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   569306篇
  免费   67390篇
  国内免费   318篇
  637014篇
  2016年   6147篇
  2015年   8685篇
  2014年   10215篇
  2013年   14644篇
  2012年   16378篇
  2011年   16491篇
  2010年   11224篇
  2009年   10297篇
  2008年   14715篇
  2007年   15329篇
  2006年   14390篇
  2005年   14109篇
  2004年   13959篇
  2003年   13786篇
  2002年   13482篇
  2001年   23062篇
  2000年   23229篇
  1999年   18949篇
  1998年   7085篇
  1997年   7293篇
  1996年   7088篇
  1995年   6724篇
  1994年   6711篇
  1993年   6583篇
  1992年   16456篇
  1991年   15969篇
  1990年   15664篇
  1989年   15304篇
  1988年   14368篇
  1987年   13973篇
  1986年   12815篇
  1985年   13045篇
  1984年   10930篇
  1983年   9708篇
  1982年   7746篇
  1981年   7138篇
  1980年   6656篇
  1979年   11153篇
  1978年   8566篇
  1977年   8152篇
  1976年   7667篇
  1975年   8323篇
  1974年   9106篇
  1973年   9018篇
  1972年   8379篇
  1971年   7714篇
  1970年   6667篇
  1969年   6587篇
  1968年   5842篇
  1967年   5103篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
BRL-3A rat liver cells synthesize mature 7484-dalton rat insulin-like growth factor II (rIGF-II) as a approximately 22-kDa precursor, presumably prepro-rIGF-II. In the present study, we have biosynthetically labeled intact BRL-3A cells with [35S]cysteine and immunoprecipitated cell lysates and media with antisera to rIGF-II. A approximately 20-kDa protein was identified in immunoprecipitates of cell lysates having properties consistent with pro-rIGF-II. The approximately 20-kDa protein is precipitated by immune sera but not by nonimmune serum. Its immunoprecipitation is specifically inhibited by unlabeled rIGF-II but not by insulin. It is not precipitated from labeled lysates of a subclone of BRL-3A cells (BRL-3A2) that does not synthesize rIGF-II. The approximately 20-kDa protein is rapidly labeled intracellularly (10 min) but is not detected in BRL-3A media. In pulse-chase experiments, radioactivity in the approximately 20-kDa protein disappears during the chase and appears, at later times, in specifically immunoprecipitated approximately 19-, approximately 10-, approximately 8-, and approximately 7-kDa proteins in media and, to a limited extent, intracellularly. A protein with electrophoretic mobility identical to that of the approximately 20-kDa protein observed in cell lysates is immunoprecipitated from 35S-proteins whose synthesis is directed by BRL-3A RNA in a reticulocyte lysate cell-free translation system supplemented with microsomal membranes, and presumably arises by cotranslational removal of the signal peptide from approximately 22-kDa prepro-rIGF-II. Processing of the approximately 20-kDa protein in intact BRL-3A cells to intermediate and mature rIGF-II species appears to occur at the time of secretion and/or shortly thereafter, with the different forms appearing at approximately the same time.  相似文献   
992.
Plant Reactions to Inoculation of Roots with Fungi and Bacteria   总被引:1,自引:0,他引:1  
The potential of 120 isolates of fungi and bacteria from plant rhizospheres to interfere with plant development and growth was studied in greenhouse experiments. The pure cultured isolates were obtained from plant roots in the field and applied as suspensions to the roots of eight test plant species. 10–20% of the isolates caused distinct symptoms on shoots, growth retardations without other symptoms or growth promotions. Responses of treated plants ranged from death of plants soon after treatment to up to about 40% higher shoot fresh weight than in control plants. Two bacterial isolates induced strong reactions in most of the plant species tested while other isolates showed a more or less pronounced specificity by giving reactions in only some of the plant species tested.  相似文献   
993.
994.
The clinical and laboratory findings in seven children with Kawasaki disease are reviewed. Four of the patients had the more complicated course that has characterized the cases diagnosed in North America. This suggests that the benign forms are often mistaken for other febrile illnesses. The patients were two girls and five boys ranging in age from 4 months to 7 years; six were Caucasian and one was a North American Indian. Fever, redness of the oral mucosa, an erythematous or scarlatiniform rash and cervical adenopathy were seen in all; six patients had the characteristic fingertip desquamation and nonexudative conjunctivitis. Cardiac involvement occurred in four patients, two of whom had coronary artery aneurysm or thrombosis. Arthritis or arthralgia was seen in six patients, and aseptic meningitis occurred in four. Of the three patients with jaundice two underwent laparotomy and excision of a hydropic gallbladder; one of them died from Klebsiella pneumoniae sepsis and disseminated intravascular coagulopathy.  相似文献   
995.
996.
Reconstruction of normal shoulder contour is possible utilizing a latissimus dorsi musculocutaneous flap at the end of a long neurovascular pedicle. The thoracodorsal vessels and their lateral divisions form the basis of the pedicle. The nerve in the pedicle is left intact if maintenance of muscle bulk is desired and sectioned if atrophy is preferred. The amount of muscle taken in conjunction with the skin island is determined by the nature of the defect to be corrected. The twin goals of a single-stage reconstruction and a satisfactory aesthetic result are achieved with this method.  相似文献   
997.
Using a slide culture technique, it was determined unequivocally that the chlamydospore of Candida albicans does germinate. The germination was by way of a multiple-budding process which was associated mostly with young spores following their transfer to a fresh environment. It is concluded the chlamydospore of C. albicans is a reproductive cell with a transient viability.  相似文献   
998.
Aliphatic aldehydes of different chain lengths were found to differ in their reaction at 22 °C with the B. harveyi luciferase peroxyflavin intermediate. Although similar quantum yields were obtained in the luciferase reaction with the different chain-length aldehydes, the catalytic turnover rates differed. The kinetics of a reaction utilizing two aldehydes of different chain lengths can thus indicate the degree to which the aldehyde reaction is reversible. By such criteria the reactions of octanal and decanal were found to be readily reversible, while that of dodecanal was not. This conclusion was supported both by the effects of long-chain alcohols, which are competitive inhibitors, and by the secondary addition of hydroxylamine, an aldehyde trapping agent. The results are consistent with a model in which there are many intermediates along the reaction path. Since the reactions are monitored by decay of luminescence intensity, it is difficult to determine the position of the rate-determining step. For octanal and decanal the rate-limiting step could be at an early reversible stage of the reaction, but later for dodecanal, subsequent to a less reversible step, but still prior to the final irreversible step which populates the excited state.  相似文献   
999.
Sporadic (less than regular weekly) coital activity is associated with a particular type of infertility—the short hyperthermic (luteal) phase. This preliminary report is the first suggestion that a reduced frequency of human sexual activity might, itself, be associated with subfertile reproductive function.  相似文献   
1000.
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