全文获取类型
收费全文 | 7191篇 |
免费 | 989篇 |
国内免费 | 1415篇 |
专业分类
化学 | 5521篇 |
晶体学 | 132篇 |
力学 | 381篇 |
综合类 | 121篇 |
数学 | 1136篇 |
物理学 | 2304篇 |
出版年
2024年 | 17篇 |
2023年 | 131篇 |
2022年 | 273篇 |
2021年 | 273篇 |
2020年 | 302篇 |
2019年 | 311篇 |
2018年 | 265篇 |
2017年 | 289篇 |
2016年 | 326篇 |
2015年 | 375篇 |
2014年 | 479篇 |
2013年 | 665篇 |
2012年 | 652篇 |
2011年 | 644篇 |
2010年 | 551篇 |
2009年 | 505篇 |
2008年 | 592篇 |
2007年 | 501篇 |
2006年 | 461篇 |
2005年 | 332篇 |
2004年 | 251篇 |
2003年 | 172篇 |
2002年 | 185篇 |
2001年 | 143篇 |
2000年 | 143篇 |
1999年 | 110篇 |
1998年 | 74篇 |
1997年 | 54篇 |
1996年 | 46篇 |
1995年 | 29篇 |
1994年 | 41篇 |
1993年 | 48篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 26篇 |
1988年 | 29篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 22篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1975年 | 9篇 |
排序方式: 共有9595条查询结果,搜索用时 0 毫秒
101.
Amphiphilic polypyridyl mthenium(Ⅱ) complex cis-di(isothiocyanato)(4,4'-di-tert-butyl-2,2'-bipyridyl)(4,4'- dicarboxy-2,2'-bipyridyl)ruthenium(Ⅱ)(K005) has been synthesized and characterized by cyclic voltammetry, ^1H NMR, UV-Vis, and FT-IR spectroscopies. The sensitizer sensitizes TiO2 over a notably broad spectral range due to its intense metal-to-ligand charge-transfer (MLCT) bands at 537 and 418 nm. The photophysical and photochemical studies of K005 were contrasted with those of cis-Ru(dcbpy)2(NCS)2, known as the N3 dye, and the amphiphilic ruthenium(Ⅱ) dye Z907. A reversible couple at E1/2=0.725 V vs. saturated calomel electrode (SCE) with a separation of 0.08 V between the anodic and cathodic peaks, was observed due to the Ru^Ⅱ/Ⅲ couple by cyclic voltammetry. Furthermore, this amphiphilic ruthenium complex was successfully used as sensitizers for dye-sensitized solar cells with the efficiency of 3.72% at the 100 mW·cm^-2 irradiance of air mass 1.5 simulated sunlight without optimization of TiO2 films and the electrolyte. 相似文献
102.
Many studies have focused on effective ways to exploit enzyme immobilization on an electrode surface to help improve the performance of enzymatic electrochemical biosensors. Herein, a novel glucose sensor was fabricated by immobilizing glucose oxidase (GOx) onruthenium-based conjugated polymer (CP) and metal-organic framework (MOF) nanocomposites. This has not only reduced the applied potential to 0.2 V (vs. Ag/AgCl), but also improved the effective surface area for enzyme immobilization.PPG@Ru@UiO-66-NH2 was tailored by controlled chemical synthesis from a pre-synthesized water-soluble conjugated polymer (poly(N-phenylglycine)) and metal-organic framework (UiO-66-NH2). The resulting nanocomposites were characterized using Fourier transform infrared spectroscopy, X-ray fluorescence, scanning electron microscopy, and cyclic voltammetry. The PPG@Ru@UiO-66-NH2/GOx coated electrodedisplayed a linear measurementrange for glucose from 1 mM to 10 mM, with a sensitivity of 45.92 μA ⋅ mM−1cm−1 and limit of detection of5 μM( ). Furthermore, the practical application of the fabricatedglucosesensor was tested in simulative blood samples with satisfactoryaccuracy. This approach alsoopens a new door for applications regarding both enzymatic electrochemical biosensors and enzymatic biofuel cells (EBFCs). 相似文献
103.
Alfonso Loaiza Dan Borchardt Francisco Zaera 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1997,53(14):2481-2493
13C NMR at 125.76 MHz with 1H and 2H decoupling, 2H NMR at 76.77 MHz with 1H decoupling, and 1H NMR at 500.14 MHz with 2H decoupling were employed as analytical tools to study the complex mixtures of deuterated ethanes resulting from the catalytic H–D exchange of normal ethane with gas-phase deuterium in the presence of a platinum foil. Reference samples consisting of 1:1 binary mixtures of pure normal ethane and ethane-dn (n=1–6) were used to identify the peak positions in the 13C, 2H, and 1H NMR spectra due to each individual isotopomer, and the effect of isotopic substitution on the chemical shifts was determined in each case. While the NMR of all three nuclei worked well for the identification of the individual components of the 1:1 standard mixtures, both 1H and 2H NMR suffered from inadequate resolution when studying complex reaction mixtures because of the broadening of the lines due to 1H–1H (1H NMR) and 2H–2H (2H NMR) couplings. 13C NMR was therefore determined to be the method of choice for the quantitative analysis of the reaction mixtures. Using the 13C NMR results, a correlation that takes into account the primary and secondary isotope substitution effects on chemical shifts was deduced. This equation was used for the identification of the individual components of the mixtures, and integration of the individual observed resonances was then employed for quantification of their composition. This study shows that 13C NMR with 1H and 2H decoupling is a viable procedure for studying mixtures of deuterated ethanes. Furthermore, the additivity of the isotopic effects on chemical shifts and the transferability of the values obtained with ethane to other molecules makes this approach general for the analysis of other isotopomer mixtures. 相似文献
104.
Barlow DE Scudiero L Hipps KW 《Langmuir : the ACS journal of surfaces and colloids》2004,20(11):4413-4421
Binary thin films of cobalt(II) phthalocyanine (CoPc) and cobalt(II) tetraphenylporphyrin (CoTPP) were prepared at submonolayer coverage on Au(111)/mica substrates byvapor deposition. All sample preparation and analysis were done under an ultrahigh vacuum. Scanning tunneling microscopy (STM) constant-current images of CoPc/CoTPP mixtures showed two close-packed surface structures, with different compositional percentages and some disorder. CoPc was also observed exclusively in one-dimensional chains and as single, isolated molecules below 220 K. Occupied and unoccupied orbital energy levels were identified by STM and tunnel-diode-based orbital-mediated tunneling spectroscopy. Occupied energy levels were also confirmed by ultraviolet photoelectron spectroscopy. The transient oxidation of the Co d(z2) orbital is identified in STM dI/dV(V) curves just negative of the 0 V sample bias for both molecules. Nearly identical constant-current contours are observed over the central Co2+ ions of CoTPP and CoPc, indicating that the attenuation of the d(z)2 orbital-mediated tunneling current induced by the structure of TPP relative to Pc is at most a factor of about 10. The orbital-mediated tunneling spectra of CoTPP and CoPc are distinctly different and allow these structurally similar species to be differentially identified. 相似文献
105.
Switching between three different adsorbed states was achieved using potential control to separately induce electrochemical behaviour associated with changes in binding and orientation of the thiophene and pyridine moieties of 2-(2'-thienyl)pyridine adsorbed to Au(111) in neutral and basic solution. 相似文献
106.
Y. M. Dan Y. R. Zhao Y. Liu S. S. Qu 《Journal of Thermal Analysis and Calorimetry》2006,84(3):531-534
The two complexes, [Ln(Ala)2(Im)(H2O)](ClO4)3 (Ln=Pr,
Gd), were synthesized and characterized. Using a solution-reaction isoperibol
calorimeter, standard enthalpies of reaction of two reactions: LnCl3⋅6H2O(s)+2Ala(s)+Im(s)+3NaClO4(s)=[Ln(Ala)2(Im)(H2O)](ClO4)3(s)+3NaCl(s)+5H2O(l) (Ln=Pr, Gd),
at T=298.15 K, were determined to be (39.26±0.10)
and (5.33±0.12) kJ mol–1 , respectively.
Standard enthalpies of formation of the two complexes at T=298.15
K, ΔfHΘm
{[Ln(Ala)2(Im)(H2O)](ClO4)3(s)} (Ln=Pr, Gd),
were calculated as –(2424.2±3.3) and –(2443.4±3.3)
kJ mol–1 , respectively. 相似文献
107.
Dan Lu Weiyang Zhang Yingnan Jiang Yu Zhang Dabo Pan Dan Zhang 《Natural product research》2019,33(19):2789-2794
A new cycloartane triterpenoid, named gardenolic acid C (1), a new ursane triterpenoid, named 3β,16β,21β,23,24-pentahydroxy urs-12,18,20-trien-28-oic acid γ-lactone (2), together with three know triterpenoids, gardenolic acid A (3), gardenolic acid B (4), and 3α,16β,23,24-tetrahydroxy-28-nor-ursane-12,17,19,21-tetraen (5) were isolated from the fruits of Gardenia jasminoides Ellis. The structures of these compounds were elucidated by analyses of spectroscopic data. All isolates were evaluated for their neuroprotective effects in vitro.
108.
Tiberiu-M. Gianga Edwige Audibert Anamaria Trandafir Gabriele Kociok-Khn G. Dan Panto 《Chemical science》2020,11(35):9685
We report herein the first all-donor aromatic [2]catenane formed through dynamic combinatorial chemistry, using single component libraries. The building block is a benzo[1,2-b:4,5-b′]dithiophene derivative, a π-donor molecule, with cysteine appendages that allow for disulfide exchange. The hydrophobic effect plays an essential role in the formation of the all-donor [2]catenane. The design of the building block allows the formation of a quasi-fused pentacyclic core, which enhances the stacking interactions between the cores. The [2]catenane has chiro-optical and fluorescent properties, being also the first known DCC-disulphide-based interlocked molecule to be fluorescent.An all-donor [2]catenane has been synthesised via dynamic combinatorial chemistry. It features stacked benzodithiophenes which are quasi-pentacyclic through hydrogen bonding. 相似文献
109.
110.
Bin XIN Dan PU Shao Xiang XIONG* Guang Hui WANG Beijing Mass Spectrometry Center Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing 《中国化学快报》2003,14(2)
Recently, capillary electrophoresis/electrospray ionization mass spectrometry (CE/ESI- MS) has been rapidly developed as a powerful analytical tool for charged species ranged from small molecules such as carboxylic acids1, phenolic compounds2, metal species3, tetramines4, herbicides5, drugs and drug metabolites6 to peptides and proteins7, 8. The ESI mode has proven to be sensitive, versatile and relatively easy to use in combination with CE. CE confers rapid analysis and efficient separ… 相似文献