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881.
Mi-Hyun Lee Bhari Mallanna Nagaraja Prakash Natarajan Ngoc Thanh Truong Kwan Young Lee Sungho Yoon Kwang-Deog Jung 《Research on Chemical Intermediates》2016,42(1):123-140
PtSn/θ-Al2O3 catalysts with different amounts of K (0.14, 0.22, 0.49, 0.72, and 0.96 wt%) are prepared to investigate the K effects on the PtSn catalyst in propane dehydrogenation (PDH). KPtSn catalyst with 0.xx wt% K, 0.5 wt% Pt and 0.75 wt% Sn is designated as xx-KPtSn. PDH was performed at 873 K and a gas hourly space velocity (GHSV) of 53,000 mL/gcat h. The temperature-programmed desorption (NH3-TPD), temperature-programmed reduction (TPR) and CO chemisorption of the KPtSn catalysts with K added revealed the potassium addition blocked the acid sites, promoted the reduction of Sn oxide and decreased the Pt dispersion. The formations of cracking products and higher hydrocarbons on acid sites were suppressed by the K effect of blocking the acid sites. In contrast, K addition at more than 0.72 wt% rather increased cracking products and the amount of coke, resulting in the severe deactivation of catalysts. The high cracking products on the KPtSn catalysts with the high amount of K should not be related to the acid sites, because the acid sites were monotonously decreased with an increase in the amount of K. Instead, the potassium affected the characteristics of PtSn. The interaction between Pt and Sn could be weakened by enriching the reduced Sn, because the K component promoted the reduction of Sn oxide in the TPR experiments. Therefore, the 14-KPtSn catalyst with the low amount of K exhibits the highest stability and selectivity among the prepared KPtSn catalysts due to the compromise of the advantageous (blocking the acid sites) and bad (weakening the interaction between Pt and Sn) effects of the K addition in PDH. 相似文献
882.
Deng B Wang Z Song J Xiao Y Chen D Huang J 《Analytical and bioanalytical chemistry》2011,401(7):2143-2152
The doxorubicin (DOX) uptake in single human leukemia K562 cells with changes in both drug dosage and exposure period was
studied using capillary electrophoresis (CE) coupled with laser-induced fluorescence (LIF) detection. The cells were treated
with DOX at different concentrations (1, 3, 10, 20, 30, and 50 μM) and for different exposure times (1, 3, 5, 24, and 48 h).
At least 20 cells were analyzed for each DOX-treated cell population. A marked heterogeneity in DOX uptake among single cells
was observed, because the relative standard deviation of the uptake of DOX by single cells ranged from 24.0% to 61.1% within
each cell population. The cell-to-cell heterogeneity in DOX uptake first decreased and then became constant with increasing
drug concentration, but it did not exhibit regular variation with increasing exposure time. The mean DOX uptake was a linear
function of drug concentration (r ≥ 0.9667). In terms of the correlation with exposure time, the mean DOX uptake reached its maximum at 3 h for the cell populations
treated with 1–10 μM DOX, while it kept increasing during 48 h exposure of cell populations to 20–50 μM DOX. Because it eliminates
DOX fluorescence quenching and sample loss, the CE-LIF method directly detects the true DOX uptake by single cells, and thus
presents accurate information on both the cell-to-cell heterogeneity in DOX uptake and the patterns of DOX uptake in K562
cells as functions of drug concentration and exposure time. 相似文献
883.
Shakya T Stogios PJ Waglechner N Evdokimova E Ejim L Blanchard JE McArthur AG Savchenko A Wright GD 《Chemistry & biology》2011,18(12):1591-1601
Kinase-mediated resistance to antibiotics is a significant clinical challenge. These enzymes share a common protein fold characteristic of Ser/Thr/Tyr protein kinases. We screened 14 antibiotic resistance kinases against 80 chemically diverse protein kinase inhibitors to map resistance kinase chemical space. The screens identified molecules with both broad and narrow inhibition profiles, proving that protein kinase inhibitors offer privileged chemical matter with the potential to block antibiotic resistance. One example is the flavonol quercetin, which inhibited a number of resistance kinases in vitro and in vivo. This activity was rationalized by determination of the crystal structure of the aminoglycoside kinase APH(2″)-IVa in complex with quercetin and its antibiotic substrate kanamycin. Our data demonstrate that protein kinase inhibitors offer chemical scaffolds that can block antibiotic resistance, providing leads for co-drug design. 相似文献
884.
Mesoporous carbons containing silver nanoparticles have been successfully synthesized under acidic conditions by employing
resorcinol and formaldehyde as carbon precursors and triblock copolymer EO101PO56EO101 (Lutrol F127) as a soft template. Silver nanoparticles of ∼90 nm were added to the synthesis mixture to achieve 10 wt% and
20 wt% of Ag loading in the carbon. Also, tetraethyl orthosilicate (TEOS) was introduced to the system in order to improve
adsorption properties of the silver-carbon composites and to reinforce its structure. The resulting carbons with incorporated
silver nanoparticles featured high surface areas, large total pore volumes and primary mesopores in the range between ∼6–7 nm. 相似文献
885.
Dialkyl phosphate esters used as gellants in some oil well fracturing processes for conventional oil production can result
in contamination of the collected crude. Though the exact mechanism is unclear, such compounds form volatile phosphorus that
compromises refinery processes. Our initial research involved producing a comprehensive two-dimensional gas chromatographic
method (GC × GC) for the detection and quantification of alkyl phosphate esters in petroleum samples, which surpassed the
current method employed in sensitivity and speciation capabilities. However, selective detection is required for such analytes
in petroleum matrices. This article describes the application of GC × GC with time-of-flight mass spectrometry for selective
detection to the analysis of di- and tri-alkyl phosphates in petroleum samples. Features in the electron impact mass spectra
of alkyl phosphates are discussed along with the GC × GC retention characteristics of the compounds. Based on these discussions,
a preliminary classification and quantification of alkyl phosphate contamination in a suite of industrial samples is then
presented. 相似文献
886.
887.
Pierozan MK Oestreicher EG Oliveira JV Oliveira D Treichel H Cansian RL 《Applied biochemistry and biotechnology》2011,165(1):75-86
The objective of this study was to provide some features on immobilization and partial characterization of lipases from wheat
seeds. The optimum pH and temperature were found to be 5.5 and 32–37 °C, respectively. The stability of the concentrated enzymatic
extract to high temperatures (25, 35, 45, and 55 °C) showed that the incubation of the extract at 55 °C led to its complete
inactivation. The concentrated enzymatic extract kept 90% of its hydrolytic and esterification activities until 70 and 40 days
of storage at 4 °C, respectively. The extract presented higher hydrolytic specificity to substrates of medium and long chains
and higher esterification affinity to fatty acids of short and medium chains and alcohols with two and three carbon atoms.
After the immobilization process using activated coal and sodium alginate as supports, an enhancement of about threefold in
lipase activity was observed. The development of the present work permitted us to point out some characteristics of lipases
from wheat seeds necessary for the proposition of new future industrial applications for this important biocatalyst. 相似文献
888.
Mohammad Yazdanbakhsh Nahid Lotfian Haman Tavakkoli Roland Boese 《Central European Journal of Chemistry》2011,9(4):585-589
A novel oxo-centered trinuclear mixed-metal carboxylate complex with unsaturated bridging ligands [Fe2Cr(μ3-O)(C3H3O2)6(H2O)3]·NO3·4H2O has been synthesized and characterized by means of Elemental analyses, Infrared spectroscopy and Crystal structure analysis.
The compound crystallizes isotypically in the monoclinic space group type P21/c. In the compound, each M(III) cation is coordinated by six O atoms from four unsaturated carboxylate groups as bridging ligands, one water molecule as
the terminal ligand, and a μ3-oxygen atom in the center of an equilateral triangle. The infrared spectra show resolved bands arising from νasym(COO) and νsym(COO) vibration of bridging carboxylate ligands along with those of νasym(M2M′O) vibration in the complex. The difference between symmetrical and asymmetrical (COO) ligands indicate that the acrylate
bridge is present in the structure of complex.
相似文献
889.
Kutscher DJ Fricker MB Hattendorf B Bettmer J Günther D 《Analytical and bioanalytical chemistry》2011,401(9):2691-2698
A method was developed for the precise and accurate determination of ovalbumin labelled with p-hydroxy-mercuribenzoic acid (pHMB) using polyacrylamide gel electrophoresis with ns-laser ablation–inductively coupled plasma
mass spectrometry. Following systematic optimisation of the ablation process in terms of detection sensitivity, two different
quantification strategies were applied: external calibration using standards of the derivatized protein after 13C+ normalization and, as a proof of concept, label-specific isotope dilution analysis (IDA) using pHMB enriched in the isotope
199Hg. Due to the inhomogeneous distribution of the protein within the gel bands, it could be demonstrated that the IDA approach
was superior in terms of precision and accuracy. Furthermore, it permits a reliable quantification, if more complex separation
protocols are applied, as typically occurring analyte loss and degradation can be compensated for as soon as complete mixture
of spike and sample is achieved. The estimated limit of detection was 160 fmol in the case of ovalbumin. In contrast to earlier
studies using metals naturally present in proteins, no loss of mercury was observed during separation under denaturing conditions
and other sample preparation steps. Using label-specific IDA, the measured isotope ratios in the gel corresponded to recoveries
between 95% and 103%. 相似文献
890.
Ehsan Jazaeri Liyuan Zhang Xungai Wang Takuya Tsuzuki 《Cellulose (London, England)》2011,18(6):1481-1485
The possibility of fabricating carbon nanofibers from cellulose nanofibers was investigated. Cellulose nanofiber of ~50 nm
in diameter was produced using ball milling in an eco-friendly manner. The effect of the drying techniques of cellulose nanofibers
on the morphology of carbon residue was studied. After pyrolysis of freeze-dried cellulose nanofibers below 600 °C, amorphous
carbon fibers of ~20 nm in diameter were obtained. The pyrolysis of oven-dried precursors resulted in the loss of original
fibrous structures. The different results arising from the two drying techniques are attributed to the difference in the spatial
distance between cellulose nanofiber precursors. 相似文献