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   750161篇
  免费   8679篇
  国内免费   1755篇
电工技术   13932篇
综合类   783篇
化学工业   116090篇
金属工艺   30147篇
机械仪表   23648篇
建筑科学   17392篇
矿业工程   4966篇
能源动力   19174篇
轻工业   61486篇
水利工程   8549篇
石油天然气   16827篇
武器工业   98篇
无线电   83819篇
一般工业技术   149364篇
冶金工业   133256篇
原子能技术   17525篇
自动化技术   63539篇
  2021年   6708篇
  2019年   6427篇
  2018年   11085篇
  2017年   11287篇
  2016年   11840篇
  2015年   7519篇
  2014年   12733篇
  2013年   34152篇
  2012年   19807篇
  2011年   26947篇
  2010年   21573篇
  2009年   24134篇
  2008年   24775篇
  2007年   24545篇
  2006年   21603篇
  2005年   19626篇
  2004年   18694篇
  2003年   18447篇
  2002年   17695篇
  2001年   17260篇
  2000年   16564篇
  1999年   16515篇
  1998年   38984篇
  1997年   28016篇
  1996年   21974篇
  1995年   16887篇
  1994年   15158篇
  1993年   14926篇
  1992年   11698篇
  1991年   11102篇
  1990年   10931篇
  1989年   10519篇
  1988年   10090篇
  1987年   9093篇
  1986年   8838篇
  1985年   10098篇
  1984年   9196篇
  1983年   8698篇
  1982年   7964篇
  1981年   8101篇
  1980年   7666篇
  1979年   7657篇
  1978年   7453篇
  1977年   8472篇
  1976年   10623篇
  1975年   6768篇
  1974年   6590篇
  1973年   6710篇
  1972年   5585篇
  1971年   5225篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
971.
This work pertains to output voltage stability of soft adjacent layer biased magnetoresistive heads with abutted permanent magnetic films for domain stabilization. A micromagnetic model has been developed to study the effect of the permanent magnet film microstructure and the micromagnetic properties of the abutted junction interface on head stability. The impact on head stability is analyzed with respect to interfacial ferromagnetic coupling across the junction interface and intergranular exchange coupling in the permanent magnet films among other film properties  相似文献   
972.
The Warehouse Scheduling Problem is a deterministic multi-item inventory problem with a restriction on warehouse floor space available. We formulate a mixed integer nonlinear programming problem for the objective of minimizing long run inventory holding and order costs per unit of time. We integrate algorithms for staggering orders, described in companion papers, with a heuristic to choose the order sequences. The result is called Sequenced Staggering. We describe a new algorithm to generate order frequencies, called the powers-of-two-factor-of-three technique, as a generalization of Roundy's roundoff technique for powers-of-two policies. We report on a computational study of four hybrid algorithms for solving the warehouse scheduling problem, including the competing algorithm of Gallego, Queyranne, and Simchi-Levi. Based on these results, we recommend the combination of powers-of-two frequencies with Sequenced Staggering.  相似文献   
973.
Translated from Izmeritel'naya Tekhnika, No. 11, pp. 66–67, November, 1994.  相似文献   
974.
975.
Continuing our work on the immunosuppressive activity of cyclolinopeptide A (CLA), a cyclic nonapeptide of the sequence: c-(-Leu-Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe), we synthesized a series of 6 linear analogs of CLA, successively shortened at the N-terminus of the peptide chain. Immunosuppressive activity of acetates as well as trifluoroacetates of these peptides was investigated using PFC (humoral immunity) and DTH (cellular immunity) tests. It was found that the immunosuppressive potency of the peptides examined diminishes with shortening of the peptide chain. Octapeptide I with the sequence Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe was found to be the most active of the whole series. The immunosuppressive activity increased again for a tripeptide fragment of CLA of the sequence Pro-Phe-Phe. The immunosuppressive activity of octapeptide probably depends on the suppression of IL-1, IL-6 and TNF production by the cells involved in immune and inflammatory response.  相似文献   
976.
A new simple method of measuring capacitance-voltage characteristics of MOS devices is presented. Proceeding from the charge-based capacitance measurement technique suggested recently, a compact test structure with high resolution has been developed, which only requires measurement of do quantities. The method was tested on a 0.6-μm CMOS process with small and large area capacitors and compared to well-known high-frequency capacitance-voltage results. Beside using a reference structure, a second means of extracting parasitic effects is demonstrated for small structures. The test structure allows measurements in a wide frequency range with high accuracy and low noise contribution at small capacitance levels  相似文献   
977.
Analysis of heart rate variability (HRV) with Holter monitoring is often difficult due to excessive artifacts and arrhythmias. While short sudden surges are treated successfully by most methods, slow heart rate (HR) variations, nocturnal trapezoidally-shaped HR increases and special types of arrhythmias which are similar to normal HRV fluctuations may distort further time domain and spectral analysis. This paper examines the advantages and disadvantages of different methods for preprocessing of HR data. We have developed the following approach to the analysis of HRV. (1) A combination method based on the absolute difference between HR values and both the last normal HR value and an updated mean is used for removal of artifacts and arrhythmias. This method can detect both sudden surges in HR values as well as longer periods of noise combined with slow normal variations. An additional stage of wild point removal is then optionally applied. (2) Certain special problems such as large T-waves, bigeminal rhythm, slow HR variations and nocturnal trapezoidally-shaped HR increases are also identified. Although none of the algorithms can be applied successfully to all cases, the final computer analysis for preprocessing described in the present study has proved to be superior to the simplified methods which are usually used and provides more suitable data for HRV analysis.  相似文献   
978.
Recent research suggests that implementing information systems presents considerable difficulties and that many implementations are total or partial failures. This paper argues that what both practitioners and students require are richer and more acceptable models of information systems implementation. Accordingly, case study data concerning the introduction of manufacturing resource planning (MRP II) are used to illustrate five patterns of behaviour (rites) which capture important social actions; and four components of changing psychological orientation. It is argued that appreciation of the rites and psychological developments identified here will support effective change programmes. Guidelines based on our model are provided for practitioners.  相似文献   
979.
980.
Fourier-transform-limited pulses ( Delta tau . Delta nu approximately=0.35) have been obtained from a microwave-modulated DBR laser at 1.56 mu m. The chirp of the gain-switched pulse is compensated for by applying a fraction of the microwave signal to the phase section, thereby creating an instantaneous frequency shift of opposite sign. The generation of short coherent pulses from such a monolithic source can be of great interest for long haul soliton transmission.<>  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