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   8003篇
  免费   216篇
  国内免费   24篇
电工技术   80篇
综合类   8篇
化学工业   1207篇
金属工艺   195篇
机械仪表   180篇
建筑科学   131篇
矿业工程   7篇
能源动力   445篇
轻工业   558篇
水利工程   73篇
石油天然气   88篇
武器工业   2篇
无线电   674篇
一般工业技术   1296篇
冶金工业   2646篇
原子能技术   62篇
自动化技术   591篇
  2023年   102篇
  2022年   202篇
  2021年   235篇
  2020年   211篇
  2019年   186篇
  2018年   276篇
  2017年   236篇
  2016年   223篇
  2015年   150篇
  2014年   217篇
  2013年   459篇
  2012年   239篇
  2011年   297篇
  2010年   218篇
  2009年   228篇
  2008年   223篇
  2007年   170篇
  2006年   168篇
  2005年   103篇
  2004年   88篇
  2003年   97篇
  2002年   76篇
  2001年   57篇
  2000年   72篇
  1999年   133篇
  1998年   792篇
  1997年   445篇
  1996年   367篇
  1995年   242篇
  1994年   182篇
  1993年   183篇
  1992年   81篇
  1991年   96篇
  1990年   83篇
  1989年   78篇
  1988年   72篇
  1987年   73篇
  1986年   79篇
  1985年   100篇
  1984年   48篇
  1983年   55篇
  1982年   61篇
  1981年   63篇
  1980年   60篇
  1979年   44篇
  1978年   30篇
  1977年   65篇
  1976年   147篇
  1974年   28篇
  1973年   23篇
排序方式: 共有8243条查询结果,搜索用时 31 毫秒
41.
The present study assesses the endocrinological, endometrial histology and vaginal ultrasound profiles of nomegestrol acetate subdermal implant users at varying times after insertion. Follicle stimulatory hormone, luteinizing hormone, oestradiol, progesterone, vaginal ultrasound assessment of the ovaries and the histological dating of the endometrium were serially assessed for a period of 50 days immediately after the insertion, and after at 6 months and 12 months of use. The endocrinological results of this prospective observational clinical trial indicated that 75% of the cycles across the study period in Uniplant users were anovulatory, 63% showing development of a persistent non-luteinized follicle. Anovulatory cycles devoid of follicular development were seen primarily in the first months after Uniplant insertion. Ovulatory cycles represented 25% of the Uniplant cycles. Inadequate luteal phase or disregulation of follicular growth was a common feature of ovulatory cycles. In conclusion, these findings suggest that the contraceptive mechanisms of a single nomegestrol acetate subdermal implant involve prevention of follicular growth, development of a persistent non-luteinized follicle, inadequate luteal phase and disruption of the endometrial architecture.  相似文献   
42.
A comparison of four different commercial immunometric thyrotropin (TSH) assays (Amerlite R TSH-30 Ultrasensitive assay from Kodak, BeriLux R hTSH from Behring Werke, Delfia R hTSH Ultra from Wallac and IMX R Ultrasensitive hTSH from Abbott) was made by measuring serum TSH in 81 consecutive patients referred to hospital for various reasons with a serum TSH less than 0.8 mlU/l in the IMX assay. The analytical and functional assay sensitivities of each of the assays were analysed. Even though three of the methods had a sensitivity corresponding to third generation assays, we could only demonstrate an overall agreement of serum TSH when comparing two of the kits. The measurements in Delfia Ultra and Berilux showed good agreement (P = 0.7, paired t-test and bias = 0.003 mIU/l), while the comparisons between the other assays showed different measurements (P < 0.00001, paired t-test and bias more than 0.07 mIU/l). Differences in the calibrators used in the assays might explain some of the discrepancy, although all methods were calibrated according to the same international standard. Also, differences in the specificity of the TSH monoclonal antibodies used in the assays might be an evident explanation and further studies of the specificity of the monoclonal antibodies are needed. An international collaborative study to clarify reasons for the differences between the TSH assays and to standardize the measurements is recommended.  相似文献   
43.
44.
45.
46.
47.
Twenty diabetic patients with neuropathy underwent clinical and neurophysiological evaluation together with a detailed morphometric assessment of capillary pathology in endoneurial and epineurial microvascular beds of the sural nerve. Morphological data were compared with ten non-diabetic control subjects. There were no significant differences in control subjects between basement membrane area, endothelial cell area, endothelial cell profile number or luminal area of endoneurial when compared with epineurial capillaries. In contrast, when compared with epineurial capillaries, endoneurial capillaries from diabetic patients demonstrated a significant increase in basement membrane (p < 0.001) and endothelial cell (p < 0.001) area and a significant reduction in luminal area (p < 0.001). There was no significant difference in endothelial cell profile number between endoneurial and epineurial capillaries amongst diabetic patients. Previous studies have demonstrated a good correlation between the degree of microangiopathy and measures of neuropathic severity. In the present study increased endoneurial capillary basement membrane area was significantly related to reduced peroneal nerve conduction velocity (p < 0.001), myelinated fibre density (p < 0.001) and elevated vibration (p < 0.05) and thermal (p < 0.001) perception. Increased endothelial cell area and reduced luminal size were related to a reduced peroneal nerve conduction (p < 0.05, p < 0.01, respectively), reduced myelinated fibre density (p < 0.05, p < 0.01) and elevated thermal perception (p < 0.05, p < 0.001). Epineurial capillary basement membrane, endothelial cell and luminal area failed to relate to measures of neuropathic severity.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
48.
49.
The Mus terricolor complex displays a stable homozygous arrangement of autosomal heterochromatin variations in the form of accretion of definitive autosomal short arms among three nonoverlapping populations, in concert with an expeditious evolutionary differentiation into three chromosomal species: M. terricolor I, II, and III. In contrast to the highly conservative M. musculus-like chromosomes in the coexisting sibling species, M. booduga, reshuffling and differentiation of centric heterochromatin has occurred in harmony with a revision of centric configurations, resulting in acrocentric and submetacentric autosomes. The chromosomal distribution of the prevalent vertebrate telomeric sequence (TTAGGG)n was examined by fluorescence in situ hybridization to metaphase cells of M. terricolor I, II, and III. An unusual centric organization of internal telomeric sequences was detected in all the submetacentric and acrocentric autosomes. An auxiliary role of these presumably fragile, recombinogenic telomeric sequences in the evolutionary revision of centric configurations in the terricolor complex is hypothesized.  相似文献   
50.
The 5 Kd (MW), retinoic acid responsive thymosin beta-10 protein is expressed at relatively high levels in embryonic tissues, and its mRNA is abundant in a variety of tumors and tumor cell lines. Recently this protein (together with other members of the same protein family) was found to be a major intracellular G-actin binding protein. In the present study, plasmid-driven overexpression of thymosin beta-10 gene results in increased susceptibility of permanently transfected fibroblasts to undergo apoptosis. Conversely, knockout of the endogenous gene via overexpression of the antisense mRNA inhibited cell death induced by TNF-alpha and calcium ionophore A23187. Differential expression of thymosin beta-10 influenced cell proliferation, cell morphology, and expression/distribution of the antiapoptotic protein bcl-2. The presence of increased cytoplasmic thymosin beta-10 precipitated significant disruption of phalloidin-stained actin stress fibers while knockout of thymosin expression promoted F-actin assembly. These and other observations suggest that thymosin beta-10 (a) plays a significant and possibly obligatory role in cellular processes controlling apoptosis possibly by acting as an actin-mediated tumor suppressor, (b) perhaps functions as a neoapoptotic influence during embryogenesis, and (c) may mediate some of the pro-apoptotic anticancer actions of retinoids.  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