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   1775篇
  免费   3篇
电工技术   2篇
化学工业   33篇
金属工艺   2篇
机械仪表   19篇
轻工业   9篇
无线电   25篇
一般工业技术   49篇
冶金工业   1597篇
自动化技术   42篇
  2023年   2篇
  2022年   4篇
  2020年   4篇
  2019年   3篇
  2018年   4篇
  2017年   2篇
  2013年   3篇
  2012年   12篇
  2011年   4篇
  2010年   5篇
  2009年   4篇
  2008年   3篇
  2007年   8篇
  2006年   6篇
  2005年   6篇
  2004年   7篇
  2003年   10篇
  2002年   3篇
  2001年   6篇
  2000年   4篇
  1999年   36篇
  1998年   474篇
  1997年   276篇
  1996年   198篇
  1995年   150篇
  1994年   94篇
  1993年   95篇
  1992年   23篇
  1991年   19篇
  1990年   15篇
  1989年   12篇
  1988年   17篇
  1987年   11篇
  1986年   7篇
  1985年   11篇
  1984年   5篇
  1983年   8篇
  1982年   6篇
  1981年   14篇
  1980年   20篇
  1979年   1篇
  1978年   8篇
  1977年   58篇
  1976年   110篇
  1975年   3篇
  1974年   1篇
  1971年   1篇
  1969年   1篇
  1968年   1篇
  1919年   1篇
排序方式: 共有1778条查询结果,搜索用时 15 毫秒
101.
Within the pituitary, folliculostellate (FS) cells are considered to regulate the intercellular communication between endocrine cells by paracrine mechanisms. One of the possible paracrine factors involved, could be interleukin-6 (IL-6) which is produced by these cells. Since IL-6 has been shown to be a growth factor of pituitary cells, we have determined whether IL-6 can also influence FS cell proliferation. To test this, a FS cell-like mouse pituitary cell line (TtT/GF cells) was used that exhibits most characteristics of normal FS cells. Under serum-free conditions the proliferation of TtT/GF cells is critically dependent on the initial seeding density: cells seeded at low density do not grow at all whereas cells seeded at high density proliferate with maximal doubling times of 34 hrs. Mouse IL-6 (mIL-6) stimulated only low density cell cultures in a dose and time dependent manner. For cells seeded at high density, exogenously added IL-6 may have failed to stimulate growth because of endogenously produced mIL-6. Conditioned medium from TtT/GF cells, in which mIL-6 concentrations up to 1017 pg/ml were measured, stimulated the proliferation of TtT/GF cells, indicating an autocrine growth stimulatory mechanism. A neutralizing mIL-6 antibody partially suppressed the growth of TtT/GF cells seeded at high density and partially reduced the growth stimulatory activity of TtT/GF conditioned medium. Thus, IL-6 is one but not the only factor that is involved in the autocrine growth stimulatory loop. The relevance of this mechanism for normal FS cells and its physiological consequence needs to be elucidated.  相似文献   
102.
In this study, several erase techniques are examined as to their effect on analog-signal performance in high-density digital magnetic recording. The success of an erasure technique was found to depend on the coercivity of the tape and whether the read-back head senses dφ/dt or flux.  相似文献   
103.
104.
The statistical (black box) remaining lifetime of some simple coherent systems is stochastically compared with the remaining lifetime based on the information at hand. Parallel and cold standby systems of s-identical components with exponentially distributed lifetimes are considered. Information-based remaining lifetime is defined via the number of the nonfailed components at the moment of observation. The main question to answer is: Given the information on the current state of the system, is the remaining lifetime better (worse) in some stochastic sense than the remaining lifetime that is defined by the black box remaining lifetime? The result of this comparison for the general case depends on the time of observation and the time since observation. Several simple examples have been considered, because it is rather difficult technically to treat the stated problem in a greater generality. The main common feature of these examples, describing systems of s-identical components is the monotonically increasing system hazard-rate. An example with a nonmonotone hazard rate for a system of two different components has also been studied  相似文献   
105.
Inpatients in Veterans Administration substance-abuse treatment programs voluntarily took the Minnesota Multiphasic Personality Inventory (MMPI) as part of a routine clinical evaluation. The alcohol-dependence-only group (n?=?207) were older (M?=?49.6 years) and had a higher percentage of White Ss (72.9%) than did either the drug-dependence group (n?=?49, M?=?32.9 years, Whites?=?53.1%) or a mixed alcohol- and drug-dependence group (n?=?160, M?=?35.0 years, Whites?=?60.0%). Previously reported differences between alcoholics and drug abusers in depression and psychopathy were obtained when age and race were not used as covariates, but no differences were found when the effects of age and race were statistically controlled. Mixed alcohol and drug abusers had somewhat more pathological MMPI scores than did alcoholics, even when effects due to age and race were partialed out. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
106.
Neoglycoconjugates based on polyacrylamide and sialic acid with N-acetylneuraminic acid or sialooligosaccharides as side chains were studied by surface-enhanced Raman scattering (SERS) spectroscopy. It had previously been found that these polymers can effectively inhibit influenza virus adhesion. This study revealed the possibility to evaluate, based on the intensity of SERS signals, the overall availability for interaction and the conformational freedom of sialic acid residues in glycoconjugates. The dependence of these two factors on the structure and density of sialylated side chains was studied. The uniformity of distribution of sialylated side chains in conjugates was shown. Comparison of the results of the SERS spectroscopic study of the conjugates and the data on their inhibitory effect on the adhesion of specific strains of influenza virus allowed the identification of the conjugates for which the availability and conformational freedom of sialic acid are the main factors determining their inhibitory properties. A conclusion was also reached about the predominance of one of the mechanisms (competitive inhibition or steric stabilization) in the inhibitory properties of the specific conjugates.  相似文献   
107.
Obese (Lepr(fa)/Lepr(fa)) Zucker rats have a missense mutation in the leptin receptor gene. One amino acid substitution in the extracellular domain common to all known leptin receptor proteins results from this mutation. Obese Zucker rats are unable to respond behaviorally to leptin which is peripherally administered. However, conflicting reports exist on whether obese Zucker rats can respond to centrally administered leptin. The purpose of this study was to determine whether obese Zucker rats responded behaviorally and metabolically to intracerebroventricularly (i.c.v.) administered leptin and to compare the responses of lean and obese Zucker rats. We found that both lean and obese Zucker rats had similar body weight and food intake responses when administered a single i.c.v. leptin injection in a range of doses (1.25, 2.5, 5, and 10 microg), as well as daily i.c.v. administered leptin for five consecutive days. Both single and daily leptin administration also decreased respiratory quotient (RQ) similarly in lean and obese Zucker rats, indicating mobilization of fat as an energy source for leptin-treated rats. After withdrawal of daily leptin treatment, lean and obese Zucker rats exhibited different recovery responses. It is concluded that obese Zucker rats can respond to exogenous leptin when leptin is delivered into the brain ventricles.  相似文献   
108.
A novel soft actuator is designed, fabricated, and optimized for applied use in soft robotics and biomedical applications. The soft actuator is powered by the expansion and contraction of a graphene-containing and encased liquid marble using the photothermal effect. Unfortunately, conventional liquid marbles are found to be too fragile and prone to cracking and failure for such applications. After experimentation, it is possible to remedy this problem by synthesizing liquid marbles encased with polymeric shells–polymerized in situ–for added mechanical strength and robustness. These marbles are shown to have intrinsic photothermal activity. They are then situated in bimorph-type soft actuators where one side of the actuator has a dramatically different Young's modulus than the other, leading to directional actuation which is successfully demonstrated in multistep walking soft robots. The soft actuators are shown to successfully activate the mechanosensitive Piezo protein in a transfected human cell line with high effectiveness and no toxicity. Overall, the liquid marble-powered soft actuators described here represent a new soft actuation methodology and a novel tool for mechanobiological studies, such as stem cell fate and organoid differentiation.  相似文献   
109.
Peripheral letter recognition was examined by presenting subjects with a letter triad centered 7.16 degrees to the right of fixation. At the same time, a single letter was presented at the point of fixation that was either the same as one of the letters in the triad or different from any of the triad letters. On other trials, no letter was presented at the point of fixation. Results supported and extended previous foveal load research. The disruptive effect of foveal load does not depend solely on the presence or absence of a foveal stimulus. Recognition of the first letter in non-words was disrupted when a foveal letter was presented that was different from the peripheral letter. Recognition of the middle letter for both words and non-words was disrupted when a foveal letter was presented that was the same as the middle letter. A significant interaction between foveal letter and triad type was also found. No evidence was found to suggest that recognition of a peripheral letter is significantly better when that same letter is also present at the point of fixation.  相似文献   
110.
RATIONALE AND OBJECTIVES: We compared adverse reactions and image quality for hysterosalpingography (HSG) performed with ionic (diatrizoate meglumine combined with iodipamide meglumine [DM + IM]) and nonionic (iohexol) contrast media. METHODS: We performed a study of 95 patients who had HSG and were randomly selected to receive DM + IM or iohexol. Patients reported episodes of abdominal pain and other adverse reactions immediately and 24 hr after the procedure and categorized severity of symptoms on a subjective scale. Two radiologists evaluated image quality for diagnosis. RESULTS: Prevalence of abdominal pain and other reactions both immediately and 24 hr after HSG was lower in patients who received iohexol than in patients who received DM + IM. Moderate or severe abdominal pain was significantly lower in the iohexol group than in the DM + IM group (p < .05). Visualization of the uterine cavity and ampullary rugae was judged excellent with both contrast media (87% with iohexol and 92% with DM + IM). CONCLUSION: Iohexol and DM + IM are excellent contrast media for use during HSG; iohexol 300 may cause fewer episodes of more severe and prolonged abdominal pain.  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