全文获取类型
收费全文 | 5192篇 |
免费 | 208篇 |
国内免费 | 28篇 |
专业分类
化学 | 3602篇 |
晶体学 | 44篇 |
力学 | 170篇 |
数学 | 842篇 |
物理学 | 770篇 |
出版年
2023年 | 30篇 |
2022年 | 42篇 |
2021年 | 70篇 |
2020年 | 71篇 |
2019年 | 101篇 |
2018年 | 65篇 |
2017年 | 37篇 |
2016年 | 137篇 |
2015年 | 144篇 |
2014年 | 170篇 |
2013年 | 299篇 |
2012年 | 328篇 |
2011年 | 389篇 |
2010年 | 241篇 |
2009年 | 199篇 |
2008年 | 291篇 |
2007年 | 307篇 |
2006年 | 327篇 |
2005年 | 303篇 |
2004年 | 301篇 |
2003年 | 207篇 |
2002年 | 199篇 |
2001年 | 64篇 |
2000年 | 67篇 |
1999年 | 46篇 |
1998年 | 53篇 |
1997年 | 54篇 |
1996年 | 58篇 |
1995年 | 50篇 |
1994年 | 37篇 |
1993年 | 48篇 |
1992年 | 28篇 |
1991年 | 27篇 |
1990年 | 22篇 |
1989年 | 37篇 |
1988年 | 23篇 |
1986年 | 26篇 |
1985年 | 44篇 |
1984年 | 50篇 |
1983年 | 34篇 |
1982年 | 39篇 |
1981年 | 40篇 |
1980年 | 51篇 |
1979年 | 29篇 |
1978年 | 26篇 |
1977年 | 32篇 |
1976年 | 26篇 |
1975年 | 29篇 |
1974年 | 21篇 |
1973年 | 29篇 |
排序方式: 共有5428条查询结果,搜索用时 218 毫秒
11.
In the first part of the paper we establish the existence of a boundary trace for positive solutions of the equation ?Δu + g(x, u) = 0 in a smooth domain Ω ? ?N, for a general class of positive nonlinearities. This class includes every space independent, monotone increasing g which satisfies the Keller‐Osserman condition as well as degenerate nonlinearities gα,q of the form gα,q (x, u) = d(x, ?Ω)α |u|q?1 u, with α > ?2 and q > 1. The boundary trace is given by a positive regular Borel measure which may blow up on compact sets. In the second part we concentrate on the family of nonlinearities {gα,q}, determine the critical value of the exponent q (for fixed α > ?2) and discuss (a) positive solutions with an isolated singularity, for subcritical nonlinearities and (b) the boundary value problem for ?Δu + gα,q (x, u) = 0 with boundary data given by a positive regular Borel measure (possibly unbounded). We show that, in the subcritical case, the problem possesses a unique solution for every such measure. © 2003 Wiley Periodicals, Inc. 相似文献
12.
Guy Bayada 《Journal of Mathematical Analysis and Applications》2003,282(1):212-231
The asymptotic behaviour of a Stokes flow with Tresca free boundary friction conditions when one dimension of the fluid domain tends to zero is studied. A specific Reynolds equation associated with variational inequalities is obtained and uniqueness is proved. 相似文献
13.
Bou-Huot Phe Véronique Bounor-Legare Laurent David Alain Michel 《Journal of Sol-Gel Science and Technology》2004,31(1-3):47-50
We study the synthesis of organic-inorganic hybrids in the molten state of the polymer without solvent, by reactive processing. The synthesis is based in a first step upon the crosslinking of ethylene vinyl acetate copolymer (EVA) through an exchange reaction between the pendant ester groups of EVA and tetrapropoxysilane (TPOS) in presence of dibutyltin oxide (DBTO) as an indispensable catalyst. Then in a second step the hydrolysis-condensation reactions of residual alkoxide groups results in silica network formation, which is covalently bonded with the organic network. An original approach was developed to correlate the evolution of the hydrolysis-condensation reactions through the assessment of propanol by gas chromatography and the evolution of the morphology through SAXS and TEM analysis. Silica-rich domains with a diameter close to 5 nm are obtained. 相似文献
14.
Thorsten Hamann Erin Osborne Heather L. Youngs Julie Misson Laurent Nussaume Chris Somerville 《Cellulose (London, England)》2004,11(3-4):279-286
We have used Affymetrix gene chips to measure the expression of 10 CESA and 29 CSL genes of Arabidopsis in different developmental stages or organs. These measurements reveal that many of the genes exhibit different levels of expression in the various organs. While several CESA genes are highly expressed in all the tissues examined, very few CSL genes approach such high levels of expression. This suggests that the CSL genes either encode enzymes for the synthesis of minor components of cell walls or are expressed only in specific cell types. The expression data also highlights the potential importance of the CESA genes for primary and secondary cell wall formation during different developmental stages and in the different organs examined. 相似文献
15.
The synthesis of 2-substituted 1,4-diacetoxybutadiene derivatives with a partial control of stereochemistry is described from two potentially precursor enals by a judicious choice of experimental conditions (Ac2O/DMAP in Et3N). These conditions have been successfully applied in the first total synthesis of caulerpenyne. 相似文献
16.
We classify all the global phase portraits of the quadratic polynomial vector fields having a rational first integral of degree 2. In other words we characterize all the global phase portraits of the quadratic polynomial vector fields having all their orbits contained in conics. For such a vector field there are exactly 25 different global phase portraits in the Poincaré disc, up to a reversal of sense. 相似文献
17.
Guy Schmitz 《国际化学动力学杂志》2007,39(1):17-21
At bromide concentrations higher than 0.1 M, a second term must be added to the classical rate law of the bromate–bromide reaction that becomes ?d[BrO3?]/dt = [BrO3?][H+]2(k1[Br?] + k2[Br?]2). In perchloric solutions at 25°C, k1 = 2.18 dm3 mol?3 s?1 and k2 = 0.65 dm4 mol?4 s?1 at 1 M ionic strength and k1 = 2.60 dm3 mol3 s?1and k2 = 1.05 dm4 mol?4 s?1 at 2 M ionic strength. A mechanism explaining this rate law, with Br2O2 as key intermediate species, is proposed. Errors that may occur when using the Guggenheim method are discussed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 17–21, 2007 相似文献
18.
Girard V Farrenq R Sorokin E Sorokina IT Guelachvili G Picqué N 《Chemical physics letters》2006,419(4-6):584-588
The spectral dynamics of a mid-infrared multimode Cr(2+):ZnSe laser located in a vacuum sealed chamber containing acetylene at low pressure is analyzed by a stepping-mode high-resolution time-resolved Fourier transform interferometer. Doppler-limited absorption spectra of C(2)H(2) in natural isotopic abundance are recorded around 4000 cm(-1) with kilometric absorption path lengths and sensitivities better than 3 10(-8) cm(-1). Two cold bands are newly identified and assigned to the ν(1)+ν(4) (1) and ν(3)+ν(5) (1) transitions of (12)C(13)CH(2). The ν(1)+ν(5) (1) band of (12)C(2)HD and fourteen (12)C(2)H(2) bands are observed, among which for the first time ν(2)+2ν(4) (2)+ν(5) (-1). 相似文献
19.
We show that there is a threshold in energy for the onset of chaos in cosmology for the Universe described as a dynamical system derived from the Einstein equations of General Relativity (GR). In the case of the mixmaster model (homogeneous and anisotropic cosmology with a Bianchi IX metric), the chaos occurs precisely at the prescribed necessary value H
vac=0 of the GR for the energy of the Universe while the system is found to be regular for H<0 and chaotic for H>0 with respect to its pure vacuum part. In the case of generalized scalar tensor theories within the Bianchi IX model, we show using the ADM formalism and a conformal transformation that the energy of the dynamical system as compared to vacuum lies below the zero energy threshold. The system is thus not exhibiting chaos and the conclusion still holds in the presence of ordinary matter as well. The suppression of chaos occurs in a similar way for stiff matter alone. 相似文献
20.