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991.
992.
The use of the ABCD matrices for the calculation of pulse propagation in second-order dispersive media is developed rigorously. Their usefulness is demonstrated by obtaining the results for the propagation of a Gaussian pulse with an arbitrary linear chirp. By analogy with ray optics, the concept of a time ray is introduced to give further insight. The analogy with paraxial optics is carried further by extending the matrix method to a complete Hermite-Gaussian basis and thus to arbitrarily shaped and nonlinearly chirped pulses. Some practical applications of the matrix method are discussed 相似文献
993.
The in vitro binding of bile acids by bananas (Musa × paradisiaca), peaches (Prunus persica), pineapple (Ananus comosus), grapes (Vitis spp.), pears (Pyrus communis), apricots (Prunus armeniaca) and nectarines (Prunus persica, nectarina) was determined using a mixture of bile acids secreted in human bile at a duodenal physiological pH of 6.3. Six treatments and two blank incubations were conducted, testing various fresh fruits on an equal dry matter basis. Considering cholestyramine (bile acid binding, cholesterol lowering drug) as 100% bound, the relative in vitro bile acid binding percentages on dry matter (DM), total dietary fibre and total polysaccharides basis were 2–9%, 15–101% and 10–101%, respectively. Bile acid binding, on a DM basis, for bananas was significantly (P ? 0.05) higher and that for nectarines significantly lower than those for peaches, pineapple, grapes, pears and apricots. The bile acid bindings for peaches and pineapple were similar and significantly higher than those for grapes, pears and apricots. Binding values for grapes and pears were significantly higher than apricots. These results point to the relative health promoting potential of bananas > peaches = pineapple > grapes = pears > apricots > nectarines, as indicated by their bile acid binding on a DM basis. The variability in bile acid binding between the fruits tested maybe related to their phytonutrients, antioxidants, polyphenols, flavonoids (anthocyanins, flavonols, and proanthocyanidins), structure, hydrophobicity of undigested fractions, anionic or cationic nature of the metabolites produced during digestion or their interaction with active binding sites. Animal studies are planned to validate in vitro bile acid binding of fruits, observed herein, to their healthful potential, atherosclerosis amelioration and cancer prevention. 相似文献
994.
MA Blank BL Ems GW Gibson WR Myers SK Berman RJ Phipps PN Smith 《Canadian Metallurgical Quarterly》1997,42(2):281-288
Mechanisms by which ketones potentiate manganese-bilirubin (Mn-BR)-induced cholestasis are unknown. The purpose of the present study was to investigate the effect of methyl isobutyl ketone (MiBK), a widely used ketonic solvent, at the level of the bile canalicular membrane (BCM) and to verify if altered membrane lipid dynamics could be involved in MiBK-potentiated Mn-BR cholestasis. Male Sprague-Dawley rats were exposed 4 hr/day for 3 days to MiBK vapors (200 or 600 ppm). Eighteen hours after the last exposure, manganese (Mn, 4.5 mg/kg) was given i.v. followed 15 min later by bilirubin (BR, 25 mg/kg). Rats were killed 30 min after BR; liver cell plasma membranes (bile canalicular and sinusoidal), microsomes, mitochondria, and cytosol were isolated by differential centrifugation. Lipids were extracted and cholesterol was measured in each fraction. After Mn-BR and MiBK exposure (600 ppm), results indicated a marked increase in BCM cholesterol content compared to rats exposed to air only. This increase was greater than that due to Mn-BR or MiBK given alone. Also, results indicated that cholesterol increased in a dose-related fashion in BCM after MiBK exposure, whereas PM cholesterol remained unaltered. To identify the source of the increased BCM cholesterol and to permit distinction between de novo cholesterol synthesis and subcellular shifts, the hepatic lipid pool was labeled in vivo with [3H]-cholesterol and [2-14C]-mevalonic acid, a cholesterol synthesis precursor. Results showed that after 600 ppm MiBK exposure, 14C-labeled cholesterol was greater than 3H-labeled cholesterol, indicating that the contribution of de novo cholesterol synthesis to the total cholesterol content of the various isolated hepatocellular fractions was more important than the contribution of intracellular pools. Therefore, increased BCM cholesterol content and enhanced accumulation of newly synthesized cholesterol appear to be involved in MiBK potentiation of Mn-BR-induced cholestasis. 相似文献
995.
The materials characterisation requirements for accurate yet practical simulation of daylighting in buildings is examined for a range of emerging and existing technologies which seek to raise the contribution of daylighting to overall lighting requirements. Algorithms based on underlying physical models can be established from analysis of data on bi-directional transmission and reflection. Demonstrations of effects in simulation relevant to glare, view and illuminance are given. 相似文献
996.
The thermal conductivities of three plasma-sprayed cermets have been determined over the temperature range 23–630°C from the measurement of the specific heat, thermal diffusivity, and density. These cermets are mixtures of Al and SiC prepared by plasma spray deposition and are being considered for various applications in magnetic confinement fusion devices. The samples consisted of three compositions: 61 vol% Al/39 vol% SiC, 74vol% Al/26vol% SiC, and 83 vol% Al/17 vol% SiC. The specific heat was determined by differential scanning calorimetry through the Al melt transition up to 720°C, while the thermal diffusivity was determined using the laser flash technique up to 630°C. The linear thermal expansion was measured and used to correct the diffusivity and density values. The thermal diffusivity showed a significant increase after thermal cycling due to a reduction in the intergrain contact resistance, increasing from 0.4 to 0.6 cm2·–1 at 160°C. However, effective medium theory calculations indicated that the thermal conductivities of both the Al and the SiC were below the ideal defect-free limit even after high-temperature cycling. The specific heat measurements showed suppressed melting points in the plasmasprayed cermets. The 39 vol% SiC began a melt endotherm at 577°C, which peaked in the 640–650°C range depending on the sample thermal history. Chemical and X-ray diffraction analysis indicated the presence of free silicon in the cermet and in the SiC powder, which resulted in a eutectic Al/Si alloy.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A. 相似文献
997.
E. Smith 《International Journal of Fracture》1986,30(3):229-233
Some stainless steel pipe weldment materials are known to have inferior fracture properties. This paper focusses on the criterion for the instability of growth of a through-wall circumferential crack in a pipe weldment, with allowance being made for the fact that the weld material might have different properties to the adjoining material.
Résumé On sait que certains métaux d'apport en soudage de tubes en acier inoxydable présentent des propriétés médiocres de résistance à la rupture. L'étude se concentre sur le critère d'instabilité lors de la croissance d'une fissure circonférentielle traversante dans une soudure de tube, en considérant que le métal fondu puisse avoir des propriétés différentes de celles du métal de base.相似文献
998.
The biconjugate gradient method for electromagnetic scattering 总被引:1,自引:0,他引:1
Smith C.F. Peterson A.F. Mittra R. 《Antennas and Propagation, IEEE Transactions on》1990,38(6):938-940
The biconjugate gradient (BCG) method for solving linear systems is shown to be more efficient than the conjugate gradient (CG) method for several examples from electromagnetic scattering. A remedy for the occasional stagnation of the algorithm is proposed. The potential flaw in the BCG algorithm may be avoided when encountered by restarting the algorithm with a perturbed estimate of the solution 相似文献
999.
Cuan Petheram Thomas A. McMahon Murray C. Peel Chris J. Smith 《Water Resources Management》2010,24(9):1791-1817
Debate about irrigation development of water resources in northern Australia has been hampered by a lack of quantitative information
to enable accurate assessment of the volume of water that could potentially be regulated in the ‘North’ (north of the tropic
of Capricorn). Too often the debate focuses solely on streamflow volumes and quantities of runoff. In this paper we present
simple calculations to estimate a representative irrigation requirement and the potential exploitable yield in each of the
12 drainage divisions of Australia in order to more fully inform this on-going debate. Environmental, social, cultural and
economic considerations are not examined. The results indicate that, despite northern Australia generating approximately 64%
of the continent’s runoff, only 45% of Australia’s potentially exploitable yield is located in that portion of Australia,
due to unfavourable streamflow characteristics, storage constraints and large evaporation losses. If exploitable yield and
irrigation requirement were the sole factors constraining sustainable irrigation, under a full development scenario, southern
Australia could hypothetically support an area of irrigation about 60% greater than that of northern Australia (based on only
36% of the country’s runoff). Using ‘best estimates’ of rainfall and evapotranspiration projected under changes in climate
resulting from a moderate emissions scenario, the percentage of Australia’s exploitable yield located in northern Australia
is estimated to increase from 45% to 47% by the year 2050, which equates to a 2% increase to the percentage of Australia’s
hypothetical area of irrigation that could be located in northern Australia. These results suggest that efforts towards achieving
and developing sustainable irrigation practices in the South will remain most important in achieving Australia’s long term
irrigation potential. This study also highlights the need for better regional scale information on the potential to regulate
streamflow in Australia, under current and future climates. Such information is essential to guide policy and planning, future
Government and private investment, and to manage community expectations of Australia’s water resources. 相似文献
1000.
The present study reports on the results of a follow-up examination of patient material, 5 years after the installation of the fixed supraconstruction. The patient group comprised 11 individuals. Briefly, a split-mouth technique of treatment was used. In the right side of the mandible the traditional 2-step surgical approach for implant installation was used. In the left jaw quadrant a 1-step surgical procedure was used. A clinical and radiographical examination was performed 5 years after the initial connection of the supraconstruction to the implants. At the 5-year follow-up examination all 61 implants examined at the 18-month follow-up were still in service and found to be clinically stable irrespective of the surgical procedure used. Furthermore, the results of the present clinical and radiographical follow-up study demonstrate that the marginal bone level at implants placed anteriorly in the edentulous mandible and supporting fixed supraconstructions is stable between 18 and 60 months irrespective of whether placed according to a 1-step or 2-step surgical procedure. 相似文献