全文获取类型
收费全文 | 701503篇 |
免费 | 6039篇 |
国内免费 | 1823篇 |
专业分类
化学 | 351048篇 |
晶体学 | 9747篇 |
力学 | 35770篇 |
综合类 | 21篇 |
数学 | 101092篇 |
物理学 | 211687篇 |
出版年
2021年 | 5731篇 |
2020年 | 6336篇 |
2019年 | 7109篇 |
2018年 | 13566篇 |
2017年 | 13860篇 |
2016年 | 15445篇 |
2015年 | 7751篇 |
2014年 | 12301篇 |
2013年 | 28780篇 |
2012年 | 24177篇 |
2011年 | 32676篇 |
2010年 | 23028篇 |
2009年 | 22955篇 |
2008年 | 30326篇 |
2007年 | 32187篇 |
2006年 | 22983篇 |
2005年 | 23405篇 |
2004年 | 20327篇 |
2003年 | 18939篇 |
2002年 | 17797篇 |
2001年 | 17950篇 |
2000年 | 14211篇 |
1999年 | 10795篇 |
1998年 | 9356篇 |
1997年 | 9261篇 |
1996年 | 8792篇 |
1995年 | 7794篇 |
1994年 | 7774篇 |
1993年 | 7596篇 |
1992年 | 8057篇 |
1991年 | 8539篇 |
1990年 | 8185篇 |
1989年 | 8085篇 |
1988年 | 7924篇 |
1987年 | 7683篇 |
1986年 | 7412篇 |
1985年 | 9520篇 |
1984年 | 9964篇 |
1983年 | 8271篇 |
1982年 | 8760篇 |
1981年 | 8179篇 |
1980年 | 7782篇 |
1979年 | 8351篇 |
1978年 | 8771篇 |
1977年 | 8570篇 |
1976年 | 8538篇 |
1975年 | 8118篇 |
1974年 | 7998篇 |
1973年 | 8384篇 |
1972年 | 5990篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Hybrid numerical—experimental approach for investigation of dynamics of microcantilever relay system
V. Ostasevicius S. Tamulevicius A. Palevicius M. Ragulskis R. Palevicius V. Grigaliunas 《Optics and Lasers in Engineering》2005,43(1):199
The time average holography measurements of the vibrating microelectromechanical switch (MEMS) were performed in this study. Experimental measurement results exhibit good agreement with computer generated holographic interferogram analysis. The validation of experimental investigations versus numerical analysis provides the necessary background to analyze the dynamical characteristics of micromechanical systems in virtual numerical environments. Direct application of fringe counting techniques for reconstruction of motion from time average holograms cannot be straightforward if the analyzed micromechanical systems contain motion limiters. Modifications of a classical time average holographic technique enable qualitative analysis of MEMS and can be applied for investigation of dynamical properties of much broader classes of MEMS systems. 相似文献
992.
Within the framework of microscopic fluctuation-dissipation theory, we obtain the stochastic equation describing the Brownian motion of an electron in the phonon field of the crystal lattice. An expression for the Green’s function of the phonon field is found in general form and for the case of linear phonon-variable interaction of an electron with the phonon field with allowance for the potential screening of crystal-lattice nuclei. An expression for the phonon drag acting on a conduction electron in the lattice field is found and analyzed with allowance for the interaction. Frequency dependence of the coefficient of the phonon drag acting on a conduction electron is studied and the contribution of the electron-phonon interaction to the effective mass of a charge carrier is determined.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 3, pp. 249–268, March 2005. 相似文献
993.
Complex impedance spectra were obtained on a crystal of CaCu3Ti4O12 (CCTO) from 289 to 456 K. As in the case of ceramic CCTO, these spectra can be interpreted as arising from a conducting material containing insulating barriers. This is then further evidence for the existence of planar defects within crystals of CCTO that act as insulating barriers and produce the large dielectric constant through a space charge mechanism. 相似文献
994.
The aim of this work is to study the dynamic formation and dissociation of trions and excitons in double barrier resonant tunneling diodes. We propose a system of rate equations that takes into account the formation, dissociation and annihilation of these complexes inside the quantum well. From the solutions of the coupled equations, we are able to study the modulation of excitons and trions formation in the device as a function of the applied bias. The results of our model agree qualitatively with the experiments showing the viability of these rate equations system to study the dynamics of complex systems. 相似文献
995.
996.
997.
T. T. Vasil'eva V. A. Kochetkova V. I. Dostovalova B. V. Nelyubin R. Kh. Freidlina 《Russian Chemical Bulletin》1989,38(11):2346-2349
The radical telomerization of 3,3,3-trifluoropropene with bromoform and methylens bromide has been studied. The nature of the products with bromoform depends substantially on the method of initiation. In the presence of Fe(CO)5 + DMF, telomers of CHBr2(CH52CHCF3)nBr are formed, while with initiation with benzoyl peroxide other compounds are also formed that contain two, three, or four bromine atoms per molecule. To elucidate the formation of these products a reaction scheme is proposed that involves rearrangement of CHBr2CH2CH(CF3)CH3CHCF3 radicals to CBr2CH2CH(CF3)CH2CH2CF3 radicals.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2558–2562, November, 1989. 相似文献
998.
999.
V. A. Maihara M. B. A. Vasconcellos 《Journal of Radioanalytical and Nuclear Chemistry》1989,132(2):329-337
Instrumental neutron activation analysis was applied to the determination of the elements Na, K, Br, As, Rb, Zn, Co, Fe and Sc in Brazilian rice samples and in biological standards. Hg and Se concentrations were determined by using a simple radiochemical separation. The chemical procedure was carried out by means of distillation of Hg and Se in HBr medium and subsequent precipitation of selenium by sodium metabisulfite and mercury by thioacetamide. The accuracy of the instrumental and radiochemical methods was evaluated by means of analysis of the Reference Materials NBS-Bovine Liver, Bowen's Kale and NBS-Rice Flour. 相似文献
1000.
W M Niessen M A de Kraa E R Verheij P J Bergers G F La Vos U R Tjaden J van der Greef 《Rapid communications in mass spectrometry : RCM》1989,3(1):1-4
On-line sample pretreatment by means of the phase-system switching approach is an interesting technique for the analysis of aqueous samples, e.g., plasma, by means of supercritical-fluid chromatography. In order to analyse plasma samples the following analytical procedure is used. The plasma sample is injected on to a short precolumn, which is washed with water and subsequently dried with nitrogen. Next, the solutes are desorbed with the supercritical mobile phase, analysed with packed-column supercritical-fluid chromatography and detected with either a UV detector or a mass spectrometer, equipped with a moving-belt interface. The herbicide diuron is selected as a test compound to study the feasibility of this approach. Using a selective detector the procedure is sufficiently sensitive to detect diuron in plasma, but not appropriate to detect the diuron metabolites in a post-mortem plasma sample. These have been identified with liquid chromatography/mass spectrometry. The detection limit of diuron in plasma using the procedure described is about 30 ng/mL. 相似文献