全文获取类型
收费全文 | 40903篇 |
免费 | 119篇 |
国内免费 | 203篇 |
专业分类
系统科学 | 384篇 |
丛书文集 | 875篇 |
教育与普及 | 76篇 |
理论与方法论 | 147篇 |
现状及发展 | 19225篇 |
研究方法 | 1599篇 |
综合类 | 18369篇 |
自然研究 | 550篇 |
出版年
2013年 | 295篇 |
2012年 | 528篇 |
2011年 | 1130篇 |
2010年 | 236篇 |
2008年 | 691篇 |
2007年 | 814篇 |
2006年 | 754篇 |
2005年 | 744篇 |
2004年 | 729篇 |
2003年 | 726篇 |
2002年 | 673篇 |
2001年 | 1283篇 |
2000年 | 1215篇 |
1999年 | 783篇 |
1992年 | 782篇 |
1991年 | 566篇 |
1990年 | 668篇 |
1989年 | 660篇 |
1988年 | 623篇 |
1987年 | 688篇 |
1986年 | 667篇 |
1985年 | 806篇 |
1984年 | 634篇 |
1983年 | 513篇 |
1982年 | 482篇 |
1981年 | 533篇 |
1980年 | 628篇 |
1979年 | 1274篇 |
1978年 | 1060篇 |
1977年 | 1063篇 |
1976年 | 861篇 |
1975年 | 888篇 |
1974年 | 1267篇 |
1973年 | 1076篇 |
1972年 | 1070篇 |
1971年 | 1210篇 |
1970年 | 1584篇 |
1969年 | 1261篇 |
1968年 | 1204篇 |
1967年 | 1220篇 |
1966年 | 1038篇 |
1965年 | 735篇 |
1964年 | 218篇 |
1959年 | 406篇 |
1958年 | 683篇 |
1957年 | 453篇 |
1956年 | 411篇 |
1955年 | 389篇 |
1954年 | 365篇 |
1948年 | 229篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
943.
Chung D. Ngo Binh V. Ngo Thuong T. Hoang Thi T.T. Nguyen Hai P. Dang 《Journal of Natural History》2015,49(39-40):2417-2436
We studied the feeding ecology of Eutropis multifasciata in the tropical plains of central Vietnam to understand better the foraging mode, spatiotemporal and sexual variation in dietary composition, and rarefaction curves of prey-taxon richness for males and females. Stomach contents (n = 161) were collected from October 2013 to May 2014 using a nonlethal stomach-flushing technique. A total of 680 food items (624 animal items and 56 plant items) was found in 161 stomachs of skinks, representing 19 unique animal categories. We found that the diet of E. multifasciata is composed mainly of small, sedentary and clumped prey and that this skink specialises on spiders, insect larvae, snails, grasshoppers and crickets (with a combined importance index of 60%). Dietary composition, prey size and total prey volume in E. multifasciata changed between dry and rainy seasons and among regions. The total volume of food items consumed by males was larger than that of females, and the diversity and evenness index of prey categories were larger in males than in females. However, using rarefaction curves revealed that females have the higher prey-taxon richness after points between 130 and 140 prey items for frequency, and between 160 and 170 prey items for number of items, and the differences were not statistically significant. The foraging behaviour of E. multifasciata best fits a ‘widely foraging’ model. 相似文献
944.
Martha M. Muñoz Kristen E. Crandell Shane C. Campbell-Staton Kristi Fenstermacher Hannah K. Frank Paul Van Middlesworth 《Journal of Natural History》2015,49(27-28):1717-1730
Aquatic anoles present an interesting ecomorphological puzzle. On the one hand, the link between habitat use and morphology is well established as convergent within the Caribbean anole radiation. On the other hand, aquatic anoles do not appear to form an ecomorphological group – rather, it appears that there may be several ways to adapt to aquatic habitats. We explore this issue by examining the ecology, morphology and performance of four species of Central American aquatic anoles belonging to two different lineages. Overall, we find that aquatic anoles overlap in multiple ecological and morphological dimensions. However, we do find some differences in substrate use, claw and limb morphology, and bite force that distinguish Anolis aquaticus from the other three species (A. lionotus, A. oxylophus and A. poecilopus). Our results suggest that A. aquaticus is adapted to climb on boulders, whereas the other species utilise vegetation in streamside habitats. 相似文献
945.
通过与经典全加器的基本模型进行比较后,讨论了一个改进后的量子平面加法器的基本构型.对其原理、组件和算法进行了研究,比较了本加法器两个主要组件与一般量子加法器的不同.作为应用的例,设计了一个n比特量子全加法器的模型,对其具体运算过程和基本功能进行了说明. 相似文献
946.
We develop coincident and leading employment indexes for the Connecticut economy. Four employment-related variables enter the coincident index while five employment-related variables enter the leading index. The peaks and troughs in the leading index lead the peaks and troughs in the coincident index by an average of 3 and 9 months. Finally, we use the leading index in vector-autoregressive (VAR) and Bayesian vector-autoregressive (BVAR) models to forecast the coincident index, non-farm employment, and the unemployment rate. 相似文献
947.
948.
Jana Fischer Gunnar Kleinau Claudia Rutz Denise Zwanziger Noushafarin Khajavi Anne Müller Maren Rehders Klaudia Brix Catherine L. Worth Dagmar Führer Heiko Krude Burkhard Wiesner Ralf Schülein Heike Biebermann 《Cellular and molecular life sciences : CMLS》2018,75(12):2227-2239
G-protein-coupled receptors (GPCRs) can constitute complexes with non-GPCR integral membrane proteins, while such interaction has not been demonstrated at a single molecule level so far. We here investigated the potential interaction between the thyrotropin receptor (TSHR) and the monocarboxylate transporter 8 (MCT8), a member of the major facilitator superfamily (MFS), using fluorescence cross-correlation spectroscopy (FCCS). Both the proteins are expressed endogenously on the basolateral plasma membrane of the thyrocytes and are involved in stimulation of thyroid hormone production and release. Indeed, we demonstrate strong interaction between both the proteins which causes a suppressed activation of Gq/11 by TSH-stimulated TSHR. Thus, we provide not only evidence for a novel interaction between the TSHR and MCT8, but could also prove this interaction on a single molecule level. Moreover, this interaction forces biased signaling at the TSHR. These results are of general interest for both the GPCR and the MFS research fields. 相似文献
949.