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   8631篇
  免费   818篇
  国内免费   586篇
电工技术   860篇
综合类   660篇
化学工业   1312篇
金属工艺   543篇
机械仪表   519篇
建筑科学   548篇
矿业工程   222篇
能源动力   245篇
轻工业   1170篇
水利工程   225篇
石油天然气   138篇
武器工业   80篇
无线电   733篇
一般工业技术   761篇
冶金工业   643篇
原子能技术   194篇
自动化技术   1182篇
  2024年   38篇
  2023年   95篇
  2022年   265篇
  2021年   354篇
  2020年   225篇
  2019年   224篇
  2018年   215篇
  2017年   247篇
  2016年   232篇
  2015年   319篇
  2014年   440篇
  2013年   555篇
  2012年   673篇
  2011年   669篇
  2010年   589篇
  2009年   613篇
  2008年   631篇
  2007年   534篇
  2006年   489篇
  2005年   433篇
  2004年   354篇
  2003年   299篇
  2002年   291篇
  2001年   250篇
  2000年   180篇
  1999年   96篇
  1998年   144篇
  1997年   103篇
  1996年   56篇
  1995年   40篇
  1994年   60篇
  1993年   52篇
  1992年   23篇
  1991年   15篇
  1990年   23篇
  1989年   20篇
  1988年   16篇
  1987年   9篇
  1986年   11篇
  1985年   15篇
  1984年   11篇
  1983年   11篇
  1982年   16篇
  1981年   8篇
  1980年   10篇
  1979年   6篇
  1977年   11篇
  1976年   19篇
  1975年   7篇
  1974年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The authors report the case of a 32 year old woman who was shot with a shotgun. Acute inferior wall infarction was detected fortuitously on electrocardiography and coronary angiography showed occlusion of the right coronary artery with lead shot. The single coronary lesion, absence, of other cardiac complications (haemopericardium, cardiac perforation, ...) and the favourable outcome with conservative medical treatment has not been previously reported to the authors' knowledge.  相似文献   
22.
Palatopharyngeal surgery is a therapeutic option for obstructive Sleep Apnea Syndrome (OSAS). This operation is based on the assumption that the soft palate is the principal apneogenic area of the upper airways. The effectiveness of palatopharyngeal surgery and of correcting nasal obstruction (co-adjuvant factor of SAOS), when present, was evaluated. Thirty patients were selected by cephalometry for surgery (3 women, 27 men; age 45.3 +/- 7.5 years). The success rate was 60%, which justifies the inclusion of surgery as a useful option for treating SAOS.  相似文献   
23.
Theprecipitationofpro eutectoidferritefromausteniteiscontrolledbydiffusioninFe Calloys .Withtheassumptionthatthemigratinginterfaceisalwaysinlocalequilibrium ,earlyin 194 9,ZenerC[1] explainedthediffusionalgrowthofpro eutec toidferritebyusingtheFick’slaw .Since…  相似文献   
24.
只读式超分辨光盘的膜层设计和分析   总被引:4,自引:3,他引:1  
李进延  阮昊  干福熹 《中国激光》2002,29(4):366-370
超分辨技术是一种无需减小记录波长或增大数值孔径而提高存储密度的方法。Ge Sb Te是一种良好的相变光存储材料 ,在超分辨光盘中可作为掩膜。利用多层膜反射率的矩阵法计算了掩膜为Ge2 Sb2 Te5薄膜的超分辨只读式光盘的光学参数与各膜层厚度之间的关系 ,最后得到了较为理想的膜层厚度匹配。采用磁控溅射法制备了只读式超分辨光盘 ,测量了光盘的光学性质。  相似文献   
25.
通过偏光显微镜观察了石油系油浆(LH)与煤系闪蒸油(SN)焦化后所得焦块的光学结构。结果表明,在较宽条件下两种原料单独焦化均得不到取向度高的流线型结构。将两种原料以一定比例混合后先热解丙焦化所得焦块的光学结构明显好于二者混合后直接焦化所得焦块的光学结构,其中LH和SN以3:2的重量比混合后在440℃、1MPa下热解3.5h然后再在530℃、1MPa下焦化8h所得焦块为具有较高取向度的流线型结构,适合于作为针状焦的起始原料。  相似文献   
26.
27.
The features of perturbation propagation in a copper crystal grain under local high-energy loading conditions were studied. The process was studied by method of molecular dynamics using multiparticle model potentials calculated within the framework of the embedded atom approximation. It is shown that a nonlinear solitary pulse is formed in the crystal, which is capable (in contrast to the case of a linear perturbation) of transferring the energy at a high density over relatively large distances. The energy transfer range depends both on the area and on the rate of local loading.  相似文献   
28.
A new method for the isolation of glucose repression-insensitive mutants in the methylotrophic yeast Pichia pinus was developed. The method is based on screening of small suspension samples derived from 2-deoxyglucose-resistant colonies for alcohol oxidase activity. Alcohol oxidase activity was evaluated by determination of formaldehyde excreted by cells. Mutants with glucose non-repressible alcohol oxidase and catalase synthesis were obtained. All mutants grew poorly on D -xylose compared to the wild type, whereas growth on L -arabinose was similar to the wild type. Changes in the glucose transport system were suggested to be responsible for altered growth characteristics and defective glucose repression.  相似文献   
29.
BACKGROUND: Friedreich's ataxia (FA), the most common inherited ataxia, is associated frequently with cardiac hypertrophy, and death is often cardiac related. Recently, the disease has been associated with a mutation that consists of an unstable expansion of GAA repeats in the first intron of the gene encoding frataxin on chromosome 9. METHODS AND RESULTS: We studied 44 consecutive patients with FA, determined the size of GAA expansions in the frataxin gene, and examined the relation between the genotype and cardiac phenotype assessed by M-mode and two-dimensional echocardiography. All the patients were homozygous for the mutation. The size of the GAA expansion on the smaller allele varied from 270 to 1200. We found a correlation between the size of GAA expansion and the left ventricular wall thickness (r = .51, P < .001) and the left ventricular mass index (r = .45, P = .002). Left ventricular hypertrophy was observed in 81% of patients with a number of GAA repeats above the median value of 770 compared with only 14% in the other group (P = .002). CONCLUSIONS: These data demonstrate that in FA, the severity of left ventricular hypertrophy is related to the number of GAA repeats. These results suggest that abnormalities of the gene encoding frataxin, a protein of unknown function highly expressed in the normal heart, may play an important role in the modulation of cardiac hypertrophy.  相似文献   
30.
Compatibility equations for large deformations are developed on the sole basis of the div and curl concepts.  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