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   524篇
  免费   16篇
  国内免费   3篇
电工技术   8篇
化学工业   142篇
金属工艺   24篇
机械仪表   6篇
建筑科学   9篇
能源动力   11篇
轻工业   31篇
水利工程   6篇
无线电   52篇
一般工业技术   69篇
冶金工业   140篇
原子能技术   7篇
自动化技术   38篇
  2023年   5篇
  2022年   9篇
  2021年   16篇
  2020年   4篇
  2019年   7篇
  2018年   7篇
  2017年   3篇
  2016年   10篇
  2015年   6篇
  2014年   21篇
  2013年   20篇
  2012年   20篇
  2011年   25篇
  2010年   15篇
  2009年   23篇
  2008年   26篇
  2007年   11篇
  2006年   12篇
  2005年   19篇
  2004年   13篇
  2003年   13篇
  2002年   12篇
  2001年   7篇
  2000年   12篇
  1999年   10篇
  1998年   60篇
  1997年   40篇
  1996年   21篇
  1995年   15篇
  1994年   18篇
  1993年   8篇
  1992年   3篇
  1991年   3篇
  1990年   7篇
  1989年   4篇
  1988年   3篇
  1987年   3篇
  1986年   5篇
  1985年   2篇
  1984年   3篇
  1983年   3篇
  1982年   2篇
  1981年   1篇
  1979年   2篇
  1978年   3篇
  1977年   2篇
  1976年   7篇
  1972年   2篇
排序方式: 共有543条查询结果,搜索用时 0 毫秒
121.
To investigate a possible association between G-proteins and presenilin-1 (PS-1), a series of glutathione S-transferase-fusion proteins containing portions of PS-1 were prepared and used in vitro in binding experiments with tissue and recombinant G-proteins. The results demonstrate that the 39 C-terminal amino acids of PS-1 selectively bind the brain G-protein, Go. Addition of guanosine 5'-3-O-(thio)triphosphate promoted Go dissociation from PS-1, indicating that this domain mimics the function of G-protein-coupling domains found in receptors. The 39-amino acid synthetic polypeptide activated Go in a magnesium ion-dependent manner. Physical interaction of full-length PS-1 and Go was also demonstrated. Following transfection of Goalpha and N-terminally FLAG-tagged PS-1 in COS-7 cells, Go was immunoprecipitated by FLAG antibodies. In addition, endogenous PS-1 and Goalpha were colocalized immunocytochemically in human glioma cell lines. The results indicate that PS-1 regulates Go activities in living cells.  相似文献   
122.
123.
124.
125.
When the DFT (discrete Fourier transform) is used as a method for obtaining NMR (nuclear magnetic resonance) spectrum, resolution of the obtained NMR spectrum depends clearly on spin-spin relaxation times of the nucleus and the sampled number of NMR signal. That is, the NMR spectrum is affected by decay of NMR signal due to the relaxation times and errors associated with discrete approximation of NMR spectrum. As a results, its resolution is degraded and the spectrum disagrees with the density distribution of the nucleus. In the present paper, we propose a new NMR spectrum estimation method for reducing their effects, demonstrating a high resolution NMR spectrum which is closer to the density distribution than that of the DFT. The proposed method is derived from applying the Kalman filter or the recursive least-square method to a NMR signal model based on Bloch equation. Under various conditions, the proposed method is compared with the DFT using a proton 1H NMR signal observed from mayonnaise in a 2 [T] static magnetic field. The results show that if spin-spin relaxation times are known previously, the proposed method can provide a higher resolution NMR spectrum than the DFT. In addition, it is shown that the method can reduce the discrete approximation errors of NMR spectrum. Finally, we demonstrate that if frequency components of sources of NMR signal are present in a limited range in frequency domain of interest, the method can magnify NMR spectrum with a sampling time and interval fixed.  相似文献   
126.
Class I major histocompatibility complex (MHC) antigens of higher eukaryotes play a crucial role in the recognition of human cytomegalovirus (HCMV)-infected cells by cytotoxic T lymphocytes. In the present study, we have demonstrated that HCMV infection resulted in a marked reduction in the surface expression of class I MHC antigens on human embryonic lung fibroblasts (HEL). Even when HCMV-infected HEL were cultured in the presence of 9-(1,3-dihydroxy-2-propoxymethyl)-guanine (DHPG), the reduction was observed to the same extent, indicating that HCMV DNA synthesis was not required for this phenomenon. However, immunoprecipitation studies have shown that there was no significant reduction in the synthesis of either the heavy chain or the light chain of class I MHC antigens after HCMV infection. In addition, Western blotting studies have revealed that the total amount of the antigens was almost unaltered after HCMV infection. These results suggest that the reduction in the cell surface expression of class I MHC antigens is due to some defect occurring post-translationally, most likely at the level of the correct complex formation and/or the intracellular transport of class I MHC antigens.  相似文献   
127.
A questionnaire was used to assess the quality of life (QOL) of forty-two outpatients with prostate cancer. Most of the patients were old, so reduced physical comfort was correlated with bodily factors other than those caused by prostate cancer. Many patients with progressive disease reported disease--and treatment--related physical problems that tended to be correlated to the extent of the disease. Many patients treated with female hormones complained of breast induration or discomfort. Patient's sexual life was impaired remarkably. Our treatment for cancer pain would be especially inadequate to cancer pain relief. We must give positive aid to cancer pain relief from now on. Most patients lost sexual interest after developing prostate cancer. Only three of the patients were able to have sexual intercourse. Some of the patients who underwent radical prostatectomy suffered from urinary incontinence after the operation. Thus, the patients' social life was remarkably affected for relative good performance status. Many patients lived only with other elderly individuals. Therefore, it is also important to manage patients in the light of their living environment.  相似文献   
128.
Smyth line (SL) chickens develop a spontaneous, autoimmune, posthatch loss of pigment cells (vitiligo) in regenerating feather tissue. Smyth line vitiligo (SLV) is associated with lymphocyte infiltrations prior to and throughout the development of the disorder. It was the purpose of this study to determine the type, relative amounts, and proportions of pulp-infiltrating lymphocytes at various times throughout the growth of regenerating feathers. Feathers were plucked from 8-week-old chickens with and without SLV. Feather pulp cell suspensions were prepared when the regenerating feathers were 2, 3, 4, and 6 weeks of age. Cells were fluorescently labeled using a panel of mouse monoclonal antibodies specific for chicken lymphocytes. Both T and B cells infiltrated the feather pulp of chickens with SLV. T cell levels remained elevated throughout the 6 weeks of feather growth, while B cell levels steadily declined to control levels over the same time. The pulp-infiltrating cells were primarily T cells with an alphabeta T cell receptor expressing the Vbeta1 gene (TCR2+). The ratio between CD4+ and CD8+ cells was 1.42 and 0.75 in 2- and 6-week-old regenerating feathers from chickens with autoimmune SLV, respectively. In non-vitiliginous chickens this ratio was always near 1. These data suggest that TCR2+ T cells play an important role in SLV. CD4+ cells may play a recruiting/activating role, whereas CD8+ cells may have cytotoxic activity specifically directed against melanocytes. Additionally, this is the first report demonstrating the infiltration of B cells into the feather pulp of vitiliginous chickens. These B cells may directly/indirectly contribute to melanocyte destruction in SLV.  相似文献   
129.
130.
STUDY DESIGN: Radiographs and charts of 61 patients sustaining cervical spine trauma were studied prospectively to determine the incidence of vertebral artery injuries and possible correlative factors. Statistical analysis was conducted using chi-square testing of a two-way classification system. OBJECTIVES: To elucidate the incidence of vertebral artery injuries associated with cervical spine trauma, and to determine the value of various factors in predicting the existence of a vertebral artery injury. SUMMARY OF BACKGROUND DATA: During a 7-month period, 61 patients (41 male patients, 20 female; average age, 40.3 years) with cervical spine trauma were studied. METHODS: All patients admitted to the authors' hospital with cervical spine injuries underwent magnetic resonance imaging and magnetic resonance angiography of their cervical spine. All magnetic resonance angiographies were examined for vertebral artery injury. Data on demographics and the injury were recorded. RESULTS: Complete disruption of blood flow through the vertebral artery was demonstrated by magnetic resonance angiography in 12 of the 61 patients (19.7%). Ten of the 12 patients (83%) had either flexion distraction or flexion compression injuries. Age, sex, mechanism of injury, neurologic impairment, and associated injuries were not statistically significant in predicting the presence of a vertebral vessel occlusion. CONCLUSION: The findings in this study may support the need for vertebral vessel evaluation in selective patients, particularly those with flexion injuries and with neurologic symptoms consistent with vertebral artery insufficiency syndrome that do not correlate with the presenting bone and soft-tissue injuries.  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