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991.
Daniel G. Cummings James D. Sommers Mary L. Adamic Marcos Jimenez Jeffrey J. Giglio Kevin P. Carney Karl Grimm 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(3):923-928
A radioactive 137Cs source has been analyzed for the radioactive parent 137Cs and stable decay daughter 137Ba. The ratio of the daughter to parent atoms is used to estimate the date when Cs was purified prior to source encapsulation
(an “age” since purification). The isotopes were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical
separation. In addition, Ba was analyzed by isotope dilution ICP-MS (ID-ICP-MS). A detailed error analysis of the mass spectrometric
work has been undertaken to identify areas of improvement, as well as quantifying the effect the errors have on the “age”
determined. This paper reports an uncertainty analysis to identifying areas of improvement and alternative techniques that
may reduce the uncertainties. In particular, work on isotope dilution using ICP-MS for the “age” determination of sealed sources
is presented. The results will be compared to the original work done using external standards to calibrate the ICP-MS instrument. 相似文献
992.
Ashootosh V. Ambade Dr. Caroline Burd Dr. Mary Nell Higley Kamlesh P. Nair Dr. Marcus Weck Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(44):11904-11911
We report the synthesis of telechelic poly(norbornene) and poly(cyclooctene) homopolymers by ring‐opening metathesis polymerization (ROMP) and their subsequent functionalization and block copolymer formation based on noncovalent interactions. Whereas all the poly(norbornene)s contain either a metal complex or a hydrogen‐bonding moiety along the polymer side‐chains, together with a single hydrogen‐bonding‐based molecular recognition moiety at one terminal end of the polymer chain. These homopolymers allow for the formation of side‐chain‐functionalized AB and ABA block copolymers through self‐assembly. The orthogonal natures of all side‐ and main‐chain self‐assembly events were demonstrated by 1H NMR spectroscopy and isothermal titration calorimetry. The resulting fully functionalized block copolymers are the first copolymers combining both side‐ and main‐chain self‐assembly, thereby providing a high degree of control over copolymer functionalization and architecture and bringing synthetic materials one step closer to the dynamic self‐assembly structures found in nature. 相似文献
993.
Suzanne Burling Dr. L. Jonas L. Häller Dr. Elena Mas‐Marzá Dr. Aitor Moreno Stuart A. Macgregor Prof. Mary F. Mahon Dr. Paul S. Pregosin Prof. Dr. Michael K. Whittlesey Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(41):10912-10923
The five‐coordinate ruthenium N‐heterocyclic carbene (NHC) hydrido complexes [Ru(IiPr2Me2)4H][BArF4] ( 1 ; IiPr2Me2=1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene; ArF=3,5‐(CF3)2C6H3), [Ru(IEt2Me2)4H][BArF4] ( 2 ; IEt2Me2=1,3‐diethyl‐4,5‐dimethylimidazol‐2‐ylidene) and [Ru(IMe4)4H][BArF4] ( 3 ; IMe4=1,3,4,5‐tetramethylimidazol‐2‐ylidene) have been synthesised following reaction of [Ru(PPh3)3HCl] with 4–8 equivalents of the free carbenes at ambient temperature. Complexes 1 – 3 have been structurally characterised and show square pyramidal geometries with apical hydride ligands. In both dichloromethane or pyridine solution, 1 and 2 display very low frequency hydride signals at about δ ?41. The tetramethyl carbene complex 3 exhibits a similar chemical shift in toluene, but shows a higher frequency signal in acetonitrile arising from the solvent adduct [Ru(IMe4)4(MeCN)H][BArF4], 4 . The reactivity of 1 – 3 towards H2 and N2 depends on the size of the N‐substituent of the NHC ligand. Thus, 1 is unreactive towards both gases, 2 reacts with both H2 and N2 only at low temperature and incompletely, while 3 affords [Ru(IMe4)4(η2‐H2)H][BArF4] ( 7 ) and [Ru(IMe4)4(N2)H][BArF4] ( 8 ) in quantitative yield at room temperature. CO shows no selectivity, reacting with 1 – 3 to give [Ru(NHC)4(CO)H][BArF4] ( 9 – 11 ). Addition of O2 to solutions of 2 and 3 leads to rapid oxidation, from which the RuIII species [Ru(NHC)4(OH)2][BArF4] and the RuIV oxo chlorido complex [Ru(IEt2Me2)4(O)Cl][BArF4] were isolated. DFT calculations reproduce the greater ability of 3 to bind small molecules and show relative binding strengths that follow the trend CO ? O2 > N2 > H2. 相似文献
994.
M. Belén Díaz-Valenzuela Dr. Scott D. Phillips Marcia B. France Prof. Mary E. Gunn Matthew L. Clarke Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(5):1227-1232
A study on the enantioselective hydrogenation of tertiary alkyl ketones catalysed by a novel class of tridentate–Ru complex is reported. In contrast to the extensively studied [RuCl2(diphos)(di-primary amine)] complexes, this new class of hydrogenation catalyst smoothly reduces these less reactive bulky ketones with up to 94 % ee. The same catalyst system can also selectively reduce other potentially problematic substrates such as bulky heterocyclic ketones. Unusually for a pressure hydrogenation catalyst, similar enantioselectivity can be obtained under transfer hydrogenation conditions. The transfer hydrogenations are somewhat slower than the pressure hydrogenations, but this drawback is readily overcome, since we have discovered that a microwave accelerated transfer hydrogenation of the above ketones occurs within 20 min at about 90 °C with similar selectivity to that obtained in the pressure hydrogenation system. 相似文献
995.
Eric P. Knoshaug Mary Ann Franden Boris U. Stambuk Min Zhang Arjun Singh 《Cellulose (London, England)》2009,16(4):729-741
l-Arabinose is one of the sugars found in hemicellulose, a major component of plant cell walls. The ability to convert l-arabinose to ethanol would improve the economics of biomass to ethanol fermentations. One of the limitations for l-arabinose fermentation in the current engineered Saccharomyces cerevisiae strains is poor transport of the sugar. To better understand l-arabinose transport and use in yeasts and to identify a source for efficient l-arabinose transporters, 165 non-Saccharomyces yeast strains were studied. These yeast strains were arranged into six groups based on the minimum time required to utilize
20 g/L of l-arabinose. Initial transport rates of l-arabinose were determined for several species and a more comprehensive transport study was done in four selected species.
Detailed transport kinetics in Arxula adeninivorans suggested both low and high affinity components while Debaryomyces hansenii var. fabryii, Kluyveromyces marxianus and Pichia guilliermondii possessed a single component, high affinity active transport systems. 相似文献
996.
The selective preconcentration of estradiol was explored using the recognition ability of a molecularly imprinted polymer (MIP) in the solid phase extraction (SPE) format. Polymeric particles were imprinted with 17β-estradiol using methacrylic acid as functional monomer and divinylbenzene as crosslinker. Binding studies of these polymeric particles towards 17β-estradiol showed selectivity over non-imprinted polymers, using acetonitrile as solvent. The imprinted polymer showed a recovery of 88% for β-estradiol in deionized water and 81% in surface water. The selectivity of the MIP over the non-imprinted polymer was relatively low, only 10% higher recovery. The results indicate that the MIP imprinted with 17β-estradiol does not appear to provide a viable approach to be used in a sample clean-up or enrichment step for the determination of estradiol in aqueous systems. 相似文献
997.
Craig P. Montgomery Elizabeth J. New Lars O. Palsson David Parker Andrei S. Batsanov Laurent Lamarque 《Helvetica chimica acta》2009,92(11):2186-2213
A series of seven emissive europium(III) and terbium(III) complexes was prepared, incorporating a 3‐pyridyl‐4‐azaxanthone or 3‐pyrazolyl‐4‐azaxanthone sensitising moiety within a polydentate macrocyclic ligand. High overall emission quantum yields in aqueous media are attenuated in the presence of protein or certain oxy anions due to displacement of the N,N′‐chelated sensitiser. Nevertheless, these complexes are taken into cells and tend to localise over the first few hours in mitochondria before being trafficked to endosomal compartments. Cell uptake studies, in the presence of competitive inhibitors or promoters of well‐defined uptake pathways, reveal a common uptake mechanism involving macropinocytosis. 相似文献
998.
Elizabeth Florez Patricio Fuentealba 《International journal of quantum chemistry》2009,109(5):1080-1093
A theoretical study of the electronic structure of the first members of the alkali metal atomic clusters series Lin to Csn (n = 2–8) has been done. The geometries of some isomers of the neutral, positive, and negative charged clusters have been determined. Some important properties have also been calculated: atomic binding energies, vertical and adiabatic ionization potentials, vertical and adiabatic electron affinities, static dipole polarizabilities, and energy gaps. Whenever possible they have been compared with experimental values yielding a reasonable agreement which supports some new values as reliable predictions. The data have been discussed in light of the periodic table of elements trends. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
999.
Elizabeth A. Gibson Dr. Amanda L. Smeigh Dr. Loïc Le Pleux Jérôme Fortage Dr. Gerrit Boschloo Dr. Errol Blart Dr. Yann Pellegrin Fabrice Odobel Dr. Anders Hagfeldt Prof. Leif Hammarström Prof. 《Angewandte Chemie (International ed. in English)》2009,48(24):4402-4405
In tandem : Employing a molecular dyad and a cobalt‐based electrolyte gives a threefold‐increase in open‐circuit voltage (VOC) for a p‐type NiO device (VOC=0.35 V), and a fourfold better energy conversion efficiency. Incorporating these improvements in a TiO2/NiO tandem dye‐sensitized solar cell (TDSC), results in a TDSC with a VOC=0.91 V (see figure; CB=conductance band, VB= valence band).
1000.
Elizabeth Diesel Madeline Schreiber Jan Roelof van der Meer 《Analytical and bioanalytical chemistry》2009,394(3):687-693
Arsenic contamination of natural waters is a worldwide concern, as the drinking water supplies for large populations can have
high concentrations of arsenic. Traditional techniques to detect arsenic in natural water samples can be costly and time-consuming;
therefore, robust and inexpensive methods to detect arsenic in water are highly desirable. Additionally, methods for detecting
arsenic in the field have been greatly sought after. This article focuses on the use of bacteria-based assays as an emerging
method that is both robust and inexpensive for the detection of arsenic in groundwater both in the field and in the laboratory.
The arsenic detection elements in bacteria-based bioassays are biosensor–reporter strains; genetically modified strains of,
e.g., Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Rhodopseudomonas palustris. In response to the presence of arsenic, such bacteria produce a reporter protein, the amount or activity of which is measured
in the bioassay. Some of these bacterial biosensor–reporters have been successfully utilized for comparative in-field analyses
through the use of simple solution-based assays, but future methods may concentrate on miniaturization using fiberoptics or
microfluidics platforms. Additionally, there are other potential emerging bioassays for the detection of arsenic in natural
waters including nematodes and clams. 相似文献