全文获取类型
收费全文 | 154760篇 |
免费 | 6630篇 |
国内免费 | 3157篇 |
专业分类
电工技术 | 4699篇 |
技术理论 | 6篇 |
综合类 | 6605篇 |
化学工业 | 23653篇 |
金属工艺 | 8631篇 |
机械仪表 | 7783篇 |
建筑科学 | 7326篇 |
矿业工程 | 2941篇 |
能源动力 | 3311篇 |
轻工业 | 8304篇 |
水利工程 | 2263篇 |
石油天然气 | 5582篇 |
武器工业 | 464篇 |
无线电 | 16686篇 |
一般工业技术 | 25267篇 |
冶金工业 | 6363篇 |
原子能技术 | 1014篇 |
自动化技术 | 33649篇 |
出版年
2024年 | 245篇 |
2023年 | 1264篇 |
2022年 | 2020篇 |
2021年 | 2949篇 |
2020年 | 2196篇 |
2019年 | 1941篇 |
2018年 | 16298篇 |
2017年 | 15533篇 |
2016年 | 11797篇 |
2015年 | 3284篇 |
2014年 | 3658篇 |
2013年 | 4386篇 |
2012年 | 7444篇 |
2011年 | 14080篇 |
2010年 | 12312篇 |
2009年 | 9380篇 |
2008年 | 10505篇 |
2007年 | 11370篇 |
2006年 | 3908篇 |
2005年 | 4627篇 |
2004年 | 3399篇 |
2003年 | 3245篇 |
2002年 | 2393篇 |
2001年 | 1731篇 |
2000年 | 1973篇 |
1999年 | 2094篇 |
1998年 | 1809篇 |
1997年 | 1435篇 |
1996年 | 1440篇 |
1995年 | 1184篇 |
1994年 | 951篇 |
1993年 | 718篇 |
1992年 | 553篇 |
1991年 | 446篇 |
1990年 | 323篇 |
1989年 | 249篇 |
1988年 | 230篇 |
1987年 | 138篇 |
1986年 | 101篇 |
1985年 | 90篇 |
1984年 | 60篇 |
1982年 | 42篇 |
1968年 | 46篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1959年 | 36篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
An agriglass composition containing different oxides acts as a slow release for macro and micro nutrients and was chosen to improve maize yield under most important abiotic stresses which affecting agriculture development; salinity and drought. A field experiment was performed in salt affected soil (EC =?7.5 dSm??1) by using different water deficit rates (I1 = 100, I2 = 85 and I3 = 70% of maize water requirements). Irrigation levels were located in main plots. Every main-plot divided into six sub-plots contained glassy fertilizer treatments [F1 = 55 kg fed?1 with 1/2 mm diameter of agriglass (fed. =?4200 m2), F2 = 55 kg fed?1 with 1 mm diameter, F3 = 80 kg fed?1 with 1/2 mm diameter, F4 = 80 kg fed?1 with 1 mm diameter, F5 = Recommendations of Ministry of Agriculture and F6 = control]. The experimental results demonstrated that, ears, straw, grains and biological yields increased with increasing both water and agriglass rates. Application of agriglass as a slow release fertilizer improved yield more than mineral fertilizer. Some growth parameters, water use efficiency (IWUE), macronutrients concentration and their relations were included. Other studies on residual effect of agriglass and the annual application rates to withstand salinity and drought stress by strategic crops are required. 相似文献
82.
Shuncheng Liu Kejian Wang Zhongfeng Zhang Yueqing Ren Lanlan Chen Xiaojie Sun Wenbin Liang 《Polymer Engineering and Science》2020,60(10):2640-2652
Three kinds of ethylene-octene copolymers (POE) were melt-blended with high-density polyethylene (PE-HD) in different proportions. Detailed characterizations were conducted to analyze their structural differences of POE and its effects in toughening PE-HD. The higher molecular weight POE can improve the toughness of PE-HD. 60:40 PE-HD/POE is elongated to break up to 700% while impact strength is 84.7 kJ/m2 at −30°C, which is 21-fold of PE-HD. In the brittle to ductile transition (BDT) during impact, the fracture mechanism changes from the crazing mode to the shear yield-plastic deformation mode. The BDT temperature decreases as the POE molecular weight and its content increase. The interface strength in tension is estimated to access their effects. The Boltzmann-type models were successfully extended to describe the typical S-shaped curves in BDT of notched impact strength vs POE content or temperature. The supplementary decay model is suggested for the attenuation in toughening. Transition map in impact is proposed to select the use range of composition (c ) and temperature (T ) for high toughness. The curves are converted into 3D graph of T -c -impact strength for illustrating their coupling-separate effects, and further into the contour map of impact strength in T -c space for finding their partial equivalence. 相似文献
83.
84.
Ahmed Obaid M. Alzahrani M. Sh. Abdel-wahab Meshari Alayash M. S. Aida 《Journal of Materials Science: Materials in Electronics》2018,29(19):16317-16324
In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector. 相似文献
85.
Video transmission over IEEE 802.11e wireless networks still shows poor performance for large bandwidth demand and frequently changed environments. Thus, several enhancements of IEEE 802.11e were proposed. On the other hand, big frames and simultaneous sending of adjacent frames always cause packet dropping for buffer overflow. In the past, we proposed an IEEE 802.11e enhancement named DFAA and a content aware mechanism to solve the above problems. The motivation of this paper is to find a proper way to integrate these two mechanisms. A DFAA enhancement (DFAA-E) is proposed to make up the insufficiency of content aware mechanism. Experiments results show that the combination of DFAA-E and content aware mechanism improves the video decoded quality greatly. And its performance can be further enhanced by selecting the suitable settings of certain parameters. 相似文献
86.
Spherical LiNi1/3Co1/3Mn1/3O2 cathode particles were resynthesized by a carbonate co-precipitation method using spent lithium-ion batteries (LIBs) as a raw material. The physical characteristics of the Ni1/3Co1/3Mn1/3CO3 precursor, the (Ni1/3Co1/3Mn1/3)3O4 intermediate, and the regenerated LiNi1/3Co1/3Mn1/3O2 cathode material were investigated by laser particle-size analysis, scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), thermogravimetry–differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), inductively coupled plasma–atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of the regenerated LiNi1/3Co1/3Mn1/3O2 was studied by continuous charge–discharge cycling and cyclic voltammetry. The results indicate that the regenerated Ni1/3Co1/3Mn1/3CO3 precursor comprises uniform spherical particles with a narrow particle-size distribution. The regenerated LiNi1/3Co1/3Mn1/3O2 comprises spherical particles similar to those of the Ni1/3Co1/3Mn1/3CO3 precursor, but with a narrower particle-size distribution. Moreover, it has a well-ordered layered structure and a low degree of cation mixing. The regenerated LiNi1/3Co1/3Mn1/3O2 shows an initial discharge capacity of 163.5 mA h g?1 at 0.1 C, between 2.7 and 4.3 V; the discharge capacity at 1 C is 135.1 mA h g?1, and the capacity retention ratio is 94.1% after 50 cycles. Even at the high rate of 5 C, LiNi1/3Co1/3Mn1/3O2 delivers the high capacity of 112.6 mA h g?1. These results demonstrate that the electrochemical performance of the regenerated LiNi1/3Co1/3Mn1/3O2 is comparable to that of a cathode synthesized from fresh materials by carbonate co-precipitation. 相似文献
87.
Yachao Dong Christos T. Maravelias Norman F. Jerome 《Optimization and Engineering》2018,19(4):937-976
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies. 相似文献
88.
89.
90.
Fenton氧化法去除酱油生产废水中焦糖色素的研究 总被引:1,自引:0,他引:1
着重考察了Fenton试剂对水中焦糖色素降解的影响因素.从试验中得出,这些影响因素包括pH、催化剂的投加方式、催化剂与氧化剂的化学计量数以及反应时间等.Fenton反应中,pH4的条件下处理效果最好,反应进行40min时去除率达到90%. 相似文献