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排序方式: 共有480条查询结果,搜索用时 156 毫秒
51.
Multiresidue analysis of multiclass plant growth regulators in grapes by liquid chromatography/tandem mass spectrometry 总被引:1,自引:0,他引:1
Oulkar DP Banerjee K Ghaste MS Ramteke SD Naik DG Patil SB Jadhav MR Adsule PG 《Journal of AOAC International》2011,94(3):968-977
A selective and rapid multiresidue analysis method is presented for simultaneous estimation of 12 plant growth regulators (PGRs), namely, auxins (indol-3-acetic acid, indol-3-butyric acid, and naphthyl acetic acid), cytokinins (kinetin, zeatin, and 6-benzyladenine), gibberellic acid (GA3), abscisic acid, and synthetic compounds, namely, forchlorfenuron, paclobutrazole, isoprothiolane, and 2,4-dichlorophenoxy acetic acid (2,4-D) in bud sprouts and grape berries at the development stages of 2-3 and 6-8 mm diameters, which are the critical phases when exogenous application of PGRs may be necessary to achieve desired grape quality and yield. The sample preparation method involved extraction of plant material with acidified methanol (50%) by homogenization for 2 min at 15000 rpm. The pH of the extract was enhanced up to 6 by adding ammonium acetate, followed by homogenization and centrifugation. The supernatant extract was cleaned by SPE on an Oasis HLB cartridge (200 mg, 6 cc). The final extract was measured directly by LC/MS/MS with electrospray ionization in positive mode, except for 2,4-D, GA3, and abscisic acid extracts, which required analysis in negative mode. Quantification by multiple reaction monitoring (MRM) was supported with full-scan mass spectrometric confirmation using "information-dependent acquisition" triggered with MRM to "enhanced product ionization" mode of the hybrid quadrupole-ion trap mass analyzer. The LOQ of the test analytes varied between 1 and 10 ng/g with associated recoveries of 80-120% and precision RSD <25% (n = 8). Significant matrix-induced signal suppression was recorded when the responses for pre- and postextraction spikes of analytes were compared; this could be resolved by using matrix-matched calibration standards. The method could successfully be applied in analyzing incurred residue samples and would, therefore, be useful in precisely deciding the necessity and dose of exogenous applications of PGRs on the basis of measured endogenous levels. 相似文献
52.
Goken EG Joshi KL Russo MF van Duin AC Castleman AW 《The journal of physical chemistry. A》2011,115(18):4657-4664
Computational chemistry simulations were performed to determine the effect that the addition of a single formic acid molecule has on the structure and stability of protonated water clusters. Previous experimental studies showed that addition of formic acid to protonated pure water results in higher intensities of large-sized clusters when compared to pure water and methanol-water mixed clusters. For larger, protonated clusters, molecular dynamics simulations were performed on H(+)(H(2)O)(n), H(+)(H(2)O)(n)CH(3)OH, and H(+)(H(2)O)(n)CHOOH clusters, 19-28 molecules in size, using a reactive force field (ReaxFF). Based on these computations, formic acid-water clusters were found to have significantly higher binding energies per molecule. Addition of formic acid to a water cluster was found to alter the structure of the hydrogen-bonding network, creating selective sites within the cluster, enabling the formation of new hydrogen bonds, and increasing both the stability of the cluster and its rate of growth. 相似文献
53.
Yang CW Chanda K Lin PH Wang YN Liao CW Huang MH 《Journal of the American Chemical Society》2011,133(49):19993-20000
By using octahedral gold nanocrystals with sizes of approximately 50 nm as the structure-directing cores for the overgrowth of Pd shells, Au-Pd core-shell heterostructures with systematic shape evolution can be directly synthesized. Core-shell octahedra, truncated octahedra, cuboctahedra, truncated cubes, and concave cubes were produced by progressively decreasing the amount of the gold nanocrystal solution introduced into the reaction mixture containing cetyltrimethylammonium bromide (CTAB), H(2)PdCl(4), and ascorbic acid. The core-shell structure and composition of these nanocrystals has been confirmed. Only the concave cubes are bounded by a variety of high-index facets. This may be a manifestation of the release of lattice strain with their thick shells at the corners. Formation of the [CTA](2)[PdBr(4)] complex species has been identified spectroscopically. Time-dependent UV-vis absorption spectra showed faster Pd source consumption rates in the growth of truncated cubes and concave cubes, while a much slower reduction rate was observed in the generation of octahedra. The concave cubes and octahedra were used as catalysts for a Suzuki coupling reaction. They can all serve as effective and recyclable catalysts, but the concave cubes gave higher product yields with a shorter reaction time attributed to their high-index surface facets. The concave cubes can also catalyze a wide range of Suzuki coupling reactions using aryl iodides and arylboronic acids with electron-donating and -withdrawing substituents. 相似文献
54.
A new chromogenic protocol has been developed for rapid and selective detection of nerve agents like tabun. The chemsensor displayed a drastic color change from its colorless solution to yellow instantaneously with an 89 nm bathochromic shift. No inference of other chemical warfare agents and its mimics was observed either with the naked-eye or by UV-Vis spectroscopy. The development of a portable chemosensor kit for tabun demonstrates its practical application in real-time monitoring. 相似文献
55.
Dasgupta S Banerjee K Utture S Kusari P Wagh S Dhumal K Kolekar S Adsule PG 《Journal of chromatography. A》2011,1218(38):6780-6791
56.
We study the asymptotic properties of both the horizontal and vertical shift functions based on independent ranked set samples
drawn from continuous distributions. Several tests derived from these shift processes are developed. We show that by using
balanced ranked set samples with bigger set sizes, one can decrease the width of the confidence band and hence increase the
power of these tests. These theoretical findings are validated through small-scale simulation studies. An application of the
proposed techniques to a cancer mortality data set is also provided.
Part of the research was conducted while Kaushik Ghosh was visiting Statistical Research and Applications Branch of the National
Cancer Institute on an Intergovernmental Personnel Assignment. 相似文献
57.
M.S. Sodha S.C. Kaushik R.P. Sharma K.P. Maheshwari 《Journal of Physics and Chemistry of Solids》1977,38(10):1197-1203
This paper presents an investigation of the enhancement of self focusing of high frequency EM waves in a compensated degenerate magnetoactive solid state plasma. The nonlinearity in the dielectric constant responsible for self focusing arises due to nonuniform heating and consequent redistribution Of carriers. A rigorous kinetic treatment valid beyond the perturbation limit has been presented assuming the carrier relaxation time to be energy dependent. The results show that the self-focusing of extraordinary waves is enhanced while that of ordinary waves is reduced with increasing. However the focusing of extraordinary waves is not possible when ωc > ω. The effect of degeneracy is also found to enhance the self-focusing of the waves while that of the enhanced absorption is to suppress the self-focusing process. 相似文献
58.
Colchiceine, a new extractive indicator, is satisfactorily used in the determination of copper(II). A highly sensitive greenish yellow complex is formed with copper, which is extractable into chloroform. The results are comparable in sensitivity and selectivity with those of its precursors. 相似文献
59.
Vijay Kumar Kaushik 《Reaction Kinetics and Catalysis Letters》1995,55(2):355-364
X-ray photoelectron spectroscopy (XPS) is a highly surface sensitive technique and is used in identification of oxidation states in catalysts at various stages. Copper, silver and platinum based catalysts are widely used in petrochemical industries. Our attempts at characterization have revealed that elements in these catalysts are normally present then one stae. It is terefore essential to identify their in more chemical as well as oxidation states. Such identification combined with quantitative analysis of data is helpful in correlating catalyst performance. Examples of mixed state identification are presented.IPCL Communication No. 266 相似文献
60.