全文获取类型
收费全文 | 18750篇 |
免费 | 2530篇 |
国内免费 | 7662篇 |
出版年
2024年 | 66篇 |
2023年 | 476篇 |
2022年 | 859篇 |
2021年 | 1084篇 |
2020年 | 1010篇 |
2019年 | 1167篇 |
2018年 | 903篇 |
2017年 | 822篇 |
2016年 | 873篇 |
2015年 | 1307篇 |
2014年 | 1557篇 |
2013年 | 1457篇 |
2012年 | 2064篇 |
2011年 | 1846篇 |
2010年 | 1371篇 |
2009年 | 1462篇 |
2008年 | 1586篇 |
2007年 | 1499篇 |
2006年 | 1359篇 |
2005年 | 1159篇 |
2004年 | 909篇 |
2003年 | 753篇 |
2002年 | 650篇 |
2001年 | 561篇 |
2000年 | 526篇 |
1999年 | 346篇 |
1998年 | 186篇 |
1997年 | 170篇 |
1996年 | 125篇 |
1995年 | 103篇 |
1994年 | 82篇 |
1993年 | 64篇 |
1992年 | 59篇 |
1991年 | 38篇 |
1990年 | 39篇 |
1989年 | 30篇 |
1988年 | 35篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 35篇 |
1984年 | 25篇 |
1983年 | 16篇 |
1982年 | 41篇 |
1981年 | 15篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1959年 | 11篇 |
1957年 | 9篇 |
1954年 | 9篇 |
1950年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
1.
Bayesian nonparametric inference for panel count data with an informative observation process 下载免费PDF全文
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.
Bin Zhu Chongwen Yang Hongrong Liu Lingpeng Cheng Feng Song Songjun Zeng Xiaojun Huang Gang Ji Ping Zhu 《Journal of molecular biology》2014
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.
Heat-shock protein 70 accumulation was induced by both increasesand decreases in temperature. An upward temperature shift ofabout 15C or a downward shift of about 10C was needed forthe response. In each case the accumulation was significantwithin 2 h and complete within about 6 h. Heat-shocked tissuecontained two new HSP70 isotypes not seen in the control tissueor in the cold-shocked tissue. Key words: Heat-shock protein, heat stress, cold stress, mung bean 相似文献
4.
5.
山岳型乡村旅游地“三生”空间演变及优化——德庆金林水乡的案例实证 总被引:1,自引:0,他引:1
以德庆县金林水乡为例,采用参与式观察和空间统计法,选取2000、2008年和2018年3个时段分析旅游发展对山岳型乡村旅游地"三生"空间的影响,并探讨了金林水乡"三生"空间的发展瓶颈及优化路径。研究发现:(1)旅游开发前,金林水乡土地结构与用地功能单一且呈片状分布;村落呈现传统乡村风貌,基础设施不健全;空间形态变化稳定,扩张缓慢。(2)旅游开发后,土地利用类型多样化,出现新型复合用地;土地功能利用复杂化,以服务旅游业为主;村庄景观风貌现代化,生活空间更加宜居。(3)旅游开发前后对比可得,土地平面占地规模化,空间用地以居民点为核心,呈圈层状向外围扩张;生产-生活-生态空间相互转化,乡村聚落重构特征较为显著;村落景观风貌的变化较大,呈现城镇化趋势。(4)金林水乡"三生"空间演化与旅游发展存在的问题表现在生产用地效率不高,生活用地质量较低,生态空间不断萎缩,在旅游产业发展上表现为旅游产品单一且缺乏创新,旅游服务功能不完善等。为此从生活空间的提质、生产空间增效、生态空间保护、旅游产业创新以及土地利用五方面提出优化建议。 相似文献
6.
Anatomy of the antennal dorsal organ in female of Neodryinus typhlocybae (Hymenoptera: Dryinidae): A peculiar sensory structure possibly involved in perception of host vibration 下载免费PDF全文
Paola Riolo Nunzio Isidoro Sara Ruschioni Roxana L. Minuz Ferdinando Bin Roberto Romani 《Journal of morphology》2016,277(1):128-137
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
7.
8.
N. J. Lassam Zheng Lin Michael G. Shennan Anouk Courseaux Bin T. Teh Patrick Gaudray Catharina Larsson 《Human genetics》1997,99(6):776-780
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
9.
植物叶片功能性状能够响应环境条件的变化,反应了植物对环境的适应策略。当前,针对藤本植物叶片功能性状地理格局及其环境驱动力的研究较少。以国家重点保护植物永瓣藤(Monimopetalum chinense)为研究对象,对其分布区内11个种群的15个叶片功能性状进行测量,并结合气候、土壤因子来解释叶性状变异。比较叶片性状在局域和区域尺度上的种内变异程度,利用多元逐步回归分析环境因子对叶性状的影响。结果表明,在局域尺度上,永瓣藤叶功能性状变异系数介于3.0%-22.5%,其中,叶面积变异程度最大,叶片碳含量变异最小。永瓣藤叶片形状随纬度上升而变得宽且圆。叶片磷含量相对较低,永瓣藤的生长可能受到了磷限制。土壤与气候因子是叶片性状的重要驱动因素,解释了25%-97%的叶片性状变异。在温度和水分充足的情况下,永瓣藤叶片趋向于的慢速生长的保守策略。总体来说,永瓣藤叶片功能性状通过一定的种内变异和性状组合,并与气候、土壤因子相互作用,适应当前的环境条件。 相似文献
10.