全文获取类型
收费全文 | 1398380篇 |
免费 | 29721篇 |
国内免费 | 7731篇 |
专业分类
化学 | 705097篇 |
晶体学 | 20667篇 |
力学 | 75901篇 |
综合类 | 105篇 |
数学 | 245995篇 |
物理学 | 388067篇 |
出版年
2021年 | 13580篇 |
2020年 | 15980篇 |
2019年 | 16105篇 |
2018年 | 14689篇 |
2017年 | 13201篇 |
2016年 | 28877篇 |
2015年 | 21037篇 |
2014年 | 30571篇 |
2013年 | 74678篇 |
2012年 | 41125篇 |
2011年 | 40570篇 |
2010年 | 39078篇 |
2009年 | 41007篇 |
2008年 | 38799篇 |
2007年 | 35219篇 |
2006年 | 39181篇 |
2005年 | 32433篇 |
2004年 | 32821篇 |
2003年 | 30482篇 |
2002年 | 31111篇 |
2001年 | 31736篇 |
2000年 | 26675篇 |
1999年 | 23422篇 |
1998年 | 21402篇 |
1997年 | 21394篇 |
1996年 | 21296篇 |
1995年 | 19326篇 |
1994年 | 18802篇 |
1993年 | 18356篇 |
1992年 | 18708篇 |
1991年 | 18922篇 |
1990年 | 18136篇 |
1989年 | 18183篇 |
1988年 | 17727篇 |
1987年 | 17656篇 |
1986年 | 16661篇 |
1985年 | 23019篇 |
1984年 | 24123篇 |
1983年 | 20236篇 |
1982年 | 21817篇 |
1981年 | 21021篇 |
1980年 | 20387篇 |
1979年 | 20771篇 |
1978年 | 21912篇 |
1977年 | 21572篇 |
1976年 | 21357篇 |
1975年 | 20021篇 |
1974年 | 19751篇 |
1973年 | 20192篇 |
1972年 | 14624篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
711.
We demonstrate a method that permits to obtain generalized solutions for some quasilinear equations and systems of hyperbolic
type. The corresponding variational principle is constructed using the theory of equilibrium of a potential in an external
field.
Dedicated to the memory of B. M. Levitan
Supported by RFBR grants Nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy
of Sciences, and by INTAS project No. 03-51-6637. 相似文献
712.
T. Kumita Y. Kamiya M. Babzien I. Ben-Zvi K. Kusche I. V. Pavlishin I. V. Pogorelsky D. P. Siddons V. Yakimenko T. Hirose T. Omori J. Urakawa K. Yokoya D. Cline F. Zhou 《Laser Physics》2006,16(2):267-271
Thomson scattering of high-power laser and electron beams is a good test of electrodynamics in the high-field region. We demonstrated production of high-intensity X-rays in the head-on collision of a CO2 laser and 60-MeV electron beams at Brookhaven National Laboratory, Accelerator Test Facility. The energy of an X-ray photon was limited at 6.5 keV in the linear (lowest order) Thomson scattering, but the nonlinear (higher order) process produces higher energy X-rays. We measured the angular distribution of the high-energy X-rays and confirmed that it agrees with theoretical predictions. 相似文献
713.
The tape stripping technique is an experimental method frequently used for reconstruction of the in-depth distribution of various topically administered substances within the horny layer of human skin, e.g., compounds contained in sunscreens. Titanium dioxide (TiO2) nanoparticles (25–200 nm in diameter) are one such compound. Optical techniques which apply blue light are found to be suitable for reconstruction. However, the presence of particles affects the light propagation within the skin and therefore causes incorrect determination of strip thickness, leading to an improper reconstructed distribution of nanoparticle concentration revealed from the experimental data. This study evaluates the errors emerging from the use of blue (400 nm) and NIR (800 nm) radiation and finds the use of longer wavelength light more advantageous. Particles of different diameters are considered, and it is revealed that the application of small particles (25–60 nm) results in the lowest rate of error. 相似文献
714.
Debendra K. Mohapatra Dhananjoy Mondal Mukund S. Chorghade Mukund K. Gurjar 《Tetrahedron letters》2006,47(52):9215-9219
The non-proteinogenic amino acid 3-hydroxy-4-methylproline (HMP) is an active constituent of some potent antimicrobials including echinocandins, nostopeptins, pneumocandins, sporiofungin and mulundocandins. A synthesis has been achieved in 10 steps with 29% overall yield; the Evans’ aldol reaction using Crimmins’ modified method was pivotal to the success of the strategy. 相似文献
715.
The direct regioselective C–H arylation of 3-methoxythiophene and 3,4-ethylenedioxythiophene (EDOT) was performed successfully under ‘Heck-type’ experimental conditions. This novel synthetic methodology has been used to prepare in a more simple way a series of oligothiophenes interesting for the electronic industry to build new synthetic organic materials. 相似文献
716.
The synthesis of rigid spirocyclic bislactams derived from pyroglutamic acid has been established. 相似文献
717.
N. N. Manuylov 《Journal of Mathematical Sciences》2006,133(6):1686-1692
Renormalization formulas connecting the points of the orbits O
0
±
, i.e., the sequences generated by an irrational shift on the half-open interval [0, 1) or (0, 1], and the points of the orbits'
derivatives dmO
0
±
, i.e., the sequences obtained by restricting O
0
±
to half-open intervals of smaller length, are obtained. Bibliography: 5 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 314, 2004, pp. 142–154. 相似文献
718.
The extended Airy kernel describes the space-time correlation functions for the Airy process, which is the limiting process for a polynuclear growth model. The Airy functions themselves are given by integrals in which
the exponents have a cubic singularity, arising from the coalescence of two saddle points in an asymptotic analysis. Pearcey
functions are given by integrals in which the exponents have a quartic singularity, arising from the coalescence of three
saddle points. A corresponding Pearcey kernel appears in a random matrix model and a Brownian motion model for a fixed time. This paper derives an extended Pearcey kernel by scaling the Brownian motion model at several times, and a system of partial differential equations whose solution determines
associated distribution functions. We expect there to be a limiting nonstationary process consisting of infinitely many paths,
which we call the Pearcey process, whose space-time correlation functions are expressible in terms of this extended kernel. 相似文献
719.
Addition of aqueous hydrogen peroxide significantly accelerates the substitution reactions of hydroxide salts with haloarenes bearing electron withdrawing substituents. A similar effect is observed in the reactions of hydroxide salts with halogenated heteroarenes. Reactions are carried out in water or water-THF at ambient temperature or at 50-60 °C. 相似文献
720.
(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)3 yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes. 相似文献