全文获取类型
收费全文 | 758113篇 |
免费 | 6232篇 |
国内免费 | 2391篇 |
专业分类
化学 | 375819篇 |
晶体学 | 10655篇 |
力学 | 39278篇 |
综合类 | 19篇 |
数学 | 119249篇 |
物理学 | 221716篇 |
出版年
2021年 | 5934篇 |
2020年 | 6478篇 |
2019年 | 7425篇 |
2018年 | 19234篇 |
2017年 | 19052篇 |
2016年 | 19329篇 |
2015年 | 8601篇 |
2014年 | 13071篇 |
2013年 | 31136篇 |
2012年 | 26679篇 |
2011年 | 37534篇 |
2010年 | 25513篇 |
2009年 | 25794篇 |
2008年 | 32085篇 |
2007年 | 33905篇 |
2006年 | 24084篇 |
2005年 | 22688篇 |
2004年 | 21269篇 |
2003年 | 19675篇 |
2002年 | 18664篇 |
2001年 | 19176篇 |
2000年 | 14895篇 |
1999年 | 11562篇 |
1998年 | 10002篇 |
1997年 | 9868篇 |
1996年 | 9299篇 |
1995年 | 8454篇 |
1994年 | 8282篇 |
1993年 | 8154篇 |
1992年 | 8619篇 |
1991年 | 9151篇 |
1990年 | 8750篇 |
1989年 | 8665篇 |
1988年 | 8509篇 |
1987年 | 8242篇 |
1986年 | 7932篇 |
1985年 | 10263篇 |
1984年 | 10724篇 |
1983年 | 9007篇 |
1982年 | 9518篇 |
1981年 | 8969篇 |
1980年 | 8578篇 |
1979年 | 9081篇 |
1978年 | 9519篇 |
1977年 | 9228篇 |
1976年 | 9385篇 |
1975年 | 8771篇 |
1974年 | 8726篇 |
1973年 | 9192篇 |
1972年 | 6477篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
912.
A. A. Dadykin 《JETP Letters》1997,65(11):857-862
It is established by direct experiments that the main component of the stationary field-emission current in fields E<105 V/cm is due to piezogeometric intensification (by a factor of 103) of the electricfield at the end faces of piezoelectrically active films. An emission mechanism governed by electrons supplied
by tunneling from the valence band of the piezoelectric is proposed.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 823–827 (10 June 1997) 相似文献
913.
914.
We use integrals of Cauchy type and the complex potentials of S. G. Lekhnitskii to solve the problem of the stress-strain
state of a piecewise-homogeneous anisotropic rock during the working of a horizontal seam of mineral. We study the stress
distribution in the deloaded zones. Three figures, 1 table. Bibliography: 4 titles.
Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 27, 1997, pp. 81–86. 相似文献
915.
916.
Induced ferroelectric S*C phases are formed by non-chiral SC host phases doped with chiral dipolar guest molecules. In those mixtures the spontaneous polarization Ps and the tilt angle Θ has been investigated as a function of the mole fraction xG of the chiral dopant. In most cases the reduced polarization P0 = PS/ sin Θ has been found to depend linearly on xG. The polarization power which is defined by δP=(∂P0/∂xG)ΔT is discussed in terms of the molecular structure of the chiral dopants. There are systems in which P0(xG) deviates positively from linearity. This behaviour can be understood by considering a local field correction to P0. By assuming a local field of Lorentz type a theoretical relation for P0(xG) has been derived which explains the experimental results. The effect of a local field is considerable if the transverse dipole moment and the polarizability of the chiral dopant are large. 相似文献
917.
The reactions of IO radicals with CH3SCH3, CH3SH, C2H4, and C3H6 have been studied using the discharge flow method with direct detection of IO radicals by mass spectrometry. The absolute rate constants obtained at 298 K are the following: IO + CH3SCH3 → products (1): k1 = (1.5 ± 0.2) × 10?14; IO + CH3SH → products (2): k2 = (6.6 ± 1.3) × 10?16; IO + C2H4 →products (3): k3 < 2 × 10?16; IO + C3H6 → products (4): k4 < 2 × 10?16 (units are cm3 molecule?1 s?1). CH3S(O)CH3 and HOI were found as products of reactions (1) and (2), respectively. The present lower value of k1 compared to our previous determination is discussed. 相似文献
918.
The 351 nm laser-damage thresholds (at 0.7 nm pulse length) of monomeric liquid crystals are reported and results from aromatic-core samples are compared with those from fully saturated systems. The role of π-electron conjugation is examined and identified as the key cause for laser damage. For UV laser compatibility of devices, the damage behaviour of an alignment-layer polymer (nylon 6/6) was also investigated. 相似文献
919.
The segmental lipid chain mobility in the gel phase of dipalmitoylphosphatidylcholine (DPPC) multilayers dispersed in buffer and in the interdigitated gel phase induced by glycerol, ethylene glycol, ethanol and chaotropic salt NaClO4 was compared by using conventional electron spin resonance (ESR) spectroscopy. The stearic acids bearing the nitroxide moiety at different positions down the acyl chain (n-NSA,n-5, 7, 10, 12 and 16) were used to characterized the chain motion, and the outer hyperfine splittings of the spectra, 2A max, were taken as indices of the rotational mobility of the chain in the gel phase. The ESR measurements revealed a gradient of increased mobility on proceeding towards the terminal methyl end in the fully hydrated gel phase of DPPC bilayers. This gradient was reduced in the interdigitated gel phase induced by ethanol and chaotropic salt NaClO4, whereas the rotational mobility throughout the length of the chain was comparable to that near the polar/apolar interface in the interdigitated gel phase in glycerol and ethylene glycol. Moreover, the motional anisotropy was much less affected by temperature in the interdigitated gel state of DPPC in glycerol and ethylene glycol as compared both to normal bilayer gel phase and to the other interdigitated DPPC systems. Finally, there was no evidence for chain interdigitation in the fluid phase of DPPC dispersions in any medium. 相似文献
920.
A. F. Blinokhvatov O. V. Markovtseva M. N. Nikolaeva 《Chemistry of Heterocyclic Compounds》1992,28(3):266-268
Substituted 4H-pyrans were obtained in high preparative yields by the reaction of 1,5-diketones with acetic anhydride and boron trifluoride etherate in diethyl ether. It is assumed that the heterocyclization of 1,5-diketones includes a step involving the formation and transformations of an acyloxy carbonium ion.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 320–322, March, 1992. 相似文献