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   5548篇
  免费   95篇
  国内免费   8篇
电工技术   271篇
综合类   11篇
化学工业   1020篇
金属工艺   98篇
机械仪表   97篇
建筑科学   93篇
能源动力   181篇
轻工业   311篇
水利工程   22篇
石油天然气   10篇
无线电   625篇
一般工业技术   949篇
冶金工业   1392篇
原子能技术   150篇
自动化技术   421篇
  2023年   23篇
  2022年   75篇
  2021年   90篇
  2020年   39篇
  2019年   59篇
  2018年   54篇
  2017年   42篇
  2016年   90篇
  2015年   42篇
  2014年   113篇
  2013年   221篇
  2012年   156篇
  2011年   199篇
  2010年   163篇
  2009年   178篇
  2008年   193篇
  2007年   165篇
  2006年   147篇
  2005年   148篇
  2004年   140篇
  2003年   141篇
  2002年   117篇
  2001年   152篇
  2000年   109篇
  1999年   153篇
  1998年   576篇
  1997年   364篇
  1996年   277篇
  1995年   148篇
  1994年   153篇
  1993年   142篇
  1992年   73篇
  1991年   75篇
  1990年   66篇
  1989年   68篇
  1988年   60篇
  1987年   57篇
  1986年   59篇
  1985年   61篇
  1984年   42篇
  1983年   46篇
  1982年   49篇
  1981年   53篇
  1980年   30篇
  1979年   32篇
  1978年   26篇
  1977年   32篇
  1976年   61篇
  1974年   16篇
  1973年   16篇
排序方式: 共有5651条查询结果,搜索用时 0 毫秒
971.
972.
The crystallization phenomenon of human midcycle cervical mucus was studied with purified mucin and sodium chloride. The drying of the purified mucin in saline was subjected to stress by the use of an air curtain, and crystallization (fern pattern) was found to follow the stress. Lithium chloride and calcium chloride were not compatible with the mucin for the formation of fernlike crystals. When a dilute solution of mucin dissolved in saline was dried, a radial crystallization pattern was observed to emanate from a single crystal in the center. Upon closer examination, the pattern was observed to emanate from the corners of the crystal.  相似文献   
973.
Compartment syndrome is caused by an increase in intracompartmental pressure above the capillary level, preventing capillary flow. The acute onset of symptoms occurs after events such as fracture, soft tissue trauma, and revascularization and usually necessitates prompt fasciotomy to avoid loss of function or even necrosis of the enclosed muscle. Compartment syndromes in athletes are of a recurrent nature and are usually referred to as chronic. Nonoperative treatment is often successful. Although compartment syndromes can occur in several anatomic regions, the most commonly seen in athletes involve the leg. Chronic compartment syndromes of the upper extremity are rare, and only a few cases have been reported in the literature. The intracompartmental pressures causing chronic symptoms in these cases ranged between 22 mm Hg at rest and 40 mm Hg after 30 minutes of exercise. Under maximal contraction, a pressure of 58 mm Hg has been recorded. The object of this paper is to report a case of a tennis player where much higher flexor-pronator muscle intracompartmental pressures than those noted above were recorded. We compared the intracompartmental pressure data of this patient with intracompartmental pressures measured in six symptom-free volunteers.  相似文献   
974.
Retinoic acid (RA) plays a major role in neuronal cell differentiation. Neuroblastoma cells differentiate in vitro by extending neurites and forming ganglion-like aggregates in response to RA. In the present study, we have examined a biological role(s) of DAN in the regulation of RA-mediated cellular differentiation in neuroblastoma cells. RTBM1 and SH-SY5Y cells undergo marked morphological changes associated with a remarkable induction of DAN gene expression when exposed to RA. By transfecting an expression vector harboring a rat DAN cDNA into SH-SY5Y cells, we have obtained two independent transfectants which express a large amount of DAN. The forced expression of DAN gene enhanced the neurite extension in the presence of RA, suggesting that DAN gene product might contain some regulatory role(s) in the RA-induced cellular differentiation in neuroblastoma cells.  相似文献   
975.
976.
We present a method through which domestic service robots can comprehend natural language instructions. For each action type, a variety of natural language expressions can be used, for example, the instruction, ‘Go to the kitchen’ can also be expressed as ‘Move to the kitchen.’ We are of the view that natural language instructions are intuitive and, therefore, constitute one of the most user-friendly robot instruction methods. In this paper, we propose a method that enables robots to comprehend instructions spoken by a human user in his/her natural language. The proposed method combines action-type classification, which is based on a support vector machine, and slot extraction, which is based on conditional random fields, both of which are required in order for a robot to execute an action. Further, by considering the co-occurrence relationship between the action type and the slots along with the speech recognition score, the proposed method can avoid degradation of the robot’s comprehension accuracy in noisy environments, where inaccurate speech recognition can be problematic. We conducted experiments using a Japanese instruction data-set collected using a questionnaire-based survey. Experimental results show that the robot’s comprehension accuracy is higher in a noisy environment using our method than when using a baseline method with only a 1-best speech recognition result.  相似文献   
977.
978.
The morphology and microstructure of splats impact the comprehensive capability of a new coating methodology called chelate flame spraying (CFS). This study addresses the quantitative characterization of the spread morphologies of flame sprayed Er2O3 splats directly deposited under different spray conditions on aluminum alloy substrates with a mirror finish. The influence of the in-flight particle temperature and velocity, carrier gas type, and carrier gas ratio on the solidification mechanism of molten droplets was investigated. Image analysis methods were employed to identify single splats from the morphology observed with field-emission scanning electron microscopy (FE-SEM). In addition, Er2O3 films were synthesized on an Al–Mg alloy (A5052) substrate using N2 or O2 as the carrier gas. When O2 was used as the carrier gas, 109-μm-thick films were deposited on the A5052 substrate. The cross-sectional porosity of the films was 3.8%. In contrast, films with 101-μm thickness were synthesized on the A5052 substrate when N2 was used as the carrier gas. The cross-sectional porosity of these films was 13.8%. The results showed that the carrier gas type (N2) and carrier gas ratio had a significant effect on the flattening behavior of the molten droplets. A spraying method combined with multidimensional modes is proposed to control the morphology of the splats.  相似文献   
979.
980.
Tumor-associated macrophages (TAMs) promote cancer cell proliferation and metastasis, as well as anti-tumor immune suppression. Recent studies have shown that tumors enhance the recruitment and differentiation of TAMs, but the detailed mechanisms have not been clarified. We thus examined the influence of cancer cells on the differentiation of monocytes to TAM subsets, including CD163+, CD204+, and CD206+ cells, in oral squamous cell carcinoma (OSCC) using immunohistochemistry, flow cytometry, and a cytokine array. Furthermore, we investigated the effect of OSCC cells (HSC-2, SQUU-A, and SQUU-B cells) on the differentiation of purified CD14+ cells to TAM subsets. The localization patterns of CD163+, CD204+, and CD206+ in OSCC sections were quite different. The expression of CD206 on CD14+ cells was significantly increased after the co-culture with OSCC cell lines, while the expressions of CD163 and CD204 on CD14+ cells showed no change. High concentrations of plasminogen activator inhibitor-1 (PAI-1) and interleukin-8 (IL-8) were detected in the conditioned medium of OSCC cell lines. PAI-1 and IL-8 stimulated CD14+ cells to express CD206. Moreover, there were positive correlations among the numbers of CD206+, PAI-1+, and IL-8+ cells in OSCC sections. These results suggest that PAI-1 and IL-8 produced by OSCC contribute to the differentiation of monocytes to CD206+ TAMs.  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