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   1655篇
  免费   14篇
电工技术   2篇
综合类   1篇
化学工业   26篇
机械仪表   4篇
建筑科学   5篇
能源动力   3篇
轻工业   39篇
水利工程   6篇
无线电   14篇
一般工业技术   9篇
冶金工业   1549篇
自动化技术   11篇
  2021年   4篇
  2019年   3篇
  2018年   4篇
  2017年   2篇
  2016年   2篇
  2014年   5篇
  2013年   4篇
  2012年   2篇
  2011年   2篇
  2010年   13篇
  2009年   5篇
  2008年   3篇
  2007年   6篇
  2006年   2篇
  2005年   5篇
  2004年   7篇
  2003年   4篇
  2002年   5篇
  2001年   5篇
  2000年   3篇
  1999年   44篇
  1998年   494篇
  1997年   266篇
  1996年   183篇
  1995年   88篇
  1994年   77篇
  1993年   94篇
  1992年   14篇
  1991年   13篇
  1990年   21篇
  1989年   15篇
  1988年   16篇
  1987年   14篇
  1986年   14篇
  1985年   15篇
  1984年   1篇
  1982年   5篇
  1981年   10篇
  1980年   22篇
  1979年   1篇
  1978年   11篇
  1977年   50篇
  1976年   99篇
  1975年   5篇
  1974年   1篇
  1964年   2篇
  1961年   1篇
  1960年   1篇
  1955年   2篇
  1954年   1篇
排序方式: 共有1669条查询结果,搜索用时 15 毫秒
81.
There are few objective means by which disability caused by low back pain (LBP) can be quantified. The purpose of this study was to investigate the usefulness of motion measurements in the assessment of LBP. The motion characteristics of 138 LBP subjects were investigated, and the data compared with a previously published database of normal subjects. Values of range of motion and angular velocity were obtained for all subjects in each plane of motion. Analysis of these motion characteristics demonstrated significant differences (P < 0.0001) between the two populations; however both populations demonstrated considerable intersubject variation. Multiple regression analysis revealed that some of the variance in the LBP population was attributable to the underlying diagnosis. Patients with a spondylolisthesis tended to be hypermobile whilst those with spinal stenosis, disc prolapse or degenerative disc disease tended to be hypomobile. All diagnostic groups showed impairments in their velocity characteristics.  相似文献   
82.
AlphaKAP is a protein produced from a gene within the gene of the a isoform of calmodulin-dependent protein kinase II (CaM-kinase IIa). It consists of the association domain of CaM-kinase IIa and a highly hydrophobic amino-terminal stretch consisting of 25 amino acids which is absent from CaM-kinase IIalpha. We previously demonstrated that alphaKAP is an integral membrane protein by subcellular fractionation analysis [Sugai, R., Takeuchi, M., Okuno, S., and Fujisawa, H. (1996) J. Biochem. 120, 773-779], but the exact subcellular localization of alphaKAP was not well understood. Here we demonstrate that alphaKAP is localized on the nuclear membrane of COS-7 cells transiently expressing alphaKAP. The nuclear membrane and perinuclear small vesicles were immunostained with an antibody against a synthetic peptide corresponding to the carboxyl-terminal 15 amino acids of alphaKAP. In contrast to the intact alphaKAP, the mutant alphaKAP, from which the hydrophobic amino-terminal segment had been deleted, accumulated within nuclei. Thus, alphaKAP may function as an anchoring protein for CaM-kinase II and/or other proteins in the perinuclear membrane.  相似文献   
83.
OBJECTIVE: To determine the levels and correlates of maternal nutritional status. DESIGN: Cross-sectional maternal weight, height, and mid-upper arm circumference (MUAC) data were correlated with sociodemographic data. SETTING: Slums of Dhaka, Bangladesh. SUBJECTS: Weight, height and MUAC were collected from a representative sample of 2417 nonpregnant mothers. Socioeconomic data such as age, education, religion and household economic status was collected from 2048 mothers; data on reproductive experiences such as number of pregnancies and number of children born alive now dead was available from 1314 mothers; and both sets of data from 1185 mothers. METHODS: Using weight, height, MUAC and body mass index (BMI) data, the levels of maternal nutritional status were estimated. Bivariate and multivariate relationships of maternal nutritional status with socioeconomic and reproductive experiences variables were examined. RESULTS: Mothers' mean weight, height, MUAC and BMI were 41.8 kg, 148.8 cm, 232.5 mm, and 18.8 respectively. In multivariate regression analyses, mothers' weight, BMI and MUAC were significantly positively correlated with mothers' years of schooling (P < 0.05) and household economic status (P < 0.01). Mothers' height was significantly positively correlated with years of schooling (P < 0.05), but not with household economic status. Maternal height and weight were significantly negatively correlated with number of child deaths (P < 0.05). CONCLUSIONS: The findings suggest a possible inter-generational effect; thus, improvement of the nutritional status of girls of this generation would improve child survival in the next generation. This, however, will require complex and long-term planning. As an interim measure, shorter mothers should be targeted for appropriate antenatal and obstetric services.  相似文献   
84.
85.
The role of radical cystectomy as the standard treatment of localised infiltrating bladder malignancy is challenged by the development radiotherapy and chemotherapy combinations. The published studies are difficult to compare because of large differences in the patients selection criteria and in the assessment of local involvement (only clinical in combined treatment, based on pathology and therefore unquestionable in surgical series). The advantages of radical surgery are its precedence and a well-established technique, simplified follow-up procedures and seemingly higher survival rates acquired after 3 years. Conversely, the combination of radiotherapy and chemotherapy allows bladder preservation in about 40% of the patients (at 5 years), but only in 23% without bladder relapses. A complete initial endoscopic resection is the best and only prognostic factor of these results which nevertheless needs a very carefully and endless follows. The comparison of the quality of life achieved by both treatment modalities remains insufficiently documented.  相似文献   
86.
87.
The conditions of labour appear to favour the development of pleural effusion. The frequency of postpartum pleural effusion was investigated in this study using thoracic ultrasonography. Thirty one postpartum and 22 healthy nonpregnant women of the same age-group were examined, both supine and seated, via an intercostal approach. Seven of the 31 (23%) postpartum women had pleural effusion within 1-24 h of normal delivery. None of the nonpregnant women had pleural effusion. No correlation was found between postpartum pleural effusion and age, weight-gain during pregnancy, duration of labour, use of intravenous fluid, or oxytocin administration. Pleural effusion seems to be a common finding postpartum, but of no clinical significance.  相似文献   
88.
BACKGROUND: The obvious advantages of rapid arterial anastomoses have prompted the continuing search for more rapid anastomotic techniques to complement the standard sutured anastomosis. Nonpenetrating, arcuate-legged titanium vascular closure staple (VCS) clips were initially developed for microvascular anastomoses. The purpose of this study was to compare VCS clips with sutured arterial end-to-end anastomosis in larger vessels. METHODS: In 6 pigs, transacted iliac arteries were reanastomosed with VCS clips on one side and continuous 6-0 polypropylene suture on the other. RESULTS: The reconstruction time was 8.4+/-5.2 minutes for clip closure and 12.0+/-6.6 minutes for suture closure (P = 0.033). All vessels were patent half an hour after completing the anastomoses with no signs of early thrombosis. CONCLUSIONS: Arterial end-to-end anastomosis can be performed more rapidly with VCS clips than continuous sutures, and are potentially useful in situations where the clamp time of the vessel is critical.  相似文献   
89.
BACKGROUND AND PURPOSE: Our purpose was to evaluate the ability of transcranial color-coded Doppler sonography (TCCD) to 1) identify Guglielmi detachable coils (GDCs) within intracranial aneurysms, 2) show endovascular aneurysmal occlusion and patency of parent and branch arteries, 3) determine the flow velocities within parent arteries and major branches before and after treatment, and 4) assess persistence of aneurysmal occlusion. METHODS: The sonographic appearance of GDCs was established experimentally by TCCD (2 to 2.5 MHz), which was then performed in 40 patients with 43 aneurysms occluded by GDCs. The patency of parent arteries and major branches was assessed qualitatively and compared with the immediate posttherapeutic angiographic appearance in every patient. Flow velocities were selectively measured and compared before and after treatment in 21 parent arteries and 24 major branches. Follow-up TCCD studies performed in 26 patients were compared with angiographic (16 cases) and MR angiographic (10 cases) findings for signs of recanalization of the treated aneurysms. RESULTS: The GDCs were identified experimentally and in the patients as hyperechoic structures of the size and shape, and in the location of, the treated aneurysm in 41 of 43 cases. TCCD in accordance with angiography showed a lack of flow in 42 aneurysms and the presence of flow signal in one large aneurysm. Patency of the parent artery was shown in 40 aneurysms and in all branches. Follow-up TCCD showed the coils unchanged in 23 of 26 cases. In three large aneurysms, TCCD indicated recanalization and reappearance of a flow signal separate from the parent artery. CONCLUSION: TCCD is a reliable, noninvasive means to assess parent artery and major branch patency and to reveal a lack of hemodynamic compromise in the vicinity of aneurysms after endovascular therapy. On follow-up examinations, TCCD was able to detect signs of aneurysmal recanalization.  相似文献   
90.
In a 4-year study we examined the longitudinal effects of deinstitutionalization programs on those who remain in institutions being downsized. Individual outcomes investigated were community access, social activities, community inclusion, family relationships, and choice. Effects of residential relocation on individual outcomes such as adaptive behavior were evaluated and total daily per-person expenditure on institutional services for participants was determined. Downsizing was associated with decreased community integration but no change in most other outcomes. Availability of therapy services fell over time, and individuals experienced many residential and day program moves within the institution. Per person expenditure on services increased substantially. Finally, no significant changes in adaptive behavior were associated with intrainstitutional moves.  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