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   6649篇
  免费   1074篇
  国内免费   3738篇
  2024年   98篇
  2023年   259篇
  2022年   368篇
  2021年   403篇
  2020年   414篇
  2019年   448篇
  2018年   273篇
  2017年   291篇
  2016年   302篇
  2015年   423篇
  2014年   619篇
  2013年   540篇
  2012年   733篇
  2011年   680篇
  2010年   574篇
  2009年   581篇
  2008年   626篇
  2007年   614篇
  2006年   534篇
  2005年   471篇
  2004年   367篇
  2003年   303篇
  2002年   242篇
  2001年   236篇
  2000年   237篇
  1999年   156篇
  1998年   91篇
  1997年   70篇
  1996年   41篇
  1995年   44篇
  1994年   21篇
  1993年   24篇
  1992年   30篇
  1991年   32篇
  1990年   32篇
  1989年   40篇
  1988年   24篇
  1987年   21篇
  1986年   33篇
  1985年   11篇
  1984年   12篇
  1983年   16篇
  1982年   27篇
  1981年   10篇
  1978年   7篇
  1977年   8篇
  1965年   6篇
  1964年   6篇
  1953年   5篇
  1950年   5篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
941.
In this study, primer pairs of 15 microsatellite markers associated with sex determination of tilapia were selected and amplified in Wami tilapia, Oreochromis urolepis hornorum. While one marker, UNH168, on linkage group 3 (LG3) was associated (P < 0.001) with the phenotypic sex in the experimental population, nine genotypes were detected in both sexes. Only 99-bp allele was detected in the female samples, while 141, 149 and 157-bp alleles were present in both male and female samples. UNH168 was localized by fluorescence in situ hybridization (FISH) on the long arm of the largest tilapia chromosome pair (chromosome 1, equivalent to LG3). This sex-linked microsatellite marker could potentially be used for marker-assisted selection in tilapia breeding programmes to produce monosex male tilapia.  相似文献   
942.
943.
944.
945.
Osseous free flaps have become the preferred method for reconstructing segmental mandibular defects. Of 457 head and neck free flaps, 150 osseous mandible reconstructions were performed over a 10-year period. This experience was retrospectively reviewed to establish an approach to osseous free flap mandible reconstruction. There were 94 male and 56 female patients (mean age, 50 years; range 3 to 79 years); 43 percent had hemimandibular defects, and the rest had central, lateral, or a combination defect. Donor sites included the fibula (90 percent), radius (4 percent), scapula (4 percent), and ilium (2 percent). Rigid fixation (up to five osteotomy sites) was used in 98 percent of patients. Aesthetic and functional results were evaluated a minimum of 6 months postoperatively. The free flap success rate was 100 percent, and bony union was achieved in 97 percent of the osteotomy sites. Osseointegrated dental implants were placed in 20 patients. A return to an unrestricted diet was achieved in 45 percent of patients; 45 percent returned to a soft diet, and 5 percent were on a liquid diet. Five percent of patients required enteral feeding to maintain weight. Speech was assessed as normal (36 percent), near normal (27 percent), intelligible (28 percent), or unintelligible (9 percent). Aesthetic outcome was judged as excellent (32 percent), good (27 percent), fair (27 percent), or poor (14 percent). This study demonstrates a very high success rate, with good-to-excellent functional and aesthetic results using osseous free flaps for primary mandible reconstruction. The fibula donor site should be the first choice for most cases, particularly those with anterior or large bony defects requiring multiple osteotomies. Use of alternative donor sites (i.e., radius and scapula) is best reserved for cases with large soft-tissue and minimal bone requirements. The ilium is recommended only when other options are unavailable. Thoughtful flap selection and design should supplant the need for multiple, simultaneous free flaps and vein grafting in most cases.  相似文献   
946.
大兴安岭地区紫貂的活动节律   总被引:10,自引:1,他引:9  
马建章  徐利 《兽类学报》1999,19(2):95-100
借助无线电遥测技术,对4只紫貂全年的活动节律进行了研究,结果表明,紫貂的活动节律春季和冬季的高峰是在晨昏二个阶段,夏秋二季的活动高峰在白昼。春季总体活动节律与夏季相比有明显差异(F=4.499,df=1,22,23;P=0.045),春季与秋季的活动节律也有差异(F=7.039;df=1,22,23;P=0.015)。其总体平均活动强度,春季活动量最小(17.53%),夏季最高(38.29%),其  相似文献   
947.
钙调素的结构生物学研究进展   总被引:1,自引:0,他引:1  
介绍了Apo-CaM、Ca2+-CaM以及CaM与其靶肽及拮抗剂复合体的空间结构.钙调素(calmodulin, CaM)作为细胞多功能的Ca2+受体,在细胞信号转导过程中发挥重要作用.近几年对它的空间结构有了较清楚的了解,使人们能够更明确地认识CaM的Ca2+激活及CaM与其靶酶的作用机制.  相似文献   
948.
蒙古栎红松林演替模型FOROAK的研究   总被引:2,自引:0,他引:2  
Based on forest dynamics theory, gap model FOROAK was developed for simulating long-termdynamics of Mongolian oak (Quercus rnongolica Fisch. )-Korean pine (Pinus koraiensis Sieb. et Zucc. )forest. The model included two parts: biological growth and environmental impacts on growth. Different areapatches were used in simulating forest changes. The results showed that this forest gap was 0.05 hm2. Themodel testing demonstrated that it could reasonably simulate forest dynamic process, and had a very highaccuracy to predict species compositions. The observed species basal areas was similar to the predicted at 60,100 and 270 year forests, the observed species compositions were similar to the predicted at old forest period.Complex changes were found through modeling forest dynamics of bare ground. Mongolian oak and white birch( Betula platyphylla Sukacz. ) dominated at early stage, forest dominated by broad leaved species was formedat middle stage, and then Korean pine dominated at latter stage. The prediction of current primary forestshowed that it was steady during the next 300 year period, the number of trees and the biomass of Korean pine changed very little.  相似文献   
949.
It was reported that the growth of Dunaliella salina Teod. cultured in medium containing 1 mol/L NaC1 was almost completely inhibited by the addition of 100 mmol/L KC1. The high K+ (100 mmol/L KC1) treatment also significantly inhibited the photosynthetic rate of D. salina and decreased chlorophyll contents in algae. This study focuses on possible effects of high K+ or alkaline pH on the ultrastructural change of chloroplasts in D. salina. After D. salina was cultured in a medium containing 100 n,anol/L KC1 or in a medium with alkaline pH for 8 to 10 days, dramatic ultrastructural changes occurred in the chloroplasts including thylakoid swelling, volume increase of chloroplast, and significant accumulation of starch grains in chloroplasts. The results are consistent with our previous report indicating that the ultrastmctuml changes in chloroplast under high K + or alkaline pH may lead to an inhibitory effects on photosynthesis and overall growth of D. salina.  相似文献   
950.
Genomic constitution of octoploid wheat-wheatgrass amphiploid Zhong 2 was analyzed by chromosome pairing and fluorescence in sim hybridization techniques. The results indicated that the octoploid wheatwheatgrass chromosomes in Zhong 2 were derived from the distant homologous genomes of wheatgrass ( Agropyron intermedium (Host) P.B. = Elytrigia intermedia (Host) Nevski = Thinotopyrum intermedium (Host) Barkworth and Dewey, and thew distant homologous genomes were not from the E geaome of T. elongatum 2x. Zhong 2 contained 12 wheatgrass chromosomes in which a pair of chromosomes was involved in translocation between wheatgrass and wheat chromosomes.  相似文献   
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