首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6983篇
  免费   614篇
  国内免费   1篇
  7598篇
  2024年   11篇
  2023年   41篇
  2022年   108篇
  2021年   203篇
  2020年   91篇
  2019年   117篇
  2018年   157篇
  2017年   130篇
  2016年   235篇
  2015年   455篇
  2014年   481篇
  2013年   467篇
  2012年   655篇
  2011年   625篇
  2010年   355篇
  2009年   301篇
  2008年   469篇
  2007年   446篇
  2006年   398篇
  2005年   368篇
  2004年   331篇
  2003年   346篇
  2002年   286篇
  2001年   48篇
  2000年   33篇
  1999年   68篇
  1998年   64篇
  1997年   44篇
  1996年   40篇
  1995年   34篇
  1994年   23篇
  1993年   31篇
  1992年   22篇
  1991年   13篇
  1990年   17篇
  1989年   7篇
  1988年   9篇
  1987年   9篇
  1986年   4篇
  1985年   10篇
  1984年   8篇
  1982年   3篇
  1981年   6篇
  1980年   7篇
  1979年   2篇
  1978年   4篇
  1977年   5篇
  1975年   2篇
  1974年   3篇
  1973年   2篇
排序方式: 共有7598条查询结果,搜索用时 15 毫秒
111.
Three case studies involving two temperate Australian seagrass species – Pondweed (Ruppia tuberosa) and Ribbon Weed (Posidonia australis) – highlight different approaches to their restoration. Seeds and rhizomes were used in three collaborative programmes to promote new approaches to scale up restoration outcomes.  相似文献   
112.
GOLPH3 is a phosphatidylinositol-4-phosphate (PI4P) effector that plays an important role in maintaining Golgi architecture and anterograde trafficking. GOLPH3 does so through its ability to link trans-Golgi membranes to F-actin via its interaction with myosin 18A (MYO18A). GOLPH3 also is known to be an oncogene commonly amplified in human cancers. GOLPH3L is a GOLPH3 paralogue found in all vertebrate genomes, although previously it was largely uncharacterized. Here we demonstrate that although GOLPH3 is ubiquitously expressed in mammalian cells, GOLPH3L is present in only a subset of tissues and cell types, particularly secretory tissues. We show that, like GOLPH3, GOLPH3L binds to PI4P, localizes to the Golgi as a consequence of its PI4P binding, and is required for efficient anterograde trafficking. Surprisingly, however, we find that perturbations of GOLPH3L expression produce effects on Golgi morphology that are opposite to those of GOLPH3 and MYO18A. GOLPH3L differs critically from GOLPH3 in that it is largely unable to bind to MYO18A. Our data demonstrate that despite their similarities, unexpectedly, GOLPH3L antagonizes GOLPH3/MYO18A at the Golgi.  相似文献   
113.
During conversation, interlocutors coordinate their behavior on many levels. Two distinct forms of behavioral coordination have been empirically linked with affiliation and cooperation during or following face-to-face interaction: behavior matching and interpersonal synchrony. Only the latter form constitutes behavioral entrainment involving a coupling between independent oscillators. We present the first study of the association between spontaneously occurring behavioral coordination and post-interaction economic game play. Triads of same-sexed strangers conversed for 10 min, after which each participant played an unannounced one-shot prisoner's dilemma (PD) toward each co-participant. When dyads had higher language style matching scores (LSM: Gonzales, A.L., Hancock, J.T., & Pennebaker, J.W. (2010). Language style matching as a predictor of social dynamics in small groups. Communication Research, 31, 3–19), the individuals evaluated each other more positively, but they were no more likely to cooperate in the PD. However, when dyads' speech rates (mean syllable duration) converged more strongly from the beginning to the end of the conversation, they were more likely to cooperate in the PD, despite no effect on interpersonal evaluations. Speech rate convergence, a form of rhythmic entrainment, could benefit interlocutors by mutually reducing cognitive processing during interaction. We suggest that spontaneous, temporally based behavioral coordination might facilitate prosocial behavior when the joint cooperative effort is itself perceived as a form of coordination.  相似文献   
114.
Nicotinic acetylcholine receptors (nAChRs) play a key role in the normal physiology of nematodes and provide an established target site for anthelmintics. The free-living nematode, Caenorhabditis elegans, has a large number of nAChR subunit genes in its genome and so provides an experimental model for testing novel anthelmintics which act at these sites. However, many parasitic nematodes lack specific genes present in C. elegans, and so care is required in extrapolating from studies using C. elegans to the situation in other nematodes. In this review the properties of C. elegans nAChRs are reviewed and compared to those of parasitic nematodes. This forms the basis for a discussion of the possible subunit composition of nAChRs from different species of parasitic nematodes. Currently our knowledge on this is largely based on studies using heterologous expression and pharmacological analysis of receptor subunits in Xenopus laevis oocytes. It is concluded that more information is required regarding the subunit composition and pharmacology of endogenous nAChRs in parasitic nematodes.  相似文献   
115.
Background aimsThe Quantum® Cell Expansion System (Quantum; Terumo BCT, Inc, Lakewood, CO, USA) is a novel hollow fiber-based device that automates and closes the cell culture process, reducing labor intensive tasks such as manual cell culture feeding and harvesting. The manual cell selection and expansion processes for the production of clinical-scale quantities of bone marrow-derived human mesenchymal stromal cells (BM-hMSCs) have been successfully translated onto the Quantum platform previously. The formerly static, manual, in vitro process performed primarily on tissue culture polystyrene substrates may raise the question of whether BM-hMSCs cultured on a hollow fiber platform yields comparable cell quality.MethodsA rigorous battery of assays was used to determine the genetic stability of BM-hMSCs selected and produced with the Quantum. In this study, genetic stability was determined by assessing spectral karyotype, micronucleus formation and tumorigenicity to resolve chromosomal aberrations in the stem cell population. Cell phenotype, adherent growth kinetics and tri-lineage differentiation were also evaluated. HMSC bone marrow aspirates, obtained from three approved donors, were expanded in parallel using T225 culture flasks and the Quantum.ResultsBM-hMSCs harvested from the Quantum demonstrated immunophenotype, morphology and tri-lineage differentiation capacity characteristics consistent with the International Society of Cell Therapy standard for hMSCs. Cell populations showed no malignant neoplastic formation in athymic mice 60 days post-transplant, no clonal chromosomal aberrations were observed and no DNA damage was found as measured by micronucleus formation.ConclusionsQuantum-produced BM-hMSCs are of comparable quality and demonstrate analogous genetic stability to BM-hMSCs cultured on tissue culture polystyrene substrates.  相似文献   
116.
117.
118.
EF24 is a curcumin analog that has improved anticancer activity over curcumin, but its therapeutic potential and mechanism of action is unknown, which is important to address as curcumin targets multiple signaling pathways. EF24 inhibits the NF-κB but not the JAK-STAT signaling pathway in DU145 human prostate cancer cells and B16 murine melanoma cells. EF24 induces apoptosis in these cells apparently by inhibiting miR-21 expression, and also enhances the expression of several miR-21 target genes, PTEN and PDCD4. EF24 treatment significantly suppressed the growth of DU145 prostate cancer xenografts in immunocompromised mice and resulted in tumor regression. EF24 enhanced the expression of the miR-21 target PTEN in DU145 tumor tissue, but suppressed the expression of markers of proliferating cells (cyclin D1 and Ki67). In syngeneic mice injected with B16 cells, EF24 treatment inhibited the formation of lung metastasis, prolonged animal survival, inhibited miR-21 expression and increased the expression of miR-21 target genes. Expression profiling of miRNAs regulated by EF24 in vitro and in vivo showed that the antitumor activity of EF24 reflected the enhanced expression of potential tumor suppressor miRNAs as well as the suppressed expression of oncogenic miRNAs, including miR-21. Taken together, our data suggest that EF24 is a potent anticancer agent and selectively targets NF-κB signaling and miRNA expression, indicating that EF24 has significant potential as a therapeutic agent in various cancers.  相似文献   
119.
120.
To better understand age differences in brain function and behavior, the current study applied network science to model functional interactions between brain regions. We observed a shift in network topology whereby for older adults subcortical and cerebellar structures overlapping with the Salience network had more connectivity to the rest of the brain, coupled with fragmentation of large-scale cortical networks such as the Default and Fronto-Parietal networks. Additionally, greater integration of the dorsal medial thalamus and red nucleus in the Salience network was associated with greater satisfaction with life for older adults, which is consistent with theoretical predictions of age-related increases in emotion regulation that are thought to help maintain well-being and life satisfaction in late adulthood. In regard to cognitive abilities, greater ventral medial prefrontal cortex coherence with its topological neighbors in the Default Network was associated with faster processing speed. Results suggest that large-scale organizing properties of the brain differ with normal aging, and this perspective may offer novel insight into understanding age-related differences in cognitive function and well-being.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号