全文获取类型
收费全文 | 1289篇 |
免费 | 18篇 |
国内免费 | 5篇 |
专业分类
系统科学 | 23篇 |
丛书文集 | 2篇 |
理论与方法论 | 31篇 |
现状及发展 | 708篇 |
研究方法 | 65篇 |
综合类 | 441篇 |
自然研究 | 42篇 |
出版年
2019年 | 10篇 |
2018年 | 24篇 |
2017年 | 25篇 |
2016年 | 27篇 |
2015年 | 20篇 |
2014年 | 25篇 |
2013年 | 28篇 |
2012年 | 40篇 |
2011年 | 75篇 |
2010年 | 37篇 |
2009年 | 14篇 |
2008年 | 47篇 |
2007年 | 31篇 |
2006年 | 42篇 |
2005年 | 52篇 |
2004年 | 42篇 |
2003年 | 45篇 |
2002年 | 37篇 |
2001年 | 35篇 |
2000年 | 23篇 |
1999年 | 18篇 |
1998年 | 13篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1985年 | 13篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 27篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 23篇 |
1975年 | 10篇 |
1974年 | 18篇 |
1973年 | 23篇 |
1972年 | 24篇 |
1971年 | 25篇 |
1970年 | 22篇 |
1969年 | 24篇 |
1968年 | 26篇 |
1967年 | 27篇 |
1966年 | 21篇 |
1965年 | 21篇 |
1964年 | 15篇 |
1954年 | 8篇 |
排序方式: 共有1312条查询结果,搜索用时 15 毫秒
31.
From April to July 2008, we surveyed for breeding plovers at 32 sites in the semiarid highlands of Jalisco, Aguascalientes, Zacatecas, and San Luis Potosí, in the Central Mexican High Plateau. We documented evidence or presumption of breeding Snowy Plovers ( Charadrius alexandrinus ) at 3 sites, Killdeer ( C. vociferus ) at 15 sites, and Mountain Plovers ( C. montanus ) at 1 site. Our surveys showed that the region is important breeding ground for only the Killdeer. We documented an apparent breeding range extension of the Mountain Plover to slightly more than 200 km south of its previously known breeding range. 相似文献
32.
Dense genotyping identifies and localizes multiple common and rare variant association signals in celiac disease 总被引:1,自引:0,他引:1
Trynka G Hunt KA Bockett NA Romanos J Mistry V Szperl A Bakker SF Bardella MT Bhaw-Rosun L Castillejo G de la Concha EG de Almeida RC Dias KR van Diemen CC Dubois PC Duerr RH Edkins S Franke L Fransen K Gutierrez J Heap GA Hrdlickova B Hunt S Izurieta LP Izzo V Joosten LA Langford C Mazzilli MC Mein CA Midah V Mitrovic M Mora B Morelli M Nutland S Núñez C Onengut-Gumuscu S Pearce K Platteel M Polanco I Potter S Ribes-Koninckx C Ricaño-Ponce I Rich SS Rybak A Santiago JL Senapati S Sood A 《Nature genetics》2011,43(12):1193-1201
Using variants from the 1000 Genomes Project pilot European CEU dataset and data from additional resequencing studies, we densely genotyped 183 non-HLA risk loci previously associated with immune-mediated diseases in 12,041 individuals with celiac disease (cases) and 12,228 controls. We identified 13 new celiac disease risk loci reaching genome-wide significance, bringing the number of known loci (including the HLA locus) to 40. We found multiple independent association signals at over one-third of these loci, a finding that is attributable to a combination of common, low-frequency and rare genetic variants. Compared to previously available data such as those from HapMap3, our dense genotyping in a large sample collection provided a higher resolution of the pattern of linkage disequilibrium and suggested localization of many signals to finer scale regions. In particular, 29 of the 54 fine-mapped signals seemed to be localized to single genes and, in some instances, to gene regulatory elements. Altogether, we define the complex genetic architecture of the risk regions of and refine the risk signals for celiac disease, providing the next step toward uncovering the causal mechanisms of the disease. 相似文献
33.
Gutiérrez-López MD Gilsanz A Yáñez-Mó M Ovalle S Lafuente EM Domínguez C Monk PN González-Alvaro I Sánchez-Madrid F Cabañas C 《Cellular and molecular life sciences : CMLS》2011,68(19):3275-3292
ADAM17/TACE is a metalloproteinase responsible for the shedding of the proinflammatory cytokine TNF-α and many other cell
surface proteins involved in development, cell adhesion, migration, differentiation, and proliferation. Despite the important
biological function of ADAM17, the mechanisms of regulation of its metalloproteinase activity remain largely unknown. We report
here that the tetraspanin CD9 and ADAM17 partially co-localize on the surface of endothelial and monocytic cells. In situ
proximity ligation, co-immunoprecipitation, crosslinking, and pull-down experiments collectively demonstrate a direct association
between these molecules. Functional studies reveal that treatment with CD9-specific antibodies or neoexpression of CD9 exert
negative regulatory effects on ADAM17 sheddase activity. Conversely, CD9 silencing increased the activity of ADAM17 against
its substrates TNF-α and ICAM-1. Taken together, our results show that CD9 associates with ADAM17 and, through this interaction,
negatively regulates the sheddase activity of ADAM17. 相似文献
34.
Translation initiation is a critical step in protein synthesis. Previously, two major mechanisms of initiation were considered
as essential: prokaryotic, based on SD interaction; and eukaryotic, requiring cap structure and ribosomal scanning. Although
discovered decades ago, cap-independent translation has recently been acknowledged as a widely spread mechanism in viruses,
which may take place in some cellular mRNA translations. Moreover, it has become evident that translation can be initiated
on the leaderless mRNA in all three domains of life. New findings demonstrate that other distinguishable types of initiation
exist, including SD-independent in Bacteria and Archaea, and various modifications of 5′ end-dependent and internal initiation
mechanisms in Eukarya. Since translation initiation has developed through the loss, acquisition, and modification of functional
elements, all of which have been elevated by competition with viral translation in a large number of organisms of different
complexity, more variation in initiation mechanisms can be anticipated. 相似文献
35.
Lopez-Castejón G Baroja-Mazo A Pelegrín P 《Cellular and molecular life sciences : CMLS》2011,68(18):3095-3107
Plasticity is a well-known property of macrophages that is controlled by different changes in environmental signals. Macrophage
polarization is regarded as a spectrum of activation phenotypes adjusted from one activation extreme, the classic (M1), to
the other, the alternative (M2) activation. Here we show, in vitro and in vivo, that both M1 and M2 macrophage phenotypes
are tightly coupled to specific patterns of gene expression. Novel M2-associated markers were characterized and identified
as genes controlling the extracellular metabolism of ATP to generate pyrophosphates (PPi). Stimulation of M1 macrophages with
PPi dampens both NLR and TLR signaling and thus mediates cytokine production. In this context extracellular PPi enhanced the
resolution phase of a murine peritonitis model via a decrease in pro-inflammatory cytokine production. Therefore, our study
reveals an additional level of plasticity modulating the resolution of inflammation. 相似文献
36.
Rodríguez-Muñoz M Sánchez-Blázquez P Vicente-Sánchez A Bailón C Martín-Aznar B Garzón J 《Cellular and molecular life sciences : CMLS》2011,68(17):2933-2949
A series of pharmacological and physiological studies have demonstrated the functional cross-regulation between MOR and NMDAR.
These receptors coexist at postsynaptic sites in midbrain periaqueductal grey (PAG) neurons, an area implicated in the analgesic
effects of opioids like morphine. In this study, we found that the MOR-associated histidine triad nucleotide-binding protein
1 (HINT1) is essential for maintaining the connection between the NMDAR and MOR. Morphine-induced analgesic tolerance is prevented
and even rescued by inhibiting PKC or by antagonizing NMDAR. However, in the absence of HINT1, the MOR becomes supersensitive
to morphine before suffering a profound and lasting desensitization that is refractory to PKC inhibition or NMDAR antagonism.
Thus, HINT1 emerges as a key protein that is critical for sustaining NMDAR-mediated regulation of MOR signaling strength.
Thus, HINT1 deficiency may contribute to opioid-intractable pain syndromes by causing long-term MOR desensitization via mechanisms
independent of NMDAR. 相似文献
37.
The problem of prediction in time series using nonparametric functional techniques is considered. An extension of the local linear method to regression with functional explanatory variable is proposed. This forecasting method is compared with the functional Nadaraya–Watson method and with finite‐dimensional nonparametric predictors for several real‐time series. Prediction intervals based on the bootstrap and conditional distribution estimation for those nonparametric methods are also compared. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
38.
One of the most important issues to resolve in parts manufactured from rapid manufacturing (RM) technologies is to know their behavior working under real conditions. Total quality manufacturing (TQM) is only possible if mechanical properties are well known in the design stage depending on the processing parameters. This work is mainly focused on testing of several samples made with different selective laser sintering (SLS) parameters and technologies. This procedure is the starting point to establish a basis for designing for RM and the standardization of RM testing. The experiments and the analysis of variance (ANOVA) analyzed the effects of several factors on mechanical properties. The SLS technologies were 3DSystem and EOS. The results show which factor has a large effect on the variables and the interaction between them. The conclusions are very useful for developing rules for designing (designing for RM) and creating new standard rules (ISO, AISI, and DIN) for RM materials and parts testing. The ANOVA gives a better knowledge of the effects of these factors and eliminates unimportant parameters. 相似文献
39.
L Feliubadaló M Font J Purroy F Rousaud X Estivill V Nunes E Golomb M Centola I Aksentijevich Y Kreiss B Goldman M Pras D L Kastner E Pras P Gasparini L Bisceglia E Beccia M Gallucci L de Sanctis A Ponzone G F Rizzoni L Zelante M T Bassi A L George M Manzoni A De Grandi M Riboni J K Endsley A Ballabio G Borsani N Reig E Fernández R Estévez M Pineda D Torrents M Camps J Lloberas A Zorzano M Palacín 《Nature genetics》1999,23(1):52-57
40.
Wójcik C 《Cellular and molecular life sciences : CMLS》1999,56(11-12):908-917
The proteasome (multicatalytic proteinase complex, prosome) is a major cytoplasmic proteolytic enzyme, responsible for degradation of the vast majority of intracellular proteins. Proteins degraded by the proteasome are usually tagged with multiple ubiquitin moieties, conjugated to the substrates by a complicated cascade of enzymes. Over the last years, evidence has accumulated that changes in the expression and activity of the different components of the ubiquitin-proteasome system occur during apoptosis. Proteasome inhibitors have been used to induce apoptosis in various cell types, whereas in others, these compounds were able to prevent apoptosis induced by different stimuli. The proteasome mediated step(s) in apoptosis is located upstream of mitochondrial changes and caspase activation, and can involve in different systems Bcl-2, Jun N-terminal kinase, heat shock proteins, Myc, p53, polyamines and other factors. 相似文献