaki T Reid M Kira M Koch SW Hegmann FA 《Physical review letters》2011,107(10):107401
The anisotropic effective mass of energetic electrons in an isotropic, nonparabolic conduction band is revealed using ultrafast THz-pump-THz-probe techniques in a n-doped InGaAs semiconductor thin film. A microscopic theory is applied to identify the origin of the observed anisotropy and to show that the self-consistent light-matter coupling contributes significantly to the THz response. 相似文献
77.
78.
In a previous paper the authors, together with Balwant Singh, introduced an elementwisc characterization of weak subintegrality for an extension A?B of commutative rings. In the present paper we improve our methods for working with this characterization. This leads us to propose two new types of “elementary weakly subintegral extension”. 相似文献
79.
We describe an algorithm based on principal-component generalized projections that is capable of unambiguous retrieval of the amplitude and phase of an ultrashort pulse from a measurement of its sonogram. Running on a personal computer, the algorithm can complete more than 50 iterations per second which enables real-time display of an ultrashort pulse intensity and phase profile. Retrieval is demonstrated for a range of pulses with commonly encountered phase errors including linear chirp, self-phase modulation, and cubic spectral phase, and experimental results illustrate good agreement between the retrieved pulse characteristics and independent spectral measurements 相似文献
80.
A mechanically programmable optical fibre lattice pulse code generator, implemented in a quasi-monolithic, splice-free polished coupler technology, has been designed, constructed and characterised. The prototype system permits the generation of reconfigurable four bit pulse sequences with a pulse repetition rate of 2 GHz, i.e. 500 ps interval within the pulses in the output train.<> 相似文献