全文获取类型
收费全文 | 142440篇 |
免费 | 8250篇 |
国内免费 | 6353篇 |
专业分类
电工技术 | 5825篇 |
技术理论 | 6篇 |
综合类 | 11076篇 |
化学工业 | 25873篇 |
金属工艺 | 6647篇 |
机械仪表 | 5630篇 |
建筑科学 | 5095篇 |
矿业工程 | 2138篇 |
能源动力 | 4885篇 |
轻工业 | 18024篇 |
水利工程 | 2208篇 |
石油天然气 | 23074篇 |
武器工业 | 754篇 |
无线电 | 7116篇 |
一般工业技术 | 15366篇 |
冶金工业 | 3330篇 |
原子能技术 | 2274篇 |
自动化技术 | 17722篇 |
出版年
2024年 | 311篇 |
2023年 | 961篇 |
2022年 | 1741篇 |
2021年 | 2348篇 |
2020年 | 2752篇 |
2019年 | 2742篇 |
2018年 | 2540篇 |
2017年 | 2846篇 |
2016年 | 3513篇 |
2015年 | 3955篇 |
2014年 | 6839篇 |
2013年 | 7991篇 |
2012年 | 7612篇 |
2011年 | 8378篇 |
2010年 | 6507篇 |
2009年 | 7734篇 |
2008年 | 7458篇 |
2007年 | 8448篇 |
2006年 | 8207篇 |
2005年 | 6959篇 |
2004年 | 6048篇 |
2003年 | 5868篇 |
2002年 | 5654篇 |
2001年 | 4412篇 |
2000年 | 4599篇 |
1999年 | 4150篇 |
1998年 | 3479篇 |
1997年 | 3210篇 |
1996年 | 3203篇 |
1995年 | 3164篇 |
1994年 | 2803篇 |
1993年 | 1723篇 |
1992年 | 1732篇 |
1991年 | 1209篇 |
1990年 | 891篇 |
1989年 | 753篇 |
1988年 | 683篇 |
1987年 | 420篇 |
1986年 | 251篇 |
1985年 | 427篇 |
1984年 | 467篇 |
1983年 | 468篇 |
1982年 | 357篇 |
1981年 | 414篇 |
1980年 | 286篇 |
1979年 | 117篇 |
1978年 | 115篇 |
1977年 | 70篇 |
1976年 | 44篇 |
1975年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
91.
前期杂交优化后赤芝菌种经液体深层发酵后,提取灵芝菌丝体多糖,并过DEAE-Sepharose Fast Flow柱分离纯化,利用高效体积排阻色谱(HPSEC)检测多糖级分的纯度,采用完全酸水解PMP柱前衍生化RP—HPLC测定多糖级分的单糖组成,多角度光散射仪联用装置(SEC—MALLS)测定其绝对重均分子量(Mw),并且根据分子旋转半径与分子摩尔数的关系曲线斜率初步推断其空间构象。结果显示:分离纯化得到3个多糖级分GLMP1、GLMP2和GLMP3,HPSEC检测其峰面积百分比分别为93.58%,97.64%,99.19%,单糖组成分析结果表明GLMP1、GLMP2和GLMP3均含有甘露糖、鼠李糖、半乳糖醛酸、葡萄糖、半乳糖、木糖、阿拉伯糖和岩藻糖,但单糖摩尔比各异。SEC—MALLS测试GLMP1、GLMP2和GLMP3的Mw分别为4.526×105,4.603×104,3.760×103 g/mol,3个多糖级分构象可能均为高度紧缩且具有分支结构的聚合物。 相似文献
92.
93.
The main aim of this work is dual computer analysis of probabilistic coefficients for the homogenized tensor of the polymer filled with the rubber particles having randomized Poisson ratios of both constituents. The major issue is to verify an influence of a randomness in rubber Poisson ratio close to the compressibility limit on the uncertainty of the effective tensor probabilistic characteristics. Probabilistic analysis presented here is carried out using mainly the stochastic perturbation technique provided by the common application of the traditional FEM commercial code ABAQUS and the symbolic computations package MAPLE. This FEM-based technique employs polynomial response function of the optimum order recovered from the weighted least squares method and following a set of deterministic solutions obtained for various values of the randomized input parameter. Optimization procedure is released entirely into a symbolic environment, where maximization of the correlation factor together with minimization of the fitting variance and approximation error are applied. Homogenization technique consists in equating of deformation energies for the real composite and the artificial one characterized by the effective elasticity tensor with uncertainty. 相似文献
94.
In this study, further analysis of the osmotic drying process was conducted to identify the optimum combination of parameters for drying rectangular alumina-gelatin beams. This study was designed to determine the effect of three variables related to the osmotic drying process (osmotic pressure, molecular weight, and immersion time) on the interaction between the liquid desiccant and the submerged alumina-gelatin samples. The water loss from the alumina-gelatin samples was positively correlated with the molecular weight, osmotic pressure, and immersion time. Up to 40% by weight of the initial water content was removed during the osmotic drying process. The samples also experienced solids gain due to the counterflow of solute from the liquid desiccant. The least amount of solids gain resulted from drying for the shortest immersion time at low osmotic pressure and high molecular weight. Evidence of possible interactions between variables was noted for the sintered density metric. Statistical methods were used to form regression equations for the measured responses (water loss, solids gain, bulk density). A verification experiment was conducted to compare the experimental outcomes to the predicted outcomes. The responses were simultaneously optimized to identify the combination of variable settings required to meet specified goals. In order to maximize water loss, minimize solids gain, and maximize bulk density, the ceramic-gelatin object should be immersed for approximately 60?min in an aqueous solution of 100,000?g/mol poly(ethylene oxide) at an osmotic pressure of 2.50?MPa. These values are valid for the range of parameter settings tested and the sample fabrication and drying methods used. 相似文献
95.
96.
The lead-free piezoelectric ceramics (Na.47Bi.47Ba.06)1-xCaxTiO3 (x?=?0, 0.01, 0.02, 0.03, 0.05, and 0.08, abbreviated as BNBTC/0, BNBTC/1, BNBTC/2, BNBTC/3, BNBTC/5, and BNBTC/8, respectively) were obtained using the solid-state reaction method. The structure, electric conductivity, and dielectric, ferroelectric, and piezoelectric properties of the Ca2+-doped (Na.47Bi.47Ba.06)TiO3 ceramics were thoroughly investigated. The ceramics sintered at 1200?°C exhibit dense microstructures, having relative densities higher than 96%. The X-ray diffraction results demonstrate that all ceramics have a pure perovskite structure. The mean grain sizes of the ceramics are related to the Ca2+ quantity. A small quantity of Ca2+ ions (x?≤?0.03) improves the piezoelectric and ferroelectric properties of the samples. The dielectric behavior of the samples is sensitive to the Ca2+ content and electric poling. The results demonstrate that the electrical properties of the (Na.47Bi.47Ba.06)TiO3 lead-free ceramics can be well tuned by varying the Ca2+ quantity. 相似文献
97.
O.N. Kondrateva G.E. Nikiforova A.V. Tyurin M.A. Ryumin V.M. Gurevich A.P. Kritskaya K.S. Gavrichev 《Ceramics International》2018,44(15):18103-18107
The heat capacity of ytterbium orthovanadate was first measured by adiabatic calorimetry in the temperature range T?=?12.28–344.06?K. No obvious anomalies were observed on the curve obtained. The values of standard thermodynamic functions in the temperature range T?=?0–400 K were calculated. Based on low-temperature calorimetry data obtained, previously published data on the high-temperature heat capacity of ytterbium orthovanadate were corrected. The anomalous contribution to heat capacity for YbVO4 was compared with the data known for YbPO4. 相似文献
98.
Amer Ibrahim Al-Omari Ibrahim M. Almanjahie Amal S. Hassan Heba F. Nagy 《计算机、材料和连续体(英文)》2020,64(2):835-857
In reliability analysis, the stress-strength model is often used to describe the life of
a component which has a random strength (X) and is subjected to a random stress (Y). In this
paper, we considered the problem of estimating the reliability R=P [Y<X] when the
distributions of both stress and strength are independent and follow exponentiated Pareto
distribution. The maximum likelihood estimator of the stress strength reliability is calculated
under simple random sample, ranked set sampling and median ranked set sampling methods.
Four different reliability estimators under median ranked set sampling are derived. Two
estimators are obtained when both strength and stress have an odd or an even set size. The
two other estimators are obtained when the strength has an odd size and the stress has an
even set size and vice versa. The performances of the suggested estimators are compared
with their competitors under simple random sample via a simulation study. The simulation
study revealed that the stress strength reliability estimates based on ranked set sampling and
median ranked set sampling are more efficient than their competitors via simple random
sample. In general, the stress strength reliability estimates based on median ranked set
sampling are smaller than the corresponding estimates under ranked set sampling and simple
random sample methods. 相似文献
99.
Self-healing is a smart and promising way to make materials more reliable and longer lasting. In the case of structural or functional composites based on a polymer matrix, very often mechanical damage in the polymer matrix or debonding at the matrix–filler interface is responsible for the decrease in intended properties. This review describes the healing behavior in structural and functional polymer composites with a so-called intrinsically self-healing polymer as the continuous matrix. A clear similarity in the healing of structural and functional properties is demonstrated which can ultimately lead to the design of polymer composites that autonomously restore multiple properties using the same self-healing mechanism. 相似文献
100.