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   700篇
  免费   14篇
  国内免费   4篇
电工技术   17篇
综合类   2篇
化学工业   150篇
金属工艺   10篇
机械仪表   19篇
建筑科学   10篇
能源动力   23篇
轻工业   47篇
水利工程   3篇
石油天然气   2篇
无线电   69篇
一般工业技术   108篇
冶金工业   182篇
原子能技术   15篇
自动化技术   61篇
  2022年   15篇
  2021年   9篇
  2020年   4篇
  2019年   7篇
  2018年   10篇
  2017年   13篇
  2016年   16篇
  2015年   16篇
  2014年   18篇
  2013年   34篇
  2012年   13篇
  2011年   42篇
  2010年   26篇
  2009年   30篇
  2008年   20篇
  2007年   25篇
  2006年   23篇
  2005年   18篇
  2004年   27篇
  2003年   22篇
  2002年   10篇
  2001年   9篇
  2000年   17篇
  1999年   15篇
  1998年   63篇
  1997年   32篇
  1996年   32篇
  1995年   17篇
  1994年   12篇
  1993年   17篇
  1992年   6篇
  1991年   8篇
  1990年   4篇
  1989年   5篇
  1988年   7篇
  1987年   6篇
  1986年   10篇
  1985年   5篇
  1984年   3篇
  1983年   3篇
  1982年   3篇
  1981年   1篇
  1980年   4篇
  1979年   4篇
  1978年   7篇
  1977年   9篇
  1976年   10篇
  1975年   6篇
  1974年   2篇
  1973年   2篇
排序方式: 共有718条查询结果,搜索用时 312 毫秒
81.
Only five cases of paraganglioma of the prostate have been reported hitherto. The tumours may be functional (phaeochromocytomas) or non-functional and benign or malignant. We present a sixth case--a non-functional, benign paraganglioma of the prostate--with a review of the literature.  相似文献   
82.
A wide variety of alkyl derivatives of Q2 (6-geranyl-2, 3-dimethoxy-5-methyl-1,4-benzoquinone) and DB (6-n-decyl-2, 3-dimethoxy-5-methyl-1,4-benzoquinone), in which methoxy groups of the 2- and/or 3-positions of the quinone ring were replaced by other bulky alkoxy groups from ethoxy to butoxy, were prepared by novel synthetic procedures. Electron-accepting activities of the bulky quinones were investigated with bovine heart mitochondrial complex I and its counterpart of Paracoccus denitrificans(NDH-1) to elucidate structural and functional features of the quinone reduction site of the enzymes. The bulky quinone analogues served as sufficient electron acceptors from the physiological quinone reduction site of bovine complex I. Considering the very poor activities of even the ethoxy derivatives as substrates for other respiratory enzymes such as mitochondrial complexes II and III [He, D. Y., Gu, L. Q., Yu, L., and Yu, C. A. (1994) Biochemistry 33, 880-884], this result indicated that the quinone reduction site of bovine complex I is spacious enough to accommodate bulky exogenous substrates. In contrast to bovine complex I, bulky quinone analogues served as poor electron acceptors with Paracoccus NDH-1. These observations indicated that bovine complex I recognizes the substrate structure with poor specificity. The substituent effects in the 2- and 3-positions of the quinone ring on the electron-transfer activity with bovine complex I differed significantly between Q2 and DB series despite having the same total number of carbon atoms in the side chain. The inhibitory effect involving Q2 due to its geranyl side chain was markedly diminished by structural modifications of the quinone ring moiety. These findings indicate that the side chain plays a specific role in the redox reaction and that the quinone ring and side-chain moieties contribute interdependently to binding interaction. Moreover, structural dependency of the proton-pumping activity of the quinone analogues was comparable to that of the electron-transfer activity with bovine complex I, indicating that the mechanism of redox-driven proton-pumping does not differ depending upon the substrate structure.  相似文献   
83.
The structure of an asymmetrically expanded optical field normal to the active layer was applied to 1020-nm ridge waveguide laser diodes in order to increase their maximum kink-free output power and reduce the aspect ratio of the output beams. As a result, a kink-free output power of more than 400 mW and an aspect ratio of less than 2.5 were achieved by this structure. Good reliability was also obtained at an output power of 300 mW at 50/spl deg/C.  相似文献   
84.
85.
We report two cases of idiopathic interstitial pneumonia (IIP) with acute deterioration after bronchoalveolar lavage (BAL). Case 1 was a 54-year-old woman, and case 2 was a 75-year-old man. Both were diagnosed as having IIP, and hospitalized with complaints of high fever and dyspnea. After BAL, the degree of dyspnea increased. White blood cell count and lactate dehydrogenase were elevated, and PaO2 was decreased. Chest X-ray revealed consolidation of the upper lung fields and reticulo-granular shadows spreading through both lungs. BAL fluid examination showed an elevated neutrophil fraction (case 1: 6.5%, case 2: 35.2%), suggesting respiratory tract infection although bacteria could not be detected. Case 1 died of respiratory failure despite corticosteroid therapy. Autopsy revealed diffuse alveolar damage with focal pneumonia in the right S6 corresponding to the upper lobe consolidation. Case 2 improved after antibiotic therapy. These findings suggest that aspiration of infected fluid during BAL can cause acute exacerbation of IIP. It is important to recognize that the BAL procedure can induce an acute exacerbation of IIP.  相似文献   
86.
rECH1, a recently identified rat cDNA (FitzPatrick, D. R., Germain-Lee, E., and Valle, D. (1995) Genomics 27, 457-466) encodes a polypeptide belonging to the hydratase/isomerase superfamily. We modeled the structure of rECH1 based on rat mitochondrial 2-enoyl-CoA hydratase 1. The model predicts that rECH1p has the hydratase fold in the core domain and two domains for interaction with other subunits. When we incubated 3,5,8,11, 14-eicosapentaenoyl-CoA with purified rECH1p, the spectral data suggested a switching of the double bonds from the Delta3-Delta5 to the Delta2-Delta4 positions. This was confirmed by demonstrating that the product was a valid substrate for 2,4-dienoyl-CoA reductase. These results indicate that rECH1p is Delta3,5-Delta2,4-dienoyl-CoA isomerase. Subcellular fractionation and immunoelectron microscopy using antibodies to a synthetic polypeptide derived from the C terminus of rECH1p showed that rECH1p is located in the matrix of both mitochondria and peroxisomes in rat liver. Consistent with these observations, the 36,000-Da rECH1p has a potential N-terminal mitochondrial targeting signal as well as a C-terminal peroxisomal targeting signal type 1. Transport of the protein into the mitochondria with cleavage of the targeting signal results in a mature mitochondrial form with a molecular mass of 32,000 Da; transport to peroxisomes yields a protein of 36,000 Da.  相似文献   
87.
A method for detecting interactions among services and service features in communication systems is proposed. The method uses three types of knowledge: knowledge for clarifying and completing the specification of each feature, knowledge for identifying the implicit relationships among the features, and knowledge for detecting the interactions from the extended feature specifications derived from the first two types of knowledge. Six types of nontrivial interaction are outlined  相似文献   
88.
Cycads, the most primitive of the living gymnosperms, have been used and continue to be used for food and medicinal purposes by many cultures, although toxins must be removed before ingestion. In our quest to identify tropical plants that contain inhibitors of the cytochrome P-450 aromatase and thus may be efficacious in treating estrogen-dependent tumors, we have screened extracts from 5 species of cycad folia encompassing 3 genera: Cycas cairnsiana F. Muell., Cycas revoluta Thunb., Cycas rumphii Miq., Dioon spinulosum Dyer and Encephalartos ferox Bertol. All extracts were found to contain inhibitors of the human enzyme.  相似文献   
89.
The paper presents an overview of ASPEN (Advanced System for Process Engineering) which is a next-generation process simulator and economic evaluation system. The system is presently under development for use in engineering of fossil energy conversion processes.  相似文献   
90.
Integration of well maintained application programs for process design is attempted using an in-house Data Base Management System. The main reason for taking the present approach is to keep the reliability of the existing application programs and to minimize revision work. Through the authors' experience described in this paper, it was found that the proposed way of integration by means of DBMS is to be recommended for these purposes when the number of application programs is small.  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