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991.
Dr. Chao Xu Dr. Guoxin Tian Dr. Simon J. Teat Dr. Guokui Liu Dr. Linfeng Rao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16690-16698
The complexation of NpO22+ and PuO22+ with dipicolinic acid (DPA) has been investigated in 0.1 M NaClO4 by spectrophotometry, microcalorimetry, and single crystal diffractometry. Formation of 1:1 and 1:2 (metal/ligand molar ratio) complexes of DPA with NpO22+ and PuO22+ were identified and the thermodynamic parameters were determined and compared with those of UO22+. All three hexavalent actinyl cations form strong 1:1 DPA complexes with slightly decreasing but comparable stability constants from UO22+ to PuO22+, whereas the stability constants of the 1:2 complexes (log β2) decrease substantially along the series (16.3 for UO2L22?, 15.17 for NpO2L22?, and 14.17 for PuO2L22? at 25 °C). The enthalpies of complexation for the 1:2 complexes become less exothermic from UO2L22? (?28.9 kJ mol?1), through NpO2L22? (?27.2 kJ mol?1), and to PuO2L22? (?22.7 kJ mol?1). The trends in the thermodynamic parameters are discussed in terms of the effective charge of the cations and the steric constraints in the structures of the complexes. In addition, the features of the absorption spectra, including the wavelength and intensity of the absorption bands, are related to the perturbation of the ligand field and the symmetry of the actinyl complexes. 相似文献
992.
Prof. Mengtao Sun Dr. Zhenglong Zhang Prof. Zee Hwan Kim Prof. Hairong Zheng Prof. Hongxing Xu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(44):14958-14962
Heterogeneous catalysts play an important role in surface catalytic reactions, but selective bond breaking and control of reaction products in catalytic processes remain significant challenges. High‐vacuum tip‐enhanced Raman spectroscopy (HV‐TERS) is one of the best candidates to realize surface catalytic reactions. Herein, HV‐TERS was employed in a new method to control dissociation by using hot electrons, generated from plasmon decay, as plasmonic scissors. In this method, the N?N bond in 4,4′‐dimercaptoazobenzene was selectively dissociated by plasmonic scissors, and the reaction products formed from the radical fragment (SC6H5N) were controlled by varying the pH value. Under acidic conditions, p‐aminothiophenol was produced from the radical fragment by attachment of hydrogen ions, whereas under alkaline conditions, 4‐nitrobenzenethiol was obtained by attachment of oxygen ions to the substrate. 相似文献
993.
Ying‐Lu Cui Ji‐Long Zhang Prof. Qing‐Chuan Zheng Rui‐Juan Niu Yu Xu Prof. Hong‐Xing Zhang Chia‐Chung Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(2):549-557
Cytochrome P450 (CYP) 7B1 is a steroid cytochrome P450 7α‐hydroxylase that has been linked directly with bile salt synthesis and hereditary spastic paraplegia type 5 (SPG5). The enzyme provides the primary metabolic route for neurosteroids dehydroepiandrosterone (DHEA), cholesterol derivatives 25‐hydroxycholesterol (25‐HOChol), and other steroids such as 5α‐androstane‐3β,17β‐diol (anediol), and 5α‐androstene‐3β,17β‐diol (enediol). A series of investigations including homology modeling, molecular dynamics (MD), and automatic docking, combined with the results of previous experimental site‐directed mutagenesis studies and access channels analysis, have identified the structural features relevant to the substrate selectivity of CYP7B1. The results clearly identify the dominant access channels and critical residues responsible for ligand binding. Both binding free energy analysis and total interaction energy analysis are consistent with the experimental conclusion that 25‐HOChol is the best substrate. According to 20 ns MD simulations, the Phe cluster residues that lie above the active site, particularly Phe489, are proposed to merge the active site with the adjacent channel to the surface and accommodate substrate binding in a reasonable orientation. The investigation of CYP7B1–substrate binding modes provides detailed insights into the poorly understood structural features of human CYP7B1 at the atomic level, and will be valuable information for drug development and protein engineering. 相似文献
994.
Dr. Lynnie Trzoss Dr. Jing Xu Michelle H. Lacoske Prof. Dr. William C. Mobley Prof. Dr. Emmanuel A. Theodorakis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(20):6398-6408
Majucin‐type sesquiterpenes from Illicium sp., such as jiadifenolide ( 2 ), jiadifenin ( 3 ), and (1R,10S)‐2‐oxo‐3,4‐dehydroxyneomajucin ( 4 , ODNM), possess a complex caged chemical architecture and remarkable neurotrophic activities. As such, they represent attractive small‐molecule leads against various neurodegenerative diseases. We present an efficient, enantioselective, and unified synthesis of 2 , 3 , and 4 and designed analogues that diverge from tetracyclic key intermediate 7 . The synthesis of 7 is highlighted by the use of an enantioselective Robinson annulation reaction (construction of the AB rings), a Pd‐mediated carbomethoxylation reaction (construction of the C ring), and a one‐pot oxidative reaction cascade (construction of the D ring). Evaluation of the neurotrophic activity of these compounds led to the identification of several highly potent small molecules that significantly enhanced the activity of nerve growth factor (NGF) in PC‐12 cells. Moreover, efforts to define the common pharmacophoric motif suggest that substitution at the C‐10 center significantly affects bioactivity, while the hemiketal moiety of 2 and 3 and the C‐1 substitution might not be critical to the neurotrophic activity. 相似文献
995.
Development of advanced functional materials from naturally abundant polymers such as cellulose are of significant importance. Of particular interest is embedding antibacterial functionality to cellulose materials to make permanent antibacterial materials and devices. In the present research, a “clickable” quaternary ammonium compound, N-(2-ethoxy-2-oxoethyl)-N,N-dimethylprop-2yn-1-aminium bromide (EdMPABr) was synthesized via a simple reaction with nearly stoichiometric yield and well characterized with 1D (1H, 13C) and 2D (COSY, HSQC) NMR and ATR-FTIR. EdMPABr can be covalently bonded to many molecules containing an azido group to form non-leaching antibacterial materials via the simple Cu(I)-catalyzed alkyne-azide [2 + 3] cycloaddition reaction. As an example, EdMPABr was attached to our previously reported 3-O-azidopropoxypoly(ethylene glycol)-2,6-di-O-thexyldimethylsilyl cellulose (3-N3PEG-2,6-TDMS cellulose, DS = 0.54 at C3 determined by 1H NMR). Significant antibacterial activity of the synthesized 3-O-quaternary ammonium-2,6-di-O-thexyldimethylsilyl cellulose (3-QA-2,6-TDMS cellulose, DS = 0.30 at C3 determined by using N content from elemental analysis) was confirmed by testing against the representative bacteria Escherichia coli. By linking the EdMPABr to the honeycomb film of 3-N3PEG-2,6-TDMS cellulose, the formed honeycomb film exhibited both antibacterial and antifouling properties. This research provides a simple and robust route towards the development of permanent antibacterial materials and biomedical devices. 相似文献
996.
以超临界二氧化碳(Sc-CO2)为物理发泡剂,在高压釜中采用两种温度设定方式和降压对聚苯乙烯(PS)进行发泡,测试、分析发泡样品的泡孔结构、泡体密度和断面润湿性能.结果表明,仅通过降压只获得单峰的泡孔结构,而升温与降压协同作用可获得双峰的泡孔结构,大、小泡孔分别在升温和降压阶段成核形成;在发泡温度100℃、饱和温度30~70℃下制备的发泡样品中,大、小泡孔的平均直径分别为50~216和10~15μm.大泡孔的直径较大和密度较高都有利于降低样品的泡体密度,最低达0.15 g/cm3.单峰泡孔结构能在一定程度上提高样品断面的疏水性,使静态接触角(CA)从PS的本征值(87.1°)增大至138.8°;双峰泡孔结构可赋予样品断面更高的CA(155.1°),呈现超疏水特性. 相似文献
997.
998.
Bifurcation analysis of a diffusive predator–prey system with a herd behavior and quadratic mortality 下载免费PDF全文
In this paper, a diffusive predator–prey system, in which the prey species exhibits herd behavior and the predator species with quadratic mortality, has been studied. The stability of positive constant equilibrium, Hopf bifurcations, and diffusion‐driven Turing instability are investigated under the Neumann boundary condition. The explicit condition for the occurrence of the diffusion‐driven Turing instability is derived, which is determined by the relationship of the diffusion rates of two species. The formulas determining the direction and the stability of Hopf bifurcations depending on the parameters of the system are derived. Finally, numerical simulations are carried out to verify and extend the theoretical results and show the existence of spatially homogeneous periodic solutions and nonconstant steady states. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
999.
Approximation properties for solutions to non‐Lipschitz stochastic differential equations with Lévy noise 下载免费PDF全文
In this paper, we consider the non‐Lipschitz stochastic differential equations and stochastic functional differential equations with delays driven by Lévy noise, and the approximation theorems for the solutions to these two kinds of equations will be proposed respectively. Non‐Lipschitz condition is much weaker condition than the Lipschitz one. The simplified equations will be defined to make its solutions converge to that of the corresponding original equations both in the sense of mean square and probability, which constitute the approximation theorems. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
1000.
Spectral analysis and stability of thermoelastic Bresse system with second sound and boundary viscoelastic damping 下载免费PDF全文
In this paper, we consider the energy decay rate of a thermoelastic Bresse system with variable coefficients. Assume that the thermo-propagation in the system satisfies the Cattaneo's law, which can eliminate the paradox of infinite speed of thermal propagation in the assumption of the Fourier's law in the classical theory of thermoelasticity. Meanwhile, we also discuss the effect of a boundary viscoelastic damping on the stability of this system. By a detailed spectral analysis, we obtain the expressions of the spectrum and deduce some spectral properties of the system. Then based on the distribution of the spectrum, we prove that the energy of the system with a boundary viscoelastic damping decays exponentially. However, it no longer decays exponentially if there is no boundary damping. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献