全文获取类型
收费全文 | 1786篇 |
免费 | 163篇 |
出版年
2023年 | 8篇 |
2022年 | 5篇 |
2021年 | 31篇 |
2020年 | 20篇 |
2019年 | 33篇 |
2018年 | 31篇 |
2017年 | 38篇 |
2016年 | 60篇 |
2015年 | 113篇 |
2014年 | 118篇 |
2013年 | 142篇 |
2012年 | 149篇 |
2011年 | 150篇 |
2010年 | 99篇 |
2009年 | 79篇 |
2008年 | 123篇 |
2007年 | 87篇 |
2006年 | 84篇 |
2005年 | 64篇 |
2004年 | 64篇 |
2003年 | 76篇 |
2002年 | 60篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 21篇 |
1998年 | 28篇 |
1997年 | 13篇 |
1996年 | 14篇 |
1995年 | 20篇 |
1994年 | 14篇 |
1993年 | 8篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1976年 | 8篇 |
1974年 | 4篇 |
1972年 | 5篇 |
1971年 | 4篇 |
1968年 | 2篇 |
排序方式: 共有1949条查询结果,搜索用时 968 毫秒
31.
Monique F. van Wordragen Pieter B. F. Ouwerkerk Hans J. M. Dons 《Plant Cell, Tissue and Organ Culture》1992,30(2):149-157
The agropine type Agrobacterium rhizogenes strain LBA9402 induced callus and roots on stems of greenhouse grown plants and on leaf disks of in vitro grown plantlets of chrysanthemum (Dendranthema grandiflora Tzvel.). In this callus and roots no opines were detected, nor were any of the other features of the hairy root syndrome observed. Experiments aimed to identify the nature of the tumour-like growth revealed that induction was correlated with the presence of the TR-DNA on the Ri-plasmid. Root induction was probably the result of auxin synthesis following transient expression of iaaM and iaaH genes, present on the TR-DNA. The chrysanthemum cultivar used, cv. Parliament, showed a high auxin sensitivity compared to tobacco. Analysis of early transformation events using the GUSintron reporter gene revealed that low efficiency gene transfer and transient gene expression took place, but most probably without stable integration of the T-DNA in the plant genome. The results presented here stress the fact that callus formation or root induction as measures for transformation efficiency should be used with caution. 相似文献
32.
A long-range restriction map of the human chromosome 19q13 region: Close physical linkage between CKMM and the ERCC1 and ERCC2 genes 总被引:12,自引:4,他引:8 下载免费PDF全文
33.
Martin J.M.C. Thoolen Pieter B.M.W.M. Timmermans Pieter A. van Zwieten 《Life sciences》1981,28(19):2103-2109
In conscious spontaneously hypertensive rats prepared with permanent indwelling aortic catheters the continuous infusion of clonidine (500 μg/kg/day) via an ALZET miniosmopump induced significant reductions in blood pressure and heart rate. These effects were well sustained during 12 days of treatment. A marked overshoot in heart rate was observed following withdrawal of clonidine administration. The tachycardia persisted for more than 36 hours. Mean arterial pressure exceeded control level slightly in the immediate withdrawal period only, whereas significant blood pressure lability was observed for more than 36 hours. These withdrawal symptoms were accompanied by an elevation of plasma noradrenaline concentration. The present study shows the consistent antihypertensive and bradycardic activities of clonidine during 12 days of infusion in spontaneously hypertensive rats. Furthermore, this model may provide a useful tool in the study of withdrawal phenomena of antihypertensive drugs. 相似文献
34.
Janssen Dick B. op den Camp Huub J. M. Leenen Pieter J. M. van der Drift Chris 《Archives of microbiology》1980,124(2-3):197-203
Glutamine synthetase from Pseudomonas aeruginosa is regulated by repression/derepression of enzyme synthesis and by adenylylation/deadenylylation control. High levels of deadenylylated biosynthetically active glutamine synthetase were observed in cultures growing with limiting amounts of nitrogen while synthesis of the enzyme was repressed and that present was adenylylated in cultures with excess nitrogen.NADP-and NAD-dependent glutamate dehydrogenase could be separated by column chromatography and showed molecular weights of 110,000 and 220,000, respectively. Synthesis of the NADP-dependent glutamate dehydrogenase is repressed under nitrogen limitation and by growth on glutamate. In contrast, NAD-dependent glutamate dehydrogenase is derepressed by glutamate. Glutamate synthase is repressed by glutamate but not by excess nitrogen. 相似文献
35.
Use of Transposons in Cloning Poorly Selectable Genes of Escherichia coli: Cloning of uvrA and Adjacent Genes 总被引:3,自引:0,他引:3 下载免费PDF全文
Jourica A. Brandsma Cees A. van Sluis Pieter van de Putte 《Journal of bacteriology》1981,147(2):682-684
A transposon was introduced close to a poorly selectable gene. This gene could be cloned by using selection for the antibiotic resistance marker of the transposon. 相似文献
36.
37.
Jeroen de Ridder Pieter Meysman Olugbenga Oluwagbemi Thomas Abeel 《PLoS computational biology》2014,10(7)
Contributing to a student organization, such as the International Society for Computational Biology Student Council (ISCB-SC) and its Regional Student Group (RSG) program, takes time and energy. Both are scarce commodities, especially when you are trying to find your place in the world of computational biology as a graduate student. It comes as no surprise that organizing ISCB-SC-related activities sometimes interferes with day-to-day research and shakes up your priority list. However, we unanimously agree that the rewards, both in the short as well as the long term, make the time spent on these extracurricular activities more than worth it. In this article, we will explain what makes this so worthwhile: soft skills. 相似文献
38.
39.
Marijn Bauters Sofie Meeus Matti Barthel Piet Stoffelen Hannes P. T. De Deurwaerder Flicien Meunier Travis W. Drake Quentin Ponette Jerme Ebuy Pieter Vermeir Hans Beeckman Francis wyffels Samuel Bod Hans Verbeeck Filip Vandelook Pascal Boeckx 《Global Change Biology》2020,26(8):4449-4461
Forests exhibit leaf‐ and ecosystem‐level responses to environmental changes. Specifically, rising carbon dioxide (CO2) levels over the past century are expected to have increased the intrinsic water‐use efficiency (iWUE) of tropical trees while the ecosystem is gradually pushed into progressive nutrient limitation. Due to the long‐term character of these changes, however, observational datasets to validate both paradigms are limited in space and time. In this study, we used a unique herbarium record to go back nearly a century and show that despite the rise in CO2 concentrations, iWUE has decreased in central African tropical trees in the Congo Basin. Although we find evidence that points to leaf‐level adaptation to increasing CO2—that is, increasing photosynthesis‐related nutrients and decreasing maximum stomatal conductance, a decrease in leaf δ13C clearly indicates a decreasing iWUE over time. Additionally, the stoichiometric carbon to nitrogen and nitrogen to phosphorus ratios in the leaves show no sign of progressive nutrient limitation as they have remained constant since 1938, which suggests that nutrients have not increasingly limited productivity in this biome. Altogether, the data suggest that other environmental factors, such as increasing temperature, might have negatively affected net photosynthesis and consequently downregulated the iWUE. Results from this study reveal that the second largest tropical forest on Earth has responded differently to recent environmental changes than expected, highlighting the need for further on‐ground monitoring in the Congo Basin. 相似文献
40.
Pathogen persistence in host communities is influenced by processes operating at the individual host to landscape‐level scale, but isolating the relative contributions of these processes is challenging. We developed theory to partition the influence of host species, habitat patches and landscape connectivity on pathogen persistence within metacommunities of hosts and pathogens. We used this framework to quantify the contributions of host species composition and habitat patch identity on the persistence of an amphibian pathogen across the landscape. By sampling over 11 000 hosts of six amphibian species, we found that a single host species could maintain the pathogen in 91% of observed metacommunities. Moreover, this dominant maintenance species contributed, on average, twice as much to landscape‐level pathogen persistence compared to the most influential source patch in a metacommunity. Our analysis demonstrates substantial inequality in how species and patches contribute to pathogen persistence, with important implications for targeted disease management. 相似文献