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   1899篇
  免费   11篇
  国内免费   4篇
电工技术   24篇
综合类   1篇
化学工业   80篇
金属工艺   19篇
机械仪表   4篇
建筑科学   13篇
矿业工程   1篇
能源动力   19篇
轻工业   37篇
水利工程   1篇
无线电   118篇
一般工业技术   80篇
冶金工业   1461篇
原子能技术   7篇
自动化技术   49篇
  2023年   2篇
  2022年   5篇
  2021年   5篇
  2020年   2篇
  2019年   3篇
  2018年   6篇
  2017年   5篇
  2016年   5篇
  2015年   7篇
  2014年   14篇
  2013年   15篇
  2012年   11篇
  2011年   26篇
  2010年   11篇
  2009年   20篇
  2008年   25篇
  2007年   15篇
  2006年   16篇
  2005年   17篇
  2004年   11篇
  2003年   21篇
  2002年   8篇
  2001年   10篇
  2000年   8篇
  1999年   43篇
  1998年   428篇
  1997年   286篇
  1996年   174篇
  1995年   99篇
  1994年   94篇
  1993年   95篇
  1992年   24篇
  1991年   38篇
  1990年   25篇
  1989年   27篇
  1988年   29篇
  1987年   32篇
  1986年   30篇
  1985年   17篇
  1984年   6篇
  1983年   10篇
  1982年   18篇
  1981年   13篇
  1980年   17篇
  1979年   6篇
  1978年   6篇
  1977年   42篇
  1976年   78篇
  1975年   4篇
  1973年   2篇
排序方式: 共有1914条查询结果,搜索用时 93 毫秒
41.
This study investigates the professional characteristics of care staff working in group homes for the mentally ill in a north London region. Opportunities for training and staff attitudes with respect to training and career prospects are examined. The majority of care staff are unqualified and in many cases the training needs of staff are not being met. Staff viewed their career prospects as limited. Training that is on offer to staff in principle is often not accessed, possibly owing to budget restrictions. The need for more stringent guidelines on staff training to maintain standards across agencies is highlighted.  相似文献   
42.
43.
44.
Artificial illumination is an important factor in the management of layers. In this study, a new monochromatic light system was developed for egg layers. Prelaying pullets (Lohmann) were marked and housed in nine light and temperature control rooms (15 battery cages, 3 hens per cage; n = 45), divided into three light treatments: 0.1 and 0.01 W/m2 light intensity using light emitting diode (LED) lamps and 0.1 W/m2 using mini-fluorescent bulbs (PL) (control). In each of the LED rooms, three wavelengths were tested: 560 (n = 9), 660 (n = 9), 880 (n = 6), and 660 intermitted lighting (15 min light 45 min dark, 660IN) (n = 9). Birds were exposed to 12 h light and 12 h of darkness using PL lamps. At 21 wk of age, the light period was increased to 12.75 h by using 5.5 h of LED lamps and 7.25 of PL light source for Groups 1 and 2, the third group received 12.75 h of PL light. Until 28 wk of age, light hours increased by 0.5 h/w using LED light for Groups 1 and 2 and PL source for the third group, reaching 16 h of light at 28 wk of age. Egg production and feed consumption were recorded daily; egg components were recorded weekly for 10 mo. A significant reduction in egg production was observed in all 880nm groups; no differences in egg production and quality were found in the other groups. Feed consumption was significantly lower by 7% in all 0.01 W/m2 groups. We suggest that an important reduction in rearing costs of laying hens may be obtained by using this system.  相似文献   
45.
The wakefulness-sleep cycle characteristics changes in Wistar line rats after unilateral lesions of the neuronal elements of the caudate nucleus head with kainic acid (at sparing the conducting ways going through this structure) were studied. It was shown that in 4 days after acid injection the share of the active wakefulness and light slow-wave sleep is significantly increased, whereas the percentage of the passive wakefulness, deep slow-wave stage, and paradoxal sleep (up to 80%) is reduced. The wakefulness-sleep cycle in rats is completely normalized on the 7th day after injection. The obtained data allow to consider the caudate nucleus as a modulator for wakefulness-sleep cycle, that is the structure involved in the motive activity regulation.  相似文献   
46.
AIM: To estimate how many neonates in New Zealand would qualify for extracorporeal membrane oxygenation (ECMO), using both standard published criteria and locally derived criteria. METHODS: Retrospective chart review of all babies with a birth weight over 2000 g admitted to neonatal intensive care in Auckland from June 1990 to June 1993. Ventilation and blood gas indices were calculated for all babies who were ventilated in 100% O2 for more than 4 hours and who met the basic criteria for ECMO (less than 1 week old with no neurological or chromosomal problems). These indices were compared with published ECMO criteria. Using a threshold of an 80% mortality, Auckland criteria for ECMO were derived. RESULTS: Of the published criteria for ECMO, only an oxygenation index of greater than 40 for 4 hours predicted a mortality of more than 80% in our population. From our own findings a PaO2 < 6.5 kPa for 4 hours predicted a mortality of 79%. CONCLUSION: Approximately 19 neonates might qualify for ECMO in New Zealand each year.  相似文献   
47.
48.
We have previously reported that in rat brain membranes, [3H]rilmenidine, in addition to labelling alpha2-adrenoceptors and the I2B-subtype of imidazoline receptor binding site (I2B-RBS), may label an additional I-RBS population, distinct from previously classified I1-RBS and I2-RBS. In this study, using crude or fractionated rat brain membranes we examined the possible association of [3H]rilmenidine-labelled I-RBS with the A- and B-isoforms of monoamine oxidase (MAO) by studying the inhibition of [3H]rilmenidine binding by a number of MAO inhibitors; and comparing the maximal binding density (Bmax) and subcellular distribution of [3H]rilmenidine binding sites with that of MAO-A and MAO-B catalytic sites labelled by [3H]RO41-1049 and [3H]RO19-6327 and 12-RBS labelled by [3H]2-BFI. Inhibition of [3H]rilmenidine binding by all MAO inhibitors tested produced very shallow curves (slope 0.29-0.56). Clorgyline and moclobemide (selective MAO-A inhibitors) displayed moderate affinities (60-140 nM), while pargyline (non-selective MAO-inhibitor), RO41-1049 (selective MAO-A inhibitor) and RO19-6327 (selective MAO-B inhibitor) exhibited very low affinities (> 2 microM) for 50-75% of [3H]rilmenidine-labelled I-RBS in crude brain membranes and even lower affinity for the remaining binding. Under identical buffer conditions, the Bmax of [3H]rilmenidine-labelled I-RBS (1.45+/-0.14 pmol/mg protein) was considerably lower than those of MAO-A (13.10+/-0.15 pmol/mg) and MAO-B (10.35+/-0.50 pmol/mg) sites. These results suggest that [3H]rilmenidine does not interact directly with the active catalytic site of either MAO enzyme and could at best only associate with a subpopulation of MAO molecules. Binding studies on five fractions of rat cortex homogenates-nuclear (N), heavy (M) and light (L) mitochondrial, microsomal non-mitochondrial (P), and soluble cytosolic (S) fractions-revealed that 45% of total [3H]rilmenidine binding was present in the P fraction cf. 20 and 23% in the M and L fractions, in contrast to [3H]RO19-6327 and [3H]2-BFI which bound 11-13% in the P fraction and 36-38% and 35-44% in the M and L fractions, respectively. Binding of all ligands in the N fraction was 6-15% of total. These studies reveal that [3H]rilmenidine-labelled I-RBS, unlike the I2-RBS, are not predominantly associated with mitochondrial fractions containing the MAO enzymes (and cytochrome oxidase activity), but appear to be distributed in both the mitochondrial and plasma membrane fractions in rat cerebral cortex.  相似文献   
49.
A new application is proposed for the on-line coupling of reversed-phase liquid chromatography to gas chromatography (RPLC-GC) that allows the GC chirospecific analysis of gamma-lactones in fruits and commercially available fruit-containing products. The use of a programmed temperature vaporizer as an interface with the system makes the transfer of large volume fractions (i.e., 2520 microL) of aqueous eluents from LC to GC possible (speed of sample transfer, 1800 microL/min). Relative standard deviations obtained for the investigated lactones under the experimental conditions vary from 7 to 14%. The described system enlarges the LC-GC application field and overcomes the limitations reported thus far concerning the use of typical normal-phase eluents (i.e., the transfer of rather small volume fractions at low speeds of sample introduction).  相似文献   
50.
OBJECTIVE: To determine whether sulfasalazine is better than placebo in slowing disability progression in MS. METHODS: In this randomized, double-blind, placebo-controlled phase III trial, 199 patients with active relapsing-remitting (n = 151) or progressive (n = 48) MS were evaluated at 3-month intervals for a minimum of 3 years (94% completed 3 years of follow-up; mean follow-up, 3.7 years). MRI studies were performed at 6-month intervals on a subset of 89 patients. RESULTS: Sulfasalazine failed to slow or prevent disability progression as measured by the primary outcome (confirmed worsening of the Expanded Disability Status Scale [EDSS] score by at least 1.0 point on two consecutive 3-month visits). Sulfasalazine influenced favorably a number of secondary outcomes during the first 18 months of the trial (e.g., annualized relapse rate, proportion of relapse-free patients; progressive subgroup only: rate of EDSS progression at 1 and 2 years, median time to EDSS progression) but these positive findings were not sustained into the second half of the trial. CONCLUSIONS: Sulfasalazine does not prevent EDSS score progression in the subset of MS patients studied by this protocol. Treatments may improve relapse-related outcomes in MS, at least temporarily, without providing sustained slowing of EDSS progression. Phase III MS trials should be of sufficient length to determine a meaningful impact on disease course.  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