全文获取类型
收费全文 | 28493篇 |
免费 | 3134篇 |
国内免费 | 1808篇 |
专业分类
化学 | 19445篇 |
晶体学 | 235篇 |
力学 | 170篇 |
综合类 | 71篇 |
数学 | 59篇 |
物理学 | 13455篇 |
出版年
2024年 | 48篇 |
2023年 | 222篇 |
2022年 | 752篇 |
2021年 | 771篇 |
2020年 | 883篇 |
2019年 | 861篇 |
2018年 | 731篇 |
2017年 | 853篇 |
2016年 | 1346篇 |
2015年 | 1303篇 |
2014年 | 1377篇 |
2013年 | 2366篇 |
2012年 | 1718篇 |
2011年 | 1894篇 |
2010年 | 1565篇 |
2009年 | 1995篇 |
2008年 | 1873篇 |
2007年 | 1986篇 |
2006年 | 1824篇 |
2005年 | 1448篇 |
2004年 | 1251篇 |
2003年 | 1049篇 |
2002年 | 816篇 |
2001年 | 656篇 |
2000年 | 586篇 |
1999年 | 528篇 |
1998年 | 451篇 |
1997年 | 401篇 |
1996年 | 339篇 |
1995年 | 276篇 |
1994年 | 214篇 |
1993年 | 194篇 |
1992年 | 155篇 |
1991年 | 121篇 |
1990年 | 79篇 |
1989年 | 69篇 |
1988年 | 116篇 |
1987年 | 59篇 |
1986年 | 35篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 9篇 |
1982年 | 28篇 |
1981年 | 29篇 |
1980年 | 24篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1976年 | 8篇 |
1973年 | 10篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
P. Macko D. Romanini O.V. Naumenko A. Jenouvrier A. Campargue 《Journal of Molecular Spectroscopy》2004,227(1):90-108
The absorption spectrum of natural water vapour around 1.5 μm has been recorded with a typical sensitivity of 5 × 10−10 cm−1 by using a CW-cavity ring down spectroscopy set up based on fibred DFB lasers. A series of 31 DFB lasers has allowed a full coverage of the 6130.8-6748.5 cm−1 (1.63-1.48 μm) region corresponding to the H transparency band of the atmosphere. The line parameters (wavenumber and intensity) of a total of 5190 lines, including 4247 lines of water vapor, were derived by a one by one fit of the lines to a Voigt profile. Different isotopologues of water (H216O, H218O, H217O, and HD16O) present in natural abundance in the sample contribute to the spectrum. For the main isotopologue, H216O, 2130 lines were measured with line intensities as weak as 10−29 cm/molecule while only 926 lines (including a proportion of 30% inaccurate calculated lines) with a minimum intensity of 3 × 10−27 cm/molecule are provided by the HITRAN and GEISA databases. Our comparison in the whole 5750-7965 cm−1 region, has also evidenced that an error in the process of conversion of the intensity units from cm−2/atm to cm−1/(molecule × cm−2) at 296 K, has led to H216O line intensities values listed in the HITRAN-2000 database, systematically 8 % below the original FTS values. The rovibrational assignment was performed on the basis of the ab initio calculations by Schwenke and Partridge with a subsequent refinement and validation using the Ritz combination principle together with all previously measured water transitions relevant to this study. This procedure allowed determining 172, 139, 71, and 115 new energy levels for the H216O, H218O, H217O, and HD16O isotopologues, respectively. The results are compared with the available databases and discussed in regard of previous investigations by Fourier transform spectroscopy. The spectrum analysis has showed that most of the transitions which cannot be assigned to water are very weak and are due to impurities such as carbon dioxide and ammonia, leaving only about 3% of the observed transitions unassigned. The interest of a detailed knowledge of water absorption for trace detectors developed in the 1.5 μm range is underlined: for instance HDO contributes significantly to the considered spectrum while no HDO line parameters are provided by the HITRAN database. 相似文献
83.
84.
Ildikó Mohammed-Ziegler Ferenc Billes 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):19-42
This review summarizes different applications of optical spectroscopic methods in calixarene chemistry including UV/Vis spectrometry,
vibrational spectroscopic techniques (FTIR and Raman spectroscopy), luminescence spectroscopy (including fluorescence and
phosphorescence), ellipsometry and various optical microscopic methods. Moreover, the results of theoretical studies (AM1,
PM3, DFT, ab initio, etc.) are summarized based on selected papers in the field of conformational studies, thermodynamics and complexation features.
About 300 references are processed systematically from the results reported mainly in the recent years with emphasis on the
potential of practical application of these molecules. 相似文献
85.
M.D. Williams S.C. Williams S.A. Yasharahla N. Jallow 《Applied Surface Science》2007,253(20):8568-8570
Ultraviolet photoemission spectroscopy is used to study the kinetics of the H-Zn complex deactivation in Zn doped InP(1 0 0). Hydrogen injected into the material electronically passivates the local carrier concentration. Reverse-biased anneals of the InP under ultra-high vacuum show a dramatic change in the work function of the material with increasing temperature. Spectral features are also shown to be sensitive to sample temperature. To our knowledge, we show the first view of hydrogen retrapping at the surface using photoemission spectroscopy. A simple photoelectron threshold energy analysis shows the state of charge compensation of the material. 相似文献
86.
J rgen Rosenqvist Kristina Axe Staffan Sj berg Per Persson 《Colloids and surfaces. A, Physicochemical and engineering aspects》2003,220(1-3):91-104
The adsorption of the dicarboxylates o-phthalate, maleate, fumarate, malonate, and oxalate (representing ligands with the general composition −O2C---Cn---CO2−; n=0, 1, or 2) on gibbsite were studied by means of quantitative batch adsorption experiments and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The interpretations of ATR-FTIR spectra were aided by comparison with IR spectra of solution species and by results from theoretical frequency calculations. The main objectives of the study were to identify the molecular level bonding mechanisms of the dicarboxylates to gibbsite, and to investigate how these were influenced by the composition and structure of the ligands. Carboxylates with n=2 formed predominantly outer sphere complexes, whereas the importance of inner sphere complexes progressively increased for n=1 and 0. The inner sphere structures were identified as mononuclear chelates with one oxygen from each carboxylate group bonded to Al(III) at the surface. This showed the importance of chelate ring structure for the formation of inner sphere surface complexes, with stabilities of the complexes increasing in the order seven-membered ring less than six-membered ring less than five-membered ring. For ligands with n=2 only small variations in surface speciation were observed as a function of steric factors; irrespective of the relative positions of the carboxylate groups and bulkiness of the ligands outer sphere bonding is the dominating adsorption mode. Adsorption experiments were also conducted with gibbsite particles exhibiting differences in shape and surface roughness. These experiments showed that inner sphere complexes were favored on the less well-developed and more irregular gibbsite particles. 相似文献
87.
S. Han H. Kühn F. W. Hsing K. Münnemann B. Blümich S. Appelt 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,167(2):187
We have visualized the melting and dissolution processes of xenon (Xe) ice into different solvents using the methods of nuclear magnetic resonance (NMR) spectroscopy, imaging, and time resolved spectroscopic imaging by means of hyperpolarized 129Xe. Starting from the initial condition of a hyperpolarized solid Xe layer frozen on top of an ethanol (ethanol/water) ice block we measured the Xe phase transitions as a function of time and temperature. In the pure ethanol sample, pieces of Xe ice first fall through the viscous ethanol to the bottom of the sample tube and then form a thin layer of liquid Xe/ethanol. The xenon atoms are trapped in this liquid layer up to room temperature and keep their magnetization over a time period of 11 min. In the ethanol/water mixture (80 vol%/20%), most of the polarized Xe liquid first stays on top of the ethanol/water ice block and then starts to penetrate into the pores and cracks of the ethanol/water ice block. In the final stage, nearly all the Xe polarization is in the gas phase above the liquid and trapped inside the pores. NMR spectra of homogeneous samples of pure ethanol containing thermally polarized Xe and the spectroscopic images of the melting process show that very high concentrations of hyperpolarized Xe (about half of the density of liquid Xe) can be stored or delivered in pure ethanol. 相似文献
88.
Daniel E. Vogler Ana Lorencak Julien M. Rey Markus W. Sigrist 《Optics and Lasers in Engineering》2005,43(3-5):527
A novel sensitive technique for the determination of losses in fiber cavities is presented. The method is based on the cavity ringdown scheme implemented in silica-based single-mode fibers. Bending losses of fiber cavities of different lengths have been measured showing all an oscillating behavior with respect to the curvature radius of the fiber as predicted by a theoretical model. The best minimum detectable absorbance per cavity pass achieved by this new method is 1.72×10−3 dB within a 10 m-long cavity. This limit suffices well for an accurate determination of optical bending losses even in bend-insensitive fibers. Furthermore, the comparison of the measured bending losses with a theoretical model allows the extraction of different fiber parameters. Good agreement has been found between the experimentally derived parameters and literature data. 相似文献
89.
Jan-Martin Heldt Michèle Salmain Gérard Jaouen 《Journal of organometallic chemistry》2004,689(25):4775-4782
The first poly(amidoamine) (PAMAM) dendrimers tethered with both (η5-cyclopentadienyl) rhenium tricarbonyl (CpRe(CO)3) units and polyethylene glycol (PEG) chains were prepared and characterized by combining NMR spectroscopy and Fourier-transform IR spectroscopy. Grafting of CpRe(CO)3 units was achieved by reductive amination of formyl-CpRe(CO)3 with the peripheral amines of generation 3 and 4 PAMAMs to yield dendrimers labeled with a variable number of CpRe(CO)3 units, ranging from 8 to 14 for PAMAM-G3 and 17-30 for PAMAM-G4. PEG chains of different lengths were then attached to some of the remaining peripheral amines, and their respective ability to improve the solubility of the metallodendrimers in aqueous buffered media was evaluated. These metallodendrimers represent new infrared probes designed to be coupled to immunological reagents for the amplification of the IR signal in carbonyl metallo immunoassay (CMIA). 相似文献
90.
研究了 2 0 0 0年 MCM— B题 ,将问题推广到有三层干扰的复杂情况 ,给出并严格证明了 ( k,1,1)问题的最优解 相似文献