全文获取类型
收费全文 | 6460篇 |
免费 | 430篇 |
国内免费 | 11篇 |
出版年
2023年 | 75篇 |
2022年 | 150篇 |
2021年 | 384篇 |
2020年 | 146篇 |
2019年 | 180篇 |
2018年 | 271篇 |
2017年 | 178篇 |
2016年 | 260篇 |
2015年 | 392篇 |
2014年 | 381篇 |
2013年 | 484篇 |
2012年 | 483篇 |
2011年 | 464篇 |
2010年 | 282篇 |
2009年 | 234篇 |
2008年 | 274篇 |
2007年 | 288篇 |
2006年 | 229篇 |
2005年 | 179篇 |
2004年 | 176篇 |
2003年 | 137篇 |
2002年 | 136篇 |
2001年 | 94篇 |
2000年 | 70篇 |
1999年 | 54篇 |
1998年 | 39篇 |
1997年 | 34篇 |
1996年 | 28篇 |
1995年 | 29篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 54篇 |
1991年 | 39篇 |
1990年 | 50篇 |
1989年 | 47篇 |
1988年 | 37篇 |
1987年 | 30篇 |
1986年 | 34篇 |
1985年 | 29篇 |
1984年 | 38篇 |
1983年 | 33篇 |
1982年 | 32篇 |
1981年 | 34篇 |
1980年 | 40篇 |
1979年 | 18篇 |
1978年 | 27篇 |
1977年 | 19篇 |
1975年 | 16篇 |
1974年 | 22篇 |
1973年 | 20篇 |
排序方式: 共有6901条查询结果,搜索用时 187 毫秒
961.
Jeong Joon Ahn Kyungsan Choi Shaw-Yhi Huang Md. Abdullah Al Baki Shabbir Ahmed Yonggyun Kim 《Journal of Asia》2018,21(4):1275-1282
The oriental fruit fly, Bactrocera dorsalis, is a serious insect pest with diverse host range. Furthermore, its invasive and polyphagous behaviors allow this species to expand its habitats. Recent climate change and increase of international trade/transportation facilitate the species expansion from subtropical to temperate regions. Low temperature during winter appears to be the major factor limiting its expansion to temperate zones in the northern hemisphere. This study reports its remarkable ability in rapid cold-hardening (RCH) along with deep supercooling capacity. A brief exposure to 9?°C significantly enhanced cold tolerance of its larvae, pupae, and adults. RCH took 1–2?h for pupae and adults, although it took 24?h for larvae. Supercooling capacity of pupae was also enhanced by RCH treatment from ?13.4?°C to ?16.6?°C. To trace genetic factors associated with RCH, calcium/calmodulin-dependent protein kinase II (Bd-CaMKII) was identified from B. dorsalis and their expression in response to RCH treatment was analyzed. Bd-CaMKII possesses three conserved domains of kinase, calmodulin, and oligomerization. Bd-CaMKII is highly homologous to CaMKII of D. melanogaster and other tephritid flies. Expression levels of Bd-CaMKII in the larvae treated with RCH were significantly increased by approximately 5.5 folds compared to those in control larvae. In addition, expression levels of HSP70 and HSP90 were also increased in response to RCH treatment. These results along with previous studies suggest that cold-hardening of B. dorsalis is functionally associated with its supercooling capacity with increased production of cryoprotectants and HSP through regulatory activity of Bd-CaMKII. 相似文献
962.
The rapid growth of nanotechnology application in various fields of science led to need of understanding their possible effects on development and physiology of insects before using them as control agents. Instead of feeding on a toxic dose, the impact of silver nanoparticles (AgNPs, 50–60?nm) and zinc oxide nanoparticles (ZnONPs, 10–30?nm) was studied at a nonlethal concentration on the larval stages of Spodoptera littoralis. Late second instar larvae of S. littoralis were treated with water, 10?mg/mL AgNPs and ZnONPs dipped castor leaves for 6?days. Both nanoparticles treated leaves caused reduction in both larval weight gain and pupal weight than water dipped leaves while ZnONPs only caused extended larval period. ZnONPs increased total hemocyte, granular cell and plasmatocyte counts while AgNPs increased plasmatocytes only. ZnONPs decreased the levels of protein, lipids and carbohydrates than control and AgNPs treated larvae. On the contrary, ZnONPs induced significant increase in the activities of amylase, glucose 6 phosphate dehydrogenase (G6PD), lipase as well as two antioxidative enzymes, the catalase and superoxide dismutase. These results clearly show that ZnONPs ingestion interfere with the digestive and immunological physiology as well as the development of S. littoralis. 相似文献
963.
Ali Zohaib Muhammad Saqib Muhammad Ammar Athar Jing Chen Awais-ur-Rahman Sial Saeed Khan Zeeshan Taj Halima Sadia Usman Tahir Muhammad Haleem Tayyab Muhammad Asif Qureshi Muhammad Khalid Mansoor Muhammad Ahsan Naeem Bing-Jie Hu Bilal Ahmed Khan Ikram Din Ujjan Bei Li Wei Zhang Yun Luo Yan Zhu Cecilia Waruhiu Iahtasham Khan Xing-Lou Yang Muhammad Sohail Sajid Victor Max Corman Bing Yan Zheng-Li Shi 《中国病毒学》2018,33(5):410-417
Middle East Respiratory Syndrome Coronavirus (MERS-CoV) is a zoonotic pathogen capable of causing severe respiratory disease in humans. Although dromedary camels are considered as a major reservoir host, the MERS-CoV infection dynamics in camels are not fully understood. Through surveillance in Pakistan, nasal (n = 776) and serum (n = 1050)samples were collected from camels between November 2015 and February 2018. Samples were collected from animal markets, free-roaming herds and abattoirs. An in-house ELISA was developed to detect IgG against MERS-CoV. A total of 794 camels were found seropositive for MERS-CoV. Prevalence increased with the age and the highest seroprevalence was recorded in camels aged [ 10 years (81.37%) followed by those aged 3.1–10 years (78.65%) and B 3 years (58.19%).Higher prevalence was observed in female (78.13%) as compared to male (70.70%). Of the camel nasal swabs, 22 were found to be positive by RT-qPCR though with high Ct values. Moreover, 2,409 human serum samples were also collected from four provinces of Pakistan during 2016–2017. Among the sampled population, 840 humans were camel herders.Although we found a high rate of MERS-CoV antibody positive dromedaries (75.62%) in Pakistan, no neutralizing antibodies were detected in humans with and without contact to camels. 相似文献
964.
Zeanap A. Mabruk Samrein B.M. Ahmed Asha Caroline Thomas Sally A. Prigent 《Biochemistry and Biophysics Reports》2018
Preliminary screening data showed that the ShcD adaptor protein associates with the proto-oncogene RET receptor tyrosine kinase. In the present study, we aimed to investigate the molecular interaction between ShcD and RET in human neuroblastoma cells and study the functional impact of this interaction. We were able to show that ShcD immunoprecipitated with RET from SK-N-AS neuroblastoma cell lysates upon GDNF treatment. This result was validated by ShcD-RET co-localization, which was visualized using a fluorescence microscope. ShcD-RET coexpression promoted ShcD and RET endosomal localization, resulting in unexpected inhibition of the downstream ERK and AKT pathways. Interestingly, ShcD-RET association reduced the viability and migration of SK-N-AS cells. Although ShcD was previously shown to trigger melanoma cell migration and tumorigenesis, our data showed an opposite role for ShcD in neuroblastoma SK-N-AS cells via its association with RET in GDNF-treated cells. In conclusion, ShcD acts as a switch molecule that promotes contrasting biological responses depending on the stimulus ad cell type. 相似文献
965.
Bare laser‐synthesized Au‐based nanoparticles as nondisturbing surface‐enhanced Raman scattering probes for bacteria identification 下载免费PDF全文
Martin Kögler Yury V. Ryabchikov Sanna Uusitalo Alexey Popov Anton Popov Gleb Tselikov Anna‐Liisa Välimaa Ahmed Al‐Kattan Jussi Hiltunen Riitta Laitinen Peter Neubauer Igor Meglinski Andrei V. Kabashin 《Journal of biophotonics》2018,11(7)
The ability of noble metal‐based nanoparticles (NPs) (Au, Ag) to drastically enhance Raman scattering from molecules placed near metal surface, termed as surface‐enhanced Raman scattering (SERS), is widely used for identification of trace amounts of biological materials in biomedical, food safety and security applications. However, conventional NPs synthesized by colloidal chemistry are typically contaminated by nonbiocompatible by‐products (surfactants, anions), which can have negative impacts on many live objects under examination (cells, bacteria) and thus decrease the precision of bioidentification. In this article, we explore novel ultrapure laser‐synthesized Au‐based nanomaterials, including Au NPs and AuSi hybrid nanostructures, as mobile SERS probes in tasks of bacteria detection. We show that these Au‐based nanomaterials can efficiently enhance Raman signals from model R6G molecules, while the enhancement factor depends on the content of Au in NP composition. Profiting from the observed enhancement and purity of laser‐synthesized nanomaterials, we demonstrate successful identification of 2 types of bacteria (Listeria innocua and Escherichia coli). The obtained results promise less disturbing studies of biological systems based on good biocompatibility of contamination‐free laser‐synthesized nanomaterials.
966.
967.
968.
Attached media reactors are used for enhancement of wastewater treatment processes including anaerobic condition. Selection of a suitable biofilm carrier is a compelling method to improve anaerobic digestion systems. This study investigates the performance of four fibrous biofilms installed in batch biogas reactors for treatment of cow manure. BioCords HS1, HS2, LS1, and LS2 are manufactured by Bishop Water Technologies, ON, Canada. Effluents and attached growth media were analyzed after batch experiment; methane production, methane yield, transfer efficiencies, organic and solid removal efficiencies, pH, and attached volatile suspended solid (VSS) were measured; VSS attached to biofilms mainly correlated with the specific surface area of each biofilm. Additionally, SEM (scanning electron microscopy) was used for further understanding of biofilm formation process for BioCords and the dissimilarity in their performance. The results indicated that BioCord LS2 had positive impact on achieving higher methane production and removal efficiencies compared to other support media utilized in batch reactors. It was also demonstrated from the experiment that BioCord LS2 potentially could generate higher methane production than conventional batch bioreactor. 相似文献
969.
Shah Ahmed Belal Allur Subramaniyan Sivakumar Da Rae Kang Sangbuem Cho Ho Sung Choe 《Animal cells and systems.》2018,22(5):324-333
This study was performed to elucidate the effects of linoleic acid (LA), oleic acid (OA) and their combination (LA?+?OA) on cell proliferation, apoptosis, necrosis, and the lipid metabolism related gene expression in bovine satellite cells (BSCs), isolated from bovine muscles. Cell viability was significantly increased with the OA and LA treatment. Furthermore, LA?+?OA enhanced cell proliferation in a dose-dependent manner (10 to 100?µM), whereas it lowered at 250?µM. In addition, a cell-cycle analysis showed that 100?µM of LA and OA markedly decreased the G0/G1 phase proportion (62.58% and 61.33%, respectively), compared to controls (68.02%), whereas the S-phase cells’ proportion was increased. The ratio of G2/M phase cells was not significantly different among the groups. Moreover, analyses with AO/EtBr staining showed that no apoptosis occurred. Necrosis were determined by flow cytometry using Annexin V-FITC/PI staining which revealed no early apoptosis in the cells pretreated with LA or OA, but occurred in the LA?+?OA group. We also analyzed the mRNA expression of lipid metabolizing genes such as peroxisome proliferator receptor alfa (PPARα), peroxisome proliferator receptor gamma (PPARγ), acyl-CoA oxidase (ACOX), lipoprotein lipase (LPL), carnitine palmitoyl transferase (CPT-1), and fatty-acid binding protein4 (FABP4), which were upregulated in LA or OA treated cells compared to the control group. In essence, LA and OA alone promote the cell proliferation without any apoptosis and necrosis, which might upregulate the lipid metabolism related gene expressions, and increase fatty-acid oxidation in the BSCs’ lipid metabolism. 相似文献
970.
Sarah Al-Sheikh Ahmed Jingjuan Zhang Wujun Ma Bernard Dell 《Plant molecular biology》2018,98(4-5):333-347