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211.
212.
Alessandro Allegri Valeriia Maslova Magda Blosi Anna Luisa Costa Simona Ortelli Francesco Basile Stefania Albonetti 《Molecules (Basel, Switzerland)》2020,25(22)
The photocatalytic oxidation of biomass-derived building blocks such as 5-hydroxymethylfurfural (HMF) is a promising reaction for obtaining valuable chemicals and the efficient long-term storage of solar radiation. In this work, we developed innovative TiO2-based materials capable of base-free HMF photo-oxidation in water using simulated solar irradiation. The materials were prepared by combining microemulsion and spray-freeze drying (SFD), resulting in highly porous systems with a large surface area. The effect of titania/silica composition and the presence of gold-copper alloy nanoparticles on the properties of materials as well as photocatalytic performance were evaluated. Among the lab-synthesized photocatalysts, Ti15Si85 SFD and Au3Cu1/Ti15Si85 SFD achieved the higher conversions, while the best selectivity was observed for Au3Cu1/Ti15Si85 SFD. The tests with radical scavengers for both TiO2-m and Au3Cu1/Ti15Si85 SFD suggested that primary species responsible for the selective photo-oxidation of HMF are photo-generated electrons and/or superoxide radicals. 相似文献
213.
Luisa C. Melo Murilo S. S. Julião Maria A. L. Milhome Ronaldo F. do Nascimento Djenaine De Souza Pedro de Lima-Neto Adriana N. Correia 《Journal of Analytical Chemistry》2018,73(7):695-704
This work describes the electroanalytical determination of Chlorpyriphos pesticide in natural waters using hanging mercury drop electrode allied to square wave adsorptive cathodic stripping voltammetry. The best responses were obtained in Britton?Robinson buffer solutions at pH 2.0, using a frequency of 100 s–1, a scan increment of 5 mV, a square wave amplitude of 25 mV and an accumulation potential of–0.4 V during 60 s. Therefore, voltammetric responses showed the presence of one well-defined and irreversible reduction peak, at–1.08 V vs. Ag/AgCl/KCl 1.0 M, which involves two electrons in the reduction of carbon?nitrogen bond in the N-heterocyclic system with the participation of protonation equilibrium preceding the electron transfer reaction. Analytical curves were constructed and compared to similar curves performed by gas chromatograph coupled to a selective nitrogen?phosphorus detector, which demonstrates that the proposed methodology is suitable for determining contamination by Chlorpyriphos in complex samples. 相似文献
214.
The halogenation of pyridinium N-(benzoazynyl) aminides with N-halosuccinimides provides a mild and regioselective method to functionalize the negatively charged diazine moiety in most cases. In some examples, however, formation of other products is explained. Finally, alkylation of the exocyclic nitrogen and reduction of the N–N bond provides a simple and straightforward strategy to obtain functionalized N-benzyl-benzoazynyl-α-amines. 相似文献
215.
We have studied the ability of an alpha-imino glyoxylamide derived from (S, S)-(+)-pseudoephedrine as a valuable chiral electrophile for the preparation of alpha-amino carbonyl compounds. In this context, the addition of Grignard reagents to the azomethine moiety of this chiral electrophile afforded the expected alpha-amino amide adducts in good yields and diastereoselectivities. Moreover, these adducts have been transformed into enantioenriched alpha-amino ketones by exploiting the ability of pseudoephedrine amides to undergo selective monoaddition to the carbamoyl group with organolithium reagents. 相似文献
216.
Pan H Liu J Dong Y Sima M Kopecková P Brandi ML Kopecek J 《Macromolecular bioscience》2008,8(7):599-605
Bone-targeting N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-PGE(1) conjugates, containing cathepsin K sensitive spacers, were incubated with induced osteoclasts and osteoblasts, their precursors, and control non-skeletal cells. The release of PGE(1) was monitored by an HPLC assay. In both murine and human cell lines, osteoclasts appeared to be the most active cells in the cleavage (PGE(1) release). Incubation with osteoblasts also resulted in fast PGE(1) release, whereas precursor and control cells released PGE(1) with a substantially slower rate than bone cells (apparently through ester bond cleavage). Experiments in the presence of inhibitors revealed that other enzymes, in addition to cathepsin K, were participating in the cleavage of the conjugate. Confocal fluorescence studies exposed internalization of the conjugate by endocytosis with ultimate localization in the lysosomal/endosomal compartment. 相似文献
217.
Rodríguez-Castrillón JA Moldovan M García Alonso JI Lucena JJ García-Tomé ML Hernández-Apaolaza L 《Analytical and bioanalytical chemistry》2008,390(2):579-590
Isotope pattern deconvolution is a mathematical technique for isolating distinct isotope signatures from mixtures of natural
abundance and enriched tracers. In iron metabolism studies measurement of all four isotopes of the element by high-resolution
multicollector or collision cell ICP–MS allows the determination of the tracer/tracee ratio with simultaneous internal mass
bias correction and lower uncertainties. This technique was applied here for the first time to study iron uptake by cucumber
plants using 57Fe-enriched iron chelates of the o,o and o,p isomers of ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA) and ethylenediamine tetraacetic acid (EDTA). Samples of root, stem, leaves, and xylem sap,
after exposure of the cucumber plants to the mentioned 57Fe chelates, were collected, dried, and digested using nitric acid. The isotopic composition of iron in the samples was measured
by ICP–MS using a high-resolution multicollector instrument. Mass bias correction was computed using both a natural abundance
iron standard and by internal correction using isotope pattern deconvolution. It was observed that, for plants with low 57Fe enrichment, isotope pattern deconvolution provided lower tracer/tracee ratio uncertainties than the traditional method
applying external mass bias correction. The total amount of the element in the plants was determined by isotope dilution analysis,
using a collision cell quadrupole ICP–MS instrument, after addition of 57Fe or natural abundance Fe in a known amount which depended on the isotopic composition of the sample. 相似文献
218.
Luisa Fattorusso 《Czechoslovak Mathematical Journal》2008,58(1):113-129
Let Ω be a bounded open subset of ℝ
n
, n > 2. In Ω we deduce the global differentiability result
for the solutions u ∈ H
1 (Ω, ℝ
n
) of the Dirichlet problem
with controlled growth and nonlinearity q = 2.
The result was obtained by first extending the interior differentiability result near the boundary and then proving the global
differentiability result making use of a covering procedure. 相似文献
219.
Preparation of second generation ionic liquids by efficient solvent-free alkylation of N-heterocycles with chloroalkanes 总被引:1,自引:0,他引:1
Cravotto G Gaudino EC Boffa L Lévêque JM Estager J Bonrath W 《Molecules (Basel, Switzerland)》2008,13(1):149-156
Non-conventional techniques, such as microwave (MW) and power ultrasound (US) as well as combined MW/US irradiation, have been used to promote one-pot synthesis of second-generation ionic liquids (ILs), cutting down reaction times and improving yields. However, the use of chloroalkanes in the alkylation of N-heterocycles requires more drastic conditions if results are to match those obtained with more reactive alkyl halides. The present paper describes a series of MW- or MW/US-promoted IL preparations starting from chloroalkanes and classic heterocycles (1-methylimidazole, pyridine and 1-methylpyrrolidine). When reactions were carried out under conventional heating in an oil bath they required longer reaction times and gave poorer yields. (1)H-NMR analysis and ion-exchange chromatography showed that the present solventless procedure afforded ILs of satisfactory purity. The observed high yields (usually 70-98% isolated), and short reaction times showed that a straightforward access to ILs can be also achieved with the use of alkyl chlorides, resulting in a considerable reduction of costs. 相似文献
220.
A general view of the different strategies used in the last years to enhance the detection sensitivity in chiral analysis by CE is provided in this article. With this purpose and in order to update the previous review by García-Ruiz et al., the articles appeared on this subject from January 2005 to March 2007 are considered. Three were the main strategies employed to increase the detection sensitivity in chiral analysis by CE: (i) the use of off-line sample treatment techniques, (ii) the employment of in-capillary preconcentration techniques based on electrophoretic principles, and (iii) the use of alternative detection systems to the widely employed on-column UV-Vis absorption detection. Combinations of two or three of the above-mentioned strategies gave rise to adequate concentration detection limits up to 10(-10) M enabling enantiomer analysis in a variety of real samples including complex biological matrices. 相似文献