全文获取类型
收费全文 | 1190篇 |
免费 | 93篇 |
出版年
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 14篇 |
2016年 | 34篇 |
2015年 | 47篇 |
2014年 | 42篇 |
2013年 | 61篇 |
2012年 | 73篇 |
2011年 | 79篇 |
2010年 | 54篇 |
2009年 | 47篇 |
2008年 | 77篇 |
2007年 | 87篇 |
2006年 | 78篇 |
2005年 | 74篇 |
2004年 | 55篇 |
2003年 | 66篇 |
2002年 | 71篇 |
2001年 | 27篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 18篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有1283条查询结果,搜索用时 15 毫秒
11.
Tubulovesicular processes emerge from trans-Golgi cisternae, extend along microtubules, and interlink adjacent trans-golgi elements into a reticulum 总被引:38,自引:0,他引:38
Morphological dynamics and membrane transport within the living Golgi apparatus of astrocytes labeled with NBD-ceramide were imaged using both electronically enhanced fluorescence video and laser confocal microscopy. In time-lapse recordings, continuous tubulovesicular processes are observed to emerge from trans-Golgi elements and extend along microtubules at average rates of 0.4 microns/s. In addition, discrete fluorescent particles are observed to emerge from the trans-Golgi and subsequently migrate along microtubules at comparable velocities. Frequently, tubulovesicular processes form stable connections that interlink adjacent trans-Golgi elements into an extensive reticulum. Laser photobleaching-recovery experiments reveal that tubulovesicular processes can provide direct pathways for the diffusion of membrane lipids between joined trans-Golgi elements. These results suggest that microtubule-based transport and membrane fusion can operate to interconnect certain cisternal membranes of adjacent Golgi elements within the cell. 相似文献
12.
D. Daniëlle de Vries Ilse J. de Wijs Gerhard Wolff Uwe-Peter Ketelsen Hans-Hilger Ropers Bernard A. van Oost 《Human genetics》1993,91(1):51-54
A family with myoclonus epilepsy has been described previously as suffering from an X-linked disorder, because at least four males were affected, and only mild and variable symptoms were seen in some female carriers. In this family, we have now identified a mitochondrial AG (8344) heteroplasmic point mutation. This point mutation has been described in families with maternally inherited myoclonus epilepsy and ragged red fibers. The degree of severity of the disorder in the different family members was reflected in the relative quantity of mutated mitochondrial DNA. It is concluded that the mode of inheritance in this family is not X-linked but maternal. 相似文献
13.
Fertilization in the clear egg (1 mm in diameter) of the ctenophore Beroe ovata and, in particular, the positioning and movements of pronuclei, and their relationship to the larval oral-aboral axis have been observed. Fertilization can take place anywhere on the egg surface. The sperm pronucleus remains at its entry site and becomes surrounded by a specialized zone (30–50 μm in diameter) beneath the surface referred to as the sperm pronuclear zone or SPZ and devoid of large cortical granules. Polyspermy has been observed to be frequent; each pronucleus is surrounded by its own SPZ. Only the egg pronucleus migrates with a continuous velocity (averaging 18 μm/min) and moves beneath the surface directly toward the immobile sperm pronucleus. In polyspermic eggs, the egg pronucleus can probe several SPZ, each containing a single sperm nucleus, before it finally enters one SPZ and fuses with the chosen sperm pronucleus. These migrations of the egg pronucleus occur over several millimeters and take hours, but the mechanism underlying the motion or how the egg pronucleus decides which SPZ to enter is not yet known. Under our experimental conditions the mitotic apparatus and the first cleavage plane which defines the oral-aboral axis of the larva (see Reverberi (1971). “Experimental Embryology of Marine and Fresh-Water Invertebrates.” North-Holland, Amsterdam. for review) pass through the point of sperm entry. During fertilization and cleavage, movements of a cortical autofluorescent material are clearly seen. This material is segregated into micromeres as cleavage progresses. 相似文献
14.
Michel Hughes Daniéle Duval Heidy Schmid Patrick Kitabgi Michel Lazdunski Jean-Pierre Vincent 《Life sciences》1982,31(5):437-443
This paper describes the interaction of apamin, the bee venom neurotoxin, with its receptor in the guinea pig colon. The pharmacological activity of the toxin was assayed by measuring its contracting effect on guinea pig colon preparations that had been previously relaxed by neurotensin. The IC50 value of apamin in this bioassay is 7 nM. These pharmacological data are compared to the binding properties of apamin to smooth muscle membranes prepared from guinea pig colon. The highly radiolabeled monoiododerivative of apamin binds to its colon receptor with a dissociation constant . The maximal binding capacity of colonic membranes is 30dfmol/mg of protein. The dissociation constant of the unmodified toxin is 23 pM. The difference between the toxin concentrations that produce half-maximal effects in the binding and pharmacological studies arises from the different experimental conditions used for the two assays. 相似文献
15.
Further observations on cell wall morphogenesis and polysaccharide arrangement during plant growth 总被引:1,自引:1,他引:0
Summary The three-dimensional arrangement of the polysaccharide chains in cell walls was investigated, using ultracryotomy and cytochemistry, in order to test the validity of the previously postulated ordered fibril hypothesis and to analyze the characteristics of the primary wall morphogenesis.Both in mung bean hypocotyl (Phaseolus aureus) and pea root (Pisum sativum) cultured in defined conditions, cell to cell endogenous specificity is marked by differences in the numbers of layers, thickness, rhythm and direction of deposition. The occurrence of bow-shaped arrangements and of strata of orientation intermediate between the main crisscrossed multifibrillar layers suggests that the sequential changes of the morphogenetic activity of the cells is progressive. The twisted polysaccharide disposition evokes certain mesomorphic states; a part of the mechanism responsible for the wall arrangement may result from a self-assembly process as in the orientation of the molecules in a liquid cristal. This possibility finds experimental support in the fact that a three-dimensional association of the hemicellulose chains spontaneously appears when precipitated in acellular conditions.Polysaccharide removal associated with shadowing indicates that the ordered disposition within the wall is extensively altered by even a slight extraction. These data may invalidate diverse results which are generally brought forward to explain the wall organization during growth. 相似文献
16.
17.
André Dautigny Ellen M. Prager Danièle Pham-Dinh Jacqueline Jollès Farzad Pakdel Bjørn Grinde Pierre Jollès 《Journal of molecular evolution》1991,32(2):187-198
Summary The complete 129-amino-acid sequences of two rainbow trout lysozymes (I and II) isolated from kidney were established using
protein chemistry microtechniques. The two sequences differ only at position 86, I having aspartic acid and II having alanine.
A cDNA clone coding for rainbow trout lysozyme was isolated from a cDNA library made from liver mRNA. Sequencing of the cloned
cDNA insert, which was 1 kb in length, revealed a 432-bp open reading frame encoding an amino-terminal peptide of 15 amino
acids and a mature enzyme of 129 amino acids identical in sequence to II. Forms I and II from kidney and liver were also analyzed
using enzymatic amplification via PCR and direct sequencing; both organs contain mRNA encoding the two lysozymes. Evolutionary
trees relating DNA sequences coding for lysozymesc and α-lactalbumins provide evidence that the gene duplication giving rise to conventional vertebrate lysozymesc and to lactalbumin preceded the divergence of fishes and tetrapods about 400 Myr ago. Evolutionary analysis also suggests
that amino acid replacements may have accumulated more slowly on the lineage leading to fish lysozyme than on those leading
to mammal and bird lysozymes. 相似文献
18.
I Eshel 《Theoretical population biology》1976,9(2):282-297
Intrinsic biological resemblance between two types is measured in terms of a correlation between their fitnesses under various possible environmental conditions. A tendency toward dominance is defined as the intrinsic biological resemblance between homozygote and heterozygote. The effect of a tendency toward dominance on the à priori survival probability of a mutant gene is studied when the fitnesses of the mutated forms are given only by their distributions. Close intrinsic resemblance between homozygous and heterozygous forms of a new mutant gene is shown to substantially increase the à priori survival probability of this gene. A probabilistic effect of selection is, thus, shown to statistically favor dominant or near dominant mutant genes to start with.This probabilistic effect is suggested as complementary to the Fisherian process of selection on the heterozygote modifiers, taking place at further stages of the progress of a mutant gene. 相似文献
19.
20.