全文获取类型
收费全文 | 13874篇 |
免费 | 1264篇 |
国内免费 | 1214篇 |
专业分类
16352篇 |
出版年
2024年 | 31篇 |
2023年 | 213篇 |
2022年 | 461篇 |
2021年 | 657篇 |
2020年 | 506篇 |
2019年 | 578篇 |
2018年 | 573篇 |
2017年 | 432篇 |
2016年 | 569篇 |
2015年 | 847篇 |
2014年 | 1024篇 |
2013年 | 1039篇 |
2012年 | 1237篇 |
2011年 | 1108篇 |
2010年 | 686篇 |
2009年 | 570篇 |
2008年 | 703篇 |
2007年 | 623篇 |
2006年 | 535篇 |
2005年 | 482篇 |
2004年 | 378篇 |
2003年 | 394篇 |
2002年 | 301篇 |
2001年 | 254篇 |
2000年 | 232篇 |
1999年 | 203篇 |
1998年 | 128篇 |
1997年 | 124篇 |
1996年 | 125篇 |
1995年 | 121篇 |
1994年 | 96篇 |
1993年 | 89篇 |
1992年 | 150篇 |
1991年 | 121篇 |
1990年 | 85篇 |
1989年 | 90篇 |
1988年 | 77篇 |
1987年 | 68篇 |
1986年 | 50篇 |
1985年 | 70篇 |
1984年 | 40篇 |
1983年 | 35篇 |
1982年 | 28篇 |
1981年 | 17篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 16篇 |
1973年 | 13篇 |
1971年 | 19篇 |
1970年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
骨质疏松等中老年的常见病和多发病也呈年轻化发展,如何进行有效的骨状况诊断,拥有一台可以信赖的、可以方便地应用的骨测量仪器显得更为重要。超声波骨测量技术是使用范围比较广泛的一种,本文对超声波测量法的最新发展进行了阐述。 相似文献
992.
Dacrycarpus imbricatus is a vulnerable conifer in China whose geographical distribution encompasses large island but small mainland populations, providing a framework for contrasting the patterns of population genetic composition. In this study, seven populations on Hainan Island and the Chinese mainland were sampled throughout its distribution range and assessed using ISSR. The results did not show significant differences neither in genetic variation nor in genetic differentiation between the island and the mainland populations (P > 0.05). Severe bottlenecks were identified at population, island/mainland as well as range-wide scales. A relatively high level of variation but a low degree of differentiation was revealed. Ecological and life traits were suggested to play main roles in the shaping of genetic variation pattern. Of them long generation times could have exerted a lagging effect on both the genetic variation and differentiation. Our findings may contribute to establish management practices. 相似文献
993.
Kejian Wang Ding Tang Lilan Hong Wenying Xu Jian Huang Ming Li Minghong Gu Yongbiao Xue Zhukuan Cheng 《PLoS genetics》2010,6(1)
Sexual reproduction is essential for the life cycle of most angiosperms. However, pseudovivipary is an important reproductive strategy in some grasses. In this mode of reproduction, asexual propagules are produced in place of sexual reproductive structures. However, the molecular mechanism of pseudovivipary still remains a mystery. In this work, we found three naturally occurring mutants in rice, namely, phoenix (pho), degenerative palea (dep), and abnormal floral organs (afo). Genetic analysis of them indicated that the stable pseudovivipary mutant pho was a double mutant containing both a Mendelian mutation in DEP and a non-Mendelian mutation in AFO. Further map-based cloning and microarray analysis revealed that dep mutant was caused by a genetic alteration in OsMADS15 while afo was caused by an epigenetic mutation in OsMADS1. Thus, OsMADS1 and OsMADS15 are both required to ensure sexual reproduction in rice and mutations of them lead to the switch of reproductive habit from sexual to asexual in rice. For the first time, our results reveal two regulators for sexual and asexual reproduction modes in flowering plants. In addition, our findings also make it possible to manipulate the reproductive strategy of plants, at least in rice. 相似文献
994.
995.
996.
应用树状DNA杂交(DDH)对生殖道尖锐湿疣中HPV DNA的分型检测 总被引:5,自引:0,他引:5
从手术切除的50例生殖道尖锐湿疣新鲜标本中,以及15例正常人血清中,提取基因组DNA,同时用树状DNA杂交(dendrimer DNA hybridizalion,DDH)技术和PCR进行HPV DNA的分型检测.结果50例尖锐湿疣中,以DDH方法检测,感染HPV6型者20例,感染11型者24例,6/11型混合感染者3例,阴性3例,总检测率达94%;以PCR方法检测,HPV6型感染者21例,11型感染者24例,6/11型混合感染者3例,阴性2例,总检测率为96%.15例正常人血清中,以DDH方法检测,HPV感染的假阳性率为0%;以PCR检测,假阳性率为6.67%.还以HPV阳性标本对DDH方法做了敏感度的测定,结果阳性病例DNA检测最低浓度为97.28pg/ml.研究表明,DDH技术具有较高敏感性和高特异性,且成本较低,操作安全简便,可适用于基层中小医院较大样本量筛查. 相似文献
997.
Xu-Dong Tang Guang-Ping Liang Chuan Li Ying Wan Ting Chen Ling Chen Song-Tao Yu Zhen Xiong Dian-Chun Fang Guo-Zheng Wang Shi-Ming Yang 《Cancer immunology, immunotherapy : CII》2010,59(7):1041-1047
Heparanase is expressed in almost all advanced tumors, and therefore it may serve as a potential target for tumor therapy. Our previous study has shown that heparanase can serve as a potential universal tumor-associated antigen (TAA) for the immunotherapy of advanced tumors. Further study demonstrated that the HLA-A*0201-restricted Cytotoxic T lymphocytes (CTL) epitopes Hpa525 (PAFSYSFFV), Hpa277 (KMLKSFLKA) and Hpa405 (WLSLLFKKL) from human heparanase could induce a potent anti-tumor immune response in vitro. The present study was designed to investigate whether the above peptides could induce immune responses in mice. Our results demonstrated that the effectors from heparanase peptide-immunized mice could effectively lyse various tumor cells that were heparanase positive and HLA-A*0201 matched. We also found that these peptide-specific CTLs did not lyse autologous lymphocytes that had low heparanase activity. Further study revealed that Hpa525, Hpa277, and Hpa405 peptides increased the frequency of IFN-γ-producing T cells as compared to a negative peptide. These results suggest that Hpa525, Hpa277, and Hpa405 peptides are novel HLA-A*0201-restricted CTL epitopes capable of inducing heparanase-specific CTLs in mice. Because heparanase is expressed in most advanced malignant tumors, Hpa525, Hpa277, and Hpa405 peptide-based vaccines may be useful for the immunotherapy of patients with advanced tumors. 相似文献
998.
999.
The temples of Angkor monuments including Angkor Thom and Bayon in Cambodia and surrounding countries were exclusively constructed
using sandstone. They are severely threatened by biodeterioration caused by active growth of different microorganisms on the
sandstone surfaces, but knowledge on the microbial community and composition of the biofilms on the sandstone is not available
from this region. This study investigated the microbial community diversity by examining the fresh and old biofilms of the
biodeteriorated bas-relief wall surfaces of the Bayon Temple by analysis of 16S and 18S rRNA gene sequences. The results showed
that the retrieved sequences were clustered in 11 bacterial, 11 eukaryotic and two archaeal divisions with disparate communities
(Acidobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, Proteobacteria; Alveolata, Fungi, Metazoa, Viridiplantae; Crenarchaeote,
and Euyarchaeota). A comparison of the microbial communities between the fresh and old biofilms revealed that the bacterial
community of old biofilm was very similar to the newly formed fresh biofilm in terms of bacterial composition, but the eukaryotic
communities were distinctly different between these two. This information has important implications for understanding the
formation process and development of the microbial diversity on the sandstone surfaces, and furthermore to the relationship
between the extent of biodeterioration and succession of microbial communities on sandstone in tropic region. 相似文献
1000.