全文获取类型
收费全文 | 33741篇 |
免费 | 178篇 |
国内免费 | 284篇 |
专业分类
化学 | 12869篇 |
晶体学 | 335篇 |
力学 | 1523篇 |
综合类 | 14篇 |
数学 | 9476篇 |
物理学 | 9986篇 |
出版年
2022年 | 55篇 |
2021年 | 122篇 |
2020年 | 113篇 |
2019年 | 171篇 |
2018年 | 1394篇 |
2017年 | 1646篇 |
2016年 | 938篇 |
2015年 | 673篇 |
2014年 | 668篇 |
2013年 | 980篇 |
2012年 | 3406篇 |
2011年 | 2611篇 |
2010年 | 2123篇 |
2009年 | 1836篇 |
2008年 | 875篇 |
2007年 | 896篇 |
2006年 | 891篇 |
2005年 | 4622篇 |
2004年 | 4068篇 |
2003年 | 2410篇 |
2002年 | 587篇 |
2001年 | 395篇 |
2000年 | 211篇 |
1999年 | 247篇 |
1998年 | 204篇 |
1997年 | 133篇 |
1996年 | 63篇 |
1995年 | 52篇 |
1994年 | 55篇 |
1992年 | 175篇 |
1991年 | 160篇 |
1990年 | 139篇 |
1989年 | 111篇 |
1988年 | 101篇 |
1987年 | 63篇 |
1986年 | 43篇 |
1985年 | 46篇 |
1984年 | 37篇 |
1983年 | 36篇 |
1981年 | 33篇 |
1979年 | 39篇 |
1976年 | 86篇 |
1975年 | 44篇 |
1974年 | 47篇 |
1973年 | 55篇 |
1972年 | 41篇 |
1970年 | 35篇 |
1969年 | 41篇 |
1968年 | 35篇 |
1966年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
1.
2.
3.
Kozetozhets I. V. Panasyuk G. P. Semenov E. A. Buzanov G. A. Avdeeva V. V. Danchevskaya M. N. Tsvetov N. S. Shapovalov S. S. Vasilev M. G. 《Russian Journal of General Chemistry》2022,91(1):S98-S105
Russian Journal of General Chemistry - Highly dispersed CaO has been synthesized by heating an aqueous solution of calcium nitrate and D-glucose up to 800°C. Calcium oxide is formed with an... 相似文献
4.
S.V. Ivanov M.Yu. Chernov V.A. Solovev P.N. Brunkov D.D. Firsov O.S. Komkov 《Progress in Crystal Growth and Characterization of Materials》2019,65(1):20-35
High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5?μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1?Å are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ~8?μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic InxAl1-xAs buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded InxAl1-xAs MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6?μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T?=?10–300?K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As4/III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3?×?107 cm?2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300?nm, the extremely low surface roughness with the RMS value of 1.6–2.4?nm, measured by AFM, as well as rather high 3.5?μm-PL intensity at temperatures up to 300?K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform. 相似文献
5.
Mathematical Notes - It is proved that the lattice of all Fitting classes of finite groups is not distributive, and conditions under which Fitting classes satisfy the distributive and modular laws... 相似文献
6.
7.
Turyanskiy A. G. Vorob’ev N. S. Gizha S. S. Makushina V. A. Mikhal’kov Yu. M. Smirnov A. V. Pirshin I. V. Senkov V. M. Shashkov E. V. Fishman R. I. Ziyatdinova M. Z. Komel’kov A. S. 《JETP Letters》2020,112(11):734-738
JETP Letters - The possibility of stable generation of intense characteristic Cs radiation upon electronic excitation of a Mo anode target heat treated in Cs and O2 vapors is demonstrated. The... 相似文献
8.
Voskresenskaya Olga O. Skorik Nina A. 《Monatshefte für Chemie / Chemical Monthly》2020,151(4):533-542
Monatshefte für Chemie - Chemical Monthly - A comparative analysis is performed on the stability constants $${\upbeta }_{1yn}$$ and intramolecular redox decomposition rate constants $$k_{n\; =... 相似文献
9.
D. V. Vyalykh A. M. Shikin G. V. Prudnikova A. Yu. Grigor’ev A. G. Starodubov V. K. Adamchuk 《Physics of the Solid State》2002,44(1):164-170
This paper reports on the first experimental observation of quantum-well states and sp-type resonances in thin single-crystal gold, silver, and copper layers formed on single-crystal W(110) surfaces, which result from spatial localization of Bloch-type electronic wave functions in a quantum well with potential barriers at the vacuum/metal and metal/W(110) interfaces. The quantization of the valence-band electronic structure in Au/W(110), Ag/W(110), and Cu/W(110) systems was studied experimentally using angle-resolved photoelectron spectroscopy. 相似文献
10.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献