全文获取类型
收费全文 | 143665篇 |
免费 | 16189篇 |
国内免费 | 6669篇 |
专业分类
电工技术 | 53391篇 |
技术理论 | 7篇 |
综合类 | 11405篇 |
化学工业 | 11622篇 |
金属工艺 | 3501篇 |
机械仪表 | 5844篇 |
建筑科学 | 8563篇 |
矿业工程 | 4055篇 |
能源动力 | 11554篇 |
轻工业 | 4065篇 |
水利工程 | 4060篇 |
石油天然气 | 3290篇 |
武器工业 | 907篇 |
无线电 | 15236篇 |
一般工业技术 | 6084篇 |
冶金工业 | 5913篇 |
原子能技术 | 3041篇 |
自动化技术 | 13985篇 |
出版年
2024年 | 571篇 |
2023年 | 1798篇 |
2022年 | 3493篇 |
2021年 | 4173篇 |
2020年 | 4486篇 |
2019年 | 3712篇 |
2018年 | 3362篇 |
2017年 | 4541篇 |
2016年 | 5049篇 |
2015年 | 5531篇 |
2014年 | 9634篇 |
2013年 | 8249篇 |
2012年 | 11085篇 |
2011年 | 11848篇 |
2010年 | 8847篇 |
2009年 | 9037篇 |
2008年 | 8602篇 |
2007年 | 10421篇 |
2006年 | 9369篇 |
2005年 | 7655篇 |
2004年 | 6406篇 |
2003年 | 5436篇 |
2002年 | 4328篇 |
2001年 | 3726篇 |
2000年 | 3221篇 |
1999年 | 2369篇 |
1998年 | 1624篇 |
1997年 | 1385篇 |
1996年 | 1265篇 |
1995年 | 1074篇 |
1994年 | 890篇 |
1993年 | 612篇 |
1992年 | 570篇 |
1991年 | 370篇 |
1990年 | 294篇 |
1989年 | 287篇 |
1988年 | 187篇 |
1987年 | 125篇 |
1986年 | 109篇 |
1985年 | 135篇 |
1984年 | 120篇 |
1983年 | 111篇 |
1982年 | 78篇 |
1981年 | 71篇 |
1980年 | 44篇 |
1979年 | 36篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1976年 | 15篇 |
1959年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
New experimental results on pressure loss for the single and two‐phase gas‐liquid flow with non‐Newtonian liquids in helical coils are reported. For a constant value of the curvature ratio, the value of the helix angle of the coils is varied from 2.56° to 9.37°. For single phase flow, the effect of helix angle on pressure loss is found to be negligible in laminar flow regime but pressure loss increases with the increasing value of helix angle in turbulent flow conditions. On the other hand, for the two‐phase flow, the well‐known Lockhart‐Martinelli method correlates the present results for all values of helix angle (2.56‐9.37°) satisfactorily under turbulent/laminar and turbulent/turbulent conditions over the following ranges of variables as: 0.57 ≤ n′ ≤ 1; Re′ < 4000; Rel < 4000; Reg < 8000; 8 ≤ x ≤ 1000 and 0.2 ≤ De′ ≤ 1000. 相似文献
992.
建立了甲苯、二甲苯、环己烷催化燃烧反应器的一维拟均相数学模型 ,在MnCuOx/Al2 O3 催化剂上催化燃烧反应动力学采用Langmuir双曲型动力学方程。模拟计算了废气处理量、废气中有机化合物的浓度、床层入口温度对净化率的影响 相似文献
993.
994.
以某电厂翻车机室为研究对象, 针对其深基坑降水降深大, 工期紧等特点, 主要介绍了该工程的工程地质及水
文地质条件, 并且运用管井和轻型真空井点组合降水的方法, 设计了基坑降水处理的施工方案, 确定了降水的各个
参数。实践证明, 管井和轻型真空井点组合应用效果良好, 有效保证了工程的顺利进行, 加快了工程进度, 缩短了工
期。结合实例提出了降水过程中应注意的问题及应对措施。 相似文献
995.
观音岩水电站装机容量 3 000 M W, 为一等大( ? ) 型工程。厂房坝段设置 5条横缝, 分为 6 个坝段。通过接缝
灌浆, 极大的改善厂房坝段受力条件, 提高大坝结构整体性和耐久性。结合观音岩水电站现场施工条件, 从施工角
度论述了接缝灌浆的施工工艺以及施工过程中可能存在的问题及处理方法。 相似文献
996.
以己二异氰酸酯(HDI)改性聚酯树脂与氨基树脂配制成家电用卷材涂料。阐述了氨酯键对涂膜性能的贡献。探讨了HDI用量对涂膜性能的影响。 相似文献
997.
998.
A stochastic control scheme is developed for scalar, discrete-time, and linear-dynamic systems driven by Cauchy distributed process and measurement noises. When addressing the optimal control problem for such systems, the standard quadratic cost criteria cannot be used. In this study we introduce a new objective function that is functionally similar to the Cauchy probability density function. The performance index, defined as the expectation of this objective function with respect to the Cauchy densities, exists. The dynamic programming solution to the fixed and finite horizon optimal control problem that uses this performance index appears to be intractable. Therefore, a moving horizon optimal model predictive control problem is implemented, for which the conditional expected value of the objective function and its gradients can be computed in closed form and without assumptions such as certainty equivalence. Numerical results are shown for this m-step model predictive optimal controller and compared to a similar, Linear-Exponential-Gaussian model predictive controller. An essential difference between the Cauchy and Gaussian controllers when applied to a system with Cauchy noises is that, while the Gaussian controller is linear and reacts strongly to all noise pulses, the Cauchy controller can differentiate between measurement and process noise pulses by ignoring the former while responding to the latter. This property of the Cauchy controller occurs when an impulsive measurement noise is more likely than an impulsive process noise. The Cauchy and Gaussian controllers react similarly when applied to a system with Gaussian noises, demonstrating the robustness of the proposed control scheme. 相似文献
999.
Quantifying Whitewater Recreation Opportunities in Cataract Canyon of the Colorado River,Utah: Aggregating Acceptable Flows and Hydrologic Data to Identify Boatable Days
下载免费PDF全文
![点击此处可从《河流研究与利用》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The structural norm approach was combined with the Potential for Conflict Index to define recreation streamflow needs for the Colorado River in Utah and Colorado. An online survey was completed by 128 commercial and non‐commercial boaters, who evaluated a range of flows for whitewater boating. For the Cataract Canyon reach, respondents rated the quality of their recreation experience of specific flows, describing the quality of boating opportunities across the full range of historical streamflows. Ranges for both acceptable and optimum flows were defined, as well as thresholds for unacceptable flows. These ranges were then evaluated against historical hydrologic records to quantify the timing, frequency, and duration of days when defined whitewater flows exist across different year types (i.e. average boatable days). Results indicated that on average, a total of 257 boatable days existed in dry years, and 353 total boatable days occurred in dry‐typical years. In wet and wet‐typical years, 362 and 365 total boatable days respectively, occurred on average. Results of the boatable days' analysis indicated that over the 23‐year period of record, whitewater boating opportunities occurred nearly every day of the year in all but the driest year types. Results from this study provide resource managers with information which can be used in the development of annual operating plans for the Colorado River Basin and help managers understand how changes in flow impact the quality of recreational opportunities. This application demonstrates the value of analysing boatable days on any river where recreation management is a priority. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
1000.
建设内陆核电是我国经济社会发展的必然需求,但由于内陆核电自然环境和社会环境的特殊性,必须更进一步考虑排放对环境和公众的安全影响,对放射性废液进行深化处理,在解控排放的基础上进一步降低排放水平。本文在内陆AP1000机组已实施的放射性废液处理系统改进的基础上,开展了放射性废液深化处理研究,通过大量实验考察了不同进水pH值、硼浓度、含盐量、水温等水质条件和不同工作压力、回收率等运行条件下反渗透装置对硼酸的去除性能和对模拟放射性核素的截留能力。结果表明,通过控制适当的工艺条件,可以去除废液中80%以上的硼酸,同时保持很好的核素去除效果,达到进一步降低排放水平的目的。研究成果可为内陆核电厂放射性废液处理系统深化处理工程应用提供有力的技术支撑,并为后续内陆核电放射性废液深化处理提供参考。 相似文献