全文获取类型
收费全文 | 1965篇 |
免费 | 209篇 |
国内免费 | 158篇 |
专业分类
2332篇 |
出版年
2024年 | 11篇 |
2023年 | 35篇 |
2022年 | 60篇 |
2021年 | 106篇 |
2020年 | 78篇 |
2019年 | 106篇 |
2018年 | 127篇 |
2017年 | 75篇 |
2016年 | 105篇 |
2015年 | 143篇 |
2014年 | 153篇 |
2013年 | 138篇 |
2012年 | 167篇 |
2011年 | 132篇 |
2010年 | 79篇 |
2009年 | 70篇 |
2008年 | 97篇 |
2007年 | 83篇 |
2006年 | 72篇 |
2005年 | 63篇 |
2004年 | 59篇 |
2003年 | 64篇 |
2002年 | 80篇 |
2001年 | 39篇 |
2000年 | 28篇 |
1999年 | 22篇 |
1998年 | 23篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 16篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有2332条查询结果,搜索用时 15 毫秒
1.
The formation of hyphae that grow solely by apical extension is a defining feature of filamentous fungi. Hyphal morphogenesis involves several key steps, including the establishment and maintenance of a stable polarity axis, as well as cell division via the deposition of septa. Several filamentous fungi have been employed in attempts to decipher the mechanisms underlying these steps. Amongst these fungi, Aspergillus nidulans has proven to be a particularly valuable model. The genetic tractability of this fungus coupled with the availability of sophisticated post-genomics resources has enabled the identification and characterization of numerous genes involved in hyphal morphogenesis. Here, we summarize current progress towards understanding the function of these genes and the mechanisms involved in polarized hyphal growth and septation in A. nidulans. We also highlight important areas for future investigation. 相似文献
2.
The purpose of this review is to provide an overview of the effects of adenovirus and influenza virus infections on obesity in various experimental models. We reviewed studies that were conducted within the past 10 years and were related to virus infection and obesity prevalence. Here, we discuss a different causal relationship between adenovirus and influenza infections with obesity. Adenovirus infection can cause obesity, whereas obesity can be a risk factor for increasing influenza virus infection and increases the risk of morbidity and mortality. The prevalence of obesity due to adenovirus infections may be due to an increase in glucose uptake and reduction in lipolysis caused by an increase in corticosterone secretion. Adenovirus infections may lead to increases in appetite by decreasing norepinephrine and leptin levels and also cause immune dysfunction. The relationship between obesity and influenza virus infection could be summarized by the following features: decreases in memory T-cell functionality and interferon (IFN)-α, IFN-β, and IFN-γ mRNA expression, increases in viral titer and infiltration, and impaired dendritic cell function in obese individuals. Moreover, leptin resistance may play an important role in increasing influenza virus infections in obese individuals. In conclusion, prevention of adenovirus infections could be a good approach for reducing obesity prevalence, and prevention of obesity could reduce influenza virus infections from the point of view of viral infections and obesity. 相似文献
3.
Summary Lactic acid produced by continuous culture of L.casei in an upflow packed bed reactor, was recovered with Amberlite IRA 400 in a fluidized bed column. Bed expansions of 1.25 and 2.25 were applied. Reutilization did not alter the capability of net recovery of 0.048 ± 0.01 g lactic acid/g resin. When 2200 cm/h of ascensional velocity was used, (bed expansion of 2.25), the resin adsorbed 39.3% of the initial lactic acid and 63.5% was eluted. This resin supported the highest exchange capacity of 0.126 g lactic acid/g resin. Applying high flow rates, the process has potential industrial applications due to the short time employed. 相似文献
4.
5.
鳜鱼的耗氧率及其池塘养殖 总被引:18,自引:1,他引:17
本文较详细地报道了鳜鱼的耗氧率和窒息点,并对鳜鱼和作其饲料的鱼同池饲养的可能性进行了探讨。结果表明,鳜鱼耗氧量和体重正相关(r=0.99),耗氧率与体重反相关(r=-0.97);在水温20℃,鱼种耗氧率约为0.14mg/g.h.,成鱼约为0.12mg/g.h.;耗氧量和耗氧率均与水温正相关(r=0.90,r=0.94),水温13—30℃时,体重230±11.7g的鳜鱼。耗氧量为14.31—42.13mg/尾。h.,耗氧率为0.059—0.175mg/g.h.;鳜鱼耗氧率昼夜变化与家鱼相反,黄昏至凌晨是高峰期,为0.12—0.15mg/g.h.(T=20℃),白天是低谷期,为0.07—0.10mg/g.h;;鳜鱼的窒息点与家鱼类较接近,变化范围为0.45—0.76mg/L;鳜鱼和作其饲料的鱼在同一池塘中饲养,既可持续不断地提供鳜鱼充足的适口饵料,又简单易行,成本低,效益高,有较大的价值。 相似文献
6.
7.
Shuai Ma Shuhui Sun Jiaming Li Yanling Fan Jing Qu Liang Sun Si Wang Yiyuan Zhang Shanshan Yang Zunpeng Liu Zeming Wu Sheng Zhang Qiaoran Wang Aihua Zheng Shuguang Duo Yang Yu Juan Carlos Izpisua Belmonte Piu Chan Qi Zhou Moshi Song Weiqi Zhang Guang-Hui Liu 《Cell research》2021,(4):415-432
Aging is a major risk factor for many diseases,especially in highly prevalent cardiopulmonary comorbidities and infectious diseases including Coronavirus Diseas... 相似文献
8.
Yi‐Zhe Zhang Juncheng Lin Zhizhong Ren Chun‐Xiang Chen Daisuke Miki Si‐Si Xie Jian Zhang Ya‐Nan Chang Jing Jiang Jun Yan Qingshun Q. Li Jian‐Kang Zhu Cheng‐Guo Duan 《植物学报(英文版)》2021,63(4):707-722
Heterochromatin is widespread in eukaryotic genomes and has diverse impacts depending on its genomic context. Previous studies have shown that a protein complex, the ASI1‐AIPP1‐EDM2 (AAE) complex, participates in polyadenylation regulation of several intronic heterochromatin‐containing genes. However, the genome‐wide functions of AAE are still unknown. Here, we show that the ASI1 and EDM2 mostly target the common genomic regions on a genome‐wide level and preferentially interacts with genetic heterochromatin. Polyadenylation (poly(A) sequencing reveals that AAE complex has a substantial influence on poly(A) site usage of heterochromatin‐containing genes, including not only intronic heterochromatin‐containing genes but also the genes showing overlap with heterochromatin. Intriguingly, AAE is also involved in the alternative splicing regulation of a number of heterochromatin‐overlapping genes, such as the disease resistance gene RPP4. We provided evidence that genic heterochromatin is indispensable for the recruitment of AAE in polyadenylation and splicing regulation. In addition to conferring RNA processing regulation at genic heterochromatin‐containing genes, AAE also targets some transposable elements (TEs) outside of genes (including TEs sandwiched by genes and island TEs) for epigenetic silencing. Our results reveal new functions of AAE in RNA processing and epigenetic silencing, and thus represent important advances in epigenetic regulation. 相似文献
9.
干旱区绿洲城镇景观生态风险时空变化分析——以张掖绿洲乡镇为例 总被引:1,自引:0,他引:1
科学评估与分析干旱区绿洲乡镇景观生态风险,对优化绿洲土地资源管控和维护干旱区绿洲生态系统稳定性具有重要现实意义。以张掖市绿洲乡镇为对象,基于土地利用数据和景观格局指数,结合ArcGIS空间分析功能,研究其景观生态风险时空特征及影响因素。结果表明:1987—2018年,耕地和建设用地变化明显,分别增加429.03 km~2和236.26 km~2;整体景观生态风险呈下降趋势,并呈“南北高、中间低”格局特征;各乡镇风险水平在空间上正向聚集,位于绿洲边缘地区的乡镇风险变化明显;人为活动干扰是近年风险水平变化的主要因素。研究成果可为西北干旱区绿洲生态保护与治理提供决策参考。 相似文献
10.
β-葡萄糖苷酶的分离纯化和性质研究 总被引:12,自引:0,他引:12
β-葡萄糖苷酶是纤维素酶的重要组分之一,它不仅可水解纤维二糖和寡糖,更可解除纤维二糖对β-1,4-内切葡聚糖酶和外切葡聚糖酶的抑制,提高水解速率和程度.利用SephadexG-150和DEAE-SephadexA-50层析法从黑曲霉变异株L-22中分离提纯了β-葡萄糖苷酶,该酶是由两个分子量相同的亚基组成的二聚体,每个亚基分子量为203kD.该酶最适pH为4.8,pH稳定范围在3.6~6.4;最适温度是60℃,温度稳定范围为4~60℃;酶分子含糖量为8.35%.它是一个酸性β-葡萄糖苷水解酶,专一性地水解β-糖苷键.而不水解α-糖苷键,对短链底物表现了相对高的活力.用动力学分析和共价化学修饰方法探讨了与该酶活力有关的必需基团.由pH对lgVm和lgVm/Km的影响,推测出酶活性部位至少有两个可解离基团为酶活性所必需,它们在酶-底物复合物中的pKes1和pKes2的值分别为4.0和5.6,在游离酶中的pK值分别为4.2和5.9.由此可初步判断这两个可解离基团可能为组氨酸和含羧基的氨基酸,它们与酶的催化和底物结合可能有关. 相似文献