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   88551篇
  免费   4003篇
  国内免费   4103篇
电工技术   4013篇
技术理论   5篇
综合类   8453篇
化学工业   12587篇
金属工艺   5625篇
机械仪表   3002篇
建筑科学   4267篇
矿业工程   1246篇
能源动力   2736篇
轻工业   5801篇
水利工程   1929篇
石油天然气   4085篇
武器工业   687篇
无线电   6700篇
一般工业技术   13981篇
冶金工业   2457篇
原子能技术   2174篇
自动化技术   16909篇
  2024年   60篇
  2023年   259篇
  2022年   371篇
  2021年   566篇
  2020年   971篇
  2019年   922篇
  2018年   1038篇
  2017年   962篇
  2016年   1478篇
  2015年   2111篇
  2014年   3887篇
  2013年   4636篇
  2012年   3933篇
  2011年   4576篇
  2010年   3847篇
  2009年   5237篇
  2008年   5242篇
  2007年   5589篇
  2006年   5130篇
  2005年   4296篇
  2004年   3707篇
  2003年   3634篇
  2002年   3682篇
  2001年   2757篇
  2000年   3143篇
  1999年   2931篇
  1998年   2465篇
  1997年   2349篇
  1996年   2503篇
  1995年   2649篇
  1994年   2403篇
  1993年   1459篇
  1992年   1486篇
  1991年   1021篇
  1990年   747篇
  1989年   664篇
  1988年   632篇
  1987年   371篇
  1986年   222篇
  1985年   369篇
  1984年   411篇
  1983年   429篇
  1982年   328篇
  1981年   404篇
  1980年   270篇
  1979年   114篇
  1978年   112篇
  1977年   69篇
  1976年   40篇
  1975年   55篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
Concerning the safety problems of conventional Li-ion batteries with liquid electrolytes, it is crucial to develop reliable solid-state electrolytes with high ionic conductivity. Li1+xAlxTi2?x(PO4)3 (LATP, x = 0.3) is regarded as one of the most promising solid electrolytes due to its high ionic conductivity and excellent chemical stability to humidity.Herein, a new strategy is proposed for improving the sintering behavior and enhancing the ionic conductivity of LATP by using LiBO2 as the sintering aid via liquid phase sintering. The as-prepared sample LATP with homogeneous microstructure and high relative density of 97.1% was successfully synthesized, yielding high total ionic conductivity of 3.5 × 10?4 S cm?1 and low activation energy of 0.39 eV at room temperature. It was found that the addition of LiBO2 could effectively enhance the densification and increase the ionic conductivity of LATP electrolyte, proving an effective way to synthesis LATP ceramics by a simple and reliable route.  相似文献   
72.
73.
Enteroaggregative Escherichia coli (EAEC) is an emerging pathogen frequently associated with acute diarrhea in children and travelers to endemic regions. EAEC was found the most prevalent bacterial diarrheal pathogen from hospitalized Bolivian children less than five years of age with acute diarrhea from 2007 to 2010. Here, we further characterized the epidemiology of EAEC infection, virulence genes, and antimicrobial susceptibility of EAEC isolated from 414 diarrheal and 74 non-diarrheal cases. EAEC isolates were collected and subjected to a PCR-based virulence gene screening of seven virulence genes and a phenotypic resistance test to nine different antimicrobials. Our results showed that atypical EAEC (a-EAEC, AggR-negative) was significantly associated with diarrhea (OR, 1.62, 95% CI, 1.25 to 2.09, p < 0.001) in contrast to typical EAEC (t-EAEC, AggR-positive). EAEC infection was most prevalent among children between 7–12 months of age. The number of cases exhibited a biannual cycle with a major peak during the transition from warm to cold (April–June). Both typical and a-EAEC infections were graded as equally severe; however, t-EAEC harbored more virulence genes. aap, irp2 and pic were the most prevalent genes. Surprisingly, we detected 60% and 52.6% of multidrug resistance (MDR) EAEC among diarrheal and non-diarrheal cases. Resistance to ampicillin, sulfonamides, and tetracyclines was most common, being the corresponding antibiotics, the ones that are frequently used in Bolivia. Our work is the first study that provides comprehensive information on the high heterogenicity of virulence genes in t-EAEC and a- EAEC and the large prevalence of MDR EAEC in Bolivia.  相似文献   
74.
This article develops a new framework of adaptive actuator failure compensation control for cooperative manipulator systems with parameter uncertainties in addition to actuator failures, and designs and analyzes effective actuator failure compensation schemes for such robotic systems. The new adaptive control design uses an integration of multiple individual failure compensators and direct adaptation to handle various types of uncertainties in such robotic systems. The design can also be used for concurrent actuator failure cases, to expand the capability of adaptive actuator failure compensation. With a complete proof and performance analysis, it is shown that the proposed control scheme guarantees the desired closed-loop stability and asymptotic output tracking, despite actuator failures whose patterns, time instants and values are all unknown. Simulation results of a benchmark cooperative manipulator system are presented to verify the desired control performance of the system with both typical constant and square-wave actuator failure signals.  相似文献   
75.
In this study, ultrafiltered (UF) Iranian white cheese made with adjunct cultures including six Lactobacillus isolates (Lactobacillus brevis, L. casei and L. plantarum) from traditional Iranian Motal cheese. The peptide extract (<5 kDa) of cheese samples were assessed for angiotensin-converting enzyme (ACE)-inhibitory activity during ripening (5 °C). Among the strains used, L. brevis KX572382 (M8) was selected because of the greater increase in (ACE)-inhibitory activity in the cheese (P < 0.05). The highest activity of M8 extract was observed on the 28th (71.72%) day of ripening (P < 0.05). Proteolytic activity assessment and RP-HPLC peptide profile of M8 water-soluble extracts (WSEs) indicated the effect of M8 on further protein degradation due to secondary proteolysis. A total of 7 different peptide sequences, previously known in the literature for their ACE-inhibitory activity, were tentatively identified by LC/ESI-MS in 28-day M8 peptide extract. Although the effect of M8 on pH and the proteolysis development in cheese was significant, no adverse effect was observed on the sensory properties. In conclusion, M8 strain can enhance the functional properties of Iranian UF white cheese.  相似文献   
76.
以油莎豆饼和高粱为原料,分别采用固态和液态发酵工艺酿造油莎豆白酒,对油莎豆白酒的发酵工艺进行选择。在此基础上,采用单因素试验及正交试验探究发酵温度、糖化酶添加量以及活性干酵母添加量对油莎豆白酒发酵及理化指标的影响,从而确定油莎豆白酒的最佳固态发酵工艺条件,并对油莎豆白酒发酵过程中酒醅的发酵指标进行实时监测。结果表明,油莎豆白酒的最佳发酵工艺为固态发酵,最佳发酵工艺条件为发酵温度23 ℃,糖化酶添加量190 U/g、活性干酵母添加量0.5‰。在此优化条件下,油莎豆白酒的酒精度为9.2%vol,总酯含量为2.96 g/L,总酸含量为1.45 g/L,乙酸乙酯含量为2.42 g/L,出酒率达到41%。油莎豆白酒发酵过程中,酒精含量逐渐升高,最后趋于平缓,发酵结束后,酒精度达9.2%vol;发酵温度先上升后下降,第6天时酒醅温度达到峰值(27.9 ℃);剩余淀粉含量逐渐下降,发酵结束后,淀粉消耗12.21%。  相似文献   
77.
In this study, the effect of co-fermentation and sequential fermentation with a typical halophilic soy sauce yeast Candida versatilis and a non-halophilic dairy bacterium Lactococcus lactis subsp. cremoris in pork hydrolysates was explored for the first time with regard to their viability, physicochemical changes and volatile compound production. It was observed that the growth of C. versatilis was suppressed (only 0.6 - 1.5 log CFU mL−1 increase), whilst L. lactis subsp. cremoris was stimulated (total cell counts exceeded 9.0 log CFU mL−1) in mixed-cultures relative to the respective monocultures. There were no significant differences between co-inoculation and sequential inoculation regarding glucose consumption, organic acid production and free amino acids utilisation. Some distinct volatile compounds such as methionol, 6-methyl-5-hepten-2-one and gamma-nonalactone were found in both co-inoculated and sequentially inoculated samples, with slightly different concentrations. These results suggest that the mixed-inoculation of C. versatilis and L. lactis have a positive impact on the volatile compounds formation in pork hydrolysates.  相似文献   
78.
ABSTRACT

We present a theoretical model to realize the symmetric and asymmetric diffraction grating in a four-level atomic medium. The proposed atomic medium follows a double lambda configuration where four fields interact with it. We get control over symmetric and asymmetric behavior of the diffraction grating by manipulating the relative phase of the fields. Interestingly, the symmetric and asymmetric diffraction grating become prominent when the vortex beam is used instead of the plane wave. Enhanced first, second, and third-order diffraction gratings are achieved via the vortex beam. Further, we find control over asymmetric diffraction gratings by the relative phase of the fields. Coherent control of asymmetric diffraction grating in negative and positive diffracted angles is also achieved via the relative phase.  相似文献   
79.
本文探索了新工科背景下“电力系统分析”课程建设情况,摸索工程教育的新理念,以学生发展为中心,尝试翻转课堂的互动式教学模式,实现了创新人才的培养目标。编著《电力系统分析》教材,实现了内容的继承和创新、重要知识点的交叉和融合。建设数字仿真及物理模拟实验室,解决高校人才培养与社会需求脱节的问题。以“注重学习过程,加强平时考核,淡化期末考试”的方式进行综合考评,提高了教学效果与教学质量。经过几年的教学探索与实践,证明了本课程建设效果良好。  相似文献   
80.
In this paper I make a personal reflection on my research and writings in the field of Project Management over the past 30 years. My research has primarily been about the management of the project-based organization. Within that I have researched governance, organizational behaviour, contingency, marketing, success and shareholder value.  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