全文获取类型
收费全文 | 5812篇 |
免费 | 17篇 |
专业分类
电工技术 | 16篇 |
综合类 | 3篇 |
化学工业 | 121篇 |
金属工艺 | 18篇 |
机械仪表 | 65篇 |
建筑科学 | 63篇 |
能源动力 | 13篇 |
轻工业 | 131篇 |
水利工程 | 15篇 |
无线电 | 131篇 |
一般工业技术 | 174篇 |
冶金工业 | 4918篇 |
原子能技术 | 7篇 |
自动化技术 | 154篇 |
出版年
2021年 | 12篇 |
2020年 | 9篇 |
2019年 | 19篇 |
2018年 | 12篇 |
2017年 | 11篇 |
2016年 | 15篇 |
2015年 | 9篇 |
2014年 | 19篇 |
2013年 | 47篇 |
2012年 | 37篇 |
2011年 | 38篇 |
2010年 | 36篇 |
2009年 | 39篇 |
2008年 | 50篇 |
2007年 | 53篇 |
2006年 | 43篇 |
2005年 | 40篇 |
2004年 | 22篇 |
2003年 | 43篇 |
2002年 | 25篇 |
2001年 | 21篇 |
2000年 | 22篇 |
1999年 | 154篇 |
1998年 | 1500篇 |
1997年 | 921篇 |
1996年 | 548篇 |
1995年 | 297篇 |
1994年 | 295篇 |
1993年 | 306篇 |
1992年 | 56篇 |
1991年 | 59篇 |
1990年 | 96篇 |
1989年 | 82篇 |
1988年 | 80篇 |
1987年 | 81篇 |
1986年 | 68篇 |
1985年 | 52篇 |
1984年 | 17篇 |
1983年 | 24篇 |
1982年 | 23篇 |
1981年 | 39篇 |
1980年 | 61篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 106篇 |
1976年 | 232篇 |
1975年 | 14篇 |
1974年 | 14篇 |
1973年 | 13篇 |
1971年 | 7篇 |
排序方式: 共有5829条查询结果,搜索用时 0 毫秒
21.
AJ Gelenberg 《Canadian Metallurgical Quarterly》1993,29(1):135-137
In the absence of a systematic monitoring program for drugs newly approved by the Food and Drug Administration (FDA), reports in clinical journals provide a legitimate forum for disseminating information about unexpected pharmacologic events. A journal editor bears the responsibility for publishing educated clinical observations that meet standards of scientific rigor while not giving premature credibility to chance and dubious reports of side effects of new drugs. Often this responsibility involves overcoming the fear of bad publicity and withstanding pressures from pharmaceutical companies to print only positive information about new products. Published preliminary observations may contribute to the problem of product liability, but they also generate testable hypotheses and healthy debate. If hypotheses later prove to be incorrect, they can be refuted by systematic studies and clarified in reviews and editorials. Our goal of effective education will be reached not by self-censorship but by scientific openness. 相似文献
22.
AJ Barsky 《Canadian Metallurgical Quarterly》1997,278(8):673-679
Catecholamines and volume repletion are currently used for the treatment of septic shock. However, the prognosis of patients suffering from this condition is very poor. An overproduction of nitric oxide (NO) seems to be related to the hypotension and tissue damage of endotoxin shock. Thus, treatment with NO synthase inhibitors has been proposed. Using a rat model of septic shock we have studied the effects of noradrenaline or the NO synthase inhibitor, NG-nitro-L-arginine methylester (L-NMMA) on arterial pressure, tissue damage and NO production. Anaesthetized rats treated with Salmonella typhosa showed a decrease in blood pressure accompanied by an increase in the plasma concentration of cytosolic enzymes (transaminases and lactate dehydrogenase, markers of cell disruption) and nitrite plus nitrate (NO2-/NO3-, markers of NO production). A large proportion of these animals (40%) died before the end of the experiment. Co-treatment with noradrenaline resulted in temporary maintenance of arterial pressure followed by a decline, despite the dose being increased progressively. No differences were observed in plasma cytosolic enzymes, NO2-/NO3- or mortality compared with animals treated with lipopolysaccharide (LPS) alone. In contrast, administration of L-NMMA (10 mg kg-1) to septic animals prevented the fall in blood pressure and death caused by endotoxin. This treatment markedly diminished cell disruption, as measured by the plasma levels of necrosis enzymes, and partially, but significantly, reduced the production of NO as assessed by plasma NO2-/NO3-. We conclude that tissue damage in septic shock is related to the overproduction of NO and not exclusively to the hypotension that follows this increased production. Thus, maintenance of blood pressure with catecholamines fails to improve cellular damage. Instead, partial inhibition of NO generation is sufficient to ameliorate the haemodynamic and tissue-damaging effects of septic shock and improves survival in this model of endotoxaemia. 相似文献
23.
We have measured cardiovascular changes associated with insufflation of carbon dioxide and the reverse Trendelenburg position during laparoscopic cholecystectomy, using transoesophageal echocardiography in 13 healthy patients. End-tidal carbon dioxide values increased after insufflation of carbon dioxide, with values significantly (P < 0.05) increased after lateral tilt positioning. Creation of a pneumoperitoneum was associated with increases (P < 0.05) in left ventricular end-systolic wall stress, concomitant with increases (P < 0.01) in peak airway pressure and systemic arterial pressure. In addition, left ventricular end-diastolic area decreased (P < 0.05) after reverse Trendelenburg positioning. Left ventricular ejection fraction was maintained throughout the study. 相似文献
24.
In this study we have investigated the role of CD4+, MHC class II-restricted cytotoxic T lymphocytes (CTLs) in the disease caused by lymphocytic choriomeningitis virus (LCMV) in beta 2-microglobulin deficient (beta 2m-) mice. Intracranial (i.c.) infection with LCMV resulted in death of six out of 11 beta 2m- mice. Mice that survived showed a marked loss in body weight. Death and loss of body weight could be prevented by immunosuppressing the mice with irradiation or cyclosporine prior to i.c. injection of LCMV. This treatment also prevented induction of virus-specific, MHC class II-restricted CTL following peripheral inoculation with LCMV. In vivo depletion of CD4+ cells with antibody also prevented death following i.c. injection whereas in vivo depletion of CD8+ cells had no effect. Disease could be transferred to recipient beta 2m- mice by adoptive transfer of beta 2m- derived immune spleen cells. Transfer of non-immune spleen cells did not result in illness. In vitro treatment of immune spleen cells with anti-CD4 antibody and complement eliminated class II-restricted CTL activity and also prevented mortality of recipients after adoptive transfer. Treatment with anti-CD8 antibody had no effect. We were unable to transfer LCM disease to beta 2m- recipients by adoptive transfer of immune spleen cells from C57BL/6 mice. These results suggest that, unlike normal mice, the pathology of LCM disease in beta 2m- mice is dependent upon virus-specific, CD4+CD8-, MHC class II-restricted T cells. 相似文献
25.
PURPOSE: The etiology of voiding dysfunction was determined in men after a cerebrovascular accident who were at risk for obstructive uropathy to evaluate whether the cause of voiding dysfunction could be predicted by the type (obstructive or irritative) or onset of symptoms. MATERIALS AND METHODS: We evaluated 38 men with complaints of voiding dysfunction following a cerebrovascular accident. All patients were of the age when bladder outlet obstruction secondary to benign prostatic hyperplasia would otherwise be prevalent. After a comprehensive history and physical examination, all patients underwent multichannel urodynamic studies at a medium fill rate (20 to 50 ml. per minute). Findings were classified by the Abrams-Griffiths nomogram as obstruction, no obstruction or equivocal. RESULTS: Mean patient age was 70 years (range 54 to 87). Patients were grouped according to the presenting voiding complaints (purely irritative in 42%, purely obstructive in 34% or mixed in 24%). In 34 patients (89%) the onset of symptoms paralleled the occurrence of the cerebrovascular accident. Detrusor hyperreflexia was noted in 82% of the patients. There was no statistically significant difference in the occurrence of detrusor hyperreflexia among the 3 symptom groups (Fisher's exact test). Pressure-flow analysis clearly showed obstruction in 24 patients (63%), no obstruction in 9 (24%) and equivocal results in 5 (13%) according to the nomogram. There was no statistically significant difference in the incidence of obstruction among the 3 symptom groups (Fisher's exact test). CONCLUSIONS: Presenting symptoms did not predict the urodynamic findings of bladder outlet obstruction or detrusor hyperreflexia. The significant incidence of onset of symptoms after stroke suggests that the cerebrovascular accident induced voiding dysfunction in the face of preexisting bladder outlet obstruction may exacerbate the symptoms of the latter condition or vice versa. 相似文献
26.
AJ Joseph 《Canadian Metallurgical Quarterly》1997,17(4):685-699
Conceptually, the Chest Pain Center model is nothing more than a system of delivering health care. It is a model that all hospitals can embrace as a framework for organizational decision making in meeting the heart-care needs of their communities. It also provides a framework for clinical decision making. By adopting some or all of the common features of the model, hospitals develop a common language, similar to what took place when CCUs first opened in the 1960s. Application of evidence-based clinical practice is promoted. Approaches that account for both clinical outcomes and financial outcomes will be further refined. One result will be simultaneous improvement in clinical outcomes and a decrease in costs, but the most important aspect of the Chest Pain Center model is that it puts the patient first. 相似文献
27.
28.
29.
Two cases of congenital absence of a cervical vertebral pedicle are reported. This condition includes hypoplasia of the ipsilateral posterior arch and may predispose to spinal cord injury. The radiographic and computed tomography (CT) findings are reviewed, and the importance of the ipsilateral oblique radiographic view and of CT in diagnosis is stressed. 相似文献
30.
The use of drugs for common pregnancy complications like premature labor, hypertensive diseases, and premature rupture of membranes with chorioamnionitis is reviewed. In addition, new publications on antiviral drugs in HIV-positive pregnant patients are also discussed. Among the drugs, suppressing premature labor side-effects of beta-mimetics are of growing concern. The effectiveness of other agents like magnesium, indomethacin, and sulindac are addressed. The various mechanisms explaining the beneficial effect of magnesium in pre-eclampsia are reviewed and new data on antihypertensives, such as labetalol, calcium channel blockers, and methyldopa are presented. The evidence from various clinical trials on the value of low-dose aspirin as a prophylactic agent against pregnancy-induced hypertension, pre-eclampsia, and intrauterine growth retardation in high-risk and low-risk patients is compared. Pharmacokinetic data including transplacental transfer of antibiotics and anti-HIV nucleosides are part of this review. 相似文献