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   1750篇
  免费   78篇
  国内免费   4篇
电工技术   75篇
综合类   3篇
化学工业   369篇
金属工艺   44篇
机械仪表   54篇
建筑科学   19篇
能源动力   40篇
轻工业   146篇
水利工程   2篇
无线电   268篇
一般工业技术   355篇
冶金工业   322篇
原子能技术   40篇
自动化技术   95篇
  2023年   11篇
  2022年   19篇
  2021年   22篇
  2020年   16篇
  2019年   18篇
  2018年   34篇
  2017年   26篇
  2016年   40篇
  2015年   29篇
  2014年   49篇
  2013年   88篇
  2012年   58篇
  2011年   74篇
  2010年   52篇
  2009年   66篇
  2008年   82篇
  2007年   50篇
  2006年   50篇
  2005年   72篇
  2004年   36篇
  2003年   41篇
  2002年   55篇
  2001年   37篇
  2000年   32篇
  1999年   41篇
  1998年   134篇
  1997年   89篇
  1996年   55篇
  1995年   42篇
  1994年   48篇
  1993年   37篇
  1992年   25篇
  1991年   24篇
  1990年   28篇
  1989年   16篇
  1988年   22篇
  1987年   15篇
  1986年   18篇
  1985年   24篇
  1984年   17篇
  1983年   13篇
  1982年   14篇
  1981年   11篇
  1980年   21篇
  1979年   16篇
  1978年   11篇
  1977年   17篇
  1976年   14篇
  1973年   6篇
  1970年   3篇
排序方式: 共有1832条查询结果,搜索用时 31 毫秒
881.
BACKGROUND: Tumor procoagulant is one of the factors responsible for disseminated intravascular coagulation and metastasis. The authors found procoagulant activity in LK52 human squamous cell carcinoma cells, which they designated cancer cell-derived blood coagulating activity 1 (CCA-1). A monoclonal antibody (MoAb) was generated to characterize this CCA-1 procoagulant activity. To date, antibodies that show an inhibitory effect on procoagulant activity as well as high reactivity in cancer cells are well known for their tissue factor specificity. METHODS: Characterization of the procoagulant activity of CCA-1 was performed and an anti-CCA-1 MoAb, FS01, was generated. CCA-1 expression on the cancer cell surface was examined by flow cytometry. Procoagulant activity of various cancer cell lines and the inhibitory effect of the FS01 MoAb on this procoagulant activity was monitored by a clot timer. RESULTS: The enzymologic character differed from that of cancer procoagulant (CP). The FS01 MoAb inhibited the procoagulant activity of CCA-1, but did not inhibit that of tissue factor. A positive correlation was observed between the expression intensity of CCA-1 and the inhibitory effect of the FS01 MoAb on the procoagulant activity of cancer cell lines. Expression of CCA-1 was observed more frequently than that of tissue factor in human cancer cell lines. CONCLUSIONS: The FS01 MoAb generated in the current study is a new antibody that reacts with various cancer cell lines, but not with normal cells. FS01 inhibits cancer cell-derived procoagulant activity and does not react with tissue factor and CP. CCA-1, which is recognized by the FS01 MoAb, appears to play a major role in cancer cell-derived procoagulant activity.  相似文献   
882.
We examined the expression kinetics of activation antigens CD38 and MHC-IIDR (DR) on circulating CD8+ lymphocytes in rhesus macaques infected with pathogenic simian immunodeficiency virus strain SIVmac239 nef-open (239) or its nonpathogenic nef-deletion mutant (delta nef). In the longitudinal study, we found for the first time the induction of DR expression on CD8+ lymphocytes in 239-infected macaques. The induction of DR was in parallel with an increasing viral load and a decreasing CD4+ lymphocyte level. In the macaques with the high viral load and low CD4 level, a considerable proportion of the DR+CD8+ subpopulation was CD69+, indicating an activated state. On the other hand, no significant increase in the DR+CD8+ subpopulation level was observed in delta nef-infected macaques. These data indicate that the evaluation of activation markers such as DR and/or CD69 on circulating CD8+ cells may be valuable as a surrogate marker in the SIV-macaque model.  相似文献   
883.
The most important issue in realizing a 4H-SiC vertical MOSFET is to improve the poor channel mobility at the MOS interface, which is related to high on-resistance. This letter focuses on a novel 4H-SiC vertical MOSFET device structure where a low acceptor concentration epitaxial layer is used as a channel. We call this structure a double-epitaxial MOSFET (DEMOSFET). In the structure, the p-well is composed of two p-type epitaxial layers, while an n-type region between the p-wells is formed by low-dose n-type ion implantation. A buried channel is formed at the surface of the upper p/sup $/epitaxial layer. A fabricated DEMOSFET showed an on-resistance of 8.5 m/spl Omega//spl middot/cm/sup 2/ at a gate voltage of 15 V and a blocking voltage of 600 V. This on-resistance is the lowest so far reported for a vertical MOSFET with a blocking voltage of 600 V.  相似文献   
884.
TAK-751S is a synthetic trisaccharide coupled to Chromosorb P using a spacer sequence of 8-methoxycarboyloctyl (MCO). Its chemical structure is similar to a human receptor (Gb3) of Stx produced by enterohemorrhagic Escherichia coli (EHEC). In vitro efficacy of TAK-715S was studied by using ACHN cultured cell assay, which is sensitive and specific for measuring low level of Stx. Under various conditions, TAK-715S was mixed with purified Stx1 and Stx2, and residual free toxins in the solution were measured by using ACHN cells. TAK-715S was demonstrated to bind specifically to Stx1 and Stx2 under the condition similar to a human intestine while Chromsorb P did not bind to any Stx. The binding activity was stable in the presence of various processed foods, fresh vegetables and fruits. Antibiotics such as fosfomycin, kanamycin and norfloxacin did not disturb its binding capability. Minimum inhibitory concentrations of these antibiotics against Staphylococcus aureus FDA209P or E. coli NIHJ JC-2 neither changed after incubating with TAK-751S for 60 min at 37 degrees C. These results suggest that TAK-751S can be given orally with various foods and antibiotics for the elimination of Stx1 and Stx2 in the gut of patients with EHEC infections.  相似文献   
885.
886.
In heart failure with low cardiac output, exercise tolerance is reduced despite modulated regional blood distribution and oxygen extraction. However, low cardiac output does not necessarily lead to reduced exercise tolerance especially during mild exercise. In the present study, in order to understand the mechanisms regulating exercise tolerance in heart failure, we measured oxygen consumption (VO2) and cardiac output (CO) during both mild and intense exercise. Patients with heart failure were divided into 2 groups; group L (n = 8) consists of patients with low anaerobic threshold (AT) < 13 ml/min per kg and group H (n = 7) consisting of patients with AT > 13 ml/min per kg. At rest, VO2 was similar between groups L and H, whereas CO was lower in group L than in group H (3.5 + 0.3 vs 4.8 + 1.4 ml/min, p < 0.01). Increase in VO2 during warm-up exercise was not significant between the 2 groups (7.4 +/- 0.5 (group L) vs 6.2 +/- 0.3 ml/min per kg (group H), ns), but increase in CO was lower in group L than in group H (2.5 +/- 0.6 vs 3.4 +/- 0.4 ml/min, p < 0.01). After warm-up to the AT point, however, the increase in not only VO2 but also CO was markedly reduced in group L than in group H (VO2: 0.5 +/- 0.4 vs 3.7 +/- 0.8 ml/min per kg, p < 0.01, CO: 0.2 +/- 0.3 vs 1.1 +/- 0.3 L/min, p < 0.01). Based on these measurements, we calculated the arteriovenous oxygen difference (c(A-V)O2 difference) during exercise in individual patients using Fick's equation. The c(A-V)O2 difference was markedly increased in severe heart failure during the warm-up stage, but between the end of warm-up and the AT point, it remained at the same level as that of group H. These results suggest the presence of a unique mechanism regulating the c(A-V)O2 difference in severe heart failure patients, activation of which may, at least during mild exercise, contribute to efficient oxygen delivery to the peripheral tissues thus compensating for the jeopardized exercise tolerance in those patients.  相似文献   
887.
Control of a Biped Walking Robot during the Double Support Phase   总被引:2,自引:0,他引:2  
This paper discusses the control problem of a biped walking robotduring the double-support phase. Motion of a biped robot during thedouble-support phase can be formulated as motion of robotmanipulators under holonomic constraints. Based on the formulation,the walking gait is generated by controlling the position of thetrunk of the robot to track a desired trajectory, referenced in theworld frame. Constrained forces at both feet were controlled suchthat firm contact is preserved between the feet and ground by using asimplified model of the double-support phase. The control scheme wasevaluated experimentally.  相似文献   
888.
889.
Cases of esophageal cancer with intramural metastasis to the stomach and esophageal cancer with metastasis to an intramural lymph node of the stomach are herein reported. The former patient was a 52 year-old male. Squamous cell carcinoma (SCC) of the lower esophagus with an intramural metastasis located at the gastric cardia and a small leiomyoma at the fornix were resected. The latter patient was a 70 year-old female. SCC of the lower esophagus and an intramural lymph node metastasis located at the anterior wall of the gastric cardia were resected. The patient died nevertheless of multiple liver metastases. These gastric involvements were detectable by endoscopy before surgery. The clinicopathological features of these esophageal cancers were characterized; the sites were the lower part of the esophagus, and extreme lymphatic and vascular invasions were shown histologically. The gastric tumors were located in the upper third of the stomach, and the findings revealed submucosal tumors. It is therefore important to discriminate other gastric tumors, and to resect them simultaneously with esophageal cancer when a gastric tube has been used for reconstruction after esophagectomy.  相似文献   
890.
We investigate the crystal growth process of an InAs-GaAs binary semiconductor by the Travelling Liquidus-Zone (TLZ) method numerically and discuss the possibility of growing a bulk In0.3Ga0.7As crystal. First, we explain this new crystal growth technique and then develop a numerical model and calculation method of the growth of binary crystals, by which the flow field in the solution, the temperature and concentration fields in both the solution and crystals, and the shape and movement of the crystal-solution interfaces are determined. We focus, in particular, on the effect of the solution zone width on the crystal growth process and the generation of supercooling in the solution in order to grow In0.3Ga0.7As. We find that a uniform In0.3Ga0.7As can be grown by the TLZ method under 1 μg conditions by adjusting the solution zone width and the temperature gradient in the solution at appropriate values, in which case buoyancy convection and supercooling induced in the solution are remarkably reduced.  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