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21.
Tyler DW  Ellerbroek BL 《Applied optics》1998,37(21):4569-4576
We use numerical calculations to examine the relation between adaptive optics (AO) turbulence compensation and power coupled through a spectrometer slit for both laser and natural guide-star AO systems. The AO system and observing parameters used are relevant to the Gemini-North 8-m telescope. For this study, we separate residual tilt from residual higher-order aberrations to isolate their relative effects under a variety of operating conditions. Our results demonstrate that slit-coupled intensity is not uniquely determined by system Strehl alone; we show that this is due to the differing effects of higher-order and tilt aberrations on the shape of the compensated point-spread function. For the Gemini spectrometer and AO system, the wider point-spread function halo associated with an added residual higher-order aberration reduces slit-coupled intensity more rapidly than a broad point-spread function core induced by residual tilt.  相似文献   
22.
Atomic force microscope analysis, with a resolution of /spl lsim/1.1 nm, shows that peak-to-peak surface roughness (/spl Delta/h/sub p-p/) of amorphous silicon films thinner than /spl ap/50 nm on silicon dioxide can be controlled to better than 5 nm. Low-pressure, chemically-vapor-deposited silicon films on silicon dioxide initially show an approximately linear increase in the surface roughness due to growing nuclei as the deposition progresses, followed by a decrease in the surface roughness as growth nuclei coalesce. A simple model based on random nucleation and nuclei growth displays similar trends. Films deposited on rougher substrates show more surface roughness. Surface treatment during the predeposition cleaning process does not significantly affect /spl Delta/h/sub p-p/. As a means of producing smooth surfaces, films thinner than about 20 nm are first deposited more thickly than needed, and then etched back to the desired dimension; the use of a binary HNO/sub 3/ and HF etching process improves roughness control. Boron-ion implanted and subsequently crystallized 45-nm-thick Si films show significant smoothing with /spl Delta/h/sub p-p//spl ap/2.2 nm. Thin amorphous silicon films deposited by source evaporation are attractive because they can be deposited at room temperature, and have smoother surfaces (/spl Delta/h/sub p-p//spl ap/2.5 nm) than comparable films produced by chemical vapor deposition.  相似文献   
23.
This literature survey is devoted to hydraulic resistance of water and carbon dioxide flows at supercritical pressures. The objectives are to assess previous studies that were done in the area of hydraulic resistance of fluids at supercritical pressures flowing in channels of various geometries and to understand the specifics of pressure drop at these conditions. The literature search showed that the majority of experimental data were obtained in vertical tubes, some data were obtained in horizontal tubes and just a few of them in other flow geometries including bundles. In general, hydraulic resistance data are limited compared to the heat transfer data at supercritical pressures. Differences in pressure drop between supercritical and subcritical forced convection seem to be related to significant variations in thermophysical properties near the critical and pseudocritical points. Due to these variations, satisfactory analytical and numerical methods have not yet been developed especially in turbulent flows and at high heat fluxes. In general, the pressure drop in supercritical fluid flow consists of four components: pressure drop due to frictional resistance, due to local flow obstruction, due to acceleration of flow and due to gravity. The total pressure drop at supercritical pressures can be estimated using general correlations for pressure drop at subcritical pressures with correction factors for the effect of significant thermophysical properties variations and high heat fluxes. Only one paper was devoted to pressure drop in tight short bundles cooled with water at supercritical pressures. Therefore, more experimental work is needed to estimate the total pressure drop in various bundle designs with the objective of providing reliable information for designing supercritical water nuclear reactors.  相似文献   
24.
The intertidal environments of estuaries represent critical exchange environments of sediment and sediment bound contaminants. Ecological and sedimentological related investigations of these environments require monitoring methods that provide rapid spatially representative data on sediment grain size distribution. Remote sensing has the potential to provide synoptic information of intertidal environments. Previous in situ and laboratory-based reflectance investigations have demonstrated that for effective quantification of sediment grain size distributions, remote sensing platforms must include measurements within the short-wave infrared (SWIR). In addition, the timing of image acquisition, in relation to tidal cycles and sediment moisture content, is critical in optimising the spectral differences between the coarser sand and finer ‘mud’ fraction of sediments. Daedalus 1268 Airborne Thematic Mapper (ATM) has been identified as an appropriate platform and sensor for providing accurate synoptic maps of estuarine sediment distributions. This paper presents the results from the application of ATM 1.75 m resolution data to the mapping of surface sediment grain-size distributions across intertidal areas of Ribble Estuary, Lancashire, UK. ATM imagery was acquired after the intertidal area was exposed to strong summer drying conditions. Pre-processing and linear unmixing of the imagery collected of the intertidal zone following a period of drying allowed accurate sub-pixel determinations (1.75 m resolution) of sediment clay (r2=0.79) but less accurate for sand (r2=0.60). The results also demonstrate deterioration in the image calibration with increasing sediment moisture content and microphytobenthos cover. However, recombining the subpixel end member abundances through multivariate regression analysis improved the image calibration significantly for both sediment clay and sand content (r2>0.8) for imagery collected in both dryer and wetter conditions. These results demonstrate that ATM data, or similar, can be used to gain quantitative information on intertidal sediment distributions and such data has application to a wide variety of estuarine research.  相似文献   
25.
The prevalence of undernutrition due to insufficient energy intake has been reduced by nearly 50% since 1990. This reduction is largely attributed to improved yields of staple crops, such as wheat, rice, and maize; however, these improvements did little for micronutrient deficiencies that affect an estimated two billion people worldwide. Starchy staple crops are energy dense but are often lacking in one or more B vitamins, making resource‐constrained people who consume monotonous diets comprised predominantly of these staples at risk for developing deficiency. B vitamin deficiencies occur due to a poor overall nondiversified diet and rarely occur alone. Many B vitamins are essential cofactors involved in the metabolism of other nutrients, including other B vitamins, whereby the deficiency of one B vitamin affects the metabolism and status measurements of another. Food fortification efforts have nearly eradicated diseases of extreme B vitamin deficiency, such as beriberi from thiamin deficiency and pellagra from niacin deficiency. However, subclinical deficiency, sometimes referred to as hidden hunger, is still common especially in low‐income countries. Most dietary B vitamins, due to their water‐soluble nature, are not a concern for excessive intakes, but synthetic forms used for fortification and supplements sometimes can have adverse effects when consumed in high amounts. Biofortified crops offer a long‐term sustainable method to increase the amount of dietary B vitamins for people who rely on staple crops for most of their caloric intake. Efforts have been made to improve B vitamin content of crops, especially for thiamin, vitamin B6, and folate, but none have undergone human feeding trials; therefore, more research is needed to provide sustainable and scalable solutions in many parts of the world.  相似文献   
26.
Twenty-one sediments collected in urban waterways of the Pearl River Delta (PRD) in China were screened for acute toxicity using Chironomus dilutus in addition to being examined for potential contributors of sediment toxicity, including 19 organochlorine, five organophosphate, and nine pyrethroid insecticides, 28 polycyclic aromatic hydrocarbons, 27 polychlorinated biphenyls, 15 polybrominated diphenyl ethers, 12 metals, and ammonia. Fifteen of the 21 sediments exhibited acute toxicity to C. dilutus, with 33% of the samples exhibiting 100% mortality. This is one of the first studies in China which directly correlates a broad range of sediment-associated contaminants to ecological effects measured by bioassays. A toxic unit approach showed that pyrethroids contributed most to the observed toxicity; as cypermethrin alone was predicted to cause significant mortality in about half of the sites. Specific toxicity identification evaluation analysis confirmed pyrethroid toxicity. Other contaminants may also be supplemental contributors at a few sites. The current study suggests that pyrethroids are the principal cause of contamination and that future risk assessment and mitigation efforts in this area should focus primarily on pyrethroids but should not disregard other contaminants as potential risk is evident.  相似文献   
27.
The objective of the current investigation is to characterize the dynamic strain aging (DSA) behavior in alloys 800H and 690. Constant extension rate tests were conducted at strain rates in the range of 10?4 s?1 to 10?7?s?1and temperatures between 295?K and 673?K (22?°C and 400?°C), in an argon atmosphere. Maps for the occurrence of serrated flow as a function of strain rate and temperature were built for both alloys. The enthalpy of serrated flow appearance of alloy 800H was found to be 1.07?±?0.30?eV.  相似文献   
28.
Suction feeding is the most common form of prey capture across aquatic feeding vertebrates and many adaptations that enhance efficiency and performance are expected. Many suction feeders have mechanisms that allow the mouth to form a planar and near-circular opening that is believed to have beneficial hydrodynamic effects. We explore the effects of the flattened and circular mouth opening through computational fluid dynamics simulations that allow comparisons with other mouth profiles. Compared to mouths with lateral notches, we find that the planar mouth opening results in higher flow rates into the mouth and a region of highest flow that is positioned at the centre of the mouth aperture. Planar mouths provide not only for better total fluid flow rates through the mouth but also through the centre of the mouth near where suction feeders position their prey. Circular mouths are shown to provide the quickest capture times for spherical and elliptical prey because they expose the prey item to a large region of high flow. Planar and circular mouths result in higher flow velocities with peak flow located at the centre of the mouth opening and they maximize the capacity of the suction feeders to exert hydrodynamic forces on the prey.  相似文献   
29.
It is demonstrated for the first time that an epoxy thermoset resin can be cured at temperatures well below its Tg. This study compared the use of a uniform variable frequency microwave (VFM) field to standard oven curing at temperatures above and below Tg. Using Tg, tan δ, modulus, and FTIR measurements, it is shown that the reaction of BFDGE with MDA to attain a product with Tg of 133 °C is achieved by VFM at temperatures from 100 to 140 °C; in contrast, the thermal cure normally requires 170 °C to attain the same Tg and the same extent of cure. By following the pregel cure reaction with 13C‐NMR spectroscopy, it was determined that the lower cure temperatures of VFM cure predominately lead to chain extension and smaller amounts of crosslinking compared to the thermal cure. To explain these results, it is suggested that, after gelation, with VFM cure there is higher mobility from dipole rotations that continues the cure to completion without vitrification. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44222.  相似文献   
30.
Molecular hydrogen ameliorates pathological states in a variety of human diseases, animal models, and cell models, but the effects of hydrogen on cancer have been rarely reported. In addition, the molecular mechanisms underlying the effects of hydrogen remain mostly unelucidated. We found that hydrogen enhances proliferation of four out of seven human cancer cell lines (the responders). The proliferation-promoting effects were not correlated with basal levels of cellular reactive oxygen species. Expression profiling of the seven cells showed that the responders have higher gene expression of mitochondrial electron transport chain (ETC) molecules than the non-responders. In addition, the responders have higher mitochondrial mass, higher mitochondrial superoxide, higher mitochondrial membrane potential, and higher mitochondrial spare respiratory capacity than the non-responders. In the responders, hydrogen provoked mitochondrial unfolded protein response (mtUPR). Suppression of cell proliferation by rotenone, an inhibitor of mitochondrial ETC complex I, was rescued by hydrogen in the responders. Hydrogen triggers mtUPR and induces cell proliferation in cancer cells that have high basal and spare mitochondrial ETC activities.  相似文献   
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