全文获取类型
收费全文 | 8429篇 |
免费 | 670篇 |
国内免费 | 620篇 |
专业分类
9719篇 |
出版年
2024年 | 17篇 |
2023年 | 109篇 |
2022年 | 281篇 |
2021年 | 448篇 |
2020年 | 326篇 |
2019年 | 366篇 |
2018年 | 388篇 |
2017年 | 263篇 |
2016年 | 364篇 |
2015年 | 515篇 |
2014年 | 579篇 |
2013年 | 608篇 |
2012年 | 766篇 |
2011年 | 638篇 |
2010年 | 395篇 |
2009年 | 376篇 |
2008年 | 413篇 |
2007年 | 380篇 |
2006年 | 352篇 |
2005年 | 281篇 |
2004年 | 241篇 |
2003年 | 205篇 |
2002年 | 178篇 |
2001年 | 144篇 |
2000年 | 115篇 |
1999年 | 136篇 |
1998年 | 81篇 |
1997年 | 90篇 |
1996年 | 80篇 |
1995年 | 74篇 |
1994年 | 86篇 |
1993年 | 60篇 |
1992年 | 73篇 |
1991年 | 70篇 |
1990年 | 60篇 |
1989年 | 33篇 |
1988年 | 36篇 |
1987年 | 25篇 |
1986年 | 19篇 |
1985年 | 23篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有9719条查询结果,搜索用时 15 毫秒
991.
多胚水稻ApⅢ(双13)的胚胎学观察 总被引:6,自引:0,他引:6
对多胚水稻(Oryza sativa L.)ApⅢ的大量成熟颖果、人工萌发的幼苗和开花后3~5 d 的幼嫩颖果进行的整体解剖和显微制片观察表明:ApⅢ的5000粒成熟颖果中,89.0% 含单胚单苗,8.9% 和1.2%分别含双胚双苗和三胚三苗;700多粒幼嫩颖果中,90.0% ~95.0% 含单胚,5.0% ~7.0% 含双胚。因制片的数目有限,未见到含三胚的;在含单胚和多胚颖果中,胚均位于同一胚囊的珠孔端,未见到胚囊以外存在不定胚。根据上述结果,似可以认为ApⅢ单粒颖果的双胚和三胚是由同一胚囊内的卵细胞和1或2个助细胞受精或不受精发育而来的 相似文献
992.
The Crc protein participates in down‐regulation of the Lon gene to promote rhamnolipid production and rhl quorum sensing in Pseudomonas aeruginosa
下载免费PDF全文
![点击此处可从《Molecular microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
993.
厦门凤林红树林湿地大型底栖动物群落 总被引:8,自引:0,他引:8
为摸清厦门集美凤林红树林湿地的大型底栖动物群落结构及其多样性现状,2002年1、4、7和10月在厦门集美凤林红树林区进行大型底栖动物调查,4个季度共获得大型底栖动物42种。生物量优势种是软体动物门的珠带拟蟹守螺(Cerithideacingulata)和节肢动物门的弧边招潮(Ucaarcuata)。密度优势种是软体动物门的短拟沼螺(Assimineabrevicula)和环节动物门的沼蚓(Limnodriloidessp.)。集美凤林红树林区大型底栖动物年平均密度和年平均生物量分别为1,990ind./m2和139.0g/m2。密度的季节变化是:1月>4月>10月>7月,生物量的季节变化是1月>10月>4月>7月。聚类分析和数量分布表明,优势种珠带拟蟹守螺、短拟沼螺、弧边招潮和沼蚓的季节变化各不相同。与2002年10月深圳湾福田红树林区大型底栖动物群落的物种多样性指数平均值(0.56)比较,厦门凤林红树林区的平均值较高(2.66)。文中分析了影响大型底栖动物多样性的环境因素。 相似文献
994.
995.
In this letter, we investigate the extraordinary optical transmission behavior of a flat continuous metal film sandwiched by magnetic plasmonic structures. A new mechanism by utilizing higher order magnetic plasmon resonance is proposed to enhance the transmission. Numerical simulation results show that 80 % electromagnetic energy can be transmitted through the middle 50-nm-thick continuous gold film in near-infrared regime. The excitation of the second-order magnetic plasmons and the propagating surface plasmons, as well as the interaction between them accounts for such a high transmission. The interaction of magnetic plasmons and surface plasmons leads to new hybrid modes, and the coupled oscillator model is introduced to analyze this hybridization. This work extends the application range of higher order magnetic plasmons and may have potential in transparent electrode and electromagnetic energy transfer applications. 相似文献
996.
Kohonen's self-organization model, a neural network model, is applied to predict the β-turns in proteins. There are 455 β-turn tetrapeptides and 3807 non-β-turn tetrapeptides in the training database. The rates of correct prediction for the 110 β-turn tetrapeptides and 30,229 non-β-turn tetrapeptides in the testing database are 81.8% and 90.7%, respectively. The high quality of prediction of neural network model implies that the residue-coupled effect along a polypeptide chain is important for the formation of reversal turns, such as β-turns, during the process of protein folding. 相似文献
997.
目的:观察重组SOD对小鼠运动能力和肝、脑组织中抗氧化能力的影响。方法:采用负重力竭性游泳实验测定小鼠的运动能力,观察重组SOD的抗运动性疲劳作用。结果:与对照组比较,给予100U重组SOD的小鼠负重力竭性游泳持续时间增加(P〈0.01)。游泳前2h给予100U重组SOD的小鼠游泳后血清中乳酸(LAC)和乳酸脱氢酶(LDH)水平非常显著提高(P〈0.01),血清尿素氮(BUN)和葡萄糖(Glc)水平则显著提高(P〈0.05);肝、脑组织中SOD活力非常显著提高(P〈0.01)。结论:重组SOD能改善小鼠的运动能力和抗组织氧化的能力。 相似文献
998.
Previous observations indicated that division of the generative cell (GC) in some plant genura such as Lilium and Tradescantia is characterized by several unusual features, including persistence of surrounding microtubule (MT) bundles during mitosis, lacking a matephase plate, the cytokinesis is completed with furrow. The authors have further studied the changes of MT organizations and the chromosome (CHs) behavior in the GC during mitosis using electron microscopy and method of tubulin localizations. No MTs in the GC before GC division and during prophase was seen under electron microscopy. However, there was tubulin in the GC with antitubulin staining. During promatephase to matephase, the CHs appeared and arranged in a complexed tangled pattern lengthwise along the cell. Correspond- ingly, transverse pairs of kinetochores were located along the length and depth of the cell. They stacked successively like the rungs of a ladder. In this phase, a large mount of MTs appeared in the GC, which distributed in the cortex of the cell and among the CHs and along the whole length of the CHs. In the beginning, one or two kinetochore pairs changed from transversely to longitudinally situated in each cell. MTs ended on the kinetochore to form kinetochore MTs (KMTs). With the electron microscopy, authors did not find the image of lateral connection between the MTs and the kinetochores as previous reported with immunofluorescent method. As karyokinesis proceeded, more transverse kinetochore pairs gradually became longitudinal, and KMTs gradually increased in number. However, a distinct spindle was not evidenced. During anaphase, CHs seperation started at various positions along the length of the cell. The distribution of MTs in the GC was similar to that of promatephase to matephase. In late anaphase, the CHs segregated as two groups. Most MTs disappeared but only some remained in the polar regions and the interzone. Authors also measured and compared the lengths of the CHs and indirectly identified the existing anaphase B. During late tolephase, the MTs increased in number gradually in the region between the two newly formed sperm nuclei. The region might be the MT interdigitating zone visualized with antitubulin localization. The MTs disappeared after the cell plate (CP) appeared. 相似文献
999.
Xi Jin Tianhai Lin Guang Yang Huawei Cai Bo Tang Xinyang Liao Huifang Li Xiaoting Chen Lina Gong Hang Xu Yi Sun Ping Tan Jianqiong Yin Hongwen Ma Jianzhong Ai Kunjie Wang Qiang Wei Lu Yang Hong Li 《Journal of cellular and molecular medicine》2020,24(9):5082-5096
Benign prostatic hyperplasia (BPH) occurs most commonly among older men, often accompanied by chronic tissue inflammation. Although its aetiology remains unclear, autoimmune dysregulation may contribute to BPH. Regulatory T cells (Tregs) prevent autoimmune responses and maintain immune homeostasis. In this study, we aimed to investigate Tregs frequency, phenotype, and function in BPH patients and to evaluate adoptive transfer Tregs for immunotherapy in mice with BPH via CD39. Prostate specimens and peripheral blood from BPH patients were used to investigate Treg subsets, phenotype and Treg‐associated cytokine production. Sorted CD39+/? Tregs from healthy mice were adoptively transferred into mice before or after testosterone propionate administration. The Tregs percentage in peripheral blood from BPH patients was attenuated, exhibiting low Foxp3 and CD39 expression with low levels of serum IL‐10, IL‐35 and TGF‐β. Immunohistochemistry revealed Foxp3+ cells were significantly diminished in BPH prostate with severe inflammatory. Although the Tregs subset was comprised of more effector/memory Tregs, CD39 was still down‐regulated on effector/memory Tregs in BPH patients. Before or after testosterone propionate administration, no alterations of BPH symptoms were observed due to CD39‐ Tregs in mice, however, CD39+Tregs existed more potency than Tregs to regulate prostatic hyperplasia and inhibit inflammation by decreasing IL‐1β and PSA secretion, and increasing IL‐10 and TGF‐β secretion. Furthermore, adoptive transfer with functional Tregs not only improved prostate hyperplasia but also regulated muscle cell proliferation in bladder. Adoptive transfer with Tregs may provide a novel method for the prevention and treatment of BPH clinically. 相似文献
1000.