全文获取类型
收费全文 | 7046篇 |
免费 | 730篇 |
国内免费 | 1144篇 |
出版年
2024年 | 26篇 |
2023年 | 105篇 |
2022年 | 231篇 |
2021年 | 393篇 |
2020年 | 289篇 |
2019年 | 376篇 |
2018年 | 355篇 |
2017年 | 281篇 |
2016年 | 306篇 |
2015年 | 447篇 |
2014年 | 538篇 |
2013年 | 588篇 |
2012年 | 666篇 |
2011年 | 582篇 |
2010年 | 423篇 |
2009年 | 355篇 |
2008年 | 414篇 |
2007年 | 365篇 |
2006年 | 316篇 |
2005年 | 307篇 |
2004年 | 280篇 |
2003年 | 263篇 |
2002年 | 249篇 |
2001年 | 142篇 |
2000年 | 134篇 |
1999年 | 110篇 |
1998年 | 73篇 |
1997年 | 77篇 |
1996年 | 57篇 |
1995年 | 40篇 |
1994年 | 40篇 |
1993年 | 27篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 1篇 |
排序方式: 共有8920条查询结果,搜索用时 15 毫秒
1.
Semiparametric Regression in Size-Biased Sampling 总被引:1,自引:0,他引:1
Ying Qing Chen 《Biometrics》2010,66(1):149-158
Summary . Size-biased sampling arises when a positive-valued outcome variable is sampled with selection probability proportional to its size. In this article, we propose a semiparametric linear regression model to analyze size-biased outcomes. In our proposed model, the regression parameters of covariates are of major interest, while the distribution of random errors is unspecified. Under the proposed model, we discover that regression parameters are invariant regardless of size-biased sampling. Following this invariance property, we develop a simple estimation procedure for inferences. Our proposed methods are evaluated in simulation studies and applied to two real data analyses. 相似文献
2.
3.
4.
Intermittent tongue, lip and cheek forces influence precise tooth position, so we here examine the possibility that tissue remodelling driven by functional bite-force-induced jaw-strain accounts for tooth eruption. Notably, although a separate true ‘eruptive force’ is widely assumed, there is little direct evidence for such a force. We constructed a three dimensional finite element model from axial computerized tomography of an 8 year old child mandible containing 12 erupted and 8 unerupted teeth. Tissues modelled included: cortical bone, cancellous bone, soft tissue dental follicle, periodontal ligament, enamel, dentine, pulp and articular cartilage. Strain and hydrostatic stress during incisive and unilateral molar bite force were modelled, with force applied via medial and lateral pterygoid, temporalis, masseter and digastric muscles. Strain was maximal in the soft tissue follicle as opposed to surrounding bone, consistent with follicle as an effective mechanosensor. Initial numerical analysis of dental follicle soft tissue overlying crowns and beneath the roots of unerupted teeth was of volume and hydrostatic stress. To numerically evaluate biological significance of differing hydrostatic stress levels normalized for variable finite element volume, ‘biological response units’ in Nmm were defined and calculated by multiplication of hydrostatic stress and volume for each finite element. Graphical representations revealed similar overall responses for individual teeth regardless if incisive or right molar bite force was studied. There was general compression in the soft tissues over crowns of most unerupted teeth, and general tension in the soft tissues beneath roots. Not conforming to this pattern were the unerupted second molars, which do not erupt at this developmental stage. Data support a new hypothesis for tooth eruption, in which the follicular soft tissues detect bite-force-induced bone-strain, and direct bone remodelling at the inner surface of the surrounding bony crypt, with the effect of enabling tooth eruption into the mouth. 相似文献
5.
6.
Wei de Zhang Fan Qing Li Xiao Yun Zhang Ying Chen 《Biological trace element research》1988,17(1):81-90
The growth of the protozoanBlepherisma is stimulated by Lanthanum (La) at concentrations as low as 0.32 ppm. In mice Yttrium (Y) and Ytterbium (Yb) are absorbed,
accumulated, and metabolized. Both rare earth elements (RE) exhibit a high affinity for teeth and bones, accumulation occurs
and metabolism is slow. In the livers of RE-exposed mice, concentrations are variable. The liver is apparently capable of
absorbing and discharging RE in a manner depending on metabolic activity. The main route of discharge for ingested REs is
the alimentary canal. Exposure of pregnant mice to RE leads to rapid placental transfer of RE; 14.1% of the total amount of
RE administered was detected in newborn mice. Young, developing organisms appear to be especially susceptible to RE accumulation. 相似文献
7.
8.
应用酶联免疫吸附试验检测马铃薯卷叶病毒 总被引:2,自引:0,他引:2
以辣根过氧化物酶标记马铃薯卷叶病毒抗体,采用双抗体夹心ELISA方法鉴定了马铃薯和洋酸浆的茎、叶、根及马铃薯块茎中的马铃薯卷叶病毒(Potato Leafroll Virus,PLRV),结果表明,对提纯的PLRV可测出的最低浓度为25ng/ml,当包被抗体浓度为40μg/ml、酶标记抗体稀释度为1/120时,可测出马铃薯茎、叶和根汁液中的PLRV,感染PLRV的洋酸浆茎、叶和根汁液的消光值,均比无病对照者高二倍以上,虽然感染PLRV的马铃薯休眠块茎维管束组织汁液的消光值高于无病毒对照,且脐部维管束组织消光值高于顶端,但测定打破休眠的感病块茎顶端维管束组织的阳性结果更为可靠和明显。 相似文献
9.
10.