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   982071篇
  免费   12868篇
  国内免费   2494篇
电工技术   17194篇
综合类   3092篇
化学工业   148568篇
金属工艺   39535篇
机械仪表   30366篇
建筑科学   23508篇
矿业工程   6066篇
能源动力   24720篇
轻工业   79016篇
水利工程   11216篇
石油天然气   19424篇
武器工业   64篇
无线电   107847篇
一般工业技术   192601篇
冶金工业   173537篇
原子能技术   20206篇
自动化技术   100473篇
  2021年   8341篇
  2020年   6147篇
  2019年   7878篇
  2018年   26396篇
  2017年   25402篇
  2016年   23205篇
  2015年   9903篇
  2014年   15767篇
  2013年   41618篇
  2012年   27084篇
  2011年   41684篇
  2010年   33877篇
  2009年   34625篇
  2008年   36321篇
  2007年   36756篇
  2006年   26142篇
  2005年   24762篇
  2004年   23670篇
  2003年   23396篇
  2002年   21914篇
  2001年   21219篇
  2000年   20119篇
  1999年   20606篇
  1998年   51173篇
  1997年   36451篇
  1996年   28178篇
  1995年   21290篇
  1994年   18862篇
  1993年   18483篇
  1992年   13714篇
  1991年   13006篇
  1990年   12865篇
  1989年   12454篇
  1988年   11831篇
  1987年   10628篇
  1986年   10379篇
  1985年   11682篇
  1984年   10677篇
  1983年   9909篇
  1982年   9136篇
  1981年   9274篇
  1980年   8839篇
  1979年   8781篇
  1978年   8587篇
  1977年   9908篇
  1976年   12841篇
  1975年   7582篇
  1974年   7214篇
  1973年   7369篇
  1972年   6170篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The synthesis of ten tris-sydnone imine derivatives, unknown up to now, is described. All compounds are alkyl or arylalkyl substituted in 3-position of the sydnone imine. The most powerful agent was the 3-propyl derivative 6c. It inhibits the aggregation of human platelets induced by collagen in a concentration of 1 mumol/L half maximally. Its N-ethoxycarbonyl derivative 7c, which was designed as a prodrug, showed only small antithrombotic effects in rats. The reason for this low degree of activity is discussed.  相似文献   
992.
993.
In 50 patients auditory threshold and brain stem evoked potential studies were carried out before and after myelography. Due to the analysis of amplitudes and latencies of auditory brain stem measurements, significant functional disorders of the hearing organ and the auditory pathway could be demonstrated. In most of the patients these functional disorders were found to be subclinical, whereas 12 patients showed alterations extending from a subjectively slight hearing loss to an audiometrically objectified acute hearing loss depending on its intensity in each case. The reasons of these functional disorders could not be clarified. An open cochlear aqueduct through which perilymph enters the subarachnoidal space leading to a secondary endolymphatic hydrops can be considered as the cause in cases where manifest symptoms develop. The changes in brain stem audiometry can be additionally explained by changes in osmolality of the inner ear fluids which may lead to the development of an endolymphatic hydrops.  相似文献   
994.
A genetic linkage map of human chromosome 21q (HC21q) containing 43 markers genotyped by the polymerase chain reaction in the CEPH pedigrees is presented. The markers placed on this map are highly polymorphic with an average heterozygosity of 61%. The average interval size of the markers localized at 1000:1 odds is 2.5 cM. The map has a total length of 65.5 cM, with male and female lengths of 47.7 and 83.3 cM, respectively. The genotypes used in the construction of this map were subjected to rigorous error checking, which is reflected in the shorter map length compared to previous maps; the estimated error rate in genotyping is less than 0.04%. As noted in previous linkage maps there is increased recombination in females on proximal HC 21q and in the male in a region near the telomere. This map of HC 21 represents a highly informative and dense meiotic linkage map and will be useful in linking disease phenotypes to loci on this chromosome.  相似文献   
995.
996.
This report details procedures to measure annihilation anxiety, a concept derived from Freud's 1926 formulation of traumatic anxiety. A 25-item pencil-and-paper inventory administered to patient and to nonpatient samples is described, along with a brief summary of earlier findings. The delineation of nine interrelated experiential components of annihilation anxiety provides the background for the construction of Rorschach and TAT measures of the concept. Findings comparing the pencil-and-paper inventory and the projective test measures are presented as well as examples of responses judged to reflect annihilation anxiety from Rorschach and TAT protocols.  相似文献   
997.
Growth hormone (GH) has recently been shown to affect polymorphonuclear neutrophil granulocyte (PMN) function and to be secreted by mononuclear cells, indicating that the hormone may be active in an immunophysiologic network, acting as an endo- or paracrine priming agent. The purpose of the present study was to evaluate the chemotactic responsiveness of canine peripheral PMN in a dog with acromegaly, caused by spontaneous, progesterone-induced hypersecretion of GH and, secondary to this, a seven-fold increase in insulin-like growth factor I (IGF-I). The chemotactic responsiveness towards zymosan-activated serum (ZAS) and leukotriene B4 (LTB4) was evaluated at a time when the dog suffered from acromegaly and again 57 days after corrective surgery (ovariohysterectomy). The experiments showed that PMN from the patient exhibited enhanced chemotactic migration that appeared to be associated with the hypersomatotropic condition as judged from the reversibility of the phenomenon. The glucose intolerance and elevated serum alkaline phosphatase that were observed in the acromegalic dog were also shown to be reversible following surgery.  相似文献   
998.
999.
Synergism between recombinant human tumour necrosis factor (rHuTNF) and DNA topoisomerase II inhibitor VP16 during the killing of cells has been studied in six human ovarian cancer cell lines (A2774, A2780, SW626, IGROV-1, SKOV3, Pa1) and a cervical carcinoma cell line (Me180). Studies were performed using an assay of colony formation inhibition (drug treatment for 1 h) and a growth inhibition assay (continuous exposure for 20 h). Concomitant treatment of cells with VP16+rHuTNF enhanced cell killing in all the cell lines tested--an effect observed in both short- and long-term cytotoxicity assays. This study suggests that the activity of VP16 in ovarian cancer cell lines might be enhanced by rHuTNF in in vitro models.  相似文献   
1000.
A multilayer theory has been developed for unidirectional/cross-ply unbalanced laminates subjected to surface shear tractions, using the assumption of plane strain. The analytical solution for the stress field in the laminate is obtained and it is shown that the stresses in each layer are in good agreement with the results of a three-dimensional finite element analysis. Approximate formulae for the analytical stresses are also derived for a laminate subjected to an offset distributed force at one end. The accuracy of this solution is shown by comparison with a three-dimensional finite element analysis.  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