全文获取类型
收费全文 | 54569篇 |
免费 | 5963篇 |
国内免费 | 4063篇 |
专业分类
电工技术 | 6247篇 |
技术理论 | 4篇 |
综合类 | 5609篇 |
化学工业 | 4279篇 |
金属工艺 | 4039篇 |
机械仪表 | 7537篇 |
建筑科学 | 2154篇 |
矿业工程 | 2388篇 |
能源动力 | 1188篇 |
轻工业 | 3525篇 |
水利工程 | 718篇 |
石油天然气 | 1117篇 |
武器工业 | 516篇 |
无线电 | 4649篇 |
一般工业技术 | 4519篇 |
冶金工业 | 2110篇 |
原子能技术 | 376篇 |
自动化技术 | 13620篇 |
出版年
2024年 | 163篇 |
2023年 | 1016篇 |
2022年 | 1620篇 |
2021年 | 1894篇 |
2020年 | 2026篇 |
2019年 | 1707篇 |
2018年 | 1462篇 |
2017年 | 1806篇 |
2016年 | 2030篇 |
2015年 | 2168篇 |
2014年 | 3416篇 |
2013年 | 3070篇 |
2012年 | 3875篇 |
2011年 | 4082篇 |
2010年 | 2980篇 |
2009年 | 2971篇 |
2008年 | 2909篇 |
2007年 | 3608篇 |
2006年 | 3503篇 |
2005年 | 2962篇 |
2004年 | 2433篇 |
2003年 | 2108篇 |
2002年 | 1868篇 |
2001年 | 1604篇 |
2000年 | 1340篇 |
1999年 | 1127篇 |
1998年 | 807篇 |
1997年 | 724篇 |
1996年 | 579篇 |
1995年 | 532篇 |
1994年 | 468篇 |
1993年 | 375篇 |
1992年 | 274篇 |
1991年 | 200篇 |
1990年 | 185篇 |
1989年 | 147篇 |
1988年 | 130篇 |
1987年 | 58篇 |
1986年 | 60篇 |
1985年 | 32篇 |
1984年 | 38篇 |
1983年 | 40篇 |
1982年 | 36篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 23篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1960年 | 7篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 921 毫秒
21.
Zenan Yu Julian Moore Jean Calderon Lei Zhai Jayan Thomas 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(39):5289-5295
Cable‐shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable‐shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable‐shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil‐type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical‐electrochemical stability. The CASECs show excellent charge–discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm−3), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets. 相似文献
22.
To improve the convertibility of reconfigurable manufacturing system (RMS), the concept of delayed reconfigurable manufacturing system (D-RMS) was proposed. RMS and D-RMS are both constructed around part family. However, D-RMS may suffer from ultra-long system problem with unacceptable idle machines using generic RMS part families. Besides, considering the complex basic system structure of D-RMS, machine selection of D-RMS should be addressed, including dedicated machine, flexible machine, and reconfigurable machine. Therefore, a system design method for D-RMS based on part family grouping and machine selection is proposed. Firstly, a part family grouping method is proposed for D-RMS that groups the parts with more former common operations into the same part family. The concept of longest relative position common operation subsequence (LPCS) is proposed. The similarity coefficient among the parts is calculated based on LPCS. The reciprocal value of the operation position of LPCS is adopted as the characteristic value. The average linkage clustering (ALC) algorithm is used to cluster the parts. Secondly, a machine selection method is proposed to complete the system design of D-RMS, including machine selection rules and the dividing point decision model. Finally, a case study is given to implement and verify the proposed system design method for D-RMS. The results show that the proposed system design method is effective, which can group parts with more former common operations into the same part family and select appropriate machine types. 相似文献
23.
High-voltage transmission networks are commonly equipped with phasor measurement units (PMU), and some of them are PMU observable. However, PMUs are seldom installed in distribution networks due to budget limitations. The state estimation equations of PMU observable areas are linear, while those of other areas remain nonlinear. This paper proposes a new distributed state estimation method for solving multi-area state estimation problems, in which linear models are used for high-voltage transmission network, while nonlinear models are adopted for other areas. In PMU observable area, we select coordinating variables as generalized cost functions which accurately represent the sensitivity between the linear SE objective function and boundary states. Consequently, SE results identical to a centralized estimator can be obtained without iterations at the coordination level. This paper presents the problem model and theoretical analysis of the proposed method, and shows its effectiveness by numerical tests. 相似文献
24.
Gel state reactions offer new direction for the reactivity of the organic molecules or metal‐organic materials upon photoirradiation with shorter reaction times and high yields compared to solid and solution states. The restricted molecular movement among the molecules in the soft solids control the stereoselectivity of the photoproducts in the gel state reactions. To date, most of the strategies based on self‐assembly have been demonstrated in the solid state, in particular for [2+2] reactions of olefins and polymerization reactions of diacetylenes via 1,4 addition. The soft materials are of emerging materials in recent days given their many applicative day‐to‐day aspects. This review gives a glimpse of recent reports on pericyclic reactions in the gel state that are designed based on the self‐assembly concept. Also it highlights how such reactions accompany the physical changes in the structure of the gels and stereo controlled products with high yields. 相似文献
25.
精准预测生物氧化预处理中的进气量对提高黄金提取率和节能降耗具有重要意义。以气体管流连续性方程和运动方程为控制方程,采用Preissmann隐格式法作为差分方法。同时,根据集合卡尔曼滤波(Ensemble Kalman filter,EnKF)算法原理,构造进气量、压强的状态空间模型。结果表明,基于气体管流控制方程建立的进气量模型预测结果与实际进气量观测值具有较好的一致性;与传统静态预测方法相比,EnKF同化方法引入实时观测值和模型参数的更新,有效提高了进气量的预测精度,其平均绝对误差、平均相对误差和均方根误差有明显的降低。可见,基于气体管流控制方程建立的预测模型结合EnKF同化方法是提高生物氧化槽进气量预测精度的有效手段。 相似文献
26.
27.
28.
The influence of the environment on the excited state transitions of meso-tetrakis(p-sulfonatophenyl) porphyrin (TPPS) is reported. TPPS was investigated in protonated and non-protonated forms, and in the presence of the cationic cetyltrimethylammonium bromide (CTAB) micelles. The singlet excited-state absorption spectra were measured by using the white-light continuum Z-scan technique and the triplet–triplet absorption spectra were acquired employing an association of laser flash photolysis and Z-scan techniques. Our results show that the perseveration of the molecular symmetry, upon excitation, depends on the state of multiplicity of the molecules, as well as on the environment and structural characteristics of the porphyrin. Additionally, it was observed that for excited molecules, the ring distortion caused by the protonation of porphyrin ring has great influence on the changes observed for the symmetry and vibronic structure. The results clearly show that the porphyrin investigated is a promising candidate for optical limiting applications for all investigated environments. 相似文献
29.
烧结机导料箱、单辊破碎机和卸料漏斗承载着烧结热矿的导料、破碎与输送,是烧结生产的重要组成部分。高温、重载的工况环境决定着机尾卸料装置必须具有抗磨损、耐高温的特性。针对邯钢1^#435m^2烧结机机尾关键部件耐磨工作面寿命短,更换不方便等问题,分析磨损机理与失效原因,提出改进抗磨工作面结构,升级耐磨材料,优化焊接工艺等措施。通过技术方案的实施,使烧结机导料箱、单辊破碎机和卸料漏斗等卸料装置维持了较高的抗磨损性能,达到了预期的改造效果。 相似文献
30.
This paper is prepared in honour of Professor E.T. Brown for his outstanding contributions to rock mechanics and geotechnical engineering and also for his personal influence on the first author's research career in geomechanics and geotechnical engineering. As a result, we have picked a topic that reflects two key research areas in which Professor E.T. Brown has made seminal contributions over a long and distinguished career. These two areas are concerned with the application of the critical state concept to modelling geomaterials and the analysis of underground excavation or tunnelling in geomaterials.Partially due to Professor Brown's influence, the first author has also been conducting research in these two areas over many years. In particular, this paper aims to describe briefly the development of a unified critical state model for geomaterials together with an application to cavity contraction problems and tunnelling in soils. 相似文献