全文获取类型
收费全文 | 450篇 |
免费 | 47篇 |
专业分类
497篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 14篇 |
2013年 | 12篇 |
2012年 | 19篇 |
2011年 | 20篇 |
2010年 | 18篇 |
2009年 | 17篇 |
2008年 | 15篇 |
2007年 | 15篇 |
2006年 | 23篇 |
2005年 | 15篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 20篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1999年 | 20篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1993年 | 4篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1971年 | 5篇 |
1968年 | 4篇 |
1967年 | 5篇 |
1914年 | 2篇 |
排序方式: 共有497条查询结果,搜索用时 15 毫秒
11.
Leslie A. Chisholm 《Systematic parasitology》1995,30(3):207-211
Heterocotyle pastinacae Scott, 1904 is redescribed and a neotype is designated. H. pastinacae is most easily distinguished from other members of the genus by the elaborate arrangement of sclerotised spines in the vagina.
The male copulatory organ also serves to differentiate it from other species in the genus. A possible function for the vaginal
spines and unique form of the male copulatory organ is discussed. The use of head organ number as a generic character is considered
questionable. 相似文献
12.
Relationship between DNA cycle and growth rate in Synechococcus sp. strain PCC 6301. 总被引:8,自引:2,他引:6 下载免费PDF全文
Flow cytometry was used to examine cell cycle regulation in Synechococcus sp. strain PCC 6301 under a variety of growth conditions. The DNA frequency distributions of exponentially growing and dark-blocked populations confirmed that this cyanobacterium contains multiple chromosome copies even at very slow growth rates. Furthermore, the presence of major peaks corresponding to other than 2" chromosome copies strongly suggests that DNA replication is initiated asynchronously. Although this suggestion is at odds with the standard formulation of the procaryotic cell cycle model, it is similar to recent observations of asynchrony in Escherichia coli replication mutants. 相似文献
13.
N H Haunerland P Andolfatto J M Chisholm Z Wang X Chen 《European journal of biochemistry》1992,210(3):1045-1051
Fatty-acid-binding protein (FABP) from the flight muscle of the locust, Schistocerca gregaria, is similar to mammalian heart FABP in its primary structure and biochemical characteristics. We have studied developmental changes using enzyme-linked immunosorbent assays, RNA hybridization and electron microscopy of immunogold-labeled sections. Locust muscle FABP is the most abundant soluble muscle protein in fully developed adult locusts, comprising 18% of the total cytosolic protein. At the beginning of the adult stage, however, no FABP is detectable. Its concentration rises during the following 10 days, after which it reaches its maximal value. FABP mRNA is present shortly after adult ecdysis; its concentration increases for 10 days, before it diminishes and reaches a constant, low level, probably needed to maintain the established FABP level. The protein is abundant in cytosol and nuclei, but virtually absent in mitochondria. 相似文献
14.
15.
L C Burkly D Olson R Shapiro G Winkler J J Rosa D W Thomas C Williams P Chisholm 《Journal of immunology (Baltimore, Md. : 1950)》1992,149(5):1779-1787
HIV use the CD4 molecule as their primary cellular receptor. Residues in the N-terminal domain (D1) of CD4 are crucial to HIV attachment through the gp120 envelope component. However, other regions of CD4 appear to be required subsequently for virus- and cell-cell fusion. Little is understood of the post-binding steps which may differ between HIV variants. We report a novel anti-CD4 mAb that does not block CD4/gp120 binding, but that does efficiently block both viral infection and cell-cell syncytia formation, and define its contact site as residues in CD4 D2 using both mouse/human CD4 chimeras and CD4 substitution mutants. We also investigated the basis for its antiviral effect. Using the CD4 D2 specific mAb, we identify another conserved step in HIV infection, as evidenced by its ability to neutralize a broad range of primary isolates and T cell-line passaged strains. Monovalent forms of the mAb were used to determine if its activity was due to masking of the D2 epitope, to steric inhibition, or bivalency. Our data indicate that both binding site and bivalency of the mAb underlie its potency. The need for bivalency is not simply explained by affinity, because monovalent forms can displace the intact mAb and reverse its protective effect. These results provide evidence that binding of the D2-specific mAb prevents structural alterations necessary for membrane fusion. 相似文献
16.
17.
18.
Monifa Fahie Fabian B. Romano Christina Chisholm Alejandro P. Heuck Mark Zbinden Min Chen 《The Journal of biological chemistry》2013,288(43):31042-31051
Cytolysin A (ClyA) is an α-pore forming toxin from pathogenic Escherichia coli (E. coli) and Salmonella enterica. Here, we report that E. coli ClyA assembles into an oligomeric structure in solution in the absence of either bilayer membranes or detergents at physiological temperature. These oligomers can rearrange to create transmembrane pores when in contact with detergents or biological membranes. Intrinsic fluorescence measurements revealed that oligomers adopted an intermediate state found during the transition between monomer and transmembrane pore. These results indicate that the water-soluble oligomer represents a prepore intermediate state. Furthermore, we show that ClyA does not form transmembrane pores on E. coli lipid membranes. Because ClyA is delivered to the target host cell in an oligomeric conformation within outer membrane vesicles (OMVs), our findings suggest ClyA forms a prepore oligomeric structure independently of the lipid membrane within the OMV. The proposed model for ClyA represents a non-classical pathway to attack eukaryotic host cells. 相似文献
19.
20.
Caroline M. Tucker Tracy Aze Marc W. Cadotte Juan L. Cantalapiedra Chelsea Chisholm Sandra Díaz Richard Grenyer Danwei Huang Florent Mazel William D. Pearse Matthew W. Pennell Marten Winter Arne O. Mooers 《Biological reviews of the Cambridge Philosophical Society》2019,94(5):1740-1760
It is often claimed that conserving evolutionary history is more efficient than species‐based approaches for capturing the attributes of biodiversity that benefit people. This claim underpins academic analyses and recommendations about the distribution and prioritization of species and areas for conservation, but evolutionary history is rarely considered in practical conservation activities. One impediment to implementation is that arguments related to the human‐centric benefits of evolutionary history are often vague and the underlying mechanisms poorly explored. Herein we identify the arguments linking the prioritization of evolutionary history with benefits to people, and for each we explicate the purported mechanism, and evaluate its theoretical and empirical support. We find that, even after 25 years of academic research, the strength of evidence linking evolutionary history to human benefits is still fragile. Most – but not all – arguments rely on the assumption that evolutionary history is a useful surrogate for phenotypic diversity. This surrogacy relationship in turn underlies additional arguments, particularly that, by capturing more phenotypic diversity, evolutionary history will preserve greater ecosystem functioning, capture more of the natural variety that humans prefer, and allow the maintenance of future benefits to humans. A surrogate relationship between evolutionary history and phenotypic diversity appears reasonable given theoretical and empirical results, but the strength of this relationship varies greatly. To the extent that evolutionary history captures unmeasured phenotypic diversity, maximizing the representation of evolutionary history should capture variation in species characteristics that are otherwise unknown, supporting some of the existing arguments. However, there is great variation in the strength and availability of evidence for benefits associated with protecting phenotypic diversity. There are many studies finding positive biodiversity–ecosystem functioning relationships, but little work exists on the maintenance of future benefits or the degree to which humans prefer sets of species with high phenotypic diversity or evolutionary history. Although several arguments link the protection of evolutionary history directly with the reduction of extinction rates, and with the production of relatively greater future biodiversity via increased adaptation or diversification, there are few direct tests. Several of these putative benefits have mismatches between the relevant spatial scales for conservation actions and the spatial scales at which benefits to humans are realized. It will be important for future work to fill in some of these gaps through direct tests of the arguments we define here. 相似文献