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   2373篇
  免费   0篇
化学工业   7篇
建筑科学   1篇
能源动力   1篇
轻工业   1篇
水利工程   1篇
一般工业技术   2篇
冶金工业   2353篇
自动化技术   7篇
  2022年   1篇
  2014年   1篇
  2012年   3篇
  2010年   1篇
  2004年   3篇
  2003年   4篇
  1999年   81篇
  1998年   803篇
  1997年   475篇
  1996年   248篇
  1995年   156篇
  1994年   124篇
  1993年   138篇
  1992年   13篇
  1991年   15篇
  1990年   22篇
  1989年   26篇
  1988年   22篇
  1987年   23篇
  1986年   12篇
  1985年   10篇
  1983年   3篇
  1982年   4篇
  1981年   15篇
  1980年   10篇
  1978年   2篇
  1977年   44篇
  1976年   106篇
  1975年   4篇
  1973年   1篇
  1955年   3篇
排序方式: 共有2373条查询结果,搜索用时 15 毫秒
991.
Two experiments were conducted to determine the effect of dietary linoleic to linolenic acid (LO:LN) ratio and dl-alpha-tocopheryl acetate (TA) supplementation on selected characteristics of the liver and cerebellum and on vitamin E status of turkey poults from hatch through 22 d of age. In Experiment 1, 1-d-old poults were fed diets containing no supplemental TA (0E) or 150 IU TA/kg diet (150E). Poults fed the 150E diet had greater (P < 0.001) concentrations of alpha-tocopherol (TOC) in the liver and plasma than those fed the 0E diet from 7 to 22 d of age. The 150E diet, however, did not completely overcome the decrease in liver and plasma TOC concentrations observed at these ages. The 150E diet had no effect on poult BW, feed efficiency, or on the weight, protein, lipid, or fatty acid concentrations of the liver. Thiobarbituric acid reactive substances assay of liver and hemolysis assay of red blood cells (RBC) showed that the 150E diet decreased the susceptibility of liver and RBC to in vitro peroxidation at 13 and 22 d of age. In Experiment 2, 1-d-old poults were fed the 0E and 150E diets in a complete factorial arrangement with decreasing ratios of LO:LN (10, 5, and 1). Dietary LO:LN ratio had no effect on RBC hemolysis or cerebellum TOC concentration. As the ratio of LO:LN decreased, the arachidonic acid content of liver and cerebellum lipids decreased. Ratios of n-6 to n-3 fatty acids in liver and cerebellum were directly related to dietary LO:LN at 13 and 22 d of age.  相似文献   
992.
Sentinel node biopsy may be useful in the staging of breast cancer. In experienced hands presence or absence of metastasis in the sentinel node accurately predicts the nodal status and in patients with a negative sentinel node biopsy axillary dissection may be avoided. The technique, however, shows a clear learning curve and hasty introduction may lead to an unacceptable rate of false negative biopsies. Moreover, the introduction of the technique in general practice should be well coordinated in order to prevent large differences between hospitals in the staging and treatment of breast cancer patients. On the initiative of NABON (Nationaal Borstkanker Overleg Nederland; 'national breast cancer consultation') and the Nederlandse Vereniging voor Chirurgische Oncologie (Netherlands Association for Surgical Oncology) a study group was formed to co-ordinate the introduction of the sentinel node biopsy in breast cancer patients in the Netherlands. Important topics are central registration of all procedures in order to evaluate its applicability and technical variations, the performance in each centre of at least 50 procedures together with axillary node dissection to evaluate the results before clinical application is considered, and nationwide co-ordination to find the best therapy for patients with positive sentinel nodes.  相似文献   
993.
Reactivation of herpes simplex virus type 1 (HSV-1) in the trigeminal ganglion (TG) was induced by UV irradiation of the corneas of latently infected mice. Immunocytochemistry was used to monitor the dynamics of cytokine (interleukin-2 [IL-2], IL-4, IL-6, IL-10, gamma interferon [IFN-gamma], and tumor necrosis factor alpha [TNF-alpha]) and viral antigen production in the TG and the adjacent central nervous system on days 1 to 4, 6, 7, and 10 after irradiation. UV irradiation induced increased expression of IL-6 and TNF-alpha from satellite cells in uninfected TG. In latently infected TG, prior to reactivation, all satellite cells were TNF-alpha+ and most were also IL-6(+). Reactivation, evidenced by HSV-1 antigens and/or infiltrating immune cells, occurred in 28 of 45 (62%) TG samples. Viral antigens were present in the TG in neurons, often disintegrating on days 2 to 6 after irradiation. Infected neurons were usually surrounded by satellite cells and the foci of immune cells producing TNF-alpha and/or IL-6. IL-4(+) cells were detected as early as day 3 and were more numerous by day 10 (a very few IL-2(+) and/or IFN-gamma+ cells were seen at this time). No IL-10 was detected at any time. Our observations indicate that UV irradiation of the cornea may modulate cytokine production by satellite cells. We confirm that neurons are the site of reactivation and that they probably do not survive this event. The predominance of TNF-alpha and IL-6 following reactivation parallels primary infection in the TG and suggests a role in viral clearance. The presence of Th2-type cytokines (IL-4 and IL-6) indicates a role for antibody. Thus, several clearance mechanisms may be at work.  相似文献   
994.
Five compounds, which inhibited the amidolytic activity of soluble tissue factor/activated factor VII complex (sTF/VIIa), were isolated from two traditional Chinese medicinal plants commonly used in the treatment of cardiovascular and cerebrovascular diseases. The active compounds were found to be linolenic, linoleic, and oleic acids from roots of Salvia miltiorrhiza; and two anacardic acids, 6-(8'Z-pentadecenyl)- and 6-(10'Z-heptadecenyl)-salicylic acids, from leaves of Ginkgo biloba. The IC50 values were in the range 30-80 micromol/L. Palmitic acid, isolated from roots of Salvia miltiorrhiza, and 2-[(3',7',11',15'-tetramethyl)-2'E,6'E,10'E, 14'E-hexadecatetraenyl]-1,4-hydroquinone, isolated from the marine sponge Adocia viola, did not inhibit sTF/VIIa. Further expansion of the structure-activity relationship to include anacardic acids, 6-(8'Z,11'Z-heptadecadienyl)- and 6-(8'Z, 11'Z, 14'Z-heptadecatrienyl)-salicylic acids from leaves of Anacardium spondias, and other fatty acids demonstrated that at least one cis double bond was essential for inhibitory activity, and that fatty acids containing two or three cis double bonds were optimal. Evidence from preincubation studies implied that these fatty acids may exert their effect by binding to VIIa and consequently preventing binding of sTF to VIIa.  相似文献   
995.
5,5'-Bis(4-aminophenyl)-2,2'-bifuryl (PFDA) with a well-defined conjugation length was synthesized, and its soluble poly(amic acid) was prepared by polycondensation with pyromellitic dianhydride (PMDA). The PMDA-PFDA polyimide films were obtained from the poly(amic acid) solution through a conventional spin-casting, baking, and thermal imidization process. The PFDA monomer exhibits intense blue photoluminescence with a maximum at 442 nm in a high quantum yield of 0.92, whereas its polyimide film also emits intense blue photoluminescence with double peak maxima at 419 and 436 nm. The polyimide is insoluble in common organic solvents and thermally stable up to 370 degreesC. Overall, the PMDA-PFDA polyimide can be considered to be a potential candidate material for fabricating optoelectronic devices that emit blue light.  相似文献   
996.
Neonatal intensive care has led to a progressive improvement in the survival of very low birth weight (VLBW, < 1,500 g) infants. However, it has not been established whether there has been a simultaneous increase or decrease in the prevalence of handicapping conditions in this group of children. To explore this question, a meta-analysis was performed using outcome data of 32 developmental studies of VLBW infants born in industrialized countries between 1947 and 1987. The authors' results show that the proportion of VLBW infants who survived and had an intact outcome progressively increased between 1947 and 1987--from 147 per 1,000 live births in the period 1947-1965 to 498 per 1,000 in the period 1980-1987 (p < 0.01). The prevalence of major handicapping conditions for the subset of VLBW infants who weighed < 1,000 g at birth increased, resulting from the increasing survival rates. However, the prevalence of major handicapping conditions among all children with VLBW decreased from 147 per 1,000 live births in 1947-1965 to 45 per 1,000 in 1980-1987 (p = 0.02). The authors' meta-analysis suggests that improved survival of VLBW infants has not been accompanied by an increase, but more likely a decrease, in the prevalence of handicapping conditions in this birth weight group.  相似文献   
997.
998.
999.
Vision is not required in order for fish to school. Five individual saithe, Pollachius virens, were able to join schools of 25 normal saithe swimming in an annular tank, while blinded with opaque eye covers. Test fish maintained position within the school indefinitely and responded to short-term movements of individuals within the school, although quantitative differences in reaction time and schooling behavior were noted. Five fish with lateral lines cut at the opercula were unable to school when wearing opaque eye covers. Although it is unlikely that blind saithe could school in the wild, the constraints of the apparatus permitted a demonstration of a role of the lateral line organ in schooling.  相似文献   
1000.
To define the role of gastrin, if any, in the response of the lower esophageal sphincter (LES) to bethanechol, serum gastrin determinations and LES pressure measurements were made in controls, patients with vagotomy and antrectomy (V&A), and patients with vagotomy and pyloroplasty (V&P). Despite significant differences in mean basal serum gastrin levels no differences were found in mean resting LES pressures among these groups. In controls significant increases in LES pressure occurred after subcutaneous bethanechol, but serum gastrin levels did not change from basal values. Subcutaneous injections of bethanechol produced significantly greater increases in LES pressures in V&P patients than in V&A patients. Serum gastrin levels did not change in either group; however, background serum gastrin concentrations were significantly greater for V&P patients than V&A patients throughout the study. Intravenous infusion of human gastrin I heptadecapeptide in controls significantly increased sphincter responses to bethanechol. Thus, these studies provide evidence to suggest that the LES response to bethanechol is affected by background serum gastrin 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