全文获取类型
收费全文 | 5433篇 |
免费 | 426篇 |
国内免费 | 270篇 |
出版年
2024年 | 6篇 |
2023年 | 62篇 |
2022年 | 141篇 |
2021年 | 253篇 |
2020年 | 175篇 |
2019年 | 207篇 |
2018年 | 188篇 |
2017年 | 135篇 |
2016年 | 211篇 |
2015年 | 341篇 |
2014年 | 384篇 |
2013年 | 414篇 |
2012年 | 504篇 |
2011年 | 443篇 |
2010年 | 270篇 |
2009年 | 243篇 |
2008年 | 267篇 |
2007年 | 242篇 |
2006年 | 189篇 |
2005年 | 177篇 |
2004年 | 167篇 |
2003年 | 120篇 |
2002年 | 108篇 |
2001年 | 106篇 |
2000年 | 93篇 |
1999年 | 99篇 |
1998年 | 40篇 |
1997年 | 51篇 |
1996年 | 41篇 |
1995年 | 38篇 |
1994年 | 29篇 |
1993年 | 33篇 |
1992年 | 41篇 |
1991年 | 37篇 |
1990年 | 46篇 |
1989年 | 36篇 |
1988年 | 23篇 |
1987年 | 24篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1973年 | 9篇 |
1972年 | 6篇 |
1971年 | 9篇 |
1968年 | 5篇 |
排序方式: 共有6129条查询结果,搜索用时 15 毫秒
51.
Jie Wang Gao-Fei Fu Luke R. Tembrock Xue-Zhu Liao Song Ge Zhi-Qiang Wu 《植物分类学报:英文版》2023,61(2):328-344
The study of genomic structural evolution associated with accelerated evolutionary rates that result in avoidance of meltdown and increase biodiversity is becoming ever more possible as the number of available plastomes increases. To more comprehensively analyze rate heterogeneity among monocots and within Poaceae, we sequenced plastomes from four Poaceae species, combined them with publicly available data from ~200 plastomes, and conducted comparative analyses to quantify the pattern of rate heterogeneity between different lineages, functional groups, and periods of evolutionary time. We compared structural differences across the Poaceae to quantify how changes in plastome size correspond to different genomic subunits and the evolution of IR–SC junction boundaries. The substitution rates among ancestral Poaceae were inferred to be exceptionally rapid compared to other monocots but slowed after divergence into extant lineages, which could not be sufficiently explained by positive selection. As such, rapid rates in the ancestral lineage leading to Poaceae might be more closely linked to large-scale structural changes like the loss of ycf1 and ycf2. The total increase in plastome size across Poaceae was positively correlated with the total length of intergenic spacers, tandem repeats, and dispersed repeats as well as large single copy, and inverted repeats (IRs). The continuous evolution of IR–SC junction boundaries was asynchronous with sizes of total genome and subunits across Poaceae. Future work is needed to better understand what factors in ancestral Poaceae evolved to harness such rapid rates of plastome evolution, avoid a mutational meltdown, and escape the stagnation of strong purifying selection as well as if these factors could be utilized to synthetically control rates. 相似文献
52.
53.
K Yamamoto D Okamura D Kurahara K Liao L Kimura R Simafranca J Musgrave D Person J Galario K Yamaga 《Cellular and molecular biology, including cyto-enzymology》2003,49(8):1333-1337
Glomerular inflammation is associated with urinary mononuclear cells (UMC) in a number of diseases including IgA nephropathy and glomerulonephritis. We examined UMC from children with lupus nephritis for a number of years to characterize the types of mononuclear cells found in urine and to determine if they were associated with active lupus nephritis. Detailed analysis of UMC by cell counts and by flow cytometry showed that monocytes were the clearly dominant cell type. Evaluation of the smaller number of lymphocytes found in the urine of patients with active lupus nephritis demonstrated a strong predominance of CD8+ lymphocytes, in contrast to the normal CD4+/CD8+ ratio that is found in peripheral blood. The degree of proteinuria strongly correlated with the presence of UMC. The UMC counts decreased as their clinical condition improved as indicated by lower indices of flare. These observations suggest that UMC may be a valuable tool in detecting and monitoring disease activity in patients with severe lupus nephritis. More importantly, this study indicated that both monocytes and cytotoxic CD8+ T cells may play a role in pathogenesis of lupus nephritis. 相似文献
54.
55.
青海湖裸鲤寄生舌状绦虫的空间格局研究 总被引:3,自引:0,他引:3
舌状绦虫裂头蚴只寄生在体长小于220mm的青海湖裸鲤中,其种群在宿主种群中呈聚集分布。其聚集分布的强度随寄生虫种群平均密度的增加而降低。由于舌状绦虫在宿主体腔生长,产生明显的空间拥挤效应,可能导致宿主死亡或被食鱼鸟类捕食而转移到终末宿主中。在体长小于120mm的宿主中,密度依赖的死亡过程可能是使聚集强度降低的原因;而体长140-200mm的鱼中,则是非密度依赖的全死过程使聚集强度增加. 相似文献
56.
超氧化物歧化酶模拟化合物的生物活性研究 总被引:16,自引:0,他引:16
根据天然超氧化物歧化酶(SOD)活性部位结构合成了含苯并咪唑的5种配体及其32种分别含Cu(Ⅱ)、Fe(Ⅲ)、Mn(Ⅱ)、Co(Ⅱ)的模拟化合物.经光谱、电化学测试证明这些化合物具有拟S3D活性,其50%抑制率浓度(IC50)为10-6~10-8mol·L-1,催化超氧离子自由基(O-·2)歧化的反应速率常数kq为106~108mol-1·L·s-1.同时观察到几种模拟化合物有抗肿瘤活性或增强水稻抗寒性. 相似文献
57.
检测香蕉花叶心腐病病原CMV的PAS—ELISA方法的改进 总被引:1,自引:0,他引:1
作为一种快速、敏感的免疫学方法,ELISA已被广泛地用于植物病毒的研究与应用性检测方面。在实验室中用PAS-ELISA检测香蕉花叶心腐病病原CMV已被证明是一种获得无CMV组培苗的有效手段。在香蕉无病毒组培苗工厂化大批量生产中,我们应用此法作为质量控制的手段之一,剔除病苗,保证产品不带CMV,获得一定成效。但同时我们也发现,香蕉组织中含有引起非特异性吸附反应的物 相似文献
58.
59.
Identification of a penicillin-binding protein 3 homolog, PBP3x, in Pseudomonas aeruginosa: gene cloning and growth phase-dependent expression.
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A homolog of Pseudomonas aeruginosa penicillin-binding protein 3 (PBP3), named PBP3x in this study, was identified by using degenerate primers based on conserved amino acid motifs in the high-molecular-weight PBPs. Analysis of the translated sequence of the pbpC gene encoding this PBP3x revealed that 41 and 48% of its amino acids were identical to those of Escherichia coli and P. aeruginosa PBP3s, respectively. The downstream sequence of pbpC encoded convergently transcribed homologs of the E. coli soxR gene and the Mycobacterium bovis adh gene. The pbpC gene product was expressed from the T7 promoter in E. coli and was exported to the cytoplasmic membrane of E. coli cells and could bind [3H] penicillin. By using a broad-host-range vector, pUCP27, the pbpC gene was expressed in P. aeruginosa PAO4089. [3H]penicillin-binding competition assays indicated that the pbpC gene product had lower affinities for several PBP3-targeted beta-lactam antibiotics than P. aeruginosa PBP3 did, and overexpression of the pbpC gene product had no effect on the susceptibility to the PBP3-targeted antibiotics tested. By gene replacement, a PBP3x-defective interposon mutant (strain HC132) was obtained and confirmed by Southern blot analysis. Inactivation of PBP3x caused no changes in the cell morphology or growth rate of exponentially growing cells, suggesting that pbpC was not required for cell viability under normal laboratory growth conditions. However, the upstream sequence of pbpC contained a potential sigma(s) recognition site, and pbpC gene expression appeared to be growth rate regulated. [3H]penicillin-binding assays indicated that PBP3 was mainly produced during exponential growth whereas PBP3x was produced in the stationary phase of growth. 相似文献
60.