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   38263篇
  免费   2338篇
  国内免费   990篇
电工技术   1482篇
技术理论   4篇
综合类   1553篇
化学工业   6089篇
金属工艺   1540篇
机械仪表   1669篇
建筑科学   1690篇
矿业工程   760篇
能源动力   1196篇
轻工业   2232篇
水利工程   448篇
石油天然气   1010篇
武器工业   146篇
无线电   5407篇
一般工业技术   5078篇
冶金工业   5896篇
原子能技术   389篇
自动化技术   5002篇
  2024年   105篇
  2023年   449篇
  2022年   863篇
  2021年   1197篇
  2020年   929篇
  2019年   799篇
  2018年   899篇
  2017年   945篇
  2016年   861篇
  2015年   1070篇
  2014年   1413篇
  2013年   2118篇
  2012年   1987篇
  2011年   2310篇
  2010年   1833篇
  2009年   1878篇
  2008年   1930篇
  2007年   1739篇
  2006年   1569篇
  2005年   1256篇
  2004年   1111篇
  2003年   1194篇
  2002年   1397篇
  2001年   1177篇
  2000年   816篇
  1999年   779篇
  1998年   1896篇
  1997年   1228篇
  1996年   966篇
  1995年   709篇
  1994年   550篇
  1993年   515篇
  1992年   267篇
  1991年   254篇
  1990年   252篇
  1989年   228篇
  1988年   194篇
  1987年   172篇
  1986年   147篇
  1985年   146篇
  1984年   110篇
  1983年   80篇
  1982年   89篇
  1981年   84篇
  1980年   114篇
  1979年   52篇
  1978年   70篇
  1977年   189篇
  1976年   334篇
  1975年   52篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
We present a structured procedure for order pick system (OPS) analysis and design that has been established on literature review and interviews with and presentations to OPS experts. In particular, we attempt to include the thinking processes that occur between OPS designers and owners. The design procedure and related issues are discussed in the order of input, selection, and evaluation stages.  相似文献   
62.
15.7% of spermatozoa were found to be abnormal in silver fox males during their first reproductive season. The total number of spermatozoa and the abnormal spermatogenesis remained unchanged during mating season. Sexual stimulation increased the testosterone level only at the beginning of the mating season.  相似文献   
63.
64.
65.
Treatment of rats with phenytoin (DPH), an anti-epileptic drug, results in lower tissue thyroid hormone (TH) levels and interferes with the metabolic pathway of TH. To test the hypothesis that DPH affects the enterohepatic cycle of TH and, thus, the kinetics of TH turnover, we performed a kinetic experiment (three-compartment analysis) and a steady-state, double-isotope equilibrium experiment in rats treated for 3 weeks with DPH (50 mg/kg body weight per day) and in untreated controls. This included measurements of TH and TH metabolite levels, as well as the activities of enzymes involved in the TH metabolic pathway. DPH treatment resulted in a decrease in the production of thyroxine (T4) (by 25%) and tri-iodothyronine (T3) (by 37%), a decrease in the T3 concentration in all three pools, and a redistribution of T4 from the fast to the slow pool. The amount of T4 increased in intestinal contents and feces by 66% and 71% respectively. Expressed as a fraction of daily TH disposal, fecal loss of T4 was enhanced from 10 to 23% and that of T3 from 16 to 21%. An increase in T4 and T3 UDP-glucuronyltransferase activities was observed, suggesting that the increased fecal loss of T4 and T3 is secondary to an increased biliary output of their glucuronides. The reduced secretion of TH and increased fecal clearance during DPH treatment can lead in the long run to depletion of TH stores.  相似文献   
66.
There were 2040 patients with temporomandibular joint (TMJ) diseases in the investigation including clinical, physiological, X-ray methods of research, contrast arthrotomography, computer arthrotomography and magnetic resonance tomography. The changes of structure in different lesions were estimated. The result of received data was elaboration of classification of TMJ internal derangements with estimation of clinical forms in according with structural changes and characteristics of syndromes.  相似文献   
67.
The purpose of this study is to investigate the precipitation characteristics of σ phase in the fusion zone of stainless steel welds at various welding passes during a tungsten are welding (GTAW) process. The morphology, quantity, and chemical composition of the δ-ferrite and σ phase were analyzed using optical microscopy (OM), a ferritscope (FS), a X-ray diffractometer (XRD), scanning electron microscopy (SEM), an electron probe micro-analyzer (EPMA), and a wavelength dispersive spectrometer (WDS), respectively. Massive δ-ferrite was observed in the fusion zone of the first pass welds during welding of dissimilar stainless steels. The σ phase precipitated at the inner δ-ferrite particles and decreased δ-ferrite content during the third pass welding. The σ and δ phases can be stabilized by Si element, which promoted the phase transformation of σ→ϱ+λ2 in the fusion zone of the third pass welds. It was found that the σ phase was a Fe−Cr−Si intermetallic compound found in the fusion zone of the third pass welds during multi-pass welding.  相似文献   
68.
Studies the anomalous variations of the OFF-state leakage current (IOFF) in n-channel poly-Si thin-film transistors (TFTs) under static stress. The dominant mechanisms for the anomalous IOFF can be attributed to (1) IOFF increases due to channel hot electrons trapping at the gate oxide/channel interface and silicon grain boundaries and (2) IOFF decreases due to hot holes accumulated/trapped near the channel/bottom oxide interface near the source region. Under the stress of high drain bias, serious impact ionization effect will occur to generate hot electrons and hot holes near the drain region. Some of holes will be injected into the gate oxide due to the vertical field (~(V_Gstress V_Dstress)/T OX) near the drain and the others will be migrated from drain to source along the channel due to lateral electric field (~V_Dstress/LCH)  相似文献   
69.
70.
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