全文获取类型
收费全文 | 16041篇 |
免费 | 152篇 |
国内免费 | 266篇 |
专业分类
系统科学 | 207篇 |
丛书文集 | 184篇 |
教育与普及 | 167篇 |
理论与方法论 | 49篇 |
现状及发展 | 5452篇 |
研究方法 | 610篇 |
综合类 | 9661篇 |
自然研究 | 129篇 |
出版年
2014年 | 185篇 |
2013年 | 164篇 |
2012年 | 344篇 |
2011年 | 459篇 |
2010年 | 234篇 |
2009年 | 252篇 |
2008年 | 401篇 |
2007年 | 453篇 |
2006年 | 392篇 |
2005年 | 385篇 |
2004年 | 321篇 |
2003年 | 293篇 |
2002年 | 330篇 |
2001年 | 555篇 |
2000年 | 532篇 |
1999年 | 498篇 |
1998年 | 263篇 |
1997年 | 285篇 |
1996年 | 282篇 |
1995年 | 238篇 |
1994年 | 240篇 |
1992年 | 369篇 |
1991年 | 302篇 |
1990年 | 296篇 |
1989年 | 286篇 |
1988年 | 299篇 |
1987年 | 270篇 |
1986年 | 227篇 |
1985年 | 265篇 |
1984年 | 228篇 |
1983年 | 172篇 |
1982年 | 176篇 |
1981年 | 181篇 |
1980年 | 170篇 |
1979年 | 403篇 |
1978年 | 340篇 |
1977年 | 250篇 |
1976年 | 290篇 |
1975年 | 259篇 |
1974年 | 272篇 |
1973年 | 224篇 |
1972年 | 244篇 |
1971年 | 308篇 |
1970年 | 374篇 |
1969年 | 254篇 |
1968年 | 307篇 |
1967年 | 292篇 |
1966年 | 249篇 |
1965年 | 178篇 |
1958年 | 162篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
J. D. Trout has recently developed a new defense of scientific realism, a new version of the No Miracles Argument. I critically evaluate Trout's novel defense of realism. I argue that Trout's argument for scientific realism and the related explanation for the success of science are self-defeating. In the process of arguing against the traditional realist strategies for explaining the success of science, he inadvertently undermines his own argument. 相似文献
2.
R.S.K. Barnes 《Journal of Natural History》2018,52(1-2):87-113
Areas of the Knysna estuarine bay in the Western Cape are dominated by three endemic South African truncatelloid microgastropods, temporarily known as ‘Hydrobia’ knysnaensis (Krauss), ‘Assiminea’ capensis (Sowerby) and ‘Assiminea’ globulus Connolly. Although first described 80–170 years ago and present in abundance (up to 100,000 m?2), they remain surrounded by confusion and still await taxonomic assignment, largely because they appear most atypical members of their groups by virtue of anatomy and/or biogeography and/or habitat. This study contributes in-life perspectives to morphological and phylogenetic analyses known to be on-going. At Knysna, they are syntopic: at least two occurring in >85% and all three in >40% of individual 0.0026 m2 samples from their region of dominance. Nevertheless, they tend to greater abundance in divergent microhabitats; ‘A.’ globulus dominating higher tidal levels, and ‘A.’ capensis and ‘Hydrobia’ lower ones; the former especially unvegetated sediment, the latter, if anything, seagrass. Interspecific feeding interactions appear unlikely to be responsible for these patterns, other evidence suggesting that all are maintained below carrying capacity. Field biology of ‘H.’ knysnaensis generally appears equivalent to that of northern-hemisphere intertidal hydrobiids and that of ‘A.’ globulus is typically assimineid, albeit at atypically low shore height. Unlike assimineids, however, ‘A.’ capensis is truly aquatic. The success of these truncatelloids in unusual circumstances may be consequent on the absence from South Africa of other microgastropod groups that fill their niches elsewhere in the southern hemisphere. 相似文献
3.
This paper undertakes a comprehensive examination of 10 measures of core inflation and evaluates which measure produces the best forecast of headline inflation out‐of‐sample. We use the Personal Consumption Expenditure Price Index as our measure of inflation. We use two sets of components (17 and 50) of the Personal Consumption Expenditure Price Index to construct these core inflation measures and evaluate these measures at the three time horizons (6, 12 and 24 months) most relevant for monetary policy decisions. The best measure of core inflation for both sets of components and over all time horizons uses weights based on the first principal component of the disaggregated (component‐level) prices. Interestingly, the results vary by the number of components used; when more components are used the weights based on the persistence of each component is statistically equivalent to the weights generated by the first principal component. However, those forecasts using the persistence of 50 components are statistically worse than those generated using the first principal component of 17 components. The statistical superiority of the principal component method is due to the fact that it extracts (in the first principal component) the common source of variation in the component level prices that accurately describes trend inflation over the next 6–24 months. 相似文献
4.
5.
6.
Emile Durkheim(1858~1917)是现代社会学的创始人,他的重要书籍被翻译成中文,他也频频"光顾"许多中文社科类书籍.不过他在中国却分身有术,善于变脸,简直可称得上是外国名人变脸之最了. 相似文献
7.
利用断裂力学理论和试手段对QY16汽车起重机主梁断裂失效进行分析,找出断裂的主要原因为焊缝开裂。 相似文献
8.
本文首先介绍了教学机器人实验系统的设计思想和系统构成,然后对其工作方式及与上位机的联机操作方法作了简要的说明,最后对该系统中模拟通用机器人语言所开发的模拟机器人语言的语句及应用这种机器人语言进行编程的特色作了专门的阐述. 相似文献
9.
10.