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91.
Comparison of Methods for Determining Specific Surface Area of Soils   总被引:1,自引:0,他引:1  
The present study was undertaken to compare the capabilities of four of the known methods; more specifically, N2 adsorption, methylene blue (MB)-titration, MB-spot test, and ethylene glycol monoethyl ether (EGME) methods were evaluated to determine the specific surface area (SSA) of 16 different clayey soils. The study showed that N2 adsorption method underpredicts the SSA of soils, especially for smectitic soils. No significant differences were observed between N2 SSA, MB SSA-titration, or MB-spot test for kaolinitic soils. The SSA estimates of MB-titration and MB-spot test methods were highly correlated for all soils. The EGME method has a very different procedure from the MB methods; however, it was highly correlated with MB methods (r2 = 0.95). The N2 adsorption method had no correlation to other methods. The cation exchange capacity of tested soils was highly correlated to the SSA, as high as r2 = 0.77. No unique relationship was determined between the clay fraction and SSA.  相似文献   
92.
The effects of intraventricular injection and epicardial application of adenosine on spontaneous electrical activity of nucleus paragigantocellularis lateralis (PGL) neurons in rostral ventrolateral medulla (RVLM) were examined in 35 anesthetized rats with sinoaortic denervation and vagotomy. The results obtained were as follows: (1) The spontaneous discharge of 121 PGL neurons (mean discharge rate: 22.5 +/- 1.9 spikes/s) were recorded in 35 rats. (2) In response to intraventricular injection of adenosine (0.5 mumol/kg), mean arterial pressure (MAP) was initially increased by 1.7 +/- 0.2 kPa(P < 0.001) and subsequently decreased by 4.6 +/- 0.5 kPa(P < 0.001), while the heart rate (HR) was decreased by 126.5 +/- 12.3 bpm (P < 0.001). Of 35 PGL spontaneous discharge units responsive to intraventricular injection of adenosine, 30 showed an average increase from 21.9 +/- 2.6 to 29.2 +/- 3.4 spikes/s (P < 0.001), 3 with no change, while 2 with a decrease. (3) Following epicardial application of 20 mmol/L adenosine, the BP and HR were not significantly changed, while the spontaneous discharge of 22 PGL neurons were increased from 18.8 +/- 1.9 to 26.9 +/- 2.8 spikes/s (P < 0.001), and that of 3 neurons was not changed. (4) The excitatory response of PGL neurons to intraventricular injection or epicardial application of adenosine was completely inhibited by pretreatment with selective adenosine A1-receptor antagonist 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX, 500 micrograms/kg). (5) Following epicardial application of phenol or bilateral stellate ganglionectomy, adenosine failed to affect the activity of PGL neurons. The results obtained indicate that adenosine may stimulate cardiac sympathetic afferents through adenosine A1-receptor, thereby resulting in the activation of PGL neurons.  相似文献   
93.
The first direct separation of Fel Ursi using octadecyl silica (ODS) open column chromatography has been accomplished and provided to provide several pure, free and conjugated bile acids, the structures of which were substantiated by spectroscopic methods.  相似文献   
94.
Mutations comprising either deletion of 32 amino acids from the NH2 terminus (alpha1M32) or a Glu233 --> Lys substitution in the first M2-M3 cytoplasmic loop (E233K) of the alpha1-subunit of the Na, K-ATPase result in a shift in the steady-state E1 left arrow over right arrow E2 conformational equilibrium toward E1 form(s). In the present study, the functional consequences of both NH2-terminal deletion and Glu233 substitution provide evidence for mutual interactions of these cytoplasmic regions. Following transfection and selection of HeLa cells expressing the ouabain-resistant alpha1M32E233K double mutant, growth was markedly reduced unless the K+ concentration in the culture medium was increased to at least 10 mM. Marked changes effected by this double mutation included 1) a 15-fold reduction in catalytic turnover (Vmax/EPmax), 2) a 70-fold increase in apparent affinity for ATP, 3) a marked decrease in vanadate sensitivity, and 4) marked (approximately 10-fold) K+ activation of the Na-ATPase activity measured at micromolar ATP under which condition the E2(K) --> --> E1 pathway is normally (alpha1) rate-limiting and K+ is inhibitory. The decrease in catalytic turnover was associated with a 5-fold decrease in Vmax and a compensatory approximately 3-fold increase in expressed alpha1M32E233K protein. In contrast to the behavior of either alpha1M32 or E233K, alpha1M32E233K also showed alterations in apparent cation affinities. K'Na was decreased approximately 2-fold and K'K was increased approximately 2-fold. The importance of the charge at residue 233 is underscored by the consequences of single and double mutations comprising either a conservative change (E233D) or neutral substitution (E233Q). Thus, whereas mutation to a positively charged residue (E233K) causes a drastic change in enzymatic behavior, a conservative change causes only a minor change and the neutral substitution, an intermediate effect. Overall, the combined effects of the NH2-terminal deletion and the Glu233 substitutions are synergistic rather than additive, consistent with an interaction between the NH2-terminal region, the first cytoplasmic loop, and possibly the large M4-M5 cytoplasmic loop bearing the nucleotide binding and phosphorylation sites.  相似文献   
95.
The efficiency and accuracy of estrus detection using HeatWatch (DDx Inc., Denver, CO) or visual observation were compared in an autumn-calving Friesian herd (n = 48 per group) and a spring-calving Jersey herd (n = 50 per group) grazing on pasture. Cows in the group monitored by the HeatWatch system were fitted with a pressure-sensitive transmitter that signaled mounting activities associated with estrus. Visual observation was carried out for about 20 min before the morning and afternoon milkings and was aided by a strip of paint applied over the tailhead. Ovarian cyclicity was monitored with progesterone concentrations in milk samples collected twice a week. The efficiency and accuracy of estrus detection were, respectively, 98.4 and 97.6% for visual observation and 91.7 and 100% for HeatWatch detection. Autumn-calving herds differed from spring-calving herds in duration of estrus (9.7 vs. 7.3 h), number of mounts (13.6 vs. 8.5), total duration of mounts (36.8 vs. 19.9 s), and mean duration of a mount (2.6 vs. 2.3 s). There was no significant variation in the distribution of the time of onset of estrus or mounting activities at different hours of the day. Conception rate was similar for AI after estrus detection with HeatWatch (65.8%) or after visual observation (65.0%). The highest conception rate was obtained when AI was carried out between 12 and 18 h after the first mount. Both the HeatWatch system and visual observation plus tail painting can be used for estrus detection of dairy cows on pasture.  相似文献   
96.
Polycrystalline La0.67(Ca1?x Sr x )0.33MnO3 with different substitution level of strontium element, were synthesized via solid state reaction. Structure of samples was characterized by X-ray diffraction (XRD). XRD patterns reveal that La0.67Ca0.33MnO3 exhibits orthorhombic structure with space group Pnma. Phase transitions from orthorhombic to rhombohedral take place as Ca ions were gradually substituted by Sr ions. The XRD data were further analyzed by Rietveld refinement technique. The data show that Mn–O–Mn bond angle increases as x increases. Microstructures obtained from SEM show that substitution of Sr ions has demoted the grain growth and densification process during sintering. The substitution of Sr ions has greatly influenced the hopping integral of electron via double exchange interaction, thus affecting the electrical properties and magnetic properties as well. The resistivity decreases and the metal–insulator transition temperature (T p ) shifts to higher temperature as x increases. The magnetoresistance (MR) effect gradually decreases and MR peak shifts to higher temperature as x increases. The magnetization measured at room temperature is found to be increasing as x increases.  相似文献   
97.
The design of a vehicle suspension system through simulation requires accurate representation of the design parameters. These parameters are usually difficult to measure or sometimes unavailable. This article proposes an efficient approach to identify the unknown parameters through optimization based on experimental results, where the covariance matrix adaptation–evolutionary strategy (CMA-es) is utilized to improve the simulation and experimental results against the kinematic and compliance tests. This speeds up the design and development cycle by recovering all the unknown data with respect to a set of kinematic measurements through a single optimization process. A case study employing a McPherson strut suspension system is modelled in a multi-body dynamic system. Three kinematic and compliance tests are examined, namely, vertical parallel wheel travel, opposite wheel travel and single wheel travel. The problem is formulated as a multi-objective optimization problem with 40 objectives and 49 design parameters. A hierarchical clustering method based on global sensitivity analysis is used to reduce the number of objectives to 30 by grouping correlated objectives together. Then, a dynamic summation of rank value is used as pseudo-objective functions to reformulate the multi-objective optimization to a single-objective optimization problem. The optimized results show a significant improvement in the correlation between the simulated model and the experimental model. Once accurate representation of the vehicle suspension model is achieved, further analysis, such as ride and handling performances, can be implemented for further optimization.  相似文献   
98.
Studies were done to determine if warm n-butyl alcohol vapor might be effective for the destruction of respiratory tract foam bubbles and for alleviation of the arterial hypoxemia accompanying severe acute pulmonary edema. In vitro studies showed that warm butyl alcohol vapors made from 5% and 7% butyl alcohol solutions at 39 degrees C were much more effective in antifoam activity against synthetic foam bubbles than ethyl alcohol vapors, made from 20% and 30% ethyl alcohol at 22 degrees C. Warm butyl alcohol vapor also slowly destroyed in vitro the fine foam bubbles of alveolar lining origin made in rabbit lung post mortem. Evolving lung edema was induced in anesthetized rabbits by aspiration of 1.1 ml/kg of 1.2 molal sorbitol/0.14 molal sodium chloride/0.01 molal hydrochloric acid solution of pH 2.0. After established severe arterial hypoxemia and in the absence of overt foam, inhalation of warm butyl alcohol/H2O vapor-air mixture, made by air humidification from 7% butyl alcohol at 39 degrees C, alleviated promptly the hypoxemia. The improvement was progressive over the first 45 minutes of continued vapor therapy. The lessened hypoxemia occurred without concurrent improvement in the amount of formed lung edema fluid. Control inhalations of warm 100% H2O vapor-air mixture did not improve the hypoxemia. The only noted side effects of warm butyl alcohol vapor treatments were slight hypotension and slight metabolic acidosis which developed very slowly. The results suggest that warm butyl alcohol vapor might prove to be an effective adjuvant agent to lessen critically severe hypoxemia in selective cases of acute pulmonary edema in man.  相似文献   
99.
The Box-Jenkins approach is applied to daily solar radiation data from four different locations in Malaysia. The deterministic annual component is obtained by Fourier analysis. The stochastic component of the time series is fitted to three models, ARMA (1,0), ARMA (2,0) and ARMA (1,1). Random shocks from these models are tested by Box-Pierce statistic and Ljung-Box for whiteness of residuals. Skewness and kurtosis coefficients are tested for normality.  相似文献   
100.
Electron microscopy of dimeric and trimeric single chain antibody Fv fragments (scFvs) complexed with anti-idiotype Fab fragments was used to reveal the orientation of antigen binding sites. This is the first structural analysis that discloses the multivalent binding orientation of scFv trimers (triabodies). Three different scFv molecules were used for the imaging analysis; NC10 scFv-5 and scFv-0, with five- and zero-residue linkers respectively between the VH and VL domains, were complexed with 3-2G12 anti-idiotype Fab fragments and 11-1G10 scFv-0 was complexed with NC41 anti-idiotype Fab fragments. The scFv-5 molecules formed bivalent dimers (diabodies) and the zero-linker scFv-0 molecules formed trivalent trimers (triabodies). The images of the NC10 diabody-Fab complex appear as boomerangs, not as a linear molecule, with a variable angle between the two Fab arms and the triabody-Fab complexes appear as tripods.  相似文献   
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