首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   54764篇
  免费   4918篇
  国内免费   2605篇
电工技术   3367篇
技术理论   4篇
综合类   3857篇
化学工业   8792篇
金属工艺   3135篇
机械仪表   3684篇
建筑科学   4310篇
矿业工程   1737篇
能源动力   1561篇
轻工业   4482篇
水利工程   1047篇
石油天然气   3624篇
武器工业   418篇
无线电   5771篇
一般工业技术   6008篇
冶金工业   2460篇
原子能技术   619篇
自动化技术   7411篇
  2024年   147篇
  2023年   1001篇
  2022年   1598篇
  2021年   2401篇
  2020年   1910篇
  2019年   1506篇
  2018年   1697篇
  2017年   1850篇
  2016年   1631篇
  2015年   2290篇
  2014年   2860篇
  2013年   3408篇
  2012年   3580篇
  2011年   4048篇
  2010年   3447篇
  2009年   3252篇
  2008年   3342篇
  2007年   3077篇
  2006年   3013篇
  2005年   2640篇
  2004年   1730篇
  2003年   1536篇
  2002年   1563篇
  2001年   1363篇
  2000年   1242篇
  1999年   1264篇
  1998年   944篇
  1997年   821篇
  1996年   705篇
  1995年   598篇
  1994年   503篇
  1993年   338篇
  1992年   282篇
  1991年   168篇
  1990年   144篇
  1989年   93篇
  1988年   84篇
  1987年   63篇
  1986年   37篇
  1985年   24篇
  1984年   18篇
  1983年   14篇
  1982年   12篇
  1981年   15篇
  1980年   13篇
  1979年   5篇
  1978年   2篇
  1959年   3篇
  1953年   1篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
液滴撞击干燥倾斜壁面铺展实验研究   总被引:2,自引:0,他引:2       下载免费PDF全文
通过高速摄影技术及像素分析方法对液滴撞击干燥倾斜壁面进行实验研究,分析了不同倾斜角及韦伯数(We)对液滴飞溅及铺展的影响,结果表明,倾斜角的增加有利于抑制飞溅的产生;We一定时,液滴的前铺展因子随着倾斜角的增加而增加,后铺展因子随着倾斜角的增加而减小;液滴的前后初始铺展速度均大于液滴的撞击速度,且随着倾斜角的增加而减小。   相似文献   
22.
Amphotericin B (AMB) was often used in intra-articular injection administration for fungal arthritis, because it could often bring a satisfactory therapeutic efficacy and a minimum systemic toxic side effect. However, because of the multiple operations and the frequent injections, the compliance of the patients was bad. Therefore, to develop a long-term sustained-released preparation of AMB for mycotic arthritis intra-articular administration is of great significance. The purpose of present study was to develop a long-term sustained-released in situ gel of a water-insoluble drug AMB for mycotic arthritis intra-articular administration. Based on the evaluations of the in vitro properties of the formulations, the formulation containing 10% (w/w) ethanol, 15% (w/w) PG, 0.75% (w/w) HA, 5% (w/w) purified soybean oil, 0.03% (w/w) α-tocopherol, 15% (w/w) water and 55% (w/w) glyceryl monooleate was selected as a suitable intra-articular injectable in situ gel drug delivery system for water-insoluble drug AMB. Furthermore, the results of the in vivo study on rabbits showed that the selected formulation was a safe and effective long-term sustained-released intra-articular injectable AMB preparation. Therefore, the presented in situ AMB gel could reduce the frequency of the administration in the AMB treatment of fungal arthritis, and then would get a good patient compliance.  相似文献   
23.
24.
Semiconductor particles doped Al2O3 coatings were prepared by cathode plasma electrolytic deposition in Al(NO3)3 electrolyte dispersed with SiC micro- and nano-particles (average particle sizes of 0.5–1.7?µm and 40?nm respectively). The effects of the concentrations and particle sizes of the SiC on the microstructures and tribological performances of the composite coatings were studied. In comparison with the case of dispersing with SiC microparticles, the dispersion of SiC nanoparticles in the coatings was more uniform. When the concentration of SiC nanoparticles was 5?g/L, the surface roughness of the composite coating was reduced by 63%, compared with that of the unmodified coating. Friction results demonstrated that the addition of 5?g/L SiC nanoparticles reduced the friction coefficient from 0.60 to 0.38 and decreased the wear volume under dry friction. The current density and bath voltage were measured to analyze the effects of SiC particles on the deposition process. The results showed that the SiC particles could alter the electrical behavior of the coatings during the deposition process, weaken the bombardment of the plasma, and improve the structures of the coatings.  相似文献   
25.
采用载荷分离法和多试样法对汽轮机某高压转子钢材料在高温下的断裂韧度值进行了测试,讨论了载荷分离法测断裂韧度的可靠性,并与传统的多试样法进行了对比。  相似文献   
26.
Effective thermal management of electronic integrated devices with high powder density has become a serious issue, which requires materials with high thermal conductivity (TC). In order to solve the problem of weak bonding between graphite and Cu, a novel Cu/graphite film/Cu sandwich composite (Cu/GF/Cu composite) with ultrahigh TC was fabricated by electro-deposition. The micro-riveting structure was introduced to enhance the bonding strength between graphite film and deposited Cu layers by preparing a rectangular array of micro-holes on the graphite film before electro-deposition. TC and mechanical properties of the composites with different graphite volume fractions and current densities were investigated. The results showed that the TC enhancement generated by the micro-riveting structure for Cu/GF/Cu composites at low graphite content was more effective than that at high graphite content, and the strong texture orientation of deposited Cu resulted in high TC. Under the optimizing preparing condition, the highest in-plane TC reached 824.3 W·m−1·K−1, while the ultimate tensile strength of this composite was about four times higher than that of the graphite film.  相似文献   
27.
在中国企业国际化背景下,本文以石油贸易公司为例,研究其绩效考核体系,重点放在全流程管控上,从职责分工、计划制定、考核维度、评分标准和强制等级分布等方面对绩效考核进行研究,提出涵盖所有员工的国际化考核体系,以期通过实现公司内部管理体系的完整,以更好地适应国际竞争。  相似文献   
28.
以中低温煤焦油沥青质为原料,采用NiMoW/γ-Al_2O_3商业催化剂,在反应温度380℃、反应压力8 MPa和反应时间1.5 h条件下,分别在不同剂油质量比(1∶25、1∶20、1∶15、1∶10)条件下进行加氢实验,通过采用元素分析、FT-IR、XRD、~1H-NMR和XPS等分析表征手段,考察不同剂油质量比对中低温煤焦油沥青质加氢转化过程的影响。结果表明,随着剂油质量比的增加,沥青质转化率提高,加氢产物分布也发生大幅变化,沥青质和芳香分轻质化转化为饱和分。但随着剂油质量比的进一步提高,同时也发生了更多的裂化反应和缩合反应,剂油质量比在合适范围能够很好地起到加氢轻质化且抑制结焦的效果。  相似文献   
29.
为改进湿法磷酸生产工艺,提高副产石膏的品质,减少湿法磷酸固体副产物磷石膏堆存产生的经济和环保压力,进行了磷酸分解磷矿制磷酸的实验研究。采用贵州某磷矿为主要原料,研究了湿法磷酸预分解磷矿的反应条件。通过单因素实验确定了湿法磷酸分解磷矿最优反应条件:反应温度为75 ℃,磷酸与磷矿的质量比(液固比)为9,反应时间为3 h,磷酸质量分数为30%(以五氧化二磷计)。在此条件下,磷矿的分解率为98.62%。  相似文献   
30.
This article focuses on the consensus problem of leader-following fractional-order multi-agent systems (MASs) with general linear and Lipschitz nonlinear dynamics. First, the distributed adaptive protocols for linear and nonlinear fractional-order MASs are constructed, respectively. We allow the control coupling gains to be time varying for each agent. Moreover, the adaptive modification schemes for the control gain are designed, which renders smaller control gains and thus requires smaller amplitude on the control input without sacrificing consensus convergence. Second, based on fractional-order Lyapunov stability theorem and Barbalat's lemma, two novel sufficient conditions in terms of linear matrix inequalities are provided to ensure that the leader-following consensus can be obtained in the case for any undirected connected communication graph. Furthermore, we show that the proposed algorithm also works for consensus of agents with intrinsic Lipschitz nonlinear dynamics. As a result, the proposed framework requires no global information and thus can be implemented in a fully distributed manner. Finally, the numerical simulations are given to demonstrate the effectiveness of obtained the theoretical results.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号