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   1620篇
  免费   4篇
化学工业   10篇
金属工艺   1篇
机械仪表   2篇
建筑科学   4篇
轻工业   8篇
水利工程   1篇
一般工业技术   4篇
冶金工业   1592篇
自动化技术   2篇
  2022年   1篇
  2021年   2篇
  2018年   3篇
  2017年   1篇
  2016年   2篇
  2014年   2篇
  2013年   1篇
  2011年   4篇
  2008年   2篇
  2007年   1篇
  2006年   2篇
  2005年   1篇
  2004年   2篇
  2003年   6篇
  1999年   41篇
  1998年   467篇
  1997年   274篇
  1996年   190篇
  1995年   109篇
  1994年   79篇
  1993年   87篇
  1992年   13篇
  1991年   14篇
  1990年   17篇
  1989年   29篇
  1988年   21篇
  1987年   17篇
  1986年   14篇
  1985年   15篇
  1982年   6篇
  1981年   17篇
  1980年   21篇
  1979年   2篇
  1978年   7篇
  1977年   45篇
  1976年   104篇
  1975年   3篇
  1955年   2篇
排序方式: 共有1624条查询结果,搜索用时 531 毫秒
171.
172.
It is not inconceivable that everything except the basic structure of an office building could be prefabricated in the near future. Quality and schedule are nearly always improved with prefabrication due to the simple change from an uncontrolled work environment to a controlled one. One Ludgate Place, is a 23,600 m2, £30,000,000 speculative commercial development in central London. This high quality office building has an exposed structural steel frame, within which are fitted prefabricated cladding panels. This paper combines the results from two research programs. The first in the area of prefabrication and the second in the management of high quality cladding construction. The writers describe the Ludgate Place project, incorporating the cladding design, testing, assembly, and installation. Factors that influenced the decision to use prefabrication are presented and evaluated, namely, cost; time; quality; past experience; design; weather joints; performance tests; site logistics; and safety. Construction interfaces and tolerances, particularly between cladding and structure, are discussed, and the future of prefabricated cladding is considered.  相似文献   
173.
174.
175.
We report a case of an 18-month-old female who presented with three supernumerary upper limbs of varying lengths on the right side. Each limb had a proximal, middle, and distal segment, and an intercalated elbow and wrist joint. A single digit was present in the superior limb, three digits in the middle limb, and two digits in the caudal-most limb. Right plagiocephaly, congenital torticollis, scoliosis involving the upper and mid thoracic region, and a hypoplastic right pectoralis major were the other abnormal features noted. Radiography showed two scapulae, humerus, a single forearm bone in each limb, and rudimentary metacarpals and phalanges. Limb duplication may rarely be encountered in parasitic conjoined twins. The role of mutagens, drugs, cellular contributions, and morphogens in the growth and differentiation of limbs has been studied in animals. It is rather difficult to deduce the time of action of the factors responsible for such a malformation.  相似文献   
176.
177.
178.
179.
Presynaptic alpha 2-autoreceptors in mouse atria were characterized in terms of the alpha 2A, alpha 2B, alpha 2C and alpha 2D subtypes. Segments of the atria were preincubated with 3H-noradrenaline and then superfused and stimulated electrically. The affinity of up to 16 antagonists for the autoreceptors was assessed as (1) pEC30% values. i.e. concentrations that increased previously autoinhibited release of 3H-noradrenaline (120 pulses, 3 Hz) by 30%, and (2) pKd values against the release-inhibiting effect of 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14,304) under conditions of no or little autoinhibition (2 trains of 20 pulses, 50 Hz, train interval 120 s). The pKd values correlated well with the pEC30% values (r = 0.98; P < 0.001; slope of regression line 0.93), indicating that UK 14,304 and released noradrenaline modulated the release of noradrenaline through pharmacologically identical receptors. Comparison with antagonist affinities for (1) prototypic native alpha 2 radioligand binding sites, (2) radioligand binding sites in COS cells transfected with alpha 2 subtype genes, and (3) previously classified presynaptic alpha 2-autoreceptors-all taken from the literature-indicated that the mouse atrial autoreceptors corresponded to the alpha 2D subtype. For example, the pKd values at mouse atrial auto-receptors correlated closely with pKd values at native alpha 2D binding sites in the bovine pineal gland (r = 0.96; P < 0.001); with pKd values at alpha 2D binding sites in COS cells transfected with the rat alpha 2D gene (r = 0.85; P < 0.01); and with pKd values at guinea-pig cerebral and atrial and mouse cerebral alpha 2D-autoreceptors (r = 0.96-0.98; P < 0.001). The antagonist pKd values at mouse atrial autoreceptors correlated less with pKd values at alpha 2A, alpha 2B and alpha 2C sites. It is concluded that the presynaptic alpha 2-autoreceptors in mouse atria are alpha 2D. This identification supports the hypothesis that at least the majority of alpha 2-autoreceptors belong to the alpha 2A/D pair of orthologous alpha 2-adrenoceptors.  相似文献   
180.
Fucosyltransferases (FTs) and various glycosidases that are involved in the biosynthesis or degradation of SSEA-1 (Le(x)) antigens and their precursors in the CNS are developmentally regulated. In forebrain and cerebellum with lactosamine (LacNAc) as acceptor the FT activity was maximal at P15-P22, but with the glycolipid substrate paragloboside (nLc4) the maximal activity in cerebellum was obtained at P10-P15. The FT activity, with these substrates, was insensitive to N-ethylmaleimide (NEM) and the glycolipid product had an alpha1,3 linkage (Fuc to GlcNAc) suggesting similarities of the investigated enzyme to the cloned human and rat FT IV. However, the observation of different patterns of FT activity in isoelectrofocused fractions (pH 3.5-10) with different types of acceptors, and the differential expression of Le(x) containing glycolipids and glycoproteins during development strongly suggest the presence of more than one type of FT during development. Data on developmental expression of the hydrolytic enzymes, alpha-L-fucosidase, beta-D-galactosidase and alpha-D-galactosidase, which can potentially hydrolyse SSEA-1 or its precursors, support the notion that SSEA-1 expression is the result of a dynamic balance between the activity of transferases and hydrolases.  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