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981.
The reactions of Cu(ClO4)2·6H2O with 6-(benzylamino)purine derivatives in a stoichiometric 1:2 metal-to-ligand ratio led to the formation of penta-coordinated dinuclear complexes of the formula [Cu2(μ-L1–8)4(ClO4)2](ClO4)2·nsolv, where L1 = 6-(2-fluorobenzylamino)purine (complex 1), L2 = 6-(3-fluorobenzylamino)purine (2), L3 = 6-(4-fluorobenzylamino)purine (3), L4 = 6-(2-chlorobenzylamino)purine (4), L5 = 6-(3-chlorobenzylamino)purine (5), L6 = 6-(4-chlorobenzylamino)purine (6), L7 = 6-(3-methoxybenzylamino)purine (7) and L8 = 6-(4-methoxybenzylamino)purine (8); n = 0–4 and solv = H2O, EtOH or MeOH. All the complexes have been fully characterized by elemental analysis, FTIR, UV–Vis and EPR spectroscopy, and by magnetic and conductivity measurements. Variable temperature (80–300 K) magnetic susceptibility data of 1–8 showed the presence of a strong antiferromagnetic exchange interaction between two Cu(II) (S = 1/2) atoms with J ranging from −150.0(1) to −160.3(2) cm−1. The compound 6·4EtOH·H2O was structurally characterized by single crystal X-ray analysis. The Cu?Cu separation has been found to be 2.9092(8) Å. The antiradical activity of the prepared compounds was tested by in vitro SOD-mimic assay with IC50 in the range 8.67–41.45 μM. The results of an in vivo antidiabetic activity assay were inconclusive and the glycaemia in pre-treated animals did not differ significantly from the positive control. 相似文献
982.
Jorge Acevedo-Martínez Igor G. Zenkevich Ramón Carrasco-Velar 《Chromatographia》2010,71(9-10):881-889
A simple algorithm is proposed for prediction of linear retention indices, RI, of organic compounds with different structures. The algorithm is based on the hypothesis that any structural moiety of a molecule contributes to gas chromatographic retention to a different extent, depending on its molecular environment. For a given moiety the mean structural increment (MSI) is calculated from the difference between the retention indices of two molecules, one containing it and one not, in different compound families. The mean of these values is the MSI for the corresponding moiety. The correlation between predicted and experimental values affords r 2 = 0.992 and the mean relative error is 1.65% for n = 92 compounds. 相似文献
983.
Biljana Jančić-Stojanović Igor Popović Anđelija Malenović Darko Ivanović Mirjana Medenica 《Chromatographia》2010,71(9-10):799-804
In this paper optimization of chromatographic retention of ramipril and its five impurities employing factorial design is presented. On the basis of preliminary experiments three factors were chosen as inputs (acetonitrile content, pH of the mobile phase and buffer concentration) and retention factor as output. As optimal full factorial design 23 was chosen, factors were examined at two different levels “low” and “high”. Three replications at zero level were added in order to check linearity and complete statistical tests. Relationship between inputs and output is presented in form of second order interaction model. Adequacy of model was explained using analysis of variance. After analysis of results optimal chromatographic conditions were set. Separations were conducted on a C18 column with a mixture of acetonitrile and water phase (TEA in potassium dihydrogen phosphate) in ratio 23:77 v/v. Finally, the LC method was validated and applied for quality control analysis of commercially available tablets. The proposed method is simpler and faster as compared to existing official methods and therefore more adequate for routine control of ramipril during shelf life. Also a general approach which includes factorial design in method optimization offers a possibility for predicting and following the chromatographic behavior of such complex mixtures. 相似文献
984.
Magnetic resonance imaging (MRI) is a very powerful instrument used extensively in modern medical diagnostics because of its ability to look inside a body in a non-invasive and non-destructive way. Furthermore, MRI is more than just a single tool for extracting structural information. It is more of a sophisticated and versatile toolkit able to provide all sorts of useful information about the internal properties of an object under study and various processes within it, including heat and mass transport, composition and chemical transformations, in a spatially resolved mode. While a living body is different from a catalyst body or a reactor, the in situ and Operando studies in catalysis can clearly benefit from the use of this non-destructive toolkit as a powerful complement to other available spectroscopic tools. This tutorial review gives an introduction to the field and describes the examples of the applications of MRI to the studies of the preparation, deactivation and regeneration of solid catalysts and to the spectroscopy, thermometry and imaging studies of heterogeneous catalysts and model catalytic reactors performed during actual catalytic processes. 相似文献
985.
Tomáš Nedelčev Igor Krupa Pavol Hrdlovič Jozef Kollár Dušan ChorvátJr. Igor Lacík 《Journal of Sol-Gel Science and Technology》2010,55(2):143-150
Fluorescent probes pyrene (Py), di(1-pyrenylmethyl)ether (DiPyM) and newly synthesized 2,3-bis-[4-(1-pyrenemethoxy)methylphenyl]butane
(DiPyS) were used to monitor the formation and aging of silica hydrogel prepared from poly(glyceryl silicate) (PGS) sol. The
fluorescence emission spectra of these probes are sensitive to their environment and this feature is utilized for monitoring
the evolution of silica hydrogels prepared in this work. The polarity of hydrogel matrix during sol–gel transition assessed
by all three pyrene probes decreases in the first stage of hydrogel formation, for about 2 h, followed by a gradual increase
in polarity and reaching the constant level after 24 h for at least 2 weeks. The process of crosslinking was assessed by DiPyM
and DiPyS. These fluorescent probes possess two pyrene structures, which ability to form a dynamic intramolecular excimer
can be used to monitor the degree of hydrogel crosslinking with time. These data support the polarity measurements that the
hydrogel network is predominatly formed within the first 2 h, stabilized within the 24 h, and that there is a minor increase
in the network density for about 10 days until reaching the constant level. In addition, utilizing the second-order diffraction
of scattered excitation light may also be used to obtain an adequate information about the silica hydrogel evolution. In summary,
this paper demonstrates that pyrene-type fluorescent probes represent simple and precise tool for characterization of formation
and aging of the silica hydrogels. 相似文献
986.
Buha J Arčon D Niederberger M Djerdj I 《Physical chemistry chemical physics : PCCP》2010,12(47):15537-15543
A simple route to niobium, hafnium and tantalum oxide nanocrystals using a nonaqueous sol-gel route based on the solvothermal reaction of the corresponding metal chlorides with benzyl alcohol is presented. This approach can easily be extended to the preparation of high quality Co-doped HfO(2) nanoparticles of uniform size and shape and with a homogenous distribution of the magnetic ions. The structural characterization of all these nanomaterials as well as the magnetic properties of pure and doped hafnia, with special attention to the doping efficiency, are discussed. The obtained Co-doped hafnia exhibits paramagnetic properties with very weak antiferromagnetic interactions between Co ions moments. 相似文献
987.
NMR modulated gradient spin echo method, which allows the quantification of polymer segmental displacement via the measurement of the velocity autocorrelation, requires the formulation of theoretical predictions in the frequency domain in order to test their validity. We worked out the velocity autocorrelation spectrum of the segmental motion according to the Rouse and the tube/reptation model to compare it to the experimental results obtained by the new NMR technique. The analysis of polybutadiene shows the segmental velocity autocorrelation spectrum typical for the reptation-like motion of polymer in a “tube”. The measurement of bulk water indicates a kind of Rouse motion in a network of hydrogen bonds. 相似文献
988.
The use of semiconductor quantum dots (QDs) in biological sensing and labeling continues to grow with each year. Current and
projected applications include use as fluorescent labels for cellular labeling, intracellular sensors, deep-tissue and tumor
imaging agents, sensitizers for photodynamic therapy, and more recently interest has been sparked in using them as vectors
for studying nanoparticle-mediated drug delivery. Many of these applications will ultimately require the QDs to undergo targeted
intracellular delivery, not only to specific cells, but also to a variety of subcellular compartments and organelles. It is
apparent that this issue will be critical in determining the efficacy of using QDs, and indeed a variety of other nanoparticles,
for these types of applications. In this review, we provide an overview of the current methods for delivering QDs into cells.
Methods that are covered include facilitated techniques such as those that utilize specific peptide sequences or polymer delivery
reagents and active methods such as electroporation and microinjection. We critically examine the benefits and liabilities
of each strategy and illustrate them with selected examples from the literature. Several important related issues such as
QD size and surface coating, methods for QD biofunctionalization, cellular physiology and toxicity are also discussed. Finally,
we conclude by providing a perspective of how this field can be expected to develop in the future. 相似文献
989.
We consider solutions to the linear wave equation □g? = 0 on a (maximally extended) Schwarzschild spacetime with parameter M > 0, evolving from sufficiently regular initial data prescribed on a complete Cauchy surface Σ, where the data are assumed only to decay suitably at spatial infinity. (In particular, the support of ? may contain the bifurcate event horizon.) It is shown that the energy flux F(??) of the solution (as measured by a strictly timelike T? that asymptotically matches the static Killing field) through arbitrary achronal subsets ?? of the black hole exterior region satisfies the bound F(??) ≤ C E(v + u), where v and u denote the infimum of the Eddington‐Finkelstein advanced and retarded time of ??, v+ denotes max{1, v}, and u+ denotes max{1, u}, where C is a constant depending only on the parameter M, and E depends on a suitable norm of the solution on the hypersurface t ? u + v = 1. (The bound applies in particular to subsets ?? of the event horizon or null infinity.) It is also shown that ? satisfies the pointwise decay estimate |?| ≤ C Ev in the entire exterior region, and the estimates |r?| ≤ CR?E(1 + |u|)?1/2 and |r1/2?| ≤ CR?Eu in the region {r ≥ R?} ∩ J+(Σ) for any R? > 2M. The estimates near the event horizon exploit an integral energy identity normalized to local observers. This estimate can be thought to quantify the celebrated red‐shift effect. The results in particular give an independent proof of the classical result |?| ≥ C E of Kay and Wald without recourse to the discrete isometries of spacetime. © 2009 Wiley Periodicals, Inc. 相似文献
990.