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61.
Xiao Chen Katharina Buddrus-Schiemann Michael Rothballer Petra M. Kr?mer Anton Hartmann 《Analytical and bioanalytical chemistry》2010,398(6):2669-2676
The Burkholderia cepacia complex (Bcc) employs a quorum sensing (QS) mechanism which is a cell density-dependent bacterial communication system to
regulate certain gene expressions. As with many other Gram-negative bacteria, Burkholderia cepacia species use (N-acyl-)homoserine lactones (AHLs or HSLs) as signalling molecules. Because of the essential role of QS in bacterial behavior,
the aim of this study was to demonstrate the applicability of our in-house-developed enzyme-linked immunosorbent assays (ELISAs)
for the detection of bacterial activities via HSLs in B. cepacia strain LA3 culture supernatants. For this purpose the previously developed monoclonal antibodies (mAbs) HSL1/2-2C10 and HSL1/2-4H5
were exploited. N-3-Oxo-decanoyl-L-homoserine lactone (3-oxo-C10-HSL) was used as main analyte throughout all experiments. With the bacterial
culture medium (named ABC medium) a matrix effect in both ELISAs was visible (slight increase in optical density, shift in
test midpoints (IC50) and working ranges). For example, ELISA with mAb HSL1/2-2C10 and enzyme tracer HSL3-HRP (HSL derivative conjugated to horseradish
peroxidase) had an IC50 of 120 μg L−1 for 3-oxo-C10-HSL in phosphate-buffered saline versus 372 μg L−1 in ABC medium. A significant increase of HSLs in B. cepacia strain LA3 culture supernatants after 12 h to 48 h of growth was observed. Although the analytical result of these immunoassays
cannot distinguish HSLs from homoserines (HSs), the appearance of these compounds can be easily followed. Hydrolysis and spiking
experiments were carried out with these biological samples. According to our knowledge, these are the first immunoassays for
the detection of quorum sensing molecules in biological culture supernatants. This study provides a cost-effective, fast,
and sensitive analytical method for detection of HSLs/HSs in biological samples without complex sample preparation and will
offer a quick idea about B. cepacia activities. The low sample amount requirement (less than 1 mL) constitutes a tremendous advantage for many analytical questions
with biological samples. 相似文献
62.
Ina Reiche Matthieu Lebon Céline Chadefaux Katharina Müller Anne-Solenn Le Hô Michael Gensch Ulrich Schade 《Analytical and bioanalytical chemistry》2010,397(6):2491-2499
Archaeological bone materials record characteristic markers of life in prehistoric times (dating, climate, environment, diet, human migration) in their isotopic and chemical composition in addition to palaeontological, archaeozoological, anthropological and palaeogenetic information. Thus, the discovery and conservation of archaeological bone materials is of great importance to get access to this information. However, archaeological materials are altered by different postmortem processes and it appears necessary to estimate if the archaeological information is still reliable or if it has been modified during burial. As archaeological bone materials present a high structural hierarchy at the micro- and nanoscale, changes induced by diagenetic phenomena have to be observed at these scales. One method for revealing post mortem changes of the bone structure and composition at the microscale is synchrotron radiation micro-FTIR imaging (SR micro-FTIR). Thus, thin sections of about 5,000-year-old archaeological bones have been analysed in transmission mode at the IRIS beamline (BESSY II, HZB Berlin) to determine markers of the state of bone preservation at the microscale. The archaeological bone material comes from station 19 of the Neolithic site of the Chalain Lake. By using SR micro-FTIR it was possible to image characteristic bone structures, e.g. osteons (the constitutive histological unit of cortical bone), using the absorption band ratios corresponding to different chemical bone constituents (collagen content and quality, phosphate crystallinity, carbonate content). These data allow us to precisely evaluate the state of preservation of a 5,000-year-old bone at the histological level. Figure
Chemical mapping of a thin section of the archaeological bone AB_CH19nb1 from the Neolithic station 19 at Chalain Lake 相似文献
63.
Parthey CG Matveev A Alnis J Bernhardt B Beyer A Holzwarth R Maistrou A Pohl R Predehl K Udem T Wilken T Kolachevsky N Abgrall M Rovera D Salomon C Laurent P Hänsch TW 《Physical review letters》2011,107(20):203001
We have measured the 1S-2S transition frequency in atomic hydrogen via two-photon spectroscopy on a 5.8 K atomic beam. We obtain f(1S-2S) = 2,466,061,413,187,035 (10) Hz for the hyperfine centroid, in agreement with, but 3.3 times better than the previous result [M. Fischer et al., Phys. Rev. Lett. 92, 230802 (2004)]. The improvement to a fractional frequency uncertainty of 4.2 × 10(-15) arises mainly from an improved stability of the spectroscopy laser, and a better determination of the main systematic uncertainties, namely, the second order Doppler and ac and dc Stark shifts. The probe laser frequency was phase coherently linked to the mobile cesium fountain clock FOM via a frequency comb. 相似文献
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Biuret is an intermediate in the bacterial metabolism of s-triazine ring compounds and is occasionally used as a ruminant feed supplement. We used bioinformatics to identify a biuret hydrolase, an enzyme that has previously resisted efforts to stabilize, purify and characterize. This newly discovered enzyme is a member of the cysteine hydrolase superfamily, a family of enzymes previously not found to be involved in s-triazine metabolism. The gene from Rhizobium leguminosarum bv. viciae strain 3841 encoding biuret hydrolase was synthesized, transformed into Escherichia coli, and expressed. The enzyme was purified and found to be stable. Biuret hydrolase catalyzed the hydrolysis of biuret to allophanate and ammonia. The k(cat)/K(M) of 1.7 × 10(5) M(-1)s(-1) and the relatively low K(M) of 23 ± 4 μM together suggested that this enzyme acts uniquely on biuret physiologically. This is supported by the fact that of the 34 substrate analogs of biuret tested, only two demonstrated reactivity, both at less than 5% of the rate determined for biuret. Biuret hydrolase does not react with carboxybiuret, the product of the enzyme immediately preceding biuret hydrolase in the metabolic pathway for cyanuric acid. This suggests an unusual metabolic strategy of an enzymatically-produced intermediate undergoing non-enzymatic decarboxylation to produce the substrate for the next enzyme in the pathway. 相似文献
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69.
Maria-Verena Kohnle Ulrich Ziener Katharina Landfester 《Colloid and polymer science》2009,287(3):259-268
High-butadiene-level styrene–butadiene rubber latexes up to high solid-contents are synthesized using the miniemulsion process.
It is shown that the miniemulsion polymerization approach offers an efficient heterophase route synthesizing styrene–butadiene
copolymer latexes with flexible copolymer composition and narrow size distribution of the resulting latex particles. Secondary
nucleation was successfully prevented by using a hydrophobic initiator. Due to the nanoreactor situation, even at high conversions,
a low crosslinking degree and, therefore, low gel contents are obtained. The microstructure of the polymers obtained in miniemulsion
is independent of the synthesis parameters, especially the temperature. The molecular weight can be easily adjusted by the
application of transfer agents while the insoluble gel content is substantially reduced. An up-scaling of the procedure is
easily possible. 相似文献
70.
Regioselective Ring‐Opening Polymerization of a Polyhydroxycarboxylic Acid for the Synthesis of a Nanoscale Carrier Material with pH‐Dependent Stability and Sustained Drug Release 下载免费PDF全文
Dipl.‐Chem. Alexander Ewe Dr. Anita Jansen de Salazar Dipl.‐Phys. Katharina Lemmnitzer Michael Marsch Prof. Dr. Achim Aigner Prof. Dr. Armin Geyer 《Angewandte Chemie (International ed. in English)》2015,54(21):6364-6369
Synthetic polyesters are usually composed of monohydroxycarboxylic acids to avoid the problem of regioselectivity during ring‐opening polymerization. In contrast, the linear polyester BICpoly contains four secondary OH groups and is nevertheless esterified regioselectively at only one of these positions. Neither the synthesis of the tricyclic monomers nor the ring‐opening polymerization requires protecting groups, making BICpoly an attractive novel and biocompatible polymer. BICpoly nanoparticles can be loaded with low‐molecular weight drugs or coated onto surfaces as thin films. The release of loaded compounds makes BICpoly an attractive depot for drug release, as shown herein by loading BICpoly with dyes or the cytostatic drug doxorubicin. BICpoly is distinguishable from other polymers by its characteristic pH‐dependent degradation. 相似文献