全文获取类型
收费全文 | 3856篇 |
免费 | 333篇 |
国内免费 | 733篇 |
出版年
2024年 | 35篇 |
2023年 | 122篇 |
2022年 | 169篇 |
2021年 | 152篇 |
2020年 | 186篇 |
2019年 | 165篇 |
2018年 | 154篇 |
2017年 | 166篇 |
2016年 | 174篇 |
2015年 | 170篇 |
2014年 | 236篇 |
2013年 | 333篇 |
2012年 | 255篇 |
2011年 | 247篇 |
2010年 | 235篇 |
2009年 | 235篇 |
2008年 | 217篇 |
2007年 | 209篇 |
2006年 | 189篇 |
2005年 | 172篇 |
2004年 | 133篇 |
2003年 | 125篇 |
2002年 | 112篇 |
2001年 | 86篇 |
2000年 | 70篇 |
1999年 | 64篇 |
1998年 | 50篇 |
1997年 | 45篇 |
1996年 | 49篇 |
1995年 | 46篇 |
1994年 | 33篇 |
1993年 | 38篇 |
1992年 | 29篇 |
1991年 | 20篇 |
1990年 | 24篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 13篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有4922条查询结果,搜索用时 750 毫秒
81.
《Animal : an international journal of animal bioscience》2017,11(1):121-130
The number and size of free-range laying hen (Gallus gallus domesticus) production systems are increasing within Australia in response to consumer demand for perceived improvement in hen welfare. However, variation in outdoor stocking density has generated consumer dissatisfaction leading to the development of a national information standard on free-range egg labelling by the Australian Consumer Affairs Ministers. The current Australian Model Code of Practice for Domestic Poultry states a guideline of 1500 hens/ha, but no maximum density is set. Radio-frequency identification (RFID) tracking technology was used to measure daily range usage by individual ISA Brown hens housed in six small flocks (150 hens/flock – 50% of hens tagged), each with access to one of three outdoor stocking density treatments (two replicates per treatment: 2000, 10 000, 20 000 hens/ha), from 22 to 26, 27 to 31 and 32 to 36 weeks of age. There was some variation in range usage across the sampling periods and by weeks 32 to 36 individual hens from the lowest stocking density on average used the range for longer each day (P<0.001), with fewer visits and longer maximum durations per visit (P<0.001). Individual hens within all stocking densities varied in the percentage of days they accessed the range with 2% of tagged hens in each treatment never venturing outdoors and a large proportion that accessed the range daily (2000 hens/ha: 80.5%; 10 000 hens/ha: 66.5%; 20 000 hens/ha: 71.4%). On average, 38% to 48% of hens were seen on the range simultaneously and used all available areas of all ranges. These results of experimental-sized flocks have implications for determining optimal outdoor stocking densities for commercial free-range laying hens but further research would be needed to determine the effects of increased range usage on hen welfare. 相似文献
82.
83.
An isometric virus was isolated from Helianthus annuus L. plants showing a yellow leaf spot mosaic on affected leaves. Infected plants were found in different ecological regions of Ukraine. A procedure of virus purification is described. The diametres of the virus particles were nonuniform and ranged from 50 to 120 nm. The sedimentation coefficient of the virus was 518–540 S and the floating density in the CsCl gradient was 1.22 g/cm3. The MW of proteins separated by electrophoresis amounted to 78±0.9, 58±0.8, 52±0.2, and 27±0.8 kDa, respectively. The virus was assigned to the tospoviruses for which sunflower is a new previously undescribed natural host plant. 相似文献
84.
Activity-based protein profiling (ABPP) is recognized as a powerful and versatile chemoproteomic technology in drug discovery. Central to ABPP is the use of activity-based probes to report the activity of specific enzymes or reactivity of amino acid types in complex biological systems. Over the last two decades, ABPP has facilitated the identification of new drug targets and discovery of lead compounds in human and infectious disease. Furthermore, as part of a sustained global effort to illuminate the druggable proteome, the repertoire of target classes addressable with activity-based probes has vastly expanded in recent years. Here, we provide an overview of ABPP and summarise the major technological advances with an emphasis on probe development. 相似文献
85.
86.
Fibrillin‐1 is the major component of extracellular matrix microfibrils. Microfibrils dysfunction is responsible for the onset of various connective tissue diseases, including Marfan syndrome. Although ADAMTSL (a disintegrin and metalloproteinase with thrombospondin motifs‐like) 6β is one of the fibrillin‐1 binding proteins, the detailed mechanism underlying the involvement of ADAMTSL6β in microfibril formation remains unclear. In this study, we created deletion mutants of ADAMTSL6β and examined their interactions with fibrillin‐1 assembly. Pull‐down assay of the ADAMTSL6β deletion mutants and fibrillin‐1 protein revealed that ADAMTSL6β binds to fibrillin‐1 through the third thrombospondin type I domain. Furthermore, we observed that formation of fibrillin‐1 matrix assembly was enhanced in MG63 cells, expressing full‐length ADAMTSL6β, when compared with that of wild type MG63 cells. While MG63 cells expressing Δ TSP3‐ADAMTSL6β form showed enhanced assembly formation, Δ TSP2‐ADAMTSL6β form did not enhance that, indicating the difference between Δ TSP2‐Δ TSP3 has a critical role for fibrillin‐1 assembly. As the difference of Δ TSP2‐Δ TSP3 is the third thrombospondin type I domain, we concluded that the third thrombospondin type I domain of ADAMTSL6β influence the microfibril formation. Our data are the functional presentation of the biological role of ADAMTSL6β in the process of microfibril formation. 相似文献
87.
AbstractThe purpose of the study was to acquire the source and evaluate the risk posed by heavy metals in road dust of steel industrial city (Anshan), Liaoning, Northeast China. Potential ecological risk index (RI), pollution index (PI) and geo-accumulation index (Igeo) were applied to evaluate the heavy metal pollution level, and the carcinogenic risk (RI) and hazard index (HI) were calculated to estimate the human health risk. The geographic information system maps clearly reveal the hot spots of heavy metal spatial distribution. Principle component analysis (PCA) and cluster analysis (CA) classified heavy metals into three groups. The metal Zn and Pb originate from the traffic emission, while Cd, Cr, Fe, Mn, Ni and Sb primarily come from industrial activities. These two pathways were the major source of heavy metals pollution by positive matrix factorization (PMF). The Igeo and PI values of heavy metals were decreased in the following order: Cd?>?Sb?>?Zn?>?Fe?>?Pb?>?Cu?>?Cr?>?Sn?>?Mn?>?Ni. The RI index showed the heavy metals were moderate to very high potential ecological risk. The HI values for children and adults presented a decreasing order of Cr?>?Pb?>?Ni?>?Cu?>?Cd?>?Zn. The HI also predicted a possibility of non-carcinogenic risk for children living in urban areas in comparison with adults. 相似文献
88.
Muhammad Tariq-Khan Tariq Mukhtar Anjum Munir Johannes Hallmann Holger Heuer 《Journal of Phytopathology》2020,168(6):322-336
The present study documents the root-knot nematodes (RKN) fauna of the Poonch division in Azad Jammu and Kashmir infecting vegetables. An overall prevalence of 40% of RKN was recorded. Of the four districts investigated, maximum prevalence was recorded in district Poonch with 59%, followed by Sudhnuti with 58%. The lowest prevalence of RKN was found in districts Bagh (29%) and Haveli (33%). Out of 15 vegetables investigated, RKN was found on five crops. The highest prevalence of 37.8% was recorded on okra, followed by 31.3% on cucumber and 17.5% on tomato. RKN was less prevalent on eggplant (8.3%) and beans (7.7%). Three RKN species, that is Meloidogyne incognita, Meloidogyne javanica and Meloidogyne arenaria, were found infecting the hosts. M. javanica was found to be the most prevalent followed by M. incognita and M. arenaria. This trend was found in all the districts. Overall prevalence of M. javanica as sole population was 9% and that of M. incognita was 2%. Meloidogyne arenaria was not found in any of the fields as sole population. The prevalence of M. incognita with M. javanica or M. arenaria as mixed populations was 8% and 5%, respectively, and that of M. javanica with M. arenaria was 4%. Similarly, all the three species prevailed as mixed populations in 12% of the fields in the division. The severity of RKN infections, measured as galling index, was found to be variable within each infected field (GI 2–9). Identification of RKN species was based on the morphology of perineal patterns and confirmed by molecular SCAR and CO1 makers based identification. In conclusion, RKN were distributed in the Poonch division and M. javanica was predominant. Cucumber, okra, tomato and eggplant were severely attacked by these nematodes warranting the adoption of stringent control strategies for their management. 相似文献
89.
90.
该研究以采自新疆的100余份饼干衣属(Rinodina)地衣标本为研究材料,通过形态解剖特征观察、地衣化学成分分析以及分子生物学鉴定方法鉴定出9个种,包括2个中国新记录种——阿富汗饼干衣(Rinodina afghanica)和古氏饼干衣(Rinodina guzzinii),7个常见种分别是:包氏饼干衣(R. bohlinii)、毕氏饼干衣(R. bischoffii)、代谢饼干衣(R. metaboliza)、密果饼干衣(R. pycnocarpa)、特雷氏饼干衣(R. trevisanii)、甘肃饼干衣(R. straussii)和地生饼干衣(R. terrestris)。并提供了新疆饼干衣属地衣的分种检索表、每个物种的详细描述、新记录种的特征图片以及系统发育分析。 相似文献