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991.
Nicholas Tchang Cervin Christian Aulin Per Tomas Larsson Lars W?gberg 《Cellulose (London, England)》2012,19(2):401-410
A novel type of sponge-like material for the separation of mixed oil and water liquids has been prepared by the vapour deposition
of hydrophobic silanes on ultra-porous nanocellulose aerogels. To achieve this, a highly porous (>99%) nanocellulose aerogel
with high structural flexibility and robustness is first formed by freeze-drying an aqueous dispersion of the nanocellulose.
The density, pore size distribution and wetting properties of the aerogel can be tuned by selecting the concentration of the
nanocellulose dispersion before freeze-drying. The hydrophobic light- weight aerogels are almost instantly filled with the
oil phase when selectively absorbing oil from water, with a capacity to absorb up to 45 times their own weight in oil. The
oil can also be drained from the aerogel and the aerogel can then be reused for a second absorption cycle. 相似文献
992.
Rosholm KR Arouri A Hansen PL González-Pérez A Mouritsen OG 《Langmuir : the ACS journal of surfaces and colloids》2012,28(5):2773-2781
Catansomes, which are vesicles prepared from mixtures of oppositely charged surfactants, have been suggested as effective alternatives to phospholipid vesicles, i.e., liposomes, in applications such as drug-delivery. This is mainly due to their enhanced chemical and physical stability as well as to their relatively easy preparation, which is an advantage for large-scale productions. In this study we have investigated catansomes prepared from a perfluorinated anionic surfactant (sodium perfluorooctanoate) premixed with a hydrogenated cationic surfactant (dodecyltrimethylammonium bromide or 1-dodecylpyridinium chloride). The aim was to gain insights into the physicochemical properties of these systems, such as size, stability, surface charge, and membrane morphology, which are essential for their use in drug-delivery applications. The catansomes were mostly unilamellar and 100-200 nm in size, and were stable for more than five months at room temperature. After loading the catansomes with the fluorescent marker calcein, they were found to exhibit an appreciable encapsulation efficiency and a low calcein leakage over time. The addition of fatty acids to calcein-loaded catansomes considerably promoted the release of calcein, and the rate and efficiency of calcein release were found to be proportional to the fatty acid concentration and chain length. Our results prove the feasibility of utilizing catansomes as drug-delivery vehicles as well as provide a means to efficiently release the encapsulated load. 相似文献
993.
Dr. Andrew W. McKinley Dr. Johanna Andersson Dr. Per Lincoln Dr. Eimer M. Tuite 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(47):15142-15150
The bi‐exponential emission decay of [Ru(L)2dppz]2+ (L=N,N′‐diimine ligand) bound to DNA has been studied as a function of polynucleotide sequence, enantiomer, and nature of L (phenanthroline vs. bipyridine). The lifetimes (τi) and pre‐exponential factors (αi) depend on all three parameters. With [poly(dA‐dT)]2, the variation of αi with [Nu]/[Ru] has little dependence on L for Λ‐[Ru(L)2dppz]2+ but a substantial dependence for Δ‐[Ru(L)2dppz]2+. With [poly(dG‐dC)]2, by contrast, the Λ‐enantiomer αi values depend strongly on the nature of L, whereas those of the Δ‐enantiomer are relatively unaffected. DNA‐bound linked dimers show similar photophysical behaviour. The lifetimes are identified with two geometries of minor‐groove intercalated [Ru(L)2dppz]2+, resulting in differential water access to the phenazine nitrogen atoms. Interplay of cooperative and anti‐cooperative binding resulting from complex–complex and complex–DNA interactions is responsible for the observed variations of αi with binding ratio. [Ru(phen)2dppz]2+ emission is quenched by guanosine in DMF, which may further rationalise the shorter lifetimes observed with guanine‐rich DNA. 相似文献
994.
Siegbahn PE 《Physical chemistry chemical physics : PCCP》2012,14(14):4849-4856
The new high-resolution X-ray structure of photosystem II has allowed more detailed studies than before of water oxidation at the oxygen evolving complex (OEC). In the present study the two final S-transitions of water oxidation are studied. The electron coupled proton transfers are followed from the center of the OEC to Asp61, which is considered as the start of the transfer chain through the protein to the lumenal side. It is found that the proton transfers occur in multiple steps. Structures of intermediates and energy diagrams are derived and compared to experimental observations. Since the new experimental structure of the OEC is very similar to the one suggested earlier by density functional calculations, the O-O bond formation step remains essentially the same as the one suggested five years ago. An interesting new result is that the barrier for proton transfer within the OEC actually competes with the O-O bond formation step of being rate-limiting. 相似文献
995.
Cassimjee KE Humble MS Land H Abedi V Berglund P 《Organic & biomolecular chemistry》2012,10(28):5466-5470
For biocatalytic production of pharmaceutically important chiral amines the ω-transaminase enzymes have proven useful. Engineering of these enzymes has to some extent been accomplished by rational design, but mostly by directed evolution. By use of a homology model a key point mutation in Chromobacterium violaceum ω-transaminase was found upon comparison with engineered variants from homologous enzymes. The variant Trp60Cys gave increased specificity for (S)-1-phenylethylamine (29-fold) and 4'-substituted acetophenones (~5-fold). To further study the effect of the mutation the reaction rates were Swain-Lupton parameterised. On comparison with the wild type, reactions of the variant showed increased resonance dependence; this observation together with changed pH optimum and cofactor dependence suggests an altered reaction mechanism. 相似文献
996.
Haq SR Chi CN Bach A Dogan J Engström Å Hultqvist G Karlsson OA Lundström P Montemiglio LC Strømgaard K Gianni S Jemth P 《Journal of the American Chemical Society》2012,134(1):599-605
Intrinsically disordered proteins are very common and mediate numerous protein-protein and protein-DNA interactions. While it is clear that these interactions are instrumental for the life of the mammalian cell, there is a paucity of data regarding their molecular binding mechanisms. Here we have used short peptides as a model system for intrinsically disordered proteins. Linear free energy relationships based on rate and equilibrium constants for the binding of these peptides to ordered target proteins, PDZ domains, demonstrate that native side-chain interactions form mainly after the rate-limiting barrier for binding and in a cooperative fashion. This finding suggests that these disordered peptides first form a weak encounter complex with non-native interactions. The data do not support the recent notion that the affinities of intrinsically disordered proteins toward their targets are generally governed by their association rate constants. Instead, we observed the opposite for peptide-PDZ interactions, namely, that changes in K(d) correlate with changes in k(off). 相似文献
997.
Due to the lack of a stable technetium isotope, and the high mobility and long half-life, 99Tc is considered to be one of the most important radionuclides in safety assessment of environmental radioactivity as well as nuclear waste management. 99Tc is also an important tracer for oceanographic research due to the high technetium solubility in seawater as TcO4−. A number of analytical methods, using chemical separation combined with radiometric and mass spectrometric measurement techniques, have been developed over the past decades for determination of 99Tc in different environmental samples. This article summarizes and compares recently reported chemical separation procedures and measurement methods for determination of 99Tc. Due to the extremely low concentration of 99Tc in environmental samples, the sample preparation, pre-concentration, chemical separation and purification for removal of the interferences for detection of 99Tc are the most important issues governing the accurate determination of 99Tc. These aspects are discussed in detail in this article. Meanwhile, the different measurement techniques for 99Tc are also compared with respect to advantages and drawbacks. Novel automated analytical methods for rapid determination of 99Tc using solid extraction or ion exchange chromatography for separation of 99Tc, employing flow injection or sequential injection approaches are also discussed. 相似文献
998.
Registration of point sets is done by finding a rotation and translation that produces a best fit between a set of data points and a set of model points. We use robust M-estimation techniques to limit the influence of outliers, more specifically a modified version of the iterative closest point algorithm where we use iteratively re-weighed least squares to incorporate the robustness. We prove convergence with respect to the value of the objective function for this algorithm. A comparison is also done of different criterion functions to figure out their abilities to do appropriate point set fits, when the sets of data points contains outliers. The robust methods prove to be superior to least squares minimization in this setting. 相似文献
999.
Per Christian Hansen James G. Nagy Konstantinos Tigkos 《BIT Numerical Mathematics》2014,54(3):649-671
We describe iterative deblurring algorithms that can handle blur caused by a rotation along an arbitrary axis (including the common case of pure rotation). Our algorithms use a sparse-matrix representation of the blurring operation, which allows us to easily handle several different boundary conditions. We also include robust stopping rules for the iterations. The performance of our algorithms is illustrated with examples. 相似文献
1000.
Let m ≥ 0, n ≥ 0 be fixed integers with m + n ≠ 0 and let R be a prime ring with char(R) = 0 or m + n + 1 ≤ char(R) ≠ 2. Suppose that there exists an additive mapping T : R → R satisfying the relation 2T(x m+n+1) = x m T(x) x n + x n T(x)x m for all ${x\in R}$ . In this case T is a two-sided centralizer. 相似文献