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   2489篇
  免费   13篇
  国内免费   3篇
电工技术   3篇
综合类   3篇
化学工业   61篇
金属工艺   5篇
机械仪表   6篇
建筑科学   18篇
矿业工程   3篇
能源动力   17篇
轻工业   34篇
水利工程   3篇
石油天然气   1篇
武器工业   1篇
无线电   60篇
一般工业技术   57篇
冶金工业   2185篇
原子能技术   2篇
自动化技术   46篇
  2021年   3篇
  2019年   3篇
  2018年   4篇
  2017年   5篇
  2016年   8篇
  2015年   6篇
  2014年   6篇
  2013年   20篇
  2012年   8篇
  2011年   18篇
  2010年   13篇
  2009年   13篇
  2008年   15篇
  2007年   11篇
  2006年   15篇
  2005年   11篇
  2004年   17篇
  2003年   14篇
  2002年   6篇
  2001年   12篇
  2000年   7篇
  1999年   68篇
  1998年   692篇
  1997年   412篇
  1996年   232篇
  1995年   125篇
  1994年   132篇
  1993年   156篇
  1992年   20篇
  1991年   34篇
  1990年   30篇
  1989年   29篇
  1988年   37篇
  1987年   32篇
  1986年   19篇
  1985年   27篇
  1983年   7篇
  1982年   15篇
  1981年   21篇
  1980年   20篇
  1978年   8篇
  1977年   53篇
  1976年   86篇
  1975年   5篇
  1974年   5篇
  1973年   3篇
  1972年   2篇
  1970年   3篇
  1968年   2篇
  1955年   2篇
排序方式: 共有2505条查询结果,搜索用时 0 毫秒
921.
OBJECTIVE: To identify potential risk and protective factors associated with attempted suicide among Inuit youth, a population known to have a high rate of both attempted and completed suicide in recent years. METHOD: A secondary analysis of data on 203 Inuit youth (aged 15 to 24 years) from a random community survey conducted by Santé Québec in 1992. Factors previously identified in the literature and in clinical consultation and ethnographic research were tested with bivariate statistics and logistic regression models for each gender. RESULTS: At the bivariate level, positive correlates included substance use (solvents, cannabis, cocaine), recent alcohol abuse, evidence of a psychiatric problem, and a greater number of life events in the last year. Regular church attendance was negatively associated with attempted suicide. Multivariate analysis indicated that a psychiatric problem, recent alcohol abuse, and cocaine or crack use were the strongest correlates of attempted suicide for females, while solvent use and number of recent life events were the strongest correlates for males. CONCLUSIONS: Suicide prevention programs can be targeted at youth who are using substances, particularly solvents, cocaine, and alcohol, have psychiatric illness, and have experienced recent negative life events. Involvement in church or other community activities may reduce the risk for suicide. Consideration of gender differences may allow more precise identification of those at risk for attempted suicide.  相似文献   
922.
OBJECTIVE: The authors investigated knowledge, attitudes, and beliefs about mental illness and providers held by a group of deaf adults. METHOD: The American Sign Language interviews of 54 deaf adults were analyzed. RESULTS: Recurrent themes included mistrust of providers, communication difficulty as a primary cause of mental health problems, profound concern with communication in therapy, and widespread ignorance about how to obtain services. CONCLUSIONS: Deaf consumers' views need due consideration in service delivery planning. Outreach regarding existing programs is essential.  相似文献   
923.
OBJECTIVES: Human cardiac muscle from failing heart shows a decrease in active tension development and a rise in diastolic tension at stimulation frequencies above 50-60 beats/min due to both systolic and diastolic dysfunction. We have investigated underlying changes in cellular [Ca2+]i regulation. METHODS: Single ventricular myocytes were isolated enzymatically from the explanted hearts of transplant recipients with ischemic cardiomyopathy (nhearts = 5 ncells = 15) or dilated cardiomyopathy (nhearts = 6, ncells = 19). Cells were studied during whole-cell patch clamp with fluo-3 and fura-red as [Ca2+]i indicators (36 +/- 1 degrees C). RESULTS: In current clamp mode (action potential recording), the amplitude of Ca2+ release from the sarcoplasmic reticulum (SR) decreased at stimulation frequencies above 0.5 Hz; this decrease was more pronounced for cells from dilated cardiomyopathy. Diastolic [Ca2+]i increased at 1 and 2 Hz for both groups. Action potential duration (APD90) decreased with frequency in all cells; in addition there was a drop in plateau potential of 10 +/- 1 mV for cells from ischemic cardiomyopathy and of 13 +/- 2 mV for cells from dilated cardiomyopathy. In voltage clamp mode the L-type Ca2+ current showed reversible decrease during stimulation at 1 and 2 Hz. Recovery from inactivation during a double pulse protocol was slow (75 +/- 3% at 500 ms, 89 +/- 3% at 1000 ms) and followed the decay of the [Ca2+]i transient. CONCLUSIONS: The negative force-frequency relation of the failing human heart is due to a decrease in Ca2+ release of the cardiac myocytes at frequencies > or = 0.5 Hz, more pronounced in dilated than in ischemic cardiomyopathy. Inhibition of ICaL at higher frequencies, at least partially related to an increase in diastolic [Ca2+]i, will contribute to this negative staircase because of a decrease in the trigger for Ca2+ release, and of decreased loading of the SR.  相似文献   
924.
Fluoroscopy guided interventions, such as transjugular intrahepatic portosystemic shunt (TIPS) procedures, can results in relatively high radiation doses to patients and staff. The purpose of this study was to evaluate the possible benefit of dedicated fluoroscopy exposure factors in the reduction of doses. Doses to patients and staff were measured during fluoroscopy-guided TIPS procedures in two Dutch university hospitals. Patient doses were calculated from dose-area product (DAP) measurements, entrance beam dimensions and DAP conversion factors. Staff doses were measured outside lead aprons using electronic personal dosemeters. Average patient entrance skin dose (ESD) rate during fluoroscopy was 49 mGy min-1 (13 cases, average fluoroscopy duration 32 min) in one hospital, and 6 mGy min-1 (10 cases, average fluoroscopy duration 50 min) in the other. Estimated staff effective dose per procedure was 28 microSv average in the first hospital compared with 4 microSv average in the other. The use of dedicated fluoroscopy exposure factors, with a relatively high tube voltage and lower tube current resulted in a significant dose reduction for patient and staff in this type of radiological intervention.  相似文献   
925.
Medical futility     
The debate on medical futility can lead to a fresh revisiting of the doctor-patient relationship and with it a restoration of common sense and reality to society's grasp of the powers and limits of medicine. In my view, the duty of the physician is to attempt that which is of therapeutic benefit to the patient. Nothing less and nothing more.  相似文献   
926.
We have previously shown that the novel anticonvulsant levetiracetam exerts potent anticonvulsant activity against both focal and secondarily generalized seizures in fully amygdala-kindled rats, i.e. , a model of temporal lobe epilepsy. We examined whether levetiracetam also exhibits antiepileptogenic activity, i.e., prevents or retards acquisition or development of amygdala-kindling in rats. Before the experiments with chronic administration of levetiracetam at different doses, we determined the pharmacokinetics of the drug after i.p. injection. Levetiracetam had a relatively short half-life (about 2-3 hr) in rats, so that any lasting effects of the drug after chronic administration were certainly not due to drug accumulation. When rats were treated with levetiracetam during kindling acquisition at daily i.p. doses of 13, 27 or 54 mg/kg, the drug dose-dependently suppressed the increase in seizure severity and duration induced by repeated amygdala stimulation. After termination of daily treatment with 54 mg/kg, duration of behavioral seizures and of afterdischarges recorded from the amygdala remained to be significantly shorter compared to vehicle controls, although amygdala stimulations were continued in the absence of drug. These data thus indicate that levetiracetam not simply masked the expression of kindled seizures through an anticonvulsant action, but exerted a true antiepileptogenic effect. Adverse effects were not observed at any dose of levetiracetam tested in kindled rats. The powerful antiepileptogenic activity of levetiracetam in the kindling model indicates that levetiracetam is not only an interesting novel drug for symptomatic treatment of epilepsy but might be suited for pharmacological prevention of this disease in patients with a high prospective risk of the development of epilepsy.  相似文献   
927.
PURPOSE: In an attempt to improve local control and survival of nonsmall cell lung cancer (NSCLC), hyperfractionated accelerated radiation therapy (HART) was carried out as a clinical phase I/II trial. METHODS AND MATERIALS: HART was delivered by 1.1 Gy/fraction, three fractions per day with intervals of 4 h and five treatment days per week. The clinical tumors were irradiated to 74.3 Gy (72.6-75.9)/66-69 fx, 33 days (29-40) (not corrected for lung density), and the subclinical lesions, to 50.0 Gy (48.4-50.6)/44-46 fx, 33 days (29-40). Sixty-nine patients with NSCLC were enrolled in this study. Nine patients were withdrawn from the study during HART due to different reasons. Sixty patients formed the study for outcome analyses. They were 57 males and 3 females with median age of 61 years (21-77). There were 41 cases of squamous cell carcinoma, 15 cases of adenocarcinoma, and 4 cases of large cell carcinoma. Overall, favorable patients (KPS > or = 70, weight loss < 5% and Stages I, II, IIIa) accounted for 73% (44 of 60) of all patients. Forty-four patients (73%) received adjuvant chemotherapy (DDP + VP16) with median cycles of 1.8 before and/or after HART. In order to compare the outcome of HART with conventional irradiation, 50 NSCLC patients treated by conventional fractionated irradiation (CFI) during the same period were chosen as the basis to evaluate relative effects of HART. They derived from the control group of another clinical trial of hyperfractionated irradiation for NSCLC in the same department. They received median tumor dose of 63.9 Gy (62.8-65.0)/34 fx (32-36), 48 days (45-53). RESULTS: 1. Acute and late complications: (a) In HART, 87% of patients (52 cases) developed acute radiation esophagitis: Grade 1-2, 46 cases (77%) and Grade 3, 6 cases (10%), at 2.5 weeks (2-3.5 weeks) after HART began. Five patients with Grade 3 esophagitis had their HART interrupted for <7 days. In CFI, esophagitis was much less (44%,p < 0.05) with 38% of Grade 1-2 and 6% of Grade 3. (b) In HART, acute pulmonary symptoms (RTOG Grade 1-2) occurred in 17% (10 cases), and acute radiation pneumonitis (Grade 3), in 8% (5 cases), while in CFI, they were 24% and 2% (p > 0.05), respectively. Late lung fibrosis (RTOG Grade 1-2) appeared in 20% (12 cases), whereas 18% in CFI (p > 0.05). (c), No other severe acute or late complications have been observed so far in HART. 2. Immediate response. In HART, 20% of patients (12 cases) achieved CR, 60% (36 cases), PR and 20% (12 cases), NR or PD. In CFI, the above three percentages were 10, 28, and 62%, respectively (p < 0.001). 3. Follow-up. The 1-, 2-, and 3-year actuarial survivals were 72, 47, and 28% for HART, and 60, 18, and 6% for CFI, respectively (p < 0.001). Better local control was seen in HART than in CFI with 1-, 2-, and 3-year local control rates being 71, 44, 29%, and 60, 20, and 5%, respectively (p = 0.001). Distant metastases developed less in HART than in CFI. The 1-, 2-, and 3-year distant metastasis rates were 23, 36, and 50% in HART, but 30, 48, and 80% in CFI (p = 0.021). CONCLUSION: 1. HART could be tolerated by most of the favorable NSCLC patients. The predominant complication was acute esophagitis. No other severe acute or late complications have been observed so far. 2. HART resulted in better survivals and local controls, and less distant metastases than CFI.  相似文献   
928.
929.
930.
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