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   10973篇
  免费   1051篇
  国内免费   1589篇
  2024年   13篇
  2023年   170篇
  2022年   210篇
  2021年   576篇
  2020年   485篇
  2019年   588篇
  2018年   572篇
  2017年   424篇
  2016年   507篇
  2015年   806篇
  2014年   892篇
  2013年   891篇
  2012年   1121篇
  2011年   1027篇
  2010年   635篇
  2009年   606篇
  2008年   645篇
  2007年   585篇
  2006年   505篇
  2005年   433篇
  2004年   381篇
  2003年   321篇
  2002年   246篇
  2001年   128篇
  2000年   142篇
  1999年   121篇
  1998年   90篇
  1997年   101篇
  1996年   77篇
  1995年   63篇
  1994年   59篇
  1993年   32篇
  1992年   30篇
  1991年   19篇
  1990年   18篇
  1989年   7篇
  1988年   14篇
  1987年   15篇
  1986年   5篇
  1985年   12篇
  1984年   4篇
  1983年   4篇
  1982年   14篇
  1979年   4篇
  1976年   2篇
  1974年   2篇
  1973年   2篇
  1965年   1篇
  1950年   5篇
  1911年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
In this paper, the panel count data analysis for recurrent events is considered. Such analysis is useful for studying tumor or infection recurrences in both clinical trial and observational studies. A bivariate Gaussian Cox process model is proposed to jointly model the observation process and the recurrent event process. Bayesian nonparametric inference is proposed for simultaneously estimating regression parameters, bivariate frailty effects, and baseline intensity functions. Inference is done through Markov chain Monte Carlo, with fully developed computational techniques. Predictive inference is also discussed under the Bayesian setting. The proposed method is shown to be efficient via simulation studies. A clinical trial dataset on skin cancer patients is analyzed to illustrate the proposed approach.  相似文献   
2.
Many double-stranded RNA (dsRNA) viruses are capable of transcribing and capping RNA within a stable icosahedral viral capsid. The turret of turreted dsRNA viruses belonging to the family Reoviridae is formed by five copies of the turret protein, which contains domains with both 7-N-methyltransferase and 2′-O-methyltransferase activities, and serves to catalyze the methylation reactions during RNA capping. Cypovirus of the family Reoviridae provides a good model system for studying the methylation reactions in dsRNA viruses. Here, we present the structure of a transcribing cypovirus to a resolution of ~ 3.8 Å by cryo-electron microscopy. The binding sites for both S-adenosyl-l-methionine and RNA in the two methyltransferases of the turret were identified. Structural analysis of the turret in complex with RNA revealed a pathway through which the RNA molecule reaches the active sites of the two methyltransferases before it is released into the cytoplasm. The pathway shows that RNA capping reactions occur in the active sites of different turret protein monomers, suggesting that RNA capping requires concerted efforts by at least three turret protein monomers. Thus, the turret structure provides novel insights into the precise mechanisms of RNA methylation.  相似文献   
3.
4.
5.
Neodryinus typhlocybae (Hymenoptera: Dryinidae) is a natural enemy of the planthopper Metcalfa pruinosa, which was introduced from North America into Europe and has become established in various regions as a pest species. Vibrational signals play a crucial role in the communication of M. pruinosa, which appears to be exploited by N. typhlocybae. Scanning and transmission electron microscopy have shown that the antennae of N. typhlocybae females have peculiar and complex sensory structures: deep longitudinal grooves that house long sensilla trichodea, termed here “Antennal Dorsal Organs.” Such structures were not present on male antennae. These sensilla extend for the length of the grooves, without contact with the groove cuticle. Their hair shaft is empty and aporous, and inserted into a specialized socket, underneath which there is a cuticular ampulla‐like chamber. Each sensillum is associated with two sensory neurons: one terminates at the proximal end of the dendritic sheath; the other continues into the sensillum sinus and is enclosed in the dendritic sheath. This second sensory neuron then enters the ampulla‐like chamber through the circular opening, and then terminates with a conspicuous tubular body at the shaft base. The possible involvement of this peculiar structure in the context of host recognition mechanism is discussed. J. Morphol. 277:128–137, 2016. © 2015 Wiley Periodicals, Inc.  相似文献   
6.
MLK-3 kinase is a widely expressed serine/ threonine kinase that bears multiple protein interaction domains and regulates signals mediated by the stress-responsive pathway. Thus, MLK-3 signaling affects numerous cellular processes, raising the possibility that MLK-3 might play a role in oncogenesis. In this report, we describe the fine mapping of the MLK-3 gene within the 11q13.1 chromosomal region. By integrating data from somatic cell hybrids and double color fluorescence in situ hybridization on metaphase chromosomes and DNA fibers, MLK-3 has been assigned approximately 1 Mb telomeric of PYGM, close to the D11S546 locus. Since the MEN1 susceptibility locus is also located within the 11q13.1 region, we have carried out Southern and Northern blot analyses, as well as protein truncation assays to establish whether abnormalities in MLK-3 lead to the development of this familial cancer syndrome. Our observations exclude MLK-3 as the MEN1 gene. Received: 25 September 1996 / Revised: 16 December 1996  相似文献   
7.
8.
The incidence of gallbladder cancer (GBC) is relatively rare but a high degree of malignancy. The migration and invasion potential of GBC severely affects the prognosis of patients with GBC. Glycochenodeoxycholate (GCDC) is one of the most important components in GBC-associated microenvironment. However, the role of GCDC in the metastatic feature of GBC cells is not fully understood. First, the results of this study found that GCDC could effectively enhance the metastasis of GBC cells. Furthermore, GCDC could lead to the enhancement of epithelial to mesenchymal transition (EMT) phenotype in GBC cells, which is concerned to be an important mechanism of tumor metastasis. Further studies showed that GCDC treatment induced the upregulation of matrix metalloproteinase-3 (MMP3), MMP9, and SOCS3/JAK2/p-STAT3 signal pathway in GBC cells, which could regulate the level of EMT. Beside that, we also found the positive expression of farnesoid X receptor (FXR) in GBC cells and inhibition of FXR could significantly block the effect of GCDC on the metastasis of GBC cells. These results indicated that GCDC promoted GBC cells metastasis by enhancing the level of EMT and inhibition of FXR could significantly block the effect of GCDC. On one hand, FXR might be an indicator for predicting the metastasis of patient with GBC. On the other hand, FXR might serve as a potential antimetastasis target in GBC therapy.  相似文献   
9.
10.
Plant Molecular Biology Reporter - Global warming threatens many aspects of human life, including a reduction in crop yields, and breeding heat-tolerant crops is a fundamental way to help address...  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