全文获取类型
收费全文 | 10331篇 |
免费 | 923篇 |
国内免费 | 13篇 |
专业分类
11267篇 |
出版年
2023年 | 44篇 |
2022年 | 121篇 |
2021年 | 205篇 |
2020年 | 108篇 |
2019年 | 146篇 |
2018年 | 194篇 |
2017年 | 203篇 |
2016年 | 278篇 |
2015年 | 485篇 |
2014年 | 536篇 |
2013年 | 684篇 |
2012年 | 838篇 |
2011年 | 805篇 |
2010年 | 525篇 |
2009年 | 450篇 |
2008年 | 686篇 |
2007年 | 634篇 |
2006年 | 598篇 |
2005年 | 572篇 |
2004年 | 513篇 |
2003年 | 481篇 |
2002年 | 468篇 |
2001年 | 125篇 |
2000年 | 85篇 |
1999年 | 100篇 |
1998年 | 128篇 |
1997年 | 76篇 |
1996年 | 64篇 |
1995年 | 45篇 |
1994年 | 68篇 |
1993年 | 54篇 |
1992年 | 47篇 |
1991年 | 50篇 |
1990年 | 54篇 |
1989年 | 39篇 |
1988年 | 42篇 |
1987年 | 41篇 |
1986年 | 42篇 |
1985年 | 37篇 |
1984年 | 48篇 |
1982年 | 43篇 |
1981年 | 35篇 |
1980年 | 40篇 |
1979年 | 50篇 |
1978年 | 34篇 |
1977年 | 31篇 |
1974年 | 33篇 |
1973年 | 25篇 |
1972年 | 34篇 |
1971年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Dejanira da Costa Lauria Elaine R. R. Rochedo Maria Luisa D. P. Godoy Eliane E. Santos Sandra S. Hacon 《Radiation and environmental biophysics》2012,51(4):367-374
This paper focuses on a survey of uranium and thorium decay chain radionuclides in food and drinking water from the thorium-rich (monazite-bearing) region of Buena, which is located in the state of Rio de Janeiro, Brazil. The radionuclide concentration values in the food and drinking water from Buena reached values higher than 100-fold the international reference values. The daily intake of radionuclides by the local population is similar to that of another high background radiation area in Brazil, but the intake is higher than that of residents from a normal background radiation area. Approximately 58?% of the food consumed by Buena inhabitants is produced locally. Based on that figure, locally produced food and the dilution of total radionuclides in the diet of residents caused by food importation are both highly relevant to a population’s intake of radionuclides. The concentration values for 210Pb and the radium isotopes in drinking water from Buena are among the highest values to be reported in the literature. 228Ra is the most important radionuclide ingested with both food and water among the inhabitants of Buena. 相似文献
72.
Mark S. Tichenor John M. Keith William M. Jones Joan M. Pierce Jeff Merit Natalie Hawryluk Mark Seierstad James A. Palmer Michael Webb Mark J. Karbarz Sandy J. Wilson Michelle L. Wennerholm Filip Woestenborghs Dominiek Beerens Lin Luo Sean M. Brown Marlies De Boeck Sandra R. Chaplan J. Guy Breitenbucher 《Bioorganic & medicinal chemistry letters》2012,22(24):7357-7362
The structure–activity relationships for a series of heteroaryl urea inhibitors of fatty acid amide hydrolase (FAAH) are described. Members of this class of inhibitors have been shown to inactivate FAAH by covalent modification of an active site serine with subsequent release of an aromatic amine from the urea electrophile. Systematic Ames II testing guided the optimization of urea substituents by defining the structure–mutagenicity relationships for the released aromatic amine metabolites. Potent FAAH inhibitors were identified having heteroaryl amine leaving groups that were non-mutagenic in the Ames II assay. 相似文献
73.
74.
Nichola A. Strandberg Mary Edwards Joanna C. Ellison Manuel J. Steinbauer Anna Walentowitz Patricia L. Fall David Sear Peter Langdon Shane Cronin Alvaro Castilla-Beltrán Ian W. Croudace Matiu Prebble William D. Gosling Sandra Nogué 《Biotropica》2023,55(4):816-827
Here, we investigate Mid- to Late-Holocene vegetation changes in low-lying coastal areas in Tonga and how changing sea levels and recurrent volcanic eruptions have influenced vegetation dynamics on four islands of the Tongan archipelago (South Pacific). To investigate past vegetation and environmental change at Ngofe Marsh (‘Uta Vava’u), we examined palynomorphs (pollen and spores), charcoal (fire), and sediment characteristics (volcanic activity) from a 6.7-m-long sediment core. Radiocarbon dating indicated the sediments were deposited over the last 7700 years. We integrated the Ngofe Marsh data with similar previously published data from Avai’o’vuna Swamp on Pangaimotu Island, Lotofoa Swamp on Foa Island, and Finemui Swamp on Ha’afeva Island. Plant taxa were categorized as littoral, mangrove, rainforest, successional/ disturbance, and wetland groups, and linear models were used to examine relationships between vegetation, relative sea level change, and volcanic eruptions (tephra). We found that relative sea level change has impacted vegetation on three of the four islands investigated. Volcanic eruptions were not identified as a driver of vegetation change. Rainforest decline does not appear to be driven by sea level changes or volcanic eruptions. From all sites analyzed, vegetation at Finemui Swamp was most sensitive to changes in relative sea level. While vegetation on low-lying Pacific islands is sensitive to changing sea levels, island characteristics, such as area and elevation, are also likely to be important factors that mediate specific island responses to drivers of change. 相似文献
75.
Constance Dubuc Sandra Winters William L. Allen Lauren J. N. Brent Julie Cascio Dario Maestripieri Angelina V. Ruiz-Lambides Anja Widdig James P. Higham 《Proceedings. Biological sciences / The Royal Society》2014,281(1794)
Sexual selection promotes the prevalence of heritable traits that increase an individual''s reproductive rate. Despite theoretically strong directional selection, sexually selected traits can show inter-individual variation. Here, we investigate whether red skin ornamentation, a rare example of a male mammalian trait involved in mate attraction, influences fecundity and is heritable in rhesus macaques (Macaca mulatta), and explore the mechanisms that are involved in maintaining trait variation. Interestingly, the trait is expressed by and is attractive to both sexes. We collected facial images of 266 free-ranging individuals and modelled skin redness and darkness to rhesus macaque vision. We used 20 years of genetic parentage data to calculate selection gradients on the trait and perform heritability analyses. Results show that males who were both darkly coloured and high-ranking enjoyed higher fecundity. Female skin redness was positively linked to fecundity, although it remains unclear whether this influences male selectiveness. Heritability explained 10–15% of the variation in redness and darkness, and up to 30% for skin darkness when sexes are considered separately, suggesting sex-influenced inheritance. Our results suggest that inter-individual variation is maintained through condition-dependence, with an added effect of balancing selection on male skin darkness, providing rare evidence for a mammalian trait selected through inter-sexual selection. 相似文献
76.
Broderick L Yokota SJ Reineke J Mathiowitz E Stewart CC Barcos M Kelleher RJ Bankert RB 《Journal of immunology (Baltimore, Md. : 1950)》2005,174(2):898-906
The implantation of small pieces of human primary lung tumor biopsy tissue into SCID mice results in a viable s.c. xenograft in which the tissue architecture, including tumor-associated leukocytes, tumor cells, and stromal cells, is preserved in a functional state. By monitoring changes in tumor volume, gene expression patterns, cell depletion analysis, and the use of function-blocking Abs, we previously established in this xenograft model that exogenous IL-12 mobilizes human tumor-associated leukocytes to kill tumor cells in situ by indirect mechanisms that are dependent upon IFN-gamma. In this study immunohistochemistry and FACS characterize the early cellular events in the tumor microenvironment induced by IL-12. By 5 days post-IL-12 treatment, the constitutively present human CD45(+) leukocytes have expanded and infiltrated into tumor-rich areas of the xenograft. Two weeks post-treatment, there is expansion of the human leukocytes and complete effacement of the tumor compared with tumor progression and gradual loss of most human leukocytes in control-treated xenografts. Immunohistochemical analyses reveal that the responding human leukocytes are primarily activated or memory T cells, with smaller populations of B cells, macrophages, plasma cells, and plasmacytoid dendritic cells capable of producing IFN-alpha. The predominant cell population was also characterized by FACS and was shown to have a phenotype consistent with a CD4(+) effector memory T cell. We conclude that quiescent CD4(+) effector memory T cells are present within the tumor microenvironment of human lung tumors and can be reactivated by the local and sustained release of IL-12 to proliferate and secrete IFN-gamma, leading to tumor cell eradication. 相似文献
77.
78.
Utz S Huetteroth W Wegener C Kahnt J Predel R Schachtner J 《Developmental neurobiology》2007,67(6):764-777
The paired antennal lobes are the first integration centers for odor information in the insect brain. In the sphinx moth Manduca sexta, like in other holometabolous insects, they are formed during metamorphosis. To further understand mechanisms involved in the formation of this particularly well investigated brain area, we performed a direct peptide profiling of a well defined cell group (the lateral cell group) of the antennal lobe throughout development by MALDI-TOF mass spectrometry. Although the majority of the about 100 obtained ion signals represent still unknown substances, this first peptidomic characterization of this cell group indicated the occurrence of 12 structurally known neuropeptides. Among these peptides are helicostatin 1, cydiastatins 2, 3, and 4, M. sexta-allatotropin (Mas-AT), M. sexta-FLRFamide (Mas-FLRFamide) I, II, and III, nonblocked Mas-FLRFamide I, and M. sexta-myoinhibitory peptides (Mas-MIPs) III, V, and VI. The identity of two of the allatostatins (cydiastatins 3 and 4) and Mas-AT were confirmed by tandem mass spectrometry (MALDI-TOF/TOF). During development of the antennal lobe, number and frequency of ion signals including those representing known peptides generally increased at the onset of glomeruli formation at pupal Stage P7/8, with cydiastatin 2, helicostatin 1, and Mas-MIP V being the exceptions. Cydiastatin 2 showed transient occurrence mainly during the period of glomerulus formation, helicostatin 1 was restricted to late pupae and adults, while Mas-MIP V occurred exclusively in adult antennal lobes. The power of the applied direct mass spectrometric profiling lies in the possibility of chemically identifying neuropeptides of a given cell population in a fast and reliable manner, at any developmental stage in single specimens. The identification of neuropeptides in the antennal lobes now allows to specifically address the function of these signaling molecules during the formation of the antennal lobe network. 相似文献
79.
Fournier HN Dupé-Manet S Bouvard D Lacombe ML Marie C Block MR Albiges-Rizo C 《The Journal of biological chemistry》2002,277(23):20895-20902
Cell adhesion-dependent signaling implicates cytoplasmic proteins interacting with the intracellular tails of integrins. Among those, the integrin cytoplasmic domain-associated protein 1alpha (ICAP-1alpha) has been shown to interact specifically with the beta(1) integrin cytoplasmic domain. Although it is likely that this protein plays an important role in controlling cell adhesion and migration, little is known about its actual function. To search for potential ICAP-1alpha-binding proteins, we used a yeast two-hybrid screen and identified the human metastatic suppressor protein nm23-H2 as a new partner of ICAP-1alpha. This direct interaction was confirmed in vitro, using purified recombinant ICAP-1alpha and nm23-H2, and by co-immunoprecipitation from CHO cell lysates over-expressing ICAP-1alpha. The physiological relevance of this interaction is provided by confocal fluorescence microscopy, which shows that ICAP-1alpha and nm23-H2 are co-localized in lamellipodia during the early stages of cell spreading. These adhesion sites are enriched in occupied beta(1) integrins and precede the formation of focal adhesions devoid of ICAP-1alpha and nm23-H2, indicating the dynamic segregation of components of matrix adhesions. This peripheral staining of ICAP-1alpha and nm23-H2 is only observed in cells spreading on fibronectin and collagen and is absent in cells spreading on poly-l-lysine, vitronectin, or laminin. This is consistent with the fact that targeting of both ICAP-1alpha and nm23-H2 to the cell periphery is dependent on beta(1) integrin engagement rather than being a consequence of cell adhesion. This finding represents the first evidence that the tumor suppressor nm23-H2 could act on beta(1) integrin-mediated cell adhesion by interacting with one of the integrin partners, ICAP-1alpha. 相似文献
80.
Carlota Pascoal Sandra Brasil Rita Francisco Dorinda Marques-da-Silva Agnes Rafalko Jaak Jaeken Paula A. Videira Luísa Barros Vanessa dos Reis Ferreira 《Orphanet journal of rare diseases》2018,13(1):215