全文获取类型
收费全文 | 2264篇 |
免费 | 207篇 |
国内免费 | 374篇 |
出版年
2024年 | 16篇 |
2023年 | 74篇 |
2022年 | 102篇 |
2021年 | 105篇 |
2020年 | 122篇 |
2019年 | 150篇 |
2018年 | 104篇 |
2017年 | 98篇 |
2016年 | 84篇 |
2015年 | 90篇 |
2014年 | 125篇 |
2013年 | 177篇 |
2012年 | 117篇 |
2011年 | 119篇 |
2010年 | 70篇 |
2009年 | 107篇 |
2008年 | 84篇 |
2007年 | 78篇 |
2006年 | 88篇 |
2005年 | 91篇 |
2004年 | 59篇 |
2003年 | 71篇 |
2002年 | 52篇 |
2001年 | 124篇 |
2000年 | 42篇 |
1999年 | 42篇 |
1998年 | 42篇 |
1997年 | 96篇 |
1996年 | 24篇 |
1995年 | 19篇 |
1994年 | 21篇 |
1993年 | 18篇 |
1992年 | 17篇 |
1991年 | 7篇 |
1990年 | 40篇 |
1989年 | 9篇 |
1988年 | 36篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 22篇 |
1979年 | 61篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有2845条查询结果,搜索用时 31 毫秒
921.
生物技术与生物学实验技术是两个内涵不同的概念。我们在生物教学以及生物有关教材的编写过程中,应给以区别和注意。 相似文献
922.
923.
Industrial Ecology and Ecological Engineering 总被引:1,自引:0,他引:1
David Rogers Tilley 《Journal of Industrial Ecology》2003,7(2):13-32
Ecological engineering (EE) and industrial ecology (IE) strive to balance humanity's activities with nature. The disciplines have emerged separately but share theoretical foundations and philosophies on how to address today's complex environmental issues. Although EE and IE share motive, goals, theories, and philosophies, there are many differences. These similarities and differences may make for a strong symbiotic relationship between the two fields. The goals of this article are (1) to compare and contrast the two fields to identify opportunities for collaboration and integration and (2) to suggest three cross-disciplinary focal areas that bridge EE and IE.
The first symbiotic area, ecosystem engineering for byproduct recovery, is defined as the design, creation, and management of living ecosystems (e.g., forests, wetlands) that utilize the by-products of industrial systems. Examples of this exist, including constructed wetlands for lead recovery and phyto-mining of nickel tailings. The second symbiotic focus is entitled "ecosystem analogues for industrial ecology", which fits with a founding principle of IE to strive to have industry emulate the energy efficiencies and material cycles of natural ecosystems. This focal area quantifies the ecological analogy and exploits the tremendous library of design alternatives that nature has developed over thousands of years to deal with varied resource situations. The third focal area is termed "eco-system information engineering." The means by which living ecosystems have created robust knowledge systems and information cycles should be understood in terms useful for managing current society's information explosion. As industrial society evolves toward the information society, holistic models are needed that account for the available energy and material resources required to operate effective information ecosystems, such as service industries. 相似文献
The first symbiotic area, ecosystem engineering for byproduct recovery, is defined as the design, creation, and management of living ecosystems (e.g., forests, wetlands) that utilize the by-products of industrial systems. Examples of this exist, including constructed wetlands for lead recovery and phyto-mining of nickel tailings. The second symbiotic focus is entitled "ecosystem analogues for industrial ecology", which fits with a founding principle of IE to strive to have industry emulate the energy efficiencies and material cycles of natural ecosystems. This focal area quantifies the ecological analogy and exploits the tremendous library of design alternatives that nature has developed over thousands of years to deal with varied resource situations. The third focal area is termed "eco-system information engineering." The means by which living ecosystems have created robust knowledge systems and information cycles should be understood in terms useful for managing current society's information explosion. As industrial society evolves toward the information society, holistic models are needed that account for the available energy and material resources required to operate effective information ecosystems, such as service industries. 相似文献
924.
Weight of individual grains is a major yield component in wheat. The non-uniform distribution of single grain weight on a wheat spike is assumed to be closely associated with starch synthesis in grains. The present study was undertaken to determine if the enzymes involved in starch synthesis cause the differences in single grain weight between superior and inferior grains on a wheat spike. Using two high-yield winter wheat (Triticum aestivum L.) varieties differing in grain weight and three nitrogen rates for one variety, the contents of amylose and amylopectin, and activities of enzymes involved in starch synthesis in both superior and inferior grains were investigated during the entire period of grain filling. Superior grains showed generally higher starch accumulation rates and activities of enzymes including SS (sucrose synthase), UDPGPPase (UDP-glucose pyrophosphorylase), ADPGPPase (ADP-glucose pyrophosphorylase), SSS (soluble starch synthase) and GBSS (starch granule bound starch synthase) and subsequently produced much higher single grain weight than inferior grains. Nitrogen increased enzyme activities and starch accumulation rates, and thus improved individual grain weight, especially for inferior grains. The SS, ADPGPPase and SSS were significantly correlated to amylopectin accumulation, while SS, ADPGPPase, SSS and GBSS were significantly correlated to amylose accumulation. This infers that SS, ADPGPPase and starch synthase play key roles in regulating starch accumulation and grain weight in superior and inferior grains on a wheat spike. 相似文献
925.
926.
应用GIS技术进行野生动物生境研究概况及展望 总被引:14,自引:1,他引:13
1 GIS的特性及对野生动物生境研究产生的影响近年来 ,生物多样性的研究和保护已在多层次、多水平上展开 [2 7] ,其中对野生动物生境的保护和研究是非常重要的一方面。生境 ( habitat)一词首先由美国的 Grinnel于 1 91 7年提出 ,指的是生物的居住场所 ,即生物个体、种群或群落能在其中完成生命过程的空间 [11]。自然界的生物都有它特定的生活环境 ,都有各自要求的适宜的环境条件。由于生物种类繁多 ,生物和环境、生物和生物之间的关系错综复杂 ,因此 ,野生动物生境的保护涉及到许多与时间动态及空间格局相关的问题。传统动物生态学和动物… 相似文献
927.
双液相系统酶化学技术制取茶色素 总被引:13,自引:0,他引:13
应用双液相酶化学技术研究茶色素的形成与制取,并以单液(水)相系统进行茶多酚酶促氧化制取茶色素为对照,引入氧载体后,构成了双液相酶化学氧化系统,对其中溶解氧浓度,PPO活性,TFs,TRs含量的变化和HPLC图谱等分析研究,制品中TFs的HPLC图谱可知:TOP-1中TFs的峰高和峰面积均高于TOP-2制品中TFs,尤以TFG与TFDG较高,TOP-1制品中儿茶素类残留量较对照少,尤其是简单儿茶素的列留量(如DL-C(-)-EC)少得更多。 相似文献
928.
细胞工程在生物制药工业中的地位 总被引:3,自引:0,他引:3
细胞工程是生物制药工业中的关键技术,它是利用动物细胞体外培养和扩增来生产生物产品,或作为发现和测试新的工具。本综述了细胞工程发展的历史、现状和未来,以及它在生物制药领域中的应用和局限。 相似文献
929.
蛋白质类药物在体内的半衰期短,主要原因是体内蛋白酶降解。利用抗体稳定活性蛋白质是一种较有前途的解决方法。本文介绍该方法的理论基础,以及随着抗体技术的进展(血清多克隆抗体→单克隆抗体→基因工程抗体)而提出的新的研究策略,这将为抗体稳定活性蛋白质开辟一条新的途径。 相似文献
930.
地下水硝酸类氮污染的修复技术 总被引:3,自引:0,他引:3
近年来,以氮化合物为代表的各种化学物质对地下水和土壤的污染,已引起了人们的广泛关注,硝酸类氮污染的地下饮用水,已严重地危害了人们的健康。在国外,硝酸类氮和亚硝酸类氮自来水水质标准的浓度及WHO的标准,分别限制在N113mg·L-1和10mg·L-1以下。我国采用20mg·L-1为基准值。饮用水中含有的大量硝酸性氮化物对健康的主要影响是引起高铁血红蛋白血症和高癌症发病率。地下水中硝酸类氮浓度上升的原因,主要与酸雨和污水中的氮化物向地下渗透,所施氮肥和家畜排泄物中含氮成分在土壤硝化作用形成硝酸类化合物有关。在我国,硝酸类… 相似文献