全文获取类型
收费全文 | 1370篇 |
免费 | 37篇 |
国内免费 | 24篇 |
专业分类
化学 | 896篇 |
晶体学 | 17篇 |
力学 | 17篇 |
数学 | 289篇 |
物理学 | 153篇 |
无线电 | 59篇 |
出版年
2022年 | 18篇 |
2021年 | 32篇 |
2020年 | 12篇 |
2019年 | 19篇 |
2018年 | 23篇 |
2017年 | 22篇 |
2016年 | 42篇 |
2015年 | 32篇 |
2014年 | 47篇 |
2013年 | 106篇 |
2012年 | 73篇 |
2011年 | 80篇 |
2010年 | 50篇 |
2009年 | 39篇 |
2008年 | 65篇 |
2007年 | 90篇 |
2006年 | 77篇 |
2005年 | 62篇 |
2004年 | 70篇 |
2003年 | 48篇 |
2002年 | 52篇 |
2001年 | 34篇 |
2000年 | 23篇 |
1999年 | 16篇 |
1998年 | 18篇 |
1997年 | 16篇 |
1996年 | 23篇 |
1995年 | 21篇 |
1994年 | 11篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 18篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1970年 | 2篇 |
排序方式: 共有1431条查询结果,搜索用时 15 毫秒
991.
Abstract The high-pressure reaction of 2-alkylfurans with diethyl mesoxalate is described. The competition between substitution at position 5 of the furan ring and at the alkyl group as well as the effect of pressure on the regiochemical outcome of this reaction are presented. 相似文献
992.
Piyush S. Sharma Marcin Dabrowski Krzysztof Noworyta Tan-Phat Huynh Chandra B. KC Janusz W. Sobczak Piotr Pieta Francis D’Souza Wlodzimierz Kutner 《Analytica chimica acta》2014
For molecular imprinting of oxidatively electroactive analytes by electropolymerization, we used herein reductively electroactive functional monomers. As a proof of concept, we applied C60 fullerene adducts as such for the first time. For that, we derivatized C60 to bear either an uracil or an amide, or a carboxy addend for recognition of the adenosine-5′-triphosphate (ATP) oxidizable analyte with the ATP-templated molecularly imprinted polymer (MIP-ATP). Accordingly, the ATP complex with all of the functional monomers formed in solution was potentiodynamically electropolymerized to deposit an MIP-ATP film either on an Au electrode of the quartz crystal resonator or on a Pt disk electrode for the piezoelectric microgravimetry (PM) or capacitive impedimetry (CI) determination of ATP, respectively, under the flow-injection analysis (FIA) conditions. The apparent imprinting factor for ATP was ∼4.0. After extraction of the ATP template, analytical performance of the resulting chemosensors, including detectability, sensitivity, and selectivity, was characterized. The limit of detection was 0.3 and 0.03 mM ATP for the PM and CI chemosensor, respectively. The MIP-ATP film discriminated structural analogues of ATP quite well. The Langmuir, Freundlich, and Langmuir–Freundlich isotherms were fitted to the experimental data of the ATP sorption and sorption stability constants appeared to be nearly independent of the adopted sorption model. 相似文献
993.
994.
Janusz Zar?bski 《Microelectronics Journal》2006,37(8):728-734
In the paper the problem of modelling PWM voltage mode controllers for SPICE is considered. SPICE library isothermal macromodel and a new form of the authors' electrothermal (including selfheating) macromodel of SG3525A controller are presented and compared. To illustrate the correctness and usefulness of these macromodels, some results of measurements and calculations of SG3525A controller operating in the catalogue test circuit and in the real BOOST converter are given as well. 相似文献
995.
996.
Fabrice R. A. Onofri Mariusz Krzysiek Janusz Mroczka Kuan-Fang Ren Stefan Radev Jean-Philippe Bonnet 《Experiments in fluids》2009,47(4-5):721-732
The newly developed critical angle refractometry and sizing technique (CARS) allows simultaneous and instantaneous characterization of the local size distribution and the relative refractive index (i.e. composition) of a cloud of bubbles. The paper presents the recent improvement of this technique by comparison of different light scattering models and inversion procedures. Experimental results carried in various air/water and air/water-ethanol bubbly flows clearly demonstrate the efficiency and the potential of this technique. 相似文献
997.
Katrina Brandstadt David L. Frost Janusz A. Kozinski 《Proceedings of the Combustion Institute》2009,32(2):1913-1919
The objective of this study was to gain understanding of the preignition oxidation of Al powders in CO2. The thermal behavior and reaction energy was studied using simultaneous thermogravimetric analysis and differential scanning calorimetry (TG–DSC). The particle morphology was examined at different stages of the process using field emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM). The corresponding chemical changes were analyzed by X-ray diffraction spectrometry (XRD) and energy dispersion X-ray spectrometry (EDS). Dimensional properties of Al particles have a significant influence on the oxidation processes. Distinctly different properties were shown between nm-Al and μm-Al, where the reactions are found to occur at different temperature ranges. The powder behavior is controlled by the oxide layer that coats each particle and prevents exposure of the metal core to the reactive CO2 gas. The properties of the oxide layer are related to the particle size. Carbon has been shown to play an important role in the reacting Al–CO2 system. A new mechanism of nano-Al particle oxidation in CO2 under gradually increasing temperature was proposed. 相似文献
998.
This paper deals with the problem of modelling current mode PWM controllers with the use of SPICE. The monolithic integrated circuit UC3842 is considered in the paper. Two isothermal models of UC3842 known in the literature are compared, tested and discussed. A new electrothermal model (ETM), including selfheating, of the considered controller is proposed and described in detail. The experimental verification of the ETM showed its much greater accuracy compared to the isothermal models of the investigated device. 相似文献
999.
Salah S. Massoud Elodie Druel Marisa Dufort Roger Lalancette Jarrett Kitchen Janusz Grebowicz Ramon Vicente Uday Mukhopadhyay Ivan Bernal Franz A. Mautner 《Polyhedron》2009,28(17):3849-3857
A novel series of 4,4′-bipyridine- and 1,2-bis(4-pyridyl)ethane-Cu(II) complexes were synthesized using a variety of amine ligands (DPA = di(2-pyridylmethyl)amine, Medpt = 3,3′-diamino-N-methyldipropylamine, Hbpca = bis(2-pyridylcarbonyl)amine, TPA = tris(2-pyridylmethyl)amine) and cyclen = 1,4,7,10-tetraazacyclododecane). Different complexes were obtained including mononuclear [Cu(cyclen)(4,4′-bipy)](ClO4)2 (1), dinuclear {[Cu(μ2-bpca)(4,4′-bipy)(H2O)]ClO4}2 (2), [Cu2(DPA)2(μ2-4,4′-bipy)(ClO4)4)]·H2O (3), [Cu2(cyclen)2(μ2-bpe)](ClO4)4 (4) and [Cu2(TPA)2(μ2-bpe)](ClO4)4 (5) and the 1-D polymer, {[Cu(Medpt)(μ2-4,4′-bipy)](ClO4)2}n (6). In the 1–6 samples, cooling up to 100 K produces only the expected, minor, changes in cell constants given no space group changes. Therefore, data for the 100 K structures are reported only. Single-crystal X-ray crystallography reveals the monodentate coordination of the 4,4′-bipy in 1 and 2, and the bridged nature of the di-pyridyl ligands in the dinuclear complexes 2–5 and in the polymeric complex 6. In this series, structures 3–6 consist of the 4,4′-bipy or bpe bridging the two Cu(II) centers, the coordination by the tri- or the tetra-N donors of the amine, and the ClO4? groups as counter ions in 4–6 complexes. In the complexes 3–6, the Cu···Cu distances across the bridged di-pyridyl ligands were found to be greater than 11 Å. The magnetic properties of complex 3 reveal no evidence for magnetic coupling between the two Cu(II) centers (J = ?0.58 cm?1). 相似文献
1000.