全文获取类型
收费全文 | 71755篇 |
免费 | 4801篇 |
国内免费 | 5篇 |
出版年
2023年 | 476篇 |
2022年 | 449篇 |
2021年 | 969篇 |
2020年 | 874篇 |
2019年 | 894篇 |
2018年 | 2131篇 |
2017年 | 1976篇 |
2016年 | 2619篇 |
2015年 | 3512篇 |
2014年 | 3460篇 |
2013年 | 4707篇 |
2012年 | 5620篇 |
2011年 | 5041篇 |
2010年 | 3200篇 |
2009年 | 2498篇 |
2008年 | 3966篇 |
2007年 | 3822篇 |
2006年 | 3543篇 |
2005年 | 3125篇 |
2004年 | 3050篇 |
2003年 | 2771篇 |
2002年 | 2670篇 |
2001年 | 1508篇 |
2000年 | 1463篇 |
1999年 | 1180篇 |
1998年 | 590篇 |
1997年 | 458篇 |
1996年 | 450篇 |
1995年 | 413篇 |
1994年 | 338篇 |
1993年 | 320篇 |
1992年 | 626篇 |
1991年 | 528篇 |
1990年 | 470篇 |
1989年 | 462篇 |
1988年 | 446篇 |
1987年 | 400篇 |
1986年 | 372篇 |
1985年 | 388篇 |
1984年 | 405篇 |
1983年 | 290篇 |
1982年 | 306篇 |
1981年 | 240篇 |
1980年 | 233篇 |
1979年 | 262篇 |
1978年 | 255篇 |
1977年 | 196篇 |
1975年 | 231篇 |
1974年 | 243篇 |
1973年 | 263篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
In this work, incorporation of plasmid DNA, pre-complexed with PEI, into polyelectrolyte multilayers has been studied to further develop platforms for local gene delivery. Polyplex embedding in synthetic and naturally degradable architectures was efficient for transfection of human hepato-cellular carcinoma cells. 相似文献
4.
Sebastián Moran Miguel Vizoso Anna Martinez-Cardús Antonio Gomez Xavier Matías-Guiu Sebastián M Chiavenna Andrés G Fernandez Manel Esteller 《Epigenetics》2014,9(6):829-833
A formalin-fixed paraffin-embedded (FFPE) sample usually yields highly degraded DNA, which limits the use of techniques requiring high-quality DNA, such as Infinium Methylation microarrays. To overcome this restriction, we have applied an FFPE restoration procedure consisting of DNA repair and ligation processes in a set of paired fresh-frozen (FF) and FFPE samples. We validated the FFPE results in comparison with matched FF samples, enabling us to use FFPE samples on the Infinium HumanMethylation450 Methylation array. 相似文献
5.
6.
T. E. Graedel Julian Allwood Jean‐Pierre Birat Matthias Buchert Christian Hagelüken Barbara K. Reck Scott F. Sibley Guido Sonnemann 《Journal of Industrial Ecology》2011,15(3):355-366
The recycling of metals is widely viewed as a fruitful sustainability strategy, but little information is available on the degree to which recycling is actually taking place. This article provides an overview on the current knowledge of recycling rates for 60 metals. We propose various recycling metrics, discuss relevant aspects of recycling processes, and present current estimates on global end‐of‐life recycling rates (EOL‐RR; i.e., the percentage of a metal in discards that is actually recycled), recycled content (RC), and old scrap ratios (OSRs; i.e., the share of old scrap in the total scrap flow). Because of increases in metal use over time and long metal in‐use lifetimes, many RC values are low and will remain so for the foreseeable future. Because of relatively low efficiencies in the collection and processing of most discarded products, inherent limitations in recycling processes, and the fact that primary material is often relatively abundant and low‐cost (which thereby keeps down the price of scrap), many EOL‐RRs are very low: Only for 18 metals (silver, aluminum, gold, cobalt, chromium, copper, iron, manganese, niobium, nickel, lead, palladium, platinum, rhenium, rhodium, tin, titanium, and zinc) is the EOL‐RR above 50% at present. Only for niobium, lead, and ruthenium is the RC above 50%, although 16 metals are in the 25% to 50% range. Thirteen metals have an OSR greater than 50%. These estimates may be used in considerations of whether recycling efficiencies can be improved; which metric could best encourage improved effectiveness in recycling; and an improved understanding of the dependence of recycling on economics, technology, and other factors. 相似文献
7.
"Pertussis toxin induces tachycardia and impairs the increase in blood pressure produced by alpha 2-adrenergic agonists" 总被引:4,自引:0,他引:4
Administration of purified pertussis toxin to rats induced persistent tachycardia, (observed in conscious rats but not after pithing); as little as 0.05 microgram/100 g produced a significant effect. Pertussis toxin-treatment did not affected the pressor response produced in the pithed rats by the alpha 2-adrenergic agonist methoxamine but markedly diminished the pressor effect of the alpha 2-adrenergic agonists clonidine and azepexole. A role of adenylate cyclase inhibition in the action of postsynaptic vascular alpha 2-adrenergic receptors is suggested. 相似文献
8.
9.
The difficulty in predicting the consequences of interactions between different cytokine networks has increased with the expansion
of the T helper (Th) cell universe and the discovery of numerous B lymphocyte-derived cytokines. Consequently, it is now difficult
to conceptualize a straightforward view of the contribution of these disturbances to the pathogenesis of primary Sj?gren's
syndrome (SS). Th1 cells, which produce interferon-γ and IL-2, and Th17 cells, which make IL-17 and TNF-α, have been cast
in the leading roles of the play. However, the complex role of T-cell subsets in SS is accentuated by the reciprocal effects
of Th17 cells and regulatory T cells found in salivary glands of SS patients. Furthermore, B lymphocyte polarization into
type-1 B effector (Be1) and Be2 cells and B-cell modulating factors of the TNF family, most notably the B-cell-activating
factor (BAFF), and their prominent role in SS are additional complicating factors. Whereas Th17 cells orchestrate autoreactive
germinal centers, local BAFF would repress the generation of Th17 cells. Such new insights into interconnected cytokines in
primary SS may lead to new treatments for these patients. 相似文献
10.
Páraic ó Cuív Rajesh Gupta Hareshwar P. Goswami Mark Morrison 《Applied and environmental microbiology》2013,79(19):6173-6175
Clostridium thermocellum encodes a cellulosomal, modular, and thermostable serine protease inhibitor (serpin), PinA. PinA stability but not inhibitory activity is affected by the Fn(III) and Doc(I) domains, and PinA is a broad inhibitor of subtilisin-like proteases and may play a key role in protecting the cellulosome from protease attack. 相似文献