全文获取类型
收费全文 | 26719篇 |
免费 | 15586篇 |
国内免费 | 9篇 |
专业分类
42314篇 |
出版年
2023年 | 47篇 |
2022年 | 136篇 |
2021年 | 471篇 |
2020年 | 2226篇 |
2019年 | 3749篇 |
2018年 | 3876篇 |
2017年 | 4127篇 |
2016年 | 4130篇 |
2015年 | 4051篇 |
2014年 | 3714篇 |
2013年 | 4144篇 |
2012年 | 1834篇 |
2011年 | 1567篇 |
2010年 | 3068篇 |
2009年 | 1816篇 |
2008年 | 705篇 |
2007年 | 289篇 |
2006年 | 262篇 |
2005年 | 325篇 |
2004年 | 307篇 |
2003年 | 278篇 |
2002年 | 286篇 |
2001年 | 266篇 |
2000年 | 199篇 |
1999年 | 148篇 |
1998年 | 23篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 17篇 |
1991年 | 8篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1981年 | 10篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 5篇 |
1975年 | 9篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1971年 | 5篇 |
1969年 | 5篇 |
1968年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
Takashi Kobayashi Hiroko Habuchi Ken Nogami Satoko Ashikari‐Hada Koji Tamura Hiroyuki Ide Koji Kimata 《Development, growth & differentiation》2010,52(2):146-156
Heparan sulfate (HS) interacts with numerous growth factors, morphogens, receptors, and extracellular matrix proteins. Disruption of HS synthetic enzymes causes perturbation of growth factor signaling and malformation in vertebrate and invertebrate development. Our previous studies show that the O‐sulfation patterns of HS are essential for the specific binding of growth factors to HS chains, and that depletion of O‐sulfotransferases results in remarkable developmental defects in Drosophila, zebrafish, chick, and mouse. Here, we show that inhibition of chick HS‐6‐O‐sulfotransferases (HS6ST‐1 and HS6ST‐2) in the prospective limb region by RNA interference (RNAi) resulted in the truncation of limb buds and reduced Fgf‐8 and Fgf‐10 expressions in the apical ectodermal ridge and in the underlying mesenchyme, respectively. HS6ST‐2 RNAi resulted in a higher frequency of limb truncation and a more marked change in both Fgf‐8 and Fgf‐10 expressions than that achieved with HS6ST‐1 RNAi. HS6ST‐1 RNAi and HS6ST‐2 RNAi caused a significant but distinct reduction in the levels of different 6‐O‐sulfation in HS, possibly as a result of their different substrate specificities. Our data support a model where proper levels and patterns of 6‐O‐sulfation of HS play essential roles in chick limb bud development. 相似文献
933.
Citlali Trueta Sergio Snchez‐Armass Miguel A. Morales Francisco F. De‐Miguel 《Developmental neurobiology》2004,61(3):309-316
We analyzed the contribution of calcium (Ca2+)‐induced Ca2+ release to somatic secretion in serotonergic Retzius neurons of the leech. Somatic secretion was studied by the incorporation of fluorescent dye FM1‐43 upon electrical stimulation with trains of 10 impulses and by electron microscopy. Quantification of secretion with FM1‐43 was made in cultured neurons to improve optical resolution. Stimulation in the presence of FM1‐43 produced a frequency‐dependent number of fluorescent spots. While a 1‐Hz train produced 19.5 ± 5.0 spots/soma, a 10‐Hz train produced 146.7 ± 20.2 spots/soma. Incubation with caffeine (10 mM) to induce Ca2+ release from intracellular stores without electrical stimulation and external Ca2+, produced 168 ± 21.7 spots/soma. This staining was reduced by 49% if neurons were preincubated with the Ca2+‐ ATPase inhibitor thapsigargin (200 nM). Moreover, in neurons stimulated at 10 Hz in the presence of ryanodine (100 μM) to block Ca2+‐induced Ca2+ release, FM1‐43 staining was reduced by 42%. In electron micrographs of neurons at rest or stimulated at 1 Hz in the ganglion, endoplasmic reticulum lay between clusters of dense core vesicles and the plasma membrane. In contrast, in neurons stimulated at 20 Hz, the vesicle clusters were apposed to the plasma membrane and flanked by the endoplasmic reticulum. These results suggest that Ca2+‐induced Ca2+ release produces vesicle mobilization and fusion in the soma of Retzius neurons, and supports the idea that neuronal somatic secretion shares common mechanisms with secretion by excitable endocrine cells. © 2004 Wiley Periodicals, Inc. J Neurobiol, 2004 相似文献
934.
Abstract The effects of recent fire frequency and time‐since‐fire on plant community composition and species abundance in open‐forest and woodland vegetation in Girraween National Park, south‐east Queensland, Australia, were examined. Cover‐abundance data were collected for shrub and vine species in at least 10 400‐m2 plots in each of four study areas. Study areas were within one community type and had burnt most recently either 4 or 9 years previously. Variations in fire frequency allowed us to compare areas that had burnt at least three times in the previous 25 years with less frequently burnt areas, and also woodlands that had experienced a 28‐year interfire interval with more frequently burnt areas. Although species richness did not differ significantly with either time‐since‐fire or fire frequency, both these factors affected community composition, fire frequency being the more powerful. Moisture availability also influenced floristics. Of the 67 species found in five or more plots, six were significantly associated with time‐since‐fire, whereas 11 showed a significant difference between more and less frequently burnt plots in each of the two fire‐frequency variables. Most species, however, did not vary in cover‐abundance with the fire regime parameters examined. Even those species that showed a marked drop in cover‐abundance when exposed to a particular fire regime generally maintained some presence in the community. Five species with the capacity to resprout after fire were considered potentially at risk of local extinction under regimes of frequent fire, whereas two species were relatively uncommon in long‐unburnt areas. Variable fire regimes, which include interfire intervals of at least 15 years, could be necessary for the continuity of all species in the community. 相似文献
935.
This work presents the mitochondrial DNA molecular organization of the control region (CR) of South American camelids. Sequencing of five individuals each of guanaco, llama, alpaca and vicuna species showed that this region spans 1060 bp including three conserved sequence blocks (CSB I–III) adjacent to the tRNAPhe gene, a conserved central domain and one extended termination‐associated sequence in the 3′ domain of the CR close to the tRNAPro gene. A repeated array formed by three units of 26 bp was detected between CSB I and II. Alignment of the CR sequences from the four species shows a 337‐bp segment that includes most of the nucleotide variability with 10 polymorphic sites. We suggest the use of this segment as a molecular marker to infer data on camelid genetic relationships and population diversity studies. 相似文献
936.
937.
Jaeyoon Kim Yoon Sup Choi Seyoung Lim Kyungmoo Yea Jong Hyuk Yoon Dong‐Jae Jun Sang Hoon Ha Jung‐Wook Kim Jae Ho Kim Pann‐Ghill Suh Sung Ho Ryu Taehoon G. Lee 《Proteomics》2010,10(3):394-405
Adipogenesis is a complex process that is accompanied by a number of molecular events. In this study, a proteomic approach was adopted to identify secretory factors associated with adipogenesis. A label‐free shotgun proteomic strategy was implemented to analyze proteins secreted by human adipose stromal vascular fraction cells and differentiated adipocytes. A total of 474 proteins were finally identified and classified according to quantitative changes and statistical significances. Briefly, 177 proteins were significantly upregulated during adipogenesis (Class I), whereas 60 proteins were significantly downregulated (Class II). Changes in the expressions of several proteins were confirmed by quantitative RT‐PCR and immunoblotting. One obvious finding based on proteomic data was that the amounts of several extracellular modulators of Wnt and transforming growth factor‐β (TGF‐β) signaling changed during adipogenesis. The expressions of secreted frizzled‐related proteins, dickkopf‐related proteins, and latent TGF‐β‐binding proteins were found to be altered during adipogenesis, which suggests that they participate in the fine regulation of Wnt and TGF‐β signaling. This study provides useful tools and important clues regarding the roles of secretory factors during adipogenic differentiation, and provides information related to obesity and obesity‐related metabolic diseases. 相似文献
938.
939.
This study reports the effect of daily mean ambient temperature on daily activity and habitat use by the giant anteater (Myrmecophaga tridactyla) in the Pantanal wetlands of Brazil. We equipped 11 giant anteaters with a global position system collar programmed to acquire a location every 10 min for 15 d. A temperature data logger left in the meteorological station at the study site registered data on ambient temperature. Giant anteaters were mainly active in open fields except during the coldest days, when they sought protection inside forests. Giant anteaters also used open habitats for resting but during the hottest or chilliest days they sheltered in forests. In the Pantanal, where temperatures are usually high, giant anteaters were active all night long, but as daily average ambient temperature decreased anteaters began and finished activity progressively earlier and reduced total activity. As a consequence, time spent active at daylight increased progressively and time spent active during the night decreased progressively, probably to allow the anteaters to expose themselves to solar radiation and to avoid heat loss during the night. 相似文献
940.