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   5734篇
  免费   88篇
  国内免费   4篇
电工技术   46篇
综合类   4篇
化学工业   713篇
金属工艺   52篇
机械仪表   63篇
建筑科学   112篇
矿业工程   13篇
能源动力   75篇
轻工业   336篇
水利工程   22篇
石油天然气   21篇
无线电   478篇
一般工业技术   613篇
冶金工业   2707篇
原子能技术   52篇
自动化技术   519篇
  2022年   28篇
  2021年   35篇
  2020年   30篇
  2018年   40篇
  2017年   33篇
  2016年   36篇
  2015年   31篇
  2014年   78篇
  2013年   188篇
  2012年   129篇
  2011年   123篇
  2010年   108篇
  2009年   112篇
  2008年   133篇
  2007年   145篇
  2006年   111篇
  2005年   122篇
  2004年   109篇
  2003年   110篇
  2002年   100篇
  2001年   89篇
  2000年   94篇
  1999年   143篇
  1998年   786篇
  1997年   406篇
  1996年   331篇
  1995年   208篇
  1994年   197篇
  1993年   214篇
  1992年   92篇
  1991年   76篇
  1990年   90篇
  1989年   80篇
  1988年   70篇
  1987年   71篇
  1986年   62篇
  1985年   78篇
  1984年   58篇
  1983年   75篇
  1982年   59篇
  1981年   53篇
  1980年   63篇
  1979年   48篇
  1978年   46篇
  1977年   91篇
  1976年   161篇
  1975年   42篇
  1974年   24篇
  1973年   32篇
  1972年   25篇
排序方式: 共有5826条查询结果,搜索用时 15 毫秒
101.
Ten patients (14 knees) with severe knee flexion contractures were treated by gradual mechanical distraction using either the Ilizarov or Orthofix external fixator. Range of motion improved from an average flexion contracture of 60 degrees before surgery to 16 degrees at the follow-up evaluation. Range of motion results were graded good or excellent in five knees, fair in two knees, and poor in three knees. Average total arc of motion remained essentially unchanged when comparing the preoperative (59 degrees) with the follow-up results (63 degrees). However, the functional position of this arc improved significantly. Problems encountered included a "rebound" phenomena after frame removal, with loss of the temporarily increased total arc of motion. The role of hamstring tenotomy and radical posterior knee release remains unclear.  相似文献   
102.
Real-Time Systems - This paper presents results and observations from a survey of 120 industry practitioners in the field of real-time embedded systems. The survey provides insights into the...  相似文献   
103.
104.
The primary goal of this article is to measure the wetting characteristics of a low melting point metal to determine the efficacy of this type of material for possible use in thermal energy storage applications. Galinstan®, a commercially available alloy consisting of Gallium, Indium, and Tin is subjected to contact angle measurements on various silicon surfaces at varying temperatures. Due to the oxidation characteristics of Galinstan, all experiments are conducted in an inert nitrogen environment (<0.5 ppm oxygen) to maintain fluid‐like properties. This work finds that although contact angle changes with substrate and surface structure, temperature has no observable effect on contact angle. Contact angles range from 141° on smooth silicon to greater than 160° on silicon micropillars. Although a temperature dependence is not observed over the range of temperatures studied, having wetting properties of Galinstan on various surfaces is a step toward better understanding the capabilities of this and similar materials in energy management.
  相似文献   
105.
BACKGROUND: Prior research has suggested reductions in the density of serotonin transporter (SERT) binding sites in blood platelets and post-mortem brain tissue of depressed patients. We sought to determine whether patients with unipolar major depression have diminished SERT availability as assessed by both brainstem [123I] beta-CIT SPECT and platelet [3H]paroxetine binding. METHODS: Drug-free depressed and healthy subjects were injected with 211 +/- 22 MBq [123I] beta-CIT and imaged 24 +/- 2 h later under equilibrium conditions. A ratio of specific to nonspecific brain uptake (V3" = (brainstem-occipital)/occipital), a measure proportional to the binding potential (Bmax/Kd), was used for all comparisons. RESULTS: Results showed a statistically significant reduction in brainstem V3" values in depressed as compared to healthy subjects (3.1 +/- .9 vs. 3.8 +/- .8, p = .02). Platelet [3H]paroxetine binding was not altered (Bmax = 2389 +/- 484 vs. 2415 +/- 538 fmol/mg protein, p = .91) and was not significantly correlated with brainstem [123I] beta-CIT binding (r = -0.14, p = .48). CONCLUSIONS: These data are the first to suggest reductions in the density of brain SERT binding sites in living depressed patients. These findings provide further support for a preeminent role for alterations in serotonergic neurons in the pathophysiology of depression.  相似文献   
106.
OBJECTIVES: An understanding of the validity and usefulness of self-reported measures (as distinct from clinically determined measures) of oral health is emerging. These self-reported measures include self-rated oral health (SROH). Three objectives were to: (1) describe self-rated oral health in dentate adults, (2) quantify associations between self-rated oral health and other measures of oral health (oral disease and tissue damage, pain and discomfort, functional limitation, and disadvantage), and (3) assess the construct validity of a model of oral health proposed herein. METHODS: The Florida Dental Care Study is a longitudinal study of oral health, which included at baseline 873 subjects who had at least one tooth, were 45 years or older, and who participated for an interview and clinical examination. RESULTS: The prevalence of self-rated oral health decrements was substantial; approximately one fourth of subjects reported their oral health as only fair or poor. Bivariate and multivariate results provided consistent evidence of the construct validity of the proposed model of oral health. Additionally, the salience of one measure of dental appearance suggests that persons may use esthetic cues when rating their oral health. CONCLUSIONS: The proposed multidimensional model of oral health has construct validity. Self-rated oral health is affected by oral disease and tissue damage, oral pain and discomfort, oral functional limitation, and oral disadvantage. These self-reported measures and the proposed model should provide useful information for dental care effectiveness research. General health status has been disaggregated into the "physical" and the "mental;" an additional separation into the "oral" aspects of health seems warranted.  相似文献   
107.
A method to derive in-water absorption coefficients from total remote-sensing reflectance (ratio of the upwelling radiance to the downwelling irradiance above the surface) analytically is presented. For measurements made in the Gulf of Mexico and Monterey Bay, with concentrations of chlorophyll-a ranging from 0.07 to 50 mg/m(3), comparisons are made for the total absorption coefficients derived with the suggested method and those derived with diffuse attenuation coefficients. For these coastal to open-ocean waters, including regions of upwelling and the Loop Current, the results are as follows: at 440 nm the difference between the two methods is 13.0% (r(2) = 0.96) for total absorption coefficients ranging from 0.02 to 2.0 m(-1); at 488 nm the difference is 14.5% (r(2) = 0.97); and at 550 nm the difference is 13.6% (r(2) = 0.96). The results indicate that the method presented works very well for retrieval of in-water absorption coefficients exclusively from remotely measured signals, and that this method has a wide range of potential applications in oceanic remote sensing.  相似文献   
108.
Nondiffracting beams are of interest for optical metrology applications because the size of the beam does not change as the beam propagates. However, accuracy can be increased if the diameter of the beam is smaller. One technique for accomplishing this is to use the dark axial intensity profile associated with a higher-order nondiffracting Bessel function beam. We generate these higher-order Bessel function beams with a programmable spatial light modulator. We study the intensity patterns and the phase dependence of these nondiffracting beams. In addition, we examine interference effects caused by recording these patterns onto a binary spatial light modulator.  相似文献   
109.
Range-finding by triangulation with nondiffracting beams   总被引:1,自引:0,他引:1  
Davis JA  Carcole E  Cottrell DM 《Applied optics》1996,35(13):2159-2161
Nondiffracting beams are useful for alignment applications because the size of the beam does not change as the beam propagates. In this research we report a technique that allows for distance measurements with nondiffracting beams. With our approach a diffractive optical element is designed that generates two off-axis, tilted, nondiffracting Bessel function beams. These beams intersect at a desired distance from the input plane, producing interference. We generate these Bessel function arrays with a programmable spatial light modulator allowing external control over the intersection distance.  相似文献   
110.
264 patients with cancer of larynx, 21 female and 234 male, had a testosterone and sex hormone binding globulin (SHBG) before the treatment in serum estimated. Because of dependence of levels of hormones the group of patients was divided into three following groups: "lower than standard", "standard", "higher than standard". The correlation between these groups and sex, age, localization of tumor, organs' advances, stage of morphological malignancy and type of cancer was reported. Anomalous values of testosterone were in male group more frequently reported. Anomalous values of SHBG were similar in male and female groups, but in the female group there was a significant majority of "lower than standard" values reported. The majority of abnormal values of testosterone and SHBG was described in groups of age higher than 50 years. There were no differences in testosterone and SHBG levels in different localization of tumors in larynx. In advanced stage T3 and T4 there were more frequent lower mean values of testosterone levels and higher values of SHBG levels in comparison to T2 stages. In tumors in G1 and G2 stages of histological malignancy higher levels of SHBG and higher mean levels of testosterone. The tumors in stage G3 the hormone levels were lowers were observed. The levels of SHBG in groups of carcinoma planoepitheliale keratodes were in 66% higher than in a group of carcinoma planoepitheliale akeratodes but in both groups the levels of testosterone were nearing the same. In group of patients with larynx cancer the negative correlation between the levels of testosterone and SHBG was not observed. Higher SHBG levels were not always accompanied by lower testosterone levels.  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