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   1363篇
  免费   13篇
  国内免费   2篇
电工技术   7篇
化学工业   78篇
金属工艺   18篇
机械仪表   17篇
建筑科学   29篇
能源动力   9篇
轻工业   30篇
水利工程   1篇
石油天然气   3篇
无线电   44篇
一般工业技术   113篇
冶金工业   949篇
原子能技术   8篇
自动化技术   72篇
  2021年   5篇
  2019年   4篇
  2018年   5篇
  2017年   8篇
  2016年   7篇
  2015年   4篇
  2014年   10篇
  2013年   28篇
  2012年   14篇
  2011年   20篇
  2010年   10篇
  2009年   12篇
  2008年   25篇
  2007年   13篇
  2006年   14篇
  2005年   19篇
  2004年   14篇
  2003年   16篇
  2002年   12篇
  2001年   19篇
  2000年   19篇
  1999年   34篇
  1998年   273篇
  1997年   167篇
  1996年   97篇
  1995年   55篇
  1994年   46篇
  1993年   48篇
  1992年   16篇
  1991年   30篇
  1990年   28篇
  1989年   27篇
  1988年   24篇
  1987年   27篇
  1986年   22篇
  1985年   17篇
  1984年   9篇
  1983年   8篇
  1982年   10篇
  1981年   6篇
  1980年   21篇
  1979年   7篇
  1978年   10篇
  1977年   26篇
  1976年   60篇
  1975年   7篇
  1974年   5篇
  1973年   4篇
  1971年   3篇
  1966年   2篇
排序方式: 共有1378条查询结果,搜索用时 31 毫秒
11.
The objective of this study was to determine the effect of long-term administration of a growth hormone (GH)-releasing factor analog (GRFa) and(or) thyrotropin-releasing hormone (TRH) on growth, feed efficiency, carcass characteristics, and blood hormones and metabolites in beef heifers. Crossbred heifers (n = 48; 345.9 +/- 2.8 kg) were divided into four equal groups: control (vehicle), 1 microgram of GRFa (human GRF 1-29 analog).kg BW-1.d-1, 1 microgram of TRH.kg BW-1.d-1, or GRFa + TRH. Daily s.c. injections continued for 86 d. Blood samples were collected from half of the heifers after injection on d 1, 36, and 78. On d 89, all heifers were slaughtered. Treatments did not affect (P > .05) ADG but GRFa + TRH decreased (P < .05) ADFI relative to all other treatments. Feed conversion efficiency tended (P < .10) to be improved in the groups given GRFa alone or TRH alone. Treatment with GRFa and(or) TRH did not affect carcass weight, dressing percentage, conformation score, backfat thickness, or weights of liver, kidneys, pituitary, and ovaries. The GRFa + TRH treatment reduced (P < .05) fat score and increased (P < .05) longissimus muscle area relative to other treatments. The GRFa treatments reduced (P < .05) the weight and fat percentage of the mammary gland and increased (P < .05) heart weight. Treatment with TRH alone failed to stimulate GH on d 1, 36, and 78. Treatment with GRFa alone increased (P < .05) GH above controls on d 36, whereas GRFa + TRH increased (P < .05) GH on d 1, 36, and 78. Treatment with GRFa alone increased (P < .05) IGF-I only on d 1, whereas GRFa + TRH was without effect on all days. Across sampling days, treatments had little effect on blood concentrations of insulin, triiodothyronine, nonesterified fatty acids, urea nitrogen, and glucose. The GRFa alone and GRFa + TRH decreased (P < .05) and TRH alone increased (P < .05) thyroxine concentrations. In conclusion, with the dose and administration regimen used, GRFa and(or) TRH yielded small but positive improvements in animal performance.  相似文献   
12.
13.
The growth of allotriomorphic ferrite from austenite in Fe-C-X alloys is studied. Two systems have been selected: the Fe-C-Ni system, in which the substitutional alloying element is expected to have a weak interaction with both the C and the moving interface, and the Fe-C-Mo system, in which these interactions are expected to be non-negligible. The ferrite growth kinetics was measured using two types of experiments: classical isothermal heat treatments and decarburization experiments. All of the experimental observations can be quantitatively rationalized using a model that describes an evolution in interfacial conditions from paraequilibrium (PE) to local equilibrium with negligible partitioning (LENP) during growth. This article is based on a presentation made in the “Hillert Symposium on Thermodynamics & Kinetics of Migrating Interfaces in Steels and Other Complex Alloys,” December 2–3, 2004, organized by the The Royal Institute of Technology in Stockholm, Sweden.  相似文献   
14.
Graves' and Hashimoto's diseases are autoimmune thyroid diseases in which the genetic contribution is complex. For this reason, identification of necessary susceptibility genes has been difficult. However, a number of immunoregulatory genes have been implicated by association studies, including: CTLA-4, a recently described protein involved in antigen presentation, located on chromosome 2q33; the T-cell receptor V alpha and V beta gene complexes, located on 14q11 and 7q35, respectively; and the Ig gene complex (IgH), located on 15q11. We used polymorphic microsatellite markers located within these genes, or gene complexes, to test for linkage (rather than association), to each of these candidates. Using markers within the loci allowed us to assume a fixed recombination fraction of 0.01 in the tested model. Three hundred eight subjects from 48 multiplex families were studied, with 142 affected subjects. Using this set of families, we have previously shown evidence of linkage with a major susceptibility locus for Graves' disease (GD-1) on 14q24.3-31, with a maximum lod (logarithm + odds) score of 2.1, at a penetrance of 80% and with a dominant mode of inheritance. In the present study, we obtained consistently negative lod scores for each of the candidate genes, assuming either dominant or recessive modes of inheritance. These data, therefore, showed evidence against linkage with all the candidate genes. Unlike association studies, linkage analyses detect major genetic influences on disease susceptibility exerted by the linked loci. The lack of linkage for the immunoregulatory genes that were studied indicated, therefore, that they were not major contributors to disease etiology.  相似文献   
15.
Delamination of residually stressed thin film strips is analyzed to expose the dependence on strip width and film/substrate elastic mismatch. Isotropic films and substrates are assumed. The residual stress in the film is tensile and assumed to originate from mismatch due to thermal expansion or epitaxial deposition. Full and partial delamination modes are explored. In full delamination, the interface crack extends across the entire width of the strip and releases all the elastic energy stored in the strip as the crack propagates along the interface. The energy release rate available to propagate the interface crack is a strong function of the strip width and the elastic modulus of the film relative to that of the substrate. The energy release rate associated with full delamination is determined as a function of the interface crack length from initiation to steady-state, revealing a progression of behavior depending in an essential way on the three dimensionality of the strip. The dependence of the energy release rate on the remaining ligament as the interface crack converges with the strip end has also been calculated, and the results provide an effective means for inferring interface toughness from crack arrest position. A partial delamination propagates along the strip leaving a narrow width of strip attached to the substrate. In this case, the entire elastic energy stored in the strip is not released because the strain component parallel to the strip is not relaxed. A special application is also considered, in which a residually stressed metal superlayer is deposited onto a polymer strip. The energy release rate for an interface crack propagating along the interface between the polymer and the substrate is determined in closed form.  相似文献   
16.
17.
Compared attributions for negative wife behavior offered by 3 groups of husbands: 22 maritally violent and distressed, 17 nonviolent but maritally distressed, and 17 nonviolent and nondistressed. Husbands rated wife behaviors presented in 9 hypothetical problematic marital situation vignettes. On a measure of responsibility attributions, violent husbands were more likely than nondistressed husbands to attribute negative intentions, selfish motivation, and blame to the wife. On a measure of possible negative wife intentions, violent husbands were more likely than either distressed or nondistressed men to attribute negative intentions to the wife. Exploratory analyses suggested that certain types of marital situations (e.g., jealousy and rejection from wife) were particularly likely to elicit attributions of negative intent from violent husbands. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
18.
19.
While abundant clinical and angiographic data are available regarding features of acute or abrupt closure at the site of balloon angioplasty, little morphologic information is available. This study discusses morphologic-histologic causes for acute closure after angioplasty in 130 necropsy patients. Intimal-medial flaps, elastic recoil, and primary thrombosis were the three leading morphologic causes for closure. Data were subdivided into time categories: abrupt (< 1 day), acute (< 1 week), and early (< 1 month). Intimal-medial flaps remained the most common cause for angioplasty closure despite time from angioplasty to documented occlusion. Morphologic recognition of types and frequencies of angioplasty closure are discussed, and specific mechanical, pharmacologic, or combined treatments are reviewed.  相似文献   
20.
STUDY DESIGN: Prospective comparative study of pain drawings with findings on lumbar spine magnetic resonance imaging. OBJECTIVES: To assess the ability of the pain drawing to predict the presence of nerve root compression. SUMMARY OF BACKGROUND DATA: Most research work has concentrated on the ability of the pain drawing to act as a screening method for psychological distress with less work directed at the influence the anatomic abnormality has on the pain drawing. METHODS: One hundred thirty-four consecutive outpatients attending for lumbar magnetic resonance imaging in the investigation of back and leg pain completed pain drawings and psychological testing immediately before the examination. The pain drawing was analyzed by previously reported criteria, and the magnetic resonance imaging was assessed independently for the presence of nerve compression by three radiologists. Multivariate stepwise discriminant analysis was used to identify patients with nerve compression on the basis of their pain drawing. RESULTS: Nerve compression was predicted by numbness in the anterolateral aspect of the foot. There was considerable overlap in the appearances of the pain drawings between patients with and without nerve compression, and the pain drawing correctly classified only 58% of patients with nerve compression. CONCLUSIONS: The pain drawing is not a good predictor of nerve compression on magnetic resonance imaging in a group of patients investigated for back and leg pain. It should be interpreted with caution and in light of the full clinical picture.  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