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   205737篇
  免费   2405篇
  国内免费   561篇
电工技术   3507篇
综合类   140篇
化学工业   31691篇
金属工艺   10263篇
机械仪表   7010篇
建筑科学   3994篇
矿业工程   2160篇
能源动力   4630篇
轻工业   12870篇
水利工程   2915篇
石油天然气   7726篇
武器工业   22篇
无线电   21488篇
一般工业技术   45169篇
冶金工业   34379篇
原子能技术   6620篇
自动化技术   14119篇
  2021年   2044篇
  2019年   1997篇
  2018年   3678篇
  2017年   3715篇
  2016年   3996篇
  2015年   2232篇
  2014年   3781篇
  2013年   8737篇
  2012年   5675篇
  2011年   7214篇
  2010年   5854篇
  2009年   6486篇
  2008年   6610篇
  2007年   6492篇
  2006年   5569篇
  2005年   5116篇
  2004年   4629篇
  2003年   4553篇
  2002年   4366篇
  2001年   4472篇
  2000年   4184篇
  1999年   4198篇
  1998年   10183篇
  1997年   7181篇
  1996年   5500篇
  1995年   4131篇
  1994年   3597篇
  1993年   3838篇
  1992年   2982篇
  1991年   2995篇
  1990年   2890篇
  1989年   2852篇
  1988年   2865篇
  1987年   2508篇
  1986年   2568篇
  1985年   2854篇
  1984年   2687篇
  1983年   2554篇
  1982年   2300篇
  1981年   2269篇
  1980年   2345篇
  1979年   2359篇
  1978年   2382篇
  1977年   2487篇
  1976年   2876篇
  1975年   2188篇
  1974年   2068篇
  1973年   2166篇
  1972年   1940篇
  1971年   1755篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
1. Procaine (0.03-10 mM) inhibited carbachol (CCh)-induced amylase release from rat isolated pancreatic acini in a competitive manner. Kinetic analysis of the relation between CCh concentrations and the amount of amylase released in the presence of various procaine concentrations indicated that procaine caused competitive inhibition with the affinity constant (pA2) value of 5.00 +/- 0.08. 2. Receptor binding assay confirmed that procaine (0.01-10 mM) competitively inhibited [N-methyl-3H]-scopolamine chloride ([3H]-NMS) binding to its receptor with binding affinity (pKi) of 4.63 +/- 0.10. 3. Procaine transformed CCh-evoked [Ca2+]i dynamics: the initial rise in [Ca2+]i followed by a gradual decay during continuous stimulation with 3 microM CCh was transformed by 0.3 mM procaine to the oscillatory [Ca2+]i dynamics, which resembled the response to 0.3 microM CCh in the absence of procaine. The initial phase of [Ca2+]i oscillation corresponded to the initial phase of CCh-induced amylase release in isolated perfused acini. 4. Procaine (0.3-3 mM) did not inhibit the secretory response to cholecystokinin octapeptide (CCK-8) in isolated incubated acini. A higher concentration of procaine (10 mM) caused weak but significant inhibition of the response to only limited concentrations of CCK-8, 30 and 100 pM. Procaine lower than 10 mM was ineffective on [125I]-BH-CCK-8 binding, although procaine (10 mM) caused weak but significant inhibition of the binding.  相似文献   
892.
The superconducting properties and the phase and chemical composition of Bi x Pb0.3Sb0.1Sr y Ca2Cu3Oz (x=1.5, 1.6, and 1.7;y=1.9, 2.0, and 2.1) materials synthesized by one-step and multistep thermal treatments have been investigated. The multistep annealing between 825–875°C promotes the 2223 phase. The change of Bi concentration has little effect on the 2223 phase formation, regardless of the kind of thermal treatment used, but increasing the Sr concentration (y> 2) strongly inhibits this phase. It has also been established that the loss of Pb after synthesis depends on the initial Bi concentration. The loss of Pb decreases when the initial Bi content is lower.  相似文献   
893.
An improved, combined staining method for myofibrillar ATPase (m-ATPase) and for acetylcholinesterase activity is described. This method allows the observations, on the same slide, of the classical histochemical m-ATPase profile following the Brooke and Kaiser technique and the neuromuscular junction morphology. Thus the pattern of innervation, nerve ending structure and number of nerve endings along the fibres is shown simultaneously for the basic differentiation between slow and fast fibres. The use of acidic and alkaline preincubation allows better visualization of endplate morphology and avoids the masking effect of a positive m-ATPase reaction. The technique has been validated on skeletal muscles from avian and mammalian species.  相似文献   
894.
The mechanical response of intervertebral joints is deeply influenced by disc degeneration. The phenomenon is expressed in terms of variations in the biomechanical properties of the material, whose compressibility characteristics change because of the liquid content loss in the tissue and, what is even more important, to prolapse. In this work, the problem is investigated by means of a computational mechanics approach; a coupled material and geometric non-linear model is developed, representing vertebra, annulus and nucleus submitted to an axial load. A transversely isotropic law is assumed for cortical bone in the vertebral body and an isotropic law for the cancellous portion; a hyperelastic formulation is assumed for the disc, allowing effective interpretation of the mechanical characteristics of degeneration. The results obtained are reported with regard to bony endplate and annulus behaviour; interaction phenomena between bony endplate and nucleus are emphasized.  相似文献   
895.
This paper presents a selection of results of a comprehensive quantitative, research literature-based study of Dutch energy research. The primary goal of this paper is to provide an overview of what bibliometric data from ISI and non-ISI databases may offer to describe the state of affairs in a scientific field. It illustrates the added value of combining bibliometric indicators of publication output, international visibility, international co-operation, and interdisciplinarity in a study of nuclear energy research in the 1980's when its budget decreased dramatically.  相似文献   
896.
In the past 15 years five neonates and children have been treated for high vaginal atresia at the Surgical Unit of Department of Pediatrics, University Medical School, Pécs, Hungary. In three of the six patients distal atresia of the vagina was found (Type III). Two of the three were neonates and had a large hydrometrocolpos and the third, a 13-year-old girl, hematometrocolpos. In the fourth patient the vaginal atresia was associated with cloacal and anorectal malformation (Type V). In the fifth there was a duplication of uterus and vagina; however, only one of the two vaginas was atretic. In three patients a pull-through of the vagina was carried out, in one of them according to Pena, in another a transvesical approach, as suggested by Monfort, was used. Following repeated surgeries in the patient with cloacal malformation the vagina was replaced with large intestine. In the case of duplication of vagina and uterus one half of the duplication was removed.  相似文献   
897.
OBJECTIVE: Although there have been many studies of the outcome of anorexia nervosa, methodological weaknesses limit their interpretation. The authors used a case-control design to try to improve knowledge about the outcome of anorexia nervosa. METHOD: All new female patients referred to an eating disorders service between Jan. 1, 1981, and Dec. 31, 1984, who had probable or definite anorexia nervosa were eligible for inclusion. Of these women, 86.4% (N = 70) were located and agreed to participate. The comparison group (N = 98) was a random community sample. All subjects were interviewed with a structured diagnostic instrument. RESULTS: A minority of the patients (10%) continued to meet the criteria for anorexia nervosa a mean of 12 years after initial referral. Even among those who no longer met these criteria, relatively low body weight and cognitive features characteristic of anorexia nervosa (perfectionism and cognitive restraint) persisted. The rates of lifetime comorbid major depression, alcohol dependence, and a number of anxiety disorders were very high. CONCLUSIONS: In the managed care/brief treatment era, therapeutic approaches with an excessive focus on weight gain that neglect the detection and treatment of associated psychological features and comorbidity may be inappropriate. Anorexia nervosa is a serious psychiatric disorder with substantial morbidity.  相似文献   
898.
899.
900.
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