全文获取类型
收费全文 | 111498篇 |
免费 | 6855篇 |
国内免费 | 7610篇 |
专业分类
电工技术 | 7634篇 |
技术理论 | 82篇 |
综合类 | 13496篇 |
化学工业 | 8480篇 |
金属工艺 | 1770篇 |
机械仪表 | 5423篇 |
建筑科学 | 27353篇 |
矿业工程 | 4626篇 |
能源动力 | 3090篇 |
轻工业 | 2630篇 |
水利工程 | 6038篇 |
石油天然气 | 2686篇 |
武器工业 | 1033篇 |
无线电 | 7725篇 |
一般工业技术 | 7426篇 |
冶金工业 | 5836篇 |
原子能技术 | 583篇 |
自动化技术 | 20052篇 |
出版年
2024年 | 176篇 |
2023年 | 1064篇 |
2022年 | 1699篇 |
2021年 | 2527篇 |
2020年 | 2686篇 |
2019年 | 1909篇 |
2018年 | 1813篇 |
2017年 | 2372篇 |
2016年 | 2961篇 |
2015年 | 3254篇 |
2014年 | 9315篇 |
2013年 | 7011篇 |
2012年 | 8155篇 |
2011年 | 8721篇 |
2010年 | 6925篇 |
2009年 | 7356篇 |
2008年 | 7313篇 |
2007年 | 8853篇 |
2006年 | 7794篇 |
2005年 | 6820篇 |
2004年 | 5942篇 |
2003年 | 4916篇 |
2002年 | 3778篇 |
2001年 | 2814篇 |
2000年 | 2260篇 |
1999年 | 1695篇 |
1998年 | 1164篇 |
1997年 | 916篇 |
1996年 | 747篇 |
1995年 | 621篇 |
1994年 | 470篇 |
1993年 | 367篇 |
1992年 | 280篇 |
1991年 | 185篇 |
1990年 | 125篇 |
1989年 | 148篇 |
1988年 | 118篇 |
1987年 | 58篇 |
1986年 | 84篇 |
1985年 | 91篇 |
1984年 | 101篇 |
1983年 | 99篇 |
1982年 | 39篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1977年 | 17篇 |
1961年 | 12篇 |
1957年 | 9篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
81.
Dr. Manuel Nieto-Domínguez Dr. Pablo I. Nikel 《Chembiochem : a European journal of chemical biology》2020,21(18):2551-2571
The diversity of life relies on a handful of chemical elements (carbon, oxygen, hydrogen, nitrogen, sulfur and phosphorus) as part of essential building blocks; some other atoms are needed to a lesser extent, but most of the remaining elements are excluded from biology. This circumstance limits the scope of biochemical reactions in extant metabolism – yet it offers a phenomenal playground for synthetic biology. Xenobiology aims to bring novel bricks to life that could be exploited for (xeno)metabolite synthesis. In particular, the assembly of novel pathways engineered to handle nonbiological elements (neometabolism) will broaden chemical space beyond the reach of natural evolution. In this review, xeno-elements that could be blended into nature's biosynthetic portfolio are discussed together with their physicochemical properties and tools and strategies to incorporate them into biochemistry. We argue that current bioproduction methods can be revolutionized by bridging xenobiology and neometabolism for the synthesis of new-to-nature molecules, such as organohalides. 相似文献
82.
Debadyuti Das 《国际生产研究杂志》2018,56(17):5776-5794
The present work is an attempt to investigate the adoption of sustainable supply chain management (SSCM) practices amongst manufacturing and process based organisations in India and its impact on organisational performance encompassing all three dimensions of sustainability. SSCM practices conceived in the present study include environmental management practices (EMP), socially inclusive practices for employees (SPE), socially inclusive practices for community (SPC), operations practices (OP) and supply chain integration (SCI) which were treated as exogenous variables. Organisational performance considered in this study includes five dimensions, namely environmental performance (EPR), employee-centred social performance (ESP), community-centred social performance (CSP), operations performance (OPR) and competitiveness, which were regarded as endogenous variables. The analysis was carried out with the help of structural equation modelling considering natural logarithm of manpower as a control variable. Few major findings are mentioned. EMP does not have any significant association with OPR, nor does it result in competitiveness. However, when jointly mediated through both EPR and OPR, EMP leads to competitiveness. SPC has significant negative association with competitiveness, when only direct relationship is considered. However, indirect relationship between SPC and competitiveness shows significant positive association when mediated through CSP. The resultant total effect between SPC and competitiveness turns out to be insignificant. Further, OPR fully mediates the relationship between OP and competitiveness. Managerial implications of the findings are discussed. 相似文献
83.
The solvent-dependent polymorphism of the active pharmaceutical ingredient (API) carbamazepine is interpreted from calculations of the solid-state and API-solvent intermolecular interactions. These simulations suggested that apolar solute-solute interactions could be disrupted by apolar solvents. In contrast, the polar solute-solute interactions were found to be easily disrupted by polar and protic solvents. This is consistent with experimental observations that the crystallization of the metastable form II is more dominant in apolar solvents. The Mercury program remains the gold standard in terms of usability; however, further expansion into more complex simulation techniques could make this package of even greater use in pharmaceutical manufacturing workflows. 相似文献
84.
C. Busuioc C.D. Ghitulica A. Stoica M. Stroescu G. Voicu V. Ionita L. Averous S.I. Jinga 《Ceramics International》2018,44(8):9433-9441
Bacterial cellulose membranes were employed as templates for calcium phosphates deposition by successive immersion in solutions of Ca(NO3)2·4H2O and (NH4)2HPO4, under ultrasonication. During the wet chemical reaction, mineral phases were loaded on bacterial cellulose fibrils, leading to precursor hybrid composites. These were subjected to a lyophilisation procedure in order to preserve the 3D porous aspect and afterwards to a thermal treatment with the aim of removing the polymeric phase and generating well crystallized structures. Different types of morphologies were achieved by varying the heating rate, as well as the calcination temperature and period. The as-prepared samples and the final ones were investigated from compositional and structural point of view through X-ray diffraction and Fourier-transform infrared spectroscopy and morphologically concerning by scanning electron microscopy. The magnetic properties were also evaluated in order to demonstrate the suitability of the obtained materials for the development of magnetic scaffolds dedicated to hard tissue applications. 相似文献
85.
筒形阀是一种新型的水轮机进水阀,它与球阀或蝴蝶阀相比较有防止机组飞逸事故扩大效果明显、减轻导叶全关时导水机构的快速破坏并减少漏水量,以及动水开启方便、所需时间短等优点,但对运行条件也有一定的要求。光照水电站是贵州省第1个拟采用筒形阀的电站,为此对装设筒形阀的可行性和必要性进行了认真的分析。 相似文献
86.
对首钢1号高炉焦炭质量恶化后增产节焦的生产经验进行了总结分析。认为提高入炉原燃料质量,综合优化高炉基本制度,合理控制稳定的操作炉型是保证炉况长期顺稳、实现效益最大化的有效手段。 相似文献
87.
由于AD HOC网络自身的特点,其网络管理很多方面与固定网络不同,如移动性管理和体系结构管理等。讨论了AD HOC网络管理的各个方面,并列举了各个方面的设计思路和已有的相关算法的简介。 相似文献
88.
基于承包商预期收益不变的不平衡报价模型 总被引:1,自引:0,他引:1
在招标实践中,通常采用最低价中标原则,使得投标人不得不压低其投标价格。基于承包商预期收益不变的不平衡报价模型,是在“工程量清单报价”的条件下,考虑到施工中工程量的变化及施工顺序的影响,体现了资金的时间价值,在保持承包商预期收益不变的前提下,通过调整各分项工程的单价,来降低工程报价,以增加中标机会而建立的。所建立的模型简单,易于操作,并配以具体的工程实例,通过计算机求得其最优解,可供承包商投标报价时参考。 相似文献
89.
90.
梁斌 《冶金标准化与质量》2006,44(6):41-43
质量管理永远是企业生命的源泉,质量管理体系是一个复杂的系统工程,企业只有不断完善质量体系,进行质量管理创新,保持质量管理体系的长期有效的进行,才能在市场竞争中保持领先。 相似文献