全文获取类型
收费全文 | 183833篇 |
免费 | 17998篇 |
国内免费 | 11207篇 |
专业分类
电工技术 | 14533篇 |
技术理论 | 10篇 |
综合类 | 21739篇 |
化学工业 | 19510篇 |
金属工艺 | 6726篇 |
机械仪表 | 12019篇 |
建筑科学 | 24531篇 |
矿业工程 | 9663篇 |
能源动力 | 6139篇 |
轻工业 | 13050篇 |
水利工程 | 9807篇 |
石油天然气 | 8384篇 |
武器工业 | 2447篇 |
无线电 | 11869篇 |
一般工业技术 | 21232篇 |
冶金工业 | 6784篇 |
原子能技术 | 3271篇 |
自动化技术 | 21324篇 |
出版年
2024年 | 668篇 |
2023年 | 2132篇 |
2022年 | 4428篇 |
2021年 | 5271篇 |
2020年 | 5718篇 |
2019年 | 4789篇 |
2018年 | 4642篇 |
2017年 | 5784篇 |
2016年 | 6611篇 |
2015年 | 6872篇 |
2014年 | 11873篇 |
2013年 | 11000篇 |
2012年 | 14590篇 |
2011年 | 14615篇 |
2010年 | 11246篇 |
2009年 | 11387篇 |
2008年 | 10548篇 |
2007年 | 12989篇 |
2006年 | 11392篇 |
2005年 | 9536篇 |
2004年 | 7756篇 |
2003年 | 6690篇 |
2002年 | 5474篇 |
2001年 | 4501篇 |
2000年 | 3927篇 |
1999年 | 3400篇 |
1998年 | 2642篇 |
1997年 | 2313篇 |
1996年 | 1916篇 |
1995年 | 1723篇 |
1994年 | 1454篇 |
1993年 | 1081篇 |
1992年 | 910篇 |
1991年 | 662篇 |
1990年 | 541篇 |
1989年 | 534篇 |
1988年 | 399篇 |
1987年 | 215篇 |
1986年 | 185篇 |
1985年 | 88篇 |
1984年 | 92篇 |
1983年 | 59篇 |
1982年 | 55篇 |
1981年 | 58篇 |
1980年 | 37篇 |
1979年 | 43篇 |
1978年 | 19篇 |
1977年 | 16篇 |
1975年 | 18篇 |
1959年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
本文基于横向积分离散纵标方程,解析得到横向积分通量中出射通量与入射通量的关系,并根据类似于扩散方程节块展开法的输运节块中子平衡方程形式,得到了一种高效的节块离散纵标法数值迭代策略。数值结果表明,本文提出的方法可行且数值结果正确。此外,粗网有限差分(CMFD)加速技术在节块离散纵标法中也取得了非常好的应用效果。 相似文献
52.
53.
对射频电缆幅相稳定性进行了介绍,阐述了射频测试电缆相位和幅度变化的因素,并详细分析了射频电缆相位性能以及幅度性能的不同测试方法,最后通过实测数据的展示,总结说明了在日常测试中该如何正确使用测试电缆。 相似文献
54.
Andrés Mario Zervigón 《History of Photography》2019,43(2):130-143
For decades now, Douglas Crimp’s landmark 1980 essay ‘The Photographic Activity of Postmodernism’ has shaped our understanding of modernism’s aftermath, at least as it unfolded in North America and Western Europe. Less remembered, however, is the degree to which the procedures of disjunction, copying, appropriation, and outright theft that he highlighted were epitomised not just by contemporary photography, but by photomontage in particular. This article recovers the debates that led critics such as Crimp, Abigail Solomon-Godeau, Christopher Phillips, Benjamin Buchloh and others to turn to photomontage as one of their principal objects of concern in what became known as the postmodern critique of photography. Why was montage tasked to perform this critical function, particularly by people around the journal October who had not otherwise devoted the balance of their writing to photography’s history? The article suggests that these men and women, along with the contemporary artists they foregrounded, manifested what Mary Anne Doane has called a ‘desire for signification’, a reaction in the late 1970s against the mute theatricality of minimalist and conceptual art. Photomontage reintroduced representation to contemporary art and to the canon of art history. But unlike the reemerging illusionism in painting that also manifested this desire, montage guarded against an uncomplicated realism by highlighting and critiquing operations of representation in a manner that painting no longer could. 相似文献
55.
Mohammed Heyouni Farid Saberi-Movahed Azita Tajaddini 《Computers & Mathematics with Applications》2019,77(1):77-92
In the first part of this paper, we investigate the use of Hessenberg-based methods for solving the Sylvester matrix equation . To achieve this goal, the Sylvester form of the global generalized Hessenberg process is presented. Using this process, different methods based on a Petrov–Galerkin or on a minimal norm condition are derived. In the second part, we focus on the SGl-CMRH method which is based on the Sylvester form of the Hessenberg process with pivoting strategy combined with a minimal norm condition. In order to accelerate the SGl-CMRH method, a preconditioned framework of this method is also considered. It includes both fixed and flexible variants of the SGl-CMRH method. Moreover, the connection between the flexible preconditioned SGl-CMRH method and the fixed one is studied and some upper bounds for the residual norm are obtained. In particular, application of the obtained theoretical results is investigated for the special case of solving linear systems of equations with several right-hand sides. Finally, some numerical experiments are given in order to evaluate the effectiveness of the proposed methods. 相似文献
56.
目的:评价应用C反应蛋白(C reaction protein,CRP)和降钙素原(procalcitonin,PCT)指导高危新生儿预防性应用抗生素的效果、安全性和经济性。方法:选取2015年7月至2017年1月慈溪市妇幼保健院收治的高危新生儿124例作为研究对象,随机数表法分为对照组(62例)和实验组(62例),对照组患儿均给予预防性应用抗生素治疗,实验组根据CRP和PCT选择性应用抗生素。比较两组患儿的细菌培养阳性率、脓毒症发生率以及不良反应发生率。结果:两组患儿的CRP和PCT水平和阳性率间均不存在统计学差异(t/χ2=0.299,-0.461,0.292,0.544,0.186,P=0.766,0.646,0.589,0.461,0.666)。两组患儿治疗前后的菌培养阳性率间均不存在统计学差异(χ2=0.040,0.287,P=0.842,0.592);两组治疗后的菌培养阳性率均明显低于治疗前(χ2=47.825,40.367,P=0.000,0.000);两组患儿脓毒症的发生率分别为12.90%和14.52%,差异无统计学意义(χ2=0.068,P=0.794)。实验组的NICU治疗和住院时间、机械通气时间以及治疗费用均显著低于对照组(t=2.904,2.729,2.152,5.337,P=0.004,0.007,0.033,0.000),两组的机械通气率间无统计学差异(χ2=0.372,P=0.542)。对照组患儿不良反应发生率为19.35%,明显高于实验组的6.46%(χ2=4.593,P=0.032)。结论:应用CRP和PCT指导高危新生儿预防性应用抗生素的效果与普遍性应用相似,可以明显减少治疗时间和治疗费用,明显降低治疗相关不良反应。 相似文献
57.
The performance of surface ionic conduction single chamber fuel cell (SIC‐SCFC) prepared by the sol gel method was studied on electric characteristics due to the differences of the operating temperature and humidity, the electrode distance and electrolyte film depth, and multiple cells with the series and parallel connections. The SIC–SCFC was arranged the both anode of Pt and cathode of Au on the boehmite electrolyte. The open circuit voltage (OCV) of single cell achieved a maximum of 530mV in the dry gas mixtures of O2/H2=50% in room temperature operation, and but it became decrease as over 60%. The OCV was maintained the constant value between operating temperatures of 30°C to 80°C, and but it was decreased sharply at over 90°C because a humidity on the cell became lower as increasing operating temperature. Then, the cell property was improved to 120°C by adding to the humidity of 70% using a humidifier. The electrode distance and the electrolyte film depth of SIC‐SCFC found to be contributed to the reductions of the cell resistance and the surface roughness on the electrode, respectively. Moreover, the power property of SIC‐SCFC was significantly improved by cell stacks comprised of the series or parallel connection of a cell. 相似文献
58.
The capture of particles by charged droplets was simulated by considering the electrostatic interactions of droplet-droplet and droplet-particle. The results indicate that the electrostatic repulsion between droplets leads to a dynamic accumulation mode of particles. However, the droplet spacing has an insignificant effect on the capture efficiency when the electrostatic deposition predominates. The increase of droplet charge remarkably improves the capture efficiency, in which the capture of fine particles accounts for the largest proportion. Compared to the droplet charge, the droplet size shows a limited improvement in the capture efficiency. Reducing the droplet velocity prolongs the capture time instead of enhancing the capture capacity per unit time, thereby improving capture efficiency. 相似文献
59.
60.