全文获取类型
收费全文 | 285864篇 |
免费 | 4267篇 |
国内免费 | 1413篇 |
专业分类
电工技术 | 5454篇 |
综合类 | 890篇 |
化学工业 | 40562篇 |
金属工艺 | 11515篇 |
机械仪表 | 8238篇 |
建筑科学 | 7296篇 |
矿业工程 | 922篇 |
能源动力 | 6746篇 |
轻工业 | 26239篇 |
水利工程 | 2414篇 |
石油天然气 | 1402篇 |
武器工业 | 8篇 |
无线电 | 33000篇 |
一般工业技术 | 49494篇 |
冶金工业 | 67779篇 |
原子能技术 | 4073篇 |
自动化技术 | 25512篇 |
出版年
2021年 | 1671篇 |
2019年 | 1502篇 |
2018年 | 3362篇 |
2017年 | 3414篇 |
2016年 | 3770篇 |
2015年 | 2823篇 |
2014年 | 3676篇 |
2013年 | 11325篇 |
2012年 | 7650篇 |
2011年 | 10374篇 |
2010年 | 7027篇 |
2009年 | 7811篇 |
2008年 | 8281篇 |
2007年 | 8376篇 |
2006年 | 7652篇 |
2005年 | 10689篇 |
2004年 | 9293篇 |
2003年 | 8663篇 |
2002年 | 7121篇 |
2001年 | 7112篇 |
2000年 | 6089篇 |
1999年 | 6930篇 |
1998年 | 21410篇 |
1997年 | 14644篇 |
1996年 | 10951篇 |
1995年 | 7835篇 |
1994年 | 6757篇 |
1993年 | 6611篇 |
1992年 | 4254篇 |
1991年 | 4226篇 |
1990年 | 3846篇 |
1989年 | 3734篇 |
1988年 | 3693篇 |
1987年 | 3082篇 |
1986年 | 3010篇 |
1985年 | 3562篇 |
1984年 | 3135篇 |
1983年 | 2832篇 |
1982年 | 2670篇 |
1981年 | 2732篇 |
1980年 | 2610篇 |
1979年 | 2332篇 |
1978年 | 2330篇 |
1977年 | 3338篇 |
1976年 | 5271篇 |
1975年 | 1992篇 |
1974年 | 1843篇 |
1973年 | 1829篇 |
1972年 | 1500篇 |
1971年 | 1356篇 |
排序方式: 共有10000条查询结果,搜索用时 47 毫秒
931.
K Cupisti D Simon C Dotzenrath PE Goretzki HD R?her 《Canadian Metallurgical Quarterly》1997,382(6):295-301
Ileal pouch-anal anastomosis is a surgical procedure used for the treatment of people with chronic ulcerative colitis and familial adenomatous polyposis. The surgery is intended to preserve anal sphincter function, but it carries a risk for certain complications, including pouchitis and anastomotic stricture. The purpose of this article is to review the clinical manifestations, causes, and treatment of anastomotic stricture and pouchitis after ileal pouch-anal anastomosis. 相似文献
932.
933.
OBJECTIVE: Experiences obtained with nonoperative treatment (NOT), i.e. total prohibition of per oral food intake for a minimum of 7 days, administration of combinations of broad-spectrum antibiotics, and parenteral hyperalimentation, are described in the management of esophageal perforations. SUMMARY BACKGROUND DATA: The place, value, and indication of NOT in the management of esophageal perforation has not yet been unequivocally defined. As a result, contradictory data have been published regarding the outcome of NOT. METHODS: During the past 15 years (1979 to 1994), 20 of 86 patients (23.3%) with esophageal perforation have been treated nonoperatively from the outset. In this group, perforations were located to the upper, middle, and lower third of the esophagus in 50%, 30%, and 20%, respectively. In the operative management group (OT)--in which conservative (drainage, endeprothesis), reconstructive (suture, reinforced suture), and radical (resection) surgical methods were applied--lesions were preponderantly located in the lower one third of the esophagus (56.1%--37/66). As to the interval between the perforation and the onset of treatment, 14 patients had been diagnosed within 24 hours, whereas in 6 cases treatment had been begun beyond 24 hours. RESULTS: NOT could be successfully carried out in 16 patients; the decision to use NOT had to be revised in 4 other cases (Table 1). Two patients were lost; the mortality rate was 10% (2 of 20). The rate of complications was lower in the NOT group (20%, or 4 of 20) than in the OT group (50%, or 33 of 66). CONCLUSIONS: NOT can be suggested for the treatment of intramural perforations. In the case of transmural perforation, this approach should be taken into consideration if the esophageal lesion is circumscribed, is not in neoplastic tissue, is not in the abdominal cavity, and is not accompanied by simultaneous obstructive esophageal disease; in addition, symptoms and signs of septicemia should be absent. 相似文献
934.
A focus on the importance of leisure in the development of student nurses has been neglected in the 1990s. This study considers 444 prospective nurses on conventional, diploma and degree courses in two areas of England. It examines their activities associated with socializing, their social support networks and their use of clubs, sports and hobbies before entering nursing. It is evident that students enter nurse training with a wide variety of leisure experiences. Changing recruitment patterns and the structure of nurse training has an effect on the leisure needs of prospective nurses which must be addressed. 相似文献
935.
936.
C Held P Hjemdahl N Rehnqvist NH Wallén I Bj?rkander SV Eriksson L Forslund B Wiman 《Canadian Metallurgical Quarterly》1997,95(10):2380-2386
BACKGROUND: Disturbed fibrinolytic function may influence the progression of coronary atherosclerosis and contribute to thrombotic cardiovascular (CV) events. METHODS AND RESULTS: In the Angina Prognosis Study in Stockholm (APSIS), patients with stable angina pectoris were studied prospectively during double-blind treatment with metoprolol or verapamil. Various measures of fibrinolytic function were studied in 631 (of 809) patients. During a median follow-up time of 3.2 years (2132 patient-years), 32 patients suffered a CV death, 21 had a nonfatal myocardial infarction (MI), and 77 underwent revascularization. Plasma levels of tissue plasminogen activator (TPA) activity and antigen (ag), plasminogen activator inhibitor (PAI-1) activity at test, and TPA responses to exercise were determined at baseline and after 1 month's treatment and were related to subsequent fatal and nonfatal CV events. Univariate Cox regression analysis revealed that elevated levels of TPA-ag at rest (P < .05), high PAI-1 activity (P < .05), and low TPA-ag responses to exercise (P < .05) were associated with increased risk of subsequent CV death. After adjustment for baseline risk factors, TPA-ag independently predicted CV death or MI. In addition, PAI-1 activity independently predicted CV death or MI in male patients. Verapamil treatment was associated with a 10% decrease of TPA-ag levels and metoprolol treatment with a 2% increase (P < .001 for treatment difference). CONCLUSIONS: Plasma TPA-ag levels at rest, and among male patients PAI-1 activity as well, independently predict subsequent CV death or MI in patients with stable angina pectoris. 相似文献
937.
The rare case of neurilemmoma of the larynx was presented. The difficulties in histopathologic diagnosis of such tumors were emphasized. The tumor was removed by surgery from external approach. 相似文献
938.
Unrecognized and untreated depression occurs frequently in Alzheimer's disease (AD) patients, adding to the agony already experienced by patient and caregiver. The authors screened AD patients living with a family caregiver for depression. Twelve patients with confirmed depression were treated in an open-label study with antidepressant medication, with dosage adjustment by a psychiatrist at Weeks 2, 4, 8, and 16. Data collection occurred at baseline, Week 4, and Week 16. Depression decreased significantly (p < .01). Contrary to expectations, patient functional capacity declined (p = .045). Cognition remained unchanged (p > .05). Caregiver burden, caregiver depressive symptomatology, and quality of life of patient and caregiver remained unchanged (p > .05). The authors conclude that depression in AD can be detected if a collateral source, such as the caregiver, is available. The depression can and should be treated. More research is needed to determine the impact on patient functioning, caregiver burden, caregiver depressive symptomatology, and quality of life of patient and caregiver. 相似文献
939.
E Kobayashi Y Yoshida A Fujimura T Yamanaka H Endo T Hamamoto Y Kagawa 《Canadian Metallurgical Quarterly》1997,24(12):1775-1777
We studied the in vivo gene transfusion using a gene gun, formerly used in plants and culture cells. The hand-held type gene gun (Helios Gene Gun System) is simple and convenient for effective gene transfection in living animals. This method has some advantages in that there is no need for use of viral vector, independence on the cell cycle and local inducement of plural genes. There is a great possibility for application to local-regional cancer. 相似文献
940.
BACKGROUND: To assess the relationship between placental inflammation, umbilical artery Doppler waveforms and fetal biophysical profile score, umbilical artery Doppler studies and fetal biophysical evaluations were performed in 24 preterm pregnants with premature rupture of membranes (PPROM). SUBJECTS: After delivery, the placentas were microscopically examined and two subgroups were formed including noninflamed or inflamed placentas. RESULTS: In the first group, which includes 14 cases with no histological signs of placental inflammation, we found increased systolic/diastolic ratio only in one patient, whereas in the second group including ten cases with microscopically proven inflammation, nine were found to have increased systolic/diastolic ratios (p < 0.05). Mean systolic/diastolic ratio in the first and the second groups were 2.74 +/- 0.18 and 4.64 +/- 0.93 respectively (p < 0.001). Mean biophysical profile score was 9 +/- 1.04 in the first group and 7 +/- 1.05 in the second group (p < 0.001). CONCLUSION: Abnormal biophysical profile scores along with increased arterial systolic/diastolic ratios have been shown to be the markers of impending clinical infection. 相似文献