全文获取类型
收费全文 | 1467篇 |
免费 | 74篇 |
出版年
2022年 | 11篇 |
2021年 | 22篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 19篇 |
2016年 | 36篇 |
2015年 | 39篇 |
2014年 | 62篇 |
2013年 | 73篇 |
2012年 | 78篇 |
2011年 | 86篇 |
2010年 | 51篇 |
2009年 | 65篇 |
2008年 | 83篇 |
2007年 | 87篇 |
2006年 | 73篇 |
2005年 | 64篇 |
2004年 | 72篇 |
2003年 | 83篇 |
2002年 | 95篇 |
2001年 | 42篇 |
2000年 | 32篇 |
1999年 | 40篇 |
1998年 | 27篇 |
1997年 | 23篇 |
1996年 | 16篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 19篇 |
1991年 | 24篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1971年 | 4篇 |
排序方式: 共有1541条查询结果,搜索用时 15 毫秒
31.
Richard R. Strathmann Lucienne Fenaux Megumi F. Strathmann 《Evolution; international journal of organic evolution》1992,46(4):972-986
Preexisting developmental plasticity in feeding larvae may contribute to the evolutionary transition from development with a feeding larva to nonfeeding larval development. Differences in timing of development of larval and juvenile structures (heterochronic shifts) and differences in the size of the larval body (shifts in allocation) were produced in sea urchin larvae exposed to different amounts of food in the laboratory and in the field. The changes in larval form in response to food appear to be adaptive, with increased allocation of growth to the larval apparatus for catching food when food is scarce and earlier allocation to juvenile structures when food is abundant. This phenotypic plasticity among full siblings is similar in direction to the heterochronic evolutionary changes in species that have greater nutrient reserves within the ova and do not depend on particulate planktonic food. This similarity suggests that developmental plasticity that is adaptive for feeding larvae also contributes to correlated and adaptive evolutionary changes in the transition to nonfeeding larval development. If endogenous food supplies have the same effect on morphogenesis as exogenous food supplies, then changes in genes that act during oogenesis to affect nutrient stores may be sufficient to produce correlated adaptive changes in larval development. 相似文献
32.
Summary DNA containing structures (cellular, chloroplast and mitochondrial nuclei) were stained with the fluorochrome DAPI. Fluorescence intensity, as a measure of DNA content, was estimated during the mitotic cycle in synchronized populations of the chlorococcal alga,Scenedesmus quadricauda. In cells yielding eight daughter cells, three consecutive steps in chloroplast DNA increase occurred over one mitotic cycle. The first step was performed shortly after releasing the daughter cells, the second and third steps occurred consecutively during the first half of the mitotic cycle. Commitment to chloroplast DNA replication was chronologically separated from commitment to division of chloroplast nuclei, revealing that these two chloroplast reproductive steps were under different control mechanisms. The replication of chloroplast DNA occurred at a different time to that of cell-nuclear DNA. The coordination of chloroplast reproductive processes and those in the nucleocytoplasmic compartment were governed by the mutual trophic and metabolic dependency of these compartments rather than by any direct or feedback control controlled by either of them.Abbreviations DAPI
46-diamidino-2-phenylindole
- ptDNA DNA
in chloroplast nuclei
- nucDNA DNA
in cell nuclei 相似文献
33.
Sachiko Terui Kuninori Suzuki Hidenori Takahashi Ryuuichi Itoh Tsuneyoshi Kuroiwa 《Journal of phycology》1995,31(6):958-961
A system of highly synchronized chloroplast divisions was developed in the unicellular red alga Cyanidioschyzon merolae De Luca, Taddei, & Varano. Chloroplast divisions were examined by epifluorescence microscopy following treatments with light and inhibitors. When the cells during stationary phase were transferred into a new medium under a 12:12 h LD cycle, chloroplasts, mitochondria, and cell nuclei divided synchronously in that order soon after the initiation of dark periods. More than 40% of the cells contained dividing chloroplasts. To obtain a system of highly synchronized cell division and chloroplast division, the cells synchronized by a 12:12 h LD cycle were treated with various inhibitors. Nocodazole and propyzamide did not affect cell and organelle divisions, whereas aphidicolin markedly inhibited cell-nuclear divisions and cytokinesis and induced a delay in chloroplast division. More than 80% of the cells contained dividing chloroplasts when cells synchronized by light were treated with aphidicolin for 12 h. This synchronized system will be useful for studies of the molecular and cellular mechanisms of organelle divisions . 相似文献
34.
Niji Ohta Naoki Sato Kunihiko Ueda Tsuneyoshi Kuroiwa 《Journal of plant research》1997,110(2):235-245
Cyanidioschyzon merolae andCyanidium caldarium are representative species among of the most primitive algae, although the two species are distinctly different in various
morphological traits. We determined the nucleotide sequence of therbcL gene and a flanking 8-kb region in the plastid genome of each of these algae. In both algae, 12 genes were identified in
this region, in an identical order. This gene order is not conserved in the plastid genomes of other species of the kingdom
Plantae that have been sequenced to data. An additional unidentified open reading frame was also found in the two algae that
we analyzed, which has not been described in any other species of algae includingPorphyra purpurea. Comparison of the amino acid sequences of selected genes also supported the conclusion thatCyanidioschyzon merolae andCyanidium caldarium are closely related and that they are distinct from other rhodophytes.
The nucleotide sequence data reported in this paper will appear in the DDBJ, EMBL and GenBank Nucleotide Sequence Databases
under the accession numbers D63675 and D63676. 相似文献
35.
When partially purified Ehrlich ascites tumor RNA polymerase II was further purified on a column of phosphocellulose, stimulation of its catalysis of RNA synthesis by stimulatory factor S-II was greatly decreased. This decrease in sensitivity to the stimulatory factor was reversible: the enzyme eluted from phosphocellulose became sensitive to the factor when mixed with a protein fraction eluted from the phosphocellulose at high salt concentration. Evidence was obtained that this protein, named helper protein, binds, to the enzyme eluted from phosphocellulose, causing it to recover sensitivity to stimulatory factor S-II. 相似文献
36.
Megumi Fujisue Masao Sakai Kiyotaka Yamanat 《Development, growth & differentiation》1991,33(4):341-351
The specification of the dorsoventral axis in naturally polyspermic eggs of the Japanese newt, Cynops pyrrhogaster , was first examined by studies on the spatial relationship between the dorsal midline of the future body plan and the sperm entrance points (SEPs 1 ). On local insemination, the dorsal blastopore lip was usually found to be formed opposite the SEPs, as in anuran monospermic eggs. Next the movements of the subcortical layer and the cortex were analyzed. "Subcortical rotation" was observed, similar to that of Xenopus laevis eggs with respect to its timing and extent, and its direction was shown to predict the embryonic axis of the eggs. Thus, the dorsoventral axis was concluded to be determined by essentially the same mechanism in the newt as in Xenopus .
Owing to their large size and long first cell cycle, newt eggs appear to be suitable material for study of subcortical rotation, but their behavior is unique in that subcortical rotation occurs in only the vegetal hemisphere so that the subcortical layer stretches in the future dorsal side. Studies on the movement of Nile blue spots suggested that the cytoplasm under the cortex in newt eggs consists of two layers. 相似文献
Owing to their large size and long first cell cycle, newt eggs appear to be suitable material for study of subcortical rotation, but their behavior is unique in that subcortical rotation occurs in only the vegetal hemisphere so that the subcortical layer stretches in the future dorsal side. Studies on the movement of Nile blue spots suggested that the cytoplasm under the cortex in newt eggs consists of two layers. 相似文献
37.
Tokuo Ogawa Junichi Sugenoya Norikazu Ohnishi Keiko Natsume Megumi Ochiai Motohiko Nishida Norihiko Shinoda Kenichi Katoh Ritsuko Imamura 《International journal of biometeorology》1991,35(1):18-23
In an attempt to detect differences in the thermal effect of infrared irradiation of different wavelengths, transient sweating response to infrared irradiation in various spectral regions was examined. In Series 1, the ventral or dorsal surface of the nude subject was irradiated repetitively for a period of 4 min (2 min on, 2 min off) by each of three kinds of infrared heaters with main emissivity in near-infrared (NIR; 0.7–2.8 m), intermediate-infrared (MIR; 1.5–5.8 m), and far-infrared (FIR; 2.8–25 m) regions. The sweating response on a non-irradiated area tended to be the greatest with MIR, while the magnitude of the sweating response on the irradiated area showed no consistent differences among various wavelengths. The results infer that MIR stimulated cutaneous thomoreceptors most effectively, while its direct effect on local sweat gland activity was minimal. In Series 2, the effects of 9–12 min irradiations in more restricted ranges of wavelength were compared by the combination of the three kinds of heaters with filters (translucent to wavelength ranges of 1.3–2.7, 2.7–3.5, 3.6–8.0 m, respectively). The sweating response on a remote area was predominantly greater with the range of 2.7–3.5 m than with the other wavelength ranges, while the local effect on sweating was minimal with this range. The results of Series 2 reinforce those of Series 1, indicating that the degree of stimulation of cutaneous thermoreceptors and of direct thermal effect on sweat gland activity differ with spectral regions incident on the skin, thus affecting local and remote effects on the sweating response. 相似文献
38.
Hiide Yoshino Nobuyuki Miyatani Megumi Saito Toshio Ariga Alessandra Lugaresi Norman Latov Yasunori Kushi Takeshi Kasama Robert K. Yu 《Journal of neurochemistry》1992,59(5):1684-1691
The gangliosides GM1 and GD1b have recently been reported to be potential target antigens in human motor neuron disease (MND) or motor neuropathy. The mechanism for selective motoneuron and motor nerve impairment by the antibodies directed against these gangliosides, however, is not fully understood. We recently investigated the ganglioside composition of isolated bovine spinal motoneurons and found that the ganglioside pattern of the isolated motoneurons was extremely complex. GM1, GD1a, GD1b, and GT1b, which are major ganglioside components of CNS tissues, were only minor species in motoneurons. Among the various ganglioside species in motoneurons, several were immunoreactive to sera from patients with MND and motor neuropathy. One of these gangliosides was purified from bovine spinal cord and characterized as N-glycolylneuraminic acid-containing GM1 [GM1(NeuGc)] by compositional analysis, fast atom bombardment mass spectra, and the use of specific antibodies. Among seven sera with anti-GM1 antibody activities, five sera reacted with GM1(NeuGc) and two did not. Two other gangliosides, which were recognized by another patient's serum, appeared to be specific for motoneurons. We conclude that motoneurons contained, in addition to the known ganglioside antigens GM1 and GD1b, other specific ganglioside antigens that could be recognized by sera from patients with MND and motor neuropathy. 相似文献
39.
40.
Summary The behavior of organelle nuclei during maturation of the male gametes ofLilium longiflorum andPelargonium zonale was examined by fluorescence microscopy after staining with 4,6-diamidino-2-phenylindole (DAPI) and Southern hybridization. The organelle nuclei in both generative and vegetative cells inL. longiflorum were preferentially degraded during the maturation of the male gametes. In the mature pollen grains ofL. longiflorum, there were absolutely no organelle nuclei visible in the cytoplasm of the generative cells. In the vegetative cells, almost all the organelle nuclei were degraded. However, in contrast to the situation in generative cells, the last vestiges of organelle nuclei in vegetative cells did not disappear completely. They remained in evidence in the vegetative cells during germination of the pollen tubes. InP. zonale, however, no evidence of degradation of organelle nuclei was ever observed. As a result, a very large number of organelle nuclei remained in the sperm cells during maturation of the pollen grains. When the total DNA isolated from the pollen or pollen tubes was analyzed by Southern hybridization with a probe that contained therbc L gene, for detection of the plastid DNA and a probe that contained thecox I gene, for detection of the mitochondrial DNA, the same results were obtained. Therefore, the maternal inheritance of the organelle genes inL. longiflorum is caused by the degradation of the organelle DNA in the generative cells while the biparental inheritance of the organelle genes inP. zonale is the result of the preservation of the organelle DNA in the generative and sperm cells. To characterize the degradation of the organelle nuclei, nucleolytic activities in mature pollen were analyzed by an in situ assay on an SDS-DNA-gel after electrophoresis. The results revealed that a 40kDa Ca2+-dependent nuclease and a 23 kDa Zn2+ -dependent nuclease were present specifically among the pollen proteins ofL. longiflorum. By contrast, no nucleolytic activity was detected in a similar analysis of pollen proteins ofP. zonale. 相似文献