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   1652篇
  免费   3篇
电工技术   1篇
综合类   2篇
化学工业   16篇
金属工艺   1篇
建筑科学   2篇
轻工业   6篇
一般工业技术   2篇
冶金工业   1619篇
自动化技术   6篇
  2023年   1篇
  2022年   1篇
  2016年   1篇
  2015年   3篇
  2014年   4篇
  2013年   2篇
  2010年   2篇
  2009年   3篇
  2008年   5篇
  2007年   1篇
  2006年   6篇
  2005年   2篇
  2004年   2篇
  2003年   3篇
  2002年   1篇
  2000年   2篇
  1999年   54篇
  1998年   504篇
  1997年   300篇
  1996年   192篇
  1995年   105篇
  1994年   68篇
  1993年   94篇
  1992年   11篇
  1991年   22篇
  1990年   17篇
  1989年   11篇
  1988年   18篇
  1987年   17篇
  1986年   13篇
  1985年   11篇
  1983年   4篇
  1982年   5篇
  1981年   14篇
  1980年   20篇
  1978年   3篇
  1977年   50篇
  1976年   80篇
  1975年   2篇
  1973年   1篇
排序方式: 共有1655条查询结果,搜索用时 15 毫秒
81.
A random-digit dialed telephone survey was conducted in a traditionally conservative southern state to determine the level of support for sexuality education in the public schools including support for specific sexuality education topics, the earliest grade level at which each topic should be taught, and the amount of instruction time required for sexuality education in the high schools. Survey data were obtained from 534 South Carolina registered voters in late January/early February 1997. Results demonstrated that most South Carolina registered voters: 1) supported sexuality education in the public schools; 2) supported instruction on a variety of sexuality education topics; 3) supported instruction at all grade levels, especially beginning in middle school; and 4) believed instruction time for sexuality education in the high schools should either remain the same or be increased. In addition, a significant increase in support for sexuality education occurred from the beginning of the survey to the end, suggesting that the instrument itself may have served as an educational tool for respondents. The characteristics of registered voters who supported sexuality education at the beginning of the survey and at the end were examined and compared. These results may assist in the development of educational and marketing strategies designed to build support for school-based sexuality education programs in South Carolina and elsewhere.  相似文献   
82.
The effects of intranasal syringing with 5% zinc sulfate were assessed in rats trained in a wind-tunnel olfactometer to detect the presence of an odor or to discriminate odors of graded intensities. The syringing produced a severe but brief interference in olfactory performance. Full recovery of detection performance occurred within 72 hr after treatment. Initial recovery of odor intensity discrimination occurred in 2-8 days and full recovery within 8-10 days. These results suggest that intranasal syringing with ZnSO4 is not an adequate control for the effects of anosmia produced by olfactory bulbectomy.  相似文献   
83.
This research was designed to follow up the observation of Thornton and Kraemer ('51) that regressed, denervated limbs of Ambystoma larvae will not regenerate upon reinnervation if all digits on the limbs were not completely resorbed. The object of this experiment was to determine whether the presence of an apical structure, protruding past the amputation surface, would affect the regenerative process. Both forearms of adult newts were amputated midway between the elbow and the wrist. One limb served as a normal regeneration control, and in the other limb the third digit from the removed hand was implanted in place of the removed radius, so that the three distal phalangeal segments protruded past the plane of amputation. Blastema formation in the experimental limbs was delayed by several weeks as compared with control limbs. Approximately one third of the experimental limbs did not regenerate. The regenerates that did form were strongly deviated (45-90 degrees) radially from the longitudinal axis of the limb. Experimental analysis showed that the delay in regeneration is due largely to the projecting part of the digit. The radial deviation of the regenerates is not due to the digital implant, but rather to the removal of the radius. Trauma alone does not account for this phenomenon.  相似文献   
84.
85.
Micropuncture studies were performed in 33 Munich-Wistar rats maintained chronically either on dietary NaCl restriction (group 1) or excess (group 2). Values for single nephron (SN) and total kidney glomerular filtration rate (GFR) were identical in both groups. Nevertheless, because of preferential efferent vasoconstriction, glomerular capillary hydraulic pressure (PGC) was higher in group 1, offsetting the lower initial glomerular plasma flow rate (QA) also found in group 1. The pressor response to infusion of exogenous angiotensin II (AII) was less in group 1 than in group 2, suggesting that vascular receptors for AII may have been occupied by endogenous hormone, the latter leading to the efferent arteriolar vasoconstriction. In addition to AII, prostaglandins also appear to be involved in the adaptations of the glomerular microcirculation to chronic variations in salt intake. In group 1, indomethacin or meclofenamate infusion mimicked exogenous AII, causing declines in QA and SNGFR. These changes were lacking in group 2. Because of relative contraction of plasma volume, the vasodilatory effects of prostaglandins appear to be needed in low salt animals to sustain SNGFR and QA. In the high salt group, however, since plasma volume is not contracted, maintenance of SNGFR and QA appears to be less critically dependent on endogenous prostaglandins.  相似文献   
86.
A consistent and relatively simple method is presented for studying the unpiloted ignition of polymeric materials in contact with hot air. The ignition behavior of a particular polymer as determined by its bulk properties may be characterized by the relationship between sample mass and ignition time at constant area for a series of furnace temperatures. Extrapolation of this linear relationship at a given furnace temperature to zero mass results in an intrinsic ignition time which represents the rate of the ignition process when the time required to heat the sample to its decomposition temperature has been eliminated, i.e., the sample is brought to its decomposition temperature instantaneously. The temperature dependence of this intrinsic ignition time shows an Arrhenius relationship with an apparent activation energy of 8–10 kcal/mole for all but one material investigated. This indicates that the mechanism controlling the kinetics of such an ignition process is a physical one, most likely the diffusion of combustible gaseous products into the heated air surrounding the sample.  相似文献   
87.
88.
89.
An eczematous eruption developed on the hands and forearms of a 68-year-old man after frequent contact with homebred specimens of the lady slipper Paphiopedilum haynaldianum. Patch tests with leaves, petals, and stems, as well as with two quinones isolated from the plant by thin-layer chromatography, gave strongly positive reactions. The results demonstrated that the recurrent skin lesions were the expression of an allergic contact dermatitis due to the quinoid constitutnets, which are the main contact allergens in this orchid species.  相似文献   
90.
Recordings of multiunit sympathetic activity were made in muscle branches of the peroneal nerve in 22 healthy subjects at rest in recumbent position. Nerve activity was quantitated in terms of burst incidence (number of pulse synchronous sympathetic bursts per 100 heart beats or per min). In a separate session, 4-45 months later, blood was drawn from an antecubital vein for noradrenaline analysis. Both sympathetic activity and plasma concentrations of noradrenaline varied widely between subjects and both parameters increased with age. There was a significant positive correlation between a subject's level of sympathetic activity and his plasma concentration of noradrenaline. It is suggested that overflow of transmitter from sympathetic terminals in muscles contributes significantly to plasma levels of noradrenaline at rest.  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