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   538254篇
  免费   7914篇
  国内免费   1490篇
电工技术   9733篇
综合类   537篇
化学工业   81825篇
金属工艺   20119篇
机械仪表   15563篇
建筑科学   13210篇
矿业工程   2301篇
能源动力   15030篇
轻工业   49494篇
水利工程   5383篇
石油天然气   9402篇
武器工业   39篇
无线电   60715篇
一般工业技术   103738篇
冶金工业   104226篇
原子能技术   10616篇
自动化技术   45727篇
  2022年   3553篇
  2021年   5484篇
  2020年   3890篇
  2019年   5016篇
  2018年   8376篇
  2017年   8188篇
  2016年   8572篇
  2015年   6012篇
  2014年   9822篇
  2013年   25246篇
  2012年   15504篇
  2011年   21107篇
  2010年   16483篇
  2009年   18416篇
  2008年   18777篇
  2007年   18340篇
  2006年   15968篇
  2005年   14540篇
  2004年   13905篇
  2003年   13664篇
  2002年   12876篇
  2001年   12969篇
  2000年   11999篇
  1999年   12718篇
  1998年   33075篇
  1997年   23066篇
  1996年   17569篇
  1995年   13130篇
  1994年   11347篇
  1993年   11042篇
  1992年   7949篇
  1991年   7445篇
  1990年   7287篇
  1989年   7037篇
  1988年   6493篇
  1987年   5792篇
  1986年   5680篇
  1985年   6294篇
  1984年   5937篇
  1983年   5199篇
  1982年   4925篇
  1981年   4977篇
  1980年   4726篇
  1979年   4623篇
  1978年   4420篇
  1977年   5350篇
  1976年   6991篇
  1975年   3803篇
  1974年   3555篇
  1973年   3673篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
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   
992.
993.
994.
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   
995.
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   
996.
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   
997.
998.
The frequency of human papillomavirus (HPV) in laryngeal papillomas varies largely among different studies. DNA in situ hybridization (ISH) has been the most widely used method for detection of HPV. The aim of this study was to compare the reproducibility and sensitivity of ISH with polymerase chain reaction (PCR) in 35 specimens of laryngeal papillomas routinely fixed in buffered or unbuffered formalin. Out of 12 specimens fixed in buffered formalin, 10 were positive for HPV 6/11 using ISH. The procedure was repeated three times and three specimens were positive only twice. Nine biopsies were positive for HPV using PCR with consensus primers (My 09/11) on dewaxed tissue without extracting DNA. In three repeated PCRs, the results were inconsistent in three samples. After DNA extraction, all 12 samples were positive with PCR. Of the 23 specimens fixed in unbuffered formalin, 14 were HPV-positive with ISH, while only one was positive with PCR. We concluded that PCR with My 09/11 consensus primers is a highly sensitive method for detection of HPV in laryngeal papillomas fixed in buffered formalin, but useless for samples fixed in unbuffered formalin. When DNA was extracted from the former type of fixed tissue, the results were highly reproducible. In contrast to PCR, ISH appeared to be less influenced by fixation procedure, but it was not as reproducible and sensitive as PCR. Negative results did not necessarily mean absence of HPV.  相似文献   
999.
Bone mass measurements are essential in the diagnosis of osteoporosis, the monitoring of its progression, and the evaluation of therapeutical responses. Among various methods of bone mass measurements, single- and dual-X-ray absorptiometry, SXA and DXA, have shown excellent fundamental performance. In this paper, the principles of SXA and DXA; i.e., factors of fundamental performance, such as precision, data-acquisition, and radiation dose, the practice of DXA, recent advances in DXA, such as the lateral spine scan, the measurement of body composition, application to BMD measurement of the bones of small animals and at sites of metal implants, morphometry of the spine, and geometrical measurement in the proxial femur, and clinical applications to osteoporosis were particularly reviewed.  相似文献   
1000.
We have previously reported that long-term priming of human polymorphonuclear neutrophilic granulocytes (PMN) with interferon-gamma (IFN-gamma) increased the fMLP-stimulated calcium influx. We now show that also after short-term incubation with IFN-gamma, PMN calcium metabolism is modulated. Single adherent cells in three different calcium-containing buffers (high, normal, and low [Ca2+]) were stimulated with the bacterial peptide fMLP or the Ca-ATPase inhibitor thapsigargin (Tg) after about 5 min preincubation with IFN-gamma. The results of this protocol indicated that IFN-gamma increases both calcium influx and calcium sequestration. Store dependent Ca2+ influx, directly measured on readdition of calcium to Tg-treated cells incubated in EGTA buffer, was significantly enhanced in IFN-gamma-treated cells. This effect of IFN-gamma was enhanced by the tyrosine kinase inhibitor herbimycin A. Strikingly, in low extracellular calcium concentrations, IFN-gamma induced calcium transients in 20%-60% of the cells. The proportion of PMN responding with Ca2+ transients increased with decreasing extracellular calcium concentration. Average lagtime from addition of IFN-gamma to a response that could be measured was 7.3 sec, and average increase in [Ca2+] above the basal level was 790 nM. These IFN-gamma-induced transients could not be depressed by herbimycin A. Thus, IFN-gamma can increase capacitative calcium influx, induce calcium transients, and possibly affect calcium sequestration in human PMN.  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