全文获取类型
收费全文 | 25743篇 |
免费 | 2299篇 |
国内免费 | 1120篇 |
学科分类
工业技术 | 29162篇 |
出版年
2024年 | 55篇 |
2023年 | 440篇 |
2022年 | 714篇 |
2021年 | 1062篇 |
2020年 | 819篇 |
2019年 | 621篇 |
2018年 | 734篇 |
2017年 | 836篇 |
2016年 | 707篇 |
2015年 | 983篇 |
2014年 | 1184篇 |
2013年 | 1475篇 |
2012年 | 1533篇 |
2011年 | 1757篇 |
2010年 | 1480篇 |
2009年 | 1373篇 |
2008年 | 1426篇 |
2007年 | 1268篇 |
2006年 | 1422篇 |
2005年 | 1335篇 |
2004年 | 869篇 |
2003年 | 798篇 |
2002年 | 805篇 |
2001年 | 679篇 |
2000年 | 663篇 |
1999年 | 815篇 |
1998年 | 603篇 |
1997年 | 559篇 |
1996年 | 446篇 |
1995年 | 374篇 |
1994年 | 333篇 |
1993年 | 217篇 |
1992年 | 199篇 |
1991年 | 145篇 |
1990年 | 117篇 |
1989年 | 94篇 |
1988年 | 80篇 |
1987年 | 38篇 |
1986年 | 26篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
61.
为保障同阶段崩落法转充填法开采顺利过渡,过渡段处须设置竖向隔离间柱。以大冶铁矿龙洞采区-170 m同阶段崩落法转充填法梯形隔离间柱为研究对象,将其简化为变惯性矩固支梁,并以间柱的水平应
变量允许值为判据,初步确定梯形隔离间柱上端的初始宽度。以梯形隔离间柱上端的初始宽度为基础,采用数值模拟方法,计算了不同梯形隔离间柱上端宽度与不同充填体灰砂比协同作用下的充填采场顶板围岩沉降
量,并对不同灰砂比下梯形隔离间柱上端宽度与顶板围岩最大沉降量进行了数据拟合,由顶板围岩允许沉降值得到与不同充填体灰砂比协同匹配下的梯形隔离间柱上端的合理宽度。数值计算结果表明:与充填体灰砂
比分别为1∶4、1∶6、1∶8、1∶10、1∶12协同匹配的梯形隔离间柱上端合理宽度分别为16、19、21、25、29 m。研究成果可为合理确定矿山同阶段崩落法转充填法开采过渡段隔离间柱宽度提供参考。 相似文献
62.
63.
北京山区推理公式是北京地区无资料山区小流域设计洪水计算的基本方法之一.结合北京山区原推理公式与改进后推理公式存在问题,分析了利用推理公式计算山区小流域设计洪水的适用性和可靠性,并提出相关使用建议.针对当前推理公式方法计算设计洪峰流量与洪水过程线计算中采用的降雨和径流资料不一致问题,提出将山区推理公式与瞬时单位线方法组合应用,解决无资料小流域设计洪水过程线计算的基本思路和方法.研究表明,该方法理论上可行,方法更为合理,建议推广使用. 相似文献
64.
Lingguo Kong Liangyuan Li Guowei Cai Chuang Liu Ping Ma Yudong Bian Tao Ma 《International Journal of Hydrogen Energy》2021,46(3):2847-2861
With the increasing proportion of renewable energy (mainly wind power and photovoltaic) connected to the grid, the fluctuation of renewable energy power brings great challenges to the safe and reliable operation of power grid. As a clean, low-carbon secondary energy, hydrogen energy is applied in renewable energy (mainly wind power and photovoltaic) grid-connected power smoothing, which opens up a new way of coupling hydrogen storage energy with renewable energy. This paper focuses on the optimization of capacity of electrolyzers and fuel cells and the analysis of system economy in the process of power output smoothing of wind/photovoltaic coupled hydrogen energy grid-connected system. Based on the complementary characteristics of particle swarm optimization (PSO) and chemical reaction optimization algorithm (CROA), a particle swarm optimization-chemical reaction optimization algorithm (PSO-CROA) are proposed. Aiming at maximizing system profit, the capacity of electrolyzers and fuel cells are constrained by wind power fluctuation, and considering environmental benefits, government subsidies and time value of funds, the objective function and its constraints are established. According to the simulation analysis, by comparing the calculated results with PSO and CROA, it shows that PSO-CROA effectively evaluates the economy of the system, and optimizes the optimal capacity of the electrolyzers and fuel cells. The conclusion of this paper is of great significance for the application of hydrogen energy storage in the evaluation of power smoothness and economy of renewable energy grid connection and the calculation of economic allocation of hydrogen energy storage capacity. 相似文献
65.
66.
Junjie Yi Meiqi Li Meilian Yang Shengbao Cai Tianrui Zhao Jianxin Cao Guiguang Cheng 《International Journal of Food Science & Technology》2021,56(2):974-987
Fermentation has been historically applied to reduce bamboo shoot (BS) toxicity. However, the underlying degradation pathway of the toxic compounds remains unknown. In this work, the cytotoxicity of BS against the BRL-3A cells was evaluated, and the changes in chemical constituents were determined to reveal the influence of fermentation on BS. The in vitro toxic evaluation revealed fermentation time was crucial in decreasing the toxicity. The main compounds in fresh and fermented were qualitatively and quantitatively determined and were further targeted isolated and identified. A mathematical model to describe the change rate as a function of fermentation time was formulated. Dynamic profiling revealed that taxiphyllin 1 , p-hydroxybenzaldehyde 2 and methyl-p-hydroxybenzoate 3 decreased and transformed into intermediate compounds (p-hydroxybenzoic acid 4 and p-hydroxybenzyl alcohol 5 ), finally converting into p-hydroxytoluene 6 during fermentation. The results provided basis on the chemical components for practical fermentation and the quality control of BS products. 相似文献
67.
68.
Chin Tat-Jun Cai Zhipeng Neumann Frank 《International Journal of Computer Vision》2020,128(3):575-587
International Journal of Computer Vision - Robust model fitting plays a vital role in computer vision, and research into algorithms for robust fitting continues to be active. Arguably the most... 相似文献
70.