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   9851篇
  免费   26篇
  国内免费   1篇
电工技术   21篇
综合类   6篇
化学工业   281篇
金属工艺   31篇
机械仪表   13篇
建筑科学   36篇
矿业工程   1篇
能源动力   14篇
轻工业   79篇
水利工程   14篇
石油天然气   3篇
武器工业   1篇
无线电   113篇
一般工业技术   186篇
冶金工业   8901篇
原子能技术   9篇
自动化技术   169篇
  2020年   14篇
  2018年   15篇
  2015年   13篇
  2014年   16篇
  2013年   48篇
  2012年   37篇
  2011年   50篇
  2010年   30篇
  2009年   32篇
  2008年   37篇
  2007年   55篇
  2006年   35篇
  2005年   34篇
  2004年   30篇
  2003年   42篇
  2002年   26篇
  2001年   31篇
  2000年   32篇
  1999年   311篇
  1998年   2796篇
  1997年   1582篇
  1996年   1008篇
  1995年   586篇
  1994年   465篇
  1993年   570篇
  1992年   85篇
  1991年   117篇
  1990年   109篇
  1989年   102篇
  1988年   111篇
  1987年   105篇
  1986年   105篇
  1985年   79篇
  1984年   17篇
  1983年   22篇
  1982年   53篇
  1981年   55篇
  1980年   90篇
  1979年   14篇
  1978年   26篇
  1977年   205篇
  1976年   477篇
  1975年   21篇
  1974年   16篇
  1973年   13篇
  1972年   16篇
  1971年   14篇
  1970年   13篇
  1969年   19篇
  1968年   13篇
排序方式: 共有9878条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
Centrifugal pumps are generally employed as nonpulsatile blood flow pumps; however, these pumps can produce pulsatile flow by periodically alternating the impeller rotation speed. This study investigates blood trauma due to the effect of pulse frequency and various ranges of pump speed. The hemolysis tests were conducted using the Gyro C1E3 pump. The study was divided into the following categories: Group 1 in a nonpulsatile mode; Group 2 operated at 40 bpm with 30% of speed variance; Group 3, 60 bpm with 30% of speed variance; Group 4, 40 bpm with 70% of speed variance; and Group 5, 60 bpm with 70% of speed variance. A flow rate of 3 L/min and a total pressure head of 200 mm Hg were employed in all groups to simulate a percutaneous cardiopulmonary support condition. There were no significant differences in the hemolysis levels among Groups 1, 2, and 3. However, Groups 4 and 5 exhibited a significantly higher hemolysis rate compared to the other groups. These results indicate that a high rate of speed variance increases hemolysis; however, a range of less than 30% does not affect hemolysis. The pulse rate has no significant effect on hemolysis. In conclusion, the higher speed variance increases the hemolysis level when a pulsatile mode is applied with a centrifugal pump at the given test conditions. However, a speed variance of less than 30% or a pulse rate of less than 60 bpm does not affect hemolysis.  相似文献   
105.
When rotating stripes or other periodic stimuli cross the retina at a critical rate, a reversal in the direction of motion of the stimuli is often seen. This illusion of motion perception was used to explore the roles of retinal and perceived motion in the generation of optokinetic nystagmus. Here we show that optokinetic nystagmus is disrupted during the perception of this illusion. Thus, when perceived and actual motion are in conflict, subjects fail to track the veridical movement. This observation suggests that the perception of motion can directly influence optokinetic nystagmus, even in the presence of a moving retinal image. A conflict in the neural representation of motion in different brain areas may explain these findings.  相似文献   
106.
It is very likely that disagreements leading to opposing factions and conflict are universal, and part of the very nature of academic (intellectually and behaviorally expressive) institutions. Analytic "education" shares in this tradition. Internal conflict and splits within and between psychoanalytic training centers have continued to reappear throughout the history of the psychoanalytic movement. They were greatly magnified with the formation of "official, formal training." The authors propose highlighting the composite of personal and professional genealogies within the training analysis couple as opportunities to provide experiential, graphic consideration of the affiliative, disaffiliative, and identification processes, greatly enhanced when analysands, training analysts, and the Institute regard this as a valuable method to study the parallel phenomena evoked, experienced, and shared communally. These personal and group considerations are part of the shared genealogy and history of psychoanalytic Institute and Society life, their "parent" organizations, and "relatives" nationally and internationally. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
107.
A method is described for searching protein sequence databases using tandem mass spectra of tryptic peptides. The approach uses a de novo sequencing algorithm to derive a short list of possible sequence candidates which serve as query sequences in a subsequent homology-based database search routine. The sequencing algorithm employs a graph theory approach similar to previously described sequencing programs. In addition, amino acid composition, peptide sequence tags and incomplete or ambiguous Edman sequence data can be used to aid in the sequence determinations. Although sequencing of peptides from tandem mass spectra is possible, one of the frequently encountered difficulties is that several alternative sequences can be deduced from one spectrum. Most of the alternative sequences, however, are sufficiently similar for a homology-based sequence database search to be possible. Unfortunately, the available protein sequence database search algorithms (e.g. Blast or FASTA) require a single unambiguous sequence as input. Here we describe how the publicly available FASTA computer program was modified in order to search protein databases more effectively in spite of the ambiguities intrinsic in de novo peptide sequencing algorithms.  相似文献   
108.
Treatment and prognosis of urinary bladder cancer largely are determined by the tumor stage and presence of metastases. MR imaging and clinical staging complement each other. MR imaging is the most accurate technique for differentiating the various stages of deep tumor infiltration and detection of metastases, whereas clinical staging is the best technique for differentiating between postbiopsy effects and the various stages of superficial tumors. The role of MR imaging in staging of this disease and monitoring of therapy is reviewed and illustrated. Finally, the authors present an overview of current and future applications of this technique.  相似文献   
109.
There complete 18S ribosomal RNA gene sequences from the rumen ciliates, Entodinium caudatum (1,639 bp), Epidinium caudatum (1,638 bp), and Polyplastron multivesiculatum (1,640 bp) were determined and confirmed in the opposite direction. Trees produced using maximum parsimony and distance-matrix methods (least squares and neighbour-joining), with strong bootstrap support, depict the rumen ciliates as a monophyletic group. Entodinium caudatum is the earliest branching rumen ciliate. However, Entodinium simplex does not pair with En. caudatum, but rather with Polyplastron multivesiculatum. Signature sequences for these rumen ciliates reveal that the published SSrRNA gene sequence from En. simplex is in fact a Polyplastron species. The free-living haptorian ciliates, The Loxophyllum, Homalozoon and Spathidium (Subclass Haptoria), are monophyletic and are the sister group to the rumen ciliates. The litostomes (Class Litostomatea), consisting of the haptorians and the rumen ciliates, are also a monophyletic group.  相似文献   
110.
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