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991.
992.
Constantino E Rodríguez-Santiago L Sodupe M Tortajada J 《The journal of physical chemistry. A》2005,109(1):224-230
Cobalt cations are open shell systems with several possible electronic states arising from the different occupations of the 3d and 4s orbitals. The influence of these occupations on the relative stability of the coordination modes of the metal cation to glycine has been studied by means of theoretical methods. The structure and vibrational frequencies have been determined using the B3LYP method. Single-point calculations have also been carried out at the CCSD(T) level. The most stable structure of Co(+)-glycine is bidentate, with the Co(+) cation interacting with the amino group and the carbonyl oxygen of neutral glycine, and the ground electronic state being (3)A. For Co(2+)-glycine, the lowest energy structure corresponds to the interaction of the metal cation with the carboxylate group of the zwitterionic glycine, the ground electronic state being (4)A'. 相似文献
993.
994.
Preparation of organic polymer monolithic columns in fused silica capillaries was aimed at fast gradient separation of proteins. For this purpose, polymerization in situ procedure was optimized, using ethylene dimetacrylate and butyl metacrylate monomers with azobisisobutyronitrile as initiator of the polymerization reaction in presence of non-aqueous porogen solvent mixtures composed of 1-propanol and 1,4-butanediol. The separation of proteins in totally monolithic capillary columns was compared with the chromatography on a new type of "hybrid interparticle monolithic" capillary columns, prepared by in situ polymerization in capillary packed with superficially porous spherical beds, 37-50 microm. The "hybrid" columns showed excellent stability and improved hydrodynamic flow properties with respect to the "totally" monolithic capillary columns. The separation selectivity is similar in the two types of columns. The nature of the superficially porous layer (bare silica or bonded C18 ligands) affects the separation selectivity less significantly than the porosity (density) of the monolithic moiety in the interparticle space, controlled by the composition of the polymerization mixture. The retention behaviour of proteins on all prepared columns is consistent with the reversed-phase gradient elution theory. 相似文献
995.
In the literature it was found that titanium oxide clusters of a few metal atoms encapsulated inside the micropores of zeolite Y exhibit large blue shifts in the Ti-O ligand-to-metal charge-transfer band as compared to non-encapsulated bulk titanium dioxide particles. This blue shift of the Ti-O absorption band is believed to have a negative effect on the photocatalytic activity of zeolite-encapsulated TiO2. We report here on circumventing this problem and increasing visible-light absorption by means of a red shift of the absorption band caused by addition of some organic molecular modifiers containing acidic OH groups that can strongly bind with titanol groups TiOH. In the studied series of zeolite-encapsulated TiO2 samples, the red shift of the optical spectrum follows the order: catechol > 4-aminobenzoic acid > benzoic acid. Also N-doping of zeolite-encapsulated TiO2 clusters by thermal treatment with urea leads to a red shift of the TiO2 absorption band that depends on the annealing and hydration conditions. By comparison to the degradation of phenol in aqueous solution, we have demonstrated that these changes in the absorption spectrum on addition of the organic modifier are also reflected in the photocatalytic activity of the samples; a greater increase in photocatalytic activity (about 30%) was observed for the additive catechol. 相似文献
996.
Cristóbal Valenzuela Calahorro Fernando José García Barros Angeles Díaz Díez Alvaro Bernalte García Eduardo Sabio Rey 《Monatshefte für Chemie / Chemical Monthly》1992,123(1-2):9-16
Summary Five Cu(II), Pd(II), Cd(II), Pt(IV), and Au(III) complexes of 6-chloropurine have been obtained. The complexes were characterized by elemental analysis, IR,1H-NMR and13C-NMR spectroscopy. On the basis of these data the structure of the complexes and the coordination of the ligand have been proposed. Thus, the physical and chemical methods supported evidence that in acidic medium, with exception of the Cu(II) complex, 6-chloropurine acts in the monoprotonated form neutralizing the charge of [PdCl4]2–, [CdCl4]2–, [AuCl4]– and [PtCl6]2– anions. The thermal behaviour of the complexes has also been studied.
Metallkomplexe von 6-Chlorpurin
Zusammenfassung Es wurden fünf Komplexe von 6-Chlorpurin mit Cu(II), Pd(II), Cd(II), Pt(IV) und Au(III) erhalten. Die Komplexe wurden mittels Elementaranalysen, IR,1H-NMR und13C-NMR charakterisiert. Auf der Basis dieser Daten wurde eine Komplexstruktur und eine bestimmte Koordination der Liganden vorgeschlagen. Physikalische und chemische Methoden beweisen, daß im sauren Bereich [mit der Ausnahme von Cu(II)] das 6-Chlorpurin in der monoprotonierten Form koordiniert, wobei die Ladung von [PdCl4]2–, [CdCl4]2–, [AuCl4]– und [PtCl6]2– jeweils neutralisiert wird. Das thermische Verhalten der Komplexe wurde ebenfalls untersucht.相似文献
997.
González-Martínez MA Puchades R Maquieira A 《Analytical and bioanalytical chemistry》2007,387(1):205-218
Immunosensing has proved to be a very interesting research area. This review discusses what has actually been achieved in
the field of optical immunosensing for environmental screening, and what still needs to be done. The review is presented from
a practical point of view. In terms of the basic design of the immunosensor, there is a trend towards decreasing assay time;
indeed, this has been reduced from 15–20 minutes to less than 5 minutes. Another goal is to simplify the manifold, and label-free
approaches combining indirect assay formats and the detection of antibody binding are popular. Rapid displacement assays have
also been investigated thoroughly. In terms of some important features of immunosensing devices, the reusability of the sensing
element has been studied in great depth, and working lifetimes of more than five hundred assays can now be found for all assay
formats. Multianalyte assays are now being investigated, and current systems are able to monitor 2–3 target compounds, although
this number is set to increase greatly (to >30) in the near future. In this sense, an increasing number of publications can
be found on microarrays intended for multianalyte determinations. The application of immunosensing to real situations is the
main challenge. Immunosensors are barely commercialized and are yet to be established as research or routine tools, due to
a lack of validated protocols for a wide range of sample matrices. Regarding compounds considered as analytes, some significant
pollutants such as dioxins or pharmaceuticals are rarely chosen as targets, although the current tendency is towards a broader
spectrum of analytes. New immunoreagents should be raised for these compounds, for use in immunosensors that can be used as
screening tools. 相似文献
998.
Z. Mikulová P. Čuba J. Balabánová T. Rojka F. Kovanda K. Jirátová 《Chemical Papers》2007,61(2):103-109
The effect of hydrothermal treatment on properties (crystallinity, porous structure, reducibility, acidity, basicity, and
catalytic activity and selectivity in toluene and ethanol total oxidation) of Ni—Al layered double hydroxide precursors and
related mixed oxides was examined. The hydrothermal treatment increased considerably both the content of crystalline phase
and LDH crystallite size. On the other hand, only a slight effect of the precursor hydrothermal treatment on crystallinity
of the related Ni—Al mixed oxides obtained by calcination at 450°C was observed. The reducibility of NiO particles appeared
to be hindered considerably compared to the reducibility of pure NiO. Catalytic activity of the Ni—Al mixed oxides prepared
from the precursors hydrothermally treated for a short time (4 h) was the highest. The highest amount of acetaldehyde formed
during the total oxidation of ethanol, i.e. the worst selectivity was found for the calcined Ni—Al LDH without hydrothermal treatment.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
999.
Pérez-Sirvent C Martínez-Sánchez MJ García-Lorenzo M López-García I Hernández-Córdoba M 《Analytical and bioanalytical chemistry》2007,388(2):495-498
Use of small membrane pumps, instead of peristaltic pumps, to introduce sample and reagent solutions into the spectrometer
has several advantages in atomic fluorescence spectrometric determination of mercury. This simple modification results in
a substantial saving in the time required for the measurements and so 90% of reagent solution volumes and 95% of sample solution
volumes are saved, with a consequent decrease in the volume of waste generated. The sampling frequency is almost tripled,
with no deterioration in sensitivity, which is similar to that obtained by use of peristaltic pumps. The relative standard
deviation for ten consecutive measurements of a 1 μg L−1 mercury solution was approximately 2%.
Figure Small membrane pumps for the atomic fluorescene spectro metric determination of mercury 相似文献
1000.
Hairy roots of Brugmansia candida produce the tropane alkaloids scopolamine and hyoscyamine. In an attempt to divert the carbon flux from competing pathways
and thus enhance productivity, the polyamine biosynthesis inhibitors cyclohexylamine (CHA) and methylglyoxal-bis-guanylhy,
drazone (MGBG) and the phenylalamine-ammonia-lyase inhibitor cinnamic acid were used. CHA decreased the specific productivity
of both alkaloids but increased significantly the release of scopolamine (approx 500%) when it was added in the mid-exponential
phase. However, when CHA was added for only 48 h during the exponential phase, the specific productivity of both alkaloids
increased (approx 200%), favoring scopolamine. Treatment with MGBG was detrimental to growth but promoted release into the
medium of both alkaloids. However, when it was added for 48 h during the exponential phase, MGBG increased the specific productivity
(approx 200%) and release (250–1800%) of both alkaloids. Cinnamic acid alone also favored release but not specific productivity.
When a combination of CHA or MGBG with cinnamic acid was used, the results obtained were approximately the same as with each
polyamine biosynthesis inhibitor alone, although to a lesser extent. Regarding root morphology, CHA inhibited growth of primary
roots and ramification. However, it had a positive effect on elongation of lateral roots. 相似文献