全文获取类型
收费全文 | 8906篇 |
免费 | 910篇 |
国内免费 | 3篇 |
出版年
2022年 | 63篇 |
2021年 | 120篇 |
2020年 | 62篇 |
2019年 | 72篇 |
2018年 | 91篇 |
2017年 | 103篇 |
2016年 | 177篇 |
2015年 | 290篇 |
2014年 | 321篇 |
2013年 | 434篇 |
2012年 | 509篇 |
2011年 | 457篇 |
2010年 | 312篇 |
2009年 | 284篇 |
2008年 | 436篇 |
2007年 | 458篇 |
2006年 | 426篇 |
2005年 | 413篇 |
2004年 | 410篇 |
2003年 | 422篇 |
2002年 | 385篇 |
2001年 | 132篇 |
2000年 | 108篇 |
1999年 | 139篇 |
1998年 | 154篇 |
1997年 | 107篇 |
1996年 | 88篇 |
1995年 | 95篇 |
1994年 | 75篇 |
1993年 | 99篇 |
1992年 | 97篇 |
1991年 | 98篇 |
1990年 | 97篇 |
1989年 | 88篇 |
1988年 | 86篇 |
1987年 | 85篇 |
1986年 | 98篇 |
1985年 | 86篇 |
1984年 | 101篇 |
1983年 | 68篇 |
1982年 | 83篇 |
1981年 | 93篇 |
1980年 | 71篇 |
1979年 | 61篇 |
1978年 | 86篇 |
1977年 | 63篇 |
1976年 | 69篇 |
1974年 | 85篇 |
1973年 | 73篇 |
1972年 | 61篇 |
排序方式: 共有9819条查询结果,搜索用时 15 毫秒
91.
Gary M. Wessel Margaret R. Truschel Scott A. Chambers David R. McClay 《Molecular reproduction and development》1987,18(4):339-348
The ultrastructural localization of B-1,3-glucanase in three species of sea urchin eggs was determined using a monospecific antibody in an electronmicroscopic immunogold procedure. In all three species, Lytechinus variegatus, Strongylocentrotus purpuratus, and Arbacia punctulata, B-1,3-glucanase was localized specifically to the cortical granules. No other organelle within the egg contained significant label. During the fertilization reaction, B-1,3-glucanase was released from cortical granules into the perivitelline space and became associated with the hyaline layer. No significant label was found in association with the fertilization envelope. 相似文献
92.
Intercurrent canine distemper and Tyzzer's disease were diagnosed in a mature raccoon (Procyon lotor) submitted for necropsy. Clinical, gross and microscopic findings characteristic of canine distemper virus (CDV), included ataxia, dyspnea, suppurative conjunctivitis, interstitial pneumonitis and generalized lymphocytolysis. Inclusion bodies typical of CDV infection were present in many epithelial tissues. Acute multifocal hepatic necrosis and acute segmental necrotizing enteritis were attributed to the presence of Bacillus piliformis organisms in these lesions, confirmed by special stains and electron microscopy. This is apparently the first reported case of Tyzzer's disease in a raccoon. 相似文献
93.
Dipple Anthony Pigott Margaret A. Milner John A. 《Biological trace element research》1986,10(2):153-157
Since selenium has been found to exert a protective action against carcinogenesis in various systems, the mechanism where-by
sodium selenite inhibits DNA binding of the carcinogen, 7,12-dimethylbenz[a]anthracene, was investigated. It was found that
selenite preferentially reduced DNA binding occurring through ananti-dihydrodiol epoxide metabolite of this carcinogen by inhibiting the induction of an enzyme system that generates this specific
reactive metabolite. 相似文献
94.
Summary A new species of Rhynchoidomonas Patton was observed in a single adult male winter moth, Operophtera brumata (L.) from England. Intracellular amastigotes, and extracellular epimastigotes and trypomastigotes with an undulating membrane and free flagellum, were present. All stages had a large, reniform kinetoplast. As transmission of the flagellate between generations of winter moths by ingestion of infected faeces is a virtual impossibility, it is suggested that the flagellate's true host may have been a dipteran parasitoid and that an egg, surface-contaminated with the flagellate, was oviposited into or ingested by a winter moth larva. If the parasitoid had died, this flagellate infection could have been carried over to the adult moth. ac]19830601 相似文献
95.
Daniel Q. Estep Thomas P. Gordon Mark E. Wilson Margaret L. Walker 《International journal of primatology》1986,7(5):507-517
Copulatory data derived from observations of social groups of rhesus and stumptail macaques were analyzed to test the hypothesis
that pairs of animals would resume copulation significantly sooner if a second male copulated with the female shortly after
the first male’s ejaculation. Data from both groups supported the hypothesis. These results, extending previous studies in Macaca nemestrina,suggest that the shortening of copulatory intervals by social stimuli occurs in several species, both in social groups and
in experimentally created triads. These findings also are consistent with the hypothesis that socially mediated resumption
of mating is related to intrasexual competition among males. 相似文献
96.
Dr. Margaret M. Bird 《Cell and tissue research》1986,245(3):563-577
Summary The differentiation of cells and synapses in explants of 9-day-old chick embryo retina has been studied by light and electron microscopy over a period of 35 days in vitro, and samples of retina from the 9-day chick foetus were directly fixed and prepared for study.At the time of explantation the retinae were poorly differentiated and no lamination was apparent. From day 14 onwards, (i) outer and inner nuclear layers (ONL, INL) separated by a layer of neuropil corresponding to the outer plexiform layer (OPL) and (ii) a layer of scattered large ganglion cells separated from the INL by a zone of neuropil resembling the inner plexiform layer (IPL) were apparent, and (iii) a well-differentiated outer limiting membrane was established close to the surface of the explants. In the oldest cultures some development of photoreceptor outer segments occurred but a distinct optic nerve fibre layer did not form.Although cell identification presented problems even in the oldest cultures, the major retinal cell types described in vivo could be identified. Photoreceptor cells developed pedicles in the OPL which became filled with synaptic vesicles and synaptic ribbons and established ribbon synapses (including triads) with and were commonly invaginated by processes from horizontal and bipolar cells. Processes of bipolar cells in the IPL formed simple and dyad synapses. At least two types of presynaptic amacrine cells were also identified in the INL, one of which contained large numbers of dense-core vesicles. The ganglion cells, though sparse, were large and well differentiated.These findings show that all the major neuronal types of the retina are capable of developing and differentiating in vitro, lagging behind the time-table of development and differentiation in vivo by approximately 7 days, but resulting in a histotypically organised retina with synaptic neuropil showing many similarities to the corresponding neuropil in vivo. 相似文献
97.
The structure and transcription start site of a major potato tuber protein gene 总被引:16,自引:4,他引:12 下载免费PDF全文
M Bevan R Barker A Goldsbrough M Jarvis T Kavanagh G Iturriaga 《Nucleic acids research》1986,14(11):4625-4638
We have isolated recombinant lambda clones containing intact major tuber protein (patatin) genes and flanking sequences from the commercial tetraploid variety Maris Piper. The gene is composed of seven exons and six introns, spread over 4 kb of DNA. Nuclease mapping defined the 5' end of the mRNA approximately 45 bp upstream of the initiation codon. The 5' end of the gene is preceeded by a canonical TATA box sequence. The three known patatin genes encode proteins of nearly identical Mr but very different isoelectric points. The sequence of the gene does not indicate a role for patatin as one of the globulin class of plant storage proteins. 相似文献
98.
99.
Host receptor sites involved in the attachment of Bdellovibrio bacteriovorus and Bdellovibrio stolpii 总被引:1,自引:0,他引:1
Abstract The location of lipoteichoic acid and 3 cell wall-associated protein antigens in fresh isolates of Streptococcus mutans (serotype c ) and in variants derived from these parental strains by repeated subculture in vitro has been examined by electrophoretic and dot-immunobinding techniques. Following subculture there was a marked shift in the distribution of all four antigens from the cell wall to the extracellular culture supernatants. It is therefore apparent that that the decreased hydrophobicity and the impaired ability of the subcultured variants to colonise in vivo, as observed by others, cannot be correlated with changes in a single surface molecule. 相似文献
100.