全文获取类型
收费全文 | 1380篇 |
免费 | 351篇 |
国内免费 | 59篇 |
专业分类
电工技术 | 113篇 |
综合类 | 101篇 |
化学工业 | 282篇 |
金属工艺 | 76篇 |
机械仪表 | 117篇 |
建筑科学 | 91篇 |
矿业工程 | 47篇 |
能源动力 | 84篇 |
轻工业 | 104篇 |
水利工程 | 11篇 |
石油天然气 | 134篇 |
武器工业 | 9篇 |
无线电 | 172篇 |
一般工业技术 | 176篇 |
冶金工业 | 55篇 |
原子能技术 | 19篇 |
自动化技术 | 199篇 |
出版年
2024年 | 42篇 |
2023年 | 127篇 |
2022年 | 223篇 |
2021年 | 262篇 |
2020年 | 156篇 |
2019年 | 100篇 |
2018年 | 105篇 |
2017年 | 117篇 |
2016年 | 74篇 |
2015年 | 93篇 |
2014年 | 71篇 |
2013年 | 83篇 |
2012年 | 44篇 |
2011年 | 33篇 |
2010年 | 25篇 |
2009年 | 33篇 |
2008年 | 26篇 |
2007年 | 22篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 18篇 |
2000年 | 5篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有1790条查询结果,搜索用时 15 毫秒
221.
Many key components of implantable medical devices are made from polymeric materials. The functions of these materials include structural support, electrical insulation, protection of other materials from the environment of the body, and biocompatibility, as well as other things such as delivery of a therapeutic drug. In such roles, the stability and integrity of the polymer, over what can be a very long period of time, is very important. For most of these functions, stability over time is desired, but in other cases, the opposite–the degradation and disappearance of the polymer over time is required. In either case, it is important to understand both the chemistry that can lead to the degradation of polymers as well as the kinetics that controls these reactions. Hydrolysis and oxidation are the two classes of reactions that lead to the breaking down of polymers. Both are discussed in detail in the context of the environmental factors that impact the utility of various polymers for medical device applications. Understanding the chemistry and kinetics allows prediction of stability as well as explanations for observations such as porosity and the unexpected behavior of polymeric composite materials in some situations. In the last part, physical degradation such interfacial delamination in composites is discussed. 相似文献
222.
A simple interference reduction method for non-orthogonal downlink CDMA channels is presented in which non-orthogonal CDMA signals are transmitted with different time offsets. An expression of multiple access interference (MAI) is developed and a reduction of MAI power is evaluated by using a numerical method and a computer simulation. The value of the time offset is determined in order to minimize the MAI and the implementation complexity. The performance of the proposed method is evaluated for various channel models. 相似文献
223.
根据某发电机组的选择性催化还原(SCR)技术烟气脱硝系统的运行参数,对设置不同直型导流板和喷氨面的反应器流场进行模拟,得到SCR烟气脱硝系统的最佳布置方案.使用Gambit软件构造模型,利用Fluent软件进行数值计算得到流场烟气速度分布和NO质量分数分布.分析表明,设置直型导流板可使催化剂层的烟气流场速度分布更均匀;直型导流板数量一定时,增大其倾斜角度有利于改善烟气流场速度分布;角度不变增加直型导流板数量不利于烟气流场速度分布;设置6块倾斜角度为80°的直行导流板,喷氨面位于烟道中部为最佳布置. 相似文献
224.
225.
渤海湾盆地南堡凹陷异常压力系统及其形成机理 总被引:1,自引:0,他引:1
渤海湾盆地南堡凹陷异常压力现象普遍发育,但对于凹陷中不同构造带异常压力的刻画与成因机制的探讨却较为薄弱。利用357口井1 354个钻杆测试数据(DST)和重复地层压力测试数据(RFT),测井曲线资料等,详细刻画了不同构造带的压力结构特征。研究表明:南堡凹陷地层压力系统纵向上可划分为3个带,浅部常压带(<1 800 m)、中部过渡带(1 800~2 400 m)和深部异常高压带(>2 400 m)。沙三段发育大规模异常高压,压力系数最高达1.9,超压带顶界面深度约为2 400 m;老爷庙构造带中、浅层发育低幅度超压带,压力系数约为1.2;滩海地区东一段和东二段局部发育异常低压。利用数值模拟技术和垂直有效应力-声波时差判别图版等方法,并结合烃源岩生排烃过程综合分析等,深入探讨了南堡凹陷不同异常压力系统的形成机理,研究认为:①深部沙三段的大规模超压主要来源于东营时期的泥岩不均衡压实作用,生烃作用也有一定贡献,但相对前者贡献较小;②明化镇时期,生烃作用是最主要的增压机制,而欠压实作用贡献则相对有限;③中浅层低幅超压带来源于深部超压的“传导”,开启的断裂带为其传递通道;④东营末期的区域抬升剥蚀作用引起岩石骨架孔隙回弹和流体收缩,是形成本区异常低压的主要原因。 相似文献
226.
227.
228.
229.
Liqiang Ren Shujie Yang Peiran Zhang Zhiguo Qu Zhangming Mao Po‐Hsun Huang Yuchao Chen Mengxi Wu Lin Wang Peng Li Tony Jun Huang 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(40)
Microfluidic fluorescence‐activated cell sorters (μFACS) have attracted considerable interest because of their ability to identify and separate cells in inexpensive and biosafe ways. Here a high‐performance μFACS is presented by integrating a standing surface acoustic wave (SSAW)‐based, 3D cell‐focusing unit, an in‐plane fluorescent detection unit, and an SSAW‐based cell‐deflection unit on a single chip. Without using sheath flow or precise flow rate control, the SSAW‐based cell‐focusing technique can focus cells into a single file at a designated position. The tight focusing of cells enables an in‐plane‐integrated optical detection system to accurately distinguish individual cells of interest. In the acoustic‐based cell‐deflection unit, a focused interdigital transducer design is utilized to deflect cells from the focused stream within a minimized area, resulting in a high‐throughput sorting ability. Each unit is experimentally characterized, respectively, and the integrated SSAW‐based FACS is used to sort mammalian cells (HeLa) at different throughputs. A sorting purity of greater than 90% is achieved at a throughput of 2500 events s?1. The SSAW‐based FACS is efficient, fast, biosafe, biocompatible and has a small footprint, making it a competitive alternative to more expensive, bulkier traditional FACS. 相似文献
230.
Qiuqiu Lyu Tenglong Zhu Hongxia Qu Zaihong Sun Kaihua Sun Qin Zhong Minfang Han 《Journal of the European Ceramic Society》2021,41(12):5931-5938
Hydrothermal reaction in Cerium and Gadolinium solution as an optimization method is developed and first reported for the densification of gadolinia doped ceria, the barrier layer between Zirconia electrolyte and (La,Sr)(Co,Fe)O3-δ cathode. This method is based on the hydrothermal reaction for nano particles in-situly grown on porous surface, to improve barrier layer density, alongside the sintering of cathode at 1075 °C. As a result, the ohmic resistance is prominently decreased by ~16.4 % at 750 °C for electrolyte supported symmetrical cell. Whereas, the cathode polarization resistance is decreased by as much as a factor of ~3 from 0.3702 Ω·cm2 to 0.1325 Ω·cm2 at 750 °C and . Furthermore, the anode supported cell exhibits higher open circuit voltage, smaller area specific resistance, elevated performance output and less degradation. And this modified barrier layer shows reduced Sr migration in 300 h operation at 750 °C. The hydrothermal reaction is demonstrated to prepare denser and sintering-active barrier layer with faster oxygen ion transfer and better interface connection, with large-scale application prospects and cost-competitiveness. 相似文献