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   531篇
  免费   44篇
  国内免费   4篇
电工技术   3篇
化学工业   179篇
金属工艺   9篇
机械仪表   7篇
建筑科学   26篇
矿业工程   1篇
能源动力   9篇
轻工业   57篇
水利工程   1篇
石油天然气   1篇
无线电   35篇
一般工业技术   97篇
冶金工业   71篇
原子能技术   1篇
自动化技术   82篇
  2023年   9篇
  2022年   20篇
  2021年   20篇
  2020年   14篇
  2019年   15篇
  2018年   13篇
  2017年   10篇
  2016年   20篇
  2015年   12篇
  2014年   27篇
  2013年   26篇
  2012年   29篇
  2011年   33篇
  2010年   27篇
  2009年   23篇
  2008年   36篇
  2007年   16篇
  2006年   16篇
  2005年   10篇
  2004年   13篇
  2003年   12篇
  2002年   14篇
  2001年   11篇
  2000年   12篇
  1999年   11篇
  1998年   32篇
  1997年   9篇
  1996年   13篇
  1995年   9篇
  1994年   7篇
  1993年   3篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1989年   2篇
  1988年   2篇
  1987年   4篇
  1986年   3篇
  1985年   4篇
  1984年   2篇
  1983年   3篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1977年   5篇
  1976年   5篇
  1975年   2篇
  1966年   2篇
  1965年   2篇
  1924年   1篇
排序方式: 共有579条查询结果,搜索用时 31 毫秒
1.
Near-haploidy is a rare cytogenetic finding in childhood acute lymphoblastic leukaemia (ALL) and is associated with a poor prognosis. A second hyperdiploid line, occurring presumably by endoreduplication of the near-haploid stemline, is often observed. We present a case of common ALL in relapse characterized morphologically by a dual population of small and large lymphoblasts. Cytogenetic analysis supplemented with fluorescence in-situ hybridization (FISH) studies localized near-haploidy and hyperdiploidy to the small and large blast population respectively. DNA ploidy determination confirmed two abnormal clones with near-haploidy as the predominant one. A novel t(9;12)(q11;q13) was present in the near-haploid clone and was duplicated in the hyperdiploid clone. This finding identified cells bearing near-haploidy to be the clonogenic population following malignant transformation and confirmed endoreduplication as the mechanism for the presence of associated hyperdiploidy.  相似文献   
2.
The theory of deconvolution of infra-red spectra is presented and illustrated using milk protein spectra. The advantage of this method is impressively demonstrated and its relevance for dairy farming shown using a simple example, the cooling of milk.  相似文献   
3.
Rats were fed an adequate or a deficient diet and offered water or buthionine sulphoximine (BSO) solution for 2 weeks, and then the same diets with vicine for another week in experiment 1. BSO in combination with the deficient diet caused a marked decrease in blood glutathione (GSH) and growth retardation but failed to show any effects resulting from supplementation with vicine. In experiment 2 the rats were given an adequate diet and BSO as before, and injected intravenously with divicine (DV). Here again, BSO depressed rat growth, and so did DV. Each of the insults also caused haematological changes, especially a fall in GSH, but the most severe changes appeared in the group treated with both BSO and DV. A decrease in haematocrit and increases in adrenal and spleen weight were also noted. In experiment 3 the rats were injected with different doses of DV, without pretreatment with BSO. The main effect was a drop in blood GSH and haematocrit, and an increase in adrenal and spleen weights, all of which were dose-related. Administration of the higher doses of DV resulted in a severe cyanosis followed by death within a relatively short period of time.  相似文献   
4.
5.
Information technology has been becoming increasingly important in all areas of engineering during the last few years. Much of the progress achieved in chemical engineering would not have been possible without the enabling methods and tools provided by information technology. This trend will continue in the future but most likely with a considerably wider scope. While individual software tools and services have been in focus until recently, their integration into engineering work processes is an emerging and challenging area of research and development. This contribution attempts to highlight state of the art and future trends in supporting the activities during the life cycle of a chemical process by means of information technology. Emphasis will be largely on the process and plant design process rather than on procurement, manufacturing, and distribution of materials in the supply chain.  相似文献   
6.
TP53 gene mutations occur in 70% of oesophageal adenocarcinomas (OACs). Given the central role of p53 in controlling cellular response to therapy we investigated the role of mutant (mut-) p53 and SLC7A11 in a CRISPR-mediated JH-EsoAd1 TP53 knockout model. Response to 2 Gy irradiation, cisplatin, 5-FU, 4-hydroxytamoxifen, and endoxifen was assessed, followed by a TaqMan OpenArray qPCR screening for differences in miRNA expression. Knockout of mut-p53 resulted in increased chemo- and radioresistance (2 Gy survival fraction: 38% vs. 56%, p < 0.0001) and in altered miRNA expression levels. Target mRNA pathways analyses indicated several potential mechanisms of treatment resistance. SLC7A11 knockdown restored radiosensitivity (2 Gy SF: 46% vs. 73%; p = 0.0239), possibly via enhanced sensitivity to oxidative stress. Pathway analysis of the mRNA targets of differentially expressed miRNAs indicated potential involvement in several pathways associated with apoptosis, ribosomes, and p53 signaling pathways. The data suggest that mut-p53 in JH-EsoAd1, despite being classified as non-functional, has some function related to radio- and chemoresistance. The results also highlight the important role of SLC7A11 in cancer metabolism and redox balance and the influence of p53 on these processes. Inhibition of the SLC7A11-glutathione axis may represent a promising approach to overcome resistance associated with mut-p53.  相似文献   
7.
CYP154C5 from Nocardia farcinica is a P450 monooxygenase able to hydroxylate a range of steroids with high regio- and stereoselectivity at the 16α-position. Using protein engineering and substrate modifications based on the crystal structure of CYP154C5, an altered regioselectivity of the enzyme in steroid hydroxylation had been achieved. Thus, conversion of progesterone by mutant CYP154C5 F92A resulted in formation of the corresponding 21-hydroxylated product 11-deoxycorticosterone in addition to 16α-hydroxylation. Using MD simulation, this altered regioselectivity appeared to result from an alternative binding mode of the steroid in the active site of mutant F92A. MD simulation further suggested that the entrance of water to the active site caused higher uncoupling in this mutant. Moreover, exclusive 15α-hydroxylation was observed for wild-type CYP154C5 in the conversion of 5α-androstan-3-one, lacking an oxy-functional group at C17. Overall, our data give valuable insight into the structure–function relationship of this cytochrome P450 monooxygenase for steroid hydroxylation.  相似文献   
8.
Directed exploitation of biological systems . During the past few decades, our knowledge of molecular process responsible for genetics has increased dramatically. Discovery of the giant molecule deoxyribonucleic acid – abbreviated as DNA – as the carrier of genetic information heralded in a development which nowadays permits us to effect directed changes in the genetic material of an organism. Thus we can provide easily cultured microorganisms with genes which were previously located in a completely different genetic environment. This helps us to obtain high yields of proteins or other substances which were formerly very difficult to obtain. Higher organisms such as animals and plants can also undergo modification of their genetic equipment. This adds a new dimension to the breeding of such species. Above all, genetic engineering provides new insights into the enormously complex interplay of molecules which go to make up a living cell. The resulting understanding of life processes on a molecular level permits recognition of malfunction and therapy of the ensuring disease by new drugs. In addition to these positive aspects, genetic engineering provides scope for conducting experiments whose ethical implications demand very earnest consideration.  相似文献   
9.
The heterogeneous bulk polymerization of acrylonitrile initiated by AIBN has been studied by means of an improved dilatometric technique and a new method of analysis, where the initial reaction rate (vw)0 results from the intercept of a straight line in a \documentclass{article}\pagestyle{empty}\begin{document}$ \frac {\ln \left( 1 \hbox{---} {\rm U} \right)} {{\rm e}^{{- 0,5} {\rm k}_{\rm s}{\rm t} \hbox{---} 1}}$\end{document} versus t plot. It has been found that the initial reaction rate is proportional to the square root of the initial catalyst concentration S0. The ratio of the rate coefficients of propagation and termination\documentclass{article}\pagestyle{empty}\begin{document}$\frac { {\rm k}_{\rm a} } { {\rm k}_{ {\rm w}^{2} } } $\end{document} could be calculated from the slope of a straight line passing through the origin in a plot of (vw)0 versus \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt { {\rm S}_{0} }$\end{document} and yielded a value of 280 mol 1?1.  相似文献   
10.
During software system evolution, software architects intuitively trade off the different architecture alternatives for their extra-functional properties, such as performance, maintainability, reliability, security, and usability. Researchers have proposed numerous model-driven prediction methods based on queuing networks or Petri nets, which claim to be more cost-effective and less error-prone than current practice. Practitioners are reluctant to apply these methods because of the unknown prediction accuracy and work effort. We have applied a novel model-driven prediction method called Q-ImPrESS on a large-scale process control system from ABB consisting of several million lines of code. This paper reports on the achieved performance prediction accuracy and reliability prediction sensitivity analyses as well as the effort in person hours for achieving these results.  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