全文获取类型
收费全文 | 30341篇 |
免费 | 2458篇 |
国内免费 | 2178篇 |
出版年
2024年 | 10篇 |
2023年 | 382篇 |
2022年 | 502篇 |
2021年 | 1570篇 |
2020年 | 1158篇 |
2019年 | 1556篇 |
2018年 | 1412篇 |
2017年 | 992篇 |
2016年 | 1432篇 |
2015年 | 1979篇 |
2014年 | 2380篇 |
2013年 | 2587篇 |
2012年 | 2824篇 |
2011年 | 2541篇 |
2010年 | 1485篇 |
2009年 | 1378篇 |
2008年 | 1616篇 |
2007年 | 1423篇 |
2006年 | 1169篇 |
2005年 | 909篇 |
2004年 | 750篇 |
2003年 | 716篇 |
2002年 | 541篇 |
2001年 | 484篇 |
2000年 | 461篇 |
1999年 | 427篇 |
1998年 | 262篇 |
1997年 | 250篇 |
1996年 | 247篇 |
1995年 | 229篇 |
1994年 | 218篇 |
1993年 | 150篇 |
1992年 | 199篇 |
1991年 | 179篇 |
1990年 | 126篇 |
1989年 | 98篇 |
1988年 | 81篇 |
1987年 | 69篇 |
1986年 | 39篇 |
1985年 | 44篇 |
1984年 | 24篇 |
1983年 | 30篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1965年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Understanding of the systematics and evolution of the Brassicaceae has advanced greatly in recent years. In particular, molecular techniques offer a way to address issues of homoplasy that had limited morphology-based research. In this study, we used sequence data from chloroplast, mitochondrial, and nuclear genomes to construct the phylogeny of Brassicaceae. We adopted maximum parsimony, maximum likelihood, and Bayesian methods to illustrate the relationships of 71 species belonging to 51 genera. Results from trnS(GCU)-trnG(UUC), nad7 second intron, and pistillata (PI) first intron analyses supported the delimitation of Lineages I–III and agreed with previous findings from phyA, ITS, and ndhF analyses. The results indicated that Pachypterygium should be placed in the tribe Isatideae. The position of Leiospora agreed with speculation based on morphology. Furthermore, Conringia planisiliqua together with Orychophragmus violaceus can be recognized as a new tribe as proposed by previous studies. Finally, this study also supported the recently recognized new tribes Dontostemoneae and Erysimeae. 相似文献
52.
Zhisheng Zhang Delin Mo Peiqing Cong Zuyong He Fei Ling Anning Li Yuna Niu Xiao Zhao Chunyan Zhou Yaosheng Chen 《Molecular biology reports》2010,37(3):1611-1618
The product of transmembrane and coiled-coil domains 1 (TMCO1) gene is a member of DUF841 superfamily of several eukaryotic proteins with unknown function. The partial DNA sequence of
porcine TMCO1 was first cloned with a pig 567 bp ORF encoding 188 amino acids. By tissues expression analysis, the TMCO1 was found highly expressed in the liver, kidney and heart. The porcine TMCO1 protein was subsequently demonstrated to localize
in the mitochondrion by confocal fluorescence microscopy. This data provides an important basis for conducing further studies
on the functions and regulatory mechanisms underlying the role of TMCO1 gene. 相似文献
53.
A new polypore, Perenniporia tibetica, collected in Xizang (Tibet), southwestern China, is described and illustrated on the basis of morphological and molecular characters. Perenniporia tibetica is characterized by an annual growth habit, resupinate basidiocarps with a creambuff to pinkish-buff pore surface and white to cream-colored rhizomorphs, a dimitic hyphal system with slightly dextrinoid and distinctly cyanophilous skeletal hyphae, and basidiospores that are ellipsoid, truncate or not, strongly dextrinoid, and cyanophilous, 6.7–8.7 × 5.3–6.8 μm. Its preliminary phylogenetic relationships are inferred based on sequence data from the ribosomal ITS and LSU regions, both suggesting that P. tibetica forms a distinct lineage in the genus Perenniporia. 相似文献
54.
A “safe” or sub-threshold dose is often estimated for oral toxicity of substances in order to protect humans from adverse health effects. This dose is referred to by several terms: reference dose (RfD), tolerable daily intake (TDI), and acceptable daily intake (ADI). Similarly, tolerable concentration (TC), and reference concentration (RfC) are commonly used terms for a “safe” concentration for inhalation. The process of deriving these doses generally involves identifying a no observed, or lowest observed adverse effect level (NOAEL or LOAEL) in animals, or humans, and application of uncertainty factors to account for the extrapolation from laboratory animals to humans and/or from an average human to a sensitive human. Public health agencies have begun to consider using a data derived approach, which uses available toxicokinetic and toxicodynamic data in the determination of uncertainty factors, rather than relying on the standard default values. Recently two different tolerable daily intake risk values were derived by two different World Health Organization (WHO) work groups. The International Programme on Chemical Safety, and the Working Group on Chemical Substances in Drinking Water both used the approach developed by Renwick (1993); however, the two groups interpreted and used the available data differently. The result was a difference of over twofold in the total uncertainty factor used. This review compares and contrasts the two approaches used by these WHO work groups. 相似文献
55.
Hong-Jin Zhao Yan Li De-Yu Wang Hai-Tao Yuan 《Journal of cellular and molecular medicine》2021,25(23):11031-11034
The administration of ACEI/ARB (angiotensin-converting enzyme inhibitors/Angiotension II receptor blockers) in COVID-19 (coronavirus disease 2019) patients with hypertension exhibits a lower risk of mortality compared with ACEI/ARB non-users. In this context, an important question arises: is ACEI or ARB more suitable for the treatment of hypertensive COVID-19 patients? Taken into consideration the following four rationales, ARB may offer a more significant benefit than ACEI for the short-term treatment of hypertensive COVID-19 patients: 1. ACEI has no inhibition on non-ACE-mediated Ang II production under infection conditions, whereas ARB can function properly regardless of how Ang II is produced; 2. ACEI-induced bradykinin accumulation may instigate severe ARDS while ARB has no effects on kinin metabolism; 3. ARB alleviates viscous sputa production and inflammatory reaction significantly in contrast to ACEI; 4. ARB may attenuate the lung fibrosis induced by mechanical ventilation in severe patients and improve their prognosis significantly compared with ACEI. To examine the advantages of ARB over ACEI on hypertensive COVID-19 patients, retrospective case-control studies comparing the clinical outcomes for COVID-19 patients receiving ARB or ACEI treatment is strikingly needed in order to provide guidance for the clinical application. 相似文献
56.
57.
58.
Members of the casein kinase 1 (CK1) family are evolutionarily conserved eukaryotic protein kinases involved in various cellular, physiological, and developmental processes in yeast. However, the biological roles of CK1 members in plants are poorly understood. Here, we report that an Arabidopsis CK1 member named casein kinase 1-like 8 (CKL8) was ubiquitously expressed in all plant organs, mainly in the stems of seedlings according to quantitative real-time PCR. Western blotting showed a remarkable expression of the AtCKL8 gene in transgenic plants induced by high salinity. A histochemical assay of AtCKL8 promoter::GUS expression revealed that the AtCKL8 promoter is very active in both seedlings and adult plants subjected to the salinity stress, while no GUS activity was detectable in all the transgenic plants grown under normal conditions. In a subcellular distribution analysis, the AtCKL8-GFP fusion protein was localized mainly in the cell membrane. AtCKL8-overexpressing transgenic plants showed an insensitivity to high salinity and an early flowering phenotype. Overall, these findings suggest that AtCKL8 plays a positive role in NaCl signaling and improves salt stress tolerance in transgenic Arabidopsis. 相似文献
59.
The isothermal crystallisation of polyethylene (PE) chains around single PE lamella in vacuum is investigated by molecular dynamic simulation. The crystallisation process is analysed in terms of the orientational order parameters, principal moments of inertia for the simulated systems. The effects of charge interactions between the polymer chains and lamella are discussed. It is found that the crystallisation process for uncharged systems can be divided into three stages: (1) adsorption, (2) orientation and (3) arrangement. The single polymer lamella changes a little during the three stages. PE chains are arranged parallel to the chain direction of the stems in the crystalline state. When considering the effect of charge interactions between the polymer chains and lamella, a different crystallisation process appears. The single polymer lamella is affected by the charged polymer chains. 相似文献
60.
In-depth structural characterization of lipids is an essential component of lipidomics. There has been a rapid expansion of mass spectrometry methods that are capable of resolving lipid isomers at various structural levels over the past decade. These developments finally make deep-lipidotyping possible, which provides new means to study lipid metabolism and discover new lipid biomarkers. In this review, we discuss recent advancements in tandem mass spectrometry (MS/MS) methods for identification of complex lipids beyond the species (known headgroup information) and molecular species (known chain composition) levels. These include identification at the levels of carbon-carbon double bond (C=C) location and sn-position, as well as characterization of acyl chain modifications. We also discuss the integration of isomer-resolving MS/MS methods with different lipid analysis workflows and their applications in lipidomics. The results showcase the distinct capabilities of deep-lipidotyping in untangling the metabolism of individual isomers and sensitive phenotyping by using relative fractional quantitation of the isomers. 相似文献