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951.
Wei Shuo FANG* Qi Cheng FANG Xiao Tian LIANG Institute of Materia Medica Chinese Academy of Medical Sciences Peking Union Medical College Xian Nong Tan Street Beijing 《中国化学快报》2001,(8)
Numerous efforts towards synthesis of anticancer drug paclitaxel (Taxol(r), 1a) with improved activities led to the modification at 13-phenylisoserine side chain and different positions of its core structure-baccatin III 1c1. At the same time, the activities of searching new taxoids for starting materials of new semi-synthetic paclitaxel analogs from Taxus spp. plant have not ever been stopped. Among these taxoids, 14?-hydroxy-10-deacetylbaccatin III 22 and 13-acetyl-9-dihydrobaccatin III … 相似文献
952.
The centrosymmetric structure of bis[tris(2‐methyl‐2‐phenylpropyl)tin]piperazinyldithiocarbamate contains four‐coordinated tin and monodentate dithiocarbamate ligands. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
953.
In this short note, we prove that if an axially symmetric, asymptotically flat, stationary solution of the Einstein Vacuum
Equation admits an involution interchanging the components of the event horizons, then the force between at least two of the
event horizons must be positive. The proof is based on an observation that in this case the force can be expressed as a line
integral with positive integrand. 相似文献
954.
Single-phase polycrystalline samples of La0.67Ca0.33Mn1−xO3 (x=0.00, 0.02, 0.04, 0.06) have been prepared using the sol-gel method. The structure, magnetocaloric properties and the Curie temperature of the samples with different Mn vacancy concentrations have been investigated. The experimental results show that vacancy doping at the Mn-sites has a significant influence on the magnetic properties of La0.67Ca0.33Mn1−xO3. The Curie temperature decreases monotonically with increasing the Mn-site vacancy concentration x. A remarkable enhancement of the magnetic entropy change has been obtained in the La0.67Ca0.33Mn0.98O3 sample. The entropy change reaches |ΔSM|=3.10 J kg−1 K−1 at its Curie temperature (264 K) under an applied magnetic field H=10 kOe, which is almost the same value as that of pure Gd. 相似文献
955.
Yihua Jiang Yaochuan Wang Jianli Hua Sanyin Qu Shiqiong Qian He Tian 《Journal of polymer science. Part A, Polymer chemistry》2009,47(17):4400-4408
A novel hyperbranched polyyne (hb‐ DPP ) with triphenylamine as the core, 2,5‐dioctylpyrrolo [3,4‐c]pyrrole‐1,4 (2H,5H)‐dione ( DPP ) as the connecting unit has been designed and synthesized by Glaser‐Hay oxidative coupling reaction, which was characterized by IR, NMR, UV‐vis, FL, and GPC. The polymer exhibits high molecular weight (Mw up to ~6.55 × 104 Da) and is readily soluble in common organic solvents such as toluene, chloroform, tetrahydrofuran, N,N‐dimethyl formamide and so on. The one‐ and two‐photon absorption (TPA) properties have been investigated. The TPA cross section of the polymer was measured by open‐aperture Z‐scan experiment using 140 femtosecond (fs) pulse, and the TPA cross section for hb‐ DPP was determined to be 579 GM per repeating unit at wavelength of 800 nm. In tetrahydrofuran, hb‐ DPP exhibits intense frequency up‐converted fluorescence with the peak located at 584 nm under the excitation of 800 nm fs pulses. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4400–4408, 2009 相似文献
956.
本依据教育专业规划的定量分析方法,讲述了规划一所中学的办学模型的数学手段,提出了需考虑的主要因素,介绍了这些因素的量化方法,所应用的数学模型。 相似文献
957.
H.L. Bai E.Y. Jiang C.D. Wang R.Y. Tian 《Applied Physics A: Materials Science & Processing》1998,66(4):423-433
286 , 176 (1996)]. (1) The interdiffusion critical wavelengths were calculated as 2.00–2.04 nm at temperatures ranging from 473
to 523 K, which is equal to those of Co/C multilayers within the experimental error, indicating that the interdiffusion behaviours
in the CoN/CN multilayers are still decided by the thermodynamic properties of the Co-C system. (2) The effective interdiffusivities
and macroscopic diffusion coefficients are smaller. (3) The activation energy for diffusion is larger. The features imply
that it is possible to improve the thermal stability of Co/C multilayers by doping with N atoms.
The high-temperature annealing results imply that the destructive threshold of the CoN/CN multilayers is 100–200 °C higher
than that of Co/C multilayers. The small-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period
expansion of the multilayers is only 4% at 400 °C, and the interface pattern still exists even if they were annealed at 700 °C.
The large-angle X-ray diffraction and transmission electron microscopy analysis reveal that the crystalline process is significantly
retarded if doped with N atoms, leading to a smaller grain size at higher annealing temperatures.
The significant improvement of the thermal stability can be interpreted with Raman spectroscopy and X-ray photoelectron spectroscopy
analysis. The Raman spectra give the evidence that the formation of the sp3 bonding in the CN sublayers can be suppressed effectively by doping with N atoms, and thus the period expansion resulting
from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra give information
about existence of the strong covalent bonding between N atoms and the ionic bonding between Co and N atoms, which can slow
down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc
Co and hcp Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420 °C,
leading to the suppression of the grain growth.
Received: 29 May 1997/Accepted: 8 September 1997 相似文献
958.
IntroductionItisnecessarytoevaluatetheamountofDNAfragmentinsuchcasesasgeneexpressioninvestigati0n.HybridizationwithradioactivitytaggedoligonucleotidesfollowedbyphotograPhyanddensitometricscanisoftenemployedtomeettheneedsofsuchrequirementS,whichislaborintensive,timec0nsumingandunautomated-CaPillaryelectrophoresis(CE)tendst0beastrongtoolintheanalysis0fDNAfragmentSwiththeadvantagesofhighsensitivity,highres0luti0nandautomation.QuantitativeanalysisofDNAfragmentshasbeendonebysomeauthorsusingC… 相似文献
959.
960.
GalnAsSb是直接带隙、窄禁带的半导体材料,其波长范围为0. 87-12μm,粗盖了2-4 m, 3-5μm和8-12μm三个重要的红外应用波段,可制作室温下工作的红外光电器件,在光纤通信、环境监测、资源勘探、空间技术及军事等方面有广泛的应用前景. 相似文献