全文获取类型
收费全文 | 2870篇 |
免费 | 225篇 |
国内免费 | 2篇 |
出版年
2023年 | 15篇 |
2022年 | 11篇 |
2021年 | 62篇 |
2020年 | 38篇 |
2019年 | 44篇 |
2018年 | 55篇 |
2017年 | 57篇 |
2016年 | 96篇 |
2015年 | 151篇 |
2014年 | 169篇 |
2013年 | 186篇 |
2012年 | 234篇 |
2011年 | 253篇 |
2010年 | 148篇 |
2009年 | 137篇 |
2008年 | 181篇 |
2007年 | 171篇 |
2006年 | 159篇 |
2005年 | 140篇 |
2004年 | 121篇 |
2003年 | 131篇 |
2002年 | 95篇 |
2001年 | 33篇 |
2000年 | 16篇 |
1999年 | 25篇 |
1998年 | 27篇 |
1997年 | 22篇 |
1996年 | 18篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1990年 | 10篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 21篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1974年 | 6篇 |
1951年 | 9篇 |
1950年 | 6篇 |
1941年 | 5篇 |
1938年 | 5篇 |
排序方式: 共有3097条查询结果,搜索用时 31 毫秒
81.
Sanna Tiikkaja Sven Sandin Ninoa Malki Bitte Modin P?r Sparén Christina M. Hultman 《PloS one》2013,8(11)
Objectives
This study explored how adult social class and social mobility between parental and own adult social class is related to psychiatric disorder.Material and Methods
In this prospective cohort study, over 1 million employed Swedes born in 1949-1959 were included. Information on parental class (1960) and own mid-life social class (1980 and 1990) was retrieved from the censuses and categorised as High Non-manual, Low Non-manual, High Manual, Low Manual and Self-employed. After identifying adult class, individuals were followed for psychiatric disorder by first admission of schizophrenia, alcoholism and drug dependency, affective psychosis and neurosis or personality disorder (N=24 659) from the Swedish Patient Register. We used Poisson regression analysis to estimate first admission rates of psychiatric disorder per 100 000 person-years and relative risks (RR) by adult social class (treated as a time-varying covariate). The RRs of psychiatric disorder among the Non-manual and Manual classes were also estimated by magnitude of social mobility.Results
The rate of psychiatric disorder was significantly higher among individuals belonging to the Low manual class as compared with the High Non-manual class. Compared to High Non-manual class, the risk for psychiatric disorder ranged from 2.07 (Low Manual class) to 1.38 (Low Non-manual class). Parental class had a minor impact on these estimates. Among the Non-manual and Manual classes, downward mobility was associated with increased risk and upward mobility with decreased risk of psychiatric disorder. In addition, downward mobility was inversely associated with the magnitude of social mobility, independent of parental class.Conclusions
Independently of parental social class, the risk of psychiatric disorder increases with increased downward social mobility and decreases with increased upward mobility. 相似文献82.
Elasmosaurid plesiosaurians are renowned for their immensely long necks, and indeed, possessed the highest number of cervical vertebrae for any known vertebrate. Historically, the largest count has been attributed to the iconic Elasmosaurus platyurus from the Late Cretaceous of Kansas, but estimates for the total neck series in this taxon have varied between published reports. Accurately determining the number of vertebral centra vis-à-vis the maximum length of the neck in plesiosaurians has significant implications for phylogenetic character designations, as well as the inconsistent terminology applied to some osteological structures. With these issues in mind, we reassessed the holotype of E. platyurus as a model for standardizing the debated cervical-dorsal transition in plesiosaurians, and during this procedure, documented a “lost” cervical centrum. Our revision also advocates retention of the term “pectorals” to describe the usually three or more distinctive vertebrae close to the cranial margin of the forelimb girdle that bear a functional rib facet transected by the neurocentral suture, and thus conjointly formed by both the parapophysis on the centrum body and diapophysis from the neural arch (irrespective of rib length). This morphology is unambiguously distinguishable from standard cervicals, in which the functional rib facet is borne exclusively on the centrum, and dorsals in which the rib articulation is situated above the neurocentral suture and functionally borne only by the transverse process of the neural arch. Given these easily distinguishable definitions, the maximum number of neck vertebrae preserved in E. platyurus is 72; this is only three vertebrae shorter than the recently described Albertonectes, which together with E. platyurus constitute the “longest necked” animals ever to have lived. 相似文献
83.
84.
85.
Jorma J. de Ronde Guillem Rigaill Sven Rottenberg Sjoerd Rodenhuis Lodewyk F. A. Wessels 《Nucleic acids research》2013,41(21):e200
Traditional methods that aim to identify biomarkers that distinguish between two groups, like Significance Analysis of Microarrays or the t-test, perform optimally when such biomarkers show homogeneous behavior within each group and differential behavior between the groups. However, in many applications, this is not the case. Instead, a subgroup of samples in one group shows differential behavior with respect to all other samples. To successfully detect markers showing such imbalanced patterns of differential signal, a different approach is required. We propose a novel method, specifically designed for the Detection of Imbalanced Differential Signal (DIDS). We use an artificial dataset and a human breast cancer dataset to measure its performance and compare it with three traditional methods and four approaches that take imbalanced signal into account. Supported by extensive experimental results, we show that DIDS outperforms all other approaches in terms of power and positive predictive value. In a mouse breast cancer dataset, DIDS is the only approach that detects a functionally validated marker of chemotherapy resistance. DIDS can be applied to any continuous value data, including gene expression data, and in any context where imbalanced differential signal is manifested. 相似文献
86.
Background and Aims
Tecophilaeaceae (27 species distributed in eight genera) have a disjunct distribution in California, Chile and southern and tropical mainland Africa. Moreover, although the family mainly occurs in arid ecosystems, it has colonized three Mediterranean-type ecosystems. In this study, the spatio-temporal history of the family is examined using DNA sequence data from six plastid regions.Methods
Modern methods in divergence time estimation (BEAST), diversification (LTT and GeoSSE) and biogeography (LAGRANGE) are applied to infer the evolutionary history of Tecophilaeaceae. To take into account dating and phylogenetic uncertainty, the biogeographical inferences were run over a set of dated Bayesian trees and the analyses were constrained according to palaeogeographical evidence.Key Results
The analyses showed that the current distribution and diversification of the family were influenced primarily by the break up of Gondwana, separating the family into two main clades, and the establishment of a Mediterranean climate in Chile, coinciding with the radiation of Conanthera. Finally, unlike many other groups, no shifts in diversification rates were observed associated with the dispersals in the Cape region of South Africa.Conclusions
Although modest in size, Tecophilaeaceae have a complex spatio-temporal history. The family is now most diverse in arid ecosystems in southern Africa, but is expected to have originated in sub-tropical Africa. It has subsequently colonized Mediterranean-type ecosystems in both the Northern and Southern Hemispheres, but well before the onset of the Mediterranean climate in these regions. Only one lineage, genus Conanthera, has apparently diversified to any extent under the impetus of a Mediterranean climate. 相似文献87.
Trotz intensiver Bemühungen im Bereich des Pflanzenschutzes sind weltweit erhebliche Verluste im Bereich pflanzlicher Erntegüter zu verzeichnen. Rund ein Drittel der Verluste werden mikrobiellen Schaderregern, also Pilzen, Bakterien und Viren, zugeschrieben. Besonders schwierig ist der Tatsache zu begegnen, dass Pilze gegenüber spezifisch wirkenden Fungiziden Insensitivitäten bzw. Resistenzen entwickeln. Aus diesem Grunde muss über geeignete Strategien beim Fungizideinsatz, beim ‘Disease management’ und bei der Suche nach neuen, hochwirksamen Fungiziden nachgedacht werden. Der Erfolg bei der Suche nach neuen Fungiziden wird stark davon abhängen, ob neue Zielmoleküle für potentielle Fungizide entdeckt werden können. Dabei können moderne molekulargenetische Techniken von großem Nutzen sein. 相似文献
88.
Small interfering RNA (siRNA) is potent and highly specific for gene silencing and there is currently a lot of enthusiasm for developing siRNA into a drug. However, for most therapeutic applications of siRNA, delivery systems are needed. These delivery systems have multiple requirements and should on one hand ideally be stable carriers protecting the siRNA from degradation and on the other hand assist the siRNA in overcoming membrane barriers for intracellular delivery to the cytosol. Long-circulating liposomes, which are sensitive to secretory phospholipase A2 (sPLA2) are feasible delivery systems for systemic administration of drugs due to their passive targeting to pathological tissue via the enhanced permeability and retention (EPR) effect and their site-specific, enzyme-triggered release of encapsulated drug in response to sPLA2 which exists locally at elevated levels at, e.g,. sites of inflammation. However, recent data suggest that endosomal membrane destabilizing approaches could be addressed to design sPLA2-sensitive liposomes as successful delivery systems for siRNA to the RNA interference pathway in the cytoplasm upon systemic administration. 相似文献
89.
Sven N. Nielsen 《Pal?ontologische Zeitschrift》2013,87(1):33-66
A new Pliocene (3.4 Ma) mollusk fauna from Mejillones Peninsula, northern Chile is described and compared with the Pliocene La Cueva fauna of little constrained age from central Chile and some species from the Huenteguapi Sandstone overlying the Ranquil Formation on Arauco Peninsula, south central Chile. Preliminary correlation is based on faunal similarities. A total of 45 taxa were identified, of which Cyclocardia kieli sp. nov. is new to science. New combinations are Macron escalonia (Vermeij and DeVries, 1997), Austrofusus steinmanni (Möricke, 1896) and Leukoma antiqua (King, 1832). For several species, the oldest occurrences and range extensions are reported. Co-occurrence of warm water taxa, previously assigned to MIS 11, and typical Pliocene taxa on Mejillones cannot be confirmed. Pliocene and Pleistocene mollusk faunas from Mejillones are listed for comparison. 相似文献
90.
Sven Moller-Tank Andrew S. Kondratowicz Robert A. Davey Paul D. Rennert Wendy Maury 《Journal of virology》2013,87(15):8327-8341
The cell surface receptor T cell immunoglobulin mucin domain 1 (TIM-1) dramatically enhances filovirus infection of epithelial cells. Here, we showed that key phosphatidylserine (PtdSer) binding residues of the TIM-1 IgV domain are critical for Ebola virus (EBOV) entry through direct interaction with PtdSer on the viral envelope. PtdSer liposomes but not phosphatidylcholine liposomes competed with TIM-1 for EBOV pseudovirion binding and transduction. Further, annexin V (AnxV) substituted for the TIM-1 IgV domain, supporting a PtdSer-dependent mechanism. Our findings suggest that TIM-1-dependent uptake of EBOV occurs by apoptotic mimicry. Additionally, TIM-1 enhanced infection of a wide range of enveloped viruses, including alphaviruses and a baculovirus. As further evidence of the critical role of enveloped-virion-associated PtdSer in TIM-1-mediated uptake, TIM-1 enhanced internalization of pseudovirions and virus-like proteins (VLPs) lacking a glycoprotein, providing evidence that TIM-1 and PtdSer-binding receptors can mediate virus uptake independent of a glycoprotein. These results provide evidence for a broad role of TIM-1 as a PtdSer-binding receptor that mediates enveloped-virus uptake. Utilization of PtdSer-binding receptors may explain the wide tropism of many of these viruses and provide new avenues for controlling their virulence. 相似文献