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981.
An amperometric sensor for the determination of indole-3-acetic acid (IAA) based on the CeCl3-DHP film modified gold electrode was developed. CeCl3 was dissolved into water in the presence of dihexadecyl hydrogen phosphate (DHP). The IAA sensor was prepared via evaporating
solvent of the CeCl3-DHP dispersion on the gold electrode surface. The amperometric response of IAA on the CeCl3-DHP film modified gold electrode was investigated. The experimental results indicate that the passivation of the electrode
due to the adsorption of the oxidation product of IAA decreases significantly at the CeCl3-DHP film modified gold electrode, in contrast to that at the bare and the DHP modified gold electrode. The experimental parameters
were optimized and an electrochemical method for the determination of IAA was established. The oxidation peak current is linearly
with the concentration of IAA from 1 × 10−7 to 2 × 10−5 mol l−1 and the detection limit is 3 × 10−8 mol l−1. The relative standard deviation of eight measurements is 3.2% for 5 × 10−7 mol l−1 IAA. The IAA in plant leaves were extracted and determined by the IAA sensor. 相似文献
982.
Isomerism, conformations, and molecular structure of a model molecule of vitamin K1 with a truncated side chain have been studied by the density functional theory calculations using B3LYP method and double-
and triple-ζ correlation consistent basis sets. The conformations of two possible (E and Z) isomers, formed by the rotations around three single C–C bonds closest to the naphthoquinone ring, have been studied. The
lowest energy conformers are stabilized by additional hydrogen bonds between hydrogen atoms of the side chain and an oxygen
atom in the naphthoquinone subunit. It is interesting to note that the structure of the energetically preferred conformer
of the E-isomer (3c) has been found to be similar to the solid state structures of phylloquinones in the photosystem I of cyanobacterium
Synechococcus elongatus. The excited electronic states of two lowest energy conformers have also been investigated. 相似文献
983.
Enthalpies (Δisom
H
(g)o), Gibbs free energies (Δisom
G
(g)o), and equilibrium constants (log K
isom) for the trans → cis isomerization of various 3,3′-, 4,4′-, and 5,5′- disubstituted 2,2′-diphenoquinones with a range of electron withdrawing
and releasing moieties (methyl, fluoro, chloro, bromo, trifluoromethyl, and amino) were calculated in the gas phase and in
the solvent phase (n-hexane, benzene, n-octanol, acetonitrile, and water). In the gas phase, the trans isomer of the parent and all substituted 2,2′-diphenoquinones is predicted to be more thermodynamically stable than the cis configuration, with log K
isom ranging from −2.8 to −7.0. For all compounds, increasing solvent polarity/proticity progressively favors shifting the cis/trans equilibrium towards greater contributions of the cis configuration and substantially increases the log K
isom by up to 5.1 units relative to the gas phase. In polar protic and polar aprotic solvents, the estimated log K
isom ranges as low as −0.4, indicating significant populations of the cis isomers should be present. The findings support the polar solvent phase mechanistic predictions for a cis configuration of 2,2′-diphenoquinones participating in the thermal transformation of trans-2,2′-diphenoquinones to oxepino[2,3-b]benzofurans. With limited exceptions for some amino derivatives, the cis-2,2′-diphenoquinone to oxepino[2,3-b]benzofuran isomerization is expected to be thermodynamically favorable for all substituents/phases
under consideration. The cis-2,2′-diphenoquinone to oxepino[2,3-b]benzofuran rearrangement is predicted to become less thermodynamically favored with
increasing solvent polarity/proticity. 相似文献
984.
Metabolome analysis of human cerebrospinal fluid (CSF) is challenging because of low abundance of metabolites present in a
small volume of sample. We describe and apply a sensitive isotope labeling LC-MS technique for qualitative analysis of the
CSF metabolome. After a CSF sample is divided into two aliquots, they are labeled by 13C-dansyl and 12C-dansyl chloride, respectively. The differentially labeled aliquots are then mixed and subjected to LC-MS using Fourier-transform
ion cyclotron resonance mass spectrometry (FTICR MS). Dansylation offers significant improvement in the performance of chromatography
separation and detection sensitivity. Moreover, peaks detected in the mass spectra can be readily analyzed for ion pair recognition
and database search based on accurate mass and/or retention time information. It is shown that about 14,000 features can be
detected in a 25-min LC-FTICR MS run of a dansyl-labeled CSF sample, from which about 500 metabolites can be profiled. Results
from four CSF samples are compared to gauge the detectability of metabolites by this method. About 261 metabolites are commonly
detected in replicate runs of four samples. In total, 1132 unique metabolite ion pairs are detected and 347 pairs (31%) matched
with at least one metabolite in the Human Metabolome Database. We also report a dansylation library of 220 standard compounds
and, using this library, about 85 metabolites can be positively identified. Among them, 21 metabolites have never been reported
to be associated with CSF. These results illustrate that the dansylation LC-FTICR MS method can be used to analyze the CSF
metabolome in a more comprehensive manner. 相似文献
985.
Voinov VG Deinzer ML Beckman JS Barofsky DF 《Journal of the American Society for Mass Spectrometry》2011,22(4):607-611
Recently, we demonstrated that a radio-frequency-free electromagnetostatic (rf-free EMS) cell could be retrofitted into a
triple quad mass spectrometer to allow electron-capture dissociation (ECD) without the aid of cooling gas or phase-specific
electron injection into the cell (Voinov et al., Rapid Commun Mass Spectrom 22, 3087–3088, 2008; Voinov et al., Anal Chem 81, 1238–1243, 2009). Subsequently, we used our rf-free EMS cell in the same instrument platform to demonstrate ECD occurring in the same space
and at the same time with collision-induced dissociation (CID) to produce golden pairs and even triplets from peptides (Voinov
et al., Rapid Commun Mass Spectrom 23, 3028–3030, 2009). In this report, we demonstrate that ECD and CID product-ion mass spectra can be recorded at high resolution with flexible
control of fragmentation processes using a newly designed cell installed in a hybrid Q-TOF tandem mass spectrometer. 相似文献
986.
Hee-Soo Kim Byoung-Ho Lee Sena Lee Hyun-Joong Kim John R. Dorgan 《Journal of Thermal Analysis and Calorimetry》2011,104(1):331-338
This study examined the interfacial adhesion, mechanical, and thermal properties of compatibilizing agent-treated and non-treated
biocomposites as a function of the type of compatibilizing agent. The tensile strength, interfacial adhesion, and heat deflection
temperature (HDT) of maleic anhydride-grafted poly(butylene succinate) (PBS-MA) and maleic anhydride-grafted poly(lactic acid)
(PLA-MA)-treated biocomposites are greater than those of untreated maleic anhydride-grafted poly(styrene-b-ethylene-co-butylene-b-styrene)
triblock copolymer (SEBS-MA) and maleic anhydride-grafted polypropylene (MAPP)-treated biocomposites. The storage modulus
(E′) values and the tan δmax temperatures (T
g) of PBS-MA and PLA-MA-treated biocomposites were slightly higher than that of the untreated biocomposites. 相似文献
987.
John A. Kilner Stephen J. Skinner Hidde H. Brongersma 《Journal of Solid State Electrochemistry》2011,15(5):861-876
The determination of the mass transport kinetics of oxide materials for use in electrochemical systems such as fuel cells,
sensors and oxygen separators is a significant challenge. Several techniques have been proposed to derive these data experimentally
with only the oxygen isotope exchange depth profile technique coupled with secondary ion mass spectrometry (SIMS) providing
a direct measure of these kinetic parameters. Whilst this allows kinetic information to be obtained, there is a lack of knowledge
of the surface chemistry of these complex processes. The advent of low-energy ion scattering (LEIS) now offers the opportunity
of correlating exchange kinetics with chemical processes at materials atomic surfaces, giving unprecedented levels of information
on electrochemical systems with isotopic discrimination. Here, the challenges of these techniques, including sample preparation,
are discussed and the advantages of the combined approach of SIMS and LEIS illustrated with reference to key literature data. 相似文献
988.
Jingsong Sun Lin Liang Jianmin Sun Yanqiu Jiang Kaifeng Lin Xianzhu Xu Runwei Wang 《Catalysis Surveys from Asia》2011,15(1):49-54
This short review presents the recent developments in the direct synthesis of cyclic carbonates from olefins and CO2. The straightforward synthesis of cyclic carbonates from olefins instead of epoxides, also called one-pot “oxidative carboxylation”
of olefins, can be viewed as the coupling of two sequential reactions of epoxidation of olefins and CO2 cycloaddition to epoxides formed. The facile synthetic approach would make carbonate synthesis simpler and even cheaper with
industrial potential from environmental and economic points of view. Some progresses have been made on this direct synthetic
reaction for cyclic carbonates with homogeneous and heterogeneous catalysts, however, this reaction system is still at a preliminary
stage. Among the catalysts reported, only a few can be considered as effective for the direct oxidative carboxylation of olefins
to cyclic carbonates. Thus active and selective catalysts should be explored to put the direct synthesis of cyclic carbonates
into practical applications. 相似文献
989.
Per Malmberg Eva Jennische Daniel Nilsson Håkan Nygren 《Analytical and bioanalytical chemistry》2011,399(8):2711-2718
The use of high-resolution, imaging TOF-SIMS is described and examples are made to demonstrate the application of the method
in medical research. Cytochemistry by TOF-SIMS is shown by localization of diacylglycerol (DG) in cryostat sections of hyaline
cartilage and by localization of corticosterone in cryostat sections of the adrenal gland cortex. Quantitative measurements
and comparison of groups is shown by comparing the lipid content of adipose tissue from two mouse strains, transgenic mouse
expressing the FOXC2 gene and wild-type controls. Finally, biopsies made for histopathological diagnosis of infantile reversible
cytochrome c oxidase deficiency myopathy were analyzed in order to define the chemical content of areas showing a pathological
structure in the light microscope. The use of high-resolution, imaging TOF-SIMS in medical research allows analysis of intact
tissue and probe-free localization of specific target molecules in cells and tissues. The TOF-SIMS analysis is not dependent
on penetration of reagents into the sample and also independent of probe reactivity such as cross-reactivity or background
staining. The TOF-SIMS method can be made quantitative and allows for analysis of specific target molecules in defined tissue
compartments. 相似文献
990.
Guiseppi-Elie A 《Analytical and bioanalytical chemistry》2011,399(1):403-419
Following hemorrhage-causing injury, lactate levels rise and correlate with the severity of injury and are a surrogate of
oxygen debt. Posttraumatic injury also includes hyperglycemia, with continuously elevated glucose levels leading to extensive
tissue damage, septicemia, and multiple organ dysfunction syndrome. A temporary, implantable, integrated glucose and lactate
biosensor and communications biochip for physiological status monitoring during hemorrhage and for intensive care unit stays
has been developed. The dual responsive, amperometric biotransducer uses the microdisc electrode array format upon which were
separately immobilized glucose oxidase and lactate oxidase within biorecognition layers, 1.0–5.0 μm thick, of 3 mol% tetraethyleneglycol
diacrylate cross-linked p(HEMA-co-PEGMA-co-HMMA-co-SPA)-p(Py-co-PyBA) electroconductive hydrogels. The device was then coated with a bioactive hydrogel layer containing phosphoryl choline
and polyethylene glycol pendant moieties [p(HEMA-co-PEGMA-co-HMMA-co-MPC)] for indwelling biocompatibility. In vitro cell proliferation and viability studies confirmed both polymers to be non-cytotoxic;
however, PPy-based electroconductive hydrogels showed greater RMS 13 and PC12 proliferation compared to controls. The glucose
and lactate biotransducers exhibited linear dynamic ranges of 0.10–13.0 mM glucose and 1.0–7.0 mM and response times (t
95) of 50 and 35–40 s, respectively. Operational stability gave 80% of the initial biosensor response after 5 days of continuous
operation at 37 °C. Preliminary in vivo studies in a Sprague–Dawley hemorrhage model showed tissue lactate levels to rise
more rapidly than systematic lactate. The potential for an implantable biochip that supports telemetric reporting of intramuscular
lactate and glucose levels allows the refinement of resuscitation approaches for civilian and combat trauma victims. 相似文献