全文获取类型
收费全文 | 3720篇 |
免费 | 360篇 |
国内免费 | 268篇 |
出版年
2024年 | 8篇 |
2023年 | 41篇 |
2022年 | 113篇 |
2021年 | 163篇 |
2020年 | 132篇 |
2019年 | 148篇 |
2018年 | 153篇 |
2017年 | 108篇 |
2016年 | 156篇 |
2015年 | 240篇 |
2014年 | 275篇 |
2013年 | 266篇 |
2012年 | 368篇 |
2011年 | 281篇 |
2010年 | 184篇 |
2009年 | 148篇 |
2008年 | 168篇 |
2007年 | 168篇 |
2006年 | 151篇 |
2005年 | 138篇 |
2004年 | 126篇 |
2003年 | 128篇 |
2002年 | 134篇 |
2001年 | 96篇 |
2000年 | 86篇 |
1999年 | 78篇 |
1998年 | 38篇 |
1997年 | 34篇 |
1996年 | 29篇 |
1995年 | 25篇 |
1994年 | 25篇 |
1993年 | 18篇 |
1992年 | 22篇 |
1991年 | 25篇 |
1990年 | 15篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1956年 | 1篇 |
1952年 | 2篇 |
排序方式: 共有4348条查询结果,搜索用时 15 毫秒
51.
Herein, polymeric micelles with glycolipid-like structure and about 40 nm diameter are prepared by self-aggregation from stearate-grafted chitosan oligosaccharides in aqueous medium. The micelles, with high degree of substitution (DS), present specific spatial structure with multiple hydrophobic "minor cores", and thus obtain excellent internalization into cancer cells and accumulation in cytoplasm. Furthermore, the micelles showed pH-sensitive properties, thus favoring intracellular delivery of encapsulated drug via endocytosis. The cell cytotoxicity of paclitaxel encapsulated in micelles was improved sharply and contributed to the increased intracellular delivery of the drug. The present micelles are a promising carrier candidate for targeting therapy of antitumor drugs with a cytoplasmic molecule target. 相似文献
52.
Tingting You Ruizhen Wang Xueming Zhang Shri Ramaswamy Feng Xu 《Biotechnology and bioengineering》2018,115(1):82-91
Ionic liquid (IL)‐acid pretreatment is known to not only enhance the enzymatic hydrolysis efficiency of lignocellulose but also to generate deposits on the surface of fiber by conventional water regeneration, which retard the increment. In this study, ethanol aqueous solution regeneration was developed as a new method to change the substrates characteristics for IL‐acid pretreatment and their effects on the enzymatic hydrolysis were evaluated. Following the IL‐acid reaction, the biomass slurry was subjected to ethanol aqueous solution at various concentration. Results indicated that anti‐solvent choice significantly influenced the reconstruction of both hemicelluloses and lignin as a result of the competition between water and ethanol. The partial removal of hemicelluloses and suitable lignin re‐localization contributed to a more porous structure. Consequently, the cellulose digestibility of aqueous ethanol regenerated samples was dramatically enhanced to ~100% and approximately 11‐ and 2‐fold higher than that of untreated and conventional water regenerated pretreated samples, respectively. A giant leap in the initial rate of enzymatic hydrolysis was also detected in 50% ethanol aqueous solution regenerated samples and only about 10 hr was needed to convert 80% of cellulose to glucose due to the appearance of cellulose II hydrate‐like and more porous structure. 相似文献
53.
Wan YJ Zhang YL Zhou ZR Jia RX Li M Song H Wang ZY Wang LZ Zhang GM You JH Wang F 《Theriogenology》2012,78(3):583-592
The objective was to investigate the effects of the transgenic donor cell synchronization method, oocyte sources, and other factors, on production of hLF-gene nucleus transfer dairy goats. Three transfected cell lines from ear biopsies from three 3-mo-old Saanen dairy goats (designated Number 1, Number 2, and Number 3, respectively) were selected as karyoplast donors for somatic cell nuclear transfer (SCNT) after detailed identification (including PCR and sequencing of PCR products). In donor cell cycle synchronization studies, the apoptosis rate of hLF transgenic fibroblasts was not different (P > 0.05) after 3 days of serum starvation or 2 days of contact inhibition. Additionally, there was no effect (P > 0.05) on developmental capacity of reconstructed embryos; however, the kidding rate of recipients in the serum starvation group was higher than that in the contact inhibition group (18 vs. 0%, respectively). The production efficiency of the transgenic cloned goats using donor cells from the Number 1 dairy goat cell line was higher than those using the Number 2 and the Number 3 cell lines (kidding rates were 18, 2, and 0%, respectively, P < 0.05). The oocyte source did not significantly affect the pregnancy rate of hLF-transgenic cloned dairy goats, but more fetuses were aborted when using in vitro matured oocytes compared to in vivo matured oocytes. In summary, utilizing transfected 3-mo-old dairy goat fibroblasts as donor cells, seven live offspring were produced, and the hLF gene was successfully integrated. This study provided additional insights into preparation of donor cells and recipient oocytes for producing transgenic cloned goats through SCNT. 相似文献
54.
两种野生花卉的扦插繁殖研究 总被引:4,自引:0,他引:4
开展野生花卉车轮梅(Raphiolepis indica)和赤楠(Syzygium buxifolium)扦插试验,结果表明:车轮梅硬枝扦插需一定浓度的外源激素方能生根;对激素浓度大小不敏感;总体上NAA组合生根质量优于IBA组合。综合不同处理生根率、根数和不定根根长3个指标,以800 mg/L NAA或800 mg/L IBA作为车轮梅生产上扦插的激素种类和浓度。赤楠生根率较低,最高扦插率达66.7%,生根时间长,约需45 d始生根。综合生根率、不定根根数和不定根根长3个生根指标,试验的4种激素均能较好促进赤楠生根,200×根太阳在生根率和根数上效果最好,生产上可用200×根太阳浸泡2 h,也可用50-100 mg/L NAA或100-400 mg/L IBA浸泡2 h后进行扦插。 相似文献
55.
56.
热带季节雨林林窗边缘不同热力作用面热力效应的季节变化特征 总被引:4,自引:0,他引:4
通过对热带季节雨林雾凉季和湿热季昼间林窗区域不同热力作用面的热力效应初步分析,指出在西双版纳,不论是雾凉季还是湿热季,热带季节雨林林窗边缘壁面均具有不可忽视的热力作用,且由于受林缘树木的影响,热力效应较强的东侧,北侧林缘壁面最大区域出现位置高于次生林林窗,而强度小于次生林林窗,显示了林窗边缘壁面的热力效应除与太阳高度角,太阳辐射的时间长短和强度有关之外,林窗边缘树木高度也是不可忽视的因子,其结果可为进一步研究林窗小气候形成机制提供研究基础,为研究林窗更新及生物多样性问题提供科学参考。 相似文献
57.
M Hu Z Pan Y Yang C Meng S Geng M You X Jiao 《In vitro cellular & developmental biology. Animal》2012,48(7):434-440
Granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced bone marrow-derived cells (BMCs) and primary peritoneal exudate cells (PECs) are usually used for antigen presentation in in vitro experiments. In order to expound their tendency for uptake and antigen presentation, we compared differences in the degree of phagocytosis, the expression of co-stimulatory molecules, and the activation of T lymphocytes between these two cell types. These assays used the F4/80 marker expression, as it is the general marker for macrophages. The BMC population was found to contain both F4/80(bright) and F4/80(dim) subtypes, while PECs were mainly composed of the F4/80(bright) subtype. Expression levels of cell surface co-stimulatory molecules, CD80, CD86, CD54, and CD40, were significantly higher for F4/80(+)BMCs than F4/80(+)PECs. Their expressions were further upregulated for F4/80(+)BMCs than for F4/80(+)PECs after stimulation with flagellin. F4/80(+)BMCs had a weaker ability to phagocytize microbeads than F4/80(+)PECs (P?0.05), and we determined no relationship between F4/80 expression and phagocytosis. T lymphocytes were activated more efficiently after incubation with BMCs pulsed with flagellin than with pulsed PECs. In this study, F4/80(+)BMCs and F4/80(+)PECs represent the bone marrow-derived macrophages (BMMs) and peritoneal macrophages (PMs), respectively. These results indicate that PMs showed greater potential for phagocytosis, whereas GM-CSF-induced BMMs showed a tendency toward antigen presentation. 相似文献
58.
Intensified plant N and C pool with more available nitrogen under experimental warming in an alpine meadow ecosystem
下载免费PDF全文
![点击此处可从《Ecology and evolution》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Fei Peng Xian Xue Quangang You Manhou Xu Xiang Chen Jian Guo Tao Wang 《Ecology and evolution》2016,6(23):8546-8555
Nitrogen (N) availability is projected to increase in a warming climate. But whether the more available N is immobilized by microbes (thus stimulates soil carbon (C) decomposition), or is absorbed by plants (thus intensifies C uptake) remains unknown in the alpine meadow ecosystem. Infrared heaters were used to simulate climate warming with a paired experimental design. Soil ammonification, nitrification, and net mineralization were obtained by in situ incubation in a permafrost region of the Qinghai‐Tibet Plateau (QTP). Available N significantly increased due to the stimulation of net nitrification and mineralization in 0–30 cm soil layer. Microbes immobilized N in the end of growing season in both warming and control plots. The magnitude of immobilized N was lower in the warming plots. The root N concentration significantly reduced, but root N pool intensified due to the significant increase in root biomass in the warming treatment. Our results suggest that a warming‐induced increase in biomass is the major N sink and will continue to stimulate plant growth until plant N saturation, which could sustain the positive warming effect on ecosystem productivity. 相似文献
59.
Yanjie You Jianfeng Liu Zhizhong Wang Yuan Zhang Yonggang Ran Xu Guo Huimin Liu Haibo Wang 《Cytotechnology》2014,66(1):17-25
Esophageal squamous cell carcinoma (ESCC) has a low 5-year patient survival rate. Radiotherapy, as a preoperative or postoperative treatment of surgery, has a crucial role in improving local control and survival of ESCC. Various chemotherapeutic and biologic agents have been used as radio-sensitizers in combination with radiotherapy. Here, we demonstrate that zoledronic acid (ZOL) has a radio-sensitizing effect on ESCC cells. Exposure of ESCC cancer cells to ZOL plus radiation resulted in increased cell death through arresting the cell cycle between S and G2/M phases. ZOL appeared to inhibit proliferation, tube formation and invasion of endothelial cells. These anti-angiogenetic effects were more marked concurrently with irradiation. In addition, synergistic suppressive effects on VEGF expression were observed after combined treatment. Our data suggest that the combination of ZOL and radiation is a promising therapeutic strategy to enhance radiation therapy for ESCC patients. 相似文献
60.