全文获取类型
收费全文 | 1701篇 |
免费 | 2篇 |
国内免费 | 13篇 |
专业分类
系统科学 | 75篇 |
丛书文集 | 3篇 |
教育与普及 | 7篇 |
理论与方法论 | 26篇 |
现状及发展 | 196篇 |
研究方法 | 274篇 |
综合类 | 1006篇 |
自然研究 | 129篇 |
出版年
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 18篇 |
2013年 | 40篇 |
2012年 | 116篇 |
2011年 | 280篇 |
2010年 | 41篇 |
2009年 | 20篇 |
2008年 | 131篇 |
2007年 | 164篇 |
2006年 | 139篇 |
2005年 | 118篇 |
2004年 | 124篇 |
2003年 | 135篇 |
2002年 | 156篇 |
2001年 | 10篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1971年 | 5篇 |
1970年 | 2篇 |
1965年 | 1篇 |
1958年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有1716条查询结果,搜索用时 15 毫秒
111.
Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} A program to control hydatid disease in central Utah was evaluated by: (1) surveillance of infection in dogs and sheep, (2) questioning adult residents of two Sanpete County communities (Fountain Green and Spring City) about their knowledge of hydatid disease and their attitudes toward preventive measures, (3) interviewing local officials to evaluate the proposed implementation of proper community-wide measures, (4) analyzing records of prophylactic treatment of dogs with praziquantel, and (5) comparing scores of tests given to third and fourth grade students before and after they colored an educational pamphlet about hydatid disease. Infection rates of Echinococcus granulosus in dogs brought to volunteer diagnostic clinics dropped from 28.3 percent in 1972 to 1.0 percent in 1979, but increased to 9.8 percent in 1981. This last rise was due mainly to the fact that some dogs were examined that belonged to range sheepmen who had either not attended a field clinic recently or had never attended at all. Prevalence of the parasite in slaughtered sheep decreased steadily from 13.2 percent in 1972 to 2.8 percent in 1981. With regard to the questionnaire phase of the project, 87.3 percent and 84.3 percent of the respondents understood the role of dogs in the life cycle of E. granulosus in Fountain Green and Spring City, respectively. Over 50 percent of the respondents of these two communities had worked directly with sheep sometime in their life. In general, residents were more willing to practice preventive measures involving sheep than they were to implement measures involving dogs alone. However, many of the recommended community-wide preventive measures were not implemented. With the coloring book, students answered an average of 62.5 percent of the questions correctly before they colored the pamphlet and 83.3 percent afterward. Overall, our results suggest that residents of Sanpete County are knowledgeable about hydatid disease and its mode of transmission, and that, in general, progress has been made in control of hydatid disease in central Utah. 相似文献
112.
Autumn musters of bison ( Bison bison ) on Antelope Island State Park, Utah, conducted annually since 1987, provided data on temporal and age-specific reproductive patterns and a basis to evaluate the efficacy of management measures implemented to elevate reproductive performance in the herd. Pregnancy rates were variable and low ( x = 46.2%) in comparison to other free-ranging, noncommercial bison herds in North America. Cows in the 3- and > 6-yr range age classes exhibited lower-than-expected pregnancy rates ( P r = 0.64, P = 0.047) linear decline of 2.5% per annum. Variance in distribution of fetal ages observed in 6 yr indicates substantial temporal fluctuation. Long-term reproductive performance of cohorts born prior to implementation of management measures did not differ from that of cohorts born subsequent to these changes. 相似文献
113.
Forests of the southern Rocky Mountains are punctuated by persistent meadows called parks that are dominated by grasses and forbs. In an attempt to elucidate the maintenance of subalpine parks in the Gunnison Basin, Colorado, soil texture and tree morphology differences along 60-m transects spanning the forest-park ecotone were studied in 6 representative parks. Seedling survivorship, percent seed germination, and soil moisture available to plants were also studied along one of the transects in Willow Park. Soil analyses revealed 40% more silt and significantly less sand and clay in all 6 parks ( P P = 0.011), with 54% more water in forest than in park soils. Measures of growth rate obtained from tree height, dbh, and age were significantly higher nearer the ecotone ( P P = 0.002). These results suggest that stress of mature Engelmann spruce ( Picea engelmannii ) and lodgepole pine ( Pinus contorta ) is an unlikely explanation of park maintenance. P. engelmanii percent seed germination and seedling survivorship were significantly higher in the forest than in the park ( P < 0.001). This may be largely due to the more severe seedling microclimate observed in the park. Results indicate that limited seedling establishment is primarily responsible for maintenance of subalpine parks in the Gunnison Basin. 相似文献
114.
115.
116.
Maize HapMap2 identifies extant variation from a genome in flux 总被引:3,自引:0,他引:3
Chia JM Song C Bradbury PJ Costich D de Leon N Doebley J Elshire RJ Gaut B Geller L Glaubitz JC Gore M Guill KE Holland J Hufford MB Lai J Li M Liu X Lu Y McCombie R Nelson R Poland J Prasanna BM Pyhäjärvi T Rong T Sekhon RS Sun Q Tenaillon MI Tian F Wang J Xu X Zhang Z Kaeppler SM Ross-Ibarra J McMullen MD Buckler ES Zhang G Xu Y Ware D 《Nature genetics》2012,44(7):803-807
Whereas breeders have exploited diversity in maize for yield improvements, there has been limited progress in using beneficial alleles in undomesticated varieties. Characterizing standing variation in this complex genome has been challenging, with only a small fraction of it described to date. Using a population genetics scoring model, we identified 55 million SNPs in 103 lines across pre-domestication and domesticated Zea mays varieties, including a representative from the sister genus Tripsacum. We find that structural variations are pervasive in the Z. mays genome and are enriched at loci associated with important traits. By investigating the drivers of genome size variation, we find that the larger Tripsacum genome can be explained by transposable element abundance rather than an allopolyploid origin. In contrast, intraspecies genome size variation seems to be controlled by chromosomal knob content. There is tremendous overlap in key gene content in maize and Tripsacum, suggesting that adaptations from Tripsacum (for example, perennialism and frost and drought tolerance) can likely be integrated into maize. 相似文献
117.
118.
Pathology of seaweeds: Current status and future prospects 总被引:3,自引:0,他引:3
John H. Andrews 《Cellular and molecular life sciences : CMLS》1979,35(4):429-429
119.
120.