全文获取类型
收费全文 | 1255809篇 |
免费 | 99049篇 |
国内免费 | 1356篇 |
专业分类
1356214篇 |
出版年
2021年 | 17701篇 |
2020年 | 12603篇 |
2019年 | 16120篇 |
2018年 | 18286篇 |
2017年 | 17130篇 |
2016年 | 28314篇 |
2015年 | 42155篇 |
2014年 | 50103篇 |
2013年 | 76401篇 |
2012年 | 33718篇 |
2011年 | 22169篇 |
2010年 | 43749篇 |
2009年 | 45079篇 |
2008年 | 21243篇 |
2007年 | 19103篇 |
2006年 | 24435篇 |
2005年 | 25926篇 |
2004年 | 24951篇 |
2003年 | 22532篇 |
2002年 | 20740篇 |
2001年 | 26155篇 |
2000年 | 23314篇 |
1999年 | 25872篇 |
1998年 | 24516篇 |
1997年 | 24117篇 |
1996年 | 23815篇 |
1995年 | 21928篇 |
1994年 | 21806篇 |
1993年 | 20769篇 |
1992年 | 22812篇 |
1991年 | 21505篇 |
1990年 | 20354篇 |
1989年 | 21470篇 |
1988年 | 19691篇 |
1987年 | 18554篇 |
1986年 | 17664篇 |
1985年 | 19920篇 |
1984年 | 20363篇 |
1983年 | 17973篇 |
1982年 | 19041篇 |
1981年 | 18489篇 |
1980年 | 17292篇 |
1979年 | 16139篇 |
1978年 | 15907篇 |
1977年 | 15388篇 |
1976年 | 14812篇 |
1975年 | 14237篇 |
1974年 | 14556篇 |
1973年 | 15026篇 |
1972年 | 12503篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
Human spermatozoa with normal structure and with different axonemal deficiencies (absence of axoneme, of arms, or of central structures) were studied by electron microscopy, SDS-polyacrylamide gel electrophoresis, and ATPase activity measurements. Normal human sperm possess a complement of high molecular weight polypeptides with an electrophoretic migration similar to that of sea urchin and other mammalian sperm dyneins. Human high molecular weight bands are numbered one to four in order of increasing of electrophoretic mobility; all of them are absent in spermatozoa that lack axoneme. The absence of doublet arms, coincides with the absence of bands 2, 3, and 4; the absence of central structures coincides with a reduction in intensity of band 2. In the latter two abnormal conditions, band 1 has an increased intensity. The data are tentatively interpreted by attributing the polypeptides forming bands 3 and 4 to the arm structure, whereas band 2 is supposed to contain a mixture of polypeptides localized in the arms and in the central structures; these abnormal sperm contain modified polypeptides which gather in band 1. Histochemical ATPase stainings indicate that this enzyme is localized mainly in the doublet arms and, to a minor extent, in the central structures. 相似文献
984.
Tryptophan, tryptamine, or indolepyruvic acid were applied to 2 systems: a bacterial (pea stem sections containing the epiphytic bacteria) and a plant system (pea stem sections under sterile conditions). In the plant system, the production of indoleacetic acid and indoleethanol (tryptophol) from each applied indole derivative is clearly reduced by the aldehyde reagents bisulfite and dimedon, respectively. Indoleacetaldehyde is chromatographically detected after alkaline liberation from its bisulfite addition product. In the bacterial system, the production of indoleacetic acid and indoleethanol is likewise reduced by bisulfite and dimedon. However, after tryptophan or tryptamine application, we could not detect indoleacetaldehyde in the described way. In one case only, namely tryptamine application to the bacterial system, indoleethanol production (contrary to indoleacetic acid production) is scarcely reduced by the aldehyde reagents. This indicates a bacterial pathway tryptamine → indoleethanol which bypasses indoleacetaldehyde. 相似文献
985.
986.
987.
ARNOLD G. KLUGE 《Zoological Journal of the Linnean Society》1993,107(4):293-351
Two major subgroups of erycine snakes, designated Charina and Eryx , are delimited with a cladistic analysis of 75 morphological characters. The hypotheses of species relationships within the two clades are ( reinhardtii ( bottae, trivirgata )) and ( colubrinus, conicus, elegans, jayakari, muelleri, somalicus ( miliaris ( tataricus ( jaculus, johnii )))), respectively. This pattern of grouping obtains without assuming multistate character additivity. At least 16 synapomorphies indicate that reinhardtii is an erycine and that it is the sister lineage of the ( bottae, trivirgata ) clade. Calabaria and Lichanura are synonymized with Charina for reasons of taxonomic efficiency, and to emphasize the New-Old World geographic distribution of the three species in that assemblage. Further resolution of Eryx species relationships is required before Gongylophis (type species conicus ) can be recognized. 相似文献
988.
989.
990.
Petronela Weisová Ujval Anilkumar Caitriona Ryan Caoimhín G. Concannon Jochen H.M. Prehn Manus W. Ward 《BBA》2012,1817(5):744-753
The preconditioning response conferred by a mild uncoupling of the mitochondrial membrane potential (Δψm) has been attributed to altered reactive oxygen species (ROS) production and mitochondrial Ca2 + uptake within the cells. Here we have explored if altered cellular energetics in response to a mild mitochondrial uncoupling stimulus may also contribute to the protection. The addition of 100 nM FCCP for 30 min to cerebellar granule neurons (CGNs) induced a transient depolarization of the Δψm, that was sufficient to significantly reduce CGN vulnerability to the excitotoxic stimulus, glutamate. On investigation, the mild mitochondrial ‘uncoupling’ stimulus resulted in a significant increase in the plasma membrane levels of the glucose transporter isoform 3, with a hyperpolarisation of Δψm and increased cellular ATP levels also evident following the washout of FCCP. Furthermore, the phosphorylation state of AMP-activated protein kinase (AMPK) (Thr 172) was increased within 5 min of the uncoupling stimulus and elevated up to 1 h after washout. Significantly, the physiological changes and protection evident after the mild uncoupling stimulus were lost in CGNs when AMPK activity was inhibited. This study identifies an additional mechanism through which protection is mediated upon mild mitochondrial uncoupling: it implicates increased AMPK signalling and an adaptive shift in energy metabolism as mediators of the preconditioning response associated with FCCP-induced mild mitochondrial uncoupling. 相似文献