全文获取类型
收费全文 | 10787篇 |
免费 | 811篇 |
国内免费 | 17篇 |
出版年
2022年 | 39篇 |
2021年 | 197篇 |
2020年 | 104篇 |
2019年 | 133篇 |
2018年 | 203篇 |
2017年 | 155篇 |
2016年 | 279篇 |
2015年 | 437篇 |
2014年 | 464篇 |
2013年 | 608篇 |
2012年 | 778篇 |
2011年 | 796篇 |
2010年 | 477篇 |
2009年 | 398篇 |
2008年 | 577篇 |
2007年 | 614篇 |
2006年 | 554篇 |
2005年 | 497篇 |
2004年 | 460篇 |
2003年 | 447篇 |
2002年 | 429篇 |
2001年 | 177篇 |
2000年 | 128篇 |
1999年 | 164篇 |
1998年 | 120篇 |
1997年 | 105篇 |
1996年 | 68篇 |
1995年 | 105篇 |
1994年 | 78篇 |
1993年 | 78篇 |
1992年 | 109篇 |
1991年 | 93篇 |
1990年 | 93篇 |
1989年 | 73篇 |
1988年 | 72篇 |
1987年 | 66篇 |
1986年 | 68篇 |
1985年 | 65篇 |
1984年 | 86篇 |
1983年 | 69篇 |
1982年 | 75篇 |
1981年 | 63篇 |
1980年 | 65篇 |
1979年 | 50篇 |
1978年 | 55篇 |
1977年 | 54篇 |
1976年 | 46篇 |
1975年 | 48篇 |
1974年 | 34篇 |
1973年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 270 毫秒
1.
2.
3.
Henry C. Stevens Elaine M. Metz Percy Saboya Del Castillo Juan Díaz Alvn Mark T. Bowler 《Journal of Field Ornithology》2019,90(1):70-79
White‐sand forests are patchily distributed ecosystems covering just 5% of Amazonia that host many specialist species of birds not found elsewhere, and these forests are threatened due to their small size and human exploitation of sand for construction projects. As a result, many species of birds that are white‐sand specialists are at risk of extinction, and immediate conservation action is paramount for their survival. Our objective was to evaluate current survey methods and determine the relative effect of the size of patches of these forests on the presence or absence of white‐sand specialists. Using point counts and autonomous recorders, we surveyed avian assemblages occupying patches of white‐sand forest in the Peruvian Amazon in April 2018. Overall, we detected 126 species, including 21 white‐sand forest specialists. We detected significantly more species of birds per survey point with autonomous recorders than point counts. We also found a negative relationship between avian species richness and distance from the edge of patches of white‐sand forest, but a significant, positive relationship when only counting white‐sand specialists. Although we detected more species with autonomous recorders, point counts were more effective for detecting canopy‐dwelling passerines. Therefore, we recommend that investigators conducting surveys for rare and patchily distributed species in the tropics use a mixed‐method approach that incorporates both autonomous recorders and visual observation. Finally, our results suggest that conserving large, continuous patches of white‐sand forest may increase the likelihood of survival of species of birds that are white‐sand specialists. 相似文献
4.
Shira Weingarten-Gabbay Susan Klaeger Siranush Sarkizova Leah R. Pearlman Da-Yuan Chen Kathleen M.E. Gallagher Matthew R. Bauer Hannah B. Taylor W. Augustine Dunn Christina Tarr John Sidney Suzanna Rachimi Hasahn L. Conway Katelin Katsis Yuntong Wang Del Leistritz-Edwards Melissa R. Durkin Christopher H. Tomkins-Tinch Pardis C. Sabeti 《Cell》2021,184(15):3962-3980.e17
5.
Victor Horsley 《BMJ (Clinical research ed.)》1910,1(2568):725-726
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
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