全文获取类型
收费全文 | 3478篇 |
免费 | 52篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 37篇 |
综合类 | 2篇 |
化学工业 | 448篇 |
金属工艺 | 110篇 |
机械仪表 | 57篇 |
建筑科学 | 140篇 |
矿业工程 | 8篇 |
能源动力 | 49篇 |
轻工业 | 293篇 |
水利工程 | 18篇 |
石油天然气 | 5篇 |
无线电 | 254篇 |
一般工业技术 | 405篇 |
冶金工业 | 1316篇 |
原子能技术 | 27篇 |
自动化技术 | 364篇 |
出版年
2021年 | 15篇 |
2020年 | 16篇 |
2019年 | 22篇 |
2018年 | 24篇 |
2017年 | 36篇 |
2016年 | 27篇 |
2015年 | 18篇 |
2014年 | 32篇 |
2013年 | 128篇 |
2012年 | 57篇 |
2011年 | 102篇 |
2010年 | 76篇 |
2009年 | 84篇 |
2008年 | 103篇 |
2007年 | 100篇 |
2006年 | 87篇 |
2005年 | 96篇 |
2004年 | 76篇 |
2003年 | 71篇 |
2002年 | 86篇 |
2001年 | 59篇 |
2000年 | 60篇 |
1999年 | 108篇 |
1998年 | 318篇 |
1997年 | 205篇 |
1996年 | 138篇 |
1995年 | 99篇 |
1994年 | 109篇 |
1993年 | 105篇 |
1992年 | 56篇 |
1991年 | 46篇 |
1990年 | 56篇 |
1989年 | 52篇 |
1988年 | 46篇 |
1987年 | 46篇 |
1986年 | 51篇 |
1985年 | 74篇 |
1984年 | 66篇 |
1983年 | 39篇 |
1982年 | 35篇 |
1981年 | 45篇 |
1980年 | 30篇 |
1979年 | 32篇 |
1978年 | 32篇 |
1977年 | 49篇 |
1976年 | 77篇 |
1975年 | 26篇 |
1974年 | 26篇 |
1973年 | 18篇 |
1972年 | 21篇 |
排序方式: 共有3533条查询结果,搜索用时 15 毫秒
91.
Microstructural Changes in High‐Protein Nutrition Bars Formulated with Extruded or Toasted Milk Protein Concentrate 下载免费PDF全文
Milk protein concentrates with more than 80% protein (that is, MPC80) are underutilized as the primary protein source in high‐protein nutrition bars as they impart crumbliness and cause hardening during storage. High‐protein nutrition bar texture changes are often associated with internal protein aggregations and macronutrient phase separation. These changes were investigated in model high‐protein nutrition bars formulated with MPC80 and physically modified MPC80s. High‐protein nutrition bars formulated with extruded MPC80s hardened slower than those formulated with toasted or unmodified MPC80. Extruded MPC80 had reduced free sulfhydryl group exposure, whereas measurable increases were seen in the toasted MPC80. High‐protein nutrition bar textural performance may be related to the number of exposed free sulfhydryl groups in MPC80. Protein aggregations resulting from ingredient modification and high‐protein nutrition bar storage were studied with sodium dodecyl sulfate polyacrylamide gel electrophoresis. Disulfide‐based protein aggregations and changes in free sulfhydryl concentration were not consistently relatable to high‐protein nutrition bar texture change. However, the high‐protein nutrition bars formulated with extruded MPC80 were less prone to phase separations, as depicted by confocal laser scanning microscopy, and underwent less texture change during storage than those formulated with toasted or unmodified MPC80. 相似文献
92.
Effects of tallow in diets based on corn silage or alfalfa silage on digestion and nutrient use by lactating dairy cows 总被引:3,自引:0,他引:3
Six multiparous Holstein cows (average 31 days in milk; 36.3 kg/d of milk) fitted with ruminal cannulas were used in a 6 x 6 Latin square with 21-d periods to investigate the effects of diets that varied in forage source and amount of supplemental tallow. Isonitrogenous diets in a 2 x 3 factorial arrangement were based on either high corn silage (40:10 corn silage to alfalfa silage, % of dry matter) or high alfalfa silage (10:40 corn silage to alfalfa silage, % of dry matter) and contained 0, 2, or 4% tallow. Intakes of dry matter and total fatty acids were lower when cows were fed the high corn silage diet. Tallow supplementation linearly decreased dry matter intake. Milk yield was unaffected by diet; yields of milk fat and 3.5% fat-corrected milk were higher for the high alfalfa silage diet but were unaffected by tallow. Milk fat percentage was higher for the high alfalfa silage and tended to decrease when tallow was added to the high corn silage diet. Contents of trans-C18:1 isomers in milk fat were increased by high corn silage and tallow, and tended to be increased more when tallow was fed in the high corn silage diet. Ruminal pH and acetate:propionate were lower when high corn silage was fed. Ruminal acetate:propionate decreased linearly as tallow increased; the molar proportion of acetate was decreased more when tallow was added to the high corn silage diet. Ruminal liquid dilution rates were higher for the alfalfa silage diet; ruminal volume and solid passage rates were similar among diets. Total tract apparent digestibilities of dry matter, organic matter, crude protein, starch, energy, and total fatty acids were unaffected by diet. Digestibilities of neutral detergent fiber, acid detergent fiber, hemicellulose, and cellulose were lower when high corn silage was fed. The high alfalfa silage diet increased intakes of metabolizable energy and N, and increased milk energy and productive N. Tallow decreased the amount of N absorbed but had few other effects on utilization of energy or N. Tallow linearly increased concentrations of nonesterified fatty acids and cholesterol in plasma; cholesterol was increased by high alfalfa silage. Overall, forage source had more pronounced effects on production and metabolism than did tallow supplementation. Few interactions between forage source and tallow supplementation were detected except that ruminal fermentation and milk fat content were affected more negatively when tallow was fed in the high corn silage diet. 相似文献
93.
Nazanin Darbanian Sameer M. Venugopal Shrinivas G. Gopalan David R. Allee Lawrence T. Clark 《Journal of the Society for Information Display》2010,18(5):346-350
Abstract— The development of a flexible, rewritable, non‐volatile memory (NVM) that is implemented on a standard, low‐temperature a‐Si:H process without additional mask steps is reported. This NVM is a part of a flexible‐display system. Each NVM cell is composed of differentially configured thin‐film‐transistors (TFTs). The cell reads out one of two stable states depending on the relative threshold voltages of the differentially configured TFTs. Information is stored in each cell by increasing the threshold voltage of one differential TFT or the other, utilizing the well‐known electrical‐stress degradation intrinsic to a‐Si:H TFTs. The stored information is retained indefinitely with no applied power. A test array of individually addressable NVM cells has been successfully fabricated and tested on flexible stainless‐steel substrates. Read and write operation, as well as preliminary reliability measurements, are described. The design is readily scalable to large memory arrays. 相似文献
94.
This paper considers the problem of shape-from-shading using nearby extended light sources. The paper reviews a number of methods that employ nearby illuminants, and describes a new technique that assumes a rectangular planar nearby distributed uniform isotropic illuminant. It is shown that such a light source illuminating a small Lambertian surface patch is equivalent to a single isotropic point light source at infinity, in the absence of shadowing. A closed-form solution is given for the equivalent point light source direction in terms of the illuminant corner locations. Equivalent point light sources can be obtained for distinct illuminant patterns allowing standard photometric stereo algorithms to be used. An extension is given to the case of a rectangular planar illuminant with arbitrary radiance distribution. Experimental results are shown demonstrating the application of the theory to photometric stereo using illumination from a LCD computer monitor. Details on the photometric calibration of the illumination source and image acquisition device are provided. 相似文献
95.
Clark Nathan Zhong Hongtao Tang Wilkin Mahlke Scott 《International journal of parallel programming》2003,31(6):429-449
General-purpose processors are often incapable of achieving the challenging cost, performance, and power demands of high-performance applications. To meet these demands, most systems employ a number of hardware accelerators to off-load the computationally demanding portions of the application. As an alternative to this strategy, we examine customizing the computation capabilities of a processor for a particular application. The processor is extended with hardware in the form of a set of custom function units and instruction set extensions. To effectively identify opportunities for creating custom hardware, a dataflow graph design space exploration engine heuristically identifies candidate computation subgraphs without artificially constraining their size or shape. The engine combines estimates of performance gain, cost, and inherent limitations of the processor to grow candidate graphs in profitable directions while pruning unprofitable paths. This paper describes the dataflow graph exploration engine and evaluates its effectiveness across a set of embedded applications. 相似文献
96.
High resolution 13C n.m.r. proton noise decoupled (75.5 MHz) spectra have been recorded for a series of nitrated celluloses and denitrated cellulose nitrates. From the detailed spectral assignments an analysis of the partial degrees of substitution and distribution of nitrate groups in the β-D-glucopyranose residues is presented. The data are compared with the predictions of a model based on the constancy of ratio of three equilibrium constants for nitration—denitration at the C2, C3 and C6 positions for differently substituted β-D-glucopyranose residues and it is shown that the situation is considerably more complex than provided for by the model. Analysis of the anomeric 13C carbon region produces some sequence information which indicates non-random distribution of nitrate ester groups. 相似文献
97.
Pressure thresholds are minimum pressures needed to start explosive initiation that ends in detonation. We obtain pressure thresholds from three sources. Run‐to‐detonation times are the poorest source but the fitting of a function gives rough results. Flyer‐induced initiation gives the best results because the initial conditions are the best known. However, very thick flyers are needed to give the lowest, asymptotic pressure thresholds used in modern models and this kind of data is rarely available. Gap test data are in much larger supply but the various test sizes and materials are confusing. We find that explosive pressures are almost the same if the distance in the gap test spacers are in units of donor explosive radius. Calculated half‐width time pulses in the spacers may be used to create a pressure‐time curve similar to that of the flyers. The very‐large Eglin gap tests give asymptotic thresholds comparable to extrapolated flyer results. The three sources are assembled into a much‐expanded set of near‐asymptotic pressure thresholds. These thresholds vary greatly with density: for TATB/LX‐17/PBX 9502, we find values of 4.9 and 8.7 GPa at 1.80 and 1.90 g/cm3, respectively. 相似文献
98.
It was found that commercial silicone grease incorporated accidentally into polystyrene bars yields a major dynamic mechanical loss peak at ca. ?128°C. This finding was followed up with a study of various polydimethylsiloxanes and silicone rubber, in which up to three peaks were found. In order of increasing temperature (at 1 Hz) these are the glass transition (Tg; ca. ?128°C), crystallization (Tc; ca. ?110°C) and melting peaks (Tm; ca. ?50°C). Hydrocarbon-based greases were also investigated. The results indicate that the methods employed may be of use for the investigation of the dynamic mechanical properties of small amounts of material of varying particle sizes, such as powders of cross-linked polymers, that need not be compatible with, or soluble in, the host matrix. The sensitivity of the method is such at a 1 percent by weight contamination of silicone grease in polystyrene gives a loss tangent peak of at least 0.002 above background, and emphasizes the necessary care to be taken during sample preparation to exclude unwanted substances. 相似文献
99.
100.
Effect of amino acid deletions in the O-glycosylated region of Aspergillus awamori glucoamylase 总被引:1,自引:0,他引:1
Libby Carol Baker; Cornett Catherine A.G.; Reilly Peter J.; Ford Clark 《Protein engineering, design & selection : PEDS》1994,7(9):1109-1114
Aspergillus awamori glucoamylase (GA) contains globular catalyticand starch-binding domains (residues 1471 and 509616,respectively). A heavily O-glycosylated sequence comprises twoparts. The first (residues 441471) in the crystal structurewraps around an /-barrel formed by residues 1440. Thesecond (residues 472508) is an extended, semi-rigid linkerbetween the two domains. To investigate the functional roleof this linker, we made internal deletions to remove residues466512 (GA1), 485512 (GA2) and 466483 (GA3).GA2 and GA3 were expressed in Saccharomyces cerevisiae culturesupernatants at 60 and 20% the wild-type level, respectively,while GA1 was almost undetectable. Western blots comparing extracellularand intracellular fractions indicated that the region deletedin GA3 was critical for secretion, while the region deletedin GA2 contributed to the production of a stable enzyme structure.The activities of purified GA2 and GA3 on soluble and insolublestarch were similar to those of wild-type GA, indicating thatfor soluble starch their deletions did not affect the catalyticdomain and for insoluble starch the linker does not coordinatethe activities of the catalytic and starch-binding domains.The deletions had a significant negative effect on GA2 and GA3thermos tabilities. 相似文献