全文获取类型
收费全文 | 70050篇 |
免费 | 6965篇 |
国内免费 | 6022篇 |
专业分类
电工技术 | 6569篇 |
技术理论 | 1篇 |
综合类 | 6668篇 |
化学工业 | 8129篇 |
金属工艺 | 13967篇 |
机械仪表 | 5037篇 |
建筑科学 | 5475篇 |
矿业工程 | 2450篇 |
能源动力 | 2105篇 |
轻工业 | 2407篇 |
水利工程 | 1858篇 |
石油天然气 | 6367篇 |
武器工业 | 1052篇 |
无线电 | 4252篇 |
一般工业技术 | 6984篇 |
冶金工业 | 2757篇 |
原子能技术 | 889篇 |
自动化技术 | 6070篇 |
出版年
2024年 | 160篇 |
2023年 | 928篇 |
2022年 | 1800篇 |
2021年 | 2161篇 |
2020年 | 2289篇 |
2019年 | 2019篇 |
2018年 | 1786篇 |
2017年 | 2581篇 |
2016年 | 2637篇 |
2015年 | 2691篇 |
2014年 | 3972篇 |
2013年 | 4075篇 |
2012年 | 4835篇 |
2011年 | 5521篇 |
2010年 | 4227篇 |
2009年 | 4553篇 |
2008年 | 3906篇 |
2007年 | 5042篇 |
2006年 | 4626篇 |
2005年 | 3754篇 |
2004年 | 3324篇 |
2003年 | 2864篇 |
2002年 | 2332篇 |
2001年 | 1941篇 |
2000年 | 1671篇 |
1999年 | 1325篇 |
1998年 | 1004篇 |
1997年 | 946篇 |
1996年 | 756篇 |
1995年 | 726篇 |
1994年 | 596篇 |
1993年 | 400篇 |
1992年 | 385篇 |
1991年 | 272篇 |
1990年 | 209篇 |
1989年 | 187篇 |
1988年 | 124篇 |
1987年 | 62篇 |
1986年 | 51篇 |
1985年 | 22篇 |
1984年 | 49篇 |
1983年 | 23篇 |
1982年 | 32篇 |
1981年 | 35篇 |
1980年 | 35篇 |
1979年 | 34篇 |
1978年 | 20篇 |
1977年 | 13篇 |
1959年 | 16篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
《Advanced Powder Technology》2020,31(1):287-299
The parameters governing the crystallisation of paracetamol using various conventional techniques has been extensively studied, however the factors influencing the drug crystallisation using spray drying is not as well understood. The aim of this work was to investigate the crystallisation of an active pharmaceutical ingredient through evaporative crystallisation using a spray dryer to study the physicochemical properties of the drug and to use semi-empirical equations to gain insight into the morphology and particle size of the dried powder. Paracetamol solutions were spray dried at various inlet temperatures ranging from 60 °C to 120 °C and also from a series of inlet feed solvent compositions ranging from 50/50% v/v ethanol/water to 100% ethanol and solid-state characterisation was done. The size and morphology of the dried materials were altered with a change in spray drying parameters, with an increase in inlet temperature leading to an increase in particle Sauter mean diameter (from 3.0 to 4.4 µm) and a decrease in the particle size with an increase in ethanol concentration in the feed (from 4.6 to 4.4 µm) as a result of changes in particle density and atomised droplet size. The morphology of the dried particles consisted of agglomerates of individual crystallites bound together into larger semi-spherical agglomerates with a higher tendency for particles having crystalline ridges to form at higher ethanol concentrations of the feed. 相似文献
64.
65.
金属基弥散燃料元件在特殊工况下会发生表面起泡失效。燃料颗粒开裂是金属基体开裂的前提条件,只有当金属基体开裂后元件才会发生表面起泡。燃料颗粒开裂后,裂纹宽度和塑性区长度等裂纹特征决定了金属基体开裂行为。基于弹塑性断裂力学和应力平衡条件,建立了基于弥散燃料颗粒开裂的金属基体裂纹特征模型。计算结果表明:裂纹张开位移随退火温度和燃耗深度的升高而增加;裂纹尖端塑性区长度主要与退火温度相关。裂纹张开位移和塑性区长度的计算结果与实验数据均符合较好,验证了金属基体裂纹特征模型的有效性。 相似文献
66.
Ali Maghami Dominik Schillinger 《International journal for numerical methods in engineering》2020,121(5):967-989
We explore a truncation error criterion to steer adaptive step length refinement and coarsening in incremental-iterative path following procedures, applied to problems in large-deformation structural mechanics. Elaborating on ideas proposed by Bergan and collaborators in the 1970s, we first describe an easily computable scalar stiffness parameter whose sign and rate of change provide reliable information on the local behavior and complexity of the equilibrium path. We then derive a simple scaling law that adaptively adjusts the length of the next step based on the rate of change of the stiffness parameter at previous points on the path. We show that this scaling is equivalent to keeping a local truncation error constant in each step. We demonstrate with numerical examples that our adaptive method follows a path with a significantly reduced number of points compared to an analysis with uniform step length of the same fidelity level. A comparison with Abaqus illustrates that the truncation error criterion effectively concentrates points around the smallest-scale features of the path, which is generally not possible with automatic incrementation solely based on local convergence properties. 相似文献
67.
ABSTRACTLearning parameters of a probabilistic model is a necessary step in machine learning tasks. We present a method to improve learning from small datasets by using monotonicity conditions. Monotonicity simplifies the learning and it is often required by users. We present an algorithm for Bayesian Networks parameter learning. The algorithm and monotonicity conditions are described, and it is shown that with the monotonicity conditions we can better fit underlying data. Our algorithm is tested on artificial and empiric datasets. We use different methods satisfying monotonicity conditions: the proposed gradient descent, isotonic regression EM, and non-linear optimization. We also provide results of unrestricted EM and gradient descent methods. Learned models are compared with respect to their ability to fit data in terms of log-likelihood and their fit of parameters of the generating model. Our proposed method outperforms other methods for small sets, and provides better or comparable results for larger sets. 相似文献
68.
随着建筑业技术进步和转型升级,高职建筑工程技术专业建设应顺应新时代要求,产教融合,办出特色。本文提出了“四个对接一个融合”的特色专业建设新思考。 相似文献
69.
本文以喷淋液滴在空气环境下运动特性为工程背景,建立单个液滴在常温、常压空气环境中的动量方程,分析液滴沉降特性、追赶特性及运动轨迹行为。计算结果表明,不同喷淋液滴初始条件下,短时间内存在重力大于曳力和重力小于曳力两种情况,但最终减速液滴均会达到受力平衡状态;液滴离开喷淋头后,垂向位移均迅速增大,液滴粒径越大、初始速度越大,垂向位移增长的速率也越大,达到相同位移的用时越短;液滴尺寸、初始速度相差越大,液滴追赶所用的时间越短,追赶位移越小,液滴尺寸、初始速度越接近,液滴追赶所用的时间越长,追赶位移越大;液滴初始速度越大、初始直径越大、喷射角度越大,横向速度消失越慢,达到的横向位移越大,喷射液滴覆盖的面积也越大。计算结果有助于优化工程实际中喷淋系统的设计与布置。 相似文献
70.
P. Matzke J. Strassmann G. Andersohn M. Oechsner 《Materialwissenschaft und Werkstofftechnik》2019,50(12):1598-1606
A sophisticated thermal management is one of the main subsystems that enables combustion engines with high power density. In this context the demands on coolants are also increasing. There has to be a certain level of corrosion protection to ensure the functionality of the cooling system. Hereafter the result of an electrochemical sensor development is presented. With the knowledge of analytical and electrochemical results a quick test for characterizing coolants corrosion protection has been developed and validated. 相似文献