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   180955篇
  免费   2611篇
  国内免费   714篇
电工技术   3342篇
综合类   104篇
化学工业   28714篇
金属工艺   7865篇
机械仪表   5185篇
建筑科学   4674篇
矿业工程   880篇
能源动力   4861篇
轻工业   16829篇
水利工程   1733篇
石油天然气   3135篇
武器工业   2篇
无线电   20226篇
一般工业技术   34123篇
冶金工业   33556篇
原子能技术   4324篇
自动化技术   14727篇
  2021年   1438篇
  2019年   1349篇
  2018年   2205篇
  2017年   2179篇
  2016年   2326篇
  2015年   1692篇
  2014年   2873篇
  2013年   8063篇
  2012年   4827篇
  2011年   6692篇
  2010年   5322篇
  2009年   6146篇
  2008年   6135篇
  2007年   6074篇
  2006年   5213篇
  2005年   4862篇
  2004年   4626篇
  2003年   4273篇
  2002年   4218篇
  2001年   4182篇
  2000年   3996篇
  1999年   4113篇
  1998年   10454篇
  1997年   7451篇
  1996年   5716篇
  1995年   4330篇
  1994年   3670篇
  1993年   3599篇
  1992年   2632篇
  1991年   2564篇
  1990年   2440篇
  1989年   2465篇
  1988年   2395篇
  1987年   2151篇
  1986年   2088篇
  1985年   2391篇
  1984年   2208篇
  1983年   2035篇
  1982年   1903篇
  1981年   1962篇
  1980年   1811篇
  1979年   1834篇
  1978年   1786篇
  1977年   2126篇
  1976年   2701篇
  1975年   1560篇
  1974年   1556篇
  1973年   1614篇
  1972年   1354篇
  1971年   1267篇
排序方式: 共有10000条查询结果,搜索用时 847 毫秒
181.
Social burden caused by paralyzed poliomyelitis was analysed, using data from a Sampling Survey of Handicapped People in China, in 1987. The study results showed: 29.94% of 1707 handicapped polio victims aged 6 or over were not able to go to school; 44.23% of them could not take care of their daily life; 36.32% of them could not play out-door and do shopping; 2.58% of them could not normally communicate with others. 84.53% of the 1487 handicapped victims caused by polio aged 15 or over wholly or partly lost their working ability. We also compared handicapped people's employment rate and the status of marriage with non-handicapped people. Data showed that the employment rate and the number of married handicapped polio victims were remarkably lower then those non-handicapped people.  相似文献   
182.
183.
184.
INTRODUCTION: Heterozygous beta-thalassemia manifests hematologically with microcytosis, reduced red blood cell hemoglobin concentration and high hemoglobin A2 levels. Almost all molecular alterations are due to point mutations. We attempt to determinate the frequency of that mutations in the Oriental Andalusia Area, and its relationship with the hematological phenotype. PATIENTS AND METHODS: We have studied 45 heterozygous patients. DNA samples were amplified by PCR, using the printers CD7 and HI1. A 16 Kb fragment corresponding to beta globin gene was obtained and analyzed by Dot Blot assay and hybridized with allelic specific oligonucleotide (ASO) probes to detect the 6 more frequent mutations found in the South of Spain. RESULTS: Codon 39 nonsense mutation (31.1%) was the most frequent finding followed by IVS-1 NT 110 (26.7%). The relationship between hematological parameters and molecular mutations concluded that IVS-I NT 6 mutation developed a minimal anemia. DISCUSSION: From the practical point of view, this study indicates that we were able to detect more than 90% of heterozygous beta-tal. with 5 out of 6 ASO probes used in this work. Thus, our data also provides a further implication in prenatal diagnosis.  相似文献   
185.
Two patients exhibited chronic, slightly asymmetric weakness and wasting with fasciculations of the upper limb and hand muscles. Motor nerve conduction studies showed features of multifocal conduction block in nerve segments other than those usually involved in entrapment syndromes. The F wave was markedly delayed in the median and ulnar nerves. Transcranial cortical and cervical root magnetic stimulation showed bilaterally delayed thenar responses with normal central conduction time. Needle electromyography demonstrated a chronic denervation pattern with large polyphasic motor units in several muscles of the upper limbs. Sensory symptoms were mild and limited to paresthesias in the fingertips. Sensory nerve conduction velocity and sensory nerve action potential amplitudes were normal in elbow-to-wrist and wrist-to-finger segments of the median and ulnar nerves, but there was a delayed cortical response and unrecognizable Erb's point and cervical responses in the somatosensory evoked potentials to median nerve electrical stimulation. Electrophysiologic examination was normal in most nerves of the lower limbs. These two patients, meeting clinical and electrophysiologic criteria of multifocal neuropathy with conduction block, demonstrate that sensory fibers may also be involved in this syndrome.  相似文献   
186.
Butyl, hexyl, and 2-ethylhexyl diesters of 1,1-bis(5-carboxyl-2-furyl)-2,2-dichloroethene, hexyl and 2-ethylhexyl diesters of 1,1-bis(5-carboxyl-2-furyl) ketone, and the hexyl diester of 1,1-bis(5-carboxyl-2-furyl)methane were synthesized from furfural and evaluated for their plasticizing abilities toward PVC, by the application of dynamic mechanical thermal analysis and [di(2-ethylhexyl) phthalate] as a standard of reference. © 1995 John Wiley & Sons, Inc.  相似文献   
187.
Based on a high-performance liquid chromatographic pump, we have built a device that allows recirculation of DNA through a 63-microm orifice with ensuing fractionation to a minimum fragment size of approximately 300 base pairs. Residence time of the DNA fragments in the converging flow created by a sudden contraction was found to be sufficiently long to allow extension of the DNA molecules into a highly extended conformation and, hence, breakage to occur at midpoint. In most instances, 30 passages sufficed to obtain a narrow size distribution, with >90% of the fragments lying within a 2-fold size distribution. The shear rate required to achieve breakage was found to be inversely proportional to the 1.0 power of the molecular weight. Compared with a restriction digest, up to 40% of all fragments could be cloned directly, with only marginal improvements in cloning efficiency having been observed upon prior end repair with Klenow, T4 polymerase or T4 polynucleotide kinase. Sequencing revealed a fairly random distribution of the fragments.  相似文献   
188.
Translated from Izmeritel'naya Tekhnika, No. 3, pp. 57–58, March, 1993.  相似文献   
189.
190.
We prove that the entropy is a supermodular and subadditive function on the lattice of all n-dimensional probability distributions, ordered according to the partial order relation defined by majorization among vectors  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