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991.
Ohne Zusammenfassung 相似文献
992.
O. Anselmino Stone Tollens L. Rosenthaler E. Spaeth Caesar Loretz Panchaud B. Hafner E. W. Mann John Barclay Fromme Fraser Ludwig Krauss P. Lemaire Denigés Kimpflin M. Nussbaum H. Runne C. Guérin G. Denigés Feldhaus Gregor E. Durien Fordos Geélis Utscher C. Gueérin Ernst Deussen E. Beckmann 《Analytical and bioanalytical chemistry》1912,51(10-11):700-712
993.
John McCuan 《Milan Journal of Mathematics》2009,77(1):385-396
Archimedes’ beautiful principle may be used to determine how an object floats in a vessel of liquid. This, in turn may be
used to determine the global configuration associated with a floating object under the assumption that the surface of the
liquid is planar. There are instances, however, in which capillary effects conspire to produce significantly nonplanar liquid interfaces and phenomena which is strikingly at odds with the predictions of the Archimedean principle. A most notable
instance involves floatation of convex objects with density greater than that of the liquid.
The effects of capillarity on liquid interface configurations invariably manifest themselves globally over the entire system,
though the magnitude of such effects is often so small as to be overlooked. This phenomenon presents a major difficulty in
obtaining an appropriate generalization of Archimedes’ principle which incorporates capillarity. 相似文献
994.
We provide a simple formula to compute the Hausdorff dimension of the attractor of an overlapping iterated function system
of contractive similarities satisfying a certain collection of assumptions. This formula is obtained by associating a non-overlapping
infinite iterated function system to an iterated function system satisfying our assumptions and using the results of Moran
to compute the Hausdorff dimension of the attractor of this infinite iterated function system, thus showing that the Hausforff
dimension of the attractor of this infinite iterated function system agrees with that of the attractor of the original iterated
function system. Our methods are applicable to some iterated function systems that do not satisfy the finite type condition
recently introduced by Ngai and Wang.
相似文献
995.
Spectral accuracy of molecular ions in an LTQ/Orbitrap mass spectrometer and implications for elemental composition determination 总被引:1,自引:0,他引:1
John C. L. Erve Ming Gu Yongdong Wang William DeMaio Rasmy E. Talaat 《Journal of the American Society for Mass Spectrometry》2009,20(11):2058-2069
In addition to mass accuracy, the ability of a mass spectrometer to faithfully measure the isotopic distribution of an ion,
defined as spectral accuracy, is also important. Although time-of-flight mass spectrometers are reported to possess high spectral
accuracy capability compared with other mass spectrometers, the Orbitrap has not yet been investigated. Ten natural products
(moxidectin, erythromycin, digoxin, rifampicin, amphotericin B, rapamycin, gramicidin S, cyclosporin A, vancomycin, and thiostrepton)
ranging in molecular weight from 639 to 1663 Da were measured on an LTQ/Orbitrap mass spectrometer with resolving power settings
of 7.5, 15, 30, 60, and 100 K. The difference in the observed profile isotope pattern compared with the theoretical calculation
after peak shape calibration, denoted spectral error, was calculated using the program MassWorks (Cerno Bioscience, Danbury,
CT, USA). Spectral errors were least at 7.5 K resolving power (≤3%) but exceeded 10% for some compounds at 100 K. The increasing
spectral error observed at higher resolving power for compounds with complex fine structure might be explained by the phenomena
of isotopic beat patterns as observed in FTICR. Several compounds with prominent doubly charged ions allowed comparison of
spectral accuracies of singly-versus doubly-charged ions. When using spectral error to rank elemental compositions with formula
constraints (C0–100H0–200N0–50O0–50Cl0–5S0–5) and a mass tolerance ≤2 parts-per-million, the correct formula was ranked first 35% of the time. However, spectral error
considerations eliminated >99% of possible elemental formulas for compounds with molecular weight >900 Da. 相似文献
996.
Nian Sun Jiangxiao Sun Elena N. Kitova John S. Klassen 《Journal of the American Society for Mass Spectrometry》2009,20(7):1242-1250
The application of the reporter molecule (Mrep) method for identifying nonspecific complexes in the ES-MS analysis of protein-ligand and DNA-ligand interactions in vitro
is described. To test the reliability of the method, it was applied to the ES-MS analysis of protein-carbohydrate complexes
originating from specific interactions in solution and from nonspecific interactions in the ES process. These control experiments
confirm the basic assumptions underlying the Mrep method, namely that nonspecific ligand binding is a random process, and that the ES droplet histories for specific and nonspecific
complexes are distinct. The application of the Mrep method to the ES-MS analysis of the sequential binding of the ethidium cation, a DNA intercalator, to single and double strand
oligodeoxynucleotides is also described, and highlights the general utility of the method. 相似文献
997.
John K. Meissen Matthew D. Sweeney Matthew Girardi Roger Lawrence Jeffrey D. Esko Julie A. Leary 《Journal of the American Society for Mass Spectrometry》2009,20(4):652-657
The presence of 3-O-sulfated glucosamine residues in heparin or heparan sulfate plays a role in binding to antithrombin III
and HSV infection. In this study, tandem mass spectrometry was used to differentiate between two heparin disaccharide isomers
containing variable sulfate at C6 in a common disaccharide and C3 in a more rare one. The dissociation patterns shown by MS2 and MS3 were clearly distinguishable between the isomers, allowing their differentiation and quantitation. Using this technique,
we show that an octasaccharide with 11 sulfate groups with high affinity for inflammatory chemokine CCL2 does not contain
3-O-sulfated disaccharides. 相似文献
998.
Hao Wang Robert M. Straubinger John M. Aletta Jin Cao Xiaotao Duan Haoying Yu Jun Qu 《Journal of the American Society for Mass Spectrometry》2009,20(3):507-519
Protein arginine (Arg) methylation serves an important functional role in eucaryotic cells, and typically occurs in domains
consisting of multiple Arg in close proximity. Localization of methylarginine (MA) within Arg-rich domains poses a challenge
for mass spectrometry (MS)-based methods; the peptides are highly charged under electrospray ionization (ESI), which limits
the number of sequence-informative products produced by collision induced dissociation (CID), and loss of the labile methylation
moieties during CID precludes effective fragmentation of the peptide backbone. Here the fragmentation behavior of Arg-rich
peptides was investigated comprehensively using electron-transfer dissociation (ETD) and CID for both methylated and unmodified
glycine-/Arg-rich peptides (GAR), derived from residues 679–695 of human nucleolin, which contains methylation motifs that
are widely-represented in biological systems. ETD produced abundant information for sequencing and MA localization, whereas
CID failed to provide credible identification for any available charge state (z=2–4). Nevertheless, CID produced characteristic
neutral losses that can be employed to distinguish among different types of MA, as suggested by previous works and confirmed
here with product ion scans of high accuracy/resolution by an LTQ/Orbitrap. To analyze MA-peptides in relatively complex mixtures,
a method was developed that employs nano-LC coupled to alternating CID/ETD for peptide sequencing and MA localization/characterization,
and an Orbitrap for accurate precursor measurement and relative quantification of MA-peptide stoichiometries. As proof of
concept, GAR-peptides methylated in vitro by protein arginine N-methyltransferases PRMT1 and PRMT7 were analyzed. It was observed that PRMT1 generated a number of monomethylated (MMA) and
asymmetric-dimethylated peptides, while PRMT7 produced predominantly MMA peptides and some symmetric-dimethylated peptides.
This approach and the results may advance understanding of the actions of PRMTs and the functional significance of Arg methylation
patterns. 相似文献
999.
1000.