全文获取类型
收费全文 | 16513篇 |
免费 | 1146篇 |
国内免费 | 623篇 |
出版年
2024年 | 31篇 |
2023年 | 133篇 |
2022年 | 321篇 |
2021年 | 589篇 |
2020年 | 385篇 |
2019年 | 468篇 |
2018年 | 487篇 |
2017年 | 370篇 |
2016年 | 545篇 |
2015年 | 878篇 |
2014年 | 1000篇 |
2013年 | 1136篇 |
2012年 | 1328篇 |
2011年 | 1318篇 |
2010年 | 802篇 |
2009年 | 700篇 |
2008年 | 877篇 |
2007年 | 830篇 |
2006年 | 770篇 |
2005年 | 659篇 |
2004年 | 580篇 |
2003年 | 557篇 |
2002年 | 499篇 |
2001年 | 236篇 |
2000年 | 196篇 |
1999年 | 210篇 |
1998年 | 181篇 |
1997年 | 158篇 |
1996年 | 134篇 |
1995年 | 134篇 |
1994年 | 128篇 |
1993年 | 119篇 |
1992年 | 122篇 |
1991年 | 90篇 |
1990年 | 93篇 |
1989年 | 73篇 |
1988年 | 65篇 |
1987年 | 59篇 |
1986年 | 49篇 |
1985年 | 63篇 |
1984年 | 61篇 |
1983年 | 51篇 |
1982年 | 59篇 |
1981年 | 49篇 |
1980年 | 55篇 |
1979年 | 29篇 |
1978年 | 36篇 |
1977年 | 32篇 |
1976年 | 27篇 |
1975年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
3.
The functioning of the vertebrate eye depends on its absolute size, which is presumably adapted to specific needs. Eye size variation in lidless and spectacled colubrid snakes was investigated, including 839 specimens belonging to 49 genera, 66 species and subspecies. Variations of adult eye diameters (EDs) in both absolute and relative terms between species were correlated with parameters reflecting behavioral ecology. In absolute terms, eye of arboreal species was larger than in terrestrial and semiaquatic species. For diurnal species, EDs of terrestrial species do not differ from semiaquatic species; for nocturnal species the ED of terrestrial species is larger than fossorial species but not different from semiaquatic species. In relative terms, ED did not differ significantly by habitat for diurnal species. Although the ED of terrestrial species is larger than fossorial species there were no differences for nocturnal species between semiaquatic and fossorial snakes. In contrast to other vertebrates studied to date, colubrid EDs in absolute and relative terms are larger in diurnal than in nocturnal species. These observations suggest that among colubrid snakes, eye size variation reflects adaptation to specific habitats, foraging strategies and daily activities, independently of phylogeny. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc. 相似文献
4.
Victor Horsley 《BMJ (Clinical research ed.)》1910,1(2568):725-726
5.
Plant and Soil - Perennial plants play important roles in maintaining ecosystem functions by forming fertile islands beneath their canopies. Little is known about how the fertile island effect... 相似文献
6.
Jin Wei Mia Madel Alfajaro Peter C. DeWeirdt Ruth E. Hanna William J. Lu-Culligan Wesley L. Cai Madison S. Strine Shang-Min Zhang Vincent R. Graziano Cameron O. Schmitz Jennifer S. Chen Madeleine C. Mankowski Renata B. Filler Neal G. Ravindra Victor Gasque Fernando J. de Miguel Ajinkya Patil Huacui Chen Craig B. Wilen 《Cell》2021,184(1):76-91.e13
- Download : Download high-res image (212KB)
- Download : Download full-size image
7.
Victor F. Medina Peter M. Jeffers Steven L. Larson Waleska Perez 《International journal of phytoremediation》2000,2(4):287-295
Bleach treatment of plants was studied as a simple alternative to axenic tissue cultures for demonstrating phytodegradation of aqueous and gas-phase environmental contaminants. Parrotfeather (Myriophyllum aquaticum), spinach (Spinacia oleracea), and wheat (Triticum aestivum) were exposed to 0.525% NaC10 solutions for 15 s, then rinsed in deionized water. Plate counts indicated that 97 to 100% of viable bacteria were removed from parrotfeather and spinach. Transformation rates for 2,4,6-trinitrotoluene (TNT) by bleached and untreated parrotfeather were virtually identical. Similarly, treated and untreated spinach, wheat heads, and wheat leaves removed methyl bromide (MeBr) from air at the same rates. However, wheat root with attendant adhering soil was rendered inactive by bleach treatment. Parrotfeather roots examined by dissecting microscope and by electron microscope showed no significant damage caused by bleach treatment. 相似文献
8.
A group of captive chimpanzees, consisting of one adult male and three mother/infant pairs, was systematically observed over a 15-month period. Over 200 hr of data were collected, using both sequential and time sampling techniques, and compared to the available data on wild chimps. Unlike many captive groups, most behavior patterns were remarkably similar, both qualitatively and quantitatively, to that of wild chimpanzees including: play, grooming, infant sexual development, tool use, food sharing, prosocial partner preferences, and aggressive displays. 相似文献
9.
Two methods were used to radioiodinate sea urchin sperm: lactoperoxidase-glucose oxidase and Iodo-Gen. Following iodination the sperm are viable, they undergo the acrosome reaction, and they fertilize eggs. Of the radioactivity associated with the labeled sperm, 28–50% is presumed to be free 125I?, 37–47% is incorporated in lipid, and 8–15% is in trypsin-digestible material believed to be protein. Digestion of the labeled, living sperm with trypsin removes 95.6–99.5% of the macromolecular label (the cells are alive after digestion) suggesting that almost all the protein label is on the external surface of the cell. Thin-layer chromatography of the lipid fraction shows that the major membrane phospholipids and cholesterol are labeled. SDS-PAGE analysis shows the protein-incorporated 125I is distributed among four glycoproteins of >250K, 84K, 64K, and 52K dalton apparent molecular weight. Twenty-eight percent of the total protein (trypsin-digestible) label is in the 84K component and 46% in the 64K band. Although both molecules contain much of the label, they are relatively minor components of the TX-100 extract of sperm. The methods outlined will be useful in determining the role of sperm surface components in fertilization. 相似文献
10.
In this paper we propose an instrument for collecting sensitive data that allows for each participant to customize the amount of information that she is comfortable revealing. Current methods adopt a uniform approach where all subjects are afforded the same privacy guarantees; however, privacy is a highly subjective property with intermediate points between total disclosure and non-disclosure: each respondent has a different criterion regarding the sensitivity of a particular topic. The method we propose empowers respondents in this respect while still allowing for the discovery of interesting findings through the application of well-known inferential procedures. 相似文献