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   1392篇
  免费   23篇
  国内免费   2篇
电工技术   41篇
化学工业   248篇
金属工艺   46篇
机械仪表   23篇
建筑科学   34篇
能源动力   41篇
轻工业   117篇
水利工程   4篇
无线电   166篇
一般工业技术   162篇
冶金工业   436篇
原子能技术   34篇
自动化技术   65篇
  2023年   6篇
  2022年   18篇
  2021年   20篇
  2020年   7篇
  2019年   14篇
  2018年   14篇
  2017年   22篇
  2016年   15篇
  2015年   9篇
  2014年   18篇
  2013年   34篇
  2012年   30篇
  2011年   49篇
  2010年   37篇
  2009年   46篇
  2008年   55篇
  2007年   42篇
  2006年   31篇
  2005年   44篇
  2004年   26篇
  2003年   37篇
  2002年   38篇
  2001年   29篇
  2000年   38篇
  1999年   41篇
  1998年   167篇
  1997年   107篇
  1996年   59篇
  1995年   56篇
  1994年   46篇
  1993年   48篇
  1992年   12篇
  1991年   24篇
  1990年   12篇
  1989年   11篇
  1988年   13篇
  1987年   8篇
  1986年   13篇
  1985年   7篇
  1984年   8篇
  1983年   8篇
  1982年   10篇
  1981年   6篇
  1980年   10篇
  1979年   7篇
  1978年   6篇
  1977年   9篇
  1976年   21篇
  1975年   6篇
  1973年   7篇
排序方式: 共有1417条查询结果,搜索用时 31 毫秒
101.
Photodarkening was investigated in CdS-doped glasses using luminescence and electron spin resonance (ESR). Photodarkening depends on manufacturers of glasses. The main origin of the difference in photodarkening is attributable to the difference in glass composition.  相似文献   
102.
Dense samples of the higher boride YB22C2N have been fabricated through the spark plasma sintering (SPS) method with different sintering aids. YB22C2N is a representative of a series of newly discovered rare-earth borocarbonitrides, which may be the long-awaited n-type counterpart of boron carbide, “B4C.” The effect of Si, SiC, Al, and TiC additions on the sintering process of YB22C2N has been studied. The best sintered bodies with densities higher than 90% of theoretical density were obtained by means of SPS at 1700°C. We show that the additive choice and pressure have an effect on grain size and density. An investigation of the effect of atmosphere on the sintering behavior has also been carried out. It was found that sinterability is enhanced under nitrogen atmosphere. Thermoelectric properties of the materials sintered with additives have been evaluated, and we discuss their dependences on the fabrication process route.  相似文献   
103.
Research and development of firefighters’ protective clothing relies on a large number of fire disaster experiments in order to assess the thermal performance. It would be substantially advantageous to substitute a virtual numerical experiment for a real one in terms of time, cost and safety. The present article reports the development of an integrated numerical simulator that makes possible the estimation of burn injuries originating from fire disasters. In the simulator, a general-purpose computational fluid dynamics program computes the fluid flow and heat transfer in an in situ fire event, while a one-dimensional program calculates the radiative–conductive heat transfer through the clothing and human skin. A data interface combines the two simulations by loose coupling so as to give the real-time burn injury progress output. The predicted surface heat fluxes and burn degrees agree with experimental measurements reasonably well. Possible numerical error sources are discussed that call for potential improvements in the future.  相似文献   
104.
The partial sequences of the mitochondrial (mt) cytochrome b gene (402 bp) were determined for species of Aspergillus section Flavi. On the basis of identities of DNA sequences, 77 strains were divided into seven DNA types, from D-1 to D-7. The type strains of A. sojae, A. parasiticus, A. flavus and A. oryzae together, A. tamarii, and A. nomius were placed in DNA types D-1. D-2, D-4, D-5 and D-7, respectively. These species could be differentiated from each other. Furthermore, two other DNA types, D-3 and D-6 were found. DNA type D-3 was closely related to A. parasiticus (D-2) and included one strain that deposited as A. flatus var. flavus and produced aflatoxins B and G. DNA types D-6 included one strain named A. flavus and closely related to A. tamarii. The observations of conidial wall texture by SEM (Scanning Electron Microscopy) supported the relationships derived from the cytochrome b gene. The production of aflatoxins was also examined. Using the DNA sequence of cytochrome b gene, several strains were reidentified. The derived amino acids sequences were all the same in the studied strains. The mt cytochrome b gene is useful and reliable in distinguishing and identifying the species in Aspergillus section Flavi.  相似文献   
105.
106.
OBJECTIVE: Although the molecular mechanism of obesity has been poorly understood, recent studies indicate that leptin plays a critical role in regulating both food intake and body weight. Because obesity decreases the sensitivity to insulin, the human ob gene is presumed to be one of the candidate genes for non-insulin-dependent diabetes mellitus (NIDDM) associated with obesity. Although the protein coding region in the ob gene has been screened for mutations, the promoter region and the non-coding first exon have not yet been studied. We investigated the involvement of the human ob gene, especially mutations at the promoter region and the non-coding first exon, in the development of NIDDM associated with obesity. SUBJECTS: The study group comprised 60 Japanese obese subjects with NIDDM (body mass index (BMI) 43.6 > or = BMI > or = 26.4, 29.0+/-0.41 (mean+/-S.E.M.)) and 24 obese individuals with impaired glucose tolerance (IGT) (30 > or = BMI > or = 26.4, 27.1+/-0.22). METHODS: Mutations at both the promoter region and all three exons in the human ob gene were screened by the single-stranded conformational polymorphism analysis. When aberrantly migrated bands were recognized, the PCR-amplified DNA fragment was directly sequenced. RESULTS: In the protein coding region a silent mutation in the second exon was detected. The non-coding first exon and the about 100 bp 5'-flanking region of the gene which contains a proximal CCAAT/enhancer-binding protein site were screened, but no mutations were found. CONCLUSION: These results suggest that no mutations in either the promoter region at the about 100 bp 5'-flanking region of the gene, or in any of the three exons, are involved in the development of NIDDM or IGT associated with obesity.  相似文献   
107.
Fifty-five samples of pus were collected from 51 acute, non-perforated, two spontaneously ruptured and two recurrent peritonsillar abscesses (35 males and 18 females; median age 18 years) and analysed regarding (i) aerobic and anaerobic bacteria (standard culturing), (ii) morphology of bacteria and inflammatory cells (direct microscopy of acridine orange-stained material), and (iii) the percentage of bacteria coated with immunoglobulins IgG, secretory IgA (SIgA) and IgM and complement cleavage product C3b (immunofluorescence assay). Seventy-one per cent of the abscesses harboured a mixed bacterial flora of various aerobes and anaerobes. In none of the cases with a single bacterial species (27 per cent) could immunoglobulin- or complement-coated bacteria be found. In abscesses with a mixed flora, 18 per cent harboured IgG-coated, 15 per cent SIgA-coated, five per cent IgM-coated and five per cent C3b-coated bacteria, respectively. All pus samples contained inflammatory cells in abundance but they were mostly deformed and only occasionally could intracellular bacteria be recognized. Insufficient immunoglobulin-coating of bacteria might be an important aetiopathogenic factor in the development of a peritonsillar abscess. Bactericide in the abscesses is accomplished chiefly by protective mechanisms not dependent on antigen recognition by antibodies.  相似文献   
108.
Histochemical studies of mammary gland sections obtained from healthy lactating Prim' Holstein cows contained numerous corpora amylacea, mainly located in active alveoli. Observations by electron microscopy revealed a cauliflower shape, with a fibrillar or multilayered organization. Mineral studies confirmed the presence of high calcium levels (12.3% of dry matter) and phosphorus (7.4%) in the corpora amylacea composition. These bodies stained positive to Von Kossa silver nitrate and to Periodic acid-Schiff. However, depending on the gland of origin, corpora amylacea stained positive or negative to Congo red. Histochemical studies seemed, therefore, insufficient to determine the presence or absence of amyloid. The amount of total protein varied by approximately 25%. Immunoblotting and analysis of the amino acid sequence of a peptidic fragment obtained from corpora amylacea gave clear evidence of the occurrence of caseins, beta-lactoglobulin and alpha-lactalbumin. However, the comparison between the amino acid composition of corpora amylacea and those of the main milk proteins indicated the presence of other proteins. Electrophoretic analysis also gave evidence of the presence of several other proteins, i.e. glycoproteins. Therefore, it is probable that corpora amylacea composition is much more complex than previously reported.  相似文献   
109.
This study was carried out as an attempt to evaluate the relationship between the results of nasal patency examinations and selected anthropometric measurements of nasal cavities in children with complete primary and secondary cleft palate. The examined group consisted of 130 children with cleft palate treated by means of surgery in early childhood owing to their clefts. Concerning the diagnostic methods the study group was divided into two subgroups. Group I consisted of 75 children in whom face photographs in frontal and axial projections towards the external nasal aperture were analysed. Group II consisted of 55 children in whom by means of P-A teleradiography projection the total area, the maximum height and width of nasal cavity were measured separately for the side with cleft and without cleft. The assessment of nasal patency tests using the objective method--active anterior rhinomanometry was carried out.  相似文献   
110.
The 32P-post-labelling assay for DNA adduct quantification gives the opportunity to examine endogenous exposure to DNA reactive compounds. Most human biomonitoring studies applied white blood cells (WBC) or cells obtained by broncho-alveolar lavages (BAL) as source of DNA, but still it is not clear what cell type represents the most reliable indicator for exposure to cigarette smoke-associated genotoxins. At first, we examined DNA adduct levels by means of nuclease P1 (NP1) enriched 32P-post-labelling in separated WBC subpopulations after in vitro incubations for 18 h with 10 microM benzo[a]pyrene (B[a]P). DNA adduct levels were highest in monocytes (10.7 +/- 2.9 adducts/10(8) nucleotides, n = 8), followed by lymphocytes (5.9 +/- 1.7, n = 8), and granulocytes (0.5 +/- 0.2, n = 8). Secondly, aromatic-DNA adduct levels were determined in BAL cells and WBC-subsets from (non-)smoking volunteers. In smoking individuals, adduct levels were in the ranking order: BAL cells (3.7 +/- 1.0, n = 5) > monocytes (2.0 +/- 0.5, n = 8) > or = lymphocytes (1.6 +/- 0.4, n = 8) > granulocytes (0.8 +/- 0.2, n = 8) by NP1-enrichment and monocytes (9.0 +/- 3.2, n = 5) > or = lymphocytes (8.0 +/- 2.1, n = 6) > granulocytes (2.1 +/- 0.3, n = 7) by butanol-enriched 32P-post-labelling. Aromatic-DNA adduct levels were significantly higher in WBC-subsets of smokers as compared with non-smokers, except for DNA adducts in granulocytes using butanol enrichment. Thirdly, dose-response relationships were investigated in mononuclear white blood cells (MNC, i.e. monocytes plus lymphocytes) and BAL-cells of a larger group of smoking individuals (n = 78). Adduct levels in MNC were related to daily exposure to cigarette-tar (r = 0.31, P < 0.01). Adduct levels in BAL cells seemed to be correlated with pack-years, but after correction for age this relationship was lost. Butanol extraction resulted in 5-6-fold higher DNA adduct levels in MNC, whereas butanol extraction of BAL-DNA of the same individuals yielded only 2-fold higher adduct levels. The two enrichment procedures of 32P-post-labelling were correlated in BAL cells (r = 0.86, P < 0.001, n = 12). We conclude that particularly MNC are good surrogates for the detection of smoking-related DNA adducts.  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