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   5010篇
  免费   30篇
  国内免费   1篇
电工技术   3篇
综合类   1篇
化学工业   140篇
金属工艺   23篇
机械仪表   20篇
建筑科学   13篇
矿业工程   1篇
能源动力   12篇
轻工业   66篇
水利工程   1篇
石油天然气   3篇
无线电   34篇
一般工业技术   90篇
冶金工业   4576篇
原子能技术   6篇
自动化技术   52篇
  2022年   13篇
  2021年   23篇
  2020年   11篇
  2019年   9篇
  2018年   11篇
  2017年   17篇
  2016年   16篇
  2015年   14篇
  2014年   23篇
  2013年   31篇
  2012年   28篇
  2011年   32篇
  2010年   23篇
  2009年   18篇
  2008年   20篇
  2007年   17篇
  2006年   14篇
  2005年   15篇
  2004年   14篇
  2003年   16篇
  2002年   8篇
  2001年   7篇
  2000年   10篇
  1999年   158篇
  1998年   1373篇
  1997年   757篇
  1996年   521篇
  1995年   277篇
  1994年   245篇
  1993年   262篇
  1992年   42篇
  1991年   73篇
  1990年   63篇
  1989年   90篇
  1988年   79篇
  1987年   66篇
  1986年   69篇
  1985年   54篇
  1984年   1篇
  1983年   6篇
  1982年   17篇
  1981年   31篇
  1980年   50篇
  1979年   3篇
  1978年   12篇
  1977年   123篇
  1976年   268篇
  1975年   7篇
  1974年   1篇
  1955年   3篇
排序方式: 共有5041条查询结果,搜索用时 93 毫秒
1.
The objective of this study was to characterise the nutritional potential of leaves and identify a diversity centre with low cyanide and high nutrient content among 178 Latin American cassava genotypes. This field-based collection represents the seven diversity centres, held at The International Center for Tropical Agriculture (CIAT Palmira, Colombia) by the Cassava Program. The cyanide, all-trans-β-carotene and lutein concentrations in cassava leaves ranged from 346 to 7484 ppm dry basis (db), from 174–547 μg g−1 db and 15–181 μg g−1 db, respectively. Cassava leaves also showed significant levels of essential amino acids leucine, lysine, phenylalanine, valine and threonine, and average total protein content of 26.24 g 100 g−1 db. Among seven diversity centres, South American rainforest group showed low cyanide and high carotene content in leaves. In addition, VEN77 and PAN51 genotypes stood out for having low cyanide in leaves and roots and high carotene in leaves. This genetic diversity can be used to select high potential progenitors for breeding purposes.  相似文献   
2.
IR与RS-232的匹配技术   总被引:2,自引:0,他引:2  
现代电子设备通常包含最新的数据通信接口,以实现更高的数据率或增进用户的便利性。红外技术(IR)是数据通信接口的一个很好例子,但有时单独使用这种最新接口还是不够的,设备还需要与采用传统接口如RS-232的老设备兼容才会被用户所接受。因此,常见的红外技术和RS-232共存于同一设备中。  相似文献   
3.
A fundamental problem for regulatory networks is to understand the relation between form and function: to uncover the underlying design principles of the network. Circadian clocks present a particularly interesting instance, as recent work has shown that they have complex structures involving multiple interconnected feedback loops with both positive and negative feedback. While several authors have speculated on the reasons for this, a convincing explanation is still lacking.We analyse both the flexibility of clock networks and the relationships between various desirable properties such as robust entrainment, temperature compensation, and stability to environmental variations and parameter fluctuations. We use this to argue that the complexity provides the flexibility necessary to simultaneously attain multiple key properties of circadian clocks. As part of our analysis we show how to quantify the key evolutionary aims using infinitesimal response curves, a tool that we believe will be of general utility in the analysis of regulatory networks. Our results suggest that regulatory and signalling networks might be much less flexible and of lower dimension than their apparent complexity would suggest.  相似文献   
4.
Phospholamban (PLN) was expressed in Escherichia coli as a protein fusion with glutathione S-transferase (GST). GST-PLN was mostly present in the insoluble protein fraction and accounted for approximately 50% of total insoluble protein. Attempts to suppress inclusion body formation or to use GST as an affinity-purification tag failed. A successful purification method is based on preparative SDS/PAGE and electrodialysis. From 1 g cells we typically purified 13.5 mg fusion protein with a PLN content of 2.8 mg. We genetically inserted an enterokinase (EK) protease site just in front of the PLN sequence and demonstrated the proteolytical liberation of PLN from the carrier protein. The approach described represents a substantial advancement in PLN expression and purification.  相似文献   
5.
Much of our understanding of the organization of the cells that comprise the hematopoietic system and the cellular and molecular mechanisms that regulate their development is derived from mouse models. However, knowledge of the human hematopoietic system and identification of human stem cells have, until recently, been hampered by the absence of in vivo assays that measure their repopulation capacity. The development of methods to transplant normal and leukemic human hematopoietic cells into immune-deficient SCID mice provides the foundation for human stem cell assays. This review will focus on recent evidence that normal and leukemic human stem cells can be assayed in these systems.  相似文献   
6.
7.
A high prevalence of epilepsy (up to 1.3%) was observed in an area hyperendemic for onchocerciasis in the province of Bururi, Burundi. Following this observation, epileptics and controls were examined in 2 communes (administrative units) with different endemicity for onchocerciasis. Altogether, onchocerciasis was more frequent in epileptics (81.8%) than in controls from the same households (68.3%; P < 0.05). This difference was more marked in the hyperendemic area. Other possible causes of epilepsy, including cysticercosis, were infrequent (18 possible cases among 110 epileptics). During this survey, 9 epileptics with growth retardation were seen. They showed most characteristics of Nakalanga syndrome, which was described from Uganda. All 9 such cases were suffering from onchocerciasis. These findings give more evidence of a possible association between onchocerciasis and epilepsy, and between onchocerciasis and Nakalanga syndrome.  相似文献   
8.
A method for generating olfactory stimuli for humans within a functional magnetic resonance imaging (fMRI) experimental design is described. The system incorporates a nasal-mask in which the change from odorant to no-odorant conditions occurs in less than 500 ms and is not accompanied by visual, auditory, tactile, or thermal cues. The mask provides an ordorant-free environment following prolonged ordorant presence. Specific imaging parameters that are conducive to the study of the human olfactory system are described. In a pilot study performed using these methods, the specific patterns of activation observed converged with published experimental and clinical findings.  相似文献   
9.
A preliminary report presenting the results of fibular strut grafting in the severely resorbed mandibular and maxillary region is presented. Thirteen patients were treated due to severe resorption of alveolar and basilar bone of 49 segments of the mandible and the maxilla. Two patients additionally had pathological fractures of the mandible. In 10 cases the strut graft was harvested by means of a new minimally invasive technique. After modelling the fibular bone it was fixed to the recipient site by miniscrews or implants. After a mean follow-up period of 20 months (max. 31, min. 11 months) a retrospective analysis of clinical and radiological findings was carried out. It showed that a mean augmentation of 16 mm was achieved. Compared to other studies the fibular strut graft was resorbed less, and due to the primary stability it could be used for the treatment of fractures of the mandible. No more than natural resorption was observed when the patients received their prostheses fixed to dental implants.  相似文献   
10.
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