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   264716篇
  免费   4423篇
  国内免费   267篇
电工技术   5379篇
综合类   493篇
化学工业   48074篇
金属工艺   15355篇
机械仪表   10429篇
建筑科学   4835篇
矿业工程   3926篇
能源动力   3967篇
轻工业   11398篇
水利工程   4206篇
石油天然气   13066篇
武器工业   28篇
无线电   20556篇
一般工业技术   65573篇
冶金工业   32510篇
原子能技术   11160篇
自动化技术   18451篇
  2021年   3389篇
  2019年   3301篇
  2018年   5961篇
  2017年   6089篇
  2016年   6637篇
  2015年   3816篇
  2014年   6120篇
  2013年   11462篇
  2012年   7839篇
  2011年   9369篇
  2010年   8073篇
  2009年   9016篇
  2008年   8595篇
  2007年   8245篇
  2006年   6634篇
  2005年   5835篇
  2004年   5705篇
  2003年   5510篇
  2002年   5247篇
  2001年   5068篇
  2000年   4999篇
  1999年   4352篇
  1998年   7364篇
  1997年   5979篇
  1996年   4617篇
  1995年   3834篇
  1994年   3582篇
  1993年   3845篇
  1992年   3375篇
  1991年   3479篇
  1990年   3631篇
  1989年   3547篇
  1988年   3407篇
  1987年   3423篇
  1986年   3337篇
  1985年   3478篇
  1984年   3422篇
  1983年   3321篇
  1982年   3150篇
  1981年   3226篇
  1980年   3222篇
  1979年   3410篇
  1978年   3593篇
  1977年   3596篇
  1976年   4053篇
  1975年   3407篇
  1974年   3473篇
  1973年   3690篇
  1972年   3193篇
  1971年   2895篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
42.
Exocytosis plays an essential role in the communication between cells in the nervous system. Understanding the regulation of neurotransmitter release during exocytosis and the amount of neurotransmitter content that is stored in vesicles is of importance, as it provides fundamental insights to understand how the brain works and how neurons elicit a certain behavior. In this minireview, we summarize recent progress in amperometric measurements for monitoring exocytosis in single cells and electrochemical cytometry measurements of vesicular neurotransmitter content in individual vesicles. Important steps have increased our understanding of the different mechanisms of exocytosis. Increasing evidence is firmly establishing that partial release is the primary mechanism of release in multiple cell types.  相似文献   
43.
Russian Engineering Research - The stability of robot-mower motion in a specific direction is considered. The direction is regulated by means of an angular sensor and a programmable controller...  相似文献   
44.
Revin  A. A.  Mikhaylova  A. M.  Konakov  A. A.  Tsyplenkov  V. V.  Shastin  V. N. 《Semiconductors》2021,55(12):879-884
Semiconductors - The wave functions of electrons localized at P, As, and Sb shallow donors in Ge are calculated in the envelope function approximation taking into account valley–orbit...  相似文献   
45.
Multimedia Tools and Applications - Discovering the relevant web services for specific applications in the dynamically changing business world becomes very critical. Researchers have used many...  相似文献   
46.
Theoretical Foundations of Chemical Engineering - The effect of the electrolyte composition, mass-transfer conditions, pore diameter, interpore distance, and electric parameters on the formation of...  相似文献   
47.
Fluoro-substituted and heteroaromatic compounds are valuable intermediates for a variety of applications in pharma- and agrochemistry and synthetic chemistry. This study investigates the chemoenzymatic preparation of chiral alcohols bearing a heteroaromatic ring with an increasing degree of fluorination in α-position. Starting from readily available picoline derivatives prochiral α-halogenated acyl moieties were introduced with excellent selectivity and 64–95 % yield. The formed carbonyl group was subsequently reduced to the corresponding alcohols using the alcohol dehydrogenase from Lactobacillus kefir, yielding an enantiomeric excess of 95–>99 % and up to 98 % yield.  相似文献   
48.
Antibiotic resistance is a growing problem for public health and associated with increasing economic costs and mortality rates. Silver and silver-related compounds have been used for centuries due to their antimicrobial properties. In this work, we show that 1,3-dibenzyl-4,5-diphenyl-imidazol-2-ylidene silver(I) acetate/NHC*-Ag-OAc (SBC3) is a reversible, high affinity inhibitor of E. coli thioredoxin reductase (TrxR; Ki=10.8±1.2 nM). Minimal inhibition concentration (MIC) tests with different E. coli and P. aeruginosa strains demonstrated that SBC3 can efficiently inhibit bacterial cell growth, especially in combination with established antibiotics like gentamicin. Our results show that SBC3 is a promising antibiotic drug candidate targeting bacterial TrxR.  相似文献   
49.
One of the drawbacks of fusible clays is the narrow sintering interval due to a sharp increase in the amount of iron-silicate melt at a temperature of 1000–1100 °C, which hardens in the form of a glass phase upon cooling. This leads to a relatively low mechanical strength of the calcined samples and causes the danger of melting the granular material surface from such clays during the firing process. To increase the strength of samples of fusible clays, the influence of diabase and granitoid rocks was considered. It was found that the strengthening effect of diabase and granitoid rock additives in an amount of 20–50% in a mixture with fusible clay is due to an increase of total content of the crystalline phase (mullite, cristobalite and residual quartz) from 18–20% in clays without additives to 22–28 % - in mixtures with diabase and to 28–34% - with granitoid additives) at a temperature of 1050–1100 °C. This increase is due to the activation of synthesis processes of secondary mullite and crystallization from alkali-rich feldspar melt of amorphous silica, released from the structure of clay minerals. The established influence of the igneous rocks used made it possible to develop compositions and propose process flow sheet for producing aluminosilicate proppants based on fusible clays. The use of granitoid and diabase rocks in an amount of 20–70% with fusible clays produces lightweight aluminosilicate proppants with bulk density of 1.40–1.46 g/cm3 at temperature range of 1050–1100 °C, which can endure destructive pressures up to 34.5–52 MPa.  相似文献   
50.
Theoretical Foundations of Chemical Engineering - The corona onset voltage is an important operating parameter in the electrostatic precipitation of nanoparticulate, however, its experimental...  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