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   345236篇
  免费   4197篇
  国内免费   1395篇
电工技术   6790篇
综合类   606篇
化学工业   52114篇
金属工艺   12935篇
机械仪表   9968篇
建筑科学   8660篇
矿业工程   1004篇
能源动力   9725篇
轻工业   32910篇
水利工程   2838篇
石油天然气   4787篇
武器工业   8篇
无线电   42945篇
一般工业技术   67414篇
冶金工业   62853篇
原子能技术   6099篇
自动化技术   29172篇
  2021年   2565篇
  2019年   2449篇
  2018年   4169篇
  2017年   3977篇
  2016年   4152篇
  2015年   2995篇
  2014年   5101篇
  2013年   16333篇
  2012年   8529篇
  2011年   11697篇
  2010年   9167篇
  2009年   10592篇
  2008年   10940篇
  2007年   11040篇
  2006年   9649篇
  2005年   8893篇
  2004年   8740篇
  2003年   8393篇
  2002年   8241篇
  2001年   8458篇
  2000年   7973篇
  1999年   8372篇
  1998年   19446篇
  1997年   14232篇
  1996年   11302篇
  1995年   8700篇
  1994年   7837篇
  1993年   7570篇
  1992年   5771篇
  1991年   5557篇
  1990年   5371篇
  1989年   5208篇
  1988年   4998篇
  1987年   4240篇
  1986年   4309篇
  1985年   5042篇
  1984年   4541篇
  1983年   4279篇
  1982年   3861篇
  1981年   4022篇
  1980年   3760篇
  1979年   3717篇
  1978年   3481篇
  1977年   4185篇
  1976年   5400篇
  1975年   3041篇
  1974年   2908篇
  1973年   2942篇
  1972年   2450篇
  1971年   2173篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
An attack on the public key cryptosystem Polly Cracker is described, that reveals the complete secret key σ ∈ Fq n by means of n (nonadaptively) chosen "fake" ciphertexts  相似文献   
122.
The airborne Millimeter-wave Imaging Radiometer (MIR) measurements conducted over the Midwest region of the continental United States during January/February 1997 and over the Alaska-Arctic region during May 1998 are used to estimate column water vapor W<0.8 g/cm/sup 2/ under a clear sky. On board the same aircraft are two other instruments, the Cloud Lidar System (CLS) and MODerate-resolution Imaging Spectrometer (MODIS) Airborne Simulator (MAS), which provide cloud cover information and independent measurements of W, respectively. The MIR-estimated W values are compared and found to be in very good agreement with those measured by rawinsondes at near concurrence. A close correlation is found between the MIR-estimated W and that estimated from the MAS near-IR reflectance ratios. Water surface emissivities at several MIR frequencies are obtained in the process of the W retrieval from several flights over the Midwest lakes. These estimated emissivities compared favorably with values calculated for a calm water surface, which are based on a di-electric permittivity model and MAS-measured surface temperatures. The results from all comparisons strongly demonstrate the soundness of the technique for estimating W.  相似文献   
123.
Simulink model for EDFA dynamics applied to gain modulation   总被引:1,自引:0,他引:1  
  相似文献   
124.
Depletion and hillock formation were examined in-situ in a scanning electron microscope (SEM) during electromigration of bamboo Al interconnect segments. Hillocks formed directly at the anode ends of the segments by epitaxial addition of Al at the bottom Al/TiN interface. Depletion occurred nonuniformly from the cathode end and stopped once the distance between the leading void and the hillock reached the critical length for electromigration at the given current density. A modified equation for the drift velocity is proposed, which includes the effect of nonuniform depletion and predicts that interconnects with nonuniform depletion are more reliable than those with uniform depletion.  相似文献   
125.
126.
127.
This study contrasted six subscales of the Brief Psychiatric Rating Scale (BPRS) to determine their sensitivity to psychosocial treatment outcome. An expanded version of the BPRS was administered to 216 clients on admission to a day program. The subscale measuring hostility and suspiciousness discriminated at intake clients who were therapeutically discharged from clients who did not complete the program and predicted discharge status after the investigators controlled for the effects of demographic variables. Significant reductions in scores were obtained on five subscales for a subset of clients to whom the BPRS was readministered before discharge. The results support the use of the expanded BPRS as an evaluative tool in psychosocial rehabilitation programs.  相似文献   
128.
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   
129.
130.
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