全文获取类型
收费全文 | 760篇 |
免费 | 3篇 |
国内免费 | 12篇 |
专业分类
系统科学 | 12篇 |
丛书文集 | 2篇 |
教育与普及 | 3篇 |
理论与方法论 | 27篇 |
现状及发展 | 247篇 |
研究方法 | 88篇 |
综合类 | 370篇 |
自然研究 | 26篇 |
出版年
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 10篇 |
2013年 | 10篇 |
2012年 | 39篇 |
2011年 | 58篇 |
2010年 | 20篇 |
2009年 | 6篇 |
2008年 | 18篇 |
2007年 | 26篇 |
2006年 | 30篇 |
2005年 | 16篇 |
2004年 | 43篇 |
2003年 | 32篇 |
2002年 | 21篇 |
2001年 | 27篇 |
2000年 | 22篇 |
1999年 | 20篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 16篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 7篇 |
1975年 | 13篇 |
1974年 | 22篇 |
1973年 | 12篇 |
1972年 | 10篇 |
1971年 | 6篇 |
1970年 | 14篇 |
1969年 | 11篇 |
1968年 | 13篇 |
1967年 | 10篇 |
1966年 | 13篇 |
1965年 | 7篇 |
排序方式: 共有775条查询结果,搜索用时 275 毫秒
31.
W. S. Moos H. Le Van B. T. Mason H. C. Mason D. L. Hebron 《Cellular and molecular life sciences : CMLS》1969,25(11):1215-1219
Zusammenfassung In «naiven» Mäusen werden Verhaltensveränderungen nach Injektion kleiner Mengen von Gehirnmaterial aus Saccharin bevorzugenden und röntgenbestrahlten Mäusen beobachtet. Es trat Vermeidung der Saccharinlösung ein, und zwar ähnlich wie sonst in «trainierten», Saccharin bevorzugenden Tieren nach der Bestrahlung. 相似文献
32.
33.
34.
35.
Carcinogenic nitrosamines formed by drug-nitrite interactions 总被引:3,自引:0,他引:3
36.
Dr. D. Keslev S. Van Puymbroeck O. Van der Borght 《Cellular and molecular life sciences : CMLS》1972,28(5):524-525
Résumé L'administration presque simultanée d'un gel de phosphate d'alumine et de226RaCl2 réduit de 800 fois l'absorption intestinale du226Ra chez la souris. La charge corporelle en85Sr et47Ca est réduite d'environ 10 resp. 3 fois. 相似文献
37.
Lodahl P Floris Van Driel A Nikolaev IS Irman A Overgaag K Vanmaekelbergh D Vos WL 《Nature》2004,430(7000):654-657
Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals' lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control of optical quantum systems. 相似文献
38.
High-quality electron beams from a laser wakefield accelerator using plasma-channel guiding 总被引:2,自引:0,他引:2
Geddes CG Toth CS Van Tilborg J Esarey E Schroeder CB Bruhwiler D Nieter C Cary J Leemans WP 《Nature》2004,431(7008):538-541
Laser-driven accelerators, in which particles are accelerated by the electric field of a plasma wave (the wakefield) driven by an intense laser, have demonstrated accelerating electric fields of hundreds of GV m(-1) (refs 1-3). These fields are thousands of times greater than those achievable in conventional radio-frequency accelerators, spurring interest in laser accelerators as compact next-generation sources of energetic electrons and radiation. To date, however, acceleration distances have been severely limited by the lack of a controllable method for extending the propagation distance of the focused laser pulse. The ensuing short acceleration distance results in low-energy beams with 100 per cent electron energy spread, which limits potential applications. Here we demonstrate a laser accelerator that produces electron beams with an energy spread of a few per cent, low emittance and increased energy (more than 10(9) electrons above 80 MeV). Our technique involves the use of a preformed plasma density channel to guide a relativistically intense laser, resulting in a longer propagation distance. The results open the way for compact and tunable high-brightness sources of electrons and radiation. 相似文献
39.
Douma S Van Laar T Zevenhoven J Meuwissen R Van Garderen E Peeper DS 《Nature》2004,430(7003):1034-1039
Metastasis is a major factor in the malignancy of cancers, and is often responsible for the failure of cancer treatment. Anoikis (apoptosis resulting from loss of cell-matrix interactions) has been suggested to act as a physiological barrier to metastasis; resistance to anoikis may allow survival of cancer cells during systemic circulation, thereby facilitating secondary tumour formation in distant organs. In an attempt to identify metastasis-associated oncogenes, we designed an unbiased, genome-wide functional screen solely on the basis of anoikis suppression. Here, we report the identification of TrkB, a neurotrophic tyrosine kinase receptor, as a potent and specific suppressor of caspase-associated anoikis of non-malignant epithelial cells. By activating the phosphatidylinositol-3-OH kinase/protein kinase B pathway, TrkB induced the formation of large cellular aggregates that survive and proliferate in suspension. In mice, these cells formed rapidly growing tumours that infiltrated lymphatics and blood vessels to colonize distant organs. Consistent with the ability of TrkB to suppress anoikis, metastases--whether small vessel infiltrates or large tumour nodules--contained very few apoptotic cells. These observations demonstrate the potent oncogenic effects of TrkB and uncover a specific pro-survival function that may contribute to its metastatic capacity, providing a possible explanation for the aggressive nature of human tumours that overexpress TrkB. 相似文献
40.