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   1477782篇
  免费   25766篇
  国内免费   7005篇
电工技术   34000篇
综合类   6365篇
化学工业   269000篇
金属工艺   63491篇
机械仪表   41176篇
建筑科学   45856篇
矿业工程   11298篇
能源动力   50107篇
轻工业   110540篇
水利工程   14982篇
石油天然气   37244篇
武器工业   130篇
无线电   194976篇
一般工业技术   278902篇
冶金工业   151146篇
原子能技术   33722篇
自动化技术   167618篇
  2021年   15485篇
  2020年   11786篇
  2019年   14583篇
  2018年   14442篇
  2017年   13645篇
  2016年   20723篇
  2015年   17181篇
  2014年   28576篇
  2013年   87513篇
  2012年   34699篇
  2011年   46353篇
  2010年   41337篇
  2009年   49870篇
  2008年   43537篇
  2007年   40544篇
  2006年   44331篇
  2005年   38635篇
  2004年   41024篇
  2003年   40993篇
  2002年   40096篇
  2001年   37083篇
  2000年   35484篇
  1999年   34353篇
  1998年   42128篇
  1997年   37299篇
  1996年   33916篇
  1995年   29884篇
  1994年   28131篇
  1993年   27965篇
  1992年   25884篇
  1991年   22960篇
  1990年   23285篇
  1989年   22294篇
  1988年   20885篇
  1987年   19124篇
  1986年   18514篇
  1985年   21880篇
  1984年   22213篇
  1983年   20211篇
  1982年   19190篇
  1981年   19269篇
  1980年   17855篇
  1979年   18467篇
  1978年   17657篇
  1977年   17159篇
  1976年   17580篇
  1975年   15943篇
  1974年   15469篇
  1973年   15559篇
  1972年   13003篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Test Case Generation as an AI Planning Problem   总被引:6,自引:0,他引:6  
While Artificial Intelligence techniques have been applied to a variety of software engineering applications, the area of automated software testing remains largely unexplored. Yet, test cases for certain types of systems (e.g., those with command language interfaces and transaction based systems) are similar to plans. We have exploited this similarity by constructing an automated test case generator with an AI planning system at its core. We compared the functionality and output of two systems, one based on Software Engineering techniques and the other on planning, for a real application: the StorageTek robot tape library command language. From this, we showed that AI planning is a viable technique for test case generation and that the two approaches are complementary in their capabilities.  相似文献   
972.
Ebert  C. 《Software, IEEE》1997,14(6):77-82
C. Ebert presents his views on the state of software engineering as a field, its roots and inherent conflicts, its relationship to other engineering disciplines, where it is headed, and what we can do to influence that direction. T. Matsubara, T. Webb, M. Pezze, and O.W. Bertelsen offer a spectrum of further insights  相似文献   
973.
At the moment, weather forecasting is still an art — the experience and intuition of forecasters play a significant role in determining the quality of forecasting. This paper describes the development of a new approach to rainfall forecasting using neural networks. It deals with the extraction of information from radar images and an evaluation of past rain gauge records to provide shortterm rainfall forecasting. All of the meteorological data were provided by the Royal Observatory of Hong Kong (ROHK). Preprocessing procedures were essential for this neural network rainfall forecasting. The forecast of the rainfall was performed every half an hour so that a storm warning signal can be delivered to the public in advance. The network architecture is based on a recurrent Sigma-Pi network. The results are very promising, and this neural-based rainfall forecasting system is capable of providing a rain storm warning signal to the Hong Kong public one hour ahead.  相似文献   
974.
Results are reported of a detailed optical and electron metallographic study of the effects of variations in quenching rate from the β-phase and aging temperature in the + ZrCr2 phase region, on the recrystallization and grain growth characteristics of Zr-1.14 wt% Cr-0.08 wt% Fe alloy used for nuclear fuel sheathing. It is shown that certain quenching rates, which produce a mixed martensitic-Widmanstätten structure, should be avoided during the fabrication of fuel sheathing, since recrystallization and grain growth occurs at a much lower temperature than a material quenched at such a rate that the structure is wholly Widmanstätten or wholly martensitic. Preaging at 350 or 450°C prior to the high-temperature (700–750°C) aging reduces the incidence of recrystallization and grain growth.  相似文献   
975.
It is time to locate connectionist representation theory in the new wave of robotics research. The utility of representations developed in artificial neural networks (ANNs) during learning has been demonstrated in cognitive science research since the 1980s. The research reported here puts learned representations to work in a decentered control task, the disembodied arm problem, in which a mobile robot operates an arm fixed to a table to pick up objects. There is no physical linkage between the arm and the robot and so the robot's point of view must be decentered. This is done by developing a modular Artificial Neural Net system in three stages: (i) a classifier net is trained with laser scan data to output transformationally invariant position classes; (ii) an arm net is trained for picking up objects; (iii) an inter net is trained to communicate and coordinate the sensing and acting. The completed system is shown to create new nonsymbolic transformationally invariant representations in order to perform the effective generalization of decentered viewpoints.  相似文献   
976.
BACKGROUND: Gastric sucrose permeability is a noninvasive marker that reliably increases in association with gastrointestinal injury due to use of nonsteroidal antiinflammatory drugs. Despite the effect of Helicobacter pylori infection on the gastric mucosa, in a previous study we were unable to demonstrate that H. pylori infection was associated with abnormal gastric sucrose permeability. Our goal in this study was to explore further whether H. pylori infection changed gastric permeability; therefore, we evaluated the effect of treatment of H. pylori infection on gastric permeability to sucrose and the relation of sucrose permeability to density of polymorphonuclear leukocytes. MATERIALS AND METHODS: Five hundred milliliters of a solution containing 100 gm of sucrose was ingested by the subject at bedtime. Overnight urine was collected and assayed for sucrose by high-performance liquid chromatography. Sucrose permeability was assessed both before and approximately 4 weeks after anti-H. pylori therapy. RESULTS: Seventeen asymptomatic H. pylori-infected volunteers participated; 8 were cured. Sucrose permeability was in the range commonly found in normal controls both before and after anti-H. pylori therapy (mean excretion, 76.3 mg; range, 13-171 mg). Gastric sucrose permeability correlated with the density of polymorphonulcear cell infiltration of the mucosa. Cure of the H. pylori infection was associated with a small but significant decrease in sucrose permeability (98.8 +/- 18 mg to 51.7 +/- 9.8 mg (p = .01). Sucrose permeability was greater in those with a high density of mucosal polymorphonuclear cells compared to those with lower scores (119.5 +/- 4 vs 71.4 +/- 13 for those with scores > or = 5 compared to scores < or = 4; p = .023). Failed therapy resulted in an increase in the mucosal density of polymorphonuclear infiltration and sucrose permeability (56.4 +/- 13 mg-99.7 +/- 19 mg pretreatment vs posttreatment, respectively; p = .031). CONCLUSION: H. pylori gastritis causes a small but measurable increase in gastric permeability to sucrose that may reflect epithelial transmigration of neutrophils.  相似文献   
977.
The energy expenditure and heart rate of five Shetland ponies were measured during transport and compared with the values recorded while they were at rest and walking. Secondary aims of the study were to investigate whether there was any correlation between heart rate and energy expenditure and whether different orientations affected the values to different degrees. The measurements were recorded at one-minute intervals while the ponies were at rest, walking and being transported in four different orientations, on journeys lasting 30 minutes. There were significant increases (P < 0.001) in both heart rate and energy expenditure during transport which were similar to those associated with walking, and there was a strong correlation between the two measurements. There was no conclusive evidence that orientation affected the measurements, but it appeared that rear facing transport might have had the least effect.  相似文献   
978.
To meet the criteria of role accountability, nursing competence and ongoing staff development, an improved peer-evaluation system was designed to continuously monitor these new roles. This peer-evaluation process converts evaluation input into data, giving staff a visual picture of how their performance compares within their peer group. This peer-evaluation process was designed as a tool to assist in staff growth and development, not as a punitive system.  相似文献   
979.
OBJECTIVE: To evaluate the relationships between patient and physician pretreatment expectations of pain relief and subsequent pain relief reported by chronic pain patients immediately after treatment. DESIGN: Prospective study of consecutive patients undergoing a procedure in a pain clinic for treatment of chronic pain. Patients rated their current pain level and their expectation of pain relief immediately prior to undergoing a procedure (e.g., intravenous drug infusion, nerve block) for the treatment of chronic pain. Simultaneously and independently, the treating physician completed a similar questionnaire. At completion of the procedure, patients rated their current pain level and degree of pain relief. SETTING: University of Washington Multidisciplinary Pain Center procedure suite. PATIENTS: Forty-six consecutive chronic pain patients. INTERVENTION: Intravenous drug infusions and nerve blocks. OUTCOME MEASURES: Current pain and pain relief ratings. RESULTS: Patients' pain relief expectation ratings were not correlated significantly with their postprocedure pain relief ratings or pre-post procedure changes in pain ratings. However, a statistically significant correlation was found between physician expectations of pain relief and patient pain relief ratings and patient pre-post procedure changes in pain. CONCLUSIONS: The results of this study suggest that physicians are better predictors than are patients of patients responses to these procedures and/or that physicians may somehow subtly communicate their expectations to patients during the procedure, and these expectations then influence patient response. Patient pretreatment expectations may not always play a significant role in nonspecific treatment effects.  相似文献   
980.
Primary biliary cirrhosis (PBC) is an immunologically mediated disease in which activated T lymphocytes attack and destroy epithelial cells in the small intralobular bile ducts of genetically susceptible patients. This article reviews the results of treatment of PBC with immunomodulatory agents. Results with drugs such as glucocorticoids, azathioprine, and chlorambucil have been disappointing because of either limited efficacy (azathioprine), toxicity (chlorambucil), or both (glucocorticoids). Colchicine improved tests of liver function in three prospective studies and was associated with improved survival for up to 4 years. However, survival benefits were lost at 8 years. Colchicine appears to slow the rate of progression of PBC but not to stop it. Preliminary results suggest that colchicine may have synergistic effects if used together with ursodeoxycholic acid, particularly in patients who are only partially responsive to ursodeoxycholic acid. Results with cyclosporine have been disappointing because of limited efficacy and predictable toxicity. The modest improvement in tests of liver function and survival are counterbalanced by the development of hypertension in some and worsening renal function in most. There is little beneficial effect on symptoms or histology. Results with methotrexate are promising. There are improvements in symptoms and tests of liver function that are equal to those seen with ursodeoxycholic acid and significant improvement in liver histology. Some patients, particularly those with striking inflammation and granulomas in portal triads, appear to have achieved sustained remission while on methotrexate. The effects of methotrexate are additive to those of ursodeoxycholic acid in patients whose blood tests have responded only partially to ursodeoxycholic acid. The most effective treatment of PBC will most likely use a combination of drugs such as ursodeoxycholic acid, colchicine, and methotrexate.  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