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   4018篇
  免费   117篇
  国内免费   17篇
电工技术   241篇
综合类   3篇
化学工业   985篇
金属工艺   85篇
机械仪表   101篇
建筑科学   102篇
能源动力   154篇
轻工业   371篇
水利工程   14篇
石油天然气   2篇
无线电   317篇
一般工业技术   733篇
冶金工业   530篇
原子能技术   150篇
自动化技术   364篇
  2023年   24篇
  2022年   51篇
  2021年   91篇
  2020年   37篇
  2019年   44篇
  2018年   92篇
  2017年   65篇
  2016年   121篇
  2015年   60篇
  2014年   115篇
  2013年   220篇
  2012年   190篇
  2011年   257篇
  2010年   179篇
  2009年   202篇
  2008年   230篇
  2007年   166篇
  2006年   153篇
  2005年   136篇
  2004年   128篇
  2003年   112篇
  2002年   118篇
  2001年   80篇
  2000年   64篇
  1999年   85篇
  1998年   206篇
  1997年   145篇
  1996年   92篇
  1995年   82篇
  1994年   72篇
  1993年   74篇
  1992年   38篇
  1991年   31篇
  1990年   31篇
  1989年   32篇
  1988年   27篇
  1987年   25篇
  1986年   32篇
  1985年   48篇
  1984年   24篇
  1983年   28篇
  1982年   13篇
  1981年   9篇
  1980年   15篇
  1978年   17篇
  1977年   16篇
  1976年   23篇
  1975年   12篇
  1974年   10篇
  1973年   8篇
排序方式: 共有4152条查询结果,搜索用时 11 毫秒
991.
Sasaki O  Hirakubo S  Choi S  Suzuki T 《Applied optics》2012,51(13):2429-2435
The positions of the front and rear surfaces of a silicon dioxide film with 4 μm thickness is measured with a novel and simple method in which both amplitude and phase of a sinusoidal wave signal corresponding to one optical path difference of a reflecting surface is utilized in a linear wavenumber-scanning interferometer. For this utilization, the scanning width and the position of the reference mirror are adjusted exactly to distinguish the two sinusoidal waves corresponding to the two surfaces of the film. The scanning width of the wavenumber and wavelength of the light source are 0.326×10(-3) nm(-1) and 140 nm, respectively.  相似文献   
992.
The radioactivation of linear accelerator components for radiation therapy is interest for radiation protection in general, and particularly, when decommissioning these structures. The energy spectra of gamma rays emitted from the heads of two accelerator models, EXL-15SP and Clinac iX, after 10-MeV X-ray irradiation, were measured using a high-purity germanium semiconductor survey meter. After spectrum analyses, activities of (24)Na, (28)Al, (54)Mn, (56)Mn, (57)Ni, (58)Co, (60)Co, (64)Cu, (65)Zn, (122)Sb, (124)Sb, (181)W, (187)W, (196)Au, and (198)Au were detected. One centimetre deep dose-equivalent rate of the heads of the linear accelerator was measured using the survey meter. The dose rate decreased to ~10 % of its initial rate after 1 week. Long-term activations were few, the radioactivity level was low, and a cooling time of several days was effective for reducing dose rate to an acceptable level for decommissioning.  相似文献   
993.
994.
995.
We have hypothesized that T cell cytokines participate in the pathogenesis of graft arterial disease (GAD). This study tested the consequences of IFN-gamma deficiency on arterial and parenchymal pathology in murine cardiac allografts. Hearts from C-H-2(bm12)KhEg (bm12, H-2(bm12)) were transplanted into C57/B6 (B6, H-2(b)), wild-type, or B6 IFN-gamma-deficient (GKO) recipients after immunosuppression by treatment with anti-CD4 and anti-CD8 mAbs. In wild-type recipients, myocardial rejection peaked at 4 wk, (grade 2. 1+/-0.3 out of 4, mean+/-SEM, n = 9), and by 8-12 wk evolved coronary arteriopathy. At 12 wk, the GAD score was 1.4+/-0.3, and the parenchymal rejection grade was 1.2+/-0.3 (n = 8). In GKO recipients of bm12 allografts, myocardial rejection persisted at 12 wk (grade 2.5+/-0.3, n = 6), but no GAD developed (score: 0.0+/-0.0, n = 6, P < 0.01 vs. wild-type). Mice treated with anti-IFN-gamma mAbs showed similar results. Isografts generally showed no arterial changes. In wild-type recipients, arterial and parenchymal cells showed increased MHC class II molecules, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 compared to normal or isografted hearts. The allografts in GKO recipients showed attenuated expression of these molecules (n = 6). Thus, development of GAD, but not parenchymal rejection, requires IFN-gamma. Reduced expression of MHC antigens and leukocyte adhesion molecules may contribute to the lack of coronary arteriopathy in hearts allografted into GKO mice.  相似文献   
996.
997.
Nine children sustained a second fracture of the distal humerus after union of an ipsilateral supracondylar fracture which had healed with cubitus varus. There were eight boys and one girl with a mean age of five years (1 to 8) at the time of the second fracture which occurred at a mean of 1.5 years after the first. In all patients, the second fracture was an epiphyseal injury of the distal humerus, either associated with a fracture of the lateral metaphysis below the site of the previous supracondylar fracture, or a fracture-separation of the entire distal humeral epiphysis. This suggests that the physis and epiphysis tend to be more subject to injury than the metaphysis of the distal humerus in children who have had a previous supracondylar fracture with varus malunion.  相似文献   
998.
The solution structure of a thermostable cytochrome c-552 from a thermophilic hydrogen oxidizing bacterium Hydrogenobacter thermophilus was determined by proton nuclear magnetic resonance spectroscopy. Twenty structures were calculated by the X-PLOR program on the basis of 902 interproton distances, 21 hydrogen bonds, and 13 torsion angle constraints. The pairwise average root-mean-square deviation for the main chain heavy atoms was 0.91 +/- 0.11 A. The main chain folding of the cytochrome c-552 was almost the same as that of Pseudomonas aeruginosa cytochrome c-551 that has 59% sequence identity to the cytochrome c-552 but is less thermostable. We found several differences in local structures between the cytochromes c-552 and c-551. In the cytochrome c-552, aromatic-amino interactions were uniquely formed between Arg 35 and Tyr 32 and/or Tyr 41, the latter also having hydrophobic contacts with the side chains of Tyr 32, Ala 38, and Leu 42. Small hydrophobic cores were more tightly packed in the cytochrome c-552 because of the occupancies of Ala 5, Met 11, and Ile 76, each substituted by Phe 7, Val 13, and Val 78, respectively, in the cytochrome c-551. Some of these structural differences may contribute to the higher thermostability of the cytochrome c-552.  相似文献   
999.
We present our experience of transcutaneous truncal anaesthesia of the maxillary nerve in association with transmucosal anaesthesia of the sphenopalatine ganglion in surgically assisted rapid maxillary expansion. Twelve patients with a skeletal transverse discrepancy of the maxilla were treated in our department from 1994 to 1995. Maxillary transcutaneous nerve block was done with a Quincke 8 cm spinal needle together with transmucosal anaesthesia of the sphenopalatine ganglion. Mepivacaine without adrenaline and sodium bicarbonate 1/10 was used for truncal anaesthesia and lidocaine-prilocaine cream for transmucosal anaesthesia. A Le Fort I osteotomy, lateral nasal wall osteotomy, pterygomaxillary osteotomy, and a palatal osteotomy were done for all patients before the maxillary expansion. Total anaesthesia of the maxillary area facilitated the operations and appreciably reduced the amount of postoperative pain. The ease of achieving effective anaesthesia before and after operation and the absence of side-effects make this form of anaesthetic particularly useful in surgically assisted rapid maxillary expansion.  相似文献   
1000.
A perceptual image can be recalled from memory without sensory stimulation. However, the neural origin of memory retrieval remains unsettled. To examine whether memory retrieval can be regulated by top-down processes originating from the prefrontal cortex, a visual associative memory task was introduced into the partial split-brain paradigm in monkeys. Long-term memory acquired through stimulus-stimulus association did not transfer via the anterior corpus callosum, a key part interconnecting prefrontal cortices. Nonetheless, when a visual cue was presented to one hemisphere, the anterior callosum could instruct the other hemisphere to retrieve the correct stimulus specified by the cue. Thus, although visual long-term memory is stored in the temporal cortex, memory retrieval is under the executive control of the prefrontal cortex.  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