全文获取类型
收费全文 | 5064篇 |
免费 | 433篇 |
国内免费 | 2篇 |
出版年
2023年 | 15篇 |
2022年 | 32篇 |
2021年 | 82篇 |
2020年 | 43篇 |
2019年 | 67篇 |
2018年 | 85篇 |
2017年 | 73篇 |
2016年 | 105篇 |
2015年 | 204篇 |
2014年 | 190篇 |
2013年 | 284篇 |
2012年 | 367篇 |
2011年 | 336篇 |
2010年 | 244篇 |
2009年 | 199篇 |
2008年 | 322篇 |
2007年 | 328篇 |
2006年 | 276篇 |
2005年 | 266篇 |
2004年 | 284篇 |
2003年 | 301篇 |
2002年 | 270篇 |
2001年 | 61篇 |
2000年 | 59篇 |
1999年 | 61篇 |
1998年 | 84篇 |
1997年 | 51篇 |
1996年 | 63篇 |
1995年 | 55篇 |
1994年 | 60篇 |
1993年 | 48篇 |
1992年 | 43篇 |
1991年 | 37篇 |
1990年 | 32篇 |
1989年 | 29篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 39篇 |
1984年 | 34篇 |
1983年 | 23篇 |
1982年 | 41篇 |
1981年 | 32篇 |
1980年 | 24篇 |
1979年 | 24篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1976年 | 10篇 |
1974年 | 18篇 |
1973年 | 10篇 |
排序方式: 共有5499条查询结果,搜索用时 15 毫秒
81.
82.
Fully grown meiotically immature (germinal vesicle stage) amphibian oocytes incorporate radioactive protein ([3H]vitellogenin) following in vitro culture. In vitro exposure of such oocytes to exogenous progesterone induces germinal vesicle breakdown and inhibits incorporation of vitellogenin. In the present studies, we have investigated the effects of cytoplasm taken from mature and immature oocytes on incorporation of vitellogenin and nuclear breakdown following microinjection of this material into immature oocytes. Vitellogenin incorporation was markedly suppressed in oocytes which underwent nuclear breakdown following injection with cytoplasm from mature oocytes. Incorporation of vitellogenin into oocytes which did not mature after injection with cytoplasm taken from mature oocytes resembled that seen in oocytes injected with immature cytoplasm. The degree of suppression of vitellogenin incorporation following cytoplasmic injections was similar to that seen in uninjected oocytes treated with progesterone. Oocytes injected with cytoplasm obtained from immature oocytes did not undergo either nuclear breakdown or changes in vitellogenin incorporation. The results suggest that cytoplasm obtained from mature oocytes contains a factor(s) which alters directly or indirectly the capacity of the oocyte cell membrane to incorporate vitellogenin. Enucleated immature oocytes also incorporated [3H]vitellogenin, and injection of such oocytes with mature, but not immature, oocyte cytoplasm suppressed vitellogenin incorporation. Suppressive effects of injected cytoplasm thus appear to be mediated through physiological changes in the recipient oocyte cytoplasm rather than the nuclear component. 相似文献
83.
Dinoflagellate chromosomes observed in thin section show regular patterns which have been shown to correspond to a liquid crystalline helicoidal arrangement of DNA. Peripheral DNA filaments form a system of loops in the surrounding nucleoplasm. When such chromosomes (studied in Prorocentrum micans) are in presence of water, they extend considerably and form a double helical bundle. At the periphery of these bundles, one observes numerous filaments, which are smooth and devoid of nucleosomes; their diameter is constant.This study, in phase contrast and in electron microscopy, allows statistical measurements. A geometrical model is proposed and shows the simplest way to pass from the intact to the extended form. The liquid crystalline character of the chromosome is probably involved in the extension mechanisms. 相似文献
84.
Anne-Marie Bourdeaux Yves Giudicelli Marie-Christine Rebourcet Joseph Nordmann Roger Nordmann 《Biochemical and biophysical research communications》1980,95(1):212-219
At concentrations corresponding to the levels usually reported in the blood of different species in the fed state, gastrin and pancreozymin but not secretin and vasoactive intestinal peptide, stimulate the lipoprotein lipase activity of adipose tissue from fasted rats. The enzyme response to gastrin is, like that to insulin, dependent on the presence of glucose and is not additive with the enzyme response to insulin. On the contrary, the effect of pancreozymin on lipoprotein lipase is glucoseindependent and is additive with the enzyme response to insulin. Both the effects of gastrin and pancreozymin depend on protein synthesis as shown by their suppression by cycloheximide. With isolated fat cells, gastrin increases both the releasable and non-releasable lipase activities whereas pancreozymin increases almost exclusively the non-releasable activity. The mechanisms and the possible physiological significance of these findings are discussed in relationship with the influence of insulin and the nutritional state on adipose tissue lipoprotein lipase. 相似文献
85.
The cellular growth ofChlamydomonas reinhardii is modified by the addition of a total exogenous histone fraction. These modifications may be related to chloroplast DNA replication; they are different according to the different classes of histones. The H1 subfraction seems to be responsible for the effect of the total histone fraction. 相似文献
86.
87.
Yves Crouau 《Zoomorphology》1981,98(2):121-134
Summary The various antennal setae can be differentiated from each other by the number and the type of their dendrites and by the cuticular structure of their external parts; these features correspond to functional differences. Moreover, the work revealed differences in relation to the corresponding setae of a marine Mysidacea previously studied by Guse (1978). Various hypotheses linking the ultrastructural differences to those that characterize the environments in which these two species live can be put forward.Abbreviations A1, A3
simple setae A1, A3
- An
antenna
- B1, B2
setulate setae B1, B2
- Bi
bifid seta
- bp
bending plane
- c1, c2, c3
type 1, 2, or 3 cilia (outer dendritic segments)
- cu
cuticle
- d1, d2, d3
type 1, 2, or 3 dendrites (inner dendritic segments)
- ec
enveloping cell
- g
Golgi apparatus
- h
helically arranged cuticle
- md
microtubule doublet
- n
nucleus
- p
apical pore
- r
ciliary root
- s
setules
- sc
scolopale
- scc
scolopale cell
- Si
sickle-shaped seta
- sm
small seta
- st
stopper
- t
extracellular matter tube 相似文献
88.
Crystalline polysaccharides with 1 → 3−β and 1 → 4−β glycosidic linkages are the most prevalent ones in nature. An interpretation of recent X-ray data on 1 → 3−α glucan shows that it has a ribbon-like crystalline conformation similar to cellulose. Comparison of the crystalline conformation of the four principal homoglucans shows that they fall either in the ‘ribbon-like’ or ‘large amplitude’ helix class. Heteroglucans with a regular sequence of glucosidic linkages show characteristics of the ‘extended conformation’ rather than the ‘coiled conformation’ even when there is 50% of a linkage which in a homoglucan leads to a large amplitude helix. It is concluded that X-ray diffraction analysis fully establishes the hypothesis that the glycosidic linkage type is the determinant of polysaccharide conformation. In this respect, polysaccharides are more like synthetic polymers than proteins or nucleotides; in the latter, it is variation in the substituents which are responsible for the conformational diversity. 相似文献
89.
Bart Marescau Armand Lowenthal Eddy Esmans Yves Luyten Frank Alderweiereldt Heinz Georg Terheggen 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1981,224(2):185-195
Liquid column chromatographic studies of monosubstituted guanidino compounds, which are excreted in the urine of patients with hyperargininaemia are reported. The guanidino-positive peaks, with the highest excretion values, were isolated from urine and the isolated compounds were identified by thin-layer chromatography and gas chromatography—mass spectrometry. Guanidinoacetic acid, N-α-acetylarginine, argininic acid, γ-guanidinobutyric acid, arginine and α-keto-δ-guanidinovaleric acid were found to be excreted at high levels in the urine of patients with hyperargininaemia compared with controls. 相似文献
90.
Chamla Yves Bilbeissi Catherine Micheau Marguerite Battin Jacques 《Human genetics》1977,38(2):245-248
Summary A new case of partial trisomy 9q was found in a child presenting two de novo aberrations: a deletion of the long arms of 9 and a 9,21 translocation. A tentative cytogenetic explanation is put forward. 相似文献