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   40248篇
  免费   4333篇
  国内免费   13篇
  44594篇
  2022年   300篇
  2021年   520篇
  2020年   343篇
  2019年   421篇
  2018年   544篇
  2017年   512篇
  2016年   894篇
  2015年   1609篇
  2014年   1562篇
  2013年   2079篇
  2012年   2354篇
  2011年   2074篇
  2010年   1440篇
  2009年   1313篇
  2008年   1807篇
  2007年   1783篇
  2006年   1598篇
  2005年   1563篇
  2004年   1468篇
  2003年   1264篇
  2002年   1261篇
  2001年   1228篇
  2000年   1228篇
  1999年   1103篇
  1998年   606篇
  1997年   564篇
  1996年   555篇
  1995年   536篇
  1994年   489篇
  1993年   512篇
  1992年   1003篇
  1991年   748篇
  1990年   772篇
  1989年   752篇
  1988年   652篇
  1987年   596篇
  1986年   610篇
  1985年   708篇
  1984年   530篇
  1983年   412篇
  1982年   340篇
  1981年   312篇
  1980年   254篇
  1979年   378篇
  1978年   343篇
  1977年   241篇
  1976年   225篇
  1975年   197篇
  1974年   289篇
  1973年   250篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
32.
33.
34.
A method is described for the histochemical detection of horseradish peroxidase in Paraplast Plus embedded brain sections. The procedure uses 150-micron-thick Vibratome-cut slices of glutaraldehyde-paraformaldehyde-fixed brain tissue. Tetramethylbenzidine stabilized by diaminobenzidine/cobalt/H2O2 is used as chromogen. The Vibratome-cut slices are dehydrated through a graded series of acetone, cleared in toluol and flat-embedded in Paraplast Plus embedding medium. Serial sections can be cut as thin as 5-7 micron. The method is universal in its application and permits optimal visualization of labeled neurons with great morphological detail at the light-microscopic level.  相似文献   
35.
Symmetrical dialkyl carbonates and dibenzyl carbonates reacted with various nucleophiles in the presence of Candida antarctica lipase B in organic solvents. For example, reaction of dibutyl and dibenzyl carbonate with an alcohol gave a mixture of the mono- and disubstituted products. Aminolysis, however, afforded only the carbamates, without subsequent reaction to the ureum derivatives. The reaction rates were rather low compared with carboxylic esters; the reactivity increased in the order dimethyl相似文献   
36.
Abstract Porcine Escherichia coli strains isolated from cases fo postweaning diarrhea or edema disease were analysed for the presence of fedA , the major subunit gene of F107 fimbriae. The E. coli isolates were known to contain colonisation factor '8813', or to express F107, 2134P or other fimbriae, different from F4, F5, F6, and F41. PCR with fedA -specific primers, restriction enzyme digestion of the PCR product, and nucleotide sequence analysis demonstrated that 2134P pili, colonisation factor '8813' and fimbriae identified on Australian strains of the O141 serotype belong to one family of F107 fimbrial antigens.  相似文献   
37.
Enveloped virus glycoproteins exhibit membrane fusion activity. We have analysed whether the G protein of vesicular stomatitis virus, reconstituted into liposomes, is able to fuse nucleated cells in a pH-dependent fashion. Proteoliposomes produced by octylglucoside dialysis did not exhibit cell fusion activity of the G protein. However, by making use of n-dodecyl octaethylene monoether (C12E8) as the solubilizing agent and by removal of the detergent in two steps, we were able to produce fusogenic G protein liposomes. These G protein liposomes fuse to the BHK-21 cell surface at pH 5.7-6.0 with an efficiency of fusion comparable with that of the parent virus. Physical and chemical analysis revealed that the fusogenic liposomes exhibited a protein to lipid weight ratio of 0.67 and showed an average diameter of 130 nm.  相似文献   
38.
Lymphatic drainage in patients after replantation of extremities   总被引:1,自引:0,他引:1  
Lymph drainage was studied by means of lymph scintigraphy in eight patients in whom successful replantation of a totally or subtotally amputated extremity had been performed. Scintigrams were made after subcutaneous injection of technetium-99m in the replanted part of the patient and the contralateral, normal extremity. In all scintigrams, axillary or inguinal lymph node activity is seen, implying drainage of lymph by means of the lymph vessels. Retention of colloid in the replanted part (79 to 94 percent) shows no significant difference with the contralateral, normal side (86 to 94 percent). Unquestionable evidence of regeneration of lymphatics in humans is delivered in the three patients, in whom lymph node activity and normal retention percentages are seen on the scintigrams after total amputation of an extremity followed by replantation without anastomosing of interrupted lymph vessels.  相似文献   
39.
A bacterial cDNA clone was identified carrying one third of the nucleotides coding for elongation factor EF-1 alpha from the brine shrimp Artemia. The sequence of codons corresponds with the known sequence of amino acids of EF-1 alpha in the region involved.  相似文献   
40.
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