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   1839837篇
  免费   50235篇
  国内免费   18706篇
电工技术   51569篇
技术理论   56篇
综合类   25492篇
化学工业   321668篇
金属工艺   81269篇
机械仪表   63396篇
建筑科学   71300篇
矿业工程   22221篇
能源动力   58968篇
轻工业   132088篇
水利工程   20660篇
石油天然气   58674篇
武器工业   2733篇
无线电   229096篇
一般工业技术   321094篇
冶金工业   203368篇
原子能技术   36996篇
自动化技术   208130篇
  2022年   16437篇
  2021年   27159篇
  2020年   20778篇
  2019年   21729篇
  2018年   24361篇
  2017年   25134篇
  2016年   29910篇
  2015年   28865篇
  2014年   43555篇
  2013年   105268篇
  2012年   55140篇
  2011年   69652篇
  2010年   60857篇
  2009年   68310篇
  2008年   62094篇
  2007年   58863篇
  2006年   62046篇
  2005年   54887篇
  2004年   51200篇
  2003年   49846篇
  2002年   47958篇
  2001年   44734篇
  2000年   43623篇
  1999年   44671篇
  1998年   60354篇
  1997年   49902篇
  1996年   43993篇
  1995年   37342篇
  1994年   34133篇
  1993年   32722篇
  1992年   28599篇
  1991年   25339篇
  1990年   25253篇
  1989年   24104篇
  1988年   22334篇
  1987年   20248篇
  1986年   19616篇
  1985年   22768篇
  1984年   22665篇
  1983年   20553篇
  1982年   19534篇
  1981年   19621篇
  1980年   18238篇
  1979年   18663篇
  1978年   17865篇
  1977年   17979篇
  1976年   19414篇
  1975年   16065篇
  1974年   15557篇
  1973年   15626篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
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   
192.
This review examines the application, limitations, and potential alternatives to the Hagberg–Perten falling number (FN) method used in the global wheat industry for detecting the risk of poor end-product quality mainly due to starch degradation by the enzyme α-amylase. By viscometry, the FN test indirectly detects the presence of α-amylase, the primary enzyme that digests starch. Elevated α-amylase results in low FN and damages wheat product quality resulting in cakes that fall, and sticky bread and noodles. Low FN can occur from preharvest sprouting (PHS) and late maturity α-amylase (LMA). Moist or rainy conditions before harvest cause PHS on the mother plant. Continuously cool or fluctuating temperatures during the grain filling stage cause LMA. Due to the expression of additional hydrolytic enzymes, PHS has a stronger negative impact than LMA. Wheat grain with low FN/high α-amylase results in serious losses for farmers, traders, millers, and bakers worldwide. Although blending of low FN grain with sound wheat may be used as a means of moving affected grain through the marketplace, care must be taken to avoid grain lots from falling below contract-specified FN. A large amount of sound wheat can be ruined if mixed with a small amount of sprouted wheat. The FN method is widely employed to detect α-amylase after harvest. However, it has several limitations, including sampling variability, high cost, labor intensiveness, the destructive nature of the test, and an inability to differentiate between LMA and PHS. Faster, cheaper, and more accurate alternatives could improve breeding for resistance to PHS and LMA and could preserve the value of wheat grain by avoiding inadvertent mixing of high- and low-FN grain by enabling testing at more stages of the value stream including at harvest, delivery, transport, storage, and milling. Alternatives to the FN method explored here include the Rapid Visco Analyzer, enzyme assays, immunoassays, near-infrared spectroscopy, and hyperspectral imaging.  相似文献   
193.
Nowadays, oil pollution has become more serious, which causes great threats both to the ecological environment and human life. In this study, a novel type of multifunctional deacetylated cellulose acetate/polyurethane (d-MCA:MTPU) composite nanofiber membranes for oil/water separation are successfully fabricated by electrospinning, which show super-amphiphilicity in air, super-hydrophilicity in oil, and oleophobicity in water. All the d-MCA:MTPU composite nanofiber membranes with different mass ratios can be used as water-removing, oil-removing, and emulsion separation substance only by gravity driving force. The highest separation flux for water and oil reaches up to 37 000 and 74 000 L m−2 h−1, respectively, and all the separation efficiencies are more than 99%. They have outstanding comprehensive mechanics performance, which can be controlled by simply adjusting the mass ratios. They show excellent antifouling and self-cleaning ability, endowing powerful cyclic stability and reusability. Those results show that d-MCA:MTPU composite nanofiber membranes have great application prospects in oil/water separation.  相似文献   
194.
Mosquito-borne Zika virus (ZIKV) became a real threat to human health due to the lack of vaccine and effective antiviral treatment. The virus has recently been responsible for a global outbreak leading to millions of infected cases. ZIKV complications were highlighted in adults with Guillain–Barré syndrome and in newborns with increasing numbers of congenital disorders ranging from mild developmental delays to fatal conditions. The ability of ZIKV to establish a long-term infection in diverse organs including the kidneys has been recently documented but the consequences of such a viral infection are still debated. Our study aimed to determine whether the efficiency of ZIKV growth in kidney cells relates to glucose concentration. Human kidney HK-2 cells were infected with different ZIKV strains in presence of normal and high glucose concentrations. Virological assays showed a decrease in viral replication without modifying entry steps (viral binding, internalization, fusion) under high glucose conditions. This decrease replication was associated with a lower virus progeny and increased cell viability when compared to ZIKV-infected HK-2 cells in normal glucose concentration. In conclusion, we showed for the first time that an elevated glucose level influences ZIKV replication level with an effect on kidney cell survival.  相似文献   
195.
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   
196.
Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic...  相似文献   
197.
Mobile Networks and Applications - 5G/6G communication are first generation high speed wireless communication network which integrates the aerial data, terrestrial data and maritime data via...  相似文献   
198.
199.
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   
200.
Crosslinking of polyolefin elastomer (POE, ENGAGE™ 8480) with Dicumyl Peroxide (DCP) can have effects on its crystallization dynamics, crystal structure, and properties. The POE crosslinked uniformly has significantly lower crystalline ability than the one with only amorphous phase crosslinked, which, in turn, has weaker crystalline ability than neat POE. The crystallinity and melting point depend on how the POE is crosslinked. The neat POE and POE crosslinked in amorphous phase only, are investigated with DSC and in-situ tensile/synchrotron radiation (WAXD/SAXS). In situ tensile/synchrotron X-ray during a uniaxial stretching process indicates that severe crystal fragmentation is observed at a strain around 45%, and with further increase in strain. The stress in the crosslinked POE is significantly larger than neat POE. For both samples, crystal orientation increases sharply within the strain range up to 88% where orientation-induced new crystals aligned in stretching direction are observed. The long period increases more in stretching direction for the crosslinked POE, consistent with larger stress in this sample, and the stress difference is more pronounced at large strains (27.3 vs. 10.9 MPa at a strain 435%). Permanent set of the crosslinked POE is smaller, consistent with less oriented crystals observed after the test for permanent set.  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