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   2838篇
  免费   8篇
电工技术   14篇
综合类   4篇
化学工业   118篇
金属工艺   35篇
机械仪表   22篇
建筑科学   21篇
矿业工程   9篇
能源动力   21篇
轻工业   47篇
水利工程   12篇
石油天然气   4篇
无线电   77篇
一般工业技术   120篇
冶金工业   2247篇
原子能技术   17篇
自动化技术   78篇
  2021年   16篇
  2020年   6篇
  2019年   6篇
  2018年   6篇
  2016年   8篇
  2014年   11篇
  2013年   30篇
  2012年   18篇
  2011年   25篇
  2010年   21篇
  2009年   20篇
  2008年   25篇
  2007年   29篇
  2006年   19篇
  2005年   31篇
  2004年   19篇
  2003年   12篇
  2002年   25篇
  2001年   21篇
  2000年   16篇
  1999年   77篇
  1998年   712篇
  1997年   372篇
  1996年   222篇
  1995年   135篇
  1994年   114篇
  1993年   142篇
  1992年   39篇
  1991年   30篇
  1990年   56篇
  1989年   58篇
  1988年   38篇
  1987年   36篇
  1986年   47篇
  1985年   33篇
  1984年   15篇
  1983年   17篇
  1982年   17篇
  1981年   29篇
  1980年   26篇
  1979年   9篇
  1978年   13篇
  1977年   47篇
  1976年   111篇
  1975年   11篇
  1974年   9篇
  1973年   8篇
  1972年   11篇
  1971年   5篇
  1970年   5篇
排序方式: 共有2846条查询结果,搜索用时 24 毫秒
31.
32.
BACKGROUND: Desflurane anesthesia can produce cerebral metabolic depression and increase cerebral blood flow. We evaluated the effect of desflurane on brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2) and pH during neurosurgery. METHODS: Following a craniotomy, the dura was opened and a Paratrend 7 sensor, which measures PO2, PCO2, pH and temperature, was inserted into brain tissue. In 6 control patients in group 1, anesthesia was maintained constant with 3% end-tidal desflurane over 60 min, including a 30-min stabilization period. In group 2, 9 patients were ventilated with 3% desflurane under baseline conditions. After a 30-min stabilization period, baseline tissue gases and pH were measured and end-tidal desflurane was increased to 6% and then 9% for 15-min intervals. Mean arterial pressure (MAP) was maintained with intravenous phenylephrine. RESULTS: Under baseline conditions, cardiovascular and brain tissue measures were similar between the 2 groups. Increasing end-tidal desflurane from 3% to 9% produced burst-suppression EEG in all patients and significantly increased tissue PO2 and pH and decreased PCO2. No parameters changed significantly in the control group during steady-state anesthesia. CONCLUSION: These results show that 9% desflurane can improve brain tissue metabolic status before temporary brain artery occlusion if cerebral perfusion pressure is maintained. This may be particularly important in patients with symptoms of ischemia before surgery.  相似文献   
33.
34.
We employed an anatomically realistic three-dimensional finite-element model to explore several biomechanical variables involved in coring or bone-grafting of a segmentally necrotic femoral head. The mechanical efficacy of several variants of these procedures was indexed in terms of their alteration of the stress:strength ratio in at-risk necrotic cancellous bone. For coring alone, the associated structural compromise was generally modest, provided that the tract did not extend near the subchondral plate. Cortical bone-grafting was potentially of great structural benefit for femoral heads in which the graft penetrated deeply into the superocentral or lateral aspect of the lesion, ideally with abutment against the subchondral plate. By contrast, central or lateral grafts that stopped well short of the subchondral plate were contraindicated biomechanically because they caused marked elevations in stress on the necrotic cancellous bone. Calculated levels of stress were relatively insensitive to variations in the diameter of the graft.  相似文献   
35.
Designing a Production Line to Maximize Profit   总被引:1,自引:0,他引:1  
The relationship between profitability and efficiency in a production line is discussed at length for the continuous production model. We prove that a solution which maximizes efficiency will not necessarily maximize profit. Several useful relationships between profitability and efficiency are developed which can greatly enhance computational efficiency. A solution procedure is developed which will determine the optimal number of work stations by maximizing an assumed profit function. An example is provided to illustrate these relationships and the entire solution procedure.  相似文献   
36.
In this paper a set of techniques for improving the performance of the fast Fourier transform (FFT) algorithm on modern vector-oriented supercomputers is presented. Single-processor FFT implementations based on these techniques are developed for the CRAY-2 and the CRAY Y-MP, and it is shown that they achieve higher performance than previously measured on these machines. The techniques include (1) using gather/scatter operations to maintain optimum length vectors throughout all stages of small-to medium-sized FFTs, (2) using efficient radix-8 and radix-16 inner loops, which allow a large number of vector loads/stores to be overlapped, and (3) prefetching twiddle factors as vectors so that on the CRAY-2 they can later be fetched from local memory in parallel with common memory accesses. Performance results for Fortran implementations using these techniques demonstrate that they are faster than Cray's library FFT routine CFFT2. The actual speedups obtained, which depend on the size of the FFT being computed and the supercomputer being used, range from about 5 to over 300%.  相似文献   
37.
38.
39.
The supernatant (CM) of long-term bone marrow culture (LTBMC) contains colony promoting activity (CPA) which does not have granulocyte-macrophage (GM) colony-stimulating activity but which enhances GM-colony formation in the presence of CSF. CPA is different from IL-1, IL-3 and GM, G-, and M-CSF. Since CPA-containing LTBMC-CM always contains a substantial level of IL-6, CPA was thought to be similar to IL-6. In the present study, we found that LTBMC with a particular batch of horse serum produced IL-6 without a corresponding production of CPA. Addition of IL-6 to GM-colony assay system in the presence of GM-CSF did not enhance the colony formation. LTBMC-CM did not stimulate proliferation nor differentiation of mast cell progenitors. Anti-IL-6 antibodies suppressed IL-6 activity, but not CPA. These results indicate that CPA is a novel factor distinct from IL-1, IL-3, G-, M-, GM-CSF, IL-6 and SCF (c-kit ligand).  相似文献   
40.
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