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   311篇
  免费   0篇
  国内免费   2篇
电工技术   28篇
综合类   1篇
化学工业   32篇
金属工艺   16篇
机械仪表   3篇
建筑科学   4篇
能源动力   13篇
轻工业   31篇
无线电   21篇
一般工业技术   35篇
冶金工业   96篇
原子能技术   25篇
自动化技术   8篇
  2023年   1篇
  2022年   1篇
  2021年   5篇
  2020年   2篇
  2019年   1篇
  2017年   2篇
  2016年   1篇
  2014年   4篇
  2013年   10篇
  2012年   9篇
  2011年   13篇
  2010年   7篇
  2009年   5篇
  2008年   9篇
  2007年   11篇
  2006年   15篇
  2005年   16篇
  2004年   12篇
  2003年   13篇
  2002年   5篇
  2001年   6篇
  2000年   7篇
  1999年   9篇
  1998年   31篇
  1997年   22篇
  1996年   10篇
  1995年   12篇
  1994年   7篇
  1993年   7篇
  1992年   4篇
  1991年   7篇
  1990年   2篇
  1989年   1篇
  1988年   5篇
  1987年   11篇
  1986年   4篇
  1985年   3篇
  1983年   1篇
  1982年   1篇
  1981年   5篇
  1980年   6篇
  1977年   1篇
  1976年   3篇
  1975年   2篇
  1973年   3篇
  1971年   1篇
排序方式: 共有313条查询结果,搜索用时 15 毫秒
61.
Regulation of GH secretion from phytohemagglutinin (PHA)-stimulated lymphocytes was investigated in six normal subjects. Peripheral blood mononuclear cells were incubated with PHA (10 micrograms/mL) in the presence of various amounts of recombinant human GH (0-100 ng/L) and/or recombinant human insulin-like growth factor-I (0-1000 micrograms/L), and the secreted GH was measured by a highly sensitive enzyme immunoassay. PHA-stimulated lymphocytes secreted immunoreactive GH in all subjects (13.6 +/- 2.4 ng/L). Exogenous GH up-regulated the GH secretion in a dose-dependent manner, while IGF-I did not affect either basal GH secretion or the up-regulation by exogenous GH. These findings suggest a difference in the regulation of GH secretion between endocrine and immune systems.  相似文献   
62.
This paper describes optical transmitter and receiver modules for package-to-package interconnection in broadband switching networks such as an asynchronous transfer mode switch fabric. These modules, which include the multiplexer and demultiplexer, can reduce the number of connections and the problem of skew between links. Five-channel optical transmitter and receiver modules were fabricated and demonstrated at 2.8 Gbit/s with a power dissipation of 4.5 W per channel. Moreover, temperature-insensitive optical interconnection was successfully demonstrated by driving a laser with a constant bias current over the threshold and by deducting the optical signal offset. The output power of the transmitter module was -4.2 dBm. Nonuniformity of the transmitter output powers across the range of optical channels was <2.1 dB. Receiver sensitivity for a bit error rate of 10-11 was -9.3 dBm. Nonuniformity of the receiver sensitivities was <1.5 dB. The power penalty of the receiver sensitivity due to crosstalk was 1 dB. The connection distance was >250 m  相似文献   
63.
Racemic 3-methyl, 2-ethyl, 2-bromo, and 2-trimethylsilyl derivatives of formylferrocene were kinetically resolved by enantioselective reduction with a fermenting baker's yeast. Moreover, 2-methyl, 3-methyl, 2-ethyl, 2-bromo, and 2-trimethylsilyl derivatives of hydroxymethylferrocene were optically resolved with lipases by transesterification using vinyl esters.  相似文献   
64.
Structure and formation process of (K,Na)-clinoptilolite   总被引:1,自引:0,他引:1  
In order to synthesize (K,Na)-clinoptilolite, a (K,Na)-aluminosilicate slurry with a seed crystal was stirred at 30 °C for 4 days and then hydrothermally treated under homogeneous mixing conditions at 120 °C for 14 days. The Si/Al:(Na+K)/Si:K/(Na+K):H2O/Al molar ratio of the starting materials was 6.0:0.42:0.5:52.5. The formation process of (K,Na)-clinoptilolite was investigated by a variety of techniques. When the materials were hydrothermally treated up to 6 days, amorphous (K,Na)-aluminosilicate was formed. After the hydrothermal treatment for 8 days, irregular particles due to the amorphous (K,Na)-aluminosilicate disappeared and plate-like particles of (K,Na)-clinoptilolite were formed, indicating that the amorphous aluminosilicate crystallized as clinoptilolite. In addition, (Na+K)/Al molar ratio in the materials varied from 1.2 to 1.0, accompanying the decrease of cation exchange capacity. During the crystallization, the wavenumber of external linkages of TO bonds shifted to higher values, implying that the SiOSi and SiOAl bonds were formed.  相似文献   
65.
Recombinant human m-calpain was produced in a soluble form at a level of 20 mg/liter of Sf-9 cell culture by the coexpression of recombinant human m-calpain large (m80K) and small (30K) subunits using a baculovirus expression system. The expressed m-calpain was purified by sequential column chromatographies on DEAE-Toyopearl, gel-filtration, and Mono Q by the same method used to purify native m-calpain. The recombinant m-calpain had a specific activity of 691 U/mg and a Ka value (Ca2+ requirement for 50% caseinolysis activity) of 0.4 mM, which are essentially identical to those of native rabbit m-calpain. A mutant m-calpain large subunit, m-C105S-80K, where the active-site cysteine-105 is converted to serine by site-directed mutagenesis, was coexpressed with 30K in Sf-9 cells, purified, and characterized. m-C105S-calpain does not degrade casein nor an artificial tetra-peptide substrate, succinyl-Leu-Leu-Val-Tyr-MCA. Further, it shows no autolytic activity with Ca2+. This is the first report of the large-scale production of a fully active m-calpain species in the baculovirus system.  相似文献   
66.
67.
At present, bone marrow analysis is performed microscopically, but is time consuming and labour intensive. No automated methods have been successfully applied to classification of bone marrows cells because automated blood cell analysers have been incapable of identifying erythroblasts. The present study was designed to evaluate automated analysis of bone marrow aspirates with the CELL-DYN 4000 (CD4000) haematology analyser, which enables automated determination of erythroblast counts in both the normal mode (haemolytic time; 11.5s) and the resistant RBC mode (34.0s). The percentages of subpopulations including lymphocytes, neutrophils and erythroblasts were obtained with the CD4000, and as a reference, differential counts by microscopic observation of May-Grünwald-Giesa-stained films of bone marrow aspirates were performed (n=98). Significant correlations (P < 0.01) between the results obtained with the two methods were observed for total nucleated cell count and lymphocytes, neutrophils, erythroblasts and myeloid/erythroid (M/E) ratio. However, there were biases in the average percentages of erythroblasts, lymphocytes and M/E ratio obtained using the normal mode with the CD4000 toward values lower than those obtained with the microscopic method. Using the RBC resistant mode with the CD4000, the average percentages of erythroblasts, lymphocytes and M/E ratio approximated those obtained with the microscopic method. In conclusion, the CD4000 in resistant RBC mode is more useful for analysis of bone marrow aspirates than is the normal mode, because the former better approximates the M/E ratio than the latter.  相似文献   
68.
69.
2-Aminomethyl-1-azetidinyl, -1-pyrrolidinyl, and -1-piperidinyl groups were designed as novel C-7 substituents for potential antibacterial quinolone agents. Of the three substituents, the 2-aminomethyl-1-azetidinyl group (compound 12a) was found to be the most favorable for enhancing the activity of the 6,8-difluoroquinoline molecule 12. Therefore the 2-aminomethyl-1-azetidinyl group was introduced into a variety of quinolines (giving 24-26a, and 28a) and naphthyridines (giving 31a and 32a). Through optical resolution of 1-benzylazetidine-2-carboxamide (19) and chiral synthesis of its R-isomer, both enantiomers of 2-aminomethyl-1-azetidinyl quinolines 12a and 24-26a were also prepared. The most active of all the compounds was 5-amino-6,8-difluoroquinoline (R)-26a. The activity of (R)-26a was more potent than those of the corresponding 1-piperazinyl derivative (3) and sparfloxacin (1), and was comparable to those of the corresponding 3-amino-1-pyrrolidinyl (4), 3-aminomethyl-1-pyrrolidinyl (5), and 3-amino-1-azetidinyl (6) derivatives.  相似文献   
70.
Pregnancy block, whereby recently mated female mice abort their pregnancies when exposed to novel (strange) males, was studied in house mice (Mus domesticus) differing in t-complex genotype; t-mutations are deleterious and +/t females avoid +/t males as mates. The results of Experiment 1, in which the genotype of the female, stud male, and strange male was systematically varied, showed that pregnancy block was most frequent when the strange male was +/+. Because this effect was not enhanced among +/t females when stud males were +/t, the results cannot clearly be explained by the hypothesis that pregnancy block is a manifestation of mate choice. Moreover, the "strange male" effect in Experiment 1 is unlikely to be a female response correlated with the risk of male infanticide, as +/+ and +/t males did not differ in their infanticidal tendencies (Experiments 2 & 3). Alternative hypotheses, including a modified version of the mate choice hypothesis, are discussed.  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