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161.
Youwen You Cornelius E. Uboh Lawrence R. Soma Fuyu Guan Xiaoqing Li Ying Liu Jinwen Chen Deborah Tsang 《Chromatographia》2010,72(11-12):1097-1106
Testosterone and testosterone enanthate are performance-enhancing substances that are banned in racehorses competing in the State of Pennsylvania (PA). A tolerance concentration of 2,000 pg mL?1 plasma has been established for testosterone in intact colts and stallions at the time they are competing in PA. Testosterone enanthate is a precursor of testosterone and can be used to boost plasma testosterone concentration above natural, age and seasonally variable plasma concentration. To control abuse, a verifiable method for rapid determination of both substances in equine plasma was needed. For this reason, an ultra high performance liquid chromatography-tandem mass spectrometry method for high-throughput analysis of both analytes in equine plasma was developed. Analytes were recovered from plasma by liquid–liquid extraction using mixture of methyl tert-butyl ether and ethyl acetate (50:50, v/v), separated on a C18 sub-2 μm column and detected on a triple quadrupole mass spectrometer using positive electrospray ionization mode with selected reaction monitoring scan. SRM ion transitions of m/z 289 → m/z 97, m/z 289 → m/z 109, m/z 289 → m/z 79 were used for testosterone identification while m/z 401 → m/z 253, m/z 401 → m/z 271, m/z 401 → m/z 97 were employed for testosterone enanthate. Retention time and product ion intensity ratio were used as confirmation criteria to ascertain the presence of both analytes in equine plasma. The limits of detection, quantification and confirmation were 50 pg 0.5 mL?1, 100 pg 0.5 mL?1 and 250 pg 0.5 mL?1, respectively for both analytes. The method was validated for recovery efficiency, sensitivity, matrix effect, linearity, precision and accuracy. This method is routinely used in the PA program for androgenic anabolic steroids doping control in racehorses and in the on-going testosterone enanthate pharmacokinetics study. The method is defensible, fast, selective, specific and reproducibly reliable. 相似文献
162.
Deborah L. Kays Dr. Simon Aldridge Dr. 《Angewandte Chemie (International ed. in English)》2009,48(23):4109-4111
Inner virtue : The reaction of [Mo0(GaCp*)6] with ZnMe2 yields the novel multinuclear zinc system [MoZn12Me9Cp*3] which geometrically resembles a classical Wade–Mingos cluster (with an interstitial molybdenum atom, see picture). In reality, its electronic structure features little direct Zn? Zn bonding, relying instead on Mo? Zn three‐center, two‐electron bonds spanning the body diagonals of the approximately icosahedral framework.
163.
Gunawan RC Silvestre J Gaskins HR Kenis PJ Leckband DE 《Langmuir : the ACS journal of surfaces and colloids》2006,22(9):4250-4258
This paper explores the effects of the surface density and concentration profiles of extra cellular matrix proteins on the migration of rat intestinal IEC-6 cells. Microfluidic devices were used to create linear, immobilized gradients of laminin. This study investigated both the impact of the steepness and local concentrations on the directedness of cell migration. The bulk concentrations of proteins in the feed streams in the mixing device determined the gradient profile and the local concentration of laminin in the device. Two sets of gradients were used to explore cell migration directedness: (i) gradients with similar change in local concentration, i.e., the same gradient steepness, and (ii) different gradients with similar local concentrations. Cells migrated up the gradients, independent of the steepness of the gradients used in this study. At the same local laminin concentration, the migration rate was independent of the gradient steepness. However, cell directedness decreased significantly at high laminin densities. 相似文献
164.
Mousset D Gillaizeau I Sabatié A Bouyssou P Coudert G 《The Journal of organic chemistry》2006,71(16):5993-5999
Symmetrical and unsymmetrical 2,6-disubstituted dihydropyridines were prepared in high yields under mild conditions using the Suzuki and Stille Pd-catalyzed coupling reactions of imide-derived bisvinyl phosphates with a range of aryl, heteroaryl, and alkenyl moieties. The alkylation reaction at C-4 easily afforded original tri- and tetrasubstituted dihydropyridines. Hydrolysis of the latter under acidic condition provided efficiently either open-chain 1,5-diketones or di- or trisubstituted pyridines. 相似文献
165.
Yan C Matsuda W Pepperberg DR Zimmerman SC Leckband DE 《Journal of colloid and interface science》2006,296(1):165-177
We report the synthesis and characterization of a new electroactive surface capable of releasing the neurotransmitter gamma-aminobutyric acid (GABA) upon reduction. The GABA was anchored to an alkanethiol via electrochemically active quinone (abbreviation, TM-GABA). The quinone unit, upon reduction to the hydroquinone, cyclizes to release GABA into solution. The half-life is 99 s. The self-assembled monolayer (SAM) of TM-GABA on gold was prepared and characterized with several surface sensitive techniques. X-ray photoelectron spectroscopy (XPS) explored the SAM formation of TM-GABA on Au surfaces. Cyclic voltammograms showed the ability to electrochemically control the quinone unit at the distal end of the chain. GABA was selectively released upon electrochemical reduction at a potential of -700 mV. The functional GABA terminal group was detected by surface plasmon resonance measurements of anti-GABA antibody binding. 相似文献
166.
Previous experimental and theoretical studies of the radical dissociation channel of T(1) acetaldehyde show conflicting behavior in the HCO and CH(3) product distributions. To resolve these conflicts, a full-dimensional potential-energy surface for the dissociation of CH(3)CHO into HCO and CH(3) fragments over the barrier on the T(1) surface is developed based on RO-CCSD(T)/cc-pVTZ(DZ) ab initio calculations. 20,000 classical trajectories are calculated on this surface at each of five initial excess energies, spanning the excitation energies used in previous experimental studies, and translational, vibrational, and rotational distributions of the radical products are determined. For excess energies near the dissociation threshold, both the HCO and CH(3) products are vibrationally cold; there is a small amount of HCO rotational excitation and little CH(3) rotational excitation, and the reaction energy is partitioned dominantly (>90% at threshold) into relative translational motion. Close to threshold the HCO and CH(3) rotational distributions are symmetrically shaped, resembling a Gaussian function, in agreement with observed experimental HCO rotational distributions. As the excess energy increases the calculated HCO and CH(3) rotational distributions are observed to change from a Gaussian shape at threshold to one more resembling a Boltzmann distribution, a behavior also seen by various experimental groups. Thus the distribution of energy in these rotational degrees of freedom is observed to change from nonstatistical to apparently statistical, as excess energy increases. As the energy above threshold increases all the internal and external degrees of freedom are observed to gain population at a similar rate, broadly consistent with equipartitioning of the available energy at the transition state. These observations generally support the practice of separating the reaction dynamics into two reservoirs: an impulsive reservoir, fed by the exit channel dynamics, and a statistical reservoir, supported by the random distribution of excess energy above the barrier. The HCO rotation, however, is favored by approximately a factor of 3 over the statistical prediction. Thus, at sufficiently high excess energies, although the HCO rotational distribution may be considered statistical, the partitioning of energy into HCO rotation is not. 相似文献
167.
168.
169.
Tonei DM Ware DC Brothers PJ Plieger PG Clark GR 《Dalton transactions (Cambridge, England : 2003)》2006,(1):152-158
Zinc metal reduction of the cobalt(III) complex [Co(1,4-bcc)](+) (1,4-bcc = 1,4-bis-carboxymethylcyclam) produces the corresponding cobalt(II) complex which crystallises as the coordination polymer {[Co(1,4-bcc)]ZnCl(2)}(n). A method has been developed for removal of the cobalt(III) ion from [Co(1,4-bcc)](+) and isolation of the free ligand as its hydrochloride salt, H(2)(1,4-bcc).4HCl. This has been used for the preparation of new metal complexes, and the syntheses and characterisation of the copper(ii), nickel(ii), zinc(ii) and chromium(iii) complexes containing the 1,4-bcc ligand are described. X-Ray crystal structures of {[Co(1,4-bcc)]ZnCl(2)}(n).2.5H(2)O, {[Cu(1,4-bcc)]CuCl(2)}(n).0.25MeOH.H(2)O and [Cu(1,4-bcc)H]ClO(4) show the complexes to have the trans(O) geometry of the 1,4-bcc ligand, while the structure of [Cr(1,4-bcc)H(0.5)](ClO(4))(1.5).EtOH exhibits the cis(O) configuration. 相似文献
170.
Jian Shen Christof Graber James Liburdy Deborah Pence Vinod Narayanan 《Experimental Thermal and Fluid Science》2010,34(4):496-503
This study examines the hydrodynamics and temperature characteristics of distilled deionized water droplets impinging on smooth and nano-structured surfaces using high speed (HS) and infrared (IR) imaging at We = 23.6 and Re = 1593, both based on initial drop impingement parameters. Results for a smooth and nano-structured surface for a range of surface temperatures are compared. Droplet impact velocity, transient spreading diameter and dynamic contact angle are measured. The near surface average droplet fluid temperatures are evaluated for conditions of evaporative cooling and boiling. Also included are surface temperature results using a gold layered IR opaque surface on silicon. Four stages of the impingement process are identified: impact, boiling, near constant surface diameter evaporation, and final dry-out. For the boiling conditions there is initial nucleation followed by severe boiling, then near constant diameter evaporation resulting in shrinking of the droplet height. When a critical contact angle is reached during evaporation the droplet rapidly retracts to a smaller diameter reducing the contact area with the surface. This continues as a sequence of retractions until final dry out. The basic trends are the same for all surfaces, but the nano-structured surface has a lower dissipated energy during impact and enhances the heat transfer for evaporative cooling with a 20% shorter time to achieve final dry out. 相似文献