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   666318篇
  免费   25654篇
  国内免费   12312篇
电工技术   22744篇
技术理论   31篇
综合类   17778篇
化学工业   106692篇
金属工艺   30603篇
机械仪表   29924篇
建筑科学   32610篇
矿业工程   10751篇
能源动力   18346篇
轻工业   52141篇
水利工程   7905篇
石油天然气   23990篇
武器工业   2254篇
无线电   81292篇
一般工业技术   107028篇
冶金工业   84163篇
原子能技术   9776篇
自动化技术   66256篇
  2023年   5414篇
  2022年   9669篇
  2021年   14203篇
  2020年   10454篇
  2019年   9819篇
  2018年   12249篇
  2017年   13340篇
  2016年   12349篇
  2015年   14184篇
  2014年   19059篇
  2013年   33341篇
  2012年   26301篇
  2011年   31466篇
  2010年   26338篇
  2009年   26872篇
  2008年   27376篇
  2007年   27066篇
  2006年   26633篇
  2005年   23827篇
  2004年   18470篇
  2003年   17508篇
  2002年   16444篇
  2001年   16072篇
  2000年   15966篇
  1999年   17768篇
  1998年   28638篇
  1997年   21476篇
  1996年   17815篇
  1995年   14149篇
  1994年   12426篇
  1993年   11114篇
  1992年   8566篇
  1991年   7874篇
  1990年   7241篇
  1989年   6772篇
  1988年   6345篇
  1987年   5406篇
  1986年   5167篇
  1985年   5695篇
  1984年   5146篇
  1983年   4862篇
  1982年   4556篇
  1981年   4391篇
  1980年   4168篇
  1979年   4002篇
  1978年   3695篇
  1977年   4465篇
  1976年   5858篇
  1975年   3181篇
  1974年   3022篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Attempts have been made to extend SQL to work with multimedia databases. We are reserved on the representation ability of extended SQL to cope with the richness in content of multimedia data. In this paper we present an example of a multimedia database system, Computer Aided Facial Image Inference and Retrieval system (CAFIIR). The system stores and manages facial images and criminal records, providing necessary functions for crime identification. We would like to demonstrate some core techniques for multimedia database with CAFIIR system. Firstly, CAFIIR is a integrated system. Besides database management, there are image analysis, image composition, image aging, and report generation subsystems, providing means for problem solving. Secondly, the richness of multimedia data urges feature-based database for their management. CAFIIR is feature-based. A indexing mechanism,iconic index, has been proposed for indexing facial images using hierarchical self-organization neural network. The indexing method operates on complex feature measures and provides means for visual navigation. Thirdly, special retrieval methods for facial images have been developed, including visual browsing, similarity retrieval, free text retrieval and fuzzy retrieval.  相似文献   
972.
C-VISION中文窗口系统综合采用了面向对象与窗口环境设计的程序方法,彻底更新了在微机上进行中文窗口设计的编程思想,同时作为一个基础系统,为软件设计节约了大量的人力和时间,实现了微机程序的共享。  相似文献   
973.
张家桂 《控制与决策》1994,9(6):459-463
本文提出励磁电流可自动控制的他励式双高调速系统设计方案。系统在提升特别是在下放重物时,具有较硬的机械性;在负载10-100%的变化范围内,可实现最大偏差Δnmax/nmin100%≤10%,调速范围D≥10;在满载运行条件下,可节约电能80%以上。  相似文献   
974.
张学群  韦钰 《功能材料》1994,25(2):97-103
本文综述了大环分子面-面堆积结构的准一维导体的结构、性质、导电机理、合成方法及研究进展。  相似文献   
975.
本文从冗余磁盘阵列的信道模型出发,研究各部分组成的理论与技术。文中在给出系统的模型描述之后,着重分析了冗余信息元生与检纠错、数据分割与同步。还研究了系统中的负荷平衡问题,指出了磁盘优化调度的方向。  相似文献   
976.
Case reports from the United Kingdom (UK) in 1989 have suggested that the introduction of human insulin in 1985 was associated with an increased risk of sudden death in insulin-treated diabetic patients. If human insulin increases the risk of sudden death, the number of these should have increased during the period where human insulin was introduced. We therefore identified all cases of sudden death in Denmark in younger insulin-treated diabetic patients, age at death below 50 years. During this period the consumption of human insulin went from 0.2% to 70% of the total consumption in Denmark. The total number of cases fulfilling the inclusion criteria was 226, and the annual number of sudden deaths did not change during the study period (p = 0.14). The number of deaths due to hypoglycaemia and cases with unexplained cause of death also remained constant (test for trend: p = 0.44). Chronic alcohol abuse or acute alcohol intoxication was found in 50% of the 135 patients dying from hypoglycaemia, ketoacidosis or unknown cause of death (including found dead in bed), while this was the case in only 16% of the remaining 91 cases dying from other natural causes. We conclude that introduction of human insulin in Denmark was not followed by an increase in sudden deaths among younger insulin-treated diabetic patients.  相似文献   
977.
OBJECTIVE: To analyze HLA-DR4 alleles in New Zealand Polynesians with rheumatoid arthritis (RA). METHODS: Thirty Polynesians and 30 Caucasians with RA, as well as 65 Polynesian and 60 Caucasian healthy blood donors, were DR4 subtyped using the polymerase chain reaction and sequence-specific oligonucleotide probes. RESULTS: The frequency of DR4 (DRB1*04) was increased in both Polynesian (P < 0.001) and Caucasian (P < 0.005) RA patients compared with race-matched controls. Dw4 (DRB1*0401) was detected in 15 of 30 Caucasian patients but only 2 of 30 Polynesian patients (P < 0.001). In Polynesians, RA was associated with Dw15 (DRB1*0405), which was present in 11 of 30 patients and 3 of 65 controls (P < 0.001). Dw13 (DRB1*0403) was the most frequent DR4 allele in healthy Polynesians, but was not significantly associated with RA. CONCLUSION: The predominance of the Dw13 subtype in Polynesians may explain in part the low prevalence of RA in this population. The association of Dw15 with RA in Polynesians supports the hypothesis that the third hypervariable region of DR beta determines susceptibility to RA.  相似文献   
978.
A 21-year-old man presented to our hospital on June 7, 1990, asymptomatic but with an abnormal shadow in his chest roentgenogram. A well-demarcated tumorous shadow was seen in the left hilum of the lung in the frontal view of the chest X-ray, and adjacent to the posterior chest wall in the lateral view. A percutaneous needle biopsy was performed, and since there were no malignant findings, the tumor was left untreated for future examinations. However, since the tumor was observed to be enlarging gradually in subsequent chest X-rays, it was resected surgically on June 18, 1991. The tumor was fist-sized and its surface smooth, and was protruding into the thoracic cavity. At surgery, the tumor was separated from the chest wall. The tumor, weighing 170 grams, was diagnosed pathologically as a liposarcoma (myxoid type). It was confirmed that there was no infiltration into the surrounding tissue and that total resection had been performed. There are few reports of liposarcomas within the thoracic cavity developing in the extra-mediastinal chest wall. As our case is the second in Japan occurring in a young patient, we present it here together with a review of the literature.  相似文献   
979.
Localization of fodrin, a membrane skeletal protein, in the outer hair cell of the guinea pig cochlea was examined by immunocytochemical techniques. By immunofluorescence microscopy, fodrin was observed in the cuticular plate, in the infracuticular network and along the lateral wall. By immunoelectron microscopy of ultrathin cryosections, labeling for fodrin along the lateral wall was localized between the cell membrane and the outermost layer of the subsurface cisternae. Furthermore, pre-embedding immunoelectron microscopy of permeabilized specimens showed that most immunogolds for fodrin were on the thin cross-linking component of the cortical lattice. The results indicate that fodrin is a constituent of the cortical lattice which is thought to play an important role in outer hair cell motility.  相似文献   
980.
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   
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