全文获取类型
收费全文 | 126152篇 |
免费 | 23232篇 |
国内免费 | 5512篇 |
专业分类
电工技术 | 8132篇 |
技术理论 | 5篇 |
综合类 | 7298篇 |
化学工业 | 29593篇 |
金属工艺 | 5507篇 |
机械仪表 | 6862篇 |
建筑科学 | 9878篇 |
矿业工程 | 2441篇 |
能源动力 | 3389篇 |
轻工业 | 13820篇 |
水利工程 | 2298篇 |
石油天然气 | 4010篇 |
武器工业 | 928篇 |
无线电 | 17610篇 |
一般工业技术 | 20760篇 |
冶金工业 | 3717篇 |
原子能技术 | 1225篇 |
自动化技术 | 17423篇 |
出版年
2024年 | 419篇 |
2023年 | 1533篇 |
2022年 | 3023篇 |
2021年 | 4521篇 |
2020年 | 4489篇 |
2019年 | 5434篇 |
2018年 | 5489篇 |
2017年 | 6179篇 |
2016年 | 6415篇 |
2015年 | 7530篇 |
2014年 | 8473篇 |
2013年 | 10318篇 |
2012年 | 9202篇 |
2011年 | 9163篇 |
2010年 | 8838篇 |
2009年 | 8546篇 |
2008年 | 8009篇 |
2007年 | 7336篇 |
2006年 | 6822篇 |
2005年 | 5589篇 |
2004年 | 4272篇 |
2003年 | 3919篇 |
2002年 | 4148篇 |
2001年 | 3699篇 |
2000年 | 3118篇 |
1999年 | 2129篇 |
1998年 | 1162篇 |
1997年 | 1033篇 |
1996年 | 910篇 |
1995年 | 725篇 |
1994年 | 591篇 |
1993年 | 406篇 |
1992年 | 333篇 |
1991年 | 240篇 |
1990年 | 175篇 |
1989年 | 157篇 |
1988年 | 118篇 |
1987年 | 87篇 |
1986年 | 49篇 |
1985年 | 43篇 |
1984年 | 26篇 |
1983年 | 18篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 25篇 |
1979年 | 16篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
81.
从老旧建筑结构现状展开论述,详细阐述了砌体墙加固设计、构造柱与圈梁加固设计、基础结构加固设计这几种老旧建筑结构改造加固设计,实现了对建筑结构改造工程施工技术的深入分析,希望能够为城乡建设事业的发展提供助力。 相似文献
82.
Tong Le Fan Ronggui Yang Shuangchun Zhang Qiushi Pan Yi 《Chemistry and Technology of Fuels and Oils》2022,57(6):991-999
Chemistry and Technology of Fuels and Oils - Application of water flooding technologies in the oilfield causes intensive heterogeneity of the oil reservoir and improper circulation of the injected... 相似文献
83.
This paper considers the state‐dependent interference relay channel (SIRC) in which one of the two users may operate as a secondary user and the relay has a noncausal access to the signals from both users. For discrete memoryless SIRC, we first establish the achievable rate region by carefully merging Han‐Kobayashi rate splitting encoding technique, superposition encoding, and Gelfand‐Pinsker encoding technique. Then, based on the achievable rate region that we derive, the capacity of the SIRC is established in many different scenarios including (a) the weak interference regime, (b) the strong interference regime, and (c) the very strong interference regime. This means that our capacity results contain all available known results in the literature. Next, the achievable rate region and the associated capacity results are also evaluated in the case of additive Gaussian noise. Additionally, many numerical examples are investigated to show the value of our theoretical derivations. 相似文献
84.
D.R. Santos‐Peñate C.M. Campos‐Rodríguez J.A. Moreno‐Pérez 《International Transactions in Operational Research》2019,26(1):340-363
The ‐centroid problem or leader–follower problem is generalized considering different customer choice rules where a customer may use facilities belonging to different firms, if the difference in travel distance (or time) is small enough. Assuming essential goods, some particular customer choice rules are analyzed. Linear programming formulations for the generalized ‐medianoid and ‐centroid problems are presented and an exact solution approach is applied. Some computational examples are included. 相似文献
85.
When solving a mathematical problem, students who do not have sufficient conceptual understanding may perform poorly and exhibit misconceptions. This study was aimed to examine students' conceptual understanding and significant misconceptions when solving number sense‐related problems. An online three‐tier diagnostic test was administered to 125 fifth‐grade students with varied socio‐economic backgrounds in Hong Kong. Only 14.40% of the students exhibited high performance with high confidence, indicating that these students had a profound conceptual understanding of number sense. In addition, the majority of the students (66.40%) did not demonstrate number sense; these students exhibited several significant misconceptions and could solve the questions only by using a rule‐based method or guessing. Accordingly, most students performed unsatisfactorily on number sense‐related problems. This study is imperative in identifying early predictors and provides information for further compatible interventions in the teaching and learning of number sense in Hong Kong in particular and worldwide in general. 相似文献
86.
87.
Wang Hay Kan Chenxi Wei Dongchang Chen Tao Bo Bao‐Tian Wang Yan Zhang Yangchao Tian Jun‐Sik Lee Yijin Liu Guoying Chen 《Advanced functional materials》2019,29(17)
Lithium‐rich disordered rock‐salt oxides have attracted great interest owing to their promising performance as Li‐ion battery cathodes. While experimental and theoretical efforts are critical in advancing this class of materials, a fundamental understanding of key property changes upon Li extraction is largely missing. In the present study, single‐crystal synthesis of a new disordered rock‐salt cathode material, Li1.3Ta0.3Mn0.4O2 (LTMO), and its use as a model compound to investigate Li concentration–driven evolution of local cationic ordering, charge compensation, and chemical distribution are reported. Through the combined use of 2D and 3D X‐ray nanotomography, it is shown that Li removal accompanied by oxygen oxidation is correlated with the development of morphological defects such as particle cracking. Chemical heterogeneity, quantified by subparticle level distribution of Mn valence state, is minimal during Mn redox, which drastically increases upon the formation of cracks during oxygen redox. Density functional theory and bond valence sum mismatch calculations reveal the presence of local short‐range ordering in the pristine oxide, which gradually disappears along with the extraction of Li. The study suggests that with cycling the transformation into true cation–disordered state can be expected, which likely impacts the voltage profile and obtainable energy density of the oxide cathodes. 相似文献
88.
针对多角度下车辆出现一定的尺度变化和形变导致很难被准确识别的问题,提出基于多尺度双线性卷积神经网络(MS-B-CNN)的车型精细识别模型。首先,对双线性卷积神经网络(B-CNN)算法进行改进,提出MS-B-CNN算法对不同卷积层的特征进行了多尺度融合,以提高特征表达能力;此外,还采用基于中心损失函数与Softmax损失函数联合学习的策略,在Softmax损失函数基础上分别对训练集每个类别在特征空间维护一个类中心,在训练过程中新增加样本时,网络会约束样本的分类中心距离,以提高多角度情况下的车型识别的能力。实验结果显示,该车型识别模型在CompCars数据集上的正确率达到了93.63%,验证了模型在多角度情况下的准确性和鲁棒性。 相似文献
89.
Changmo Kim Izhar Livne‐Bar Karsten Gronert Jeremy M. Sivak 《Molecular nutrition & food research》2020,64(4)
Lipoxins (LXs) are autacoids, specialized proresolving lipid mediators (SPMs) acting locally in a paracrine or autocrine fashion. They belong to a complex superfamily of dietary small polyunsaturated fatty acid (PUFA)–metabolites, which direct potent cellular responses to resolve inflammation and restore tissue homeostasis. Together, these SPM activities have been intensely studied in systemic inflammation and acute injury or infection, but less is known about LX signaling and activities in the central nervous system. LXs are derived from arachidonic acid, an omega‐6 PUFA. In addition to well‐established roles in systemic inflammation resolution, they have increasingly become implicated in regulating neuroinflammatory and neurodegenerative processes. In particular, chronic inflammation plays a central role in Alzheimer's disease (AD) etiology, and dysregulated LX production and activities have been reported in a variety of AD rodent models and clinical tissue samples, yet with complex and sometimes conflicting results. In addition, reduced LX production following retinal injury has been reported recently by the authors, and an intriguing direct neuronal activity promoting survival and homeostasis in retinal and cortical neurons is demonstrated. Here, the authors review and clarify this growing literature and suggest new research directions to further elaborate the role of lipoxins in neurodegeneration. 相似文献
90.
电器外壳制品形状结构复杂,有两处侧凸(孔)较难处理。通过对矩形孔内侧凸的结构分析,在其局部设计了分型面,避免了使用侧向抽芯机构;对侧孔部位设计了斜顶杆侧向抽芯机构,其结构简单、紧凑。模具采用一模二腔、平衡式布局,采用经扁推杆由制品内部进料的潜伏式浇口,S型流道。在NX 8.0中完成了模具结构设计。经实践证明,该模具结构合理,产品合格。 相似文献