全文获取类型
收费全文 | 54684篇 |
免费 | 3491篇 |
国内免费 | 2646篇 |
出版年
2024年 | 115篇 |
2023年 | 863篇 |
2022年 | 1216篇 |
2021年 | 1647篇 |
2020年 | 1590篇 |
2019年 | 2109篇 |
2018年 | 1781篇 |
2017年 | 1278篇 |
2016年 | 1376篇 |
2015年 | 1745篇 |
2014年 | 2672篇 |
2013年 | 3560篇 |
2012年 | 1921篇 |
2011年 | 2476篇 |
2010年 | 1841篇 |
2009年 | 2223篇 |
2008年 | 2318篇 |
2007年 | 2480篇 |
2006年 | 2238篇 |
2005年 | 2145篇 |
2004年 | 1899篇 |
2003年 | 1724篇 |
2002年 | 1640篇 |
2001年 | 1429篇 |
2000年 | 1209篇 |
1999年 | 1146篇 |
1998年 | 1086篇 |
1997年 | 1033篇 |
1996年 | 958篇 |
1995年 | 936篇 |
1994年 | 943篇 |
1993年 | 865篇 |
1992年 | 868篇 |
1991年 | 835篇 |
1990年 | 687篇 |
1989年 | 640篇 |
1988年 | 599篇 |
1987年 | 517篇 |
1986年 | 424篇 |
1985年 | 526篇 |
1984年 | 595篇 |
1983年 | 309篇 |
1982年 | 423篇 |
1981年 | 430篇 |
1980年 | 344篇 |
1979年 | 294篇 |
1978年 | 213篇 |
1977年 | 179篇 |
1976年 | 194篇 |
1973年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
131.
132.
133.
134.
Aqueous extracts of smoke, derived from Themeda triandra, a fire-climax grass, and Passerina vulgaris, a fynbos plant, stimulated the growth of primary root sections of tomato roots in suspension culture. The optimal dilution for both extracts was 1:2000. Several of the fractions obtained from TLC separation of the Themeda and the Passerina extracts significantly promoted primary root growth. The auxins naphthaleneacetic acid (NAA), indolebutyric acid (IBA) and indoleacetic acid (IAA) were found to stimulate the growth of the primary root axis, with IAA and NAA significantly promoting lateral root number. Similarly, the naturally occurring cytokinins, zeatin and its derivatives (zeatin-O-glucoside; dihydrozeatin and zeatin riboside) stimulated primary root length. Zeatin and dihydrozeatin promoted secondary root growth, but only at very low concentrations. 相似文献
135.
Prion colonization of secondary lymphoid organs (SLOs) is a critical step preceding neuroinvasion in prion pathogenesis. Follicular dendritic cells (FDCs), which depend on both tumor necrosis factor receptor 1 (TNFR1) and lymphotoxin β receptor (LTβR) signaling for maintenance, are thought to be the primary sites of prion accumulation in SLOs. However, prion titers in RML-infected TNFR1−/− lymph nodes and rates of neuroinvasion in TNFR1−/− mice remain high despite the absence of mature FDCs. Recently, we discovered that TNFR1-independent prion accumulation in lymph nodes relies on LTβR signaling. Loss of LTβR signaling in TNFR1−/− lymph nodes coincided with the de-differentiation of high endothelial venules (HEVs)—the primary sites of lymphocyte entry into lymph nodes. These findings suggest that HEVs are the sites through which prions initially invade lymph nodes from the bloodstream. Identification of HEVs as entry portals for prions clarifies a number of previous observations concerning peripheral prion pathogenesis. However, a number of questions still remain: What is the mechanism by which prions are taken up by HEVs? Which cells are responsible for delivering prions to lymph nodes? Are HEVs the main entry site for prions into lymph nodes or do alternative routes also exist? These questions and others are considered in this article. 相似文献
136.
137.
138.
139.
David A. Smith John L. Glover Laurace E. Townsend Diane E. Maupin 《In vitro cellular & developmental biology. Animal》1991,27(12):914-920
Summary Myocardial cell culture methods are now well established for animal and fetal human tissue. We present here a method for harvesting
and culturing adult human atrial myocardiocytes. Cells are obtained from fresh atrial tissue normally discarded after being
removed to cannulate the right atrium during open heart surgery. The atrial tissue is minced and then digested using collagenase.
The single cell suspension is initially cultured in serum-containing growth medium, then transferred to defined medium, selective
for myocardial cell growth. The cells are characterized by immunoperoxidase stains and transmission electron microscopy. The
cultured cells stain positive for myoglobin, whereas control cultured fibroblasts and endothelial cells do not. Electron microscopy
shows the presence of numerous myofibrils, Z-bodies, pleomorphic mitochondria, and secretory granules. The chronological age
of the donor was an important factor in culturing the adult tissue, the younger tissue correlated with a higher success rate.
This method provides a means for in vitro study of human adult myocardial cells and provides guidelines for appropriate atrial
tissue to use. 相似文献
140.
The Annual bioProcessUK Conference has acted as the key networking event for bioprocess scientists and engineers in the UK for the past 10 years. The following article is a report from the sessions that focused on continuous bioprocessing during the 10th Annual bioProcessUK Conference (London, December 2013). These sessions were organized by the ‘EPSRC Centre for Innovative Manufacturing in Emergent Macromolecular Therapies’ hosted at University College London. A plenary lecture and workshop provided a forum for participants to debate topical issues in roundtable discussions with industry and academic experts from institutions such as Genzyme, Janssen, Novo Nordisk, Pfizer, Merck, GE Healthcare and University College London. The aim of these particular sessions was to understand better the challenges and opportunities for continuous bioprocessing in the bioprocessing sector. 相似文献