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   3238篇
  免费   4篇
  国内免费   1篇
电工技术   2篇
化学工业   25篇
金属工艺   4篇
建筑科学   2篇
矿业工程   2篇
能源动力   4篇
轻工业   7篇
无线电   3篇
一般工业技术   11篇
冶金工业   3170篇
原子能技术   1篇
自动化技术   12篇
  2020年   4篇
  2018年   1篇
  2017年   3篇
  2015年   3篇
  2014年   1篇
  2013年   5篇
  2012年   2篇
  2011年   3篇
  2010年   2篇
  2008年   3篇
  2007年   1篇
  2006年   4篇
  2005年   4篇
  2004年   5篇
  2003年   4篇
  1999年   70篇
  1998年   924篇
  1997年   539篇
  1996年   391篇
  1995年   235篇
  1994年   162篇
  1993年   183篇
  1992年   20篇
  1991年   33篇
  1990年   28篇
  1989年   30篇
  1988年   24篇
  1987年   19篇
  1986年   18篇
  1985年   19篇
  1983年   5篇
  1982年   19篇
  1981年   25篇
  1980年   33篇
  1979年   4篇
  1978年   10篇
  1977年   132篇
  1976年   258篇
  1975年   9篇
  1974年   1篇
  1973年   2篇
  1965年   1篇
  1964年   1篇
  1954年   1篇
  1928年   1篇
  1917年   1篇
排序方式: 共有3243条查询结果,搜索用时 62 毫秒
991.
The aim of the present study was to make a clinical and angiographic assessment of early outcomes of the use of heparin-coated new "Jo Stents M". The Study comprised 41 patients who were implanted a heparin-coated new "Jo Stent M". There was an immediate success in 45 (97.6%) of 46 cases, the optimal angiographic and suboptimal (the maximum residual stenosis (13%)) results being achieved in 43 (93.4%) and 2 (4.4%) cases, respectively. The first success of the procedure was 97.8%. Due to acute stent thrombosis, acute occlusion with evolving myocardial infarction occurred in 1 (2.4%) patient. Following the procedure, the mean proportion of the stenotic diameter was (-5.8 +/- 6)%. After the procedure, the minimum stenotic diameter with the mean due diameter of 2.9 +/- 0.5 mm was 3.0 +/- 0.2 mm. The procedure-induced diameter increase was 2.1 +/- 0.5 mm. The total number of lateral branches involved in the stenting area was 11 (100%), 2 (18.2) of them closed after stent implantation. Two branches came into the stenting area in 1 (2.4%) case. At discharge, angina pectoris was absent in 30 (74%) patients. The heparin-coated "Jo Stent M" are effective and safe in treating patients with various clinical and angiographic manifestations of coronary atherosclerotic lesions.  相似文献   
992.
993.
The present cross-sectional study analyzed the extent to which illness perceptions and coping strategies (as measured by the Illness Perception Questionnaire and the Utrecht Coping List, respectively) are associated with levels of daily functioning, as indicated by the Medical Outcomes Study SF-20, and disease-specific measures in 244 adults: 84 with rheumatoid arthritis (RA); 80 with chronic obstructive lung disease (COPD); and 80 with psoriasis. The results of stepwise regression analyses indicated that a strong illness identity, passive coping, belief in a long illness duration, belief in more severe consequences, and an unfavorable score on medical variables were associated with worse outcome on disease-specific measures of functioning and on general role and social functioning. Coping by seeking social support and beliefs in controllability/curability of the disease were significantly related to better functioning. The implications of these findings for future interventions and research are discussed.  相似文献   
994.
OBJECTIVE: Because C5a induces tissue injury by activating polymorphonuclear leukocytes, the hypothesis was that inhibition of C5a activity would reduce cardioplegia-related injury. METHODS: Pigs were placed on cardiopulmonary bypass. The hearts were arrested for 1 hour with hyperkalemic cardioplegia. Pigs were then separated from bypass, and the hearts were reperfused for 2 hours. Anti-porcine C5a monoclonal antibody (1.6 mg/kg, intravenously; n = 6) was administered 20 minutes before the onset of cardiopulmonary bypass. Six pigs received saline solution vehicle. Reactivity of coronary arterioles was studied in vitro with videomicroscopy. Microvessels from uninstrumented pigs served as controls for vascular studies. RESULTS: Endothelium-dependent relaxation to adenosine diphosphate (percent relaxation of precontraction) was reduced after cardioplegic reperfusion (63% +/- 14% vs 77% +/- 10% in control at 10 micromol/L; P =.01). This impairment in endothelium-dependent relaxation was improved with anti-porcine C5a monoclonal antibody (80% +/- 22%; P =.01 vs saline solution), as was the impaired endothelium-dependent relaxation to clonidine (64% +/- 12% control; 26% +/- 17% saline solution; 55% +/- 24% anti-porcine C5a monoclonal antibody at 10 micromol/L; P =.01 saline solution vs control or anti-porcine C5a monoclonal antibody). Myeloperoxidase activity was significantly decreased (0.2 +/- 0.2 units/g protein; P =.04) in the anti-porcine C5a monoclonal antibody group compared with 5.2 +/- 2.7 in the saline solution group. CH50 2 hours after bypass was not statistically different (0.57 +/- 0.41 unit and 0.65 +/- 0.41 unit, respectively) between the anti-porcine C5a monoclonal antibody and saline solution groups. Despite less myocardial polymorphonuclear leukocyte infiltration after C5a inhibition, maximum rate of rise of left ventricular pressure, percent segmental shortening, and blood flow through the left anterior descending coronary artery were similar in the anti-porcine C5a monoclonal antibody and saline solution groups. CONCLUSIONS: Inhibition of C5a limits neutrophil-mediated impairment of endothelium-dependent relaxation after cardiopulmonary bypass and cardioplegic reperfusion, but it has no effect on short-term myocardial functional preservation.  相似文献   
995.
With the diversity of our communities and waiting rooms increasing, can we continue to justify the lack of diversity among healthcare professionals? This article reports the demographic composition of the U.S. and compares those data with the professional healthcare workforce. With a non-White population of nearly 25%, only 10% of RNs are non-White and about 12% of medical students are non-White. Four reasons are presented for increasing diversity among healthcare professionals. These four include: improved culturally competent care, access to healthcare, healthcare outcomes and research, and provider access in high-need service areas. Healthcare organizations have gone on record as supporting increased diversity within high-skilled healthcare professions but without a commitment to increasing enrollments in professional healthcare programs, diversity goals will never be reached.  相似文献   
996.
A technique of phase-polarisation contrast (PPC) for the enhancement of the contrast of a surface plasmon resonance (SPR) intensity profile is proposed and experimentally realised. The technique exploits the peculiarities of light phase and polarisation behaviour under SPR. It applies to non-optimum SPR coupling conditions and enables one to lower the resonant minimum of reflected intensity nearly to zero, and hence to increase substantially the ratio of the intensity from the resonance to that at the minimum. We observed the contrast enhancement by more than one order of magnitude when we applied the PPC scheme. The PPC can be efficiently employed in commercial SPR sensors, as it significantly reduces restrictions on allowable parameters of SPR-supporting metal films and biomolecular layers immobilised on them, facilitates SPR observation, and increases the accuracy of SPR shift measurements.  相似文献   
997.
For many years, hairless and rhino mouse mutants have provided a useful and extensively exploited model for studying different aspects of skin physiology, including skin aging, pharmacokinetic evaluation of drug activity and cutaneous absorption, skin carcinogenesis, and skin toxicology. Interestingly, however, hairless and rhino mice have rarely been studied for their primary cellular defect - hairlessness - and thus, the hairless gene itself and its physiological functions have been largely overlooked for decades. The recent identification of the human homolog of the hairless gene on human Chromosome 8p12 confirmed the clinical significance of the phenomenon of "hairlessness" in humans, which was predicted on the basis of similarities between hairless mice and a congenital hair disorder characterized by atrichia with papules. Mutations in the hairless gene of mice provide instructive models for further studies of hr gene function, and may facilitate insights into the pathophysiology of different human disorders associated with the disruption of hr gene activity. We provide an overview of current data on the structure and expression patterns of the hr gene, and of mutations at the hairless locus in mice and humans, including the genetic basis of different alleles, the pathology of hairlessness, reproductive and immunological defects, and susceptibility to dioxin toxicity. On the basis of our current understanding of hairlessness, we speculate on the putative functions of the hr gene product in skin physiology, and particularly, in hair follicle biology.  相似文献   
998.
We studied the mechanisms of MHC class II-restricted bacterial Ag processing of the surface fibrillar M5 protein from viable Streptococcus pyogenes in murine macrophages. Two previously defined T cell epitopes were studied using T cell hybridomas specific for 308-319/Ad, associated with the cell wall on the surface of streptococci, and 17-31/Ed, located at the protruding amino terminus of M5. Studies with metabolic inhibitors showed that slow (1 h) processing of M5 308-319 occurred in late endosomes and was dependent on newly synthesized MHC class II molecules and microtubules and on communications between early and late endosomes, consistent with engagement of the classical MHC class II processing pathway. In contrast, fast (15 min) bacterial Ag processing of 17-31 occurred in early endosomes independently of newly synthesized MHC class II molecules and microtubules and of trafficking between early and late endosomes, consistent with the recycling MHC class II processing pathway. Finally, bacterial Ag processing of the epitopes exhibited differential sensitivity to blocking with anti-MHC class II Abs. Thus, two T cell epitopes of a single protective Ag from the surface of whole bacteria are routed to distinct MHC class II processing pathways.  相似文献   
999.
Time-kill studies, even those performed with in vitro dynamic models, often do not provide definitive comparisons of different antimicrobial agents. Also, they do not allow determinations of equiefficient doses or predictions of area under the concentration-time curve (AUC)/MIC breakpoints that might be related to antimicrobial effects (AMEs). In the present study, a wide range of single doses of trovafloxacin (TR) and twice-daily doses of ciprofloxacin (CI) were mimicked in an in vitro dynamic model. The AMEs of TR and CI against gram-negative bacteria with similar susceptibilities to both drugs were related to AUC/MICs that varied over similar eight-fold ranges [from 54 to 432 and from 59 to 473 (microg . h/ml)/(microg/ml), respectively]. The observation periods were designed to include complete bacterial regrowth, and the AME was expressed by its intensity (the area between the control growth in the absence of antibiotics and the antibiotic-induced time-kill and regrowth curves up to the point where viable counts of regrowing bacteria equal those achieved in the absence of drug [IE]). In each experiment monoexponential pharmacokinetic profiles of TR and CI were simulated with half-lives of 9.2 and 4.0 h, respectively. Linear relationships between IE and log AUC/MIC were established for TR and CI against three bacteria: Escherichia coli (MIC of TR [MICTR] = 0.25 microg/ml; MIC of CI [MICCI] = 0.12 microg/ml), Pseudomonas aeruginosa (MICTR = 0.3 microg/ml; MICCI = 0.15 microg/ml), and Klebsiella pneumoniae (MICTR = 0.25 microg/ml; MICCI = 0.12 microg/ml). The slopes and intercepts of these relationships differed for TR and CI, and the IE-log AUC/MIC plots were not superimposed, although they were similar for all bacteria with a given antibiotic. By using the relationships between IE and log AUC/MIC, TR was more efficient than CI. The predicted value of the AUC/MIC breakpoint for TR [mean for all three bacteria, 63 (microg . h/ml)/(microg/ml)] was approximately twofold lower than that for CI. Based on the IE-log AUC/MIC relationships, the respective dose (D)-response relationships were reconstructed. Like the IE-log AUC/MIC relationships, the IE-log D plots showed TR to be more efficient than CI. Single doses of TR that are as efficient as two 500-mg doses of CI (500 mg given every 12 h) were similar for the three strains (199, 226, and 203 mg). This study suggests that in vitro evaluation of the relationships between IE and AUC/MIC or D might be a reliable basis for comparing different fluoroquinolones and that the results of such comparative studies may be highly dependent on their experimental design and datum quantitation.  相似文献   
1000.
Motion between the humerus and scapula commonly is described as glenohumeral motion. However, humeroscapular motion occurs at two distinct sites. In addition to the motion at the diarthrodial glenohumeral joint, movement occurs between the proximal humerus and related structures and the surrounding sleeve of structures, including the acromion, deltoid, coracoid, coracoacromial ligament, and the muscles attached to the coracoid. This site of nonarticular shoulder motion is defined as the humeroscapular motion interface. Nonarticular humeroscapular motion can be documented and measured using standard magnetic resonance imaging techniques. The maximum average interfacial motion using axial images was 29.1 mm, which occurred at the level of the maximum diameter of the humeral head. Interfacial motion varied depending on the site measured. If pathologic conditions such as adhesions secondary to trauma or surgery interfere with or obliterate this space at sites of significant sliding motion, overall shoulder motion will be limited. Successful treatment of shoulder stiffness related to humeroscapular restraints is likely to require restoration of the normal sliding motion at the humeroscapular motion interface, in addition to resolving restraints affecting the glenohumeral joint motion.  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