首页 | 官方网站   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   1842篇
  免费   0篇
工业技术   1842篇
  2022年   3篇
  2014年   1篇
  2013年   2篇
  2012年   3篇
  2011年   3篇
  2010年   1篇
  2009年   2篇
  2007年   2篇
  2006年   3篇
  2005年   2篇
  2004年   2篇
  2003年   2篇
  2002年   1篇
  2000年   1篇
  1999年   55篇
  1998年   539篇
  1997年   318篇
  1996年   218篇
  1995年   109篇
  1994年   103篇
  1993年   107篇
  1992年   12篇
  1991年   27篇
  1990年   20篇
  1989年   28篇
  1988年   25篇
  1987年   23篇
  1986年   18篇
  1985年   26篇
  1983年   3篇
  1982年   7篇
  1981年   10篇
  1980年   10篇
  1979年   3篇
  1978年   5篇
  1977年   33篇
  1976年   93篇
  1975年   3篇
  1973年   3篇
  1972年   1篇
  1969年   1篇
  1968年   1篇
  1967年   1篇
  1963年   1篇
  1961年   1篇
  1960年   1篇
  1959年   1篇
  1956年   1篇
  1955年   4篇
  1951年   1篇
排序方式: 共有1842条查询结果,搜索用时 0 毫秒
71.
72.
The purpose of this work was to study intraobserver and interobserver variation in the interpretation of colposcopic images of cervical intraepithelial neoplasia (CIN). Twenty-three experienced colposcopists were asked to assess colposcopic images presented on slides and to select the biopsy site. Eleven cases were independently interpreted twice with an interval of 2-3 months by all observers. No information about the cytological classification was available. In each case the "majority assessment" was considered as the standard, being "no CIN" in 2 cases, CIN I in 4 cases, CIN II in 3 cases, and CIN III in 2 cases. Intraobserver concordance was 66.7%, the kappa value was 0.54. Interobserver agreement was found to be 52.4 and 51.0% in the first and second sessions, respectively, while the mean kappa values were 0.41 and 0.33, respectively. In selecting the site for biopsy, 77.4% of all observers agreed while the same site was selected in 85.3% of cases by the individual colposcopist in the two sessions. Overall, CIN I and II interpretations revealed lower levels of agreement than no CIN or CIN III interpretations. It is concluded that observer variability in interpreting colposcopic images and selecting the site for biopsy is in the same range as observer variation in other subjective diagnostic tests such as cytology and histopathology. This variation should be taken into account in the colposcopical management of patients with abnormal cytology.  相似文献   
73.
OBJECTIVES: The purpose of this study was to determine the safety and efficacy of three dosing regimens of intracoronary urokinase for facilitated angioplasty of chronic total native coronary artery occlusions. BACKGROUND: Percutaneous transluminal coronary angioplasty of chronically occluded (>3 months) native coronary arteries is associated with low initial success secondary to an inability to pass the guide wire beyond the occlusion. METHODS: Patients were enrolled if a chronic total occlusion >3 months old could not be crossed with standard angioplasty equipment. Of the 101 patients enrolled, 41 had successful guide wire passage and were excluded from urokinase treatment. The remaining 60 patients were randomized to receive one of three intracoronary dosing regimens of urokinase over 8 h (group A = 0.8 million U; group B = 1.6 million U; group C = 3.2 million U), and angioplasty was again attempted after completion of the urokinase infusion in 58 patients. RESULTS: Coronary angioplasty was successful in 32 patients (53%) (group A 52%, group B 50%, group C 59%, p = 0.86). This study had a 90% power to detect at least a 50% difference between dosing groups at alpha 0.05. Bleeding complications requiring blood transfusion did not differ significantly among the dosing groups (A 0%, B 15%, C 6%, p = 0.14), although major bleeding episodes were less common in group A (p < 0.05). There were no major procedural or in-hospital complications. Angiographic follow-up in 69% of the patients with successful angioplasty revealed target vessel patency in 91% but an angiographic restenosis rate of 59%. CONCLUSIONS: A prolonged supraselective intracoronary infusion of urokinase can be safely administered and may facilitate angioplasty of chronic total occlusions. Lower doses of urokinase are equally effective and result in fewer bleeding complications than do higher dosage regimens. Vessel patency is frequently maintained, but restenosis remains a problem.  相似文献   
74.
A series of variants of the neuroactive 17-residue gamma-carboxyglutamate-(Gla)-containing polypeptide, conantokin-G (con-G), were synthesized with the intention of determining those features that were important for its N-methyl-D-aspartate (NMDA) receptor-targeted antagonist activity and for adoption of its divalent cation-dependent alpha-helical conformation. Employing the binding of [3H]dizolcipine (MK-801) as an assay for open receptor ion channels in rat brain membranes, which displays inhibition by con-G (IC50 = 0.48 microM), it was found that replacement by an Ala residue of Gla4 led to complete inactivation of the peptide, whereas a similar replacement of Gla3 resulted in a 20-fold decreased potency. Ala substitutions for Gla10 and Gla14 did not substantially affect [3H]MK-801 binding. This same substitution at Gla7 appeared to slightly enhance binding. Ala replacements of non-Gla residues demonstrated that four of them, viz. Glu2, Leu5, Gln9, and Ile12, possessed at least 200-fold decreases in inhibitory potency, whereas similar replacements at Gly1, Leu11, and Arg13 resulted in peptides with 8- to 12-fold increases in the IC50 values. The remaining amino acid residues tested in the single Ala replacement series showed no significant changes in the inhibitory characteristics of wild-type con-G. Additional studies with carboxyl-terminal truncated peptides revealed that the carboxyl-terminal 4 amino acids were unimportant for this activity. There was no strict correlation of inhibition of [3H]MK-801 binding with the ability of these peptides to form cation-dependent alpha-helices. Peptides with notably low alpha-helical content in the presence of these cations were lacking at least one, or both, of Gla10 and Gla14. Con-G[Gla3,4,7,10,14E] and con-G[Gla7,10,14E] were the only peptides that remained in a completely random conformation upon metal ion addition.  相似文献   
75.
In 1982, the World Health Organization (WHO) identified inadequate relief from cancer pain as an international health problem. WHO recommended that governments develop and implement national policies and programs for cancer pain relief. This report evaluates national health policy and the systems of health care delivery in relation to cancer pain management in the new South Africa. This field study included multiple methods of data collection: analysis of documents, field trips with participant observation in sites of care delivery, focused interviews, and in-depth interviews of key informants. The purposive sample of key informants (n = 33) represented multiple stakeholders in a variety of settings. Strengths of the developing health policy include specific recommendations related to palliative care; the shift to universal primary care; policies to support drug availability; the inclusion of morphine and codeine as essential drug at the primary health care level; and the development of a national standard related to cancer pain management. Health services are characterized by two parallel systems of care (private and public) with numerous vestiges of the inequities of apartheid. The management of pain varies by provider and setting; major problems with access exist in the rural areas. Health services in South Africa have been plagued by inequity and inadequate resources. New health policies have set a path to ensure universal access to health care including palliative care for cancer. Their successful implementation is the next necessary step toward improving health services and alleviating the suffering of increasing numbers of individuals with cancer.  相似文献   
76.
This article reviews issues concerning the training and credentialing of vascular surgeons in the use of endovascular techniques in the peripheral vascular system. These guidelines update a prior document that was published in 1993. They have been rewritten to accommodate the rapid evolution that has occurred in the field and to provide the appropriate requirements that a vascular surgeon should fulfill to be competent in the basic skills needed to safely and effectively perform all presently accepted diagnostic and therapeutic endovascular procedures.  相似文献   
77.
78.
79.
80.
PURPOSE: Arteriography is the diagnostic test of choice before lower extremity revascularization, because it is a means of pinpointing stenotic or occluded arteries and defining optimal sites for the origin and termination of bypass grafts. We evaluated whether a duplex ultrasound scan, used as an alternative to arteriography, could be used as a means of accurately predicting the proximal and distal anastomotic sites in patients requiring peripheral bypass grafts and, therefore, replace standard preoperative arteriography. METHODS: Forty-one patients who required infrainguinal bypass grafts underwent preoperative duplex arterial mapping (DAM). Based on these studies, an observer blinded to the operation performed predicted what operation the patient required and the best site for the proximal and distal anastomoses. These predictions were compared with the actual anastomotic sites chosen by the surgeon. RESULTS: Whether a femoropopliteal or an infrapopliteal bypass graft was required was predicted correctly by means of DAM in 37 patients (90%). In addition, both anastomotic sites in 18 of 20 patients (90%) who had femoropopliteal bypass grafts and 5 of 21 patients (24%) who had infrapopliteal procedures were correctly predicted by means of DAM. CONCLUSION: DAM is a reliable means of predicting whether patients will require femoropopliteal or infrapopliteal bypass grafts, and, when a patient requires a femoropopliteal bypass graft, the actual location of both anastomoses can also be accurately predicted. Therefore, DAM appears able to replace conventional preoperative arteriography in most patients found to require femoropopliteal reconstruction. Patients who are predicted by means of DAM to require crural or pedal bypass grafts should still undergo preoperative contrast studies to confirm these results and to more precisely locate the anastomotic sites.  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-23

京公网安备 11010802026262号