全文获取类型
收费全文 | 392篇 |
免费 | 0篇 |
专业分类
系统科学 | 6篇 |
教育与普及 | 2篇 |
现状及发展 | 91篇 |
研究方法 | 50篇 |
综合类 | 232篇 |
自然研究 | 11篇 |
出版年
2018年 | 2篇 |
2017年 | 2篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 14篇 |
2011年 | 23篇 |
2010年 | 7篇 |
2009年 | 3篇 |
2008年 | 16篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 14篇 |
2004年 | 16篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 17篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 8篇 |
1972年 | 2篇 |
1971年 | 6篇 |
1970年 | 11篇 |
1969年 | 8篇 |
1968年 | 14篇 |
1967年 | 8篇 |
1966年 | 4篇 |
1965年 | 9篇 |
1960年 | 2篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有392条查询结果,搜索用时 772 毫秒
131.
132.
Richardson DJ Berks BC Russell DA Spiro S Taylor CJ 《Cellular and molecular life sciences : CMLS》2001,58(2):165-178
Prokaryotic nitrate reduction can serve a number of physiological roles and can be catalysed by a number of biochemically distinct nitrate reductases. Three distinct nitrate reductase classes can be indentified in prokaryotes, NAS, NAR and NAP. NAS is located in the cytoplasmic compartment and participates in nitrogen assimilation. NAR is usually a three-subunit complex anchored to the cytoplasmic face of the membrane with its active site located in the cytoplasmic compartment and is involved in anaerobic nitrate respiration. NAP is a two-subunit complex, located in the periplasmic compartment, that is coupled to quinol oxidation via a membrane anchored tetraheme cytochrome. It shows considerable functional flexibility by participating in anaerobic respiration or redox energy dissipation depending on the organism in which it is found. The members of all three classes of enzymes bind the bis-molybdopterin guanine dinucleotide cofactor at the active site, but they differ markedly in the number and nature of cofactors used to transfer electrons to this site. Analysis of prokaryotic genome sequences available at the time of writing reveals that the different nitrate reductases are phylogenetically widespread. 相似文献
133.
134.
Daniel M. Taylor 《西北部美国博物学家》2011,46(2)
An annotated list of 108 bird species is reported from several spring and two summer visits, as well as one fall and one winter visit, into Hells Canyon on the Idaho-Oregon border. This is the first report on the avifauna of one of the deepest gorges in earth. 相似文献
135.
Joanna Halkias Heather J. Melichar Kayleigh T. Taylor Ellen A. Robey 《Cellular and molecular life sciences : CMLS》2014,71(16):3101-3117
Specialized microenvironments within the thymus are comprised of unique cell types with distinct roles in directing the development of a diverse, functional, and self-tolerant T cell repertoire. As they differentiate, thymocytes transit through a number of developmental intermediates that are associated with unique localization and migration patterns. For example, during one particular developmental transition, immature thymocytes more than double in speed as they become mature T cells that are among the fastest cells in the body. This transition is associated with dramatic changes in the expression of chemokine receptors and their antagonists, cell adhesion molecules, and cytoskeletal components to direct the maturing thymocyte population from the cortex to medulla. Here we discuss the dynamic changes in behavior that occur throughout thymocyte development, and provide an overview of the cell-intrinsic and extrinsic mechanisms that regulate human thymocyte migration. 相似文献
136.
137.
Hepatitis B virus contains pre-S gene-encoded domains 总被引:6,自引:0,他引:6
138.
T. S. Emudianughe Q. D. Bickle M. G. Taylor B. Andrews 《Cellular and molecular life sciences : CMLS》1985,41(11):1407-1409
Summary The metabolism of benzoic acid was studied inPlasmodium berghei infected mice both in vitro and in vivo. Results of in vitro studies showed a considerable decrease in the ability of the infected liver to detoxify benzoic acid by hippuric acid formation. The in vivo study showed that hippuric acid formation decreases with increasing parasitemia and the emergence of benzoyl-glucoronide. This new pathway stops operating with further increase in parasitemia. 相似文献
139.
A common sequence of calcium and pH signals in the mitogenic stimulation of eukaryotic cells 总被引:4,自引:0,他引:4
T R Hesketh J P Moore J D Morris M V Taylor J Rogers G A Smith J C Metcalfe 《Nature》1985,313(6002):481-484
When normal quiescent (G0) cells are stimulated by mitogens to enter the cell cycle, the metabolic derepression which occurs is similar in a variety of cells. The mechanisms initiating these responses and their relationship to subsequent progression through G1 to DNA synthesis in S phase, however, are generally undefined. The clearest evidence has been obtained in sea urchin eggs, where fertilization by sperm causes a rapid, transient increase in the concentration of free cytoplasmic Ca2+ [(Ca]i), followed by a sustained increase in cytoplasmic pH (pHi). It has been demonstrated clearly that these ionic responses are obligatory for progression to DNA synthesis by the normal pathway after fertilization, although the Ca2+ signal can be bypassed by parthenogenetic agents which elevate directly pHi (for example, NH+4 ions). These observations raise the questions of whether other eukaryotic cells show the same sequence of ionic responses when stimulated by mitogens and whether such signals are an obligatory component of their mitogenic pathways. We show here that a common sequence of [Ca]i and pHi responses occurs in both quiescent mouse thymocytes and Swiss 3T3 fibroblasts stimulated by appropriate mitogens. Furthermore, 'opportunistic' mitogens (those that do not act on the cells in vivo, such as concanavalin A (Con A), the Ca2+ ionophore A23187 and 12-o-tetradecanoyl phorbol 13-acetate CTPA] that are mitogenic for both mouse thymocytes and 3T3 fibroblast, each produce characteristic ionic responses that are the same in both types of cell. 相似文献
140.
The temporal and spatial dynamics of intracellular signals and protein effectors are being defined as a result of imaging using fluorescent reagents within living cells. We have described a new class of fluorescent analogues termed optical biosensors, which sense chemical or molecular events through their effects on protein transducers. One example of this new class of indicators is MeroCaM, an environmentally sensitive fluorophore which when it is attached to calmodulin reflects the activation of calmodulin by calcium in vitro. We report here that the rise in free calcium and MeroCaM activation occur in the same period during serum stimulation of quiescent fibroblasts. MeroCaM activation also correlates with the spatial pattern of increased free calcium and the contraction of transverse fibres during wound healing. Finally, migrating fibroblasts in the later stages of wound-healing exhibit an increasing gradient of free calcium and MeroCaM activation from the front to the rear. 相似文献