全文获取类型
收费全文 | 43926篇 |
免费 | 312篇 |
国内免费 | 291篇 |
专业分类
系统科学 | 558篇 |
丛书文集 | 1034篇 |
教育与普及 | 140篇 |
理论与方法论 | 243篇 |
现状及发展 | 17781篇 |
研究方法 | 1647篇 |
综合类 | 22305篇 |
自然研究 | 821篇 |
出版年
2013年 | 441篇 |
2012年 | 791篇 |
2011年 | 1637篇 |
2010年 | 506篇 |
2009年 | 453篇 |
2008年 | 950篇 |
2007年 | 1033篇 |
2006年 | 1075篇 |
2005年 | 1011篇 |
2004年 | 810篇 |
2003年 | 763篇 |
2002年 | 772篇 |
2001年 | 1242篇 |
2000年 | 1207篇 |
1999年 | 821篇 |
1992年 | 732篇 |
1991年 | 605篇 |
1990年 | 626篇 |
1989年 | 610篇 |
1988年 | 613篇 |
1987年 | 614篇 |
1986年 | 589篇 |
1985年 | 723篇 |
1984年 | 618篇 |
1983年 | 501篇 |
1982年 | 455篇 |
1981年 | 443篇 |
1980年 | 569篇 |
1979年 | 1232篇 |
1978年 | 1055篇 |
1977年 | 1069篇 |
1976年 | 755篇 |
1975年 | 855篇 |
1974年 | 1218篇 |
1973年 | 1058篇 |
1972年 | 1058篇 |
1971年 | 1307篇 |
1970年 | 1640篇 |
1969年 | 1289篇 |
1968年 | 1227篇 |
1967年 | 1295篇 |
1966年 | 1106篇 |
1965年 | 819篇 |
1959年 | 486篇 |
1958年 | 708篇 |
1957年 | 567篇 |
1956年 | 475篇 |
1955年 | 440篇 |
1954年 | 468篇 |
1948年 | 246篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
J. L. Heilbron 《Annals of science》2019,76(3-4):387-389
2.
Matthew L. Buffington Massimo Giorgini Chia-Hua Lue Giorgio Formisano Pasquale Cascone Mattias Forshage 《Journal of Natural History》2020,54(9-12):565-583
ABSTRACT In the search for native Asian parasitoids of Drosophila suzukii, the notorious spotted-wing Drosophila (SWD), an odd new species of Eucoilinae was discovered. Leptopilina lasallei sp. nov. is herein described and diagnosed relative to other eucoilines associated with drosophilid hosts. Morphologically, L. lasallei is somewhat aberrant within Leptopilina; phylogenetically, L. lasallei is sister group to the core Leptopilina. In the process of investigating L. lasallei, a de novo molecular phylogeny of Leptopilina was generated and is included here. The integrated approach used for the characterisation of L. lasallei, and the resulting phylogeny of Leptopilina, produced data useful to select parasitoid species for SWD biological control.http://www.zoobank.org/urn:lsid:zoobank.org:act:402D504A-4616-4524-85D7-1C13A6276F06 http://www.zoobank.org/urn:lsid:zoobank.org:act:402D504A-4616-4524-85D7-1C13A6276F06 相似文献
3.
李莹 《辽宁师专学报(自然科学版)》2014,(2):20-22
通过对辽阳职业技术学院生物制药专业2010级、2011级学生顶岗实习情况的调查分析,构建"五化三落实"顶岗实习管理机制,提出顶岗实习是培养高技能人才的重要环节,是充分就业的有效途径. 相似文献
4.
Shalik Ram Sigdel Jayram Pandey Eryuan Liang Sher Muhammad Flurin Babst Steven W.Leavitt Miaogen Shen Haifeng Zhu Franco Salerno Shilong Piao J.Julio Camarero Josep Peuelas 《科学通报(英文版)》2021,(18):1825-1829
Global temperature has been increasing at unprecedented rates during the Anthropocene,impacting both natural and human sys-tems [1].Alpine biomes,among the most... 相似文献
5.
A pessimistic strain of thought is fomenting in the health studies literature regarding the status of medicine. Ioannidis’s (2005) now famous finding that “most published research findings are false” and Stegenga’s (2018) book-length argument for medical nihilism are examples of this. In this paper, we argue that these positions are incorrect insofar as they rest on an untenable account of the nature of facts. Proper attention to fallibilism and the social organization of knowledge, as well as Bayesian probabilities in medical reasoning, prompt us to ask why the cynics expect the results of quantitative studies to be incontrovertibly true in the first place. While we agree with Ioannidis and others’ identified flaws in the medical research enterprise, and encourage rectification, we conclude that medical nihilism is not the natural outcome of the current state of research. 相似文献
6.
A central thesis of Steven French's brand of ontic structural realism has always been his eliminativism about objects. Unsurprisingly, this bold and controversial thesis has seen a lot of critical discussion. In his book The Structure of the World—Metaphysics & Representation, French accordingly defends this thesis against a range of challenges. A novel feature of this defense is the use of dependence relations to articulate his eliminativism. In this paper I take a critical look at French's defense of eliminativism and argue that the dependence relations invoked do not eliminate objects. 相似文献
7.
María Camila Basto-Riascos Jhulyana López-Caro Fernando Vargas-Salinas 《Journal of Natural History》2017,51(41-42):2535-2550
Population and reproductive behaviour aspects of the glass frog Espadarana prosoblepon are well known for populations from Central America, but similar information is lacking for populations from South America. We recorded the reproductive ecology of a population of the glass frog E. prosoblepon in the city of Armenia, Central Andes of Colombia. With weekly surveys with mark-recapture between December 2013 and November 2015, we monitored activity patterns and evaluated if the probability of males mating is associated to their body size or to chorus tenure (i.e. the number of nights a same individual is calling for attracting a mate). In addition, upon observing an amplexus, we recorded the behaviour of the individuals until oviposition and noted characteristics of egg clutch. We recorded 47 males and 32 females, nine amplexus events, eight ovipositions, and 21 egg clutches (35.4 ± 4.79 eggs per clutch, N = 29). Activity of males and females and the number of egg clutches were positively correlated to rainfall. Mating success of males was not associated to their body size, but it was positively associated to longer chorus tenure; clutches from large females had a higher number of eggs than clutches from small females. Oviposition occurred on average 3.76 ± 1.74 hours after we first observed the amplexus, occurring 93.1% of the time in fronds of Selaginella geniculata at an average height of 1.58 ± 0.44 m. After the oviposition, the male left the site, while the female remained between 30 and 45 min, partially covering the eggs. The reproductive behaviour of E. prosoblepon did not vary widely between a population in Costa Rica and our population in time to oviposition, and mating success of males associated to chorus tenure; however, in our study population we recorded a larger clutch size and the preference for S. geniculata fronds as oviposition substrate. 相似文献
8.
For analysts there is a tradeoff between the accuracy and the timeliness of their forecasts. Prior literature heavily investigates analyst forecast accuracy. Few papers investigate the importance of timeliness. To our best knowledge, there are no empirical papers to date to investigate the dynamic interplay between these key characteristics. We show that if analysts experience a period of high accuracy relative to their peers, they subsequently focus more on the timeliness of their forecasts in the subsequent period and thus issue their forecasts earlier than they did in the prior period. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
9.
Nicola Raftery Nigel J. Stevenson 《Cellular and molecular life sciences : CMLS》2017,74(14):2525-2535
Interferon-alpha (IFN-α) is a potent anti-viral cytokine, critical to the host immune response against viruses. IFN-α is first produced upon viral detection by pathogen recognition receptors. Following its expression, IFN-α embarks upon a complex downstream signalling cascade called the JAK/STAT pathway. This signalling pathway results in the expression of hundreds of effector genes known as interferon stimulated genes (ISGs). These genes are the basis for an elaborate effector mechanism and ultimately, the clearance of viral infection. ISGs mark an elegant mechanism of anti-viral host defence that warrants renewed research focus in our global efforts to treat existing and emerging viruses. By understanding the mechanistic role of individual ISGs we anticipate the discovery of a new “treasure trove” of anti-viral mediators that may pave the way for more effective, targeted and less toxic anti-viral therapies. Therefore, with the aim of highlighting the value of the innate type 1 IFN response in our battle against viral infection, this review outlines both historic and recent advances in understanding the IFN-α JAK/STAT pathway, with a focus on new research discoveries relating to specific ISGs and their potential role in curing existing and future emergent viral infections. 相似文献
10.
Immunological properties of oxygen-transport proteins: hemoglobin,hemocyanin and hemerythrin 总被引:2,自引:0,他引:2
It is now well documented that peptides with enhanced or alternative functionality (termed cryptides) can be liberated from larger, and sometimes inactive, proteins. A primary example of this phenomenon is the oxygen-transport protein hemoglobin. Aside from respiration, hemoglobin and hemoglobin-derived peptides have been associated with immune modulation, hematopoiesis, signal transduction and microbicidal activities in metazoans. Likewise, the functional equivalents to hemoglobin in invertebrates, namely hemocyanin and hemerythrin, act as potent immune effectors under certain physiological conditions. The purpose of this review is to evaluate the true extent of oxygen-transport protein dynamics in innate immunity, and to impress upon the reader the multi-functionality of these ancient proteins on the basis of their structures. In this context, erythrocyte–pathogen antibiosis and the immune competences of various erythroid cells are compared across diverse taxa. 相似文献