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   6343篇
  免费   1篇
综合类   1篇
化学工业   22篇
机械仪表   3篇
建筑科学   1篇
轻工业   56篇
石油天然气   1篇
无线电   2篇
一般工业技术   8篇
冶金工业   6245篇
自动化技术   5篇
  2021年   4篇
  2019年   4篇
  2018年   5篇
  2017年   7篇
  2015年   2篇
  2014年   4篇
  2013年   2篇
  2012年   4篇
  2011年   2篇
  2010年   1篇
  2009年   3篇
  2008年   1篇
  2007年   4篇
  2006年   1篇
  2005年   4篇
  2004年   5篇
  2003年   18篇
  2002年   4篇
  2001年   3篇
  2000年   3篇
  1999年   204篇
  1998年   1984篇
  1997年   1082篇
  1996年   777篇
  1995年   401篇
  1994年   333篇
  1993年   365篇
  1992年   43篇
  1991年   89篇
  1990年   50篇
  1989年   67篇
  1988年   64篇
  1987年   67篇
  1986年   68篇
  1985年   49篇
  1983年   6篇
  1982年   24篇
  1981年   38篇
  1980年   62篇
  1979年   6篇
  1978年   16篇
  1977年   136篇
  1976年   314篇
  1975年   11篇
  1973年   1篇
  1955年   5篇
  1954年   1篇
排序方式: 共有6344条查询结果,搜索用时 15 毫秒
21.
Tibial torsion?     
A longitudinal study evaluating the degree of rotation of the bimalleolar axis of tibia and fibula at birth, 6 month, 12 months and 24 months revealed a gradual statistically significant external rotation from a mean of 4 degrees at birth to a mean of 11 degrees at 24 months. There was no correlation with the sex or race of the child or with the age at which the child began independent walking. It is concluded that this external rotation is a part of normal growth and development of the infants' lower extremities.  相似文献   
22.
The uni-arterial vascularisation of the lateral bilary duct makes it impossible to systematise the arteries which supply the common bile duct. Only the cystic artery is seen at coelio-mesenteric catheterization. The techniques essential for visualisation of the cystic artery are discussed, on the basis of one hundred coelio-mesenteric arteriograms: frequency of demonstration, origin, course, termination, calibre and length. The frequent finding of opacification of the wall of the gall bladder under normal conditions is stressed.  相似文献   
23.
24.
25.
There are two forms of ornithine decarboxylase with respect to pyridoxal 5'-phosphate (pyridoxal-P) affinity in exponentially-growing Swiss 3T3 mouse fibroblasts: form I (Km approximately 10 muM) accounts for 30% of the total activity, and form II (Km approximately 0.4 muM) the remainder. Each form of the enzyme is in rapid equilibrium with ornithine and pyridoxal-P; neither form recognizes the Schiff base between ornithine and pyridoxal-P as a substrate. Total pyridoxal-P concentrations indicate that both forms may normally be at least partially active in vivo. Upon stimulation of 3T3 cells by pituitary growth factors, form I becomes undetectable within 4 h. As total activity increases over 10-fold during this time and continues to increase thereafter, a possible conversion of form I to form II could account for this increase only if the Km change reflects other changes in preexisting enzyme. The rates of cofactor dissociation are apparently the same for each form and neither rate changes with the growth state. Since rapid equilibrium kinetics apply, the forms apparently differ in their rate of cofactor association. The half-lives of the two forms in vivo are the same in unstimulated cells when measured concurrently. Also, the half-life of total activity decreases markedly upon stimulation as form II becomes dominant. These and other observations are not consistent with pyridoxal-P serving a major protective function for the enzyme in vivo.  相似文献   
26.
Serum complement levels were assayed in 26 patients with disseminated cancer, who received immunotherapy with infusion of C. parvum. Complement activation, indicated by the consumption of C3 or C4 or both, was found in 46% of the patients. Serum samples showed direct correlation between decreased C3 and conversion of C3 proactivator, whereas such conversion did not occur when C4 alone was decreased. It is concluded that the bypass (properdin) pathway was activated in patients in whom C3 consumption was detected, while the classical (C1) pathway was activated in the patients with C4 consumption unaccompanied by C3 decrease. Direct correlation was observed between delayed cutaneous hypersensitivity reactions to recall antigens and the incidence of C. parvum-associated complement activation.  相似文献   
27.
By reviewing the syndromic manifestation, transsexualism in characterized as a psychiatric entity, apart from homossexualism and transvestism. The two main feasible etiologic causes of transsexualism are discussed: the psychoanalytical hypothesis based upon psycossexual regression with imprinting of maternal figure and the neuroendocrine model which assumes alterations of the gender role identity centers in the hypothalamus. On the grounds of the latter explanation and after the scheme that seems to occure in the Morris syndrome whose cells (XY) do not respond to the masculinizing effect of plasma testosterone, it is proposed that transsexuals should possess detectable or cryptic sex-chromosome mosaicism affecting hypothalamic centers of gender role identity which do not respond to the androgenic secretion produced by primitive gonad. This possibliity explains the excessive prevalence of the syndrome among men, its typical features in the male as well as its sporadic occurrence. Cytogenetic investigation reveals that the frequency (32%) of sex-chromosome mosaicism among 25 transsexuals and 40 normal control people, both groups presenting the proportion of the mosaicism practically null. The karyotypic criterion as a valuable aid in the syndrome diagnosis is considered.  相似文献   
28.
As a step toward defining in molecular terms the sperm-triggered block to polyspermy reaction established by the egg at fertilization, vitelline (VE) and fertilization (FE) envelopes were isolated from eggs of the Sounth African clawed toad Xenopus laevis and some of their physicochemical properties determined. Envelopes were isolated after lysis of the fertilized or unfertilized eggs by sieving techniques; isolated envelopes retained their in situ morphology as determined by electron microscopy. The isolated envelopes had different solubility properties and, in general, VE was more readily dissolved by aqueous solvents than FE, although both could be completely dissolved by detergents or chaotropic agents. Changes in envelope solubility correlated with the progression of the cortical reaction implicating a role for cortical granule material in modifying the solubility properties of the envelope. The VE and FE were composed of protein and carbohydrate with no lipid components detected. As determined by immunodiffusion experiments, the FE contained the same antigens as the VE plus components derived from the cortical granules and the innermost jelly layer, J. The macromolecular composition of the envelopes was determined by sodium dodecyl sulfate gel electrophoresis. The VE contained at least 11 glycoproteins with molecular weights ranging from 125 000 to less than 16 000 with two components (40 000 and 33 000) accounting for almost two-thirds of the total stainable material. The FE contained ten glycoproteins that had the same molecular weights as those in the VE. One glycoprotein component underwent a reduction in molecular weight from 77 000 to 67 500 when the VE was converted to the FE. This molecular weight change was interpreted as the probable result of limited proteolysis. In addition, the FE gel electrophoresis patterns contained macromolecular components derived from the cortical granules and jelly layer, J, consistent with the immunodiffusion experiments. These components were absent when the FE was prepared in the absence of Ca2+, suggesting a role for Ca2+ in binding the VE, cortical granules, and J components together. We concluded that the conversion of the glycoproteinaceous VE to FE at fertilization is caused by interaction of the VE with components from the cortical granules and jelly layer J. These interactions are of both a chemical and physical nature.  相似文献   
29.
30.
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