全文获取类型
收费全文 | 3672篇 |
免费 | 305篇 |
国内免费 | 2篇 |
出版年
2022年 | 13篇 |
2021年 | 73篇 |
2020年 | 36篇 |
2019年 | 57篇 |
2018年 | 72篇 |
2017年 | 50篇 |
2016年 | 93篇 |
2015年 | 161篇 |
2014年 | 163篇 |
2013年 | 202篇 |
2012年 | 241篇 |
2011年 | 264篇 |
2010年 | 173篇 |
2009年 | 144篇 |
2008年 | 233篇 |
2007年 | 193篇 |
2006年 | 193篇 |
2005年 | 190篇 |
2004年 | 153篇 |
2003年 | 169篇 |
2002年 | 143篇 |
2001年 | 56篇 |
2000年 | 50篇 |
1999年 | 49篇 |
1998年 | 49篇 |
1997年 | 27篇 |
1996年 | 30篇 |
1995年 | 23篇 |
1994年 | 36篇 |
1993年 | 32篇 |
1992年 | 45篇 |
1991年 | 21篇 |
1990年 | 30篇 |
1989年 | 28篇 |
1988年 | 32篇 |
1987年 | 45篇 |
1986年 | 35篇 |
1985年 | 23篇 |
1984年 | 28篇 |
1983年 | 22篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1975年 | 12篇 |
1973年 | 15篇 |
1972年 | 17篇 |
1967年 | 11篇 |
排序方式: 共有3979条查询结果,搜索用时 15 毫秒
1.
2.
Current MR methods use T2? relaxation time as a surrogate measure of ligament strength. Currently, a multi-echo voxel-wise least squares fit is the gold standard to create T2? maps; however, the post-processing is time-intensive and serves as a stopgap for clinical use. The study objective was to determine if an alternative method could improve post-processing time without sacrificing fidelity of T2? values for eventual translational use in the clinic. Using a 6 echo FLASH sequence, three different methods were used to determine intact posterior cruciate ligament (PCL) median T2? Two of these methods utilized a voxel-wise method to establish T2? maps: (1) a current “gold standard” method using a voxel-wise 6 echo least-squares fit (6LS) and (2) a voxel-wise 2 echo point T2? determination (2MM). The third method used median ligament signal intensity and a single nonlinear least-squares fit (6LSROI) instead of a voxel-wise basis. The resulting median T2? values of the PCL and computational time were compared. The median T2? values were 42% higher using the 2MM compared to the 6LS method (p<0.0001). However, a strong correlation was found for the median T2? values between the 2MM and 6LS methods (R2=0.80). The median T2? values were not significantly different between the 6LS and 6LSROI methods (p=0.519). Using the 2MM (which provides a regional map) and the 6LSROI (which efficiently provides the median T2? value) methods in tandem would take only minutes of post-processing computational time compared to the 6LS method (~540 min), and hence would facilitate clinical application of T2? maps to predict ligament structural properties as a patient outcome measure. 相似文献
3.
Christian P Craddock Nicolette Adams Fiona M Bryant Smita Kurup Peter J Eastmond 《Plant signaling & behavior》2015,10(10)
Coordination of membrane lipid biosynthesis is important for cell function during plant growth and development. Here we summarize our recent work on PHOSPHATIDIC ACID PHOSPHOHYDROLASE (PAH) which suggests that this enzyme is a key regulator of phosphaticylcholine (PC) biosynthesis in Arabidopsis thaliana. Disruption of PAH activity elevates phosphatidic acid (PA) levels and stimulates PC biosynthesis and biogenesis of the endoplasmic reticulum (ER). Furthermore, the activity of PHOSPHOCHOLINE CYTIDYLYLTRANSFERASE (CCT), which is the key enzyme controlling the rate of PC biosynthesis, is directly stimulated by PA and expression of a constitutively active version of CCT replicates the effects of PAH disruption. Hence PAH activity can control the abundance of PA, which in turn can modulate CCT activity to govern the rate of PC biosynthesis. Crucially it is not yet clear how PAH activity is regulated in Arabidopsis but there is evidence that PAH1 and PAH2 are both phosphorylated and further work will be required to investigate whether this is functionally significant. 相似文献
4.
5.
6.
Summary A mutant of Streptomyces coelicolor A3(2) highly resistant to chloramphenicol was selected. It had amplified some chromosomal DNA fragments to a copy number of 20–50. Some of the amplified fragments were cloned and used as hybridisation probes to investigate the spontaneous chloramphenicol-sensitive mutants which occur at high frequency in this species and the closely related species Streptomyces lividans 66. These investigations demonstrated that chloramphenicol sensitivity in both species is associated with large deletions that are at least 40 kb in length. 相似文献
7.
1. The optimal temperature for in vitro development of fertilized eggs of Ascaris suum was 24 degrees C. 2. Samples (2 X 10(7) eggs) were obtained from in vitro embryonating cultures every 3 days for 4 weeks; lipids were extracted, partially purified, fractionated with HPLC and analyzed for ecdysteroids by radioimmunoassay. 3. Free ecdysone and 20-hydroxyecdysone (20-HE) were at low levels (less than 20 pg) in freshly excised eggs and rose to maximal values on day 6 of embryonation. 4. Conjugated ecdysone and conjugated 20-HE rose to maximal values on day 9. 5. Both free and conjugated ecdysteroids were undetectable from days 15 to 27 of cultivation. 6. These profiles indicate that ecdysteroids might have a selective role in nematode embryonation and/or tanning of the egg shell. 相似文献
8.
P R Fleming 《BMJ (Clinical research ed.)》1982,285(6348):1099-1100
9.
10.