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991.
Peterka DS Kim JH Wang CC Poisson L Neumark DM 《The journal of physical chemistry. A》2007,111(31):7449-7459
The photoionization and photoelectron spectroscopy of pure He droplets were investigated at photon energies between 24.6 eV (the ionization energy of He) and 28.0 eV. Time-of-flight mass spectra and photoelectron images were obtained at a series of molecular beam source temperatures and pressures to assess the effect of droplet size on the photoionization dynamics. At source temperatures below 16 K, where there is significant production of clusters with more than 10(4) atoms, the photoelectron images are dominated by fast electrons produced via direct ionization, with a small contribution from very slow electrons with kinetic energies below 1 meV arising from an indirect mechanism. The fast photoelectrons from the droplets have as much as 0.5 eV more kinetic energy than those from atomic He at the same photon energy. This result is interpreted and simulated within the context of a "dimer model", in which one assumes vertical ionization from two nearest-neighbor He atoms to the attractive region of the He2+ potential energy curve. Possible mechanisms for the slow electrons, which were also seen at energies below IE(He), are discussed, including vibrational autoionizaton of Rydberg states comprising an electron weakly bound to the surface of a large HeN+ core. 相似文献
992.
Park HY Jeon YK Shin HJ Kim IJ Kang HC Jeong SJ Chung DH Lee CW 《Experimental & molecular medicine》2007,39(2):195-204
The BubR1 mitotic-checkpoint protein monitors proper attachment of microtubules to kinetochores, and links regulation of chromosome-spindle attachment to mitotic-checkpoint signaling. Thus, disruption of BubR1 activity results in a loss of checkpoint control, chromosomal instability caused by a premature anaphase, and/or the early onset of tumorigenesis. The mechanisms by which deregulation and/or abnormalities of BubR1 expression operate, however, remain to be elucidated. In this study, we demonstrate that levels of BubR1 expression are significantly increased by demethylation. Bisulfite sequencing analysis revealed that the methylation status of two CpG sites in the essential BubR1 promoter appear to be associated with BubR1 expression levels. Associations of MBD2 and HDAC1 with the BubR1 promoter were significantly relieved by addition of 5-aza-2'-deoxycytidine, an irreversible DNA methyltransferase inhibitor. However, genomic DNA isolated from 31 patients with colorectal carcinomas exhibited a +84A/G polymorphic change in approximately 60% of patients, but this polymorphism had no effect on promoter activity. Our findings indicate that differential regulation of BubR1 expression is associated with changes in BubR1 promoter hypermethylation patterns, but not with promoter polymorphisms, thus providing a novel insight into the molecular regulation of BubR1 expression in human cancer cells. 相似文献
993.
Kim EK Kwon KB Han MJ Song MY Lee JH Lv N Ka SO Yeom SR Kwon YD Ryu DG Kim KS Park JW Park R Park BH 《Experimental & molecular medicine》2007,39(2):149-159
We demonstrated previously that Coptidis rhizoma extract (CRE) prevented S-nitroso-N-acetylpenicillamine-induced apoptotic cell death via the inhibition of mitochondrial membrane potential disruption and cytochrome c release in RINm5F (RIN) rat insulinoma cells. In this study, the preventive effects of CRE against cytokine-induced beta-cell death was assessed. Cytokines generated by immune cells infiltrating pancreatic islets are crucial mediators of beta-cell destruction in insulin-dependent diabetes mellitus. The treatment of RIN cells with IL-1beta and IFN-gamma resulted in a reduction of cell viability. CRE completely protected IL-1beta and IFN-gamma-mediated cell death in a concentration-dependent manner. Incubation with CRE induced a significant suppression of IL-1beta and IFN-gamma-induced nitric oxide (NO) production, a finding which correlated well with reduced levels of the iNOS mRNA and protein. The molecular mechanism by which CRE inhibited iNOS gene expression appeared to involve the inhibition of NF-kappaB activation. The IL-1beta and IFN-gamma-stimulated RIN cells showed increases in NF-kappaB binding activity and p65 subunit levels in nucleus, and IkappaB alpha degradation in cytosol compared to unstimulated cells. Furthermore, the protective effects of CRE were verified via the observation of reduced NO generation and iNOS expression, and normal insulin-secretion responses to glucose in IL-1beta and IFN-gamma-treated islets. 相似文献
994.
Giseop Kwak Hong‐Qing Wang Kyu‐Han Choi Kyu‐Ho Song Soon‐Hak Kim Hyeok‐Soo Kim Sam‐Jong Lee Ho‐Young Cho Eon‐Ju Yu Hyo‐Jeong Lee Eun‐Jung Park Lee‐Soon Park 《Macromolecular rapid communications》2007,28(12):1317-1324
New poly(diphenylacetylene)s with alkoxy and fluoroalkyl groups as electron‐donating and electron‐withdrawing groups, respectively, were synthesized by using a WCl6‐n‐Ph4Sn catalyst. The polymer solutions emitted strong, bluish‐green lights when photo‐excited. The polymers that contained the electron‐donating alkoxy groups showed longer fluorescence‐maximum peaks when compared to the polymers that contained the electron‐withdrawing fluoroalkyl groups. However, such an effect of the substituent on the absorption property was not clearly seen. The emission bands of the solid films did not show any significant red shift, relative to that of the dilute solution.
995.
CW Kim U Pal S Park J Kim YS Kang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(39):12314-12321
We demonstrate a facile wet chemical approach for fabricating spherical metal/metal-oxide core@mesoporous silica shell hybrid nanoparticles with different core and shell thicknesses. Vertically aligned mesoporous silica (mSiO(2) ) shells were fabricated over the pre-synthesized spherical SiO(2) nanoparticles through a three-step strategy: 1)?synthesis of core materials, 2)?covering the core with an organic-inorganic composite layer, and 3)?removing the organic template through calcinations in air. The mechanisms of hybrid structure formation are proposed. The multifunctional nature of the hybrid structures could be induced by incorporating guest ions/molecules, such as Ag, Mn, and TiO(2) , into the pores of an mSiO(2) shell. Mn and TiO(2) cluster- incorporated composite structures have been tested to be antioxidizing agents and effective photocatalysts through electron spin resonance, radical scavenging tests, and the photocatalytic degradation of rhodamine B. The possibility of incorporating several hetero-element guest clusters in these mesoporous composite particles makes them highly attractive for multifunctional applications. 相似文献
996.
A retention theory in sedimentation field-flow fractionation (SdFFF) was developed by exploiting the effective slip boundary condition (BC) that allows a finite velocity for particles to have at the wall, thereby alleviating the limitations set by the no-slip BC constraint bound to the standard retention theory (SRT). This led to an expression for the retention ratio R as R = (R(o) + v*(b))/(R(o) + v*(b)), where R(o) is the sterically corrected SRT retention ratio and v*(b) is the reduced boundary velocity. Then, v*(b) was modeled as v*(b) = v*(b,o)/[1 + (7K*S(o))(1/2)], where S(o) is the surfactant (FL-70) concentration and K* is the distribution coefficient associated with the langmuirian isotherm of the apparent effective mass against S(o). We applied this to study the surfactant effect on the retention behaviors of polystyrene (PS) latex beads of 170-500 nm in diameter. As a result, an empirical relation was found to hold between v*(b,o) and d(o) (estimated from R(o) at S(o) = 0) as v*(b,o) - v*(o,o)[1 - (d(c)/d(o))], where v*(o,o) is the asymptotic value of v*(b,o) in the vanishing d(c)/d(o) limit and d(c) is the cutoff value at which v*(b,o) would vanish. According to the present approach, the no-slip BC (v*(b,o) = 0) was predicted to recover when d(o) ~ d(c), and the boundary slip effect could be significant for S(o) ≤ 0.05%, particularly for large latex beads. 相似文献
997.
Pure separation and sorting of microparticles from complex fluids are essential for biochemical analyses and clinical diagnostics. However, conventional techniques require highly complex and expensive labeling processes for high purity separation. In this study, we present a simple and label-free method for separating microparticles with high purity using the elasto-inertial characteristic of a non-Newtonian fluid in microchannel flow. At the inlet, particle-containing sample flow was pushed toward the side walls by introducing sheath fluid from the center inlet. Particles of 1 μm and 5 μm in diameter, which were suspended in viscoelastic fluid, were successfully separated in the outlet channels: larger particles were notably focused on the centerline of the channel at the outlet, while smaller particles continued flowing along the side walls with minimal lateral migration towards the centerline. The same technique was further applied to separate platelets from diluted whole blood. Through cytometric analysis, we obtained a purity of collected platelets of close to 99.9%. Conclusively, our microparticle separation technique using elasto-inertial forces in non-Newtonian fluid is an effective method for separating and collecting microparticles on the basis of size differences with high purity. 相似文献
998.
Chi YS Lee KB Kim Y Choi IS 《Langmuir : the ACS journal of surfaces and colloids》2007,23(3):1209-1214
This report describes the reactivity of acid fluoride (AF)-terminated self-assembled monolayers (SAMs) on gold toward amine and alcohol compounds and the potentiality of AF as a reactive intermediate for surface functionalizations. The AF group was generated in situ on a gold surface by reacting the terminal carboxylic acid group in the SAM of 16-mercaptohexadecanoic acid with cyanuric fluoride and pyridine under the optimized conditions. AF was found to be highly reactive toward various amine groups, such as primary and secondary amines, but it did not react effectively with alcohol. In addition, the amide coupling reaction by microcontact printing (microCP) was compared with the solution-based reaction: when amine-derivatized ferrocene compound was used for 1-min microCP on the AF-activated surface, the surface coverage of the reaction product was about 83% of 3.45 x 1014 cm-2, the coverage obtained in the solution-based reaction. On the basis of the high reaction efficiency of microCP, the AF-activated surface was also used as a platform for patterning a biological ligand, biotin. 相似文献
999.
Advanced multidimensional time-correlated single photon counting (mdTCSPC) and picosecond time-resolved fluorescence in combination with site-directed fluorescence labeling are valuable tools to study the properties of membrane protein surface segments on the pico- to nanoseconds time scale. Time-resolved fluorescence anisotropy changes of protein bound fluorescent probes reveal changes in protein dynamics and steric restriction. In addition, the change in fluorescence lifetime and intensity of the covalently bound fluorescent dye is indicative of environmental changes at the protein surface. In this study, we have measured the changes in fluorescence lifetime traces of the fluorescent dye fluorescein covalently bound to the first cytoplasmic loop of bacteriorhodopsin (bR) after light activation of protein function. The fluorescence is excited by a picosecond laser pulse. The retinylidene chromophore of bR is light-activated by a 10 ns laser pulse, which in turn triggers recording of a sequence of fluorescence lifetime traces in the mdTCSPC-module. The fluorescence decay changes upon protein function occur predominantly in the 100 ps time range. The kinetics of these changes shows two transitions between three intermediate states in the second part of the bR photocycle. Correlation with photocycle kinetics allows for the determination of reaction intermediates at the proteins surface which are coupled to changes in the retinal binding pocket. 相似文献
1000.
Chiral molecular squares 1-12 based on [M(dppe)](2+) metallocorners (M = Pd or Pt, and dppe = bis(diphenylphosphino)ethane) and new angular bipyridine bridging ligands derived from the 1,1'-binaphthyl framework were readily assembled and characterized by a variety of techniques including infrared, UV-vis, circular dichroism (CD), and NMR spectroscopy, and ESI mass spectrometry. All these chiral metallocycles are highly luminescent in solution at room temperature with quantum efficiency of 0.06-0.63. Interestingly, when equal molar enantiopure molecular squares of opposite handedness were mixed in solution, a new meso dimeric metallocycle with C(2) symmetry formed. This result indicates the lability of the M-pyridyl bonds in these metallocycles, which may hinder their applications in many enantioselective processes. 相似文献