全文获取类型
收费全文 | 6978篇 |
免费 | 208篇 |
国内免费 | 23篇 |
专业分类
化学 | 5091篇 |
晶体学 | 87篇 |
力学 | 124篇 |
数学 | 336篇 |
物理学 | 1571篇 |
出版年
2023年 | 32篇 |
2022年 | 48篇 |
2021年 | 76篇 |
2020年 | 100篇 |
2019年 | 88篇 |
2018年 | 75篇 |
2017年 | 60篇 |
2016年 | 145篇 |
2015年 | 125篇 |
2014年 | 177篇 |
2013年 | 327篇 |
2012年 | 400篇 |
2011年 | 494篇 |
2010年 | 242篇 |
2009年 | 221篇 |
2008年 | 406篇 |
2007年 | 392篇 |
2006年 | 410篇 |
2005年 | 372篇 |
2004年 | 358篇 |
2003年 | 306篇 |
2002年 | 315篇 |
2001年 | 173篇 |
2000年 | 142篇 |
1999年 | 91篇 |
1998年 | 79篇 |
1997年 | 77篇 |
1996年 | 86篇 |
1995年 | 64篇 |
1994年 | 74篇 |
1993年 | 68篇 |
1992年 | 80篇 |
1991年 | 49篇 |
1990年 | 55篇 |
1989年 | 57篇 |
1988年 | 48篇 |
1987年 | 47篇 |
1986年 | 44篇 |
1985年 | 96篇 |
1984年 | 91篇 |
1983年 | 42篇 |
1982年 | 57篇 |
1981年 | 43篇 |
1980年 | 56篇 |
1979年 | 76篇 |
1978年 | 54篇 |
1977年 | 59篇 |
1976年 | 51篇 |
1975年 | 39篇 |
1974年 | 28篇 |
排序方式: 共有7209条查询结果,搜索用时 15 毫秒
41.
42.
43.
This paper presents a simple chaotic circuit consisting of two capacitors, one linear two-port VCCS and one time-state-controlled
impulsive switch. The impulsive switch causes rich chaotic and periodic behavior. The circuit dynamics can be simplified into
a one-dimensional return map that is piecewise linear and piecewise monotone. Using the return map, we clarify parameter conditions
for existence of chaotic and periodic attractors and coexistence state of attractors. 相似文献
44.
By time-resolved electron paramagnetic resonance (TREPR), four (tetraphenylporphinato) zinc (ZnTPP) complexes coordinated by an axial ligand containing a nitroxide radical (NRX; X=4, 5, 8, and 10, denotes the bond number from zinc to nitroxide nitrogen) have been studied in terms of magnetic interactions between the photoexcited triplet state of ZnTPP and NRX. The TREPR spectrum of ZnTPP coordinated by NR10 is almost the same as the one of ZnTPP coordinated by pyridine, indicating that the electron exchange interaction,J, between ZnTPP and the doublet nitroxide is negligibly small. On the other hand, TREPR spectra of the NR4 and NR5 complexes are assigned to the Q1 state constituted by the ZnTPP and the nitroxide radical. In the case of the ZnTPP-NR8 complex, both T1 and Q1 TREPR signals are seen, which may originate from two conformations or degenerate T1 states of ZnTPP. This EPR study is useful for understanding the photophysical and photochemical properties of chromophores. 相似文献
45.
R. M. Vlasova N. V. Drichko B. V. Petrov V. N. Semkin E. I. Zhilyaeva R. N. Lyubovskaya I. Olejniczak A. Kobayashi H. Kobayashi 《Physics of the Solid State》2004,46(11):1985-1993
Polarized reflectance and optical conductivity spectra of single crystals of two new isostructural organic conductors based
on the BEDT-TSeF molecule, namely, the κ-(BETS)4Hg2.84Br8 superconductor (T
c
=2 K) and the κ-(BETS)4Hg3Cl8 metal, which undergoes a smooth transition to the dielectric state near 35 K, have been obtained in the spectral region 700–6500
cm−1 at temperatures of 300–15 K. At 300 K, the spectra of both compounds are nearly identical and differ from the Drude spectrum
characteristic of metals. The nature of the observed difference is discussed, and the spectra are described in terms of a
cluster approach with inclusion of electron-electron correlations in the Hubbard approximation combined with the Drude model.
The parameters of the theory were determined, including the electron transfer integrals between molecules in a cluster. The
spectra in the conducting plane of the crystals were found to be essentially anisotropic, which should be assigned to specific
features of in-plane interaction between molecules. The spectra of the superconductor and the metal become increasingly different
as the temperature is lowered. The spectra of the metal obtained for T<150 K exhibit splitting of the broad electronic maximum in the mid-IR region into two bands, which is accompanied by a splitting
of a vibronic feature deriving from electron interaction with intramolecular BETS vibrations of ν3(A
g
) symmetry. No such splitting is observed in the superconductor spectra with decreasing temperature.
__________
Translated from Fizika Tverdogo Tela, Vol. 46, No. 11, 2004, pp. 1921–1929.
Original Russian Text Copyright ? 2004 by Vlasova, Drichko, Petrov, Semkin, Zhilyaeva, Lyubovskaya, Olejniczak, A. Kobayashi,
H. Kobayashi. 相似文献
46.
For the purpose of testing the spherical uniformity based on i.i.d. directional data (unit vectors) zi, i=1,…,n, Anderson and Stephens (Biometrika 59 (1972) 613–621) proposed testing procedures based on the statistics Smax=maxu S(u) and Smin=minu S(u), where u is a unit vector and nS(u) is the sum of squares of u′zi's. In this paper, we also consider another test statistic Srange=Smax−Smin. We provide formulas for the P-values of Smax, Smin, Srange by approximating tail probabilities of the limiting null distributions by means of the tube method, an integral-geometric approach for evaluating tail probability of the maximum of a Gaussian random field. Monte Carlo simulations for examining the accuracy of the approximation and for the power comparison of the statistics are given. 相似文献
47.
Synthesis of Bioactive and Porous Organic-Inorganic Hybrids for Biomedical Applications 总被引:2,自引:0,他引:2
Kanji Tsuru Satoshi Hayakawa Akiyoshi Osaka 《Journal of Sol-Gel Science and Technology》2004,32(1-3):201-205
Bioactivity has been exhibited by a limited range of ceramics since the invention of Bioglass®. Recently, some bioactive polymeric organic-inorganic hybrids were introduced, including not only organically modified silicates (Ormosils) synthesized from polydimethylsiloxane (PDMS) and tetraethoxysilane but also those with gelatin and 3-glycidoxypropyl-tremethoxysilane. Preparation of the bulk and porous hybrids and their polymeric structures analyzed by Si NMR spectroscopy were presented. In vitro bioactivity or apatite deposition in a simulated body fluid of the Kokubo recipe were also described for those hybrids. Freeze-drying techniques introduced porosity (up to 90%) and pores extending in a preferred direction. 相似文献
48.
Precise characterization of noncollinear optical parametric amplifier idler pulses that have bandwidths of more than an octave with a center wavelength at 990 nm was demonstrated. The method employed was cross-correlation frequency-resolved optical gating with broadband sum-frequency mixing to take advantage of the idler's angular dispersion. Compression to near the transform limit was achieved to produce quasi-monocyclic near-infrared pulses by use of a deformable membrane mirror. 相似文献
49.
Mitsunori Oda Yosuke Fukuchi Satoshi Ito Nguyen Chung Thanh Shigeyasu Kuroda 《Tetrahedron letters》2007,48(52):9159-9162
Reactions of pyrrolidine with 2 equiv of aldehydes without any catalyst in a pressurized vessel at 140–200 °C yielded 1,3-disubstituted pyrroles. -Branched aldehydes gave fairly good yields of the corresponding products by this method, which provides a facile non-oxidative procedure for synthesizing 1,3-dialkylpyrroles from inexpensive pyrrolidine and aldehydes. 相似文献
50.
Kazuro Shiomi Satoshi mura 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2004,80(6):245
Microorganisms produce many useful antiparasitic agents. Antiparasitic activities and biochemical targets of antiprotozoal and anthelmintic antibiotics are reviewed. Antimalarial apicidin, thiolactomycin, fosmidomycin, and borrelidin, antitrypanosomal ascofuranone, and nematocidal emodepside, 2-deoxoparaherquamide A, and nafuredin are recently discovered antibiotics, and they have potential as useful drugs. 相似文献