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   548767篇
  免费   7889篇
  国内免费   1505篇
电工技术   9854篇
综合类   560篇
化学工业   83827篇
金属工艺   20346篇
机械仪表   15645篇
建筑科学   13916篇
矿业工程   2375篇
能源动力   15116篇
轻工业   48666篇
水利工程   5410篇
石油天然气   9414篇
武器工业   37篇
无线电   61572篇
一般工业技术   105853篇
冶金工业   108016篇
原子能技术   10762篇
自动化技术   46792篇
  2022年   3491篇
  2021年   5384篇
  2020年   3787篇
  2019年   4953篇
  2018年   8284篇
  2017年   8028篇
  2016年   8516篇
  2015年   6053篇
  2014年   9903篇
  2013年   25443篇
  2012年   15645篇
  2011年   21518篇
  2010年   16761篇
  2009年   18648篇
  2008年   19142篇
  2007年   18770篇
  2006年   16376篇
  2005年   14932篇
  2004年   14282篇
  2003年   14017篇
  2002年   13153篇
  2001年   13217篇
  2000年   12215篇
  1999年   13006篇
  1998年   33560篇
  1997年   23417篇
  1996年   17866篇
  1995年   13441篇
  1994年   11628篇
  1993年   11318篇
  1992年   8169篇
  1991年   7604篇
  1990年   7529篇
  1989年   7277篇
  1988年   6680篇
  1987年   5999篇
  1986年   5889篇
  1985年   6533篇
  1984年   6126篇
  1983年   5399篇
  1982年   5104篇
  1981年   5180篇
  1980年   4868篇
  1979年   4810篇
  1978年   4589篇
  1977年   5537篇
  1976年   7208篇
  1975年   3965篇
  1974年   3696篇
  1973年   3782篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
961.
The radiative properties of patterned silicon wafers have a major impact on the two critical issues in rapid thermal processing (RTP), namely wafer temperature uniformity and wafer temperature measurement. The surface topography variation of the die area caused by patterning and the roughness of the wafer backside can have a significant effect on the radiative properties, but these effects are not well characterized. We report measurements of room temperature reflectance of a memory die, logic die, and various multilayered wafer backsides. The surface roughness of the die areas and wafer backsides is characterized using atomic force microscopy (AFM). These data are subsequently used to assess the effectiveness of thin film optics in providing approximations for the radiative properties of patterned wafers for RTP applications  相似文献   
962.
In reference to the above-titled paper by R.A. DeMillo and A.J. Offutt (see ibid., vol.17, no.9, p.900-10, Sept. 1991), the commenter rates that he and M.R. Woodward (1985) implemented a system for FORTRAN-77 programs that integrates weak mutation and data flow analysis. He reports here that experiments have been carried out by them (1986), using the system to compare the error exposing ability of weak mutation, data flow, and control flow testing strategies  相似文献   
963.
The paper presents a review of results concerning the aspartic proteinase cathepsin D and its role in tumor invasion and metastasis. Special attention was paid to the clinical prognostic value of cathepsin D determination in the breast cancer cytosol.  相似文献   
964.
This paper addresses the problem of assessing the quality of an a posteriori error estimate of a finite element solution. An error estimate based on local L2-projections is analysed in the case of translation-invariant meshes. It is shown that for general meshes this technique does not lead to an asymptotically exact estimator. The problem is analysed in detail in the one-dimensional setting. It is shown that an asymptotically exact estimator is not the optimal one when the solution is not sufficiently smooth. An optimal estimator for adaptively constructed meshes is given. Finally, a general mathematical framework for the quality assessment of estimators is introduced.  相似文献   
965.
The authors report an exceedingly rare complication of rheumatoid arthritis, i.e. acquired hemophilia due to anti-factor VIII autoantibody production. Treatment with intravenous immune globulin ensured control of hemorrhagic manifestations by inducing a transient rise in factor VIII level.  相似文献   
966.
It was found, that To?pa Peat Preparation (TPP) administered to healthy volunteers in doses of 100-300 mg/day during 14 days evoked the stimulation of the phagocytic and bactericidal activity of the granulocytes. The dose of 600 mg/day causes only a transient and insignificant increase of phagocytic and bactericidal properties of the granulocytes.  相似文献   
967.
968.
To evaluate right atrial (RA) contractile performance in patients with myocardial infarction, we validated a cineangiographic method of RA volume measurement, and investigated RA volume change in 'normal' individuals and patients with a previous myocardial infarction. Sixteen silicone rubber RA casts made from human cadavers were filmed in the postero-anterior and left lateral projections. The cast volumes calculated following Simpson's rule were in good agreement with those measured by water replacement (r = 0.992, P < 0.01). At cardiac catheterization, biplane RA cineangiography was performed in 19 'normal' individuals (N group), in 14 patients with a previous antero-septal infarction (AMI group) and in seven patients with a previous inferior infarction (IMI group). The RA volume-time curve was constructed at 20-40 ms intervals for one cardiac cycle. RA volume at the beginning of the atrial contraction (RAVd), which was defined as the 'preload' of the RA, tended to be larger in both the AMI and IMI groups compared with 'normal' individuals. The RA ejection volume was significantly larger in both the AMI (18.4 +/- 2.1 ml.m-2, P < 0.01) and IMI groups (19.4 +/- 2.8, P < 0.01) than in the N group (14.5 +/- 1.9), even for a comparable level of RAVd (range from 26 to 36 ml.m-2) (18.6 +/- 2.1, P < 0.01, 18.2 +/- 2.0, P < 0.01, 14.7 +/- 1.9, respectively). These results suggest that RA contraction increases in patients with myocardial infarction by increasing both the 'preload' and 'contractility' of the RA.  相似文献   
969.
The plasma membrane (PM) H(+)-ATPase has been proposed to play important transport and regulatory roles in plant physiology, including its participation in auxin-induced acidification in coleoptile segments. This enzyme is encoded by a family of genes differing in tissue distribution, regulation, and expression level. A major expressed isoform of the maize PM H(+)-ATPase (MHA2) has been characterized. RNA gel blot analysis indicated that MHA2 is expressed in all maize organs, with highest levels being in the roots. In situ hybridization of sections from maize seedlings indicated enriched expression of MHA2 in stomatal guard cells, phloem cells, and root epidermal cells. MHA2 mRNA was induced threefold when nonvascular parts of the coleoptile segments were treated with auxin. This induction correlates with auxin-triggered proton extrusion by the same part of the segments. The PM H(+)-ATPase in the vascular bundies does not contribute significantly to auxin-induced acidification, is not regulated by auxin, and masks the auxin effect in extracts of whole coleoptile segments. We conclude that auxin-induced acidification in coleoptile segments most often occurs in the nonvascular tissue and is mediated, at least in part, by increased levels of MHA2.  相似文献   
970.
Fuzzy logic control of a switched reluctance motor drive   总被引:2,自引:0,他引:2  
The paper deals with the fuzzy logic control of a switched reluctance motor (SRM) drive. The fundamentals of the fuzzy logic are first illustrated, pointing out the aspects related to the control under consideration. A fuzzy logic controller (FLC) of the motor speed is then designed and simulated. The results show that the use of an FLC in the speed loop gives the drive superior performances. In particular, the robustness of the drive has been proved  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