全文获取类型
收费全文 | 16224篇 |
免费 | 1511篇 |
国内免费 | 1702篇 |
出版年
2024年 | 48篇 |
2023年 | 211篇 |
2022年 | 476篇 |
2021年 | 686篇 |
2020年 | 531篇 |
2019年 | 710篇 |
2018年 | 698篇 |
2017年 | 509篇 |
2016年 | 716篇 |
2015年 | 1056篇 |
2014年 | 1266篇 |
2013年 | 1263篇 |
2012年 | 1570篇 |
2011年 | 1478篇 |
2010年 | 931篇 |
2009年 | 823篇 |
2008年 | 1041篇 |
2007年 | 953篇 |
2006年 | 783篇 |
2005年 | 704篇 |
2004年 | 581篇 |
2003年 | 526篇 |
2002年 | 507篇 |
2001年 | 226篇 |
2000年 | 208篇 |
1999年 | 193篇 |
1998年 | 135篇 |
1997年 | 96篇 |
1996年 | 63篇 |
1995年 | 61篇 |
1994年 | 57篇 |
1993年 | 34篇 |
1992年 | 44篇 |
1991年 | 34篇 |
1990年 | 34篇 |
1989年 | 22篇 |
1988年 | 17篇 |
1987年 | 18篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1969年 | 5篇 |
1965年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Mapping of ben genes of Pseudomonas aeruginosa 总被引:1,自引:0,他引:1
Abstract Four ben genes responsible for the conversion of benzoate to catechol in Pseudomonas aeruginosa PAO have been mapped to a 4.6 kb Kpn I fragment. ben -1 and ben -4 were known to be separate genes but now ben-1508 has been found to be different from ben-2 . The two genes were distinguished by Tn 5 mutagenesis of a cosmid clone and deletion mapping. It is likely that the four genes mapped ( ben-4, ben-2, ben-1508 and ben-1 ) correspond to the previously characterized benR (regulatory gene) and benABC (benzoate dioxygenase) respectively. 相似文献
42.
【目的】土壤重金属污染问题日益受到关注,其中钒污染逐渐成为研究热点。淋洗是土壤修复的重要手段,但存在污染大、成本高的缺点。生物淋洗技术因其经济高效且环保的特点能够应用于土壤的修复,但其对钒污染土壤的修复,认识仍非常有限。【方法】本研究采用嗜酸性氧化亚铁硫杆菌对钒污染土壤进行了生物淋洗试验,通过影响因素试验探究了钒的最佳浸出条件,并应用扫描电子显微镜-能量色散X射线谱分析了钒在淋洗过程中的变化,最后对代谢产物进行了解析。【结果】微生物次生代谢产物能促进土壤中钒的溶出。氧化亚铁硫杆菌对土壤钒的浸出效率较高,生物淋洗20 d后土壤中钒的浸出率达到27.4%,进一步的影响因素试验表明,在固体浓度为3%、接种体积为10%、初始pH值为1.8、初始Fe2+的浓度为3.0 g/L的条件下,土壤中钒的浸出效果最佳。SEM-EDS分析证实生物淋洗后土壤中钒含量减少,其中以非残渣态形式存在的钒更容易被浸出。代谢组学分析显示氧化亚铁硫杆菌在浸出过程中产生了大量代谢产物来应对重金属胁迫。【结论】生物淋洗技术能够有效地实现土壤钒污染的修复,本研究为钒污染土壤提供了一种环境友好的修复方式。 相似文献
43.
Qian Xiang Dong Zhu Min Qiao Xiao-Ru Yang Gang Li Qing-Lin Chen Yong-Guan Zhu 《Environmental microbiology》2023,25(2):505-514
Soil bacteria are diverse and form complicated ecological networks through various microbial interactions, which play important roles in soil multi-functionality. However, the seasonal effects on the bacterial network, especially the relationship between bacterial network topological features and soil resistomes remains underexplored, which impedes our ability to unveil the mechanisms of the temporal-dynamics of antibiotic resistance genes (ARGs). Here, a field investigation was conducted across four seasons at the watershed scale. We observed significant seasonal variation in bacterial networks, with lower complexity and stability in autumn, and a wider bacterial community niche in summer. Similar to bacterial communities, the co-occurrence networks among ARGs also shift with seasonal change, particularly with respect to the topological features of the node degree, which on average was higher in summer than in the other seasons. Furthermore, the nodes with higher betweenness, stress, degree, and closeness centrality in the bacterial network showed strong relationships with the 10 major classes of ARGs. These findings highlighted the changes in the topological properties of bacterial networks that could further alter antibiotic resistance in soil. Together, our results reveal the temporal dynamics of bacterial ecological networks at the watershed scale, and provide new insights into antibiotic resistance management under environmental changes. 相似文献
44.
Aamir Hamid Khan Ling Min Yizan Ma Muhammad Zeeshan Shuangxia Jin Xianlong Zhang 《Plant biotechnology journal》2023,21(4):680-697
Global food security is one of the utmost essential challenges in the 21st century in providing enough food for the growing population while coping with the already stressed environment. High temperature (HT) is one of the main factors affecting plant growth, development and reproduction and causes male sterility in plants. In male reproductive tissues, metabolic changes induced by HT involve carbohydrates, lipids, hormones, epigenetics and reactive oxygen species, leading to male sterility and ultimately reducing yield. Understanding the mechanism and genes involved in these pathways during the HT stress response will provide a new path to improve crops by using molecular breeding and biotechnological approaches. Moreover, this review provides insight into male sterility and integrates this with suggested strategies to enhance crop tolerance under HT stress conditions at the reproductive stage. 相似文献
45.
Hui Wang Lingling Wang Meihua Wu Minghao Fang Zhaohui Huang Xin Min 《Luminescence》2023,38(2):208-215
This paper reports a sequence of a Ca3YAl3B4O15:xEu3+ red phosphor prepared using a high-temperature solid-state reaction. At the excitation of 396 nm, the samples emitted intense red emission centred at ~623 nm, which could be attributed to the 5D0→7F2 transition of the Eu3+ ion. The results showed that the optimum Eu3+ doping concentration of Ca3YAl3B4O15:Eu3+ phosphor was x = 80 mol%, and the concentration quenching mechanism of Ca3YAl3B4O15:Eu3+ red phosphor belonged to the exchange coupling between Eu3+ ions. The Commission Internationale de l'éclairage (CIE) coordinates and colour purity of Ca3Y0.2Al3B4O15:0.8Eu3+ were calculated as (0.6375, 0.3476) and 95.5%, respectively. Moreover, the red emission of the obtained phosphor Ca3YAl3B4O15:0.8Eu3+ exhibited a low thermal quenching behaviour with an intensity retention rate of 92.85% at 150°C. The above results manifest that the Eu3+-activated Ca3YAl3B4O15 phosphor is predicted to be a promising red luminescent component for white light-emitting diodes. 相似文献
46.
植物的形态结构和光合作用能够反映植物对城市空气污染的响应特性。探究城市道路机动车尾气中的典型污染物NO2气体,对植物叶片的生理光合响应特性。以二年生三角梅(Bougainvillea spectabilis)幼苗为对象,利用智能化人工熏气室模拟熏气(NO2体积分数分别为0 μL/L (自然空气)、4 μL/L,8 μL/L,记作CK、T1、T2),观察NO2胁迫后三角梅的叶片形态、微观结构和光合特征。结果表明:(1)通过叶片形态观察发现,与CK相比,低浓度T1组叶片变化不明显,随着NO2气体胁迫浓度的增加,高浓度T2组叶片逐渐出现失水、叶表面有明显的水渍状或烧灼状黄色斑点。(2)通过叶片微观结构解剖发现,高浓度NO2胁迫后气孔皱缩程度增加,气孔开度减小;叶绿体结构变形,尤其是类囊体结构疏松,膨胀等变化。(3)叶片光合特性分析发现,T1和T2组的NO2胁迫导致光饱和点(LSP)和最大净光合速率(Pnmax)下降、光补偿点(LCP)增加,表观量子效率(AQE)和暗呼吸速率(Rd)在4种光响应模型中变化规律存在一定的差异性。(4)4种光响应模型中,CK组决定系数(R2)越高,均方根误差(RMSE)越低,精度最高,尤以叶子飘等机理模型为最优,拟合效果最好,其次是直角双曲线模型。研究结果表明三角梅可通过自身的形态变化、调整光合特征参数,较好地适应不同浓度的NO2,尤其是高浓度急性胁迫下,该研究结果有助于促进不同道路绿地三角梅的推广应用,对探究三角梅的景观效益和生态效益,揭示其对环境异质性的适应机制具有重要意义。 相似文献
47.
48.
Phytophthora nicotianae causes substantial economic losses in most countries where tobacco is produced. At present, the control of P. nicotianae mainly depends on chemical methods, with considerable environmental and
health issues. We investigated the effects of ethanol extracts from Scutellaria baicalensis Georgi (SBG) and Magnolia officinalis (MO). On mycelial growth, sporangium formation, and zoospore release of P. nicotianae. Both
extracts inhibited the growth of P. nicotianae, with mycelial growth inhibition rates of 88.92% and 93.92%, respectively, at 40 mg/mL, and EC50 values of 5.39 and 5.74 mg/mL, respectively. The underlying mechanisms were the
inhibition of sporangium formation, the reduction of zoospore number, and the destruction of the mycelium
structure. At an SBG extract concentration of 16.17 mg/mL, the inhibition rates for sporangia and zoospores were
98.66% and 99.39%, respectively. At an MO extract concentration of 2.87 mg/mL, the production of sporangia
and zoospores was completely inhibited. The hyphae treated with the two plant extracts showed different degrees
of deformation and damage. Hyphae treated with SBG extract showed adhesion and local swelling, whereas treatment with MO extract resulted in broken hyphae. Mixture of the extracts resulted in a good synergistic effect. 相似文献
49.
50.
【目的】本研究旨在明确氰氟虫腙对草地贪夜蛾Spodoptera frugiperda幼虫的毒力水平和田间防治效果,为科学使用氰氟虫腙防治草地贪夜蛾提供参考依据。【方法】采用饲料混毒法在室内测定了氰氟虫腙与4种常用杀虫剂甲维盐、氯虫苯甲酰胺、虱螨脲和茚虫威对草地贪夜蛾3和6龄幼虫的致死中浓度(LC50)及LC90值,以及LC90浓度的这些杀虫剂对3龄幼虫的致死中时(medium lethal time, LT50)值。采用人工喷雾方法测定了玉米田中22%氰氟虫腙悬浮剂(6.6 g/667 m2)、22%氰氟虫腙悬浮剂(17.6 g/667 m2)、5.7%甲维盐水分散剂(1 g/667 m2)和150 g/L茚虫威悬浮剂(2 g/667 m2)对草地贪夜蛾幼虫的防效。【结果】室内生测结果显示,供试的5种杀虫剂中氰氟虫腙对草地贪夜蛾3和6龄幼虫均具有较高的毒力,其LC50值分别为2.64和4.3... 相似文献