全文获取类型
收费全文 | 185篇 |
免费 | 16篇 |
国内免费 | 1篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 7篇 |
2012年 | 11篇 |
2011年 | 9篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 1篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有202条查询结果,搜索用时 31 毫秒
111.
Here, we review progress and prospects to explicitly test for long distance dispersal biogeographic events. Long distance dispersal represents a “jump” across some kind of barrier, such as a topographic feature or a zone of unsuitable climate and may include repeated jumps, or stepping‐stone dispersals. Long distance dispersals were considered integral for explaining the organization of biodiversity at large and small scales by early biogeographers, such as Darwin and Wallace. Darwin, Wallace, and others envisioned that long distance dispersals were predictable events because the vectors for dispersal, such as animals, winds, and currents, behaved in non‐random ways. However, these early biogeographers found that dispersal was hard to observe, and, later, with the advent of the theory of Continental Drift, vicariance became regarded as a better scientific explanation for the arrangement of biodiversity, because it represented a falsifiable hypothesis. Thus, long distance dispersal was reduced to a nuisance parameter in biogeography; a random possibility that could never fully be ruled out in a scenario in which evidence supported vicariance. Today, there is strong interest to more fully integrate long distance dispersal into understanding the assembly and organization of biodiversity on earth. In this review, we discuss progress and prospects for explicitly testing long distance dispersal hypotheses including through uses of molecular, morphological, paleontological, and informatics methods. We focus on hypothesis testing of long distance dispersals involved in the assembly of the flora of North America, which is a robust preliminary study system on account of its extant and extinct biodiversity being well‐catalogued. 相似文献
112.
113.
Jun Wen AJ Harris Yash Kalburgi Ning Zhang Yuan Xu Wei Zheng Stefanie M. Ickert-Bond Gabriel Johnson Elizabeth A. Zimmer 《植物分类学报:英文版》2018,56(4):297-308
Vitis L. (the grape genus) is the economically most important fruit crop, as the source of grapes and wine. Phylogenetic relationships within the genus have been highly controversial. Herein, we employ sequence data from whole plastomes to attempt to enhance Vitis phylogenetic resolution. The results support the New World Vitis subgenus Vitis as monophyletic. Within the clade, V. californica is sister to the remaining New World Vitis subgenus Vitis. Furthermore, within subgenus Vitis, a Eurasian clade is robustly supported and is sister to the New World clade. The clade of Vitis vinifera ssp. vinifera and V. vinifera ssp. sylvestris is sister to the core Asian clade of Vitis. Several widespread species in North America are found to be non‐monophyletic in the plastome tree, for example, the broadly defined Vitis cinerea and V. aestivalis each needs to be split into several species. The non‐monophyly of some species may also be due to common occurrences of hybridizations in North American Vitis. The classification of North American Vitis by Munson into nine series is discussed based on the phylogenetic results. Analyses of divergence times and lineage diversification support a rapid radiation of Vitis in North America beginning in the Neogene. 相似文献
114.
Question: What are the consequences of grazing abandonment on the Stipa lessingiana dominated steppe‐like grasslands? What is the relative importance of management and environmental factors in causing variation in species composition and abundance in the continuously grazed and abandoned grassland stands? Location: Transylvanian Lowland, Romania. Methods: Repeated vegetation mapping of a grassland stand, where grazing was abandoned 35 years ago; re‐sampling six grassland stands surveyed 29–57 years ago. For revealing long‐term changes in species composition and rank abundance PCoA ordination was applied. The relative importance of management and environmental factors in structuring vegetation were explored by CCA ordination. Diversity, evenness and the relative number and abundance of red‐listed species were compared between managed and abandoned stands. Results: Our results pointed out that grasslands which were formerly grazed and dominated by S. lessingiana, in the long‐term absence of grazing, have been transformed into a S. pulcherrima dominated type. Management, probably by creating bare surfaces and preventing litter accumulation, had the strongest effect on the species composition and abundance in the grasslands. Abandoned grassland stands had lower diversity and evenness compared to continuously grazed stands. While at the same time, the relative number of threatened, rare species did not differ between managed and abandoned sites. Conclusion: Maintaining extensively grazed, as well as un‐managed, Stipa dominated grasslands would be important in order to create various habitat conditions for plant species, especially threatened and rare species, and promote diversity on the landscape scale. 相似文献
115.
MG Mullender NA Blom M De Kleuver JM Fock WMGC Hitters AMC Horemans CJ Kalkman JEH Pruijs RR Timmer PJ Titarsolej NC Van Haasteren Tol-de MJ Van Jager AJ Van Vught BJ Van Royen 《Scoliosis》2008,3(1):1-14
Background
Children with neuromuscular disorders with a progressive muscle weakness such as Duchenne Muscular Dystrophy and Spinal Muscular Atrophy frequently develop a progressive scoliosis. A severe scoliosis compromises respiratory function and makes sitting more difficult. Spinal surgery is considered the primary treatment option for correcting severe scoliosis in neuromuscular disorders. Surgery in this population requires a multidisciplinary approach, careful planning, dedicated surgical procedures, and specialized after care.Methods
The guideline is based on scientific evidence and expert opinions. A multidisciplinary working group representing experts from all relevant specialties performed the research. A literature search was conducted to collect scientific evidence in answer to specific questions posed by the working group. Literature was classified according to the level of evidence.Results
For most aspects of the treatment scientific evidence is scarce and only low level cohort studies were found. Nevertheless, a high degree of consensus was reached about the management of patients with scoliosis in neuromuscular disorders. This was translated into a set of recommendations, which are now officially accepted as a general guideline in the Netherlands.Conclusion
In order to optimize the treatment for scoliosis in neuromuscular disorders a Dutch guideline has been composed. This evidence-based, multidisciplinary guideline addresses conservative treatment, the preoperative, perioperative, and postoperative care of scoliosis in neuromuscular disorders. 相似文献116.
Background
Obligate asexual reproduction is rare in the animal kingdom. Generally, asexuals are considered evolutionary dead ends that are unable to radiate. The phytophagous mite genus Bryobia contains a large number of asexual species. In this study, we investigate the origin and evolution of asexuality using samples from 111 populations in Europe, South Africa and the United States, belonging to eleven Bryobia species. We also examine intraspecific clonal diversity for one species, B. kissophila, by genotyping individuals from 61 different populations. Knowledge on the origin of asexuality and on clonal diversity can contribute to our understanding of the paradox of sex. 相似文献117.
Padányi R Pászty K Penheiter AR Filoteo AG Penniston JT Enyedi A 《The Journal of biological chemistry》2003,278(37):35798-35804
The access of three proteases to their sites of cleavage was used as a measure of regulatory interactions in the plasma membrane Ca2+ pump isoform 4b (PMCA4b). When the proteases could not cut at their sites in the C-terminal regulatory region, the interaction was judged to be tight. This was the case in the absence of Ca2+, when chymotrypsin and caspase cut PMCA only very slowly. Ca2+ accelerated the fragmentation, but the digestion remained incomplete. In the presence of Ca2+ plus calmodulin, the digestion became nearly complete in all cases, indicating a more flexible conformation of the carboxyl terminus in the fully activated state. The acceleration of proteolysis by Ca2+ or Ca2+ plus calmodulin occurred equally at the caspase site upstream of the calmodulin-binding domain and the chymotrypsin and calpain sites downstream of that domain. Replacing Trp1093 (a key residue within the calmodulin-binding domain) with alanine had a much more specific effect, because it exposed only proteolytic sites within the calmodulin-binding domain that had previously been shielded in the native protein. At these sites, both calpain and chymotrypsin cut the Trp1093 --> Ala mutant in the absence of calmodulin. These data indicate that, in the auto-inhibited conformation, the calmodulin-binding/auto-inhibitory sequence and the regions both upstream and downstream are in close contact with the catalytic core. Trp1093 plays an essential role not only in stabilizing the Ca2+-calmodulin/calmodulin-binding domain complex but also in the formation or stability of the inhibitory conformation of that domain when it interacts with the catalytic core of PMCA4b. 相似文献
118.
Bas Brinkhof Helena TA van Tol Marian JA Groot Koerkamp Frank M Riemers Sascha G IJzer Kaveh Mashayekhi Henk P Haagsman Bernard AJ Roelen 《BMC genomics》2015,16(1)
Background
Genes and signalling pathways involved in pluripotency have been studied extensively in mouse and human pre-implantation embryos and embryonic stem (ES) cells. The unsuccessful attempts to generate ES cell lines from other species including cattle suggests that other genes and pathways are involved in maintaining pluripotency in these species. To investigate which genes are involved in bovine pluripotency, expression profiles were generated from morula, blastocyst, trophectoderm and inner cell mass (ICM) samples using microarray analysis. As MAPK inhibition can increase the NANOG/GATA6 ratio in the inner cell mass, additionally blastocysts were cultured in the presence of a MAPK inhibitor and changes in gene expression in the inner cell mass were analysed.Results
Between morula and blastocyst 3,774 genes were differentially expressed and the largest differences were found in blastocyst up-regulated genes. Gene ontology (GO) analysis shows lipid metabolic process as the term most enriched with genes expressed at higher levels in blastocysts. Genes with higher expression levels in morulae were enriched in the RNA processing GO term. Of the 497 differentially expressed genes comparing ICM and TE, the expression of NANOG, SOX2 and POU5F1 was increased in the ICM confirming their evolutionary preserved role in pluripotency. Several genes implicated to be involved in differentiation or fate determination were also expressed at higher levels in the ICM. Genes expressed at higher levels in the ICM were enriched in the RNA splicing and regulation of gene expression GO term. Although NANOG expression was elevated upon MAPK inhibition, SOX2 and POU5F1 expression showed little increase. Expression of other genes in the MAPK pathway including DUSP4 and SPRY4, or influenced by MAPK inhibition such as IFNT, was down-regulated.Conclusion
The data obtained from the microarray studies provide further insight in gene expression during bovine embryonic development. They show an expression profile in pluripotent cells that indicates a pluripotent, epiblast-like state. The inability to culture ICM cells as stem cells in the presence of an inhibitor of MAPK activity together with the reported data indicates that MAPK inhibition alone is not sufficient to maintain a pluripotent character in bovine cells.Electronic supplementary material
The online version of this article (doi:10.1186/s12864-015-1448-x) contains supplementary material, which is available to authorized users. 相似文献119.
Blaney Davidson EN Vitters EL van Lent PL van de Loo FA van den Berg WB van der Kraan PM 《Arthritis research & therapy》2007,9(5):R102
Bone morphogenetic protein-2 (BMP-2) has been proposed as a tool for cartilage repair and as a stimulant of chondrogenesis.
In healthy cartilage, BMP-2 is hardly present, whereas it is highly expressed during osteoarthritis. To assess its function
in cartilage, BMP-2 was overexpressed in healthy murine knee joints and the effects on proteoglycan (PG) synthesis and degradation
were evaluated. Moreover, the contribution of BMP in repairing damage induced by interleukin-1 (IL-1) was investigated. Ad-BMP-2
was injected intra-articularly into murine knee joints, which were isolated 3, 7, and 21 days after injection for histology,
immunohistochemistry, and autoradiography. In addition, patellar and tibial cartilage was isolated for RNA isolation or measurement
of PG synthesis by means of 35SO4
2- incorporation. To investigate the role for BMP-2 in cartilage repair, cartilage damage was induced by intra-articular injection
of IL-1. After 2 days, Ad-BMP-2, Ad-BMP-2 + Ad-gremlin, Ad-gremlin, or a control virus was injected. Whole knee joints were
isolated for histology at day 4 or patellae were isolated to measure 35SO4
2- incorporation. BMP-2 stimulated PG synthesis in patellar cartilage on all days and in tibial cartilage on day 21. Aggrecan
mRNA expression had increased on all days in patellar cartilage, with the highest increase on day 7. Collagen type II expression
showed a similar expression pattern. In tibial cartilage, collagen type II and aggrecan mRNA expression had increased on days
7 and 21. BMP-2 overexpression also induced increased aggrecan degradation in cartilage. VDIPEN staining (indicating matrix
metalloproteinase activity) was elevated on day 3 in tibial cartilage and on days 3 and 7 in patellar cartilage, but no longer
was by day 21. Increased NITEGE staining (indicating aggrecanase activity) was found on days 7 and 21. In IL-1-damaged patellar
cartilage, BMP-2 boosted PG synthesis. Blocking of BMP activity resulted in a decreased PG synthesis compared with IL-1 alone.
This decreased PG synthesis was associated with PG depletion in the cartilage. These data show that BMP-2 boosts matrix turnover
in intact and IL-damaged cartilage. Moreover, BMP contributes to the intrinsic repair capacity of damaged cartilage. Increased
matrix turnover might be functional in replacing matrix molecules in the repair of a damaged cartilage matrix. 相似文献
120.
Series resistance compensation for whole-cell patch-clamp studies using a membrane state estimator 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Whole-cell patch-clamp techniques are widely used to measure membrane currents from isolated cells. While suitable for a broad range of ionic currents, the series resistance (R(s)) of the recording pipette limits the bandwidth of the whole-cell configuration, making it difficult to measure rapid ionic currents. To increase bandwidth, it is necessary to compensate for R(s). Most methods of R(s) compensation become unstable at high bandwidth, making them hard to use. We describe a novel method of R(s) compensation that overcomes the stability limitations of standard designs. This method uses a state estimator, implemented with analog computation, to compute the membrane potential, V(m), which is then used in a feedback loop to implement a voltage clamp; we refer to this as state estimator R(s) compensation. To demonstrate the utility of this approach, we built an amplifier incorporating state estimator R(s) compensation. In benchtop tests, our amplifier showed significantly higher bandwidths and improved stability when compared with a commercially available amplifier. We demonstrated that state estimator R(s) compensation works well in practice by recording voltage-gated Na(+) currents under voltage-clamp conditions from dissociated neonatal rat sympathetic neurons. We conclude that state estimator R(s) compensation should make it easier to measure large rapid ionic currents with whole-cell patch-clamp techniques. 相似文献