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   46447篇
  免费   3387篇
  国内免费   10篇
  2023年   259篇
  2022年   295篇
  2021年   572篇
  2020年   540篇
  2019年   586篇
  2018年   1065篇
  2017年   964篇
  2016年   1548篇
  2015年   2361篇
  2014年   2360篇
  2013年   3111篇
  2012年   4109篇
  2011年   3813篇
  2010年   2170篇
  2009年   1784篇
  2008年   3015篇
  2007年   2884篇
  2006年   2845篇
  2005年   2485篇
  2004年   2408篇
  2003年   2274篇
  2002年   2089篇
  2001年   760篇
  2000年   854篇
  1999年   519篇
  1998年   360篇
  1997年   248篇
  1996年   265篇
  1995年   261篇
  1994年   232篇
  1993年   221篇
  1992年   209篇
  1991年   175篇
  1990年   157篇
  1989年   150篇
  1988年   118篇
  1987年   91篇
  1986年   96篇
  1985年   137篇
  1984年   149篇
  1983年   104篇
  1982年   119篇
  1981年   97篇
  1980年   93篇
  1979年   85篇
  1978年   80篇
  1977年   67篇
  1976年   75篇
  1975年   68篇
  1974年   65篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
This study provides sound evidence of the spawning activity of common dolphinfish (Coryphaena hippurus) in the Gulf of Cadiz (southwest Spain) during summer months. Along with waters off Côte d'Ivoire, this area adjacent to the Mediterranean Sea is the easternmost Atlantic spawning ground documented for the species. All the fish analysed (5 males and 15 females) were at spawning stage, except the smallest female (61.5 cm in fork length), which might not have yet reached sexual maturation. The oceanographic conditions during the samplings were similar to those occurring during the peak spawning season in the Gulf of Mexico. The study results are consistent with recent genetic studies indicating differentiation between Mediterranean and Atlantic dolphinfish populations, with the Strait of Gibraltar representing a boundary between two distinct reproductive units. The present results may contribute to improve the understanding of the dynamics of dolphinfish population and the management of eastern Atlantic and Mediterranean stocks.  相似文献   
992.

Aim

Diaper dermatitis (DD) is an inflammatory irritating condition that is common in infants. Most cases are associated with the yeast colonization of Candida or diaper dermatitis candidiasis (DDC), and therefore, the signs and symptoms improve with antimycotic treatment. Sertaconazole is a broad-spectrum third-generation imidazole derivative that is effective and safe for the treatment for superficial mycoses, such as tineas, candidiasis, and pityriasis versicolor. Our goal was to assess the efficacy and safety of sertaconazole cream (2 %) in DDC.

Materials and methods

Twenty-seven patients with clinical and mycological diagnosis of DDC were enrolled and treated with 2 daily applications for 14 days and were followed-up for 2 further weeks.

Results

Three etiologic agents were isolated: Candida albicans in 88.8 %, Candida parapsilosis in 7.3 %, and Candida glabrata in 3.2 %. There was an average symptom reduction from 7.1 to 3.2 in the middle of treatment and to 1.2 and 0.4 units at the end of treatment and follow-up, respectively. The treatment evaluation at the end of the follow-up period showed a total clinical and mycological cure in 88.8 %, improvement in 3.7 %, and failure in 7.4 %. There was side effect (3.7 %) of skin irritation, but the drug was not discontinued.

Conclusions

Based on its safety and effectiveness, sertaconazole cream may be considered a new alternative for DDC treatment.  相似文献   
993.
This paper addresses the building of stochastic models that adequately describe dynamic phenomena and, in particular, those that occur in the Biosciences. In this context, the empirical fitting of a Gaussian diffusion process from sample data of a dynamic growth phenomenon is considered. In order to do this, a methodology based on approximations to its mean and variance functions is presented. Finally, several applications based on simulated and real data have been carried out.  相似文献   
994.
Ribosome biogenesis requires >300 assembly factors in Saccharomyces cerevisiae. Ribosome assembly factors Imp3, Mrt4, Rlp7 and Rlp24 have sequence similarity to ribosomal proteins S9, P0, L7 and L24, suggesting that these pre-ribosomal factors could be placeholders that prevent premature assembly of the corresponding ribosomal proteins to nascent ribosomes. However, we found L7 to be a highly specific component of Rlp7-associated complexes, revealing that the two proteins can bind simultaneously to pre-ribosomal particles. Cross-linking and cDNA analysis experiments showed that Rlp7 binds to the ITS2 region of 27S pre-rRNAs, at two sites, in helix III and in a region adjacent to the pre-rRNA processing sites C1 and E. However, L7 binds to mature 25S and 5S rRNAs and cross-linked predominantly to helix ES7Lb within 25S rRNA. Thus, despite their predicted structural similarity, our data show that Rlp7 and L7 clearly bind at different positions on the same pre-60S particles. Our results also suggest that Rlp7 facilitates the formation of the hairpin structure of ITS2 during 60S ribosomal subunit maturation.  相似文献   
995.
The RNA helicase Upf1 is a multifaceted eukaryotic enzyme involved in DNA replication, telomere metabolism and several mRNA degradation pathways. Upf1 plays a central role in nonsense-mediated mRNA decay (NMD), a surveillance process in which it links premature translation termination to mRNA degradation with its conserved partners Upf2 and Upf3. In human, both the ATP-dependent RNA helicase activity and the phosphorylation of Upf1 are essential for NMD. Upf1 activation occurs when Upf2 binds its N-terminal domain, switching the enzyme to the active form. Here, we uncovered that the C-terminal domain of Upf1, conserved in higher eukaryotes and containing several essential phosphorylation sites, also inhibits the flanking helicase domain. With different biochemical approaches we show that this domain, named SQ, directly interacts with the helicase domain to impede ATP hydrolysis and RNA unwinding. The phosphorylation sites in the distal half of the SQ domain are not directly involved in this inhibition. Therefore, in the absence of multiple binding partners, Upf1 is securely maintained in an inactive state by two intramolecular inhibition mechanisms. This study underlines the tight and intricate regulation pathways required to activate multifunctional RNA helicases like Upf1.  相似文献   
996.
997.
998.
999.
1000.
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