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991.
Summary In this study a new approach is presented for on-line radiometric detection in reversed phase LC of medium to low polarity
compounds labelled with14C.
The test compounds,14C-carbaryl and14C-parathion, are extracted post-column into a non-water miscible liquid scintillation cocktail. The segmented two-phase system
formed is introduced into the beta-detector without phase separation and collected in a capillary storage tube.
After completion of the LC separation and detection process, the direction of the flow in the storage system is reversed and
the segmented contents of the loop led at lower flow-rates through the beta-detector again. An enhanced signal, corresponding
to the increase in counting time is obtained without measurable peak broadening.
The lowest possible detection limit of the system is 9 counts per peak corresponding to subnanogram quantities of tested pesticides.
Calibration curves are linear over at least 2 orders of magnitude and have the expected theoretical slopes.
The reproducibility of the system is better than 4 % rel. S.D. An application to a recovery study of parathion shows the practical
potential of this technique.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献
992.
Summary A computer interactive identification system is proposed which is based on the relationship between retention and molecular
properties such as the size and shape of polycyclic aromatic hydrocarbons (PAHs). This system offers an automatic analytical
process for liquid chromatography, providing a reliable identification of the separated components. The identification can
be further enhanced by the use of multiple detectors such as a multichannel UV detector. The system can be used for optimization
procedures, resulting in a highly automatic complex analytical system. 相似文献
993.
The thermal reaction between the tris(μ-hydrido)dodecacarbonyltrirhenium (o) cluster and triphenylphosphine or triphenylphosphite results in a trisubstituted rhenium cluster as the major product. The results of an X-ray structural analysis of H3Re2(CO)9(PPh3) are: Mr=1597.57, Monoclinic, P21/n, a=15.598(1), b=9.530(2), c=41.685(3) Å, β=80.60(1)°, V=6113.(1) Å3, Z=4, Dc=1.736 g/cm3, CuKe, λ-1.54056 Å, μ-121.23 cm?1, F(000)=3059.17, room temperature, R=0.049 for 7361 reflections with I≥2.5σ(I). The molecule has a triangular Re2 core coordinated propellerwise by three PPh3 ligands in the molecular plane with virtual C3k symmetry. 相似文献
994.
Coupled-column liquid chromatography with fluorescence detection was applied to the determination of o-phenylphenol and bitertanol residues in orange and banana fruits. After extraction with a mixture of acetone, dichloromethane-petroleum ether, and ethyl acetate, an extract aliquot of 100 microL was injected directly without any additional clean-up into the chromatographic system using two reversed phase C18 coupled columns. The LC-LC approach allowed automated sample clean up of the vegetal extracts, leading to a simple and rapid analytical procedure, with limits of quantification between 0.01 and 0.05 mg kg(-1). Recovery experiments performed on orange and banana samples fortified at different concentrations (0.01 - 4 mg kg(-1)) gave average recoveries between 70 and 113% with relative standard deviations lower than 15%. The procedure developed was finally applied to orange and banana samples from different geographical locations and the results were confirmed by GC-MS. 相似文献
995.
1 INTRODUCTION Tri-butyl phosphate (TBP) has been widely used as the extraction reagent in U-Th fuel to separate uranium from thorium. But di-butyl phos- phate (DBP) and butyl phosphate (MBP), the radio- lytic products of TBP, exhibit some coordinated ability to the fission elements, such as Zr and Nb. The substitutes for TBP have being studied for several decades[1~4]. The physical and chemical properties of amides are similar to those of TBP and they selectively extract U(Ⅵ… 相似文献
996.
997.
Some polymer melts (of high viscosity ) can wet completely the surface of a non miscible, simple liquid. We discuss here the laws of spreading for a macroscopic droplet of this type, when the internal friction of the droplet dominates. We predict a droplet radius increasing liket
1/4 wheret is the spreading time, or equivalently a droplet curvature decreasing liket
–1. The droplet should be surrounded by a precursor film, which is not discussed in the present note. 相似文献
998.
The Born→Green→Yvon equation for molecular fluid has been deduced considering the orientational distribution functions. The
isotropic and anisotropic parts of the distribution function have been separated. The expressions deduced can be used in the
case of mixtures and for the non-central type of intermolecular potential energy. 相似文献
999.
Drying dissipative structural patterns formed in the course of drying colloidal crystals of silica spheres (110 nm in diameter)
in water, methyl alcohol, ethyl alcohol, 1-propyl alcohol, diethyl ether, and in the mixtures of ethyl alcohol with the other
solvents above have been studied on a cover glass. The macroscopic broad rings were formed in the outside edges of the dried
film for all the solvents examined. Furthermore, much distinct broad rings appeared in the inner area when the solvents were
ethyl alcohol, methyl alcohol, and their mixtures. Profiles of the thickness of the dried films were sensitive to the organic
solvents and explained well with changes in the surface tensions, boiling points, and viscosities of the solvents. The macroscopic
and microscopic spoke-like crack patterns formed. The drying area (or the drying time) increased (or decreased) as the surface
tension of the solvent decreased. However, the absolute values of these drying parameters are determined also by the boiling
points of the solvents. Importance of the fundamental properties of the solvents is supported in addition to the characteristics
of colloidal particles in the drying dissipative pattern formation. 相似文献
1000.
M. J. Medina-Hernández M. Catalá-Icardo M. C. García-Alvarez-Coque 《Chromatographia》1995,41(5-6):455-461
Summary Hydrophobic character is usually expressed in terms of the partition coefficient in 1-octanol-water (log Po/w). However, measurement of this coefficient is often problematic. Retention in micellar liquid chromatography is mainly due
to hydrophobic interactions and can also be used as an index of hydrophobicity. A hydrophobicity scale was established with
retention data foro-phthalaldehyde (OPA)-N-acetyl-L-cysteine (NAC) amino acid derivatives, using the glycine derivative as reference. Since the
OPA-NAC derivatives only differ in the nature of R1 in the amino acid (R1CH (COOH)NH2), in the absence of electrostatic interactions the hydrophobic character of the substituent was responsible for retention.
Linear relationships were obtained between log of the ratiok′ of amino acid derivatives:k′ of the glycine derivative for a given mobile phase, and logP
o/w for the R1 substituent. Good correlations were also found for phenylthiohydantoin amino acid derivatives. 相似文献