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   2435篇
  免费   1篇
化学工业   9篇
轻工业   2篇
石油天然气   2篇
无线电   1篇
一般工业技术   3篇
冶金工业   2418篇
自动化技术   1篇
  2016年   1篇
  2013年   1篇
  2011年   1篇
  2009年   1篇
  2006年   1篇
  2005年   1篇
  2004年   1篇
  2003年   5篇
  1999年   80篇
  1998年   805篇
  1997年   455篇
  1996年   273篇
  1995年   161篇
  1994年   141篇
  1993年   148篇
  1992年   10篇
  1991年   18篇
  1990年   30篇
  1989年   27篇
  1988年   25篇
  1987年   26篇
  1986年   31篇
  1985年   15篇
  1983年   1篇
  1982年   5篇
  1981年   4篇
  1980年   13篇
  1979年   1篇
  1978年   3篇
  1977年   43篇
  1976年   105篇
  1975年   2篇
  1955年   2篇
排序方式: 共有2436条查询结果,搜索用时 15 毫秒
51.
The leukocyte-specific adapter molecule SLP-76 (Src homology 2 domain-containing leukocyte protein of 76 kilodaltons) is rapidly phosphorylated on tyrosine residues after receptor ligation in several hematopoietically derived cell types. Mice made deficient for SLP-76 expression contained no peripheral T cells as a result of an early block in thymopoiesis. Macrophage and natural killer cell compartments were intact in SLP-76-deficient mice, despite SLP-76 expression in these lineages in wild-type mice. Thus, the SLP-76 adapter protein is required for normal thymocyte development and plays a crucial role in translating signals mediated by pre-T cell receptors into distal biochemical events.  相似文献   
52.
The expression of full-length dystrophin and various dystrophin deletion mutants was monitored in mdx mouse muscle after intramuscular injection of dystrophin-encoding plasmid DNAs. Recombinant dystrophin proteins, including those lacking either the amino terminus, carboxyl terminus, or most of the central rod domain, showed localization to the plasma membrane. This suggests that there are multiple attachment sites for dystrophin to the plasma membrane. Only those constructs containing the carboxyl terminus were able to stabilize dystrophin-associated proteins (DAP) at the membrane, consistent with other studies that suggest that this domain is critical to DAP binding. Colocalization with DAP was not necessary for membrane localization of the various dystrophin molecules. However, stabilization and co-localization of the DAP did seem to be a prerequisite for expression and/or stabilization of mutant dystrophins beyond 1 wk and these same criteria seemed important for mitigating the histopathological consequences of dystrophin deficiency.  相似文献   
53.
54.
Growth hormone prepared by recombinant DNA technology (somatropin) has been commercially available for over 11 years. More than 38,000 children have been treated with different growth hormone products. While the best response to treatment occurs in children with severe growth hormone deficiency, therapy with growth hormone will increase the rate of statural growth in children with short stature of many different aetiologies. There are few studies of the effect of growth hormone treatment of final adult height, and the magnitude of this effect is harder to gauge, particularly in children with idiopathic short stature. Other benefits of growth hormone treatment in children include improvement in psychosocial functioning and physiological parameters, such as bone mineral density. Adverse effects associated with growth hormone treatment have been relatively uncommon. Most of the safety data on growth hormone have come from large postmarketing databases maintained by 2 pharmaceutical companies. The adverse event profile reported in children treated with growth hormone is different from that found in adults. Peripheral oedema and carpal tunnel syndrome, which are common in adults treated with growth hormone and frequently result in treatment discontinuation, are rare in children. Intracranial hypertension is rare, but can occur in children with growth hormone deficiency, Ullrich-Turner syndrome or renal insufficiency during the first 8 to 12 weeks after the start of growth hormone treatment; it has seldom been reported in adults with growth hormone deficiency. Children with growth hormone deficiency, Ullrich-Turner syndrome or renal insufficiency are prone to develop slipped capital femoral epiphyses both before and during growth hormone treatment. Therefore, limping and complaints of hip or knee pain should be carefully investigated.  相似文献   
55.
PURPOSE: Many patients attend orthopedic departments complaining of pain on the plantar aspect of the calcaneum. The symptoms may subside spontaneously, but often persist. Treatment is usually by local injection of a corticosteroid, orthopedic devices or other standard treatment. If these methods fail, X-ray treatment may be considered. The efficacy of radiotherapy of the calcaneal spur was evaluated. PATIENTS AND METHODS: From April 1981 through December 1991, 18 patients with painful heel were irradiated mostly with the caesium or telecobalt unit, usually with a dose of 4 times 0.5 Gy. Among these patients, 12 could be followed up during a prolonged period on the basis of questionnaires. RESULTS: According to the categories of v. Pannewitz 17% of the patients were pain-free by the end of the treatment course, 22% showed marked improvement, 33% showed improvement and in 28% the pain was not influenced. Over an average of 41.5 months 58% of the patients reported freedom from pain. CONCLUSIONS: Low-dose radiotherapy appears to relieve the painful heel syndrome in a high proportion of patients. The overall treatment risk appears to be very small. The mechanism of low-dose radiotherapy is unknown.  相似文献   
56.
The purpose of this exploratory investigation was to evaluate the heuristic potential of 31P magnetic resonance spectroscopy (MRS) in elucidating a neurobiologic component of the liability for a substance use disorder (SUD). We investigated 31P MRS spectra employing chemical shift imaging (CSI) derived from four distinct anatomic brain locations (i.e. frontal, occipital, right parietal, left parietal) in three groups of peripubertal children who are hypothesized to be at increasing levels of familial SUD risk. Specifically, we studied children with a positive paternal family history of SUD and a disruptive behavior disorder (DBD) diagnosis (SUD+/DBD+; n = 10), in contrast, to those with a positive paternal SUD history in the absence of other psychopathology (SUD+/DBD-; n = 13) and matched control children from normal families (SUD-/DBD-; n = 13). In addition, we examined neurocognitive tests of our subjects to determine any associations between cognitive capacities with regional 31P MRS spectra. The highest-risk sample (SUD+/DBD+) demonstrated a diminished proportion of phosphodiesters confined to the right parietal voxel. This right parietal phosphodiester proportion correlated only with the Information Scale score on a standard intelligence test for children. This suggested a relationship between general learning ability and motivation for academic achievement and right parietal physiology in the highest-risk sample. Variations in synaptic pruning could account for this observation.  相似文献   
57.
58.
59.
Pancreatic cancer is an aggressive disease with a dismal prognosis. It has long been regarded as one of the most difficult cancers to accurately diagnose and stage preoperatively. The purpose of this review is to provide an update of the state-of-the-art for early detection, diagnosis, and staging of pancreatic cancer. These methods include spiral CT scans, magnetic resonance imaging, positron emission tomography (PET) imaging, laparoscopy, endoscopic ultrasound, CA 19-9 serology, fine needle aspiration cytology, ERCP brush cytology, and screening for p53 and ras oncogenes. These advanced techniques should help us to detect pancreatic cancers in high-risk populations at a curative stage and to decrease pancreaticoduodenectomies for benign disease which could otherwise be treated with less morbid procedures. In addition, these tests will help reliably diagnose pancreatic cancer preoperatively.  相似文献   
60.
A postmyocardial infarction left ventricular pseudoaneurysm occurs when a rupture of the ventricular free wall is contained by overlying, adherent pericardium. A postinfarction aneurysm, in contrast, is caused by scar formation resulting in thinning of the myocardium. Although the usual treatment for patients with pseudoaneurysm is urgent surgical repair, the imaging characteristics of pseudoaneurysm and aneurysm, for which treatment is more conservative, are quite similar. The literature on the natural history and imaging characteristics of the two entities is reviewed, and an approach to distinguishing between the two entities is proposed.  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