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   481篇
  免费   3篇
  国内免费   5篇
系统科学   6篇
丛书文集   1篇
教育与普及   1篇
理论与方法论   11篇
现状及发展   122篇
研究方法   43篇
综合类   269篇
自然研究   36篇
  2021年   2篇
  2020年   2篇
  2019年   2篇
  2018年   5篇
  2017年   4篇
  2016年   7篇
  2015年   6篇
  2014年   10篇
  2013年   9篇
  2012年   47篇
  2011年   102篇
  2010年   22篇
  2009年   2篇
  2008年   29篇
  2007年   28篇
  2006年   26篇
  2005年   26篇
  2004年   15篇
  2003年   13篇
  2002年   25篇
  2000年   3篇
  1998年   4篇
  1997年   3篇
  1994年   2篇
  1991年   2篇
  1990年   3篇
  1988年   2篇
  1987年   3篇
  1986年   1篇
  1985年   4篇
  1984年   5篇
  1983年   4篇
  1982年   2篇
  1980年   3篇
  1979年   8篇
  1978年   2篇
  1977年   7篇
  1974年   6篇
  1973年   7篇
  1972年   1篇
  1971年   5篇
  1970年   4篇
  1969年   2篇
  1968年   6篇
  1967年   4篇
  1966年   3篇
  1965年   3篇
  1957年   1篇
  1954年   1篇
  1946年   1篇
排序方式: 共有489条查询结果,搜索用时 13 毫秒
1.
2.
3.
A wide range of literature concerning classical asymptotic properties for linear models with adaptive control is available, such as strong laws of large numbers or central limit theorems. Unfortunately, in contrast with the situation without control, it appears to be impossible to find sharp asymptotic or nonasymptotic properties such as large deviation principles or exponential inequalities. Our purpose is to provide a first step towards that direction by proving a very simple exponential inequality for the standard least squares estimator of the unknown parameter of Gaussian autoregressive process in adaptive tracking.  相似文献   
4.
5.
Crystal structure of the β2 adrenergic receptor-Gs protein complex   总被引:1,自引:0,他引:1  
G protein-coupled receptors (GPCRs) are responsible for the majority of cellular responses to hormones and neurotransmitters as well as the senses of sight, olfaction and taste. The paradigm of GPCR signalling is the activation of a heterotrimeric GTP binding protein (G protein) by an agonist-occupied receptor. The β(2) adrenergic receptor (β(2)AR) activation of Gs, the stimulatory G protein for adenylyl cyclase, has long been a model system for GPCR signalling. Here we present the crystal structure of the active state ternary complex composed of agonist-occupied monomeric β(2)AR and nucleotide-free Gs heterotrimer. The principal interactions between the β(2)AR and Gs involve the amino- and carboxy-terminal α-helices of Gs, with conformational changes propagating to the nucleotide-binding pocket. The largest conformational changes in the β(2)AR include a 14 ? outward movement at the cytoplasmic end of transmembrane segment 6 (TM6) and an α-helical extension of the cytoplasmic end of TM5. The most surprising observation is a major displacement of the α-helical domain of Gαs relative to the Ras-like GTPase domain. This crystal structure represents the first high-resolution view of transmembrane signalling by a GPCR.  相似文献   
6.
We identified constitutional truncating mutations of the BRCA1-interacting helicase BRIP1 in 9/1,212 individuals with breast cancer from BRCA1/BRCA2 mutation-negative families but in only 2/2,081 controls (P = 0.0030), and we estimate that BRIP1 mutations confer a relative risk of breast cancer of 2.0 (95% confidence interval = 1.2-3.2, P = 0.012). Biallelic BRIP1 mutations were recently shown to cause Fanconi anemia complementation group J. Thus, inactivating truncating mutations of BRIP1, similar to those in BRCA2, cause Fanconi anemia in biallelic carriers and confer susceptibility to breast cancer in monoallelic carriers.  相似文献   
7.
I examine the information content of option‐implied covariance between jumps and diffusive risk in the cross‐sectional variation in future returns. This paper documents that the difference between realized volatility and implied covariance (RV‐ICov) can predict future returns. The results show a significant and negative association of expected return and realized volatility–implied covariance spread in both the portfolio level analysis and cross‐sectional regression study. A trading strategy of buying a portfolio with the lowest RV‐ICov quintile portfolio and selling with the highest one generates positive and significant returns. This RV‐Cov anomaly is robust to controlling for size, book‐to‐market value, liquidity and systematic risk proportion. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
8.
Walker-Warburg syndrome (WWS) is an autosomal recessive multisystem disorder characterized by complex eye and brain abnormalities with congenital muscular dystrophy (CMD) and aberrant a-dystroglycan glycosylation. Here we report mutations in the ISPD gene (encoding isoprenoid synthase domain containing) as the second most common cause of WWS. Bacterial IspD is a nucleotidyl transferase belonging to a large glycosyltransferase family, but the role of the orthologous protein in chordates is obscure to date, as this phylum does not have the corresponding non-mevalonate isoprenoid biosynthesis pathway. Knockdown of ispd in zebrafish recapitulates the human WWS phenotype with hydrocephalus, reduced eye size, muscle degeneration and hypoglycosylated a-dystroglycan. These results implicate ISPD in a-dystroglycan glycosylation in maintaining sarcolemma integrity in vertebrates.  相似文献   
9.
Aging is associated with reductions in hippocampal volume that are accelerated by Alzheimer's disease and vascular risk factors. Our genome-wide association study (GWAS) of dementia-free persons (n = 9,232) identified 46 SNPs at four loci with P values of <4.0 × 10(-7). In two additional samples (n = 2,318), associations were replicated at 12q14 within MSRB3-WIF1 (discovery and replication; rs17178006; P = 5.3 × 10(-11)) and at 12q24 near HRK-FBXW8 (rs7294919; P = 2.9 × 10(-11)). Remaining associations included one SNP at 2q24 within DPP4 (rs6741949; P = 2.9 × 10(-7)) and nine SNPs at 9p33 within ASTN2 (rs7852872; P = 1.0 × 10(-7)); along with the chromosome 12 associations, these loci were also associated with hippocampal volume (P < 0.05) in a third younger, more heterogeneous sample (n = 7,794). The SNP in ASTN2 also showed suggestive association with decline in cognition in a largely independent sample (n = 1,563). These associations implicate genes related to apoptosis (HRK), development (WIF1), oxidative stress (MSR3B), ubiquitination (FBXW8) and neuronal migration (ASTN2), as well as enzymes targeted by new diabetes medications (DPP4), indicating new genetic influences on hippocampal size and possibly the risk of cognitive decline and dementia.  相似文献   
10.
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