全文获取类型
收费全文 | 77808篇 |
免费 | 329篇 |
国内免费 | 374篇 |
专业分类
化学 | 24025篇 |
晶体学 | 790篇 |
力学 | 6721篇 |
数学 | 31957篇 |
物理学 | 15018篇 |
出版年
2018年 | 10431篇 |
2017年 | 10263篇 |
2016年 | 6066篇 |
2015年 | 840篇 |
2014年 | 295篇 |
2013年 | 327篇 |
2012年 | 3758篇 |
2011年 | 10479篇 |
2010年 | 5623篇 |
2009年 | 6033篇 |
2008年 | 6575篇 |
2007年 | 8739篇 |
2006年 | 202篇 |
2005年 | 1288篇 |
2004年 | 1517篇 |
2003年 | 1960篇 |
2002年 | 1005篇 |
2001年 | 239篇 |
2000年 | 285篇 |
1999年 | 151篇 |
1998年 | 189篇 |
1997年 | 142篇 |
1996年 | 195篇 |
1995年 | 114篇 |
1994年 | 74篇 |
1993年 | 92篇 |
1992年 | 52篇 |
1991年 | 62篇 |
1990年 | 49篇 |
1989年 | 58篇 |
1988年 | 58篇 |
1987年 | 57篇 |
1986年 | 57篇 |
1985年 | 46篇 |
1984年 | 42篇 |
1983年 | 36篇 |
1982年 | 41篇 |
1981年 | 38篇 |
1980年 | 46篇 |
1979年 | 44篇 |
1978年 | 34篇 |
1973年 | 25篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1910年 | 24篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32篇 |
1904年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Unconditional uniqueness of solution for $$\dot H^{s_c }$$ critical 4th order NLS in high dimensions 下载免费PDF全文
In this paper, we study the unconditional uniqueness of solution for the Cauchy problem of Ḣsc(0 ≤ sc < 2) critical nonlinear fourth-order Schrödinger equations i∂tu + Δ2u-εu=λ|u|αu. By employing paraproduct estimates and Strichartz estimates, we prove that unconditional uniqueness of solution holds in Ct(I; Ḣsc(Rd)) for d ≥ 11 and min{1-, (8)/(d-4)} ≥ α >(-(d-4)+√4(d-4)2+64)/4. 相似文献
992.
On the Characterization of Maximal Planar Graphs with a Given Signed Cycle Domination Number 下载免费PDF全文
Xiao Ming Pi 《数学学报(英文版)》2018,34(5):911-920
Let G =(V, E) be a simple graph. A function f : E → {+1,-1} is called a signed cycle domination function(SCDF) of G if ∑_(e∈E(C))f(e) ≥ 1 for every induced cycle C of G. The signed cycle domination number of G is defined as γ'_(sc)(G) = min{∑_(e∈E)f(e)| f is an SCDF of G}. This paper will characterize all maximal planar graphs G with order n ≥ 6 and γ'_(sc)(G) = n. 相似文献
993.
A novel heterogeneous strong acid catalyst was synthesized through the copolymerization of p-toluenesulfonic acid and paraformaldehyde and utilized for the synthesis of fructone. The results showed that the catalyst was very efficient for the reaction with the yield over 95%. The advantages of extremely high density of acidity, high thermal and chemical stability, low cost for the simple synthetic procedure, and reusability made the catalyst one of the best choices for the reaction. 相似文献
994.
Metal-organic complex (H3NCH2CH2NH2)3[MoO2(OC6H4O)2] with a lamellar morphology has been syn- thesized. Its crystal structure was confirmed by single-crystal X-ray diffraction. The morphology of the crystal was observed by scanning electron microscopy (SEM). The metal-organic nanoparticles have been prepared by using an ultrasonic method. The morphology of the as-prepared nanoparticles was observed by transmission electron microscopy (TEM). The possible formation mechanism has also been proposed. 相似文献
995.
Compared with the traditional thin film techniques, the matrix-assisted pulsed laser evaporation (MAPLE) technique has many advantages in the deposition of polymer and organic thin films. It has a wide range of applications in many fields, such as non-linear optics, luminescent devices, electronics, various sensors. We have successfully deposited polyimide thin films by using the MAPLE technique. These films were characterized with XPS. The XPS spectra showed that the single-photon effect is ob-vious at low laser fluence and the chemical bonds will be broken, resulting in decomposition of the films. Contrarily, the single-photon effect will decrease and the multi-photon effect and the photothermal effect will increase at high laser fluence, resulting in the protection of the structure of the polyimide thin films and the obvious decrease in decomposition. High laser fluence is more suitable for the deposition of polymer and organic thin films than low laser fluence. 相似文献
996.
The effect of substrate concentration on biohydrogen production by using kinetic models 总被引:5,自引:0,他引:5
The effect of substrate concentration ranging from 0 to 300 g/L on fermentative hydrogen production by mixed cultures was investigated in batch tests using glucose as substrate. The experimental results showed that, at 35℃ and initial pH 7.0, during the fermentative hydrogen production, the hydrogen production potential and hydrogen production rate increased with increasing substrate concentration from 0 to 25 g/L. The maximal hydrogen production potential of 426.8 mL and maximal hydrogen pro-duction rate of 15.1 mL/h were obtained at the substrate concentration of 25 g/L. The maximal hydrogen yield and the maximal substrate degradation efficiency were respectively 384.3 mL/g glucose and 97.6%, at the substrate concentration of 2 g/L. The modified Logistic model could be used to describe the progress of cumulative hydrogen production in this study successfully. The Han-Levenspiel model could be used to describe the effect of substrate concentration on fermentative hydrogen production rate. 相似文献
997.
The importance of anharmonic effect in dissociation of molecular systems especially clusters has been noted. In this paper, we shall study the effect of coupled anharmonic oscillator of the standard bilinear form (SBF) Morse oscillator (MO) potential on unimolecular reaction. We shall use the systematic theoretical approach, YL method, proposed by Yao and Lin (YAO L, et. al. J Phys Chem A, 2007, 111(29): 6722-6729), which can evaluate anharmonic effects on the rate constants based on the transition state theory. In treating the anharmonic effect with the Morse oscillator potential on unimolecular reactions under collision-free conditions by using the RRKM (Rice-Ramsperger-Kassel-Marcus) theory, the in-verse Laplace transformation of the partition functions was used to obtain the total amount of state and density of state by using the first-order and the second-order approximations of the saddle-point method. To demonstrate the anharmonic effect of the SBF Morse model, we choose some model systems and a real reaction as examples. 相似文献
998.
A novel amperometric sensor for uric acid based on ordered mesoporous carbon modified pyrolytic graphite electrode was developed.
Uric acid oxidation was easily catalyzed by this electrode in a phosphate buffer solution at pH 7.0, with an anodic potential
decrease about 140 mV compared to bare pyrolytic graphite electrode. The uric acid level was determined by the amperometric
method, at a constant potential of 0.31 mV, the catalytic current of uric acid vs. its concentration showed a good linearity
in the range of 1.0 × 10−6−1.0 × 10−4 mol L−1, with a correlation coefficient of 0.999. The detection limit was 4.0 × 10−7 mol L−1. The proposed method could be effectively used for uric acid amperometric sensing in human urine. 相似文献
999.
Iisa Outola Kenneth Inn Robert Ford Steve Markham Petri Outola 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(2):321-327
The environmental mobility/availability behavior of radionuclides in soils and sediments depends on their speciation. Experiments
have been carried out to develop a simple but robust radionuclide sequential extraction method for identification of radionuclide
partitioning in sediments and soils. The sequential extraction protocol was optimized for temperature, concentration of reagents
and reaction time. Optimum extraction conditions were chosen based on the release of 239,240Pu, 238U and stable elements. Results from the experiments with lake sediment (SRM 4354) are compared to the previous trials where
the sequential extraction protocol was optimized with the ocean sediment (SRM 4357). Based on these two trials the NIST standard
sequential extraction protocol is established for defined extraction settings for temperature, reagent concentration and time. 相似文献
1000.
Song-hua Ye Sheng Chen Fan Zhang Wei Wang Qin Tian Jin-zhi Liu Fang Chen Jin-ku Bao 《Applied biochemistry and biotechnology》2009,158(3):615-630
Plant lectins have been reported as transgenic resistance factors against a variety of insect pests. Herein, homologous analysis
demonstrated that Zephyranthes grandiflora agglutinin (ZGA) exhibited high similarity with other monocot mannose-binding lectins (MBLs). Phylogenetic analysis revealed
that it had taxonomical relationships with insecticidal MBLs. Subsequently, a plasmid expression vector pBI121 containing
zga gene (pBIZGA) was constructed using the zga sequence, under the control of CaMV35S promoter and nos terminator. pBIZGA was then integrated into the genome of Nicotiana tabacum L. Polymerase chain reaction and Southern blot analysis demonstrated that this zga gene was integrated into the plant genome. Western blotting and agglutinating activity analysis also showed that transgenic
tobacco plants expressed different levels of ZGA. Carbohydrate inhibition analysis indicated that recombinant ZGA and the
native shared the same carbohydrate-binding specificity. Moreover, genetic analysis confirmed Mendelian segregation (3:1)
of the transgenic in T1 progenies. In planta bioassays on T0 plants and their progenies indicated that expressed ZGA had an
effect on reducing the survivability and fecundity of tobacco aphids (Myzus nicotianae). These findings demonstrate that the novel zga gene of ZGA can be expressed in crop plants susceptible to various sap-sucking insects. 相似文献