全文获取类型
收费全文 | 2460篇 |
免费 | 125篇 |
国内免费 | 2篇 |
出版年
2023年 | 25篇 |
2022年 | 22篇 |
2021年 | 86篇 |
2020年 | 46篇 |
2019年 | 50篇 |
2018年 | 78篇 |
2017年 | 55篇 |
2016年 | 89篇 |
2015年 | 113篇 |
2014年 | 139篇 |
2013年 | 190篇 |
2012年 | 244篇 |
2011年 | 204篇 |
2010年 | 134篇 |
2009年 | 88篇 |
2008年 | 125篇 |
2007年 | 118篇 |
2006年 | 102篇 |
2005年 | 110篇 |
2004年 | 101篇 |
2003年 | 89篇 |
2002年 | 85篇 |
2001年 | 23篇 |
2000年 | 25篇 |
1999年 | 23篇 |
1998年 | 17篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1971年 | 2篇 |
排序方式: 共有2587条查询结果,搜索用时 15 毫秒
1.
2.
Francisco Javier Tovar-Lopez Gary Rosengarten Mahyar Nasabi Vijay Sivan Khashayar Khoshmanesh Shaun P. Jackson Arnan Mitchell Warwick S. Nesbitt 《PloS one》2013,8(10)
This paper reports on an investigation of mass transport of blood cells at micro-scale stenosis where local strain-rate micro-gradients trigger platelet aggregation. Using a microfluidic flow focusing platform we investigate the blood flow streams that principally contribute to platelet aggregation under shear micro-gradient conditions. We demonstrate that relatively thin surface streams located at the channel wall are the primary contributor of platelets to the developing aggregate under shear gradient conditions. Furthermore we delineate a role for red blood cell hydrodynamic lift forces in driving enhanced advection of platelets to the stenosis wall and surface of developing aggregates. We show that this novel microfluidic platform can be effectively used to study the role of mass transport phenomena driving platelet recruitment and aggregate formation and believe that this approach will lead to a greater understanding of the mechanisms underlying shear-gradient dependent discoid platelet aggregation in the context of cardiovascular diseases such as acute coronary syndromes and ischemic stroke. 相似文献
3.
4.
John A. Schneider Rakhi Dandona Shravani Pasupneti Vemu Lakshmi Chuanhong Liao Vijay Yeldandi Kenneth H. Mayer 《PloS one》2010,5(7)
Studies of HIV prevention interventions such as pre-exposure prophylaxis (PREP) and circumcision in India are limited. The present study sought to investigate Indian truck-drivers initial commitment to PREP and circumcision utilizing the AIDS Risk Reduction Model. Ninety truck-drivers completed an in-depth qualitative interview and provided a blood sample for HIV and HSV-2 testing. Truck-drivers exhibited low levels of initial commitment towards PREP and even lower for circumcision. However, potential leverage points for increasing commitment were realized in fear of infecting family rather than self, self-perceptions of risk, and for PREP focusing on cultural beliefs towards medication and physicians. Cost was a major barrier to both HIV prevention interventions. Despite these barriers, our findings suggest that the ARRM may be useful in identifying several leverage points that may be used by peers, health care providers and public health field workers to enhance initial commitment to novel HIV prevention interventions in India. 相似文献
5.
Sunita Sharma S. K. Thulasidas Madhuri J. Kulkarni V. Natarajan Vijay K. Manchanda 《International journal of phytoremediation》2016,18(1):10-15
Sorption capacity of four plants (Funaria hygrometrica, Musa acuminata, Brassica juncea and Helianthus annuus) extracts/fractions for uranium, a radionuclide was investigated by EDXRF and tracer studies. The maximum sorption capacity, i.e., 100% (complete sorption) was observed in case of Musa acuminata extract and fractions. Carbohydrate, proteins, phenolics and flavonoids contents in the active fraction (having maximum sorption capacity) were also determined. Further purification of the most active fraction provided three pure molecules, mannitol, sorbitol and oxo-linked potassium oxalate. The characterization of isolated molecules was achieved by using FTIR, NMR, GC-MS, MS-MS, and by single crystal-XRD analysis. Of three molecules, oxo-linked potassium oxalate was observed to have 100% sorption activity. Possible binding mechanism of active molecule with the uranyl cation has been purposed. 相似文献
6.
Contrary to earlier reports, well-organized but fewer stomata develop on the lower surface of the leaves of Nelumbo nucifera Willd. during aerial growth. The stomata, however, become obliterated by the readjustment of neighboring epidermal cells. During initial stages of degeneration the guard cells show irregularly thickened walls, disintegrated nuclei, and highly vacuolated cytoplasm. Such abnormal features finally lead to the disappearance of stomata from the lower surface of leaves. The ontogeny, structure and distribution of stomata on leaves, perianth lobes, stamens, receptacles and carpels are described. The stomata are haplocheilic in development and are anomocytic (ranunculaceous) at maturity. The concept of a meristemoid and the significance of this study in taxonomy and phylogeny are discussed. 相似文献
7.
8.
Apert (1906) was the first to identify a syndrome characterized by the association of acrocephaly with syndactyly, acrocephalosyndactylism. Since then Apert syndrome has been recognized as a clinical entity. Although hydrocephalus was rarely reported as an associated malformation, it was suggested that hydrocephalus might be responsible for mental retardation in some cases of Apert syndrome. We report a case of Apert syndrome presenting as fetal hydrocephaly at 28 weeks gestational age, and we review the literature. We suggest that hydrocephalus should be considered as a major associated malformation, and a complete evaluation with sonogram and computed tomography scan is recommended in any newborn suspected of having Apert syndrome after routine cephalometric measurement. 相似文献
9.
10.
The responses of the cotton plant, Gossypium hirsutum L. to herbivory by Spodoptera litura F. was studied in various laboratory experiments as a measure to understand the defense strategies of certain plant metabolites. Insect feeding damage enhanced the concentration of total phenol content and proteins, whereas amount of carbohydrates and amino acids were reduced. The experiments on estimation of anti-oxidative enzymes revealed stimulation in peroxidase, catalase, and superoxide dismutase levels and reduction in polyphenol oxidase and phenylanine ammonia lyase levels, signifying their defensive role in the plant. Specific phenolic acid changes were further carried out using High Performance Liquid Chromatography (HPLC), and distinct elevations in the gallic acid, catechin, and caffeic acid levels were observed in the infested cotton plant. Feeding assays towards S. litura with these phenolic compounds revealed activated detoxifying enzymes including β-glucosidase, carboxyl esterase, and glutathione-S-transferase in the insect gut indicating the toxicity. The aim of present study is to aid in further use of these specific phenolic acids towards effective management of the cotton pest, S. litura. 相似文献