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   3644篇
  免费   4篇
电工技术   2篇
化学工业   49篇
金属工艺   12篇
机械仪表   21篇
建筑科学   20篇
能源动力   8篇
轻工业   39篇
水利工程   2篇
石油天然气   4篇
无线电   27篇
一般工业技术   50篇
冶金工业   3312篇
原子能技术   1篇
自动化技术   101篇
  2021年   5篇
  2019年   2篇
  2018年   4篇
  2017年   6篇
  2016年   5篇
  2015年   8篇
  2014年   6篇
  2013年   17篇
  2012年   5篇
  2011年   10篇
  2010年   9篇
  2009年   9篇
  2008年   13篇
  2007年   12篇
  2006年   9篇
  2005年   8篇
  2004年   8篇
  2003年   15篇
  2002年   3篇
  2001年   4篇
  2000年   7篇
  1999年   117篇
  1998年   1100篇
  1997年   622篇
  1996年   427篇
  1995年   211篇
  1994年   166篇
  1993年   212篇
  1992年   18篇
  1991年   47篇
  1990年   53篇
  1989年   44篇
  1988年   35篇
  1987年   40篇
  1986年   24篇
  1985年   23篇
  1984年   12篇
  1983年   6篇
  1982年   14篇
  1981年   13篇
  1980年   35篇
  1979年   6篇
  1978年   12篇
  1977年   72篇
  1976年   137篇
  1975年   11篇
  1974年   5篇
  1973年   7篇
  1972年   2篇
  1968年   2篇
排序方式: 共有3648条查询结果,搜索用时 23 毫秒
31.
In the anatomy of 416 hearts, the seat of tricuspid stenosis or atresia is examined, with special reference to Fontan-like surgical procedures. A classification is offered which includes cases with and without regular or inverted transposition, and with decreased or increased pulmonary flow. The size and thickness of the right atrium, the size and architecture of the right ventricle, the size of the pulmonary tree, the types of atrial and ventricular septal defects, the condition of the mitral valve, and the size and thickness of the left atrium and left ventricle are analyzed. In addition the various intracardiac and extracardiac abnormalities are enumerated. Reference is also made to the tendency of the aorta and pulmonary trunk to override the septum, in some cases producing double-outlet left ventricle. It is considered that many cases of tricuspid valve atresia and stenosis with or without transposition may be amenable to Fontan-like procedures in the proper age group. All the above anatomic considerations have a bearing on the suitability and type of operative tricuspid bypass procedures, and they may influence the prognosis of surgical therapy.  相似文献   
32.
In many cases of drug-induced allergic hepatitis, peripheral lymphocytes were transformed by the stimulation with a given drug in the presence of autologous serum. However, when rat liver microsome fraction of soluble liver specific antigen fraction was added to the culture instead of autologous serum, the drug-induced lymphocyte transformation was more efficiently seen than autologus serum, while rat liver mitochondria fraction was less effective. On the other hand, in the cases of allergic drug eruption which did not show any liver injury, the addition of liver subcellular fractions were much less effective to induce the lymphocyte transformation than autologous serum. These results may suggest that liver subcellular component is involved in pathogenesis of drug-induced allergic hepatitis.  相似文献   
33.
Ribosomes from higher-plant mitochondria contain 5S rRNA, in contrast with the mitochondrial ribosomes of animals and fungi, in which such a component has not been detected. In common with the ribosomes of prokaryotes and chloroplasts, higher-plant mitochondrial ribosomes do not appear to contain an RNA equivalent to the 5.8 S rRNA that is found in eukaryoytes hydrogen-bonded to the largest of the cytoplasmic rRNA species.  相似文献   
34.
Five quaternary ammonium germicides (QAGs) were tested for their adsorption by agar. This was found to be in the following ascending order: alkylbenzylmethyl-ammonium chloride, alkyltrimethylammonium bromide, cetyltrimethylammonium bromide, cetylpyrimidinium chloride and cetylbenzyldimethylammonium chloride. An inverse relationship was established between the extent of agar binding of the QAGs and their inhibition zones. In an attempt to develop a sensitive cup-plate assaying technique suitable for QAGs, important factors affecting the agar-diffusion of QAGs were investigated. These included the influence of various polysorbates, buffer ions, agars and test organisms. Furthermore, the effect of the pH and/or the concentration of the selected polysorbate and the buffer were studied. The best medium developed for the sensitive agar-diffusion assay of QAGs was nutrient agar-Tris (0.05 M, pH 8) provided that distilled water and polysorbate 20 (0.5%) were used as diluents for the mixed alkyl and the pure cetyl QAGs, respectively.  相似文献   
35.
Experimental colitis   总被引:1,自引:0,他引:1  
Ulcerative colitis and Crohn's disease are complex, problematic diseases of unknown etiology in man, and appropriate experimental models would be useful in elucidating their pathogenesis and treatment. Although there have been numerous attempts to produce inflammatory ulcerative colonic disease in laboratory animals resembling those human disease forms, none has been entirely successful. Investigators have conducted experiments involving almost every etiological factor suggested for initiation of these diseases. The methods reviewed in this paper include production of experimental colitis by vascular impairment, and immunological methods such as bacterial infection, allergic reactions, direct and indirect hypersensitivity reactions, as well as autoimmune mechanisms. The results of carrageenan-induced colitis, irradiation, dietary, and drug-induced techniques are also discussed and the frequency and nature of spontaneous colonic lesions in animals is summarized.  相似文献   
36.
An acromegalic patient with galactorrhea-amenorrhea who conceived following long-term 2-bromo-alpha-ergocryptine (CB-154) therapy is described. During CB-154 therapy, determinations of serum prolactin (PRL), luteinizing hormone (LH)-human chorionic gonadotropin, follicle-stimulating hormone a reduction in PRL level followed by an LH peak, a rise in basal body temperature and menstruation. The patient became pregnant during the next cycle, but therapeutic abortion was performed because of the active acromegaly. These results demonstrate that CB-154 can restore ovulatory function not only to the patient with a hypothalamic disorder but also to the acromegalic patient with an enlarged sella turcica.  相似文献   
37.
38.
The distribution of 10 nutrient elements was assessed in three fractions of herbage samples of perennial ryegrass, tall fescue, white clover and lucerne. The cell wall fraction, prepared by mechanical disintegration of undried material, contained the following proportions of the total herbage content of the major elements: N, 2.9–16.4%; P, 3.0–6.9%; S, 3.6–17.2%; Ca, 11.3–51.8%; Mg. 6.4–27.6% and K, 0.1–1.7%. Substantial though more variable proportions of the trace element cations, Fe, Mn, Zn and Cu were also present in the cell wall fraction. The extent to which the elements were soluble in water was assessed by analysis of the water-insoluble fraction prepared from freeze-dried samples of each herbage. The proportions of the total herbage content of the major elements soluble in water were: N, 30–57%; P, 80–92%; S, 35–71%; Ca, 48–69%; Mg. 65–83% and K, 90–96%. With the trace element cations the proportions soluble in water were more variable, though they were generally less than 70% of the total. The extent to which the various elements were soluble in 80% aqueous ethanol was assessed by analysis of the insoluble fraction prepared from freeze-dried materials. With each of the major elements, smaller proportions of the total herbage content were soluble in 80% ethanol than in water, which may reflect in part the lower solubility of proteins and pectin. With the trace element cations, the differences in solubility between 80% ethanol and water were generally small and inconsistent.  相似文献   
39.
40.
Density sorted, matched-samples of Western hemlock were dried in order to quantify the physical changes of conventionally kiln dried wood when exposed to the equilibrium moisture contents of a typical Japanese winter. Physical changes were monitored for 14 weeks by sampling board weight, dimensions, shell and core moisture contents (oven-dry basis) and warp. The difference of 7% in equilibrium moisture content between Tokyo and Vancouver is large enough to elicit a response in shell moisture content, dimensions and warp. However, the responses found should be expected when wood is examined in context of its natural variability. Drying 105 mm by 105 mm Western hemlock to 19% moisture content at the core should be considered the maximum target moisture content. A target moisture content of 15% at the core would balance drying time and end-use stability as the lumber is equalized to Japanese conditions.  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