全文获取类型
收费全文 | 483354篇 |
免费 | 42064篇 |
国内免费 | 966篇 |
出版年
2018年 | 16822篇 |
2017年 | 15724篇 |
2016年 | 13355篇 |
2015年 | 7856篇 |
2014年 | 8515篇 |
2013年 | 11927篇 |
2012年 | 18419篇 |
2011年 | 28460篇 |
2010年 | 22887篇 |
2009年 | 18401篇 |
2008年 | 23393篇 |
2007年 | 25925篇 |
2006年 | 11776篇 |
2005年 | 12602篇 |
2004年 | 12515篇 |
2003年 | 12273篇 |
2002年 | 11858篇 |
2001年 | 15249篇 |
2000年 | 15084篇 |
1999年 | 12089篇 |
1998年 | 4663篇 |
1997年 | 4510篇 |
1996年 | 4321篇 |
1995年 | 4340篇 |
1994年 | 4334篇 |
1993年 | 4265篇 |
1992年 | 10329篇 |
1991年 | 9865篇 |
1990年 | 9579篇 |
1989年 | 9332篇 |
1988年 | 8738篇 |
1987年 | 8329篇 |
1986年 | 7537篇 |
1985年 | 7688篇 |
1984年 | 6480篇 |
1983年 | 5677篇 |
1982年 | 4617篇 |
1981年 | 4075篇 |
1980年 | 3844篇 |
1979年 | 6313篇 |
1978年 | 4826篇 |
1977年 | 4543篇 |
1976年 | 4174篇 |
1975年 | 4517篇 |
1974年 | 4870篇 |
1973年 | 4914篇 |
1972年 | 5118篇 |
1971年 | 4764篇 |
1970年 | 3562篇 |
1969年 | 3441篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Jakub Horák 《Journal of Insect Conservation》2017,21(1):1-5
Insect and veteran trees are important parts of ecosystems and are usually included in ecological studies of forest management. The loss of veteran trees in woodlands and open landscapes would lead to the loss of saproxylic organisms—an important part of biodiversity. Hence, the persistence of many specialized insects depends on the presence of veteran trees scattered in woodlands (e.g. ancient wood pastures, game parks or protected areas), cities, towns and villages (e.g. avenues, parks or chateau parks) or open landscapes (e.g. fishpond dams, solitary trees or fruit orchards). Veteran tree conditions could be fairly well described by three components—diameter, age and microhabitats present. The problem is that diameter belongs to the most studied characteristics, while age and microhabitats, which can be quite complicated to measure, are much less studied. This paper illustrates that, due to this unbalanced use of indicators of veteran-tree conditions, we are still missing some important information on saproxylic species ecology—and sometimes only large trees might be studied, rather than real veterans. Although we already know that veteran trees are essential habitat for a range of saproxylic organisms, there are still gaps in our knowledge of the specific conditions that veteran trees provide. It is vital that these are quantified and understood so that this information can be used to conserve veteran trees and their associated species. 相似文献
2.
Human organ-on-a-chip systems for drug screening have evolved as feasible alternatives to animal models, which are unreliable, expensive, and at times erroneous. While chips featuring single organs can be of great use for both pharmaceutical testing and basic organ-level studies, the huge potential of the organ-on-a-chip technology is revealed by connecting multiple organs on one chip to create a single integrated system for sophisticated fundamental biological studies and devising therapies for disease. Furthermore, since most organ-on-a-chip systems require special protocols with organ-specific media for the differentiation and maturation of the tissues, multi-organ systems will need to be temporally customizable and flexible in terms of the time point of connection of the individual organ units. We present a customizable Lego®-like plug & play system, μOrgano, which enables initial individual culture of single organ-on-a-chip systems and subsequent connection to create integrated multi-organ microphysiological systems. As a proof of concept, the μOrgano system was used to connect multiple heart chips in series with excellent cell viability and spontaneously physiological beat rates. 相似文献
3.
Michael P. Gustafson Yi Lin Mary L. Maas Virginia P. Van Keulen Patrick B. Johnston Tobias Peikert Dennis A. Gastineau Allan B. Dietz 《PloS one》2015,10(3)
The development of flow cytometric biomarkers in human studies and clinical trials has been slowed by inconsistent sample processing, use of cell surface markers, and reporting of immunophenotypes. Additionally, the function(s) of distinct cell types as biomarkers cannot be accurately defined without the proper identification of homogeneous populations. As such, we developed a method for the identification and analysis of human leukocyte populations by the use of eight 10-color flow cytometric protocols in combination with novel software analyses. This method utilizes un-manipulated biological sample preparation that allows for the direct quantitation of leukocytes and non-overlapping immunophenotypes. We specifically designed myeloid protocols that enable us to define distinct phenotypes that include mature monocytes, granulocytes, circulating dendritic cells, immature myeloid cells, and myeloid derived suppressor cells (MDSCs). We also identified CD123 as an additional distinguishing marker for the phenotypic characterization of immature LIN-CD33+HLA-DR- MDSCs. Our approach permits the comprehensive analysis of all peripheral blood leukocytes and yields data that is highly amenable for standardization across inter-laboratory comparisons for human studies. 相似文献
4.
Antoine Poncet Baris Gencer Marc Blondon Marianne Gex-Fabry Christophe Combescure Dipen Shah Peter J. Schwartz Marie Besson Fran?ois R. Girardin 《PloS one》2015,10(6)
ImportanceSudden cardiac death is a leading cause of mortality in psychiatric patients. Long QT (LQT) is common in this population and predisposes to Torsades-de-Pointes (TdP) and subsequent mortality.ObjectiveTo estimate the cost-effectiveness of electrocardiographic screening to detect LQT in psychiatric inpatients.ResultsIn the base-case scenario, the numbers of patients needed to screen were 1128 and 2817 to avoid one TdP and one death, respectively. The ICER of systematic ECG screening was $8644 (95%CI, 3144-82 498) per QALY. The probability of cost-effectiveness was 96% at a willingness-to-pay of $50 000 for one QALY. In sensitivity analyses, results were sensitive to the case-fatality of TdP episodes and to the TdP reduction following the diagnosis of LQT.
Conclusion and Relevance
In psychiatric hospitals, performing systematic ECG screening at admission help reduce the number of sudden cardiac deaths in a cost-effective fashion. 相似文献5.
6.
7.
8.
9.