全文获取类型
收费全文 | 22264篇 |
免费 | 1528篇 |
国内免费 | 990篇 |
专业分类
24782篇 |
出版年
2024年 | 53篇 |
2023年 | 299篇 |
2022年 | 638篇 |
2021年 | 1021篇 |
2020年 | 679篇 |
2019年 | 909篇 |
2018年 | 892篇 |
2017年 | 682篇 |
2016年 | 960篇 |
2015年 | 1344篇 |
2014年 | 1519篇 |
2013年 | 1760篇 |
2012年 | 1955篇 |
2011年 | 1823篇 |
2010年 | 1019篇 |
2009年 | 911篇 |
2008年 | 1015篇 |
2007年 | 934篇 |
2006年 | 849篇 |
2005年 | 725篇 |
2004年 | 633篇 |
2003年 | 527篇 |
2002年 | 476篇 |
2001年 | 309篇 |
2000年 | 320篇 |
1999年 | 282篇 |
1998年 | 174篇 |
1997年 | 161篇 |
1996年 | 182篇 |
1995年 | 162篇 |
1994年 | 136篇 |
1993年 | 102篇 |
1992年 | 151篇 |
1991年 | 150篇 |
1990年 | 124篇 |
1989年 | 97篇 |
1988年 | 98篇 |
1987年 | 101篇 |
1986年 | 70篇 |
1985年 | 89篇 |
1984年 | 50篇 |
1983年 | 53篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1975年 | 29篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Yiming An Xia Long Ming Ma Jue Hu He Lin Dan Zhou Zheng Xing Bolong Huang Shihe Yang 《Liver Transplantation》2019,9(41)
Currently, in addition to the electroactive non‐noble metal water‐splitting electrocatalysts, a scalable synthetic route and simple activity enhancement strategy is also urgently needed. In particular, the well‐controlled synthesis of the well‐recognized metal–metal nanointer face in a single step remains a key challenge. Here, the synthesis of Cu‐supported Ni4Mo nanodots on MoOx nanosheets (Ni4Mo/MoOx) with controllable Ni4Mo particle size and d‐band structure is reported via a facile one‐step electrodeposition process. Density functional theory (DFT) calculations reveal that the active open‐shell effect from Ni‐3d‐band optimizes the electronic configuration. The Cu‐substrate enables the surface Ni–Mo alloy dots to be more electron‐rich, forming a local connected electron‐rich network, which boosts the charge transfer for effective binding of O‐related species and proton–electron charge exchange in the hydrogen evolution reaction. The Cu‐supported Ni4Mo/MoOx shows an ultralow overpotential of 16 mV at a current density of 10 mA cm?2 in 1 m KOH, demonstrating the smallest overpotential, at loadings as low as 0.27 mg cm?2, among all non‐noble metal catalysts reported to date. Moreover, an overpotential of 105 mV allows it to achieve a current density of 250 mA cm?2 in 70 °C 30% KOH, a remarkable performance for alkaline hydrogen evolution with competitive potential for applications. 相似文献
972.
Yu‐Zuo Wang Xu‐Yi Shan Li‐Po Ma Jia‐Wei Wang Da‐Wei Wang Zhang‐Quan Peng Hui‐Ming Cheng Feng Li 《Liver Transplantation》2019,9(12)
Understanding the electric double layer is essential for achieving efficient electrochemical energy storage technologies. A conventional solid–liquid electrode interface suffers from serious self‐discharge and a narrow voltage window, which makes the development of a solid–solid interface imperative. However, an in‐depth understanding of the electric double layer with a solid–solid interface is lacking. Here, a solid–solid interfacial electric double layer is proposed with excellent electrochemical performance. The solid layer is constructed by the electrochemical decomposition of lithium difluoro(oxalate)borate, which provides a desolvated environment for the establishment of a electric double layer. This makes a stronger interaction between the electrode surface and the ions. Based on this unique property, it is found that the solid–solid interfacial electric double layer has an increased capacitance, which suggests a way to develop high‐energy electrochemical capacitors. 相似文献
973.
Seven new polyhydroxypregnane glycosides, named cynotophyllosides P–V, together with three known analogs were isolated from the roots of Cynanchum otophyllum C.K.Schneid . Their structures were elucidated by a variety of spectroscopic techniques, as well as acid‐catalyzed hydrolysis. All isolates were tested for their immunological activities in vitro against Con A‐ and LPS‐induced proliferation of mice splenocytes. Immunoenhancing (for 1 , 9 ) and immunosuppressive (for 2 ) activities were observed. Furthermore, cynotophylloside R ( 3 ) showed immunomodulatory as it enhanced the proliferation of splenocytes in low concentration and suppressed immune cells in concentration more than 1.0 μg/ml. 相似文献
974.
Four new biphenyl derivatives ( 1 – 4 ), along with six known biphenyl derivatives ( 5 – 10 ) were isolated and elucidated by their detailed analyses of spectroscopic data and references from the aerial parts of Oenanthe javanica for the first time. Compounds ( 1 – 10 ) were assayed for their activities about the inhibition of COX‐2 enzyme in vitro for the first time. Compounds 1 , 2 , 4 , and 6 showed inhibitory activities against COX‐2 with IC50 values ranging from 22.18±0.29 to 108.54±0.42 μm . 相似文献
975.
Lifang Yang Jipeng Ma Ying Tan Qijun Zheng Maolong Dong Wei Guo Lize Xiong Jian Yang Jun Ren 《Journal of cellular and molecular medicine》2019,23(7):4640-4652
Hypertension contributes to the high cardiac morbidity and mortality. Although oxidative stress plays an essential role in hypertensive heart diseases, the mechanism remains elusive. Transgenic mice with cardiac overexpression of metallothionein, a heavy metal‐binding scavenger, were challenged with NG‐nitro‐L‐arginine methyl ester (L‐NAME) for 14 days prior to measurement of myocardial contractile and intracellular Ca2+ anomalies as well as cell signalling mechanisms using Western blot and immunofluorescence analysis. L‐NAME challenge elicited hypertension, macrophage infiltration, oxidative stress, inflammation and cardiac dysfunction manifested as increased proinflammatory macrophage marker F4/80, interleukin‐1β (IL‐1β), intracellular production, LV end systolic and diastolic diameters as well as depressed fractional shortening. L‐NAME treatment reduced mitochondrial membrane potential (MMP), impaired cardiomyocyte contractile and intracellular Ca2+ properties as evidenced by suppressed peak shortening, maximal velocity of shortening/relengthening, rise in intracellular Ca2+, along with elevated baseline and peak intracellular Ca2+. These unfavourable mechanical changes and decreased MMP (except blood pressure and macrophage infiltration) were alleviated by overexpression of metallothionein. Furthermore, the apoptosis markers including BAD, Bax, Caspase 9, Caspase 12 and cleaved Caspase 3 were up‐regulated while the anti‐apoptotic marker Bcl‐2 was decreased by L‐NAME treatment. Metallothionein transgene reversed L‐NAME‐induced changes in Bax, Bcl‐2, BAD phosphorylation, Caspase 9, Caspase 12 and cleaved Caspase 3. Our results suggest that metallothionein protects against L‐NAME‐induced myocardial contractile anomalies in part through inhibition of apoptosis. 相似文献
976.
977.
Dai Chunxiao Ma Qiao Li Yan Zhou Duandi Yang Bingyu Qu Yuanyuan 《Bioprocess and biosystems engineering》2019,42(12):1963-1971
Bioprocess and Biosystems Engineering - Indigo, one of the most widely used dyes, is mainly produced by chemical processes, which generate amounts of pollutants and need high energy consumption.... 相似文献
978.
The site-specific nature and ease of handling of clustered regularly interspaced palindromic repeat(CRISPR)/Cas9 has fulfilled the decades-long goal of genome engineering,and thus has pushed the biological sciences into a new era in which site-directed manipulation of DNA is no longer a short slab(Doudna and Charpentier,2014).The incomparable power of this system also enabled unprecedented new opportunities for practical applications in agriculture,ecosystem and human health(Liu,2017).However,with the extremely rapid development and application of CRISPR system,concerns about its bio-safety have been increasing(Caplan et al.,2015;Taning et al.,2017).While multiple studies have addressed this issue,alternative options for regulating Cas9 are of great interest.As has been proved by increasing evidences,another well?known concern is the off-target effects,which could not only confound research experiments or breeding,but also cause unwanted side effects in the forthcoming therapeutic uses(Fu et aL,2013;Taning et al.,2017;Zhang et al.,2018). 相似文献
979.
Oxymatrine(OMT), as the main active component of Sophoraflavescens, exhibits a variety of pharmacological properties,including anti-oxidative, anti-inflammatory, anti-tumor, and anti-viral activities, and currently is extensively employed to treat viral hepatitis; however, its effects on parvovirus infection have yet to be reported. In the present study, we investigated the effects of OMT on cell viability, virus DNA replication, viral gene expression, cell cycle, and apoptosis in Walter Reed canine cells/3873 D infected with minute virus of canines(MVC). OMT, at concentrations below 4 mmol/L(no cellular toxicity), was found to inhibit MVC DNA replication and reduce viral gene expression at both mRNA and protein levels, which was associated with the inhibition of cell cycle S-phase arrest in early-stage of MVC infection.Furthermore, OMT significantly increased cell viability, decreased MVC-infected cell apoptosis, and reduced the expression of activated caspase 3. Our results suggest that OMT has potential application in combating parvovirus infection. 相似文献
980.