全文获取类型
收费全文 | 24380篇 |
免费 | 2078篇 |
国内免费 | 2503篇 |
专业分类
28961篇 |
出版年
2024年 | 75篇 |
2023年 | 331篇 |
2022年 | 791篇 |
2021年 | 1258篇 |
2020年 | 862篇 |
2019年 | 1019篇 |
2018年 | 970篇 |
2017年 | 739篇 |
2016年 | 996篇 |
2015年 | 1635篇 |
2014年 | 1739篇 |
2013年 | 1986篇 |
2012年 | 2343篇 |
2011年 | 2037篇 |
2010年 | 1203篇 |
2009年 | 1143篇 |
2008年 | 1362篇 |
2007年 | 1144篇 |
2006年 | 1123篇 |
2005年 | 900篇 |
2004年 | 716篇 |
2003年 | 588篇 |
2002年 | 511篇 |
2001年 | 392篇 |
2000年 | 347篇 |
1999年 | 339篇 |
1998年 | 237篇 |
1997年 | 196篇 |
1996年 | 201篇 |
1995年 | 186篇 |
1994年 | 167篇 |
1993年 | 130篇 |
1992年 | 198篇 |
1991年 | 166篇 |
1990年 | 121篇 |
1989年 | 132篇 |
1988年 | 87篇 |
1987年 | 75篇 |
1986年 | 80篇 |
1985年 | 87篇 |
1984年 | 31篇 |
1983年 | 35篇 |
1982年 | 40篇 |
1981年 | 18篇 |
1980年 | 29篇 |
1979年 | 22篇 |
1978年 | 24篇 |
1977年 | 24篇 |
1974年 | 13篇 |
1972年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Max A B Haase Jacek Kominek Dana A Opulente Xing-Xing Shen Abigail L LaBella Xiaofan Zhou Jeremy DeVirgilio Amanda Beth Hulfachor Cletus P Kurtzman Antonis Rokas Chris Todd Hittinger 《Genetics》2021,217(2)
Dollo’s law posits that evolutionary losses are irreversible, thereby narrowing the potential paths of evolutionary change. While phenotypic reversals to ancestral states have been observed, little is known about their underlying genetic causes. The genomes of budding yeasts have been shaped by extensive reductive evolution, such as reduced genome sizes and the losses of metabolic capabilities. However, the extent and mechanisms of trait reacquisition after gene loss in yeasts have not been thoroughly studied. Here, through phylogenomic analyses, we reconstructed the evolutionary history of the yeast galactose utilization pathway and observed widespread and repeated losses of the ability to utilize galactose, which occurred concurrently with the losses of GALactose (GAL) utilization genes. Unexpectedly, we detected multiple galactose-utilizing lineages that were deeply embedded within clades that underwent ancient losses of galactose utilization. We show that at least two, and possibly three, lineages reacquired the GAL pathway via yeast-to-yeast horizontal gene transfer. Our results show how trait reacquisition can occur tens of millions of years after an initial loss via horizontal gene transfer from distant relatives. These findings demonstrate that the losses of complex traits and even whole pathways are not always evolutionary dead-ends, highlighting how reversals to ancestral states can occur. 相似文献
142.
Powdery mildew disease caused by Blumeria graminis f. sp. tritici (Bgt) is an economically important disease in wheat worldwide. The identification of germplasms resistant to the disease can not
only facilitate the breeding of resistant cultivars, but can also broaden the diversity of resistance genes. The Mexican M53
is a synthetic hexaploid wheat line developed at the International Maize and Wheat Improvement Center (CIMMYT) from the cross
between Triticum durum and Aegilops tauschii249. Infection of M53 with 15 different pathogen races revealed that the resistance in M53 was race-dependent and effective
against the majority of the tested Bgt races, including the race 15 predominant in the Beijing wheat growing area. Inoculation of the parents of M53 with the race
15 demonstrated that M53 and Ae. tauschii249 were resistant, whereas T. durum was susceptible. The inoculation of three segregating F2 populations developed from the crosses between M53 and three susceptible Chinese wheat cultivars with the race 15 showed
that the resistant gene in M53 segregated in a single dominant manner. Amplified fragment length polymorphism (AFLP) and simple
sequence repeat (SSR) markers were used to map the gene in a segregating F2 population consisting of 213 lines developed from the cross Wan7107 × M53. Two closely linked AFLP markers, Apm109 and Apm161, were identified to flank the gene with genetic distances of 1.0 cM and 3.0 cM, respectively. The recognized gene was assigned
to the long arm of chromosome 5D as determined by three linked SSR markers, Xwmc289b, Xgwm583, and Xgwm292, and by the physical mapping of Apm109 using Chinese Spring nullisomic–tetrasomic and ditelosomic stocks. The resistance gene identified in M53, temporarily designated
as Pm-M53, could be used in local wheat-breeding programs to improve powdery mildew resistance. 相似文献
143.
Siwei Xiao Yanyun Gao Xiaolong Wang Wei Shen Jinjia Wang Xiangshan Zhou 《Preparative biochemistry & biotechnology》2017,47(3):229-235
Although the human antimicrobial peptide LL37 has a broad spectrum of antimicrobial activities, it easily damages host cells following heterologous expressions. This study attempted two strategies to alleviate its damage to host cells when expressed in Pichia pastoris using the AOX1 promoter. Tandem repeat multimers of LL37 were first designed, and secretion expression strains GS115-9K-(DPLL37DP)n (n?=?2, 4, 6 and 8) containing different copies of the LL37 gene were constructed. However, LL37 tandems still killed the cells after 96?hr of induction. Subsequently, peroxisome-targeted expression was performed by adding a peroxisomal targeting signal 1 (SKL) at the C-terminus of LL37. The LL37 expression strain GS115-3.5K-LL37-SKL showed no significant inhibition in the cells after induction. Antibacterial activity assays showed that the recombinant LL37 expressed in peroxisomes had good antimicrobial activities. Then, a strain GS115-3.5K-LL37-GFP-SKL producing LL37, green fluorescent protein, and SKL fusion proteins was constructed, and the fusion protein was confirmed to be targeting the peroxisomes. However, protein extraction analysis indicated that most of the fusion proteins were still located in the cell debris after cell disruption, and further studies are required to extract more proteins from the peroxisome membrane. 相似文献
144.
Xiangbin Xu Jufang Bian Songbai Liu Hongmiao Song Nongnong Shi Yuezhi Tao Huizhong Wang 《Molecular breeding : new strategies in plant improvement》2011,27(3):337-346
The PROMOTION OF CELL SURVIVAL 1 (PCS1) gene, encoding an aspartic protease, has an important role in determining the fate of cells in embryonic development and
reproduction processes in Arabidopsis. To explore the potential function of the PCS1 gene in generating reproductive sterility, we placed the PCS1 gene under the control of an 1,869-bp nucleotide sequence from the 3′ end of the second intron (AG-I) of Arabidopsis AGAMOUS and CaMV 35S (–60) minimal promoter [AG-I-35S (–60)::PCS1], and introduced it into tobacco. RT–PCR results demonstrated that the PCS1 gene driven by AG-I-35S (–60) chimeric promoter was expressed only in anthers and carpels in the reproductive tissues of transgenic tobacco. Compared to
wild-type plants, all AG-I-35S (–60) and AG-I-35S (–60)::PCS1 transgenic lines showed a normal phenotype throughout the vegetative growth phase. However, during the reproductive stage,
most AG-I-35S (–60)::PCS1 transgenic plant anthers displayed delayed dehiscence, failed dehiscence, petalody and hypoplasia, and the pollen grains
had different shapes and sizes with a distorted, shrunken, or collapsed morphology. Moreover, three transgenic lines, PCS1-1,
PCS1-3 and PCS1-4, showed higher sterility than wild-type and AG-I-35S (–60) transgenic plants, respectively. These results showed that the construct of AG-I-35S (–60)::PCS1 was partially effective at preventing seed set and provided a novel sterility strategy. 相似文献
145.
146.
Zhang Hao Qing Zhao Xue Qiang Chen Yi Ling Zhang Ling Yu Shen Ren Fang 《Plant and Soil》2019,439(1-2):293-308
Plant and Soil - Biocrusts are important functional units in dryland ecosystems. Regarded as ecosystem engineers, cyanobacteria in biocrusts contribute several major physico-chemical and biological... 相似文献
147.
Tao Tan Jun Wu Chenyang Si Shaoxing Dai Youyue Zhang Nianqin Sun E Zhang Honglian Shao Wei Si Pengpeng Yang Hong Wang Zhenzhen Chen Ran Zhu Yu Kang Reyna Hernandez-Benitez Llanos Martinez Martinez Estrella Nuñez Delicado W. Travis Berggren Juan Carlos Izpisua Belmonte 《Cell》2021,184(8):2020-2032.e14
148.
Promoter methylation of the O6-methylguanine-DNA-methyltransferase (MGMT) gene has been considered a prognostic marker and has become more important in the treatment of glioblastoma. However, reports on the correlation between MGMT and clinical outcomes in Chinese glioblastoma patients are very scarce. In this study, quantitative methylation data were obtained by the pyrosequencing of tumor tissues from 128 GBM patients. The median overall survival (OS) was 13.1 months, with a 1-year survival of 45.3%. The pyrosequencing data were reproducible based on archived samples yielding data for all glioblastomas. MGMT promoter methylation was detected in 75/128 cases (58.6%), whereas 53/128 (41.4%) cases were unmethylated. Further survival analysis also revealed that methylation was an independent prognostic factor associated with prolonged OS but not with progression-free survival (PFS) (p = 0.029 and p = 0.112, respectively); the hazard radios were 0.63 (95% CI: 0.42–0.96) and 0.72 (95% CI: 0.48–1.09), respectively. These data indicated that MGMT methylation has prognostic significance in patients with newly diagnosed high-grade glioblastoma undergoing alkylating agent-based chemotherapy after surgical resection. 相似文献
149.
150.
Linghua Zhou Yong Shen Libo Jiang Danni Yin Jingxin Guo Hui Zheng Hao Sun Rongling Wu Yunqian Guo 《PloS one》2015,10(5)
Cells with the same genotype growing under the same conditions can show different phenotypes, which is known as “population heterogeneity”. The heterogeneity of hematopoietic progenitor cells has an effect on their differentiation potential and lineage choices. However, the genetic mechanisms governing population heterogeneity remain unclear. Here, we present a statistical model for mapping the quantitative trait locus (QTL) that affects hematopoietic cell heterogeneity. This strategy, termed systems mapping, integrates a system of differential equations into the framework for systems mapping, allowing hypotheses regarding the interplay between genetic actions and cell heterogeneity to be tested. A simulation approach based on cell heterogeneity dynamics has been designed to test the statistical properties of the model. This model not only considers the traditional QTLs, but also indicates the methylated QTLs that can illustrate non-genetic individual differences. It has significant implications for probing the molecular, genetic and epigenetic mechanisms of hematopoietic progenitor cell heterogeneity. 相似文献