全文获取类型
收费全文 | 9621篇 |
免费 | 1011篇 |
国内免费 | 525篇 |
出版年
2024年 | 6篇 |
2023年 | 139篇 |
2022年 | 165篇 |
2021年 | 426篇 |
2020年 | 402篇 |
2019年 | 426篇 |
2018年 | 408篇 |
2017年 | 286篇 |
2016年 | 409篇 |
2015年 | 658篇 |
2014年 | 731篇 |
2013年 | 770篇 |
2012年 | 882篇 |
2011年 | 757篇 |
2010年 | 519篇 |
2009年 | 420篇 |
2008年 | 531篇 |
2007年 | 459篇 |
2006年 | 406篇 |
2005年 | 325篇 |
2004年 | 270篇 |
2003年 | 252篇 |
2002年 | 186篇 |
2001年 | 173篇 |
2000年 | 151篇 |
1999年 | 166篇 |
1998年 | 87篇 |
1997年 | 81篇 |
1996年 | 73篇 |
1995年 | 71篇 |
1994年 | 91篇 |
1993年 | 46篇 |
1992年 | 49篇 |
1991年 | 62篇 |
1990年 | 38篇 |
1989年 | 46篇 |
1988年 | 29篇 |
1987年 | 25篇 |
1986年 | 32篇 |
1985年 | 25篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1973年 | 4篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1968年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
通过杂交和自交实验,对重唇石斛授粉亲和力和结实性进行分析,并对其开花期间花粉及蕊柱结构的动态变化进行显微观察,以探讨重唇石斛的最佳杂交授粉时间.结果表明:(1)花器表面结构差异较大,唇瓣、药帽、萼片表皮布满突起、钩刺等,花瓣表皮较平滑;(2)杂交时以重唇石斛为父本或母本均具有选择性,但作为父本亲和力强,杂交结实率可达100%,作为母本杂交结实率最高为60%;自交结实率非常低,为4.3%;(3)花粉培养的最佳配方为30%蔗糖+0.15 mg·L-1 CaCl2;(4)花开第4天后花粉发育饱满,第5~12天花粉发芽率稳定大于70%,蕊柱的乳突细胞于开花第6~10 天时发育饱满.研究表明,重唇石斛花开第5~12 天为最佳授粉时间. 相似文献
2.
Yu Song Xin Yao Yunhong Tan Yi Gan Junbo Yang Richard T. Corlett 《Tree Genetics & Genomes》2017,13(6):120
Phoebe is an economically important genus from the family Lauraceae. It is widely distributed in tropical and subtropical Asia, but systematics of the genus is unclear, and currently there is no species-level phylogeny. Here, we determined the complete chloroplast genome sequences of two species with long-range PCR and next genome sequencing technologies, and identified mutation sites and highly variable regions. These highly variable sites were used to reconstruct the phylogeny. The plastomes of Phoebe sheareri and P. omeiensis were 152, 876, and 152, 855 bp, respectively. Comparative genomic analysis indicated that there are 222 mutation sites including 146 substitutions, 73 indels, and 3 microinversions in both plastomes. Fifty-six single-nucleotide changes were identified in gene-coding regions, and 45 microsatellite sites were found for use in species identification. Fourteen divergence hotspots of 38 variable regions were located. Phylogeny was reconstructed using a Bayesian and maximum likelihood approach for 12 Phoebe species and other five related Lauraceae based on 15 of the highly variable regions including accD-psaI, atpB-rbcL, ndhC-trnV, ndhF-rpl32, petA-psbJ, psaA, psbA-trnH, rbcL, rps8-rpl14, rps16-trnQ, rpl32-trnL, trnC-petN, trnL-trnF, trnS-trnG, and ycf1 indicated that variability in the chloroplast regions proposed as variable is enough to detect divergence events among 12 taxa of Phoebe, and that maybe also useful to help to elucidate further relationships among other taxa of the genus. 相似文献
3.
Xinglei Yao Na Zhou Li Wan Xiaodong Su Zhao Sun Hiroyuki Mizuguchi Yasuo Yoshioka Shinsaku Nakagawa Robert Chunhua Zhao Jian-Qing Gao 《Biochemical and biophysical research communications》2014
Mesenchymal stem cells (MSCs) are non-hematopoietic cells with multi-lineage potential, which makes them attractive targets for regenerative medicine applications. Efficient gene transfer into MSCs is essential for basic research in developmental biology and for therapeutic applications involving gene-modification in regenerative medicine. Adenovirus vectors (Advs) can efficiently and transiently introduce an exogenous gene into many cell types via their primary receptors, the coxsackievirus and adenovirus receptors (CARs), but not into MSCs, which lack CAR expression. To overcome this problem, an Adv coated with cationic polymer polyethyleneimine (PEI) was developed. In this study, we demonstrated that PEI coating with an optimal ratio can enhance adenoviral transduction of MSCs without cytotoxicity. We also investigated the physicochemical properties and internalization mechanisms of the PEI-coated Adv. These results could help to evaluate the potentiality of the PEI-coated Adv as a prototype vector for efficient and safe transduction into MSCs. 相似文献
4.
5.
【目的】猪链球菌1、2、14和1/2型间存在单向或双向的交叉抗原性,这种交叉抗原性的产生原因至今未被揭示。【方法】采用Sephacryl S-300凝胶层析柱对猪链球菌14和1/2型荚膜多糖进行分离纯化,经苯酚-硫酸检测和dot-ELISA辅助鉴定,确定荚膜多糖成分。采用高效凝胶渗透色谱法测定14和1/2型猪链球菌荚膜多糖分子量分别为487.38 kDa和512.72 kDa。【结果】经柱前衍生高效液相色谱法、荧光标记液相色谱法和核磁共振测定14和1/2型猪链球菌荚膜多糖单糖组成分别为:Glc/Gal/GlcNAc/Rha/Neu5Ac(1∶2.94∶1.35∶0.24∶0.37)和Glc/Gal/GlcNAc/GalNAc/Rha/Neu5Ac(1∶1.67∶1.05∶0.93∶0.72∶0.7)。并与已知的猪链球菌1、2型荚膜多糖的单糖组成进行比较分析,发现4种血清型荚膜多糖都具有Glc、GlcNAc、Gal和Neu5Ac,但单糖组成和比列并无明显相似性,这种交叉抗原性可能是由于荚膜多糖的空间结构相似性和(或)细胞表面的其他成分引起的。 相似文献
6.
Xinghong Ding Jinbo Hu Jinfeng Li Yan Zhang Bingjie Shui Zhishan Ding Li Yao Yongsheng Fan 《Analytical biochemistry》2014
A serum metabolomics method based on rapid resolution liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (RRLC-Q-TOF-MS) was performed for a holistic evaluation of the metabolic changes of collagen-induced arthritis (CIA) in rats and to assess the interventional effects of type II collagen (CII) in this model. Partial least-squares-discriminant analysis (PLS-DA) was employed to study the metabolic profiling of CIA rats and control rats. Ten metabolites, namely, 12(S)-HHTrE, 12(S)-HEPE, PGE2, TXB2, 12(S)-HETE, LysoPE(16:0), PE(O-18:0/0:0), Lyso-PE(18:2), Lyso-PE(20:4), and Lyso-PC(22:5) were identified as differential metabolites associated with the pathogenesis of CIA. These results suggested that dysregulation of the arachidonic acid (AA) and phospholipid metabolic networks is involved in the pathomechanism of CIA. Differential metabolomics and histopathological analyses demonstrated that CII inhibits the progress of arthritis. Furthermore, the therapeutic effects of CII on CIA may involve regulation of the disordered AA and phospholipid metabolic networks. This metabolomics study provides new insights into the pathogenesis of arthritis and, furthermore, indicates the potential mechanism underlying the significantly increased prevalence of metabolic syndrome, defined as a clustering of cardiovascular disease (CVD) risk factors, in arthritis patients. 相似文献
7.
Xianchao Yang Ying Lu Liangcheng Duan Baolin Liu Jianquan Yao 《Plasmonics (Norwell, Mass.)》2017,12(6):1805-1811
A temperature sensor based on hollow fiber (HF) filled with graphene-Ag composite nanowire and liquid is presented. The coupling properties and sensing performance are numerically analyzed by finite element method using wavelength and amplitude interrogations. Results show that the sensor exhibiting strong birefringence with x-polarized peak provides much higher sensitivities and better signal-to-noise ratio (SNR) than y-polarized, which is more suitable for temperature detection. The graphene-Ag composite nanowire can not only solve the oxidation problem but also avoid the metal coating. Moreover, it provides better performance than other similar works like Au-Ag nanowire-filled, Au nanowire-filled, and Ag nanowire-filled sensors. Contrary to the blue shift of traditional SPR temperature sensors, the resonance peak shifts to the longer wavelength in our device when temperature increases and the high sensitivity 9.44 nm/ °C is obtained. The influences of nanowire diameter, grapheme-layer thickness on the designed sensor, are also investigated. This work can provide a reference for developing a high sensitivity, real-time, remote sensing, and distributed temperature SPR sensor. 相似文献
8.
了解城市内河中病原菌含量对城市生态安全具有重要意义。应用定量PCR( qPCR)方法,对宁波市城区6条重要内河水体中的病原菌含量及主要水质指标进行分析。结果表明,祖关山河、苏家河、南北河、后西河、史魏家河和直落河每升水体中含有病原菌基因的拷贝数分别为:3.34×105、1.47×105、4.68×105、1.75×106、9.65×106和1.33×106;且病原菌基因的含量与水体溶解氧负相关,与总氮、氨氮、浊度、总磷、高锰酸钾指数、叶绿素a和电导率呈正相关关系,但与水体透明度、温度和酸碱度无明显关系。定量PCR分析结果可望为评价城市内河水体质量提供重要参考。 相似文献
9.
Background
Bipolar disorder types I (BD I) and II (BD II) behave differently in clinical manifestations, normal personality traits, responses to pharmacotherapies, biochemical backgrounds and neuroimaging activations. How the varied emotional states of BD I and II are related to the comorbid personality disorders remains to be settled.Methods
We therefore administered the Plutchick – van Praag Depression Inventory (PVP), the Mood Disorder Questionnaire (MDQ), the Hypomanic Checklist-32 (HCL-32), and the Parker Personality Measure (PERM) in 37 patients with BD I, 34 BD II, and in 76 healthy volunteers.Results
Compared to the healthy volunteers, patients with BD I and II scored higher on some PERM styles, PVP, MDQ and HCL-32 scales. In BD I, the PERM Borderline style predicted the PVP scale; and Antisocial predicted HCL-32. In BD II, Borderline, Dependant, Paranoid (-) and Schizoid (-) predicted PVP; Borderline predicted MDQ; Passive-Aggressive and Schizoid (-) predicted HCL-32. In controls, Borderline and Narcissistic (-) predicted PVP; Borderline and Dependant (-) predicted MDQ.Conclusion
Besides confirming the different predictability of the 11 functioning styles of personality disorder to BD I and II, we found that the prediction was more common in BD II, which might underlie its higher risk of suicide and poorer treatment outcome. 相似文献10.