全文获取类型
收费全文 | 1788篇 |
免费 | 2篇 |
国内免费 | 13篇 |
专业分类
系统科学 | 75篇 |
丛书文集 | 4篇 |
教育与普及 | 7篇 |
理论与方法论 | 26篇 |
现状及发展 | 211篇 |
研究方法 | 277篇 |
综合类 | 1074篇 |
自然研究 | 129篇 |
出版年
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 18篇 |
2013年 | 40篇 |
2012年 | 119篇 |
2011年 | 288篇 |
2010年 | 42篇 |
2009年 | 22篇 |
2008年 | 133篇 |
2007年 | 168篇 |
2006年 | 139篇 |
2005年 | 118篇 |
2004年 | 139篇 |
2003年 | 140篇 |
2002年 | 158篇 |
2001年 | 12篇 |
2000年 | 22篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 7篇 |
1972年 | 2篇 |
1971年 | 6篇 |
1970年 | 3篇 |
1969年 | 5篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有1803条查询结果,搜索用时 15 毫秒
801.
Dorner M Horwitz JA Robbins JB Barry WT Feng Q Mu K Jones CT Schoggins JW Catanese MT Burton DR Law M Rice CM Ploss A 《Nature》2011,474(7350):208-211
Hepatitis C virus (HCV) remains a major medical problem. Antiviral treatment is only partially effective and a vaccine does not exist. Development of more effective therapies has been hampered by the lack of a suitable small animal model. Although xenotransplantation of immunodeficient mice with human hepatocytes has shown promise, these models are subject to important challenges. Building on the previous observation that CD81 and occludin comprise the minimal human factors required to render mouse cells permissive to HCV entry in vitro, we attempted murine humanization via a genetic approach. Here we show that expression of two human genes is sufficient to allow HCV infection of fully immunocompetent inbred mice. We establish a precedent for applying mouse genetics to dissect viral entry and validate the role of scavenger receptor type B class I for HCV uptake. We demonstrate that HCV can be blocked by passive immunization, as well as showing that a recombinant vaccinia virus vector induces humoral immunity and confers partial protection against heterologous challenge. This system recapitulates a portion of the HCV life cycle in an immunocompetent rodent for the first time, opening opportunities for studying viral pathogenesis and immunity and comprising an effective platform for testing HCV entry inhibitors in vivo. 相似文献
802.
Alföldi J Di Palma F Grabherr M Williams C Kong L Mauceli E Russell P Lowe CB Glor RE Jaffe JD Ray DA Boissinot S Shedlock AM Botka C Castoe TA Colbourne JK Fujita MK Moreno RG ten Hallers BF Haussler D Heger A Heiman D Janes DE Johnson J de Jong PJ Koriabine MY Lara M Novick PA Organ CL Peach SE Poe S Pollock DD de Queiroz K Sanger T Searle S Smith JD Smith Z Swofford R Turner-Maier J Wade J Young S Zadissa A Edwards SV Glenn TC Schneider CJ Losos JB Lander ES Breen M Ponting CP Lindblad-Toh K 《Nature》2011,477(7366):587-591
The evolution of the amniotic egg was one of the great evolutionary innovations in the history of life, freeing vertebrates from an obligatory connection to water and thus permitting the conquest of terrestrial environments. Among amniotes, genome sequences are available for mammals and birds, but not for non-avian reptiles. Here we report the genome sequence of the North American green anole lizard, Anolis carolinensis. We find that A. carolinensis microchromosomes are highly syntenic with chicken microchromosomes, yet do not exhibit the high GC and low repeat content that are characteristic of avian microchromosomes. Also, A. carolinensis mobile elements are very young and diverse-more so than in any other sequenced amniote genome. The GC content of this lizard genome is also unusual in its homogeneity, unlike the regionally variable GC content found in mammals and birds. We describe and assign sequence to the previously unknown A. carolinensis X chromosome. Comparative gene analysis shows that amniote egg proteins have evolved significantly more rapidly than other proteins. An anole phylogeny resolves basal branches to illuminate the history of their repeated adaptive radiations. 相似文献
803.
804.
805.
城乡规划类专业制图软件比较分析 总被引:1,自引:0,他引:1
提高学生实验应用技能是高等学校教学改革的重要内容之一。重点分析了AutoCAD、Photoshop、Corel draw、Mapin-fo、Arcgis等城乡规划类专业制图软件的优劣势。提出了制图课程教学改革的相关对策建议:加强师资队伍建设,及时进行制图课程教学改革,加大实验室建设投入,最终达到提高城乡规划类专业学生制图操作技能之目的。 相似文献
806.
This paper investigates the issue of stabilization for discrete-time dynamical systems (DDS) by event-triggered impulsive control (ETIC). Based on some relatively simple threshold constants, three levels of event conditions are set and thus the ETIC scheme is designed. Three cases for ETIC with and without time-delays and data dropouts are studied respectively, and the criteria on exponential stability are derived for the controlled DDS. The stabilization in the form of exponential stability is achieved for DDS under the designed ETIC with or without time-delays. And in the case of the ETIC data dropouts, the conditions of exponential stabilization are derived for DDS and the maximal allowable dropout rates for ETIC are estimated. Finally, one example with numerical simulations is worked out for illustration. 相似文献
807.
This article views a particular example of action research through the theoretical lens provided by the Concerns Based Adoption
Model of professional development. A small group of teachers in Lesotho, used action research to investigate their understanding
and practice in the midst of externally initiated change. Data was collected from teachers’ discussions during the 2 years
of the project. Teachers interacted during planning sessions; lesson observations and reflection meetings. Results indicated
that these teachers’ development and change through action research corresponded with the seven levels of the Concerns-Based
Adoption Model (CBAM) which are awareness, information, personal concerns, management, consequences, collaboration and refocusing.
The demonstrated resonance between CBAM and action research is significant, given the differing orientations of the two models.
There is a need however to conduct further studies with larger samples and possibly from diverse areas to further explore
the relationship between the Concerns-Based Adoption Model and action research. 相似文献
808.
This paper argues for a novel way of addressing questions about the relationship between politics and science: in terms of norms of communication, rather than norms of cognition. The first half of the paper motivates this general shift through close study of the concept of "wishful speaking"; arguing that this vice - rather than the more familiar "wishful thinking" - better captures real-life cases, such as the Lysenko affair. The second half builds on the ethics of communication to develop an account of the proper role of non-epistemic values in justification in terms of "value-aptness". 相似文献
809.
John E. Stewart 《Foundations of Science》2012,17(1):47-50
Vidal’s (Found Sci, 2010) and Rottiers’s (Found Sci, 2010) commentaries on my (2010) paper raised a number of important issues about the possible future trajectory of evolution and
its implications for humanity. My response emphasizes that despite the inherent uncertainty involved in extrapolating the
trajectory of evolution into the far future, the possibilities it reveals nonetheless have significant strategic implications
for what we do with our lives here and now, individually and collectively. One important implication is the replacement of
postmodern scepticism and relativism with an evolutionary grand narrative that can guide humanity to participate successfully
in the future evolution of life in the universe. 相似文献
810.