全文获取类型
收费全文 | 1085篇 |
免费 | 51篇 |
专业分类
化学 | 698篇 |
晶体学 | 2篇 |
力学 | 46篇 |
数学 | 155篇 |
物理学 | 235篇 |
出版年
2023年 | 5篇 |
2022年 | 15篇 |
2021年 | 27篇 |
2020年 | 20篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 37篇 |
2015年 | 33篇 |
2014年 | 35篇 |
2013年 | 47篇 |
2012年 | 56篇 |
2011年 | 72篇 |
2010年 | 21篇 |
2009年 | 45篇 |
2008年 | 66篇 |
2007年 | 62篇 |
2006年 | 47篇 |
2005年 | 40篇 |
2004年 | 39篇 |
2003年 | 27篇 |
2002年 | 45篇 |
2001年 | 18篇 |
2000年 | 13篇 |
1999年 | 17篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1989年 | 13篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 5篇 |
1973年 | 8篇 |
1970年 | 4篇 |
1905年 | 4篇 |
排序方式: 共有1136条查询结果,搜索用时 31 毫秒
81.
Alfredo De Rossi Gaetano Assanto Stefano Trillo William E. Torruellas 《Optics Communications》1998,150(1-6):390-398
We have identified a family of (2+1)D spatial solitary waves which can stably propagate in bulk media in the presence of coexisting diffraction, self-focusing Kerr and quadratic nonlinearities. In a conspicuous range of excitation conditions close to the stationary solutions, the emerging wavepackets are immune to the detrimental occurrence of filamentation and collapse, typical of pure Kerr media. The presence of a second-order contribution to the cubic nonlinear response is, therefore, able to prevent optical damage in applications relying on self-guidance. We show that the cross-phase modulation plays an important effect on stability. Our estimate shows that the effects of the cubic susceptibility cannot be neglected below a certain beam size in realistic crystals (e.g. KTP or similar). 相似文献
82.
The computations performed in a previous paper for hypothetical structures of the site active in the polymerization of olefins at the (110) surfaces of TiCl3-α are extended to edges, steps and reliefs on (111) surfaces of all the layered modifications of TiCl3. Our computations suggest that edges, steps and reliefs of all the layered modifications of TiCl3 should behave similarly in providing active sites; polymerization should occur on these more exposed sites because of the much lower activation energies than for plain surfaces. A unique general model emerges: lower steric repulsions appear to be implied for a coordination of the polymeric chain on the more hindered octahedral position at a titanium atom and this, in turn, causes a chiral orientation of the first carbon-carbon bond of the chain. This orientation may be the main factor in determining the stereospecificity. 相似文献
83.
Gaetano Zingone 《Meccanica》1972,7(2):117-123
Summary The limit analysis of indefinite plates resting on a continuous elastoplastic medium and subjected to a load distributed over a partial surface with a circular boundary yields the fundamental equation governing the problem. Minimum conditions are set and the solution that supplies the collapse load of the plate-soil system is found by variational calculus.
This research was supported by the CNR (National Research Council). 相似文献
Sommario Si analizza lo stato limite delle piastre indefinite, appoggiate su un mezzo elastoplastico continuo e sottoposte a carico ripartito su una superficie parziale a contorno circolare, pervenendo all'equazione fondamentale che regge il problemaImponendo quindi delle condizioni minimizzanti, si trova, tramite il calcolo variazionale, la soluzione che fornisce il carico di collasso del sistema piastra-suolo.
This research was supported by the CNR (National Research Council). 相似文献
84.
Gaetano Liso Giuseppe Trapani Vincenza Berardi Andrea Latrofa Paolo Marchini 《Journal of heterocyclic chemistry》1980,17(4):793-796
The reaction between 2-aminothiophenol 1 and acetylenic nitriles or esters 2a-d leads to the vinyl thio-ethers 3a-d. The conversion of 3 into benzothiazoles 8 and/or 1,4-benzothiazines 9 , in boiling dimethyl sulfoxide, has been achieved. A possible pathway involving benzothiazolines 5 as key intermediates is suggested. 相似文献
85.
Gaetano Villari 《Annali di Matematica Pura ed Applicata》1966,73(1):103-110
Sommario. Si studia il problema della esistenza di soluzioni armoniche per una classe di equazioni differenziali periodiche del terz’
ordine di tipo quasi lineare, e si stabilisce un criterio di esistenza che estende precedenti risultati.
Ricerca eseguita nell’ambito del Gruppo di Ricerca n. 11 del Comitato per la Matematica del C. N. R. 相似文献
86.
The bioadhesive properties of a novel chemical hydrogel based on a polymer of protein-like structure, have been investigated by using ATR FT-IR spectroscopy. In particular, the copolymer PHG obtained by partial derivatization of PHEA with GMA was chemically crosslinked by UV irradiation at 313 nm. Crosslinked PHG was treated with water to obtain a swelled sample, named PHG-UV gel, that was brought into contact with a phosphate buffer/citric acid solution at pH 7.0 in the absence or in the presence of mucin at various concentrations (0.01, 0.1 and 1 wt.-%). Preliminary dynamic swelling studies have evidenced the occurrence of an interaction between the PHG-UV gel and the glycoprotein. This result was confirmed by ATR FT-IR measurements. A diffusion model using a solution of Ficks' second law was employed to determine the diffusion coefficient of water into PHG-UV gel as a consequence of adsorption and/or interdiffusion which occur at the PHG-UV gel/mucin solution interface. Experimental results suggest a potential use of PHG-UV gel to prepare bioadhesive devices. 相似文献
87.
Piotr?BilerEmail author Marco?Cannone Ignacio A.?Guerra Grzegorz?Karch 《Mathematische Annalen》2004,330(4):693-708
The existence of solutions of a nonlinear parabolic equation describing the gravitational interaction of particles is studied for the initial data in spaces of (generalized) pseudomeasures. This approach permits us to relax regularity assumptions on the initial conditions and to prove asymptotic stability results for the above problem.Mathematics Subject Classification (2000):35B40, 35K15, 82C21 相似文献
88.
Bolognese A Correale G Manfra M Lavecchia A Novellino E Barone V 《Organic & biomolecular chemistry》2004,2(19):2809-2813
Microwave irradiation of a mixture of benzylidene-anilines and mercaptoacetic acid in benzene gives 1,3-thiazolidin-4-ones in very high yield (65-90%), whereas the same reaction performed through using the conventional method, at reflux temperature, requires a much longer time and gives a much lower yield (25-69%). This difference seems to be due to some intermediates and by-products formed during the conventional reaction. On the basis of 1H NMR studies, two different mechanisms, acting in benzene and in DMF, respectively, have been hypothesized for the thiazolidin-4-one system formation. 相似文献
89.
The reaction of O-alkylated p-aminocalix[n]arenes (n=4, 6, 8) with N,N′-di(tert-butoxycarbonyl)thiourea in the presence of HgCl2 and subsequent removal of the protective groups with hydrochloric acid led to the new water soluble calix[n]guanidinium derivatives (p-guanidiniumcalix[n]arenes) 20-23. With the exception of tetraoctyl-p-guanidiniumcalix[4]arene 21, which forms a macroscopic gelatinous aggregate even at very low concentration, all the synthesised guanidinium calixarenes show good solubility in water and sharp NMR signals. Moreover, these compounds are not cytotoxic and bind to plasmid DNA. 相似文献
90.
Using three-dimensional time-domain numerical simulations of the nonlinear dispersive Maxwell equations for a defect microcavity in a photonic crystal wire, we show that the transmission through the bandgap can be all-optically modulated via the generation of transient states associated with the nonlinear splitting of the defect mode. Analytical results based on time-domain coupled-mode theory are derived as well. 相似文献