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   270025篇
  免费   37436篇
  国内免费   255篇
  2020年   3438篇
  2019年   5198篇
  2018年   6315篇
  2017年   6499篇
  2016年   7331篇
  2015年   7476篇
  2014年   8060篇
  2013年   10414篇
  2012年   8877篇
  2011年   9295篇
  2010年   8264篇
  2009年   6503篇
  2008年   7523篇
  2007年   7362篇
  2006年   6975篇
  2005年   6714篇
  2004年   6606篇
  2003年   6435篇
  2002年   6274篇
  2001年   12291篇
  2000年   12169篇
  1999年   9305篇
  1998年   2697篇
  1997年   2758篇
  1996年   2711篇
  1995年   2497篇
  1994年   2439篇
  1993年   2335篇
  1992年   7213篇
  1991年   7015篇
  1990年   7077篇
  1989年   6875篇
  1988年   6384篇
  1987年   6037篇
  1986年   5399篇
  1985年   5688篇
  1984年   4483篇
  1983年   3876篇
  1982年   2677篇
  1981年   2511篇
  1979年   4127篇
  1978年   3147篇
  1977年   2899篇
  1976年   2840篇
  1975年   3285篇
  1974年   3511篇
  1973年   3544篇
  1972年   3067篇
  1971年   2853篇
  1970年   2538篇
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
921.
Summary The child with iminoglycinuria is in our observation. Hyperprolinuria was seen at 5 months by screening program. The child was repeatedly examined in the hospital and was seen last time at 16 months. IQ was 67, in the urine were excessive amounts of glycine, proline a hydroxyproline. In the blood aminoacids were in normal levels. In the child was noticed the same increase of proline in the blood as in the control child of the same age following loading test with L-proline, indicating normal intestinal absoption. Both parents and father's sister's 2-year-old mentally retarded child exhibit excessive glycinuria. The father, his sister, father's father, and grandfather are partialy, congenitaly deaf.  相似文献   
922.
The influence of He-Ne laser radiation (632.8 nm, 56 J/m2, t = 10 s) and phytohaemagglutinin (PHA, 2 micrograms/ml) on chromatin structure in human lymphocytes was studied by electron microscopy using ultrathin cell sections. Morphometric analysis of extranuclear condensed chromatin masses was performed 1 h after the irradiation or after the beginning of PHA treatment. In the irradiated cells the following insignificant changes were revealed: decrease in the relative area of the nucleoplasmic chromatin, increase in the relative area of decondensation zones as well as increase in the number of clumps of nucleoplasmic chromatin and relative length at their boundary with nucleoplasma. The tendency of these morphological changes may be interpreted as functional activation of extranucleolar RNA synthesis in response to irradiation by red laser light. Action of PHA results in significant changes of the surfaces of chromatin clumps, namely increase in relative length of nucleoplasmic chromatin boundary and decrease in relative length of perimembranous chromatin boundary with nucleoplasma as well as some less expressed delamination of the chromatin masses from the nuclear membrane. These essential changes may reflect chromatin activation by proliferative stimulus. Peculiarities of the ultrastructural reorganisation in the condensed chromatin after irradiation and PHA-treatment probably reflect the differences in the processes of gene activation caused by the two agents.  相似文献   
923.
924.
925.
Vacuum ultraviolet circular dichroism spectra are reported for poly(galacturonic acid) solution and film, sodium polygalacturonate solution and film, and calcium polygalacturonate gel. In addition to the positive c.d. band near 208 nm previously observed, we find a pair of higher energy bands at 170 180 nm (negative) and 145 nm (positive). The low energy band, assigned to an n-π1 carboxyl transition, is blue-shifted upon gelation or film formation.  相似文献   
926.
F N Dodoo 《Social biology》1992,39(1-2):102-108
Data from the 1988 Ghana Demographic and Health Survey is employed to determine the existence of a relationship between the amount of education a woman has and her intent to cease childbearing. The findings are that with increasing levels of education, a female's desire to cease reproduction also increases. However, this relationship is obscured if parity is not controlled.  相似文献   
927.
928.
Baby hamster kidney cells were seeded onto Western blots of fetal serum proteins which had been extracted from several foreign surfaces. This revealed that the major cell adhesive proteins adsorbed onto these surfaces from fetal serum were (1) fibronectin of Mr 220,000 Da and (2) vitronectin of Mr 65,000 and 78,000 Da. Two minor bands of cell attachment were observed at Mr 153,000 and Mr 134,000 Da in the fetal serum proteins extracted from heparin-agarose and serotonin-agarose. However, by exposing the Western blots of separated proteins to a second round of serum proteins, prior to cell blotting, very strong cell adhesive bands were revealed at Mr 153,000, 134,000, and 120,000 Da. By (i) modifying the composition of the serum proteins used to treat the Western blots, (ii) using specific antibodies to fibronectin, and (iii) using radiolabeled fibronectin, it was conclusively demonstrated that the new cell adhesive bands owed their increased cell attachment activity to secondary binding of fibronectin. The new bands were shown (i) to be trypsin sensitive and collagenase sensitive and therefore to be collagen-like proteins and (ii) to react negatively in immunoblots using anti-fibronectin, anti-vitronectin, anti-fibrinogen, anti-fetuin or anti-thrombospondin. In SDS-PAGE (i) the Mr 120,000-Da protein comigrated with the alpha 2-chain of Type I collagen, (ii) the Mr 134,000-Da protein comigrated with the alpha 1-chain of Type I collagen, and (iii) the Mr 153,000-Da protein comigrated with the pN-alpha 1-chain of Type III collagen. Since the novel collagen-like proteins acted as strong sites of cell attachment on nitrocellulose blots by binding fibronectin, they might well promote cell attachment on the foreign surfaces from which they were extracted.  相似文献   
929.
930.
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