全文获取类型
收费全文 | 19805篇 |
免费 | 1856篇 |
国内免费 | 1175篇 |
专业分类
电工技术 | 1414篇 |
技术理论 | 6篇 |
综合类 | 2062篇 |
化学工业 | 2389篇 |
金属工艺 | 401篇 |
机械仪表 | 905篇 |
建筑科学 | 2586篇 |
矿业工程 | 447篇 |
能源动力 | 464篇 |
轻工业 | 449篇 |
水利工程 | 494篇 |
石油天然气 | 403篇 |
武器工业 | 169篇 |
无线电 | 2129篇 |
一般工业技术 | 1248篇 |
冶金工业 | 807篇 |
原子能技术 | 211篇 |
自动化技术 | 6252篇 |
出版年
2024年 | 24篇 |
2023年 | 159篇 |
2022年 | 272篇 |
2021年 | 361篇 |
2020年 | 393篇 |
2019年 | 360篇 |
2018年 | 351篇 |
2017年 | 429篇 |
2016年 | 530篇 |
2015年 | 613篇 |
2014年 | 1146篇 |
2013年 | 1119篇 |
2012年 | 1233篇 |
2011年 | 1384篇 |
2010年 | 1158篇 |
2009年 | 1215篇 |
2008年 | 1270篇 |
2007年 | 1493篇 |
2006年 | 1360篇 |
2005年 | 1178篇 |
2004年 | 1002篇 |
2003年 | 853篇 |
2002年 | 766篇 |
2001年 | 684篇 |
2000年 | 576篇 |
1999年 | 486篇 |
1998年 | 388篇 |
1997年 | 365篇 |
1996年 | 271篇 |
1995年 | 248篇 |
1994年 | 235篇 |
1993年 | 165篇 |
1992年 | 155篇 |
1991年 | 108篇 |
1990年 | 71篇 |
1989年 | 79篇 |
1988年 | 57篇 |
1987年 | 37篇 |
1986年 | 39篇 |
1985年 | 34篇 |
1984年 | 27篇 |
1983年 | 28篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1957年 | 6篇 |
1955年 | 10篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
《中国有色金属学会会刊》2021,31(11):3530-3548
In-situ LA-ICP-MS and S isotopes of pyrite from the Baoshan Cu polymetallic deposit were conducted to investigate the ore-forming process and the enrichment mechanism of elements. Three generations of pyrite (Py I, Py II, and Py III) in the skarn-type ores and pyrite in the carbonate-hosted sulfide ores from central, western, and northern (C_Py, W_Py, and N_Py) mining districts are selected for comparison. Compared with Py I and Py III, the contents of most elements in Py II are apparently higher. The As and Se contents are high within a wide range and are decoupled in the growth band of the C_Py. The highest As, Se, and Pb contents were found in W_Py and N_Py. These results indicate the drastic changes in the temperature and fluid mixing during the mineralization. The occurrence of fluctuation and change in temperature and f(O2) was triggered by intermittent pulses of magmatic-hydrothermal fluids, mixing with meteoric water, and water−rock interactions. The sulfur isotopes of all species of pyrite indicated the magmatic source. The change in the f(O2) conditions caused slight differences in the sulfur isotope compositions. Consequently, a metallogenic model was proposed to explain the ore-forming processes. 相似文献
2.
Oguzhan Oguz Nicolas Candau Adrien Demongeot Mehmet Kerem Citak Fatma Nalan Cetin Grégory Stoclet Véronique Michaud Yusuf Z. Menceloglu 《Polymer Engineering and Science》2021,61(4):1028-1040
There is currently considerable interest in developing stiff, strong, tough, and heat resistant poly(lactide) (PLA) based materials with improved melt elasticity in response to the increasing demand for sustainable plastics. However, simultaneous optimization of stiffness, strength, and toughness is a challenge for any material, and commercial PLA is well-known to be inherently brittle and temperature-sensitive and to show poor melt elasticity. In this study, we report that high-shear mixing with cellulose nanocrystals (CNC) leads to significant improvements in the toughness, heat resistance, and melt elasticity of PLA while further enhancing its already outstanding room temperature stiffness and strength. This is evidenced by (i) one-fold increase in the elastic modulus (6.48 GPa), (ii) 43% increase in the tensile strength (87.1 MPa), (iii) one-fold increase in the strain at break (∼6%), (iv) two-fold increase in the impact strength (44.2 kJ/m2), (v) 113-fold increase in the storage modulus at 90°C (787.8 MPa), and (vi) 103-fold increase in the melt elasticity at 190°C and 1 rad/s (∼105 Pa) via the addition of 30 wt% CNC. It is hence possible to produce industrially viable, stiff, strong, tough, and heat resistant green materials with improved melt elasticity through high-shear mixing. 相似文献
3.
4.
Jiewei Chen Ting Zhang Jingli Wang Ning Zhang Wei Ji Shuyun Zhou Yang Chai 《Advanced functional materials》2021,31(40):2104192
Charge-based field-effect transistors (FETs) greatly suffer from unavoidable carrier scattering and heat dissipation. Analogous to valley degree of freedom in semiconductors, chiral anomaly current in Weyl/Dirac semimetals is theoretically predicted to be nearly nondissipative over long distances, but still lacks experimental ways to efficiently control its transport. Here, field-effect chirality devices are demonstrated with Dirac semimetal PtSe2, in which its Fermi level is close to the Dirac point in the conduction band owing to intrinsic defects. The chiral anomaly is further corroborated by the planar Hall effect and nonlocal valley transport measurement, which can also be effectively modulated by external fields, showing robust nonlocal valley transport with micrometer diffusion length. Similar to charge-based FETs, the chiral conductivity in PtSe2 devices can be modulated by electrostatic gating with an ON/OFF ratio of more than 103. Basic logic functions in the devices are also demonstrated with electric and magnetic fields as input signals. 相似文献
5.
Hao Yuan Haifeng Dai Wei Wu Jiaping Xie Jun Shen Xuezhe Wei 《International Journal of Hydrogen Energy》2021,46(7):5714-5728
In a vehicular fuel cell system, alternative load and frequent purge action can lead to anode pressure varies with the hydrogen mass flow fluctuation. It's crucial to control the pressure difference between anode and cathode within a reasonable range to avoid adverse phenomena such as membrane failure, reactant starvation, or even water management fault. In this paper, an improved proportional integrative (PI) controller by the fuzzy logic technique that considers the engineer experience and knowledge on the hydrogen supply system behavior is proposed for hydrogen pressure control, in which the PI parameters are tuned by a fuzzy decision process. Furthermore, load current and purge action regarded as input disturbances are applied for feedforward compensation to reduce the pressure response hysteresis. A hydrogen supply subsystem based on the proportional valve is modeled, and corresponding parameters are determined by analyzing the response time and steady pressure fluctuation. The performance of the conventional PI controller, the fuzzy logic PI (FLPI) controller and fuzzy logic PI with feedforward (FLPIF) controller is validated. The presented results indicated that the FLPI controller significantly improves the dynamic response of hydrogen pressure compared to the PI controller, and the FLPIF controller can further reduce overshoot caused by disturbance. Finally, the proposed FLPIF controller is implemented on a rapid prototype platform of the hydrogen supply subsystem and an actual fuel cell system, exhibiting satisfactory performance. 相似文献
6.
Margarida S. C. A. Brito Joana Matos Marina V. L. Torres Claudio P. Fonte Madalena M. Dias José Carlos B. Lopes Ricardo J. Santos 《American Institute of Chemical Engineers》2022,68(4):e17597
Product formulations for industrial processes are typically developed at laboratory scale. However, the mixing conditions are not easily mimicked in the laboratory. A rotational device is proposed in this study as a fast laboratory-scale formulation development, which enables mimicking the mixing conditions in the industrial process. The geometrical configurations of the rotational device are from rheometry devices (plate-plate and cone-plate). The main advantages of this method are the small amounts of raw materials and shorter testing times. This methodology is applied to an industrial case study, the reaction injection molding (RIM) process. The mixing length scales evolution in the rotational rheometer were matched to those in RIM machines. The main novelty of this study is the introduction of a protocol that bridges the processing conditions at laboratory using small amounts of raw materials to high throughput continuous flow reactors. 相似文献
7.
Elham Shafiei Gol Mari-Klara Stein Michel Avital 《The Journal of Strategic Information Systems》2019,28(2):175-195
Crowdwork, a new form of digitally mediated employment and part of the so-called gig economy, has the capacity to change the nature of work organization and to provide strategic value to workers, job providers, and intermediary platform owners. However, because crowdwork is temporary, large-scale, distributed, and mediated, its governance remains a challenge that often casts a shadow over its strategic value. The objective of this paper is to shed light on the making of value-adding crowdwork arrangements. Specifically, the paper explores crowdwork platform governance mechanisms and the relationships between these mechanisms and organizational value creation. Building on a comprehensive review of the extant literature on governance and crowdwork, we construct an overarching conceptual model that integrates control system and coordination system as two complementary mechanisms that drive crowdwork platform governance effectiveness and the consequent job provider benefits. Furthermore, the model accentuates the role of the degree of centralization and the degree of routinization as critical moderators in crowdwork platform governance. Overall, the paper highlights the potential of crowdwork to contribute not only to inclusion, fair wages and flexible work arrangements for workers but also to organizations’ value and competitive edge. 相似文献
8.
9.
In this paper, a novel interval type-2 fuzzy fractional order super twisting algorithm (IT2FFOSTA) which is essentially a second order sliding mode controller is presented. The proposed IT2FFOSTA enhances fractional order super twisting algorithm (FOSTA) by taking advantage of an interval type-2 fuzzy fractional order sliding surface (IT2FFOSS) for some classes of fully-actuated and under-actuated nonlinear systems in presence of uncertainty. The FOSTA significantly reduces the amount of chattering and the IT2FFOSS results in decreasing the tracking error, control effort, and chattering level. In order to control under-actuated systems, a hierarchical sliding surface is employed. The multi-tracker optimization algorithm is utilized to adjust the controller’s parameters; this leads to an optimal performance for the IT2FFOSTA. To examine the performance of the IT2FFOSTA, some simulation and experimental tests on three examples of different classes of fully-actuated and under-actuated systems, including ball and plate, inverted pendulum, and ball and beam systems are carried out. The simulation and experimental results demonstrate the superiority of the IT2FFOSTA in reducing the amount of chattering, tracking error, and control effort compared to those of the other control methods. 相似文献
10.