全文获取类型
收费全文 | 15820篇 |
免费 | 1075篇 |
国内免费 | 1290篇 |
专业分类
电工技术 | 202篇 |
技术理论 | 1篇 |
综合类 | 1104篇 |
化学工业 | 3368篇 |
金属工艺 | 1888篇 |
机械仪表 | 408篇 |
建筑科学 | 721篇 |
矿业工程 | 194篇 |
能源动力 | 455篇 |
轻工业 | 2001篇 |
水利工程 | 155篇 |
石油天然气 | 201篇 |
武器工业 | 86篇 |
无线电 | 1331篇 |
一般工业技术 | 4595篇 |
冶金工业 | 720篇 |
原子能技术 | 136篇 |
自动化技术 | 619篇 |
出版年
2024年 | 47篇 |
2023年 | 260篇 |
2022年 | 515篇 |
2021年 | 591篇 |
2020年 | 488篇 |
2019年 | 512篇 |
2018年 | 418篇 |
2017年 | 539篇 |
2016年 | 550篇 |
2015年 | 555篇 |
2014年 | 795篇 |
2013年 | 988篇 |
2012年 | 819篇 |
2011年 | 1146篇 |
2010年 | 890篇 |
2009年 | 930篇 |
2008年 | 906篇 |
2007年 | 927篇 |
2006年 | 790篇 |
2005年 | 695篇 |
2004年 | 664篇 |
2003年 | 519篇 |
2002年 | 475篇 |
2001年 | 382篇 |
2000年 | 381篇 |
1999年 | 284篇 |
1998年 | 299篇 |
1997年 | 249篇 |
1996年 | 212篇 |
1995年 | 171篇 |
1994年 | 153篇 |
1993年 | 128篇 |
1992年 | 147篇 |
1991年 | 139篇 |
1990年 | 128篇 |
1989年 | 84篇 |
1988年 | 71篇 |
1987年 | 38篇 |
1986年 | 39篇 |
1985年 | 47篇 |
1984年 | 59篇 |
1983年 | 31篇 |
1982年 | 25篇 |
1981年 | 20篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1977年 | 13篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
根据灵丘县2014年4月下旬到9月下旬的气象观测资料和玉米获得高产所需的农业气象条件,对灵丘县春玉米生育期的气象条件进行了综合分析,得出2014-04—09的综合气象条件能满足春玉米生长发育的需求。其中,有3个时段的气象条件与春玉米生育阶段的需求不吻合,即5月上旬出现冷害、7月中下旬降水偏少、9月出现阶段性低温和阴雨寡照天气,这些不利气象条件都会对春玉米的发育造成不同程度的影响。 相似文献
42.
43.
In an organization operating in the bancassurance sector we identified a low-risk IT subportfolio of 84 IT projects comprising together 16,500 function points, each project varying in size and duration, for which we were able to quantify its requirements volatility. This representative portfolio stems from a much larger portfolio of IT projects. We calculated the volatility from the function point countings that were available to us. These figures were aggregated into a requirements volatility benchmark. We found that maximum requirements volatility rates depend on size and duration, which refutes currently known industrial averages. For instance, a monthly growth rate of 5% is considered a critical failure factor, but in our low-risk portfolio we found more than 21% of successful projects with a volatility larger than 5%. We proposed a mathematical model taking size and duration into account that provides a maximum healthy volatility rate that is more in line with the reality of low-risk IT portfolios. Based on the model, we proposed a tolerance factor expressing the maximal volatility tolerance for a project or portfolio. For a low-risk portfolio its empirically found tolerance is apparently acceptable, and values exceeding this tolerance are used to trigger IT decision makers. We derived two volatility ratios from this model, the π-ratio and the ρ-ratio. These ratios express how close the volatility of a project has approached the danger zone when requirements volatility reaches a critical failure rate. The volatility data of a governmental IT portfolio were juxtaposed to our bancassurance benchmark, immediately exposing a problematic project, which was corroborated by its actual failure. When function points are less common, e.g. in the embedded industry, we used daily source code size measures and illustrated how to govern the volatility of a software product line of a hardware manufacturer. With the three real-world portfolios we illustrated that our results serve the purpose of an early warning system for projects that are bound to fail due to excessive volatility. Moreover, we developed essential requirements volatility metrics that belong on an IT governance dashboard and presented such a volatility dashboard. 相似文献
44.
随机非线性系统的输出反馈控制 总被引:2,自引:0,他引:2
针对满足线性增长条件的一类随机非线性系统, 本文研究了输出反馈镇定问题. 然而不同于现有的所有文献, 由于线性增长条件中含有不可量测的状态, 引入了一个待定的高增益观测器. 利用反推设计技术, 构造性地给出了一个输出反馈控制器的设计, 通过适当地选取高增益参数, 保证了闭环系统的零解是概率意义下全局渐近稳定的, 输出几乎处处调节于零. 相似文献
45.
46.
This paper examines the dynamics of entrepreneurial acquisitions undertaken by UK high growth small and medium enterprises (SMEs). While entrepreneurial acquisitions are increasingly deployed by SMEs, little is known about their antecedents, motivational drivers and organisational outcomes. Drawing on detailed case study evidence from Scotland, the key factor found to be driving these acquisitions was the desire to augment and exploit technological complementarities between the acquiring and acquired firms. Acquisition can therefore be conceptualised as an advanced stage of the outside-in ‘open innovation’ strategies proactively used within these innovative SMEs. Firms executing this strategy typically have an acute propensity for risk, a desire for close customer engagement, effective business models and strong external orientation. The work suggests that greater attention should be paid within M&A theory to the dynamics of these types of smaller scale entrepreneurial acquisitions. 相似文献
47.
Ke Wang Baodan Liu Jing Li Xiaoyuan Liu Yang Zhou Xinglai Zhang Xiaoguo Bi Xin Jiang 《材料科学技术学报》2019,35(4):615-622
TiO_2 nanostructures with strong interfacial adhesion and diverse morphologies have been in-situ grown on Ti foil substrate through a multiple-step method based on conventional plasma electrolytic oxidation(PEO) technology, hydrothermal reaction and ion exchange process. The PEO process is critical to the formation of TiO_2 seeding layer for the nucleation of Na_2Ti_3O_7 and H_2Ti_3O_7 mediates that are strongly attached to the Ti foil. An ion exchange reaction can finally lead to the formation of H_2Ti_3O_7 nanostructures with diverse morphologies and the calcination process can turn the H_2Ti_3O_7 nanostructures into TiO_2 nanostructures with enhanced crystallinity. The morphology of the TiO_2 nanostructures including nanoparticles(NP), nanowhiskers(NWK), nanowires(NW) and nanosheets(NS) can be easily tailored by controlling the NaOH concentration and reaction time during hydrothermal process. The morphology, composition and optical properties of TiO_2 photocatalysts were analyzed using scanning electron microscope(SEM), X-ray diffraction(XRD), photoluminescence(PL) spectroscopy and UV–vis absorption spectrum. Photocatalytic tests indicate that the TiO_2 nanosheets calcined at 500?C show good crystallization and the best capability of decomposing organic pollutants. The decoration of Ag cocatalyst can further improve the photocatalytic performance of the TiO_2 nanosheets as a result of the enhanced charger separation efficiency. Cyclic photocatalytic test using TiO_2 nanostructures grown on Ti foil substrate demonstrates the superior stability in the photodegradation of organic pollutant, suggesting the promising potential of in-situ growth technology for industrial application. 相似文献
48.
本文在对数据挖掘相关技术、关联规则挖掘算法进行深入研究的基础上,归纳总结了基于粗糙集理论的关联规则挖掘模型和属性约简算法,并将其应用于高校教师的成长中。 相似文献
49.
针对海洋食品对虾生产加工的特点,设计与开发了对虾生产加工中微生物生长智能通用预测平台,为海洋食品的安全生产与加工提供分析手段。 相似文献
50.