全文获取类型
收费全文 | 3466篇 |
免费 | 227篇 |
出版年
2022年 | 15篇 |
2021年 | 34篇 |
2019年 | 28篇 |
2018年 | 38篇 |
2017年 | 35篇 |
2016年 | 79篇 |
2015年 | 92篇 |
2014年 | 130篇 |
2013年 | 140篇 |
2012年 | 227篇 |
2011年 | 255篇 |
2010年 | 188篇 |
2009年 | 141篇 |
2008年 | 190篇 |
2007年 | 191篇 |
2006年 | 172篇 |
2005年 | 177篇 |
2004年 | 155篇 |
2003年 | 179篇 |
2002年 | 160篇 |
2001年 | 43篇 |
2000年 | 28篇 |
1999年 | 57篇 |
1998年 | 58篇 |
1997年 | 45篇 |
1996年 | 57篇 |
1995年 | 41篇 |
1994年 | 43篇 |
1993年 | 31篇 |
1992年 | 52篇 |
1991年 | 30篇 |
1990年 | 46篇 |
1989年 | 28篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1985年 | 18篇 |
1984年 | 27篇 |
1983年 | 23篇 |
1982年 | 31篇 |
1981年 | 33篇 |
1980年 | 21篇 |
1979年 | 35篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1971年 | 15篇 |
1970年 | 16篇 |
1969年 | 14篇 |
1968年 | 14篇 |
1967年 | 17篇 |
排序方式: 共有3693条查询结果,搜索用时 328 毫秒
851.
852.
853.
Christopher Kramer Denis Jordan Alexander Kretschmer Veronika Lehmeyer Kristine Kellermann Stephan J. Schaller Manfred Blobner Eberhard F. Kochs Heidrun Fink 《PloS one》2014,9(12)
Spontaneous reinnervation after diaphragmatic paralysis due to trauma, surgery, tumors and spinal cord injuries is frequently observed. A possible explanation could be collateral reinnervation, since the diaphragm is commonly double-innervated by the (accessory) phrenic nerve. Permutation entropy (PeEn), a complexity measure for time series, may reflect a functional state of neuromuscular transmission by quantifying the complexity of interactions across neural and muscular networks. In an established rat model, electromyographic signals of the diaphragm after phrenicotomy were analyzed using PeEn quantifying denervation and reinnervation. Thirty-three anesthetized rats were unilaterally phrenicotomized. After 1, 3, 9, 27 and 81 days, diaphragmatic electromyographic PeEn was analyzed in vivo from sternal, mid-costal and crural areas of both hemidiaphragms. After euthanasia of the animals, both hemidiaphragms were dissected for fiber type evaluation. The electromyographic incidence of an accessory phrenic nerve was 76%. At day 1 after phrenicotomy, PeEn (normalized values) was significantly diminished in the sternal (median: 0.69; interquartile range: 0.66–0.75) and mid-costal area (0.68; 0.66–0.72) compared to the non-denervated side (0.84; 0.78–0.90) at threshold p<0.05. In the crural area, innervated by the accessory phrenic nerve, PeEn remained unchanged (0.79; 0.72–0.86). During reinnervation over 81 days, PeEn normalized in the mid-costal area (0.84; 0.77–0.86), whereas it remained reduced in the sternal area (0.77; 0.70–0.81). Fiber type grouping, a histological sign for reinnervation, was found in the mid-costal area in 20% after 27 days and in 80% after 81 days. Collateral reinnervation can restore diaphragm activity after phrenicotomy. Electromyographic PeEn represents a new, distinctive assessment characterizing intramuscular function following denervation and reinnervation. 相似文献
854.
Throughout development and adult life the vasculature exhibits a remarkably dynamic capacity for growth and repair. The vasculature also plays a pivotal role in the execution of other diverse biologic processes, such as the provisioning of early hematopoietic stem cells during embryonic development or the regulation of vascular tone and blood pressure. Adding to this importance, from an anatomical perspective, the vasculature is clearly an omnipresent organ, with few areas of the body that it does not penetrate. Given these impressive characteristics, it is perhaps to be expected that the vasculature should require, or at least be associated with, a ready supply of stem and progenitor cells. However, somewhat surprisingly, it is only now just beginning to be broadly appreciated that the vasculature plays host to a range of vessel-resident stem and progenitor cells. The possibility that these vessel-resident cells are implicated in processes as diverse as tumor vascularization and adaptive vascular remodeling appears likely, and several exciting avenues for clinical translation are already under investigation. This review explores the various stem and progenitor cell populations that are resident in the microvasculature, endothelium, and vessel walls and vessel-resident cells capable of phenotypic transformation. 相似文献
855.
856.
857.
858.
Manfred Marsmann Sven Olaf Ryding Helias Udo de Haes James Fava Willie Owens Kevin Brady Konrad Saur Rita Schenck 《The International Journal of Life Cycle Assessment》1999,4(2):65-65
Life Cycle Impact Assessment describes indicators and does not predict actual impacts. The value of an LCA is its comprehensive review of all stages of a product’s life cycle and its synoptic view of all relevant environmental issues. The current version of the 14042 draft describes the uniqueness of Life Cycle Impact Assessment approach which is distinct from other assessment techniques. The wording was designed to help users of the standard understand how and why LCIA is distinct from other assessment methods. In closing, we would like to highlight our opinion that the present document on the level of a DIS is sound, stable and practical within the ISO 14040 series of standards. We do not agree withHertwich & Pease that the present document prevents the use of LCIA. It makes a choice regarding the exclusion of weighting across categories in order to prevent misuse in deriving inappropriate claims. And for characterisation it has achieved a well founded synthesis. In addition, we strongly believe that this standard will stimulate the international scientific discussion of LCA and will substantially contribute to enhanced and more valuable applications of LCA in the future. 相似文献
859.
Manfred Schmehl Andreas Jahn Andreas Meyer zu Vilsendorf Silke Hennecke Bernd Masepohl Markus Schuppler Martin Marxer Jürgen Oelze Werner Klipp 《Molecular genetics and genomics : MGG》1993,241(5-6):602-615
DNA sequence analysis of a 12236 by fragment, which is located upstream of nifE in Rhodobacter capsulatus nif region A, revealed the presence of ten open reading frames. With the exception of fdxC and fdxN, which encode a plant-type and a bacterial-type ferredoxin, the deduced products of these coding regions exhibited no significant homology to known proteins. Analysis of defined insertion and deletion mutants demonstrated that six of these genes were required for nitrogen fixation. Therefore, we propose to call these genes rnfA, rnfB, rnfC, rnfD, rnfE and rnfF (for Rhodobacter nitrogen fixation). Secondary structure predictions suggested that the rnf genes encode four potential membrane proteins and two putative iron-sulphur proteins, which contain cysteine motifs (C-X2-C-X2-C-X3-C-P) typical for [4Fe-4S] proteins. Comparison of the in vivo and in vitro nitrogenase activities of fdxN and rnf mutants suggested that the products encoded by these genes are involved in electron transport to nitrogenase. In addition, these mutants were shown to contain significantly reduced amounts of nitrogenase. The hypothesis that this new class of nitrogen fixation genes encodes components of an electron transfer system to nitrogenase was corroborated by analysing the effect of metronidazole. Both the fdxN and rnf mutants had higher growth yields in the presence of metronidazole than the wild type, suggesting that these mutants contained lower amounts of reduced ferredoxins. 相似文献
860.