全文获取类型
收费全文 | 1998篇 |
免费 | 249篇 |
国内免费 | 131篇 |
专业分类
电工技术 | 108篇 |
综合类 | 162篇 |
化学工业 | 375篇 |
金属工艺 | 124篇 |
机械仪表 | 112篇 |
建筑科学 | 118篇 |
矿业工程 | 67篇 |
能源动力 | 59篇 |
轻工业 | 174篇 |
水利工程 | 53篇 |
石油天然气 | 64篇 |
武器工业 | 20篇 |
无线电 | 314篇 |
一般工业技术 | 243篇 |
冶金工业 | 117篇 |
原子能技术 | 13篇 |
自动化技术 | 255篇 |
出版年
2024年 | 40篇 |
2023年 | 71篇 |
2022年 | 130篇 |
2021年 | 164篇 |
2020年 | 123篇 |
2019年 | 70篇 |
2018年 | 77篇 |
2017年 | 63篇 |
2016年 | 79篇 |
2015年 | 95篇 |
2014年 | 106篇 |
2013年 | 98篇 |
2012年 | 137篇 |
2011年 | 137篇 |
2010年 | 112篇 |
2009年 | 117篇 |
2008年 | 93篇 |
2007年 | 101篇 |
2006年 | 94篇 |
2005年 | 98篇 |
2004年 | 51篇 |
2003年 | 36篇 |
2002年 | 31篇 |
2001年 | 31篇 |
2000年 | 32篇 |
1999年 | 33篇 |
1998年 | 26篇 |
1997年 | 20篇 |
1996年 | 25篇 |
1995年 | 15篇 |
1994年 | 19篇 |
1993年 | 3篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1980年 | 3篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有2378条查询结果,搜索用时 15 毫秒
101.
102.
103.
In this work, the graphene/α-SiO2(0001) interface is calculated using density functional theory. On the oxygen-terminated SiO2 surface, atomic structure reconstruction occurs at the graphene/SiO2 interface to eliminate the dangling bonds. The interface interaction is 77 meV/C atom, which indicates that van der Waals force dominates the interaction, but it is stronger than the force between the graphene layers in graphite. The distance between graphene and the SiO2 surface is 2.805 Å, which is smaller than the 3.4 Å interlayer distance of graphite. In addition, the SiO2 substrate induces p-type doping in graphene and opens a small gap of 0.13 eV at the Dirac point of graphene, which is desirable for electronic device applications. 相似文献
104.
采用共沉淀法和沉淀浸渍法制备了纳米氧化铈-二氧化硅(CeO2-SiO2)介孔材料吸附剂,主要考察了其对水中铜离子(Cu2+)的吸附行为。通过X射线衍射(XRD)、扫描电镜(SEM)和氮吸附(BET)等手段对合成的介孔材料进行了性能表征,并通过静态吸附实验分析了溶液pH、溶液初始金属离子质量浓度、吸附剂用量、吸附时间等条件对介孔材料吸附Cu2+性能的影响。结果表明:共沉淀法制备的纳米CeO2-SiO2介孔材料对Cu2+的去除效果较沉淀浸渍法要好;当溶液pH=7.0时CeO2-SiO2介孔材料对Cu2+的吸附效果最好,20 min时基本达到吸附平衡;溶液初始Cu2+浓度增大Cu2+去除率降低,Cu2+累计吸附量增大;随着吸附剂用量增加Cu2+去除率增大,当CeO2-SiO2吸附剂用量为0.15 g/L时对Cu2+的去除率趋于稳定;CeO2-SiO2吸附剂对不同金属离子吸附性能由大到小的顺序为Cu2+、Fe2+、Mn2+,该吸附过程均符合准二级动力学模型。 相似文献
105.
Lei Zu Yueting Li Huiqin Lian Yanou Hu Wei Chang Bingxin Liu Yang Liu Xiang Ao Qiang Li Xiuguo Cui 《大分子材料与工程》2016,301(9):1076-1083
A facile method to fabricate ionic polymer‐metal composite (IPMC) actuators is proposed. A blend of mesoporous graphene (MG) and Nafion is used as the ionic matrix, which is sandwiched by two layers of blend of reduced graphene oxide (rGO) and Nafion as the electrodes. When subjected to an electrical field of 3 V, the IPMC actuator exhibits a blocking force of 10 gf g?1 for 20 s, and the same behavior can be repeatedly played for hundreds of cycles. MG improves the mechanical properties of Nafion‐based IPMC, more importantly, the mesopores in graphene provide additional pathway for the diffusion of cationic clusters and thus enhance the actuation speed. In addition, the surface electrodes of rGO protect the interlamellar liquid from evaporation thus ensure the durability.
106.
Ao Pan Minghui Xie Jianye Xia Ju Chu Yingping Zhuang 《Korean Journal of Chemical Engineering》2018,35(1):61-72
The influence of impeller structure on the mass transfer characteristics was studied with the steady-state method for gas-liquid volumetric mass transfer coefficient (k L a). The single-impeller configurations included eight impeller types (three radial flow impellers, four axial flow impellers and one mixed flow impeller), and the doubleimpeller included three configurations (RT+RT, RT+WH D , WH D +WH D ). For single-impeller, the gas-liquid mass transfer rates of radial flow impellers were better than those of axial flow impellers under the same rotation speed and gas flow rate. The mass transfer performance (defined as the volumetric mass transfer coefficient per unit power input) of radial flow impellers were also better than that of axial flow impellers. With the same kLa value under a certain gas flow rate, the local bubble size distribution between radial flow impeller and axial flow impeller was similar. As for double impellers, RT+RT provided the highest mass transfer rate under certain rotation speed and gas flow rate, while WH D +WH D gave the highest values of gas-liquid mass transfer coefficient with the same power consumption. 相似文献
107.
Polyimide/Graphene Nanocomposites with Improved Gas Barrier and Thermal Properties due to a “Dual‐Plane” Structure Effect 下载免费PDF全文
Yiwu Liu Junjie Liu Qian Ding Jinghua Tan Zhiquan Chen Junyi Chen Xuri Zuo Ao Tang Kejian Zeng 《大分子材料与工程》2018,303(7)
Graphene nanosheets are prepared by solution‐phase exfoliation of graphite and successfully incorporated with polyimide to obtain polyimide/graphene (DABPI/G) nanocomposites via in situ polymerization. Compared with those of pure DABPI, the DABPI/G nanocomposites exhibit better barrier and thermal properties. The oxygen and water vapor transmission rates of the DABPI/G (0.5 wt%) nanocomposite are 0.69 cm3 m?2 d?1 and 0.44 g m?2 d?1, respectively, which are 92 and 85% lower than those of pure DABPI. Meanwhile, the DABPI/G (0.5 wt%) nanocomposite exhibits excellent thermal stability with a Td5% of 578 °C and a coefficient of thermal expansion of ?0.19 ppm K?1. The excellent barrier and thermal properties of DABPI/G nanocomposites are mainly attributed to the fine dispersion and orientation of the graphene nanosheets, increased crystallinity, and low free volume of the DABPI matrix. These are the result of the “dual‐plane” structure effect, which is the synergistic orientation effect between the rigid planar molecular chains of DABPI and the nanosheets of graphene. 相似文献
108.
Meijie Zhang Miaolin He Huazhi Gu Ao Huang Wuguo Xiang 《Ceramics International》2018,44(16):19319-19329
The microstructures of porous alumina materials with different porosities were established by introducing the departure factor of pore position and acentric factor of pore diameter to describe the distribution of pores in space and in size, respectively. The contribution of radiation and influence of pore distribution on the equivalent thermal conductivity were discussed based on numerical simulations by the finite volume method (FVM) considering both thermal conduction and radiation. When the pore diameter was less than 10?µm, the radiation component was less than 2%, and radiation could be neglected. Radiative heat transfer played a dominant role for materials with high porosity and large pore size at high temperatures. For micro pore materials (<?100?µm), broad pore size and non-uniform pore space distribution decreased the thermal conductivity across the entire temperature range. For materials with macro pores (>1?mm), broad pore distribution decreased the thermal conductivity at low temperatures and increased it at high temperatures. The basic prediction model of effective thermal conductivity for a two-component material, the Maxwell–Eucken model (ME1) and its modified model were corrected by introducing the pore structure factor. The results from experiments prove that the numerical values were satisfactory. 相似文献
109.
The solid–liquid equilibria(SLE)for binary and ternary systems consisting of N-Vinylpyrrolidone(NVP),2-Pyrrolidone(2-P)and water are measured.The phase diagrams of NVP(1)+2-P(2),NVP(1)+water(2),NVP(1)+2-P(2)+1 wt%water(3)and NVP(1)+2-P(2)+2 wt%water(3)are identified as simple eutectic type with the eutectic points at 263.75 K(x_(1E)=0.5427),251.65 K(x_(1E)=0.3722),260.25 K(x_(1E)=0.5031)and256.55 K(x_(1E)=0.4684),respectively.The phase diagram of 2-P(1)+water(2)has two eutectic points(x_(1E)=0.1236,T_E=259.15 K and x_(1E)=0.7831,T_E=286.15 K)and one congruent melting point(x_(1C)=0.4997,T_C=303.55 K)because of the generation of a congruently melting addition compound:2-P·H_2O.The ideal solubility and the UNIFAC models were applied to predict the SLE,while the Wilson and NRTL models were employed in correlating the experimental data.The best correlation of the SLE data has been obtained by the Wilson model for the binary system of NVP+2-P.The UNIFAC model gives more satisfactory predictions than the ideal solubility model. 相似文献
110.
建立了同时测定保健品口服液中睾酮、孕酮和雄酮等10种性激素的液相色谱-串联质谱(LC-MS/MS)分析方法。以甲醇为提取溶剂,超声提取,经酸性氧化铝、C18固相萃取柱净化,采用LC-MS/MS进行检测。10种激素在1~200ng/m L范围内线性良好(r20.99),方法检出限为0.2~5μg/kg,在5、10、20μg/kg的3个添加水平范围内的平均回收率为70.92%~111.33%,相对标准偏差均小于15%,方法可满足口服液中性激素快速检测要求。 相似文献