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   1664篇
  免费   8篇
电工技术   6篇
综合类   1篇
化学工业   23篇
机械仪表   4篇
建筑科学   3篇
矿业工程   4篇
轻工业   20篇
水利工程   1篇
无线电   25篇
一般工业技术   52篇
冶金工业   1519篇
原子能技术   2篇
自动化技术   12篇
  2022年   2篇
  2021年   1篇
  2017年   2篇
  2015年   2篇
  2013年   24篇
  2012年   7篇
  2011年   3篇
  2010年   4篇
  2009年   3篇
  2008年   7篇
  2007年   4篇
  2006年   3篇
  2005年   6篇
  2004年   6篇
  2003年   7篇
  2002年   4篇
  2001年   5篇
  2000年   3篇
  1999年   47篇
  1998年   471篇
  1997年   244篇
  1996年   180篇
  1995年   126篇
  1994年   85篇
  1993年   83篇
  1992年   8篇
  1991年   15篇
  1990年   21篇
  1989年   27篇
  1988年   29篇
  1987年   20篇
  1986年   13篇
  1985年   17篇
  1984年   2篇
  1983年   4篇
  1982年   9篇
  1981年   5篇
  1980年   14篇
  1979年   2篇
  1978年   6篇
  1977年   45篇
  1976年   87篇
  1975年   5篇
  1973年   2篇
  1972年   1篇
  1970年   1篇
  1955年   2篇
  1944年   1篇
  1890年   4篇
  1882年   2篇
排序方式: 共有1672条查询结果,搜索用时 15 毫秒
51.
At most maternity units all premature infants are investigated by cranial ultrasonography as a routine. We examined the correlation between autopsy findings and ultrasound examination in 30 premature newborn. The ultrasound examination demonstrated bleeding in 17 (65%) of the 26 cases where autopsy had revealed bleeding. In these 17 patients good correlation was found between the degree of bleeding in the two examinations (ultrasonography and autopsy). In ten patients autopsy showed periventricular leucomalacia, but ultrasonography showed this condition in only two of these. In five cases bleeding made the examination and interpretation of the ultrasound findings difficult. In three patients ultrasonography was thought to be normal, while autopsy demonstrated periventricular leucomalacia.  相似文献   
52.
53.
The sex pheromone emitted by the female oleander scale, Aspidiotus nerii (Homoptera, Diaspididae), has been isolated and characterized as (1R, 2S)-cis-2-isopropenyl-1-(4'-methyl-4'-penten-1'-yl)cyclobutaneethanol acetate by using advanced MS and NMR spectroscopic methods, as well as a variety of microderivatization sequences. The structure has been confirmed by stereo- and enantioselective synthesis of the four possible stereoisomers. The absolute configuration has been determined by comparison of the activity of the cis (1S,2R) and (1R, 2S) enantiomers with that exhibited by the natural material in greenhouse bioassays and field tests. The structure of this sesquiterpenoid pheromone is new in the coccids and in the pheromone field in general.  相似文献   
54.
BACKGROUND: Significant changes are restructurng the U.S. health care delivery system. National health reform is now extending itself into the public sector. Increased health and medical costs by federal and state governments are forcing a reevaluation of major entitlement programs, especially Medicaid. METHODS/RESULTS: Because Medicaid is the single largest item in many state budgets, states are now enrolling Medicaid patients into managed and coordinated care arrangements as a means to control costs and increase access to care. HMOs are not only competing for private patients but also actively seeking the Medicaid population. Nationally, almost one-fourth of all Medicaid patients are now enrolled in managed care plans. Various models and approaches have been developed by individual states. CONCLUSIONS: Because managed care enrollment in the Medicaid program has increased substantially in recent years, selected services including vision care are no longer rendered by any practitioner willing to accept Medicaid fees. Freedom of choice is now restricted to pre-selected and panel practitioners participating with the managed care program. The rules, regulations, billing procedures, fees, and program requisites will differ under managed care programs. Private optometric practitioners must consider entering economic and organizational relationships and linkages that make them attractive to managed care organizations.  相似文献   
55.
Germline mutations in the presenilin 1 (PS1) gene apparently account for the majority of early-onset, familial Alzheimer's disease (AD). Using a mutation-screening strategy (denaturing gradient gel electrophoresis; DGGE), we analyzed a large family with early onset AD and seizures. The patients in this family showed a novel missense mutation in exon 5 of the PS1 gene (A to T change in codon 120, altering glutamine to aspartic acid). This novel mutation is located within the second hydrophilic domain of the molecule, a region not particularly involved in previously described germline mutations, and is of unknown biological significance. These results also demonstrate that DGGE can be used effectively to screen for mutations within this gene.  相似文献   
56.
57.
A quantitative and non-occlusive deep vein thrombosis model was developed in rabbits. We used this model to test the antithrombotic activity of the prothrombinase complex inhibitors factor rXai and its chemical analog glutamyl-glycyl-arginyl chloromethyl ketone inactivated human factor Xa (EGR-Xai), along with the thrombin inhibitors D-phenylalanyl-prolyl-arginyl chloromethyl ketone (PPACK) and heparin. Dose dependent effects of the inhibitors during constant infusion were monitored. Measurements included thrombus weights, hemostatic parameters and both cuticle and ear bleeding times. In this model, factor rXai and EGR-Xai had comparable in-vivo efficacy, and showed 80%-93% inhibition at plasma levels of 6.5 nM (rXai) and 8 nM (EGR-Xai). Effects on ex-vivo clotting times varied among the inhibitors. At 80-100% thrombus inhibition, factor rXai and EGR-Xai had no statistically significant effect, while PPACK extended thrombin clotting time (TCT) times 2.3-fold, and heparin prolonged both activated partial thromboplastin time (APTT), prothrombin time (PT) and TCT ex-vivo clotting times 6.9-, 1.2-, and 7-fold respectively. At these dosages, cuticle and ear bleeding times were prolonged for all inhibitors and showed increases of 177%-389% (cuticle) and 45%-129% (ear). Our results demonstrate that direct inhibition of prothrombinase complex assembly is effective in arresting venous thrombosis.  相似文献   
58.
The purpose of the study reported here was to investigate the impact of prophylaxis against gram-positive infections in patients undergoing high-dose chemotherapy and autologous bone marrow transplantation in a randomized trial. Forty-three patients undergoing high-dose chemotherapy with autologous bone marrow transplant were enrolled in a nonblinded randomized trial to receive or not to receive prophylaxis for gram-positive infections with 10(6) U of penicillin intravenously (i.v.) every 6 h (q6h) (if penicillin allergic, 750 mg of vancomycin i.v. q12h) in addition to standard antimicrobial prophylaxis with 400 mg of norfloxacin orally three times a day, 200 mg of fluconazole orally once a day, and 5 mg of acyclovir per kg of body weight i.v. q12h. The patients were being treated for germ cell cancer (n = 15), breast cancer (n = 16), Hodgkin's disease (n = 3), non-Hodgkin's lymphoma (n = 4), acute myeloid leukemia (n = 1), acute lymphoblastic leukemia (n = 1), and ovarian cancer (n = 3). The trial was stopped because of excess morbidity in the form of streptococcal septic shock in the group not receiving gram-positive prophylaxis. There were significantly fewer overall infections (10 versus 3; P = 0.016) and streptococcal infections (9 versus 1; P = 0.0078) in the group receiving gram-positive prophylaxis. There were no significant differences in the numbers of deaths, duration of broad-spectrum antibiotics, or incidence of neutropenic fever between the two groups. Prophylaxis for gram-positive infections with penicillin or vancomycin is effective in reducing the incidence of streptococcal infections in patients undergoing high-dose chemotherapy and autologous bone marrow transplant. However, this approach may carry a risk of fostering resistance among streptococci to penicillin or vancomycin.  相似文献   
59.
Objective * To evaluate the effectiveness of a medical food-supplemented detoxification program versus a hypoallergenic, calorie-controlled diet alone in the management of symptoms in chronically ill patients. Design * Outcome-focused study of patient response to dietary interventions. Setting * Clinical outpatient research facility. Patients * 106 chronically ill patients. Intervention * A medical food supplement designed to provide nutritional support for gastrointestinal healing and hepatic detoxification in addition to an oligoantigenic, calorie-controlled diet, versus an oligoantigenic, calorie-controlled diet alone. Results * The 84 patients in the experimental group, who consumed the medical food supplement, had a 52% reduction in symptoms over 10 weeks as measured by the Metabolic Screening Questionnaire. In comparison, the 22 patients on the control diet had only a 22% reduction of symptoms. Symptom reduction in the intervention group occurred concomitantly with the normalization of hepatic phase I cytochrome P450 activity in relation to phase II glycine conjugation detoxification function measured before and after intervention. The intervention group also had a statistically significant increase in urinary sulfate-to-creatinine ratio after treatment, suggesting improved reserves of sulfur-conjugating nutrients and glutathione status. Enhanced nutrient absorption after intervention was implied by the increased absorption and urinary excretion of mannitol after the 10 weeks of therapy, although the results were only marginally significant. Conclusions * These results suggest that this supplemental medical food program may provide an important adjunctive therapy for the management of many complex symptoms associated with the chroni  相似文献   
60.
Neutrophils have been implicated in the acute formation of gastric mucosal erosions induced by nonsteroidal antiinflammatory drugs. The aims of the present study were to determine, in rats, the role of neutrophils in the pathogenesis of etodolac- and indomethacin-induced gastrointestinal ulceration and blood loss. Both drugs caused gastrointestinal ulceration, which was associated with increased blood loss, a rise in plasma haptoglobin concentration, and a rise in the number of circulating neutrophils. A marked infiltration of neutrophils occurred only in ileal tissue. Pretreatment with a selective antineutrophil serum induced a significant neutropenia, which failed to inhibit either etodolac- or indomethacin-induced gastrointestinal ulceration and blood loss. A further study demonstrated that the antineutrophil serum did not prevent gastric erosions induced by indomethacin, but it inhibited carrageenan paw edema, which is dependent, in part, on neutrophil infiltration and activation. It is concluded that neutrophils do not contribute to gastrointestinal ulceration and blood loss induced by nonsteroidal antiinflammatory drugs. Furthermore, in contrast with previous studies, our results provide no evidence that neutrophils contribute to indomethacin-induced acute gastric erosion formation.  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