全文获取类型
收费全文 | 2721篇 |
免费 | 212篇 |
国内免费 | 371篇 |
出版年
2024年 | 8篇 |
2023年 | 70篇 |
2022年 | 95篇 |
2021年 | 106篇 |
2020年 | 130篇 |
2019年 | 138篇 |
2018年 | 96篇 |
2017年 | 101篇 |
2016年 | 96篇 |
2015年 | 98篇 |
2014年 | 134篇 |
2013年 | 184篇 |
2012年 | 142篇 |
2011年 | 150篇 |
2010年 | 88篇 |
2009年 | 166篇 |
2008年 | 157篇 |
2007年 | 133篇 |
2006年 | 163篇 |
2005年 | 128篇 |
2004年 | 93篇 |
2003年 | 96篇 |
2002年 | 69篇 |
2001年 | 64篇 |
2000年 | 43篇 |
1999年 | 48篇 |
1998年 | 46篇 |
1997年 | 31篇 |
1996年 | 37篇 |
1995年 | 40篇 |
1994年 | 33篇 |
1993年 | 36篇 |
1992年 | 37篇 |
1991年 | 31篇 |
1990年 | 23篇 |
1989年 | 23篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 19篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1972年 | 2篇 |
排序方式: 共有3304条查询结果,搜索用时 265 毫秒
41.
Lindl T 《Cytotechnology》1996,21(3):183-193
This article describes the current status in the development of human monoclonal antibodies. Over the last ten years a lot of information about the human immune system has emerged. Combining these with the many new (bio-)technologies it is plausible that the long awaited breakthrough of this technology is close. This paper focuses on the classical cell-biological methods of achieving stable, antibody-producing human cell lines via cell fusion methods or virus derived transformations of human B-lymphocytes, as well as genetic engineering methods e.g. DNA libraries or phage display technology. The available in vitro immunization methods are critically reviewed and their impact on this topic is discussed. Therapeutic applications for cancer treatment or passive immunization against infectious diseases with antibodies derived by both ways are also reviewed. 相似文献
42.
Increasingly electronic communication and a variety of electronic resources are accessible to a larger group of people within the scientific community. This paper outlines the range of resources that are available, and comments on their current and future value to the phycological community. Resources discussed include mailing lists and newsgroups. These are useful tools for rapid, informal, targeted communication, although the technology employed places limitations on the type and format of information which may be distributed. The World Wide Web (WWW) has the potential to overcome these limitations, the quality, complexity and value to the phycological community of the sites on the WWW are extremely variable, with some material being of dubious quality. However, it is possible to access high quality resources including culture collection catalogues, high quality images and microbial and molecular databases. As well as some of the current resources, this paper discusses some possible directions for the future of phycology on the internet.http://wiua.nwi.ac.uk/ 相似文献
43.
棉铃虫病毒杀虫乳悬剂的生产及其药效试验 总被引:5,自引:1,他引:4
成功研制出棉铃虫病毒(NPV)杀虫乳悬剂,改进了生产工艺和设备,建立了棉铃虫的室内品系,提高了生产效率,建立了产品的检测方法,提高了产品质量,促使棉铃虫病毒杀虫剂商品开发获得成功。大田试验证明,病毒乳悬剂的防治效果,相当于当前推广的化学农药,优于原病毒可湿性粉剂。相同剂量(0.53一1.07×10(10)PIB/公顷)的病毒乳悬剂可使虫口平均减退91.7%,而病毒可湿性粉剂为83.7%。 相似文献
44.
笼养白腹锦鸡觅食活动的观察 总被引:10,自引:2,他引:8
笼养条件下白腹锦鸡(Chrysolophus amherstiae)的日觅食活动呈现早(7:00-8:00)和晚(18:00-19:00)两个明显高峰期,不同季节和天气其觅食节律有一定的差异;在一年中9月翌年4月的觅食频次较高,这可能与鸟类补充繁殖期能量消耗、积累能量御寒和保证生殖腺发育有关;逐步回归分析结果表明:影响雄鸟觅食活动的主要因素为求偶、理羽和游走;影响雄鸟觅食的主要因素是游走、理羽和静 相似文献
45.
水库对投饵网箱养鱼的负荷力 总被引:35,自引:2,他引:33
本文用18个14.3m ̄3的围隔组成的围隔群,以鲤为材料,研究了水库对投饵网箱养鱼的负荷力。实验中观测了水温、透明度、pH值、溶氧、化学耗氧量、生化需氧量与非离子氨等环境因素的变化。结束时将这些变化与我国渔业水质标准相比较,查明该负荷力约为3000kg·ha ̄(-1),建议增加25-35%的安全储备,以最大载鱼量1800-2300kg·ha ̄(-1)作为推荐值。 相似文献
46.
Stephen J. M. Blaber David T. Brewer John P. Salini 《Environmental Biology of Fishes》1994,40(2):159-174
Synopsis The diets of 13 species of ariid catfishes from the tropical waters of the Gulf of Carpentaria are described and compared. Fishes were collected from two estuaries and inshore and offshore marine areas. Up to 10 species have been recorded from a single estuary. Although all are carnivorous and consume a variety of prey, diet analyses and statistical ordination reveal three feeding guilds - piscivores, polychaete-eaters and molluscivores. The diets of most species are similar between sites. There are strong relationships between dietary guild and the size and arrangement of the palatine teeth. The piscivorous group of catfish (guild 1) have large mouths with relatively large multiple palatine tooth plates, either in a band or in a triangular pattern and armed with sharp recurved teeth. The primarily polychaete-feeding group (guild 2) have a variable mouth size but it is usually smaller than that of guild 1 fish; their palatine teeth plates are fewer and smaller, and they have small, sharp recurved teeth. Guild 3 eat mainly molluscs, and have a small mouth and large posteriorly situated palatine plates with globular, truncated teeth. Overlaps in diet between species are probably reduced by differential distribution patterns within estuaries and different habitat preferences. The mouth-width and tooth-plate arrangements of ariids in tropical Australia are suitable for dealing with broad classes of prey rather than specific items, conferring dietary flexibility. This probably optimizes the trade-off for most species between occupation of broad feeding niches and the ability to shift diet easily. 相似文献
47.
A recent model of parental provisioning (the tradeoff model) suggests that the maximum delivery rate of food to nestlings represents a tradeoff between parental residual reproductive value and nestling survival. In contrast, Lack's hypothesis suggests that maximum provisioning rate determines brood size and therefore delivery rates are limited by shortages of food or foraging time, not by tradeoffs of parental investment. Several authors have examined the shape of the per-nestling feeding curves to test the tradeoff model against Lack's hypothesis. We show that Lack's hypothesis can produce per-nestling feeding curves consistent with the tradeoff model. Therefore, the shape of the per-nestling feeding curve cannot be used to distinguish between the models. 相似文献
48.
49.
The cultural reproduction of lithic technology, long an implicit assumption of archaeological theories, has garnered increasing attention over the past decades. Major debates ranging from the origins of the human culture capacity to the interpretation of spatiotemporal patterning now make explicit reference to social learning mechanisms and cultural evolutionary dynamics. This burgeoning literature has produced important insights and methodological innovations. However, this rapid growth has sometimes led to confusion and controversy due to an under-examination of underlying theoretical and methodological assumptions. The time is thus ripe for a critical assessment of progress in the study of the cultural reproduction of lithic technology. Here we review recent work addressing the evolutionary origins of human culture and the meaning of artifact variation at both intrasite and intersite levels. We propose that further progress will require a more extended and context-specific evolutionary approach to address the complexity of real-world cultural reproduction. 相似文献
50.
Troy A. Baird 《Environmental Biology of Fishes》1993,38(4):393-397
Synopsis The bar jack,Caranx Tuber, was commonly observed to follow individual puddingwife wrasses,Halichoeres radiatus, that were foraging on the substrate. Individuals of both species actively pursued the other to maintain these heterospecific foraging teams, were sometimes attracted to feeding acts initiated by team partners, and the foraging rates of teamed jacks and wrasses were positively correlated. Pilfering of food items was rare, suggesting little, if any, competition cost of this foraging association. The ratio of bites to search in teamed jacks was over three times that when solitary, and jacks were sometimes aggressive to conspecifics attempting to join their team, suggesting that the association is beneficial to the jacks. Both bite and search rates were higher in puddingwifes when teamed with a jack, indicating that the association also benefits the wrasses. Benefits to puddingwifes may be derived directly from attendants because wrasses were sometimes attracted to jack foraging acts. However, increased foraging in wrasses may also be a consequence of heightened motivation to feed owing to heterospecific social facilitation. 相似文献