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   6502篇
  免费   337篇
  国内免费   1篇
电工技术   37篇
综合类   5篇
化学工业   1498篇
金属工艺   142篇
机械仪表   121篇
建筑科学   186篇
矿业工程   9篇
能源动力   256篇
轻工业   1308篇
水利工程   49篇
石油天然气   33篇
无线电   257篇
一般工业技术   991篇
冶金工业   1140篇
原子能技术   31篇
自动化技术   777篇
  2024年   9篇
  2023年   48篇
  2022年   144篇
  2021年   177篇
  2020年   131篇
  2019年   155篇
  2018年   194篇
  2017年   210篇
  2016年   207篇
  2015年   179篇
  2014年   231篇
  2013年   435篇
  2012年   363篇
  2011年   428篇
  2010年   316篇
  2009年   306篇
  2008年   311篇
  2007年   279篇
  2006年   214篇
  2005年   192篇
  2004年   190篇
  2003年   159篇
  2002年   144篇
  2001年   119篇
  2000年   99篇
  1999年   112篇
  1998年   403篇
  1997年   283篇
  1996年   198篇
  1995年   118篇
  1994年   98篇
  1993年   87篇
  1992年   37篇
  1991年   32篇
  1990年   31篇
  1989年   23篇
  1988年   33篇
  1987年   25篇
  1986年   16篇
  1985年   16篇
  1984年   9篇
  1983年   3篇
  1982年   9篇
  1981年   4篇
  1980年   6篇
  1977年   12篇
  1976年   36篇
  1973年   1篇
  1972年   3篇
  1971年   2篇
排序方式: 共有6840条查询结果,搜索用时 15 毫秒
991.
Liver fibrosis     
Surfactant abnormalities may contribute to the impairment of gas exchange observed in Pneumocystis carinii pneumonia. Analysis of rat bronchoalveolar lavage (BAL) lipid extracts from normal controls, steroid controls, trimethaprim-sulfamethoxazole (TMP-SMX) controls, TMP-SMX/P. carinii pneumonia controls, and P. carinii pneumonia animals reveal similar total phospholipid and total protein levels. However, there was a marked reduction in phosphatidylglycerol (PG) from the BAL of P. carinii pneumonia rats as compared with control animals, with a decrease from 4.91 +/- 1.29 nmol/mg protein to 0.46 +/- 0.57 nmol/mg protein (p<0.05) and a decrease, as a percent of total phospholipids, from 7.7% +/- 0.88% to 0.91% +/- 0.59% (p<0.001). Furthermore, in vitro surface activities of BAL lipid extracts from control and P. carinii pneumonia rats revealed minimum surface tension increases from 9.38 +/- 1.71 mN/m in controls to 16.36 +/- 0.83 mN/m in P. carinii pneumonia rats (p<0.05) and likewise maximum surface tension increases from 22.14 +/- 4.34 mN/m to 38.57 +/- 2.07 mN/m (p<0.01). Of interest, the surface activity of PG-deficient P. carinii pneumonia BAL lipid extracts is completely restored to that of normal controls by the addition of exogenous PG. These findings suggest that a functionally abnormal surfactant occurs in P. carinii pneumonia and that this may account, in part, for the impairment of gas exchange observed in this disorder.  相似文献   
992.
Whether a sulfonylurea may be used together with insulin for treating NIDDM has been controversial. One view, based on older studies, has been that the additional benefit is too small or the level of glucose control achieved usually too poor to recommend this method. More recent studies of a more specific way of combining a sulfonylurea with insulin are more supportive. When a single injection of insulin taken in the evening is added to a sulfonylurea at the time of secondary failure of the sulfonylurea alone, glycemic control is quite simply and consistently restored to acceptable levels. At this time in the natural history of NIDDM, evening insulin combined therapy is more effective than a single injection of insulin alone, and just as effective as a more complex multiple-injection regimen without an oral agent. A recent multicenter trial of a new sulfonylurea, glimepiride, in combination with a single injection of 70/30 insulin before dinner has confirmed that this approach is safe and more consistently effective than insulin alone for obese patients beginning insulin in a setting resembling clinical practice. The available evidence suggests this form of combined therapy is suitable for routine use.  相似文献   
993.
The authors report four cases of prolonged bradyarrhythmias after isolated coronary artery bypass graft surgery. All the four patients required permanent pacemaker implantation. Etiologic factors of conduction disturbances after coronary artery bypass and long term follow-up are discussed.  相似文献   
994.
Initial reports on antiproteinuric effect of pefloxacine in small groups of patients with minimal-change nephropathy (MCN) and focal and segmental glomerulosclerosis (FSGS) have not been confirmed in other papers. To assess its antiproteinuric effect in experimental animals we administered pefloxacine to rats with adriamycin nephropathy showing morphological changes resembling human minimal-change disease or focal segmental glomerulosclerosis, and clinically with full-blown nephrotic syndrome. Pefloxacine treatment was at least partially effective in preventing further increase of proteinuria in rats with adriamycin nephropathy. The mechanism of this effect remains unclear and deserves further studies concentrating on the glomerular cytokine network and glomerular production of reactive oxygen species.  相似文献   
995.
OBJECTIVE: Septo-optic dysplasia, which consists of the association of the hypoplasia of the optic nerves and the agenesis of the septum pellucidum, is frequently associated with deficiency of hypothalamic releasing factors. In Magnetic Resonance (MR) of these patients, anomalies in the form and size of the pituitary stalk, adenohypophysis and neurohypophysis are found. Some cases show schizencephaly and it has been proposed as an added component of the syndrome by some authors. This fact has been refuted by others. PATIENTS AND METHODS: We present the clinical and neuroanatomic revision of six children with septo-optic dysplasia studied by MR imaging over the last five years in our Department of Neuropediatrics. The aim was, that through the neuroembryological discussion of the morphopathological aspects of the patients, to determine the malformation and the time in which the injury, which was the underlying cause, occurred. RESULTS: From the six cases, in two only disruptive signs were evident with the optic nerves being affected asymmetrically, disruption of the corpus callosum, falx cerebri indemnity and effects in the cortex conformation. This was opposed to the dysgenic features in the other four cases which had no disruptive features. CONCLUSIONS: Our findings suggest that this entity could be the result of at least two different pathogenic processes, that is, a minor form of holoprosencephaly (dysgenesis) or a disruption which, therefore, occurs later in gestation.  相似文献   
996.
OBJECTIVE: The objective of the study is to evaluate the infectious complications of the ultrasound-guided prostate transrectal biopsy using two different antibiotic prophylactic regimes. Also, patient tolerance to ultrasound-guided transrectal biopsy is assessed. METHODS: Prospective study in 100 patients randomized to antibiotic prophylaxis with Pefloxacin (800 mg as single dose) versus Ciprofloxacin (250 mg/8 h/72 h). Tolerance data collection was done through completion of a questionnaire immediately after biopsy. RESULTS: Out of the 92 patients eligible for the study, 44 (48%) were assigned to Pefloxacin and 28 (52%) to Ciprofloxacin. In-house validation indicated both groups were matched. 90% patients showed good tolerance to the ultrasound technique and 81.5% patients to the transrectal biopsy. 31.5% patients presented no post-biopsy events; among the remaining only one patient (1%) required medical care and hospitalization. No patient had infectious complications. CONCLUSIONS: Prostate transrectal ultrasound and transrectal prostate biopsy was an approach well tolerated by most (81.5%) patients studied. Percentage of major complications was very small (1%), while post-biopsy events (haematuria, rectorrhage, etc) which do not require medical care should be considered not as complications but as effects intrinsic to the approach itself. Antibiotic prophylaxis whether with Pefloxacin or Ciprofloxacine was highly effective, although Pefloxacin is preferred due to its single dose administration and lower cost.  相似文献   
997.
OBJECTIVE: To review serious childhood injuries provoked by tractors in our country and to propose adequate preventative strategies. PATIENTS AND METHODS: Clinical data of eleven children admitted to our unit due to a tractor related accident have been evaluated. RESULTS: The majority of the events occurred in males and during the summer months, resulting in polytraumatisms with the abdominal region affected in most cases. Mortality was very high (64%). CONCLUSIONS: Accidents with tractors are a major preventable morbimortality factor in rural areas. Several preventive strategies that could reduce the incidence and severity of these injuries are proposed.  相似文献   
998.
Menopause has often been described as a time of loss and decay in the lay and medical literature. The present research aims at defining women's perception of themselves and their health care needs in this period of life. Through a community-based sample of women, participative assessments were performed and their conclusions contrasted with the opinions of male and female gynecologists. Though both groups coincided concerning the relevance of loneliness, partnership, beauty and the "empty nest" syndrome, several items showed a marked difference between both groups. Gynecologists tended to perceive women as much more striving for an active sex-life, depressed, lacking projects for the future and worried about their health care than they actually were. Women, instead, stressed the relevance of menopause as a life crisis laden with opportunities for self-accomplishment and positive changes in life-style towards greater autonomy.  相似文献   
999.
The authors describe 9 patients with bipolar affective disorder associated with cerebrovascular lesions. Eight had negative family histories of affective disorders and late age at onset (after age 40) of manic-depressive symptoms. Only one, with positive family history of affective disorders, developed mood swings before age 40. Clinical subtypes of bipolar disorder and patterns of affective cycling in these stroke patients resembled those previously reported in functional bipolar disorder. Five patients had concurrent hyperkinetic movement disorders, and one depressed patient presented with unilateral left-sided parkinsonism that disappeared during a manic switch. In most patients, bipolar affective disorder was associated with right hemisphere lesions that involved subcortical and midline structures. Findings suggest that damage to frontal-basal ganglia-thalamocortical circuits by subcortical vascular lesions may simultaneously provoke disorders of movement and mood regulation.  相似文献   
1000.
Comparing the sensitivity of similar direct and indirect measures is proposed as the best way to provide evidence for unconscious learning. The authors apply this approach, first proposed by E. M. Reingold and P. M. Merikle (see record 1989-21201-001), to a choice reaction-time task in which the material is generated probabilistically on the basis of a finite-state grammar (A. Cleeremans, see record 93:127012). The data show that participants can learn about the structure of the stimulus material over training with the choice reaction-time task, but only to a limited extent - a result that is well predicted by the simple recurrent network model of A. Cleeremans and J. L. McClelland (see record 1992-00389-001). Participants can also use some of this knowledge to perform a subsequent generation task. However, detailed partial correlational analyses that control for knowledge as assessed by the generation task show that large effects of sequence learning are exclusively expressed through reaction time. This result suggests that at least some of this learning cannot be characterized as conscious. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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