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   1701篇
  免费   12篇
电工技术   4篇
综合类   2篇
化学工业   85篇
金属工艺   5篇
机械仪表   7篇
建筑科学   29篇
能源动力   6篇
轻工业   28篇
水利工程   1篇
石油天然气   3篇
无线电   57篇
一般工业技术   65篇
冶金工业   1345篇
原子能技术   3篇
自动化技术   73篇
  2022年   7篇
  2021年   4篇
  2020年   5篇
  2019年   6篇
  2018年   5篇
  2017年   8篇
  2016年   6篇
  2015年   6篇
  2014年   11篇
  2013年   17篇
  2012年   12篇
  2011年   25篇
  2010年   8篇
  2009年   14篇
  2008年   19篇
  2007年   12篇
  2006年   17篇
  2005年   21篇
  2004年   15篇
  2003年   9篇
  2002年   9篇
  2001年   16篇
  2000年   13篇
  1999年   55篇
  1998年   424篇
  1997年   246篇
  1996年   177篇
  1995年   77篇
  1994年   68篇
  1993年   82篇
  1992年   15篇
  1991年   15篇
  1990年   18篇
  1989年   23篇
  1988年   31篇
  1987年   21篇
  1986年   21篇
  1985年   24篇
  1984年   5篇
  1983年   4篇
  1982年   4篇
  1981年   8篇
  1980年   11篇
  1979年   5篇
  1978年   6篇
  1977年   21篇
  1976年   65篇
  1975年   4篇
  1974年   3篇
  1972年   3篇
排序方式: 共有1713条查询结果,搜索用时 31 毫秒
101.
102.
An infant with neonatal meningitis caused by Pseudomonas cepacia responded promptly to treatment with trimethoprim-sulfamethoxazole (Bactrim) after other abtibiotics had failed. Pseudomonas cepacia has proven to be resistant to most of the commonly used antibiotics.  相似文献   
103.
The unstable hemoglobin (Hb) Saint Etienne (alpha2beta295F8 His replaced by G1n) (betaSE) was found in the red blood cells of an 8-year-old boy. The composition of this hemoglobin was 26% Saint Etienne, 52% A, 3% A2 and 19% HbF. Studies of hemoglobin synthesis indicate: a) a balanced synthesis of alpha and non-alpha chains (alpha=betaA + betaSE + gamma), b) an increased pool of free alpha hemoglobin chains, and c) a rapid exchange of alpha chains between this pool and HbSE. The alpha chain pool resulted from the dissociation of HbSE and the greater instability of betaSE chains than alpha chains upon heating. Hemoglobin F is of the fetal type and is heterogeneously distributed among the red cells. Furthermore, two populations of red blood cells could be separated according to their i antigen content. Analysis of the hemoglobins revealed a heterogeneous distribution. Thus, F hemoglobin was preferentially associated with cells having low i antigen level, while Saint Etienne hemoglobin was increased in cells having a high i antigen level. HbF and HbSE were not present in the parents of the propositus. Study of the genetic markers confirmed the filiation. The parents were normal upon clinical and hematological examination; they exhibited a normal pattern and synthesis of hemoglobin. The Hb Saint Etienne case is compared with Hb Istanbul, which in spite of the same amino acid substitution is not associated with increased HbF level.  相似文献   
104.
105.
Granulosa cells from small (less than 2mm) antral porcine follicles were grown in culture to study the effects of various hormones on growth, morphology and progesterone secretion. Culture medium 199D + 4% serum was found to be most suitable since it maintained a fairly constant cell population. Estradiol (1mug/ml) and human FSH stimulated cell growth. LH and FSH stimulated progesterone secretion and induced morphological changes associated with luteinization. Estradiol (0.1 mug/ml) inhibited progesterone secretion by granulosa cells.  相似文献   
106.
"God" and "Devil" are abstract concepts often linked to vertical metaphors (e.g., "glory to God in the highest," "the Devil lives down in hell"). It is unknown, however, whether these metaphors simply aid communication or implicate a deeper mode of concept representation. In 6 experiments, the authors examined the extent to which the vertical dimension is used in noncommunication contexts involving God and the Devil. Experiment 1 established that people have implicit associations between God-Devil and up-down. Experiment 2 revealed that people encode God-related concepts faster if presented in a high (vs. low) vertical position. Experiment 3 found that people's memory for the vertical location of God- and Devil-like images showed a metaphor-consistent bias (up for God; down for Devil). Experiments 4, 5a, and 5b revealed that people rated strangers as more likely to believe in God when their images appeared in a high versus low vertical position, and this effect was independent of inferences related to power and likability. These robust results reveal that vertical perceptions are invoked when people access divinity-related cognitions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
107.
Airborne laser scanning (ALS) is a remote-sensing technique that provides scale-accurate 3D models consisting of dense point clouds with x, y planimetric coordinates and altitude z. Using ALS, very high-resolution (VHR) digital surface models (DSMs) have been widely used for commercial and scientific applications since the early 1990s. Although there is widespread usage, there has been little comprehensive investigation of quality control for ALS DSMs in the literature, as most studies have been limited to assessing point-based vertical accuracy. This article is dedicated to investigating the quality of ALS DSMs for different land classes using statistical and visual approaches based on absolute and relative vertical accuracy metrics. Rather than a limited number of ground control points (GCP), the model-to-model-based approach is applied and DSMs derived from terrestrial laser scanning (TLS) point clouds that have around 5 mm absolute and 3 mm relative geolocation accuracy were used as the reference data for comparison. The results demonstrate that in open, grass, and building land classes, the ALS DSMs reached both standard deviation (σ) and normalized median absolute deviation (NMAD) of 3–5 cm after the elimination of any systematic biases. This result sufficiently satisfies the vertical accuracy requirements for 1/1000-scale topographic maps determined by National Digital Elevation Program (NDEP) specifications. In tall vegetation, a higher number of discrepancies larger than 0.5 m exist, reversing the relation between σ and NMAD. These vegetation errors also do not appear to be normally distributed. As an additional investigation, the performance of ALS DEMs under dense high-vegetation areas was assessed. These under-canopy ALS DEMs, created using only classified ground returns, offer both σ and NMAD of 12–14 cm, a performance level that is difficult to achieve under-canopy using photogrammetric techniques.  相似文献   
108.
109.
110.
The genes of the trithorax group (trxG) in Drosophila melanogaster are required to maintain the pattern of homeotic gene expression that is established early in embryogenesis by the transient expression of the segmentation genes. The precise role of each of the diverse trxG members and the functional relationships among them are not well understood. Here, we report on the isolation of the trxG gene moira (mor) and its molecular characterization. mor encodes a fruit fly homolog of the human and yeast chromatin-remodeling factors BAF170, BAF155, and SWI3. mor is widely expressed throughout development, and its 170-kDa protein product is present in many embryonic tissues. In vitro, MOR can bind to itself and it interacts with Brahma (BRM), an SWI2-SNF2 homolog, with which it is associated in embryonic nuclear extracts. The leucine zipper motif of MOR is likely to participate in self-oligomerization; the equally conserved SANT domain, for which no function is known, may be required for optimal binding to BRM. MOR thus joins BRM and Snf5-related 1 (SNR1), two known Drosophila SWI-SNF subunits that act as positive regulators of the homeotic genes. These observations provide a molecular explanation for the phenotypic and genetic relationships among several of the trxG genes by suggesting that they encode evolutionarily conserved components of a chromatin-remodeling complex.  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