全文获取类型
收费全文 | 3976篇 |
免费 | 356篇 |
国内免费 | 2篇 |
专业分类
4334篇 |
出版年
2023年 | 26篇 |
2022年 | 40篇 |
2021年 | 61篇 |
2020年 | 53篇 |
2019年 | 60篇 |
2018年 | 65篇 |
2017年 | 84篇 |
2016年 | 123篇 |
2015年 | 178篇 |
2014年 | 223篇 |
2013年 | 255篇 |
2012年 | 333篇 |
2011年 | 304篇 |
2010年 | 218篇 |
2009年 | 170篇 |
2008年 | 232篇 |
2007年 | 249篇 |
2006年 | 204篇 |
2005年 | 199篇 |
2004年 | 181篇 |
2003年 | 156篇 |
2002年 | 179篇 |
2001年 | 50篇 |
2000年 | 50篇 |
1999年 | 52篇 |
1998年 | 47篇 |
1997年 | 31篇 |
1996年 | 45篇 |
1995年 | 32篇 |
1994年 | 31篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1991年 | 28篇 |
1990年 | 27篇 |
1989年 | 32篇 |
1988年 | 33篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1974年 | 7篇 |
1973年 | 14篇 |
排序方式: 共有4334条查询结果,搜索用时 15 毫秒
131.
Solar Cells: Large Efficiency Improvement in Cu2ZnSnSe4 Solar Cells by Introducing a Superficial Ge Nanolayer (Adv. Energy Mater. 21/2015) 下载免费PDF全文
132.
Aurélien Saghaï Samiran Banjeree Florine Degrune Anna Edlinger Pablo García-Palacios Gina Garland Marcel G. A. van der Heijden Chantal Herzog Fernando T. Maestre David S. Pescador Laurent Philippot Matthias C. Rillig Sana Romdhane Sara Hallin 《Environmental microbiology》2022,24(1):341-356
Archaeal communities in arable soils are dominated by Nitrososphaeria, a class within Thaumarchaeota comprising all known ammonia-oxidizing archaea (AOA). AOA are key players in the nitrogen cycle and defining their niche specialization can help predicting effects of environmental change on these communities. However, hierarchical effects of environmental filters on AOA and the delineation of niche preferences of nitrososphaerial lineages remain poorly understood. We used phylogenetic information at fine scale and machine learning approaches to identify climatic, edaphic and geomorphological drivers of Nitrososphaeria and other archaea along a 3000 km European gradient. Only limited insights into the ecology of the low-abundant archaeal classes could be inferred, but our analyses underlined the multifactorial nature of niche differentiation within Nitrososphaeria. Mean annual temperature, C:N ratio and pH were the best predictors of their diversity, evenness and distribution. Thresholds in the predictions could be defined for C:N ratio and cation exchange capacity. Furthermore, multiple, independent and recent specializations to soil pH were detected in the Nitrososphaeria phylogeny. The coexistence of widespread ecophysiological differences between closely related soil Nitrososphaeria highlights that their ecology is best studied at fine phylogenetic scale. 相似文献
133.
Information structure facilitates communication between interlocutors by highlighting relevant information. It has previously been shown that information structure modulates the depth of semantic processing. Here we used event-related potentials to investigate whether information structure can modulate the depth of syntactic processing. In question-answer pairs, subtle (number agreement) or salient (phrase structure) syntactic violations were placed either in focus or out of focus through information structure marking. P600 effects to these violations reflect the depth of syntactic processing. For subtle violations, a P600 effect was observed in the focus condition, but not in the non-focus condition. For salient violations, comparable P600 effects were found in both conditions. These results indicate that information structure can modulate the depth of syntactic processing, but that this effect depends on the salience of the information. When subtle violations are not in focus, they are processed less elaborately. We label this phenomenon the Chomsky illusion. 相似文献
134.
The mechanism of nutrient transfer from the digestive system to the gonad acini and developing oocytes was investigated in the gonad-intestinal loop system of the queen scallop Pecten maximus L. Ferritin was injected directly into the purged intestine of specimens from the wild. Subsequently, a histochemical reaction and transmission electron microscopy were used to localize ferritin in various cell types. Ferritin was rapidly absorbed by the intestinal epithelium, and then appeared in hemocytes in the surrounding connective tissue. In the hemocytes, ferritin was stored in variously sized inclusions, as well as in the general cytoplasm. In all sections examined for the 12 experimental individuals, hemocytes were always found in association with connective tissue fibers extending from the base of the intestinal epithelium to gonad acini. After 30-min incubation, ferritin appeared inside the acini of all individuals. Ferritin-bearing cells were rarely found in association with male acini or gametes, nor with mature female gametes, but often with developing female gametes. Not all individuals showed the same temporal dynamics of ferritin transport, suggesting that nutrient transfer to oocytes is either not a continuous process, or that among individuals, transfer is not synchronized on short time scales. This is the first demonstration of a pathway of nutrient transfer from the intestine, and more generally the digestive system, to developing oocytes in the Bivalvia. 相似文献
135.
Jimmy Stalin Karim Harhouri Lucas Hubert Caroline Subrini Daniel Lafitte Jean-Claude Lissitzky Nadia Elganfoud Stéphane Robert Alexandrine Foucault-Bertaud Elise Kaspi Florence Sabatier Michel Aurrand-Lions Nathalie Bardin Lars Holmgren Fran?oise Dignat-George Marcel Blot-Chabaud 《The Journal of biological chemistry》2013,288(13):8991-9000
The melanoma cell adhesion molecule (CD146) contains a circulating proteolytic variant (sCD146), which is involved in inflammation and angiogenesis. Its circulating level is modulated in different pathologies, but its intracellular transduction pathways are still largely unknown. Using peptide pulldown and mass spectrometry, we identified angiomotin as a sCD146-associated protein in endothelial progenitor cells (EPC). Interaction between angiomotin and sCD146 was confirmed by enzyme-linked immunosorbent assay (ELISA), homogeneous time-resolved fluorescence, and binding of sCD146 on both immobilized recombinant angiomotin and angiomotin-transfected cells. Silencing angiomotin in EPC inhibited sCD146 angiogenic effects, i.e. EPC migration, proliferation, and capacity to form capillary-like structures in Matrigel. In addition, sCD146 effects were inhibited by the angiomotin inhibitor angiostatin and competition with recombinant angiomotin. Finally, binding of sCD146 on angiomotin triggered the activation of several transduction pathways that were identified by antibody array. These results delineate a novel signaling pathway where sCD146 binds to angiomotin to stimulate a proangiogenic response. This result is important to find novel target cells of sCD146 and for the development of therapeutic strategies based on EPC in the treatment of ischemic diseases. 相似文献
136.
Yíngyún Caì Shu?qìng Yú Steven Mazur Lián D?ng Krisztina Janosko Téngfēi Zhāng Marcel A. Müller Lisa E. Hensley Sina Bavari Peter B. Jahrling Sheli R. Radoshitzky Jens H. Kuhn 《Journal of virology》2013,87(24):13930-13935
Ocozocoautla de Espinosa virus (OCEV) is a novel, uncultured arenavirus. We found that the OCEV glycoprotein mediates entry into grivet and bat cells through transferrin receptor 1 (TfR1) binding but that OCEV glycoprotein precursor (GPC)-pseudotyped retroviruses poorly entered 53 human cancer cell lines. Interestingly, OCEV and Tacaribe virus could use bat, but not human, TfR1. Replacing three human TfR1 amino acids with their bat ortholog counterparts transformed human TfR1 into an efficient OCEV and Tacaribe virus receptor. 相似文献
137.
A method is described for purification of MSV-MuLV from culture supernatant of chronically infected 78A1 rat embryo cell line. This method involves direct polyethylene glycol-NaCl precipitation of the low speed supernatant of culture fluid followed by digestion of the pellet with trypsin. This procedure efficiently disrupts large aggregates which normally entrap most of the virus. Highly purified virus can be obtained in very good yield by a combination of sedimentation velocity and isopycnic centrifugation : yields up to 100 A280 units (17 mg of protein) of purified virus per liter of culture fluid can be observed. This procedure appears well suited for large scale isolation of virion associated enzymatic activities. 相似文献
138.
Wayne Reeve Rui Tian Sofie De Meyer Vanessa Melino Jason Terpolilli Julie Ardley Ravi Tiwari John Howieson Ronald Yates Graham O’Hara Mohamed Ninawi Hazuki Teshima David Bruce Chris Detter Roxanne Tapia Cliff Han Chia-Lin Wei Marcel Huntemann James Han I-Min Chen Konstantinos Mavromatis Victor Markowitz Natalia Ivanova Galina Ovchinnikova Ioanna Pagani Amrita Pati Lynne Goodwin Sam Pitluck Tanja Woyke Nikos Kyrpides 《Standards in genomic sciences》2013,9(2):243-253
Rhizobium leguminosarum bv. trifolii strain TA1 is an aerobic, motile, Gram-negative, non-spore-forming rod that is an effective nitrogen fixing microsymbiont on the perennial clovers originating from Europe and the Mediterranean basin. TA1 however is ineffective with many annual and perennial clovers originating from Africa and America. Here we describe the features of R. leguminosarum bv. trifolii strain TA1, together with genome sequence information and annotation. The 8,618,824 bp high-quality-draft genome is arranged in a 6 scaffold of 32 contigs, contains 8,493 protein-coding genes and 83 RNA-only encoding genes, and is one of 20 rhizobial genomes sequenced as part of the DOE Joint Genome Institute 2010 Community Sequencing Program. 相似文献
139.
Pascal Bonnarme Michel Delattre Georges Corrieu Marcel Asther 《Applied microbiology and biotechnology》1992,37(5):670-673
Summary Lignin (LiP) and manganese peroxidase (MnP) excretion by Phanerochaete chrysosporium INA-12 was significantly increased in response to fungal extract supplementation. LiP and MnP production was increased 1.7- and 1.8-fold, respectively, with fungal extracts from agitated pellet cultures of strain INA-12, namely fungal extracts P6 and P4. In cultures supplemented with a fungal extract harvested from static cultures of strain INA-12 (fungal extract S4), LiP and MnP production was increased 1.8- and 1.6-fold, respectively. Succinate dehydrogenase activity, a mitochondrial marker, was significantly enhanced (2.7-fold) in cultures with the addition of fungal extracts.
Correspondence to: M. Asther 相似文献
140.
Lipopolysaccharide-Enhanced Expression of Interleukin-6 in Dibutyryl Cyclic AMP-Differentiated Rat C6 Glioma 总被引:1,自引:1,他引:1
Abstract: Rat C6 glioma synthesizes a low basal level of interleukin-6 (IL-6). Stimulation with 10 µg/ml of lipopolysaccharide (LPS) and induction of differentiation with 1 m M N 6 , O 2' -dibutyryl cyclic AMP (dbcAMP) for 48 h increased the secreted activity to 400 and 800 U/ml, respectively. An LPS stimulation of dbcAMP-differentiated cells strongly enhanced the secreted activity. Depending on the dbcAMP concentration, the cell number, and the stimulation time, the secreted IL-6 level increased up to 120,000 U/ml. After 48 h of costimulation with 10 µg/ml of LPS and 1 m M dbcAMP, northern blotting and immunoassay demonstrated an eightfold increase in IL-6 mRNA concentration and IL-6 immunoreactivity, whereas titration of the biological activity indicated a 100-fold increase in the secreted IL-6 activity. The enhanced secretion of IL-6 is correlated with the induction of differentiation. Chromatography on heparin-Sepharose and on DEAE-5PW separated the secreted activity into several fractions, indicating that they differ in heparin affinity and charge either by posttranslational modifications or by binding to a carrier protein. Each of the partially purified IL-6-like activities could be neutralized by an anti-murine IL-6 antibody. Our observations demonstrate that in vivo inflammatory signals can trigger astrocytes and their precursors to secrete substantially different levels of immunoregulatory cytokines depending on their degree of differentiation. 相似文献