全文获取类型
收费全文 | 12890篇 |
免费 | 764篇 |
国内免费 | 580篇 |
专业分类
化学 | 8656篇 |
晶体学 | 187篇 |
力学 | 258篇 |
综合类 | 2篇 |
数学 | 262篇 |
物理学 | 4869篇 |
出版年
2024年 | 23篇 |
2023年 | 474篇 |
2022年 | 282篇 |
2021年 | 264篇 |
2020年 | 506篇 |
2019年 | 319篇 |
2018年 | 342篇 |
2017年 | 378篇 |
2016年 | 607篇 |
2015年 | 535篇 |
2014年 | 602篇 |
2013年 | 655篇 |
2012年 | 697篇 |
2011年 | 430篇 |
2010年 | 533篇 |
2009年 | 531篇 |
2008年 | 330篇 |
2007年 | 470篇 |
2006年 | 649篇 |
2005年 | 411篇 |
2004年 | 277篇 |
2003年 | 327篇 |
2002年 | 307篇 |
2001年 | 462篇 |
2000年 | 211篇 |
1999年 | 381篇 |
1998年 | 226篇 |
1997年 | 147篇 |
1996年 | 106篇 |
1995年 | 89篇 |
1994年 | 81篇 |
1993年 | 78篇 |
1992年 | 84篇 |
1991年 | 58篇 |
1990年 | 66篇 |
1989年 | 89篇 |
1988年 | 383篇 |
1987年 | 804篇 |
1986年 | 810篇 |
1985年 | 118篇 |
1984年 | 47篇 |
1983年 | 25篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Jerald S. Bradshaw Reed M. Izatt James J. Christensen Krzystof E. Krakowiak Bryon J. Tarbet Ronald L. Bruening S. Lifson 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(2):127-136
Silica gel-bound crown ethers and aza macrocycles have been synthesized with the attaching arm connected to the carbon framework of the macrocycles. The interactions of these bound macrocycles with cations are almost identical to those involving the analogous free macrocycles. This has allowed for predictable cation separation, concentration, and removal processes to be performed on a small scale. Quantum mechanical calculations and NMR measurements indicate that similarly bound chiral macrocycles will be capable of use in separating chiral organic amines.Dedicated to the memory of Professor James J. Christensen who died on 5 September 1987. 相似文献
82.
Tomoya Kinumi Kazuo Tsujimoto Mamoru Ohashi Reiko Hara Tomiyuki Hara Koichi Ozaki Miho Saka Yuko Katsuta Akimori Wada Masayoshi Ito 《Photochemistry and photobiology》1993,58(3):409-412
Abstract— 3, 7-Dimethyl-2, 4, 6, 8, 10-dodecapentaenal was synthesized for reconstitution of the retinochrome analog. Its opsin shift was 1000 cm 1 smaller than that of native retinochrome, whose chromophore contains the same number of double bonds. The conformational change from 6-s-trans to 6-s-cis , as figured in a retinal molecule, plays an important role in the formation of the retinochrome analog, based on the estimation of opsin shifts for retinal analogs locked in the 6-s conformation. Thus the conformation of the 6–7 single bond in the native retinochrome was suggested to be 6 -cis . Analysis of the circular dichroic spectra of retinochrome analogs revealed that the 6-s conformation is independent of the appearance of the β-band. The stereoselectivity in the photoisomerization of the retinal analogs by a retinochrome template depends on the hydrophobic binding in the region of the β-ionone ring. 相似文献
83.
Four para-dialkylaminophenyl (PDAAP1-PDAAP4) bearing carboxyl groups were studied for application to the dye-sensitized solar cells (DSC). It was found the short spacer CH2 between carboxyl and dialkylaminophenyl chromophore in PDAAP3 and PDAAP4 led to highly efficient monochromatic incident photon-to-current conversion efficiencies (IPCE), however the long alkyl group C4H9 attached on aniline moieties in PDAAP2 and PDAAP4 favored improvement of open-circuit photovoltage. Thus, the solar cell sensitized by PDAAP4, having both short carboxyl groups CH2COOH and long alkyl groups C4H9, exhibited the IPCE maximum of 73% at 670 nm and overall energy conversion efficiency η of 3.06%, representing the highest IPCE and η values so far in dialkylaminophenyl-based organic dye-sensitized semiconductor solar cells. Taking advantage of the highly efficient sensitizing ability of PDAAP4 in far-red region, the data of IPCE above 630 nm of the solar cells were improved greatly by cosensitization with both N3 and PDAAP4. The influences of the TiO2 film thickness and the concentration of 4-tert-butylpyridine (TBP) in electrolyte were also investigated. 相似文献
84.
Chaowei Yuan Wen Cui Yanjuan Sun Jiadong Wang Ruimin Chen Jin Zhang Yuxin Zhang Fan Dong 《中国化学快报》2020,31(3):751-754
It is of a great challenge to develop semiconductor photocatalysts with potential possibilities to simultaneously enhance photocatalytic efficiency and inhibit generation of toxic intermediates.In this study,we developed a facile method to induce the La doping and cationic vacancie(V(Zn))on ZnO for the highly efficient complete NO oxidation.The photocatalytic NO removal efficiency increases from 36.2%to 53,6%.Most importantly,a significant suppressed NO2 production also has been realized.According to the DFT calculations,ESR spectra and in situ FTIR spectra,the introduction of La^3+induce the redistribution of charge carriers in La-ZnO,which promote the production of·O2^- and lead to the formation of V(Zn)for the formation of·OH,contributing to the complete oxidation of NO to nitrate.Besides,the conversion pathway of photocatalytic NO oxidation has been elaborated,This work paves a new way to simultaneously realize the photocatalytic pollutants removal and the inhibition of toxic intermediates generation for efficient and safe air purification. 相似文献
85.
《Spectrochimica Acta Part B: Atomic Spectroscopy》2005,60(7-8):1002-1013
Laser-induced breakdown spectroscopy (LIBS) has been performed on immersed solid samples with different grades of surface roughness and material homogeneity and on bulk water solutions. The underwater plasma was produced by applying double-pulse excitation at 1064 nm, with different sets of laser pulse energies. LIBS spectra were recorded separately for each couple of laser pulses in order to monitor shot-to-shot plasma behavior and to apply signal post processing. The latter was aimed at improving the detection limits for elemental analyses. Except in the case of flat homogeneous solid samples at high laser pulse energies, the measurements were affected by strong shot-to-shot signal oscillations. Automatic elimination of low intensity spectra reduced the detection limit up to a factor of seven. The optimum level for spectral filtering depends strongly on sample properties. For bulk water, a poor correlation was observed between the peak line intensities and the plasma continuum emission, making the peak-to-background ratio unsuitable for internal standardization purposes. The analytical performance of LIBS for bulk liquid was also affected by the spatial fluctuations of the breakdown location, a phenomenon known as “moving breakdown” in the literature, which was responsible for the signal depletion in the detection region. In preliminary measurements on water solutions, the detection limit of 0.2 mg/l for magnesium has been obtained after applying data post processing. 相似文献
86.
Uniform and sphere-like nanoparticles of crystalline Pr3+-doped CaTiO3 have been prepared from complex polymer precursor at 600°C, in which, metal atoms are previously dispersed by citric acid in ethylene glycol solvent. The decomposition process of the precursor, crystallization, and particle sizes of CaTiO3 have been investigated by using thermal analysis, powder X-ray diffraction and transmission electron microscopy. Diffuse reflectance spectra, photoluminescence and decay curve indicate that a strong red emission located at the nearly NTCS “ideal red” site is deduced from the energy transfer from the band gap absorption to doping Pr3+ ions. The thermoluminescence curves exhibit that a potential long phosphorescent material based on Pr3+-doped CaTiO3 will be explored in future. 相似文献
87.
Summary A detector for microchromatography in which Raman spectroscopy is used to identify the eluted species has been developed.
The detector is designed to be applicable to a wide range of compounds without requiring the presence of a chromophore. Its
use is illustrated in the analysis of nitro compounds on a 250 μm i.d. column. Raman spectra of each of the compounds could
be identified as they passed the detector. The advatages of the use of fully deuterated solvents are demonstrated by the analysis
of nitrobenzenes in methanol/water mobile phases. The detection limit for nitrobenzene using the Raman line at 1342 cm−1 was 75ng. 相似文献
88.
《Vibrational Spectroscopy》2006,40(1):20-24
The Langmuir–Blodgett (LB) films of 14,15-bis(hydroxyimino)-13-thiaoctacosane (TOC) on aluminium plated substrates were investigated using Fourier transform infrared (FTIR), grazing angle (GAIR) and horizontal attenuated total reflectance (HATR) techniques. The LB films of TOC can be transferred onto the solid substrate successfully. The molecular structure of LB films was analysis by comparing the GAIR and HTAR spectra. The intense bands at 2848 and 2918 cm−1 are assigned to symmetric νs(CH2) and asymmetric νa(CH2) stretching vibrations of methylene groups. These peaks suggest that the alkyl chains in TOC are nearly in all-trans conformational state. The presence in the infrared spectra of several bands due to the methylene wagging and twisting modes and of the splitting of the bands due to the methylene scissoring mode at 1467 and 1459 cm−1 and the CH2 rocking mode at 720 and 731 cm−1 also indicates that in films of TOC alkyl chains are in the all-trans conformation and packed in either an orthorhombic or a monoclinic structure with an orthorhombic subcell containing two mutually orthogonal molecules. Another conclusion presented in this paper that the alkyl chain tilt, which is the angle between the axis, which bisects the C–C bonds and the surface normal, was quite large by comparing the GAIR and HATR spectra. 相似文献
89.
A new crystal-engineering motif has been developed where a ditopic receptor 1 shows a novel syn-syn hydrogen-bonded polymeric supramolecular complex (Fig. 4b) (instead of a 1:1 dimeric syn-syn or polymeric syn-anti complex) giving rise to a hydrogen-bonded stair-like polymeric ribbon structure between the binding groups of the receptor pyridine amide and the carboxyl groups of the guest substrate. 相似文献
90.
The composites with nano-particles of Ni-Fe alloys dispersed on the nano-layers of expanded graphite (EG) were prepared by the impregnation of EG with ethanol solutions of nickel and iron acetates, followed by drying and reduction in H2. The square nano-particles of Ni-Fe alloys with particle sizes of mainly 20~40 nm were found to be well spread on the layers of EG. The alloy nano-particles exhibited high shielding effectiveness (SE) for electromagnetic radiations at low frequencies due to their high magnetic conductivity. Since EG is electronically conductive and displayed high SE at high frequencies, the composites exhibited good SE at wide range of frequencies. The electric and magnetic conductivities of the composites could be monitored through regulating the loadings of alloy nano-particles on EG, and it was found that the composites with 20%~40% of the alloys exhibited good SE. Specifically, the composite 27%Ni-3%Fe-EG showed the excellent SE from 66 to 110 dB at the frequencies from 300 kHz to 1.5 GHz. 相似文献