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   1619篇
  免费   26篇
  国内免费   3篇
电工技术   17篇
综合类   5篇
化学工业   112篇
金属工艺   10篇
机械仪表   29篇
建筑科学   78篇
矿业工程   3篇
能源动力   21篇
轻工业   57篇
水利工程   9篇
石油天然气   3篇
无线电   128篇
一般工业技术   164篇
冶金工业   888篇
原子能技术   10篇
自动化技术   114篇
  2021年   14篇
  2020年   6篇
  2019年   15篇
  2018年   10篇
  2016年   13篇
  2015年   10篇
  2014年   23篇
  2013年   38篇
  2012年   30篇
  2011年   32篇
  2010年   28篇
  2009年   31篇
  2008年   34篇
  2007年   43篇
  2006年   31篇
  2005年   27篇
  2004年   24篇
  2003年   34篇
  2002年   20篇
  2001年   24篇
  2000年   19篇
  1999年   39篇
  1998年   270篇
  1997年   157篇
  1996年   113篇
  1995年   55篇
  1994年   43篇
  1993年   49篇
  1992年   28篇
  1991年   23篇
  1990年   23篇
  1989年   16篇
  1988年   23篇
  1987年   23篇
  1986年   15篇
  1985年   16篇
  1984年   14篇
  1983年   12篇
  1982年   16篇
  1981年   13篇
  1980年   21篇
  1979年   16篇
  1978年   12篇
  1977年   22篇
  1976年   55篇
  1975年   5篇
  1974年   7篇
  1973年   9篇
  1971年   8篇
  1966年   5篇
排序方式: 共有1648条查询结果,搜索用时 0 毫秒
211.
There has been a revived interest in the enhanced radio fields that are encountered in the presence of trapping or dueting atmospheric refractivity gradients either aloft or at and near the surface. Recent progress in the theoretical formulation of ducted fields is summarized, some resulting expressions for interference problems are presented, and those areas still in need of additional development are identified.  相似文献   
212.
IgA class reticulin antibodies were not found in patients with Crohn's disease, ulcerative colitis, and hiatus hernia despite a significant incidence of IgG class reticulin antibodies. None of 56 normal healthy subjects was positive. In contrast, 13 (76%) of the sera from 17 patients with coeliac disease on normal diet were positive for IgA class antibodies as were 19 (20%) of 93 first degree relatives. Seventy-three relatives underwent jejunal biopsy. Grade III (flat) histology was found in 13 and, of these patients, 10 (77%) showed IgA class reticulin antibody in their serum. It is suggested that determination of IgA class reticulin antibodies was a useful test to determine which relative must be biopsied.  相似文献   
213.
We have investigated in anaesthetised pigs the electrical responses of the retina to light after blunt injuries to the eye. Retinograms, cortical visual evoked responses and intraocular pressures were recorded before and after non-perforating mechanical trauma of sufficient severity to produce traumatic retinal opacification. After injury, applanation pressures rose up to 34 mm. Hg above normal, reaching peak values 4 to 12 minutes after trauma and returning to pre-trauma levels after about 45 minutes. These pressure changes were not responsible for the immediate abolition of the B wave of the retinogram or of the cortical visual evoked responses which occurred after trauma, but increases of intraocular pressure modified the recovery pattern of the visual evoked response.  相似文献   
214.
A highly potent inhibitor of calmodulin-sensitive phosphodiesterase (PDE) activity was isolated from the culture broth of an unidentified fungal isolate, SCF-125. A chemically defined medium was developed for production of this compound. The PDE inhibitor was isolated from the fermentation filtrate by adsorption on a macro-reticular resin and further purified by gel filtration chromatography and reverse-phase HPLC. The major PDE inhibitor was identified as cephalochromin, a bis-naphthopyrone, by spectral data analysis. The compound, SCH 45752, inhibited calmodulin-sensitive PDE activities with IC50 values of 40-47 nM. It inhibited the activities of calmodulin-independent PDE and various protein kinases with higher IC50 values (2-40 microM). SCH 45752 does not appear to be a calmodulin antagonist. Furthermore, SCH 45752 affects smooth muscle contraction at a concentration of 30 microM; it potentiated the relaxing effect of sodium nitroprusside on carotid artery media contracted by histamine. Thus SCH 45752 is one of the most potent inhibitors of calmodulin-sensitive PDE activity known, and it is capable of exerting a pharmacological effect in at least one intact tissue model.  相似文献   
215.
216.
The combination of manual and automated extraction procedures using low sample volumes (5-50 ml) with large-volume oncolumn injection (LVI) (200 microliters) in capillary gas chromatography with flame photometric detection (GC-FPD) has allowed the determination of 16 organophosphorus pesticides in clean water samples at the low ng l-1 level with an important simplification in the sample preparation step. A simple and fast offline liquid-liquid microextraction procedure (2-5 ml water/l ml methyl tert.-butyl ether) has been applied to spiked groundwater samples (containing 0.5 ng of each pesticide) with good recoveries (over 80%) and precision (better than 10%), giving detection limits between 5 and 100 ng l-1 using 200 microliters injections in the GC-FPD system. The application of an inline automated liquid-liquid microextraction-LVI-GC procedure (2 ml water/2 ml methyl tert.-butyl ether: injection of 200 microliters in GC-FPD) using the autosampler ASPEC XL led to lower recoveries (> 50%) as a result of the low efficiency for mixing organic and aqueous phases, although with very satisfactory coefficients of variation (lower than 7%) and detection limits between 20 and 200 ng l-1. Manual and automated solid-phase extraction procedures using the well known C18 cartridges and the new Oasis HLB have been applied to groundwater samples (5-50 ml) spiked with 1 ng of each pesticide. Results obtained for both the manual and the automated procedures were satisfactory (recoveries over 80%) and the limits of detection for 50 ml sample volume ranged from 1 to 6 ng l-1.  相似文献   
217.
To disclose the cytoprotective mechanism of 1,6-dihydro-2[2-(2-methyoxypropoxy)anilino]-6-oxo-5-pyrimidinecarb oxylic acid (CAS 98772-05-5, MAR-99), the effect of this compound on the microvascular injury in gastric mucosa induced by 99.5% ethanol in rats was studied. In this experiment, it was found that the elevation of vascular permeability observed at the early state of ethanol-induced gastric mucosal injury was closely correlated with the combined action of histamine and slow reacting substance (leukotriene C4, LTC4). MAR-99 (0.3-10 mg/kg p.o.) prevented dose-dependently the increase in vascular permeability. Furthermore, MAR-99 (10 mg/kg p.o.) improved the decrease in the number of histamine containing cells and histamine content, and prevented the production of LTC4. These results suggest that MAR-99 exerts its anti-microvascular injury effect by regulating the release of histamine and the production of LTC4 in glandular stomach against ethanol, and this effect may contribute to the anti-lesion effect of this compound.  相似文献   
218.
219.
220.
Nearly 4 million women in the United States were physically hurt by their husbands or boyfriends in 1994. The health and well-being of these women and their children, as well as the women who are overlooked in these statistics, are jeopardized by past and current experiences with abuse within intimate relationships. Strategies for nurses in women's health care settings to screen women for current or past abuse within their intimate personal relationships, guidelines for effective responses to disclosure of abuse, and supportive interventions are described.  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