全文获取类型
收费全文 | 998篇 |
免费 | 29篇 |
国内免费 | 8篇 |
专业分类
化学 | 491篇 |
晶体学 | 18篇 |
力学 | 29篇 |
数学 | 143篇 |
物理学 | 354篇 |
出版年
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 16篇 |
2014年 | 24篇 |
2013年 | 60篇 |
2012年 | 33篇 |
2011年 | 48篇 |
2010年 | 16篇 |
2009年 | 22篇 |
2008年 | 39篇 |
2007年 | 43篇 |
2006年 | 44篇 |
2005年 | 48篇 |
2004年 | 29篇 |
2003年 | 30篇 |
2002年 | 31篇 |
2001年 | 26篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 22篇 |
1995年 | 13篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 24篇 |
1988年 | 15篇 |
1987年 | 18篇 |
1986年 | 8篇 |
1985年 | 28篇 |
1984年 | 19篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 19篇 |
1978年 | 18篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1969年 | 8篇 |
排序方式: 共有1035条查询结果,搜索用时 15 毫秒
91.
P. Meunier C. Blancpain F. R. Olson D. M. Hegstedt W. H. Peterson D. W. Bolin A. M. Khalapur A. Fujita T. Ebihara und Fr. Folkmann 《Fresenius' Journal of Analytical Chemistry》1942,124(1-2):68-69
Ohne Zusammenfassung 相似文献
92.
Evaluation of toluene LIF thermometry detection strategies applied in an internal combustion engine 总被引:1,自引:0,他引:1
Brian Peterson Elias Baum Benjamin Böhm Volker Sick Andreas Dreizler 《Applied physics. B, Lasers and optics》2014,117(1):151-175
In the context of toluene laser-induced fluorescence (LIF) thermometry, the two common LIF detection strategies, namely one-color and two-color detection, have been simultaneously applied to compare each strategy’s ability to accurately resolve thermal gradients during an engine cycle within an optically accessible internal combustion (IC) engine. Temperature images are obtained from high-speed toluene LIF measurements and are combined with high-speed particle image velocimetry. The combination with flow data and Mie scattering images facilitates the interpretation of differences between the toluene LIF detection strategies. Two-color temperature images are limited in their ability to detect thermal gradients near the end of compression due to larger precision uncertainties. Local regions of cold gases in the two-color images are better identified with the guidance of the one-color images when homogeneous toluene mixtures preside. During expansion, large differences exist between one- and two-color temperature images and likely caused by local mixture fraction heterogeneities that bias the one-color detection strategy. Toluene condensation occurs during the expansion and exhaust stroke and causes local mixture fraction heterogeneities in the combustion chamber. Liquid toluene is in contact with solid surfaces and crevices of the combustion chamber and can evaporate during compression or expansion causing both local temperature and mixture stratification. This work demonstrates the advantage of high-speed imaging and use of multiple image diagnostics to reveal the development of natural temperature and mixture stratification in a motored IC engine. This work also suggests that natural temperature stratification typically regarded from gas-wall heat transfer may also be caused by liquid droplet evaporation on solid surfaces. Such phenomenon, however, is expected to be pertinent for all modern-day engine operating systems. 相似文献
93.
94.
95.
96.
Paulo A. Machicao Scott R. Burt Ryan K. Christensen Nathan B. Lohner J.D. Singleton Matt A. Peterson 《Tetrahedron letters》2017,58(24):2318-2321
Treatment of N-[(4-hydroxy-6-phenyl)pyrimidin-2-yl]cyanamide with 1° alkyl or arylamines in isopropyl alcohol for only 10 min at 110–120 °C under microwave conditions gave the corresponding N′-alkyl(aryl)guanidine derivatives in excellent yields (65–84%). Isolated yields were greatest when >1.0 equiv. of amines were employed, but excellent results were also obtained when aryl and alkylamines were reacted with a more atom-economical loading (1.0 equiv.; 70% and 72% ave. yields, respectively). Arylamines with either highly electron withdrawing substituents (e.g. CO2H) or pi-deficient heterocycles (e.g. variously substituted aminopyridines) did not work well under these conditions, and reaction with ureas and/or amino acids did not give detectable products. Work-up was exceedingly simple, and involved simple collection and washing of product on a sintered glass funnel. Products were obtained in analytically pure form and required approximately 1 h to prepare, start to finish. 相似文献
97.
This work demonstrated for the first time that myoglobin cross‐linked in polylysine films is electrochemically active at 6 °C. At 6 °C, these protein films exhibited reversible reduction/oxidation peaks which are characteristic of FeIII/FeII redox couple. The estimated current function densities (J=1.6×10?4 C/V cm2), surface concentrations (ΓT=0.10 nmol/cm2) and standard electron transfer constant (ks=13.86 s?1) at 6 °C for the data taken at a scan rate of 0.1 V/s were similar to those which were obtained at 10, 15 and 23 °C. Basically, this study shows a possible electrocatalytic application of these myoglobin/polylysine films, for example in low temperature sensing applications. 相似文献
98.
Gordon J. Thorogood Brendan J. Kennedy Vanessa K. Peterson Vittorio Luca 《Journal of Physics and Chemistry of Solids》2011,72(6):692-700
The structure of the defect pyrochlore NaW2O6+δ·nH2−zO after ion exchange with K, Rb, Sr or Cs for Na has been investigated using thermal analysis, solid-state nuclear magnetic resonance, laboratory X-ray and neutron diffraction methods. Neutron diffraction studies show that both the A-type cations (Na+, K+, Rb+, and/or Cs+) and the water molecules reside within the channels that form in the 111 direction of the W2O6 framework and that these strongly interact. The analytical results suggest that the water and A-type cations compete for space in the tunnels within the W2O6 pyrochlore framework, with the total number of water molecules and cations being approximately constant in the six samples investigated. The interplay between the cations and water explains the non-linear dependence of the a lattice parameter on the choice of cation. It appears that the ion-exchange capacity of the material will be controlled by the amount of water initially present in the sample. 相似文献
99.
S.D. Gopal Ram G. Ravi MR. Manikandan T. Mahalingam M. Anbu Kulandainathan 《Superlattices and Microstructures》2011,50(4):296-302
In the present work, a controlled growth of ZnO nanostructures by manipulating Zn metal ion concentration by the chelating action of ethylene diaminetetra acetic acid in hydrothermal method is studied. EDTA produces metal–chelate complex by the formation of bidentate ligand with Zn2+ in the solution and diminishes the reactivity of Zn metal cations. Concentration of EDTA in the mother solution was varied in different ranges like 3, 5 and 10 mM while retaining the zinc metal salt and the NaOH concentration the same. Three different morphologies of wurtzite structured ZnO nanostructures such as nanorods-bunch, separate/discrete uniformly sized hexagonal nanorods and tapered flower petals like shapes are achieved by 3, 5 and 10 mM strengths of EDTA, respectively. The medium concentration 5 mM of EDTA is found to have moderate control over producing ZnO nanostructures of uniform diameter and a high aspect (length to diameter) ratio. An array of vertically aligned free standing ZnO nanorods with uniform spacing is successfully achieved by the addition of 5 mM of EDTA in the mother solution and the same is studied for its fluorescence property at an excitation of 325 nm and it has exhibited a characteristic UV emission of ZnO around 383 nm. 相似文献
100.
William J. Durand Andrew A. Peterson Felix Studt Frank Abild-Pedersen Jens K. Nørskov 《Surface science》2011,605(15-16):1354-1359
Polycrystalline copper electrocatalysts have been experimentally shown to be capable of reducing CO2 into CH4 and C2H4 with relatively high selectivity, and a mechanism has recently been proposed for this reduction on the fcc(211) surface of copper, which was assumed to be the most active facet. In the current work, we use computational methods to explore the effects of the nanostructure of the copper surface and compare the effects of the fcc(111), fcc(100) and fcc(211) facets of copper on the energetics of the electroreduction of CO2. The calculations performed in this study generally show that the intermediates in CO2 reduction are most stabilized by the (211) facet, followed by the (100) facet, with the (111) surface binding the adsorbates most weakly. This leads to the prediction that the (211) facet is the most active surface among the three in producing CH4 from CO2, as well as the by-products H2 and CO. HCOOH production may be mildly enhanced on the more close-packed surfaces ((111) and (100)) as compared to the (211) facet, due to a change in mechanism from a carboxyl intermediate to a formate intermediate. The results are compared to published experimental data on these same surfaces; the predicted trends in voltage requirements are consistent between the experimental and computational data. 相似文献