全文获取类型
收费全文 | 23647篇 |
免费 | 4079篇 |
国内免费 | 2719篇 |
专业分类
化学 | 17165篇 |
晶体学 | 233篇 |
力学 | 1298篇 |
综合类 | 136篇 |
数学 | 2718篇 |
物理学 | 8895篇 |
出版年
2024年 | 46篇 |
2023年 | 464篇 |
2022年 | 672篇 |
2021年 | 798篇 |
2020年 | 922篇 |
2019年 | 904篇 |
2018年 | 841篇 |
2017年 | 728篇 |
2016年 | 1174篇 |
2015年 | 1067篇 |
2014年 | 1340篇 |
2013年 | 1772篇 |
2012年 | 2142篇 |
2011年 | 2193篇 |
2010年 | 1546篇 |
2009年 | 1479篇 |
2008年 | 1594篇 |
2007年 | 1403篇 |
2006年 | 1322篇 |
2005年 | 1099篇 |
2004年 | 881篇 |
2003年 | 731篇 |
2002年 | 694篇 |
2001年 | 524篇 |
2000年 | 438篇 |
1999年 | 500篇 |
1998年 | 349篇 |
1997年 | 350篇 |
1996年 | 365篇 |
1995年 | 283篇 |
1994年 | 251篇 |
1993年 | 254篇 |
1992年 | 177篇 |
1991年 | 193篇 |
1990年 | 153篇 |
1989年 | 108篇 |
1988年 | 96篇 |
1987年 | 83篇 |
1986年 | 79篇 |
1985年 | 56篇 |
1984年 | 58篇 |
1983年 | 35篇 |
1982年 | 35篇 |
1981年 | 24篇 |
1980年 | 26篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1973年 | 16篇 |
1968年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
In this paper, we construct a second order algorithm based on the spectral deferred correction method for the time-dependent magnetohydrodynamics flows at a low magnetic Reynolds number. We present a complete theoretical analysis to prove that this algorithm is unconditionally stable, consistent and second order accuracy. Finally, two numerical examples are given to illustrate the convergence and effectiveness of our algorithm. 相似文献
972.
973.
The optimal information feedback has a significant effect on many socioeconomic systems like stock market and traffic systems aiming to make full use of resources. In this Letter, we study dynamics of traffic flow with real-time information. The influence of a feedback strategy named Corresponding Angle Feedback Strategy (CAFS) is introduced, based on a two-route scenario in which dynamic information can be generated and displayed on the board to guide road users to make a choice. Our model incorporates the effects of adaptability into the cellular automaton models of traffic flow and simulation results adopting this optimal information feedback strategy have demonstrated high efficiency in controlling spatial distribution of traffic patterns compared with the other three information feedback strategies, i.e., vehicle number and flux. 相似文献
974.
Plínio T. Berardo Maurício S. Abrao Maísa L.S. Souza Daniel E. Machado Luiz-Cláudio F. Silva Luiz E. Nasciutti 《Micron (Oxford, England : 1993)》2009,40(5-6):639-645
The composition of sulfated glycosaminoglycans (GAGs) and the tissue distribution of chondroitin sulfate (CS) were analyzed in deeply infiltrating endometriosis (DIE) of rectosigmoid, using metachromatic staining, and biochemical analysis employing electrophoresis before and after specific enzymatic or chemical degradations, and immunostaining with an antibody against CS. The sulfated GAGs were characterized as dermatan sulfate (DS), heparan sulfate (HS) and CS; and DS strongly predominated compared to HS and CS. Immunostaining procedures showed that CS was concentrated in the endometriosis foci, distributed throughout the stroma around the glands. This is the first report describing the composition of sulfated GAGs and the tissue location of CS in DIE by means of histochemical, biochemical and immunohistochemical analyses. These results confirmed that in DIE of rectosigmoid, as in eutopic endometrium [Nasciutti, L.E., Ferrari, R., Berardo, P.T., Souza, M.L.S., Takiya, C.M., Borojevic, R., Abrao, M.S., Silva, L.C.F., 2006. Distribution of chondroitin sulfate in human endometrium. Micron 37, 544–550], CS was the dominant sulfated GAG in stroma of the lesion foci. 相似文献
975.
Minghua Min Yuyuan Shi Haiyou Ma Hongliang Huang Jiangao Shi Xiaoxue Chen 《Journal of Macromolecular Science: Physics》2015,54(4):411-423
The effects of addition of synthesized organic-suspension silver nanoparticles on the crystallization and thermal stability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (XRD), UV-Vis absorption spectroscopy, polarized optical microscopy (POM), and thermal gravimetric analysis (TGA). The TEM images showed the average primary size of the as-synthesized silver nanoparticles, coated with a monolayer of the surfactants consisting of oleic acid and an alkylamine, was about 5 nm with narrow distribution, and that they were uniformly dispersed in n-heptane. PHBV/silver nanocomposites were prepared by melt mixing in an internal mixer and then injection molded into rectangle-shaped specimens by a labscale injection molding device. The coated silver nanoparticles showed a homogenuous dispersion in the PHBV matrix when the content of coated silver nanoparticles was about 1%. Both the DSC and POM data showed the efficient heterogeneous nucleation by the coated silver nanoparticles for facilitating PHBV crystallization. The thermal stability of the PHBV/silver nanocomposites improved with the increase in the content of the coated silver nanoparticles. 相似文献
976.
977.
Maciej Makowski Krzysztof Pawełczak Paweł Kafarski Jolanta M. Dzik Barbara Gołos Małgorzata Balinska 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1639-1651
The synthesis of six analogues of the potent thymidylate synthase (TS) inhibitor N -[4-[ N -[(3,4-dihydro-2-methyl-4-oxo-6-quinazolinoyl)-methyl]- N -prop-2-ynylamino]benzoyl]- L -glutamic acid 2 is described in which the glutamic acid residue has been replaced by DL -aminophosphonic acids. New antifolates were tested as inhibitors of TS isolated from mouse L1210 leukemic cells as well as inhibitors of growth mouse leukemic L5178Y cells. In general these modifications result in compounds that are considerably less potent than 2 as TS inhibitors with K i 's 0.17-1.10 w M. Very poor solubility in water limited their proper assay of growth cells inhibition. 相似文献
978.
Qianqian Zhai Zhihua Lu Jing Wang Weina Wang Yudong Ma Caili Yue 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):803-811
AbstractA method of Fourier transform near-infrared (FT-NIR) spectroscopy combined with partial least squares (PLS) model was successfully applied to investigate the hydrolysis kinetics of four kinds of silane coupling agents (phenyltriethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltriethoxysilane, 3-chloropropyltriethoxysilane) in an acid-catalyzed EtOH system. The fast scanning speed and high sensitivity of the FT-NIR spectroscopy, and the powerful data processing ability of the PLS, enabled the method to quantitatively and accurately catch the fast changing H2O concentration during the hydrolysis processes without delay, realizing the study of the fast-paced hydrolysis reactions of the silane coupling agents. The results showed that electrophilic substitution occurred in the hydrolysis reactions, which followed second-order reactions and greatly depend on the catalyst concentration and reaction temperature. The hydrolysis rate constants, activation energy, and Arrhenius Frequency factors were gained. In conclusion, the FT-NIR PLS model is a powerful tool for hydrolysis kinetics researching of the silane coupling agents. 相似文献
979.
Xiao-Bo Ma Jing-Lin Zhang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):227-231
Abstract The condensation of N-phenyl-N′-(2-hydroxylphenyl)urea or N-phenyl-N′-(2-aminophenyl)urea with tris(dia1kylamino)phosphine afforded derivatives of 4,5-benzo-1,3,2-oxaza (or diaza)-phospholane which formed intramolecular hydrogen bond. The cleavage of the amide bond to give N,N-dialky1-N′-phenylurea together with polymers of 1,3,2-benzodiazaphosphole was observed in the latter reaction. 相似文献
980.
Xiao-Bo Ma Jing-Lin Zhang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):233-237
Abstract 1,3,2-Diazaphosphetidin-4-one derivatives were synthesized. Their 1H NMR signals at ambient temperature displaed a broad doublet which eventually coalesced before becoming sharp upon warming, and the 13C NMR spectra also showed that the α-and β-carbons of the dialkylamino group were non-equivalent. The phenomena were ascribed to restricted rotation about the exocyclic P—N bond. 相似文献