全文获取类型
收费全文 | 6703篇 |
免费 | 546篇 |
国内免费 | 2篇 |
出版年
2021年 | 80篇 |
2020年 | 62篇 |
2019年 | 83篇 |
2018年 | 95篇 |
2017年 | 89篇 |
2016年 | 134篇 |
2015年 | 249篇 |
2014年 | 272篇 |
2013年 | 338篇 |
2012年 | 466篇 |
2011年 | 496篇 |
2010年 | 313篇 |
2009年 | 291篇 |
2008年 | 398篇 |
2007年 | 392篇 |
2006年 | 345篇 |
2005年 | 343篇 |
2004年 | 308篇 |
2003年 | 328篇 |
2002年 | 296篇 |
2001年 | 129篇 |
2000年 | 103篇 |
1999年 | 99篇 |
1998年 | 77篇 |
1997年 | 61篇 |
1996年 | 43篇 |
1995年 | 49篇 |
1994年 | 44篇 |
1993年 | 32篇 |
1992年 | 65篇 |
1991年 | 68篇 |
1990年 | 64篇 |
1989年 | 53篇 |
1988年 | 56篇 |
1987年 | 52篇 |
1986年 | 40篇 |
1985年 | 53篇 |
1984年 | 50篇 |
1983年 | 68篇 |
1982年 | 30篇 |
1981年 | 45篇 |
1980年 | 27篇 |
1979年 | 31篇 |
1978年 | 36篇 |
1977年 | 39篇 |
1976年 | 32篇 |
1975年 | 28篇 |
1974年 | 32篇 |
1972年 | 24篇 |
1969年 | 29篇 |
排序方式: 共有7251条查询结果,搜索用时 187 毫秒
1.
Yohannes M. S. Samosir Steve Adkins 《In vitro cellular & developmental biology. Plant》2014,50(4):493-501
An in vitro photoautotrophic step based on the supply of CO2-enriched air (1,600 μmol mol?1) during the light phase and ambient air (350 μmol mol?1 CO2) during the dark phase has been used to promote the ex vitro establishment of coconut (Cocos nucifera L.) seedlings. The introduction of this step into a previously developed in vitro protocol was found to improve the quality of the seedlings (as assessed by fresh weight increase, physical stature, leaf area and thickness, stomatal density, and chlorophyll a content, and primary and secondary root production), the proportion of seedlings successfully transferred to soil (improvement from 40% to 100%) and achieved in a shorter time (reduction from 10 to 6 mo). Best results using this photoautotrophic growth step were obtained when a low medium concentration of sucrose (43.8 mM or lower) was used, when it was applied to seedlings that had already reached 4 or 5 mo of age in the in vitro culture step, and when seedlings were cultured in the photoautotrophic system for 2 mo or more before transfer to soil. Our improved protocol is more efficient and it reduces the cost per plant for the international exchange of coconut germplasm. 相似文献
2.
3.
4.
Isoproterenol-stimulated cyclic AMP (cAMP) accumulation in lymphocytes is an index of beta-adrenergic receptor functioning. It is not known if a delay between blood collection and subsequent cell preparation influences cAMP accumulation. We compared cAMP levels in lymphocytes processed from whole blood immediately after collection and following a 3.5 hour delay. There were no significant changes in either basal or stimulated levels of cAMP. This information may alleviate time constraints in certain experimental designs where immediate isolation of lymphocytes from whole blood may not be practical. 相似文献
5.
Daren Lee Seth Ruffins Queenie Ng Nikhil Sane Steve Anderson Arthur Toga 《BMC bioinformatics》2010,11(1):608
Background
Digital atlases provide a common semantic and spatial coordinate system that can be leveraged to compare, contrast, and correlate data from disparate sources. As the quality and amount of biological data continues to advance and grow, searching, referencing, and comparing this data with a researcher's own data is essential. However, the integration process is cumbersome and time-consuming due to misaligned data, implicitly defined associations, and incompatible data sources. This work addressing these challenges by providing a unified and adaptable environment to accelerate the workflow to gather, align, and analyze the data. 相似文献6.
7.
8.
The lipid composition of swimming spores, cysts and five hour germlings was established. Spores utilized triglycerides first, then phospholipids. Upon encystment all glycolipid components decreased, while in germlings the phospholipids, monoglycerides and sterol esters exhibited a marked increase. 相似文献
9.
The incorporation of U-14C-leucine into the cuticle occurs within the first 2 hr after ecdysis whereas U-14C-tyrosine is incorporated at a steady rate for approximately 8 hr. These data suggest that most of the cuticle protein is synthesized and laid down within a short time after ecdysis. On the other hand, tyrosine and/or metabolites (such as N-acetyl-dopamine) are translocated into the cuticle for several hours. This indicates that the sclerotization process may take place over an extended period. 相似文献
10.
Sam Mavandadi Steve Feng Frank Yu Stoyan Dimitrov Karin Nielsen-Saines William R. Prescott Aydogan Ozcan 《PloS one》2012,7(10)
We propose a methodology for digitally fusing diagnostic decisions made by multiple medical experts in order to improve accuracy of diagnosis. Toward this goal, we report an experimental study involving nine experts, where each one was given more than 8,000 digital microscopic images of individual human red blood cells and asked to identify malaria infected cells. The results of this experiment reveal that even highly trained medical experts are not always self-consistent in their diagnostic decisions and that there exists a fair level of disagreement among experts, even for binary decisions (i.e., infected vs. uninfected). To tackle this general medical diagnosis problem, we propose a probabilistic algorithm to fuse the decisions made by trained medical experts to robustly achieve higher levels of accuracy when compared to individual experts making such decisions. By modelling the decisions of experts as a three component mixture model and solving for the underlying parameters using the Expectation Maximisation algorithm, we demonstrate the efficacy of our approach which significantly improves the overall diagnostic accuracy of malaria infected cells. Additionally, we present a mathematical framework for performing ‘slide-level’ diagnosis by using individual ‘cell-level’ diagnosis data, shedding more light on the statistical rules that should govern the routine practice in examination of e.g., thin blood smear samples. This framework could be generalized for various other tele-pathology needs, and can be used by trained experts within an efficient tele-medicine platform. 相似文献