全文获取类型
收费全文 | 1194篇 |
免费 | 127篇 |
国内免费 | 1篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 31篇 |
2020年 | 19篇 |
2019年 | 37篇 |
2018年 | 24篇 |
2017年 | 28篇 |
2016年 | 48篇 |
2015年 | 59篇 |
2014年 | 82篇 |
2013年 | 79篇 |
2012年 | 93篇 |
2011年 | 95篇 |
2010年 | 61篇 |
2009年 | 70篇 |
2008年 | 71篇 |
2007年 | 84篇 |
2006年 | 49篇 |
2005年 | 56篇 |
2004年 | 61篇 |
2003年 | 56篇 |
2002年 | 45篇 |
2001年 | 19篇 |
2000年 | 13篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有1322条查询结果,搜索用时 15 毫秒
1.
2.
Kristel Van Steen Nadia Tahri Geert Molenberghs 《Biometrical journal. Biometrische Zeitschrift》2004,46(2):187-202
Until recently, the most common parametric approaches to study the combined effects of several genetic polymorphisms located within a gene or in a small genomic region are, at the genotype level, logistic regressions and at the haplotype level, haplotype analyses. An alternative modeling approach, based on the case/control principle, is to regard exposures (e.g., genetic data such as derived from Single Nucleotide Polymorphisms – SNPs) as random and disease status as fixed and to use a marginal multivariate model that accounts for inter‐relationships between exposures. One such model is the multivariate Dale model. This model is based on multiple logistic regressions. That is why the model, applied in a case/control setting, leads to straightforward interpretations that are similar to those drawn in a classical logistic modeling framework. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
Freshly harvested seeds of Agrostemma githago L. do not germinate when they are imbibed at 20°C. The block is located in the embryo and is relased by dry storage at 20°C (after-ripening). Freshly harvested seeds complete only a small part of the processes that occur in after-ripened seeds during the lag phase prior to germination (radicle protrusion). After-ripening removed the block on lag phase processes much faster than the block on germination. This was shown both by direct determinations of the completion of lag phase processes and by measurements of the rate of axial protein synthesis, which approximately doubles when seeds are progressing through the lag phase. It is concluded that the percentage germination does not adequately reflect the extent to which the dormancy mechanism has been overcome. 相似文献
4.
M de Hoop S Asgeirsdottir M Blaauw M Veenhuis J Cregg M Gleeson A B Geert 《Protein engineering》1991,4(7):821-829
Alcohol oxidase of methylotrophic yeast is an FAD-containing enzyme. When in its active form, the enzyme is an octamer and located in the peroxisomes. To study the importance of FAD-binding on the activity, octamerization and intracellular localization of the enzyme, alcohol oxidase of Hansenula polymorpha was mutated in its presumed nucleotide-binding domain, which is formed by the N-terminal sequence. Whereas mutations of a glutamic acid residue (E42) reduced the stability of the octamer, it hardly affected enzyme activity and expression. However, replacements of three conserved glycines (G13, G15 and G18) and a conserved glutamic acid (E39) within the fold had severe effects. The mutations not only resulted in loss of enzyme activity but in reduced protein levels as well, probably due to decreased stability of the mutant alcohol oxidase. However, octamerization of the protein still occurred. The existence of inactive octameric proteins provides information about the formation pathway of this octameric flavoprotein. 相似文献
5.
Jozef Anné Patrick Verheyen Guido Volckaert Hendrik Eyssen 《Molecular & general genetics : MGG》1985,200(3):506-507
Summary A physical map of the actinophage VWB has been constructed using the restriction endonucleases BglII, ClaI, EcoRI, EcoRV, HindIII, KpnI and SphI. Phage VWB, genome size 47.3 kb, propagates on Streptomyces venezuelae, and it can also lysogenise this species. The three BglII-generated fragments of VWB DNA were cloned in pBR322, and subsequently mapped. In this manner the restriction map of the VWB phage genome was constructed.Abbreviations
dam
DNA adenine methylase activity
- kb
kilobase pairs
- ::
novel joint 相似文献
6.
Localization of calcium in skeletal and cardiac muscle 总被引:3,自引:0,他引:3
Summary The requirement of calcium (Ca2+) in the excitation-contraction coupling of both skeletal and cardiac muscle is well established. However, the exact location of the intracellular storage sites of Ca2+ is not firmly established. We report here on the ultrastructural distribution of Ca2+ in white and red skeletal muscle and in cardiac muscle of the rat using combined phosphate-pyroantimonate (PPA) and oxalate-pyroantimonate (OPA) procedures. The methods are based on (a) stabilization and/or trapping of Ca2+ during the primary fixation step in glutaraldehyde by potassium phosphate or oxalate; (b) subsequent wash-out of all non-trapped cations such as Na+ and Mg2+ in potassium phosphate or oxalate; (c) conversion of the complexed or trapped Ca2+ into an electron-dense calcium pyroantimonate salt in 100 m-thick tissue sections; and (d) wash-out of the excess potassium pyroantimonate at alkaline pH.With the OPA procedure, mitochondria of all muscle types showed little precipitate. The junctional sarcoplasmic reticulum was stongly reactive in relaxed white skeletal muscle, negative in contracted white fibres and negative in red skeletal and cardiac muscle, independent of the state of relaxation-contraction. Other organelles were essentially free of deposits.With the PPA method, the precipitate was almost exclusively confined to the sarcolemma and its T-tubular invaginations in cardiac and slow skeletal muscle, and was absent in fast skeletal muscle. Apart from occasional deposits in mitochondria, all other organelles were free of precipitate. The sarcolemma-associated deposits were clearly confined to the inner leaflet of the lipid bilayer. The amount of precipitate varied within the contraction cycle, relaxed cells possessing the highest density.Exposure of the tissue to La3+ resulted in the complete absence of sarcolemma-bound precipitate suggesting that the Ca2+ is exchangeable. Furthermore, these cytological data suggest a basic difference in Ca2+ storage between white skeletal muscle on the one hand, and red skeletal and cardiac muscle on the other. 相似文献
7.
Metastasis is a major, life-threatening complication of cancer. The bloodstream is the most important disseminative route
for cancer cells liberated from their parent tumors. Single circulating cancer cells are arrested in the microvasculature,
where the vast majority are killed by rapid or slow processes, and the relatively few survivors grow into micrometastases.
We review the underlying causes of one type of rapid cancer cell death in the microcirculation, namely, that caused by biomechanical
interactions of cancer cells with microvessel walls, which may result in cell surface membrane expansion and lethal rupture.
These lethal interactions appear to be important rate-regulators in hematogenous metastasis, and to dictate some aspects of
metastatic patterns. Although these are not the only interactions involving cancer cells, in contrast to others involving
cellular and humoral defense mechanisms, they have received comparatively little attention. 相似文献
8.
The volatile organic compounds produced during a sequence of soil incubations under controlled conditions, with either added NH4
+-N or NO3
--N, were collected and identified. The nature and relative amounts of the volatile organic compounds produced by the microorganisms in the soils were remarkably reproducible and consistent. 相似文献
9.
Hemoglobin concentrations ofChironomus cf.plumosus larvae were measured in two different habitats of the same pond. Larger larvae have higher hemoglobin concentrations than small larvae. There is strong indication that the animals of poorly oxygenated deep water, have higher hemoglobin concentrations than the animals from the well-oxygenated littoral zone. 相似文献
10.
An ecosystems approach to base-rich freshwater wetlands,with special reference to fenlands 总被引:1,自引:1,他引:0
Geert van Wirdum 《Hydrobiologia》1993,265(1-3):129-153
A survey of base-rich wetlands in The Netherlands is presented. The main area of their occurrence is the low-lying Holocene
part of the country, until some thousand years ago a large and coherent wetland landscape: the Holland wetland. The development
of various parts of the Holland wetland into marshes, fens and bogs can be understood from hydrological relations in mire
basins, as recognized in the distinction of primary, secondary and tertiary mire basin stages. Presently, the remnants of
the Holland wetland are separate base-rich wetlands. The succession of their vegetation reflects various abiotic conditions
and human influences. Three main developmental periods are distinguished as regards these factors. The first, geological period
of mire development is seen as a post-glacial relaxation, with the inertia due to the considerable mass of wetland as a stabilizing
factor. Biological “grazing” influences, as an aspect of utilization by humans, converted base-rich wetlands to whole new
types in the second, historical period. Presently, mass and harvesting have decreased in importance, and actual successions
in terrestrializing turbaries seem to reflect rapidly changing environmental conditions. Human control could well become the
most important factor in the future development of wetland nature. The present value of open fen vegetation strongly depends
on the continuation of the historical harvesting. The development of wooded fen may help to increase the mass of wetland in
the future. Best results in terms of biodiversity are expected when their base state is maintained through water management.
The vegetation and hydrology of floating fens in terrestrializing turbaries is treated in some more detail. Various lines
and phases in the succession are distinguished. Open fen vegetation at base-rich, yet nutrient-poor sites is very rich in
species threatened elsewhere. The fast acidification of certain such fens is attributed to hydrological and management factors.
This acidification is illustrated in the profile of a floating raft sample. At the scale of these small fens, the elemental
structure comprising base-rich fen, transitional fen and bog vegetation, is not as stable as it was in the large Holland wetland.
A critical role seems to be played by the supply of bases with the water influx. The changing base state is supposed to change
the nutrient cycling to such an extent that it would be correct to call this trophic excitation of the ecosystem, rather than
just eutrophication. Eutrophication indicates a quantitative reaction to an increased nutrient supply, the internal system
being unaltered. The drainage of fens, resulting in an increased productivity of the vegetation, provides another example
of excitation, to the effect that the functional system is dramatically changed internally. 相似文献