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   3594篇
  免费   188篇
  国内免费   7篇
电工技术   57篇
综合类   7篇
化学工业   839篇
金属工艺   56篇
机械仪表   66篇
建筑科学   102篇
矿业工程   21篇
能源动力   111篇
轻工业   295篇
水利工程   26篇
石油天然气   20篇
无线电   376篇
一般工业技术   704篇
冶金工业   369篇
原子能技术   37篇
自动化技术   703篇
  2023年   32篇
  2022年   91篇
  2021年   139篇
  2020年   82篇
  2019年   98篇
  2018年   106篇
  2017年   95篇
  2016年   131篇
  2015年   90篇
  2014年   143篇
  2013年   237篇
  2012年   193篇
  2011年   241篇
  2010年   169篇
  2009年   150篇
  2008年   149篇
  2007年   156篇
  2006年   143篇
  2005年   117篇
  2004年   108篇
  2003年   103篇
  2002年   93篇
  2001年   54篇
  2000年   54篇
  1999年   60篇
  1998年   69篇
  1997年   58篇
  1996年   51篇
  1995年   42篇
  1994年   29篇
  1993年   38篇
  1992年   27篇
  1991年   18篇
  1990年   17篇
  1989年   24篇
  1988年   29篇
  1987年   23篇
  1986年   16篇
  1985年   25篇
  1984年   18篇
  1983年   19篇
  1982年   21篇
  1981年   12篇
  1980年   19篇
  1979年   23篇
  1978年   18篇
  1977年   18篇
  1976年   23篇
  1975年   19篇
  1973年   13篇
排序方式: 共有3789条查询结果,搜索用时 15 毫秒
11.
Recent research has proposed the use of asphalt and tall-oil-pitch emulsions for stabilizing radioactive contamination deposited on surfaces in urban areas. The objective of this project was to investigate whether surface applied emulsions could capture airborne radioactive particulate. Laboratory experiments included wind-blown particulate capture studies using an acrylic column and particulate retainment experiments using a wind box capable of producing wind speeds of 96?km/h. A probe methodology was developed to relate particulate retainment to a tack force on the emulsion surface. Experiments were also performed to determine the potential for such emulsions to absorb particulate matter into their emulsion matrix. Tall-oil-pitch emulsions outperformed asphalt emulsions in terms of particulate retention, tack force, and the ability to absorb magnesium silicate. Both tall-oil-pitch and asphalt emulsions were capable of extracting 22–24?g?m?2 of powder from particulate-laden airflow. Tall-oil-pitch emulsions were capable of retaining as much as 5–10% of magnesium silicate powder applied (i.e., retainment densities of 10–20?g?m?2) even after seven?days of curing and after applying 96.5?km/h (60?mph) wind. Tall-oil-pitch emulsions were able to absorb surface-applied magnesium silicate (approximately 0.1–0.2?g of magnesium silicate per 1.0?g of emulsion within three?days) into their emulsion matrix, preventing the magnesium silicate from being exposed to the external environment. Initial results with these five different emulsion formulations suggested particulate capture was feasible. Future emulsion formulations (i.e., longer curing times with greater acid concentrations) should be tested to optimize this postdetonation response strategy.  相似文献   
12.
13.
14.
Near-haploidy is a rare cytogenetic finding in childhood acute lymphoblastic leukaemia (ALL) and is associated with a poor prognosis. A second hyperdiploid line, occurring presumably by endoreduplication of the near-haploid stemline, is often observed. We present a case of common ALL in relapse characterized morphologically by a dual population of small and large lymphoblasts. Cytogenetic analysis supplemented with fluorescence in-situ hybridization (FISH) studies localized near-haploidy and hyperdiploidy to the small and large blast population respectively. DNA ploidy determination confirmed two abnormal clones with near-haploidy as the predominant one. A novel t(9;12)(q11;q13) was present in the near-haploid clone and was duplicated in the hyperdiploid clone. This finding identified cells bearing near-haploidy to be the clonogenic population following malignant transformation and confirmed endoreduplication as the mechanism for the presence of associated hyperdiploidy.  相似文献   
15.
This paper sketches the contours of the evolving international/monetary system and examines the various roles of the intemediation mechanisms. Then it examines the extent to which the financial system is independent from the “real economy” and the various ways in which it impacts it. The paper discusses some views in good currency on the dynamics of the technology-trade-finance nexus and shows how the financial system influences organization, location and technology choices in meso-innovation systems. The final section of the paper looks at the policy implications that might be derived from the analysis and suggests some directions for the future research.  相似文献   
16.
17.
Satellite scatterometer winds over the northwestern Pacific were analyzed with the vector empirical orthogonal function (VEOF) method. The Hilbert-Huang transform (HHT), a newly developed non-linear and non-stationary time series data processing method, was also employed in the analysis. A combination of European Remote Sensing Satellite (ERS) −1/2 scatterometer, NASA Scatterometer (NSCAT) and NASA's Quick Scatterometer (QuikSCAT) winds covering the period from January 1992 to April 2000 and the area of 0-50°N, 100-148°E constitutes the baseline for this study. The results indicate that annual cycles dominate the two leading VEOF modes. The first VEOF shows the East Asian monsoon features and the second represents a spring-autumn oscillation. We removed the annual signal from the data set and calculated the interannual VEOFs. The first interannual VEOF represents the interannual variability existing in the spring-autumn oscillation. The temporal mode is correlated with the Southern Oscillation Index (SOI), but has a half-year lag with respect to the SOI. The spatial mode of the first interannual VEOF reflects the response of the tropical and extratropical winds to ENSO events. The second interannual VEOF is another ENSO related mode, and the temporal VEOF mode is correlated with the SOI with a correlation coefficient of 0.78, revealing the wind variability over mid-latitudes, which is associated with ENSO events. Further analysis indicated that the wind variability over the coast of East Asia represents anomalies of a Hadley cell. The quasi-biennial oscillation (QBO) was found in the temporal mode, indicating and verifying that the QBO in the wind fields is related to ENSO events. The third VEOF shows the interannaul variability in the winter-summer mode and displays the interannual variability of the East Asian monsoon. The three leading interannual VEOFs are statistically meaningful as confirmed by a significance test.  相似文献   
18.
19.
We present a study of magneto-thermal instabilities in polycrystalline MgB2 superconductor, by magnetic hysteresis loop measurements and by investigations of magnetic flux dynamics with a miniature Hall probe. Temperature and magnetic field ranges where the flux jumps may be observed have been determined. On the basis of measurements of the magnetic flux dynamics, an average magnetic diffusivity describing the process of the flux jump is estimated. This parameter is compared with the thermal and magnetic diffusivities calculated on the basis of available data for thermal conductivity, heat capacity and resistivity. It is shown that the estimated value of the field of the first flux jump is influenced significantly by the field dependence of specific heat. In order to explain the observed phenomenon, the temperature reached by the sample during the flux jump at different magnetic fields is calculated.  相似文献   
20.
Studied change in client identity and self-organization during the treatment of a 38-yr-old man with multiple personality disorder. Assessment measures were administered to the host personality and 2 secondary personalities before and after 12 wks of intensive treatment. Measures included the MMPI and the Bell Object Relations Reality Testing Inventory (BORRTI). Therapy focused on the posttraumatic aspects of the patient's early childhood sexual abuse. A cognitive-affective approach combined psychoanalytically informed psychotherapy with abreactive-hypnotic work for recovering and reexamining traumatic memories. A greater degree of intrapsychic awareness and interpersonal sensitivity was suggested by changes in BORRTI ratings. The magnitude of observed changes in self-organization was substantial. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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