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   12227篇
  免费   362篇
  国内免费   12篇
电工技术   92篇
综合类   10篇
化学工业   1562篇
金属工艺   184篇
机械仪表   326篇
建筑科学   129篇
矿业工程   3篇
能源动力   314篇
轻工业   1074篇
水利工程   20篇
石油天然气   8篇
武器工业   1篇
无线电   1080篇
一般工业技术   1319篇
冶金工业   5592篇
原子能技术   59篇
自动化技术   828篇
  2023年   83篇
  2022年   117篇
  2021年   208篇
  2020年   157篇
  2019年   150篇
  2018年   181篇
  2017年   181篇
  2016年   214篇
  2015年   190篇
  2014年   297篇
  2013年   484篇
  2012年   432篇
  2011年   468篇
  2010年   347篇
  2009年   339篇
  2008年   369篇
  2007年   279篇
  2006年   224篇
  2005年   224篇
  2004年   190篇
  2003年   165篇
  2002年   150篇
  2001年   117篇
  2000年   116篇
  1999年   248篇
  1998年   1718篇
  1997年   995篇
  1996年   701篇
  1995年   414篇
  1994年   366篇
  1993年   389篇
  1992年   89篇
  1991年   126篇
  1990年   94篇
  1989年   119篇
  1988年   128篇
  1987年   122篇
  1986年   98篇
  1985年   74篇
  1984年   36篇
  1983年   45篇
  1982年   52篇
  1981年   53篇
  1980年   78篇
  1978年   60篇
  1977年   171篇
  1976年   372篇
  1975年   43篇
  1974年   31篇
  1972年   35篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Reinstatement and spontaneous recovery of previously extinguished nicotine-taking behavior were examined in rats. Male subjects were trained to self-administer nicotine (30 microg/kg per infusion, IV; one 60-min session per day for 3 weeks). Extinction sessions were then given for 5-10 days during which saline was substituted for nicotine. Subsequently, in the first set of tests for nicotine seeking, the reinstatement of lever presses that previously delivered nicotine was examined after priming injections of saline and nicotine (75, 150 and 300 microg/kg, SC; and 30 and 60 microg/kg, IV). In the second set of tests for nicotine-seeking, rats were tested after an additional 21-day drug-free period during which they were not exposed to the self-administration chambers (a test for the spontaneous recovery of drug seeking), and after priming injections of nicotine (150 and 300 microg/kg, SC). Reinstatement of extinguished food-reinforced behavior after exposure to nicotine was also determined. Priming injections of nicotine reinstated nicotine seeking regardless of the route of administration. In addition, previously extinguished nicotine seeking recovered spontaneously after a 21-day period during which rats were not exposed to the drug-taking environment. Nicotine also reinstated extinguished food-reinforced behavior in rats with a history of nicotine self-administration, but not in drug-naive rats. The present results extend previous work with opioid and stimulant drugs on reinstatement of drug seeking by the self-administered drug. It also appears that, as with other positive reinforcers, the mere passage of time is a sufficient condition for the spontaneous recovery of extinguished nicotine seeking.  相似文献   
112.
Security of the Cao-Li public key cryptosystem   总被引:1,自引:0,他引:1  
The author shows that the Cao-Li cryptosystem proposed [1991] is not secure. Its private key can be reconstructed from its public key using elementary means such as LU-decomposition and the Euclidean algorithm  相似文献   
113.
Cyclosporine A (CsA) in liposomes of dilauroylphosphatidylcholine (DLPC), containing 118 micrograms of CsA/L of aerosol with a particle size of 1.6 to 1.7 micron diameter, was inhaled by 10 nonsmoking, normal volunteers each for 45 min. Aerosol was administered through an Aerotech II nebulizer (CIS-US, Inc., Bedford, MA) mouthpiece. Eight of the 10 volunteers had tracheal irritation and intermittent coughing following exposure. FEV1 and FVC values were mildly reduced, but returned to normal in 1 h. Blood chemical and hematologic values were unchanged at any time point after as opposed to before inhalation. Nine of the 10 volunteers later inhaled DLPC only, administered through the nebulizer mouthpiece. There was no change in FEV1 or FVC values, and there was no coughing or tracheal irritation. Subsequently, five of the volunteers who had previously had respiratory reactions inhaled CsA-DLPC liposome aerosol for 45-min, but through a mouth-only face mask. There was no tracheal irritation, coughing, or changes in spirometric measures. Blood concentrations of CsA at 15 min after the 45-min inhalation with a face mask averaged 83 +/- 42 ng/ml (mean +/- SD). At 24 h after treatment, CsA was undetectable in blood of the initial 10 volunteers. These studies indicate that CsA-DLPC liposome aerosol can be safely explored as a treatment for patients with moderately severe asthma.  相似文献   
114.
115.
Thermal washout curves have been proposed as noninvasive tools for analysing lower airway dimensions and pulmonary blood flow, but how upper airway heat transfer affects these washout curves is unclear. The present study was designed to compare extrathoracic and tracheobronchial contributions to thermal washout curves. Respiratory frequency, air ambient temperature, and body core temperature (tc) were varied in six male subjects before and after immersion in cold (1.1 degrees C) water for up to 2 h under three conditions: 1) control: ambient temperature (tamb) = 25 degrees C, rectal temperature change (delta tre) = 0 degrees C; 2) pre-immersion: tamb = 4 degrees C, delta tre = 0 degrees C; and 3) post-immersion: tamb = 25 degrees C, delta tre = -0.7 degrees C. Both peak expiratory nasal (tpn) and oral (tpo) airstream temperatures were measured. Each subject was tested twice. Expiratory tpo was generally higher than tpn in all conditions. Increasing breathing rates lowered tpn and tpo in the control and cold air environments. Orifice temperatures, which are presumed to reflect upper airway blood temperatures, correlated with both tpn and tpo. Lowering tc had no effect on washout curves during quiet breathing and affected only tpn during rapid breathing. The results suggest that while tracheobronchial conditions may contribute to thermal washout curves, extrathoracic conditions predominate. Strong correlations between orifice temperatures, peak expiratory nasal temperatures and peak expiratory oral temperature demonstrate the dominant role of upper airway heat exchange in determining thermal washout curves.  相似文献   
116.
117.
118.
119.
Lactic acid concentration of coarsely ground beef, packaged in low oxygen permeability casings, is inversely related to sensory acceptability of the meat following regrinding and aerobic storage for six additional days. Samples, reground and stored aerobically after periods of anaerobic storage, were assayed for total aerobic bacterial counts, percentage of gram-positive microflora, and pH. Lactic acid concentration ranged from 130 to 1055 mg per 100g ground beef and increased with anaerobic storage. During 6 days of aerobic storage, both increases and decreases in concentration were noted and related to changes in microbial flora. A positive correlation was found between the proportion of gram-positive bacteria (lactic acid bacteria) and lactic acid and pH.  相似文献   
120.
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