全文获取类型
收费全文 | 40364篇 |
免费 | 4353篇 |
国内免费 | 12篇 |
专业分类
44729篇 |
出版年
2022年 | 300篇 |
2021年 | 521篇 |
2020年 | 344篇 |
2019年 | 422篇 |
2018年 | 549篇 |
2017年 | 515篇 |
2016年 | 898篇 |
2015年 | 1619篇 |
2014年 | 1566篇 |
2013年 | 2081篇 |
2012年 | 2358篇 |
2011年 | 2080篇 |
2010年 | 1448篇 |
2009年 | 1318篇 |
2008年 | 1810篇 |
2007年 | 1791篇 |
2006年 | 1601篇 |
2005年 | 1569篇 |
2004年 | 1471篇 |
2003年 | 1270篇 |
2002年 | 1265篇 |
2001年 | 1227篇 |
2000年 | 1231篇 |
1999年 | 1107篇 |
1998年 | 606篇 |
1997年 | 563篇 |
1996年 | 556篇 |
1995年 | 536篇 |
1994年 | 490篇 |
1993年 | 513篇 |
1992年 | 1004篇 |
1991年 | 749篇 |
1990年 | 770篇 |
1989年 | 754篇 |
1988年 | 652篇 |
1987年 | 596篇 |
1986年 | 612篇 |
1985年 | 709篇 |
1984年 | 531篇 |
1983年 | 414篇 |
1982年 | 343篇 |
1981年 | 314篇 |
1980年 | 255篇 |
1979年 | 378篇 |
1978年 | 343篇 |
1977年 | 243篇 |
1976年 | 228篇 |
1975年 | 202篇 |
1974年 | 294篇 |
1973年 | 252篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
To test Gray's proposal (1979, 1982) that prepared cues (snakes, spiders) are unconditioned, innate fear stimuli, a classical conditioning procedure was carried out in which a neutral, conditioned stimulus (CS; slides of flowers, mushrooms or apples) was repeatedly followed by a prepared, unconditioned stimulus (US; slides of snakes or spiders). Dependent variables were subjective evaluation of, and skin conductance responses to the CS slides, while respiration was used as a control variable. In one group of subjects (n = 12), skin conductance was recorded from the left hand, whereas in a second group (n = 11) it was recorded from the right hand. No evidence of skin conductance response - or of evaluative conditioning to the neutral CS as a result of its being paired with the prepared US was found. Thus, the results lend no support to Gray's proposal. No differences in skin conductance responses as a function of left versus right hand recording were found. 相似文献
72.
73.
74.
75.
M J Bussemakers A van Bokhoven J J van Groningen F M Debruyne J A Schalken 《Biochemical and biophysical research communications》1992,182(1):318-324
Differential hybridization analysis revealed two cDNA clones, pBUS19 and pBUS30, to be overexpressed in progressionally advanced rat prostatic tumors. Northern blot analysis suggested the clones to be related although no homology in nucleotide sequence could be shown. Isolation and characterization of a pBUS19-related clone, pJG116, and computer-assisted database comparison showed that all three clones could be mapped within a rat-specific endogenous retrovirus. The importance of overexpression of retroviral sequences in advanced prostatic cancer remains unclear. 相似文献
76.
J. P. van der Walt 《Antonie van Leeuwenhoek》1992,62(4):247-250
The Lipomycetaceae (Endomycetales) are known from the generaDipodascopsis, Lipomyces andZygozyma with budding anamorphic states inMyxozyma. The family is easily recognized culturally and physiologically but is phenotypically and ecologically extremely diverse. This natural taxon is phylogenetically distinct from the Saccharomycetaceae, but probably related to the Dipodascaceae. The possible evolution of the lipomycetaceous anamorphs is discussed. 相似文献
77.
Cytokine production in a model of wound healing: the appearance of MIP-1, MIP-2, cachectin/TNF and IL-1 总被引:9,自引:1,他引:8
T J Fahey B Sherry K J Tracey S van Deventer W G Jones J P Minei S Morgello G T Shires A Cerami 《Cytokine》1990,2(2):92-99
Macrophages are essential for normal wound repair and many of their effects on healing wounds are likely to be mediated by the secretion of cytokines. This study examines the appearance of messenger RNA (mRNA) for cachectin/tumor necrosis factor (TNF), IL 1, and macrophage inflammatory proteins 1 and 2 (MIP-1 and MIP-2), as well as the mature peptides, in a model of wound healing using wound chambers. RNA for all four cytokines can be detected in wound inflammatory cells by polymerase chain reaction amplification throughout the first 7 days. Cachectin/TNF and IL 1 protein levels peaked on the first day after wound chamber implantation, and MIP-1 and MIP-2 were detected only on day 3. The data suggest that these cytokines participate in the early inflammatory response to wounding. 相似文献
78.
Phenology, morphology, life history and responses to different temperature and photoperiod conditions were studied in Japanese Stypocaulon durum (Ruprecht) Okamura. Erect thalli of the species were collected year-round, but the mature thalli forming either uniloc-ular sporangia or two different types of plurilocular structures (evidently gametangia) on separate thalli were found only in winter. ln culture, an isomorphic life history is suggested for the species, alternating between a sporophyte forming unilocular sporangia and gam-etophytes forming plurilocular macro- (female) and micro- (male) gametangia. Contents of unilocular sporangia were not released, but germinated in situ, developing into erect thalli forming plurilocular gametangia. Macrogametangia released aplanogametes (oospores), but male gametangia appeared to be non-functional, although flagellated cells were once formed in the loc-uli. This is the first report of plurilocular gametangia in the species. Although the species grew well and matured under considerably lower temperature conditions than European Stypocaulon scoparium (L.) Sauvageau, its temperature requirements showed similarity to northwestern Atlantic Stypocaulon species. This supports the notion that northwestern Atlantic Stypocaulon is conspecific with S. durum. 相似文献
79.
80.
The ability of Bacillus subtilis, strain BB, to colonise cabbage seedlings endophytically was examined following seed inoculation. Strain BB was recovered from different plant parts including leaves (cotyledons), stem (hypocotyl) and roots. While high bacterial populations persisted in the roots and lower stem, they were lower in the upper stem and leaves through time. In addition to cabbage, strain BB colonised endophytically the roots of 5 other vegetable brassicas. Fatty acid methyl ester (FAME) and PCR fingerprinting analysis confirmed the reliability of the detection method. Studies conducted with transmission electron microscope (TEM) showed that BB mainly colonised intercellular spaces of cortical tissues including intercellular spaces close to the conducting elements of roots and stem of cabbage seedlings. Gold labelling was specifically associated with BB and the fibrillar material filling the intercellular spaces where bacterial cells were found. 相似文献