全文获取类型
收费全文 | 30879篇 |
免费 | 4035篇 |
国内免费 | 2578篇 |
专业分类
电工技术 | 3441篇 |
技术理论 | 5篇 |
综合类 | 3129篇 |
化学工业 | 5810篇 |
金属工艺 | 1543篇 |
机械仪表 | 1318篇 |
建筑科学 | 1747篇 |
矿业工程 | 693篇 |
能源动力 | 1043篇 |
轻工业 | 1417篇 |
水利工程 | 541篇 |
石油天然气 | 840篇 |
武器工业 | 332篇 |
无线电 | 3497篇 |
一般工业技术 | 4464篇 |
冶金工业 | 1031篇 |
原子能技术 | 474篇 |
自动化技术 | 6167篇 |
出版年
2024年 | 71篇 |
2023年 | 630篇 |
2022年 | 757篇 |
2021年 | 1100篇 |
2020年 | 1213篇 |
2019年 | 1239篇 |
2018年 | 1087篇 |
2017年 | 1242篇 |
2016年 | 1261篇 |
2015年 | 1231篇 |
2014年 | 1700篇 |
2013年 | 2086篇 |
2012年 | 1841篇 |
2011年 | 2105篇 |
2010年 | 1556篇 |
2009年 | 1614篇 |
2008年 | 1667篇 |
2007年 | 1840篇 |
2006年 | 1809篇 |
2005年 | 1525篇 |
2004年 | 1395篇 |
2003年 | 1274篇 |
2002年 | 1125篇 |
2001年 | 891篇 |
2000年 | 786篇 |
1999年 | 700篇 |
1998年 | 499篇 |
1997年 | 505篇 |
1996年 | 443篇 |
1995年 | 389篇 |
1994年 | 350篇 |
1993年 | 315篇 |
1992年 | 242篇 |
1991年 | 178篇 |
1990年 | 168篇 |
1989年 | 113篇 |
1988年 | 101篇 |
1987年 | 58篇 |
1986年 | 49篇 |
1985年 | 47篇 |
1984年 | 57篇 |
1983年 | 48篇 |
1982年 | 48篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1960年 | 5篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Studying the distribution of the patent cooperation networks from the perspective of assignees provides a very important reference to improve the analysis of the market situation, master the layout of industrial technology and seek partners or mergers and acquisitions. This study uses the Derwent patent database and the patent metric approach to investigate the cooperative network structure of the assignees. The overall patent output in the artificial intelligence field on a global scale exhibited a rapid growth, and the proportion of cooperative patents significantly increased; the cooperation structure between the assignees was loose, and the innovation efficiency was low. 相似文献
72.
73.
从提高流屑角突变模型的预测精度出发,建立了切削状态参数与3个切削控制参数之间关系的新经验公式。提出了一种通过迭代法准确设定有限元仿真软件刀-屑摩擦因数的方法,并通过直角切削Al6061-T6工件的有限元仿真试验,获得了一组不同切削控制参数组合条件下的切削状态参数数据。根据该数据拟合出剪切角φ、刀-屑摩擦角β、剪切应力τs关于刀具前角γ0、进给量f和切削速度v的经验公式,并通过一组直角切削试验,验证了所得经验公式的有效性。将新建经验公式应用于流屑角突变建模过程后,所得模型关于突变临界切削宽度的平均预测误差减小了27.2%。 相似文献
74.
分析反应堆压力容器(RPV)锻件制造过程中关键化学元素含量及基准无塑性转变温度(RTNDT)数值,通过引入修正淬透性系数,建立了反映RTNDT变化规律的修正淬透性系数函数表达式,并给出了实例验证,结果表明,通过本文建立的修正淬透性系数函数式可以比较精确地预估RPV锻件的RTNDT值。 相似文献
75.
Yifei Li Akshay Singh Kate Reidy Seong Soon Jo Frances M. Ross Rafael Jaramillo 《Advanced functional materials》2020,30(36)
The synthesis of large‐area TiS2 thin films is reported at temperatures as low as 500 °C using a scalable two‐step method of metal film deposition followed by sulfurization in an H2S gas furnace. It is demonstrated that the lowest‐achievable sulfurization temperature depends strongly on the oxygen background during sulfurization. This dependence arises because Ti? O bonds present a substantial kinetic and thermodynamic barrier to TiS2 formation. Lowering the sulfurization temperature is important to make smooth films, and to enable integration of TiS2 and related transition metal dichalcogenides—including metastable phases and alloys—into device technology. 相似文献
76.
Wonjun Choi Sungjae Hong Yeonsu Jeong Yongjae Cho Hyung Gon Shin Ji Hoon Park Yeonjin Yi Seongil Im 《Advanced functional materials》2021,31(9):2009436
Among many of 2D semiconductor-based devices, type III PN junction diodes are given special attentions due to their unique function, negative differential resistance (NDR). However, it has been found uneasy to achieve well-matched type III PN junctions from 2D–2D van der Waals heterojunctions. Here, the authors present other alternatives of type III heterojunctions, using 2D p-MoTe2/organic n-type dipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) and 2D p-WSe2/n-MoOx systems. Those junction diodes appear to well-demonstrate static and dynamic NDR behavior via resonant tunneling and electron–hole recombination. Extended to an inverter circuit, p-MoTe2/n-HAT-CN diode enables multilevel inverter characteristics as monolithically integrated with p-MoTe2 channel field effect transistor. The same NDR diode shows dynamic LC oscillation behavior under a constant DC voltage, connected to an external inductor. From p-WSe2/n-MoOx oxide diode, similar NDR behavior to those of p-MoTe2/n-HAT-CN is again observed along with LC oscillations. The authors attribute these visible oscillation results to high peak-to-valley current ratios of their organic or oxide/2D heterojunction diodes. 相似文献
77.
《Ceramics International》2021,47(18):25901-25909
Dielectric tunable properties in ferroelectric ceramics have been optimized by a variety of approaches, e.g., isovalent/aliovalent substitution, system composite et al., while the study of non-stoichiometric regulation on the performance of BCZT ceramics was rarely concerned. Herein, a series of novel non-stoichiometric (Ba0·91Ca0.09)x (Zr0·18Ti0.82)O3 (BCZTx) ceramic specimens were successfully prepared via solid-state reaction. The microstructures of BCZTx ceramics are simultaneously investigated through XRD and SEM. The diffuse phase transition (DPT) behaviour of BCZTx ceramics are studied by the Lorentz-type empirical formula. The significant enhancement of DPT behaviour is observed at x = 1.03, which probably due to the coaction of the generation of partial Schottky defects and prominent reduction of grain size. Furthermore, a high tunability (k) 87.80%, low dielectric loss (tan δ) 0.141%, and a remarkably enhanced FOM of 623 are achieved in x = 0.99 at a low DC bias electric fields (BEFs) of 7.28 kV/cm and room temperature (RT), which is superior to that of the stoichiometric BCZT ceramics and other available reported BT-based ceramics systems in term of the dielectric tunable properties. Meanwhile, it shows that the temperature dependent CQF value of x = 0.99 remained advantageous around the RT. These findings suggested that non-stoichiometric BCZTx ceramics with x = 0.99 are significantly competitive in the applications of dielectric tunable devices at RT. The non-stoichiometric regulation is an effective approach in improving the dielectric tunability properties of BCZT ceramics. 相似文献
78.
The ways in which environmental priorities are framed are varied and influenced by political forces. One technological advance--the proliferation of government open data portals (ODPs)--has the potential to improve governance through facilitating access to data. Yet it is also known that the data hosted on ODPs may simply reflect the goals and interests of multiple levels of political power. In this article, I use traditional statistical correlation and regression techniques along with newer natural language processing and machine learning algorithms to analyze the corpus of datasets hosted on government ODPs (total: 49,066) to extract patterns that relate scales of governance and political liberalism/conservatism to the priorities and meaning attached to environmental issues. I find that state-level and municipal-level ODPs host different categories of environmental datasets, with municipal-level ODPs generally hosting more datasets pertaining to services and amenities and state-level ODPs hosting more datasets pertaining to resource protection and extraction. Stronger trends were observed for the influences of political conservatism/liberalism among state-level ODPs than for municipal-level ODPs. 相似文献
79.
Xueli Chen Ke Liu Qianwan Qin Zhenlu Yu Meiqing Li Xingyu Qu Yu Zhou Aichun Dou Mingru Su Yunjian Liu 《Ceramics International》2021,47(11):15400-15407
With excellent specific capacity, superior cycle stability, safety and strong practical, Nb2O5 has been considered as one of the prospective anode materials for lithium-ion batteries (LIBs). However, current study suggests that Nb2O5 electrode materials for LIBs still face the vital issues of low electrical conductivity and poor rate performance. Therefore, carbon-coated TT-Nb2O5 materials are designed and synthesized through solid state method in this work, which present high specific capacity (228 mA h g?1 at 0.2C), satisfactory rate properties (107 mA h g?1 at 20 C). The outstanding electrochemical property can not only give the credit to the pseudocapacitance effect of TT-Nb2O5, but also attribute to introduction of carbon. The homogeneous carbon-coated materials enhance the electrical conductivity, increase the electron transmission speed and alleviate particle crushing. This research not only offers a new method for preparing excellent electrode materials, but also provides a kind of excellent anode material with prospective application for LIBs. 相似文献
80.
Ziwen Wu Tianping Zhang 《International Journal of Adaptive Control and Signal Processing》2021,35(9):1768-1788
In this article, the issue of adaptive finite-time dynamic surface control (DSC) is discussed for a class of parameterized nonlinear systems with full state constraints. Using the property of logarithmic function, a one-to-one nonlinear mapping is constructed to transform a constrained system into an unconstrained system with the same structure. The nonlinear filter is constructed to replace the first-order linear filter in the traditional DSC, and the demand on the filter time constant is reduced. Based on finite-time stable theory and using modified DSC, the finite-time controller is designed via DSC. Theoretical analysis shows that all the signals in the closed-loop system are semiglobal practical finite-time stable. Furthermore, none of the states are outside the defined open set. In the end, simulation results are presented to demonstrate the effectiveness of the proposed control schemes with both linear filters and nonlinear filters. 相似文献