全文获取类型
收费全文 | 1733篇 |
免费 | 80篇 |
国内免费 | 3篇 |
专业分类
化学 | 1104篇 |
晶体学 | 11篇 |
力学 | 59篇 |
数学 | 133篇 |
物理学 | 509篇 |
出版年
2023年 | 22篇 |
2022年 | 27篇 |
2021年 | 58篇 |
2020年 | 57篇 |
2019年 | 44篇 |
2018年 | 41篇 |
2017年 | 30篇 |
2016年 | 66篇 |
2015年 | 40篇 |
2014年 | 84篇 |
2013年 | 109篇 |
2012年 | 103篇 |
2011年 | 140篇 |
2010年 | 94篇 |
2009年 | 85篇 |
2008年 | 113篇 |
2007年 | 68篇 |
2006年 | 67篇 |
2005年 | 78篇 |
2004年 | 45篇 |
2003年 | 38篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 23篇 |
1999年 | 23篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 18篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有1816条查询结果,搜索用时 31 毫秒
1.
2.
Tanja Vidaković-Koch Tamara Miličić Luka A. Živković Hoon Seng Chan Ulrike Krewer Menka Petkovska 《Current Opinion in Electrochemistry》2021
The nonlinear frequency response analysis (NFRA) can be seen as an extension of electrochemical impedance spectroscopy. NFRA gives a full and detailed representation of the system response and can establish a connection between model parameters and the experimentally observed phenomena. In this article, different theoretical NFRA approaches and the most recent application examples are discussed. A simple electrochemical example is used to showcase the benefits and disadvantages of analyzing the system response by using different approaches. In addition, it was shown how to extract experimental harmonic values and analyze them. 相似文献
3.
K. Dasgupta P. Barat A. Sarkar P. Mukherjee D. Sathiyamoorthy 《Applied Physics A: Materials Science & Processing》2007,87(4):721-726
The use of graphite as a moderator in a low temperature thermal nuclear reactor is restricted due to accumulation of energy
caused by displacement of atoms by neutrons and high energetic particles. Thermal transients may lead to a release of stored
energy that may raise the temperature of the fuel clad above the design limit. Disordered carbon is thought to be an alternative
choice for this purpose. Two types of disordered carbon composites, namely, CB (made up of 15 wt. % carbon black dispersed
in carbonized phenolic resin) and PAN (made up of 20 vol. % chopped polyacrylonitrile carbon fibre dispersed in carbonized
phenolic resin matrix) have been irradiated with 145 MeV Ne6+ ions at three fluence levels of 1.0×1013, 5.0×1013 and 1.5×1014 Ne6+/cm2, respectively. The XRD patterns revealed that both the samples remained disordered even after irradiation. The maximum release
of stored energy for CB was 212 J/g and that of PAN was 906 J/g. For CB, the release of stored energy was a first order reaction
with activation energy of 2.79 eV and a frequency factor of 3.72×1028 per second. 13% of the defects got annealed by heating up to 700 °C. PAN showed a third-order release rate with activation
energy of 1.69 eV and a frequency factor of 1.77×1014 per second. 56% of the total defects got annealed by heating it up to 700 °C. CB seems to be the better choice than PAN as
it showed less energy release with a slower rate.
PACS 61.80.Jh; 61.80.-x; 61.43Er; 61.43.-j; 68.43.Vx 相似文献
4.
The study of the angular distribution of slow particles during high energy hadron-nucleus interaction indicates that emission of slow particles takes place from a thermally non-equilibrated system. This evidence has come out from the presence of intermittency - a phenomenon that reveals a fractal structure and represents a self-similarity in the particle production process. Hence, this study highlights inadequacy of cascade-evaporation model and advocates the need of its refinement. 相似文献
5.
S. Sarkar A. D. Thakur C. V. Tomy G. Balakrishnan D. McK Paul S. Ramakrishnan A. K. Grover 《Pramana》2006,66(1):193-207
New experimental data are presented on the scan rate dependence of the magnetization hysteresis width ΔM(H) (∞ critical current densityJ
c(H)) in isothermalMH scans in a weakly pinned single crystal of Ca3Rh4Sn13, which displays second magnetization peak (SMP) anomaly as distinct from the peak effect (PE). We observe an interesting
modulation in the field dependence of a parameter which purports to measure the dynamical annealing of the disordered bundles
of vortices injected through the sample edges towards the destined equilibrium vortex state at a givenH. These data, in conjunction with the earlier observations made while studying the thermomagnetic history dependence inJ
c(H) in the tracing of the minor hysteresis loops, imply that the partially disordered state heals towards the more ordered state
between the peak field of the SMP anomaly and the onset field of the PE. The vortex phase diagram in the given crystal of
Ca3Rh4Sn13 has been updated in the context of the notion of the phase coexistence of the ordered and disordered regions between the
onset field of the SMP anomaly and the spinodal line located just prior to the irreversibility line. A multi-critical point
and a critical point in the (H,T) region of the Bragg glass phase have been marked in this phase diagram and the observed behavior is discussed in the light
of recent data on multi-critical point in the vortex phase diagram in a single crystal of Nb. 相似文献
6.
Pongaglabol [8-hydroxy-5-phenyl-furo[2,3-h]benzo(b)pyran-7-one] was synthesized and tested for antibacterial effects againstShigella dysenteriae, Salmonella typhi, Streptococcus β-haemolyticus andStaphylococcus aureus. The synthesized compounds were characterized using UV, IR and1H NMR spectral data 相似文献
7.
Monoclinic (N2H6)3Zr2F13·F crystallizes in space group P21-C
2
2
(No. 4) with unit cell dimensionsa=5.670(1),b=10.984(2),c=10.601(2) Å,=93.88(1)°,V=658.7(4) Å3 andZ=2. Two different types of N2H6
2+ ions are present. One is involved in strong H-bonds to F– ions in infinite chains running along the a axis (the shortest N-F distance is 2.437(5) Å), and the other links the structure through weaker bi- and trifurcated H-bonds to fluorine ligands of the Zr2F13
5– ions. The N-N bond lengths range from 1.430(5) to 1.446(5) Å with apparently no meaningful correlation to the type of N2H2
2+ ions. The Zr2F13
5– ions have very nearly C2 point symmetry and are formed by joining two distorted bicapped trigonal prisms of ZrF8-units through a common face. Distances of Zr-F terminal bonds range from 2.015(2) to 2.112(2) Å and of bridging bonds from 2.133(2) to 2.212(2) Å. (N2H6)3Hf2F13·F is isomorphous. The vibrational spectra of the two compounds are nearly identical, with the exception of a strong infrared band, which is assigned to a stretching mode with the moving central atom within the anion. The anion part of the spectrum is simple, showing broad unresolved bands. The cation part shows two types of N2H6
– ions. H-Bonding is strongly present in the spectra, but no simple correlations with the H-bond strength is evident. 相似文献
8.
Studies on the thermal stability of FeCr2O4 in air show that surface oxidation preceeds bulk oxidation. Electrical resistivity and thermoelectric power measurements show that above 47 K, Fe2+ ions are oxidised by the oxygen adsorbed on the surface and above 523K diffusion of the ions into the bulk occur. DTA and TG show that the bulk oxidation starts above 673 K and the change from the defect spinel phase to the rhombohedral phase occurs during oxidation and is not a sharp transition.
The authors wish to thank DST for some financial help. 相似文献
Zusammenfassung Untersuchungen der thermischen Stabilität von FeCr2O4 in Luft zeigen, daß der Masseoxidation eine Oxidation an der Oberfläche vorangeht. Messungen des elektrischen Widerstandes und der thermo-elektromotorischen Kraft zeigen, daß die Fe2+-Ionen oberhalb 47 K durch den an der Oberfläche adsorbierten Sauerstoff oxidiert werden und daß oberhalb 523 K eine Diffusion der Ionen in das Innere abläuft. DTA- und TG- Untersuchungen zufolge setzt die Masseoxidation oberhalb 673 K ein und während der Oxidation verläuft ein unscharfer Übergang von der defekten Spinellphase in die rhomboedrische Phase.
The authors wish to thank DST for some financial help. 相似文献
9.
Dinabandhu Pramanick Jyotish Sarkar Ramanath Bhattacharyya 《Journal of polymer science. Part A, Polymer chemistry》1988,26(5):1457-1463
The reactions of OH radical with Cl?, Br?, I?, and F? ions have been studied by entrapping the product radicals as polymer endgroup which have been detected and estimated by the sensitive dye partition technique. The rate constants of the reactions with Br?, Cl?, and F? ions have been determined to be 1.51 × 109, 1.32 × 109, and 0.92 × 109 L mol?1 s?1, respectively at 25°C and pH 1.00. Oxidation of I? ions liberates I, which inhibits the polymerization and the reaction could not be followed by polymer endgroup analysis. The observed order of reactivity Br? > Cl? > F? is in accordance with the electron affinities of the halide ions. The acidity of the reaction medium has a strong influence on the rate of reaction. With Br? ions, the rate constant of the reaction falls from 1.51 × 109 to 0.75 × 109 L mol?1 s?1 at 25°C as the pH is raised from 1.0 to 2.8. The method is simple and accurate and can be applied to study very reactive radicals. 相似文献
10.
Summary Typical precipitation curves of various metal phosphates have been obtained using the turbidimetric technique. The following
systems have been investigated: Al(NO3)3-K3PO4, Al(NO3)3-KH2PO4, Al(NO3)3NaH2PO4, FeCl3-K3PO4, FeCl3-(NH4)2HPO4, FeCl3K2HPO4, FeCl3-KH2PO4, FeCl3-NaH2PO4, La(NO3)3K3PO4,La(NO3)3-K2HPO4,La(NO3)3-KH2PO4,La(NO3)3NaH2PO4 and Th(NO3)4-K2HPO4. Typical precipitation curves indicated concentration ranges of phosphate precipitation and of complex solubility.
Supported in part by the U.S. Army Research Office, Contract No. DA-ORD-10. 相似文献
Zusammenfassung Typische F?llungskurven verschiedener Metallphosphate, die mittels Trübungsmessungen erhalten wurden, wurden graphisch dargestellt. Die folgenden Systeme wurden untersucht: Al(NO3)3-K3PO4,Al(NO3)3KH2PO4, Al(NO3)3-NaH2PO4, FeCl3-K3PO4, FeCl3(NH4)2HPO4, FeCl3-K2HPO4, FeCl3-KH2PO4, FeCl3NaH2PO4, La(NO3)3-K3PO4, La(NO3)3-K2HPO4, La(NO3)3-KH2PO4, La(NO3)3-NaH2PO4 und Th(NO3)4K2HPO4. Typische F?llungskurven zeigten Konzentrationsgebiete, in welchen die Metallphosphate gef?llt werden, sowie Konzentrationen, die zur Komplexbildung führten.
Supported in part by the U.S. Army Research Office, Contract No. DA-ORD-10. 相似文献