全文获取类型
收费全文 | 42138篇 |
免费 | 235篇 |
国内免费 | 438篇 |
专业分类
系统科学 | 555篇 |
丛书文集 | 824篇 |
教育与普及 | 112篇 |
理论与方法论 | 162篇 |
现状及发展 | 16789篇 |
研究方法 | 1602篇 |
综合类 | 21851篇 |
自然研究 | 916篇 |
出版年
2013年 | 507篇 |
2012年 | 808篇 |
2011年 | 1751篇 |
2010年 | 532篇 |
2009年 | 476篇 |
2008年 | 922篇 |
2007年 | 1119篇 |
2006年 | 1067篇 |
2005年 | 1041篇 |
2004年 | 969篇 |
2003年 | 864篇 |
2002年 | 1034篇 |
2001年 | 1348篇 |
2000年 | 1293篇 |
1999年 | 896篇 |
1992年 | 731篇 |
1991年 | 554篇 |
1990年 | 584篇 |
1989年 | 548篇 |
1988年 | 545篇 |
1987年 | 549篇 |
1986年 | 559篇 |
1985年 | 720篇 |
1984年 | 559篇 |
1983年 | 431篇 |
1982年 | 401篇 |
1981年 | 431篇 |
1980年 | 514篇 |
1979年 | 1179篇 |
1978年 | 906篇 |
1977年 | 930篇 |
1976年 | 715篇 |
1975年 | 750篇 |
1974年 | 1086篇 |
1973年 | 915篇 |
1972年 | 995篇 |
1971年 | 1092篇 |
1970年 | 1428篇 |
1969年 | 1158篇 |
1968年 | 1034篇 |
1967年 | 1087篇 |
1966年 | 1009篇 |
1965年 | 741篇 |
1964年 | 258篇 |
1959年 | 387篇 |
1958年 | 715篇 |
1957年 | 511篇 |
1956年 | 401篇 |
1955年 | 375篇 |
1954年 | 405篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
1.
Giulia Furfaro Sergio De Matteo Paolo Mariottini Salvatore Giacobbe 《Journal of Natural History》2018,52(11-12):645-657
The first record from Sicily of the introduced facelinid nudibranch Godiva quadricolor allowed the detection of trophic relationships with the polycerid Polycera hedgpethi, another non-native nudibranch, and with two bryozoan species, namely the naturalized Cheilostomatida Bugula neritina and the cryptogenic Ctenostomatida Amathia verticillata. The settlement of both nudibranchs was presumably promoted by a trophic shift of P. hedgpethi from the natural prey B. neritina towards the largely available and not exploited A. verticillata. This short food web, without evident links with native fauna and having G. quadricolor as the top predator, is described. A DNA barcoding approach was used to confirm the identity of this facelinid species and to explore the possible genetic divergence occurring among the samples analysed. 相似文献
2.
3.
4.
5.
Aristotle Said “Happiness is a State of Activity” — Predicting Mood Through Body Sensing with Smartwatches 总被引:1,自引:1,他引:0
Peter A. Gloor Andrea Fronzetti Colladon Francesca Grippa Pascal Budner Joscha Eirich 《系统科学与系统工程学报(英文版)》2018,27(5):586-612
We measure and predict states of Activation and Happiness using a body sensing application connected to smartwatches. Through the sensors of commercially available smartwatches we collect individual mood states and correlate them with body sensing data such as acceleration, heart rate, light level data, and location, through the GPS sensor built into the smartphone connected to the smartwatch. We polled users on the smartwatch for seven weeks four times per day asking for their mood state. We found that both Happiness and Activation are negatively correlated with heart beats and with the levels of light. People tend to be happier when they are moving more intensely and are feeling less activated during weekends. We also found that people with a lower Conscientiousness and Neuroticism and higher Agreeableness tend to be happy more frequently. In addition, more Activation can be predicted by lower Openness to experience and higher Agreeableness and Conscientiousness. Lastly, we find that tracking people’s geographical coordinates might play an important role in predicting Happiness and Activation. The methodology we propose is a first step towards building an automated mood tracking system, to be used for better teamwork and in combination with social network analysis studies. 相似文献
6.
Archive for History of Exact Sciences - We show that Dedekind, in his proof of the principle of definition by mathematical recursion, used implicitly both the concept of an inductive cone from an... 相似文献
7.
Russell L. Burke Beverly Clendening Alexandra Kanonik 《Journal of Natural History》2018,52(25-26):1723-1732
Clutch size (CS) is a well-studied life history characteristic, and optimal egg size theory predicts that CS should correlate positively with reproductive investment. Turtles are good subjects for studies of reproductive strategies because few turtle species exhibit parental care; therefore quantifying their short-term reproductive investment is mostly limited to measuring egg size and number. Clutch size is usually reported as an average value for each turtle population, and where CS variation is noted, it is usually attributable to variation in adult body size. In two long-term studies of ecologically dissimilar species we detected a dramatic increase in CS in a common snapping turtle (Chelydra serpentina) population and in a diamondback terrapin (Malaclemys terrapin) population. It is unknown whether these changes are due to either variation in adult body size or resource availability; but the temporal patterns we observed have apparently never been reported previously. These trends remain unexplained and should be explored further. 相似文献
8.
9.
杨建荣 《科技情报开发与经济》2004,14(6):157-158
根据我国当前电力系统运行情况,对电网无功功率补偿的必要性及通用补偿方法及其装置进行了具体阐述。 相似文献
10.
系统地总结和介绍了我国高性能计算机,包括“银河”系列巨型机、“曙光”系列巨型机、“神威”系列巨型机、“深腾”系列巨型机以及“深超”系列巨型机的开发研制以及应用情况。 相似文献