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   3485篇
  免费   196篇
  国内免费   7篇
  2022年   10篇
  2021年   43篇
  2020年   24篇
  2019年   36篇
  2018年   51篇
  2017年   37篇
  2016年   70篇
  2015年   110篇
  2014年   141篇
  2013年   221篇
  2012年   215篇
  2011年   183篇
  2010年   102篇
  2009年   101篇
  2008年   194篇
  2007年   223篇
  2006年   188篇
  2005年   199篇
  2004年   195篇
  2003年   173篇
  2002年   167篇
  2001年   69篇
  2000年   89篇
  1999年   59篇
  1998年   45篇
  1997年   34篇
  1996年   32篇
  1995年   31篇
  1994年   15篇
  1993年   18篇
  1992年   63篇
  1991年   55篇
  1990年   58篇
  1989年   46篇
  1988年   48篇
  1987年   36篇
  1986年   28篇
  1985年   23篇
  1984年   28篇
  1983年   28篇
  1982年   19篇
  1981年   27篇
  1980年   21篇
  1979年   17篇
  1978年   10篇
  1976年   9篇
  1975年   9篇
  1971年   9篇
  1969年   9篇
  1968年   10篇
排序方式: 共有3688条查询结果,搜索用时 281 毫秒
21.
Tissue maceration was generally elucidated by the action of endo-polygalacturonase and endo-pectate or -pectin lyase (endo-PAL or -PNL). In a process of screening of Erwinia and Pseudomonas strains for enzymatic pulping of pectocellulosic bast fibers, it was found that their PAL productivity was not completely related with defibration activity, i.e., the fact that an E.chrysanthemi strain showed high PAL productivity but possessed rather low defibration activity. Moreover, defibration activity was parallel to the amount of neutral sugars released during pulping. Based on these fact, the maceration or enzymatic pulping of basts was estimated to proceed not only by cleavage of interfiber bonding cause by PAL action but also another factors. Among three possibilities proposed on the maceration mechanism of basts, it was elucidated by a concerted action of PAL and PNL with an aid of xylanase. In addition, a quantitative determinative method of maceration activity toward basts was also presented.  相似文献   
22.
Human leukemia cell lines--clinical and theoretical significances   总被引:2,自引:0,他引:2  
Y Matsuo  J Minowada 《Human cell》1988,1(3):263-274
Establishment and total characterization of permanent growth-factor independent human leukemia cell lines are reviewed. Among others, a few significant contributions in the utility of leukemia cell lines described include establishment of immunodiagnosis of human leukemias and lymphomas, discovery of EB virus and of human retroviruses, proposed model of normal hematopoietic cell differentiation scheme, lymphokine-monokine production, identification and characterization, studies on genes responsible for immunobiological and growth regulatory molecules, and pharmacotoxicological and kinetic research. It is conceivable that the future leads by the utility of human leukemia cell lines to the advancement of research are indeed unlimited.  相似文献   
23.
24.
Monocytic leukemia (MoL) cells were obtained from the peripheral blood of a patient in whom the leukemic cells infiltrating various lymphoreticular organs exhibited features intermediate between interdigitating reticulum cells (IDC) and ordinary phagocytic macrophages, whereas the leukemic cells in the peripheral blood were essentially monocytic and lacked such features. Peripheral blood CD4+ T-cells were established as an interleukin-2-dependent T-cell line. When the MoL cells were exposed for a few days to conditioned medium from the T-cell line, they extended several dendritic cytoplasmic projections and became intensely positive for HLA-DR antigen, cytoplasmic S-100β protein, and CD1 antigen. Functionally, the conditioned medium significantly down-regulated Fc-mediated and Fc-independent phagocytic activities, and the levels of lysosomal enzymes such as lysozyme and nonspecific esterase in the MoL cells. Moreover, the conditioned medium significantly up-regulated the accessory cell function of the MoL cells as measured by the primary allogenic mixed leukocyte reaction (MLR). Furthermore, the conditioned medium significantly down-regulated the expression of CD14 antigen. Biochemical analysis indicated that the factor responsible for these changes is a protein which is distinct from known human cytokines and whose molecular weight is approximately 31 kDa. These findings suggest that IDC are closely related the monocytic lineage and that helper T-cells play an important role in constructing the microenvironment of T-lymphoid tissues which is necessary for the differentiation and maturation of IDC.  相似文献   
25.
A simple method to reconstruct the midlateral lid margin defect is described using an orbicularis oculi musculocutaneous advancement flap and a free conchal cartilage graft. This method is easy to perform not only in the lower eyelid, but also in the upper one, provides a natural gray line and a stable lid margin without postoperative eversion, and substitutes for the Leone and van Gemert procedure.  相似文献   
26.
Apical flower buds of Cymbidium goeringli Reichenbach fil. (ca 2 mm long) exeised from infloreseences (ca 5 cm long) were explanted on modified Murashige & Skoog medium (=MS medium) supplemented with N6-benzyladenine (BA) and -naphthaleneacetic acid (NAA). Within 107 days of culture, swelling growth, chlorophyll synthesis, and subsequent rhizome differentiation were observed. MS medium containing 0.1 mg l-1 BA and 10 mg l-1 NAA was found to be optimal for initiating rhizome development and subsequent plantlet regeneration.Explants cultured on MS medium supplemented with 1 mg l-1 NAA alone formed a mass of rhizome branches. Multiple shoots of rhizome branches were induced from apical segments when rhizomes were transferred to MS medium containing 0.1 mg l-1 BA and 10 mg l-1 NAA.Abbreviations NAA -naphthaleneacetic acid - BA N6-benzyladenine  相似文献   
27.
28.
The cytologic presentation of a case of chondrosarcoma of the trachea in a 72-year-old man is described. A mass detected on routine chest roentgenogram and defined by CT scan was used to make a touch imprint smear during partial tumor resection. The cytologic findings included round or polygonal cells with occasional binucleation, round hyperchromatic nuclei and prominent nucleoli, present in an amorphous pink-violet or light-blue background containing fragments of chondroid tissue. The histopathology was interpreted as a low-grade chondrosarcoma. Cartilaginous tumors of the trachea should be considered in the differential diagnosis of upper airway obstruction.  相似文献   
29.
Using a single-probe method, we have cloned the gene for an immunogenic MPB57 protein of Mycobacterium bovis BCG. The nucleotide sequence includes an ORF of 300 base pairs encoding a protein of 99 amino acids with an Mr of 10,818. This cloned gene was expressed in an Escherichia coli expression vector to give a mature protein which reacted with a polyclonal antibody raised against MPB57.  相似文献   
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