全文获取类型
收费全文 | 13310篇 |
免费 | 870篇 |
国内免费 | 1137篇 |
出版年
2023年 | 143篇 |
2022年 | 144篇 |
2021年 | 224篇 |
2020年 | 300篇 |
2019年 | 385篇 |
2018年 | 305篇 |
2017年 | 296篇 |
2016年 | 449篇 |
2015年 | 489篇 |
2014年 | 625篇 |
2013年 | 1020篇 |
2012年 | 767篇 |
2011年 | 689篇 |
2010年 | 463篇 |
2009年 | 589篇 |
2008年 | 654篇 |
2007年 | 663篇 |
2006年 | 579篇 |
2005年 | 528篇 |
2004年 | 480篇 |
2003年 | 472篇 |
2002年 | 498篇 |
2001年 | 394篇 |
2000年 | 371篇 |
1999年 | 328篇 |
1998年 | 307篇 |
1997年 | 285篇 |
1996年 | 306篇 |
1995年 | 318篇 |
1994年 | 246篇 |
1993年 | 216篇 |
1992年 | 208篇 |
1991年 | 192篇 |
1990年 | 203篇 |
1989年 | 155篇 |
1988年 | 80篇 |
1987年 | 58篇 |
1986年 | 69篇 |
1985年 | 82篇 |
1984年 | 76篇 |
1983年 | 41篇 |
1982年 | 68篇 |
1981年 | 68篇 |
1980年 | 113篇 |
1979年 | 132篇 |
1978年 | 74篇 |
1977年 | 43篇 |
1976年 | 27篇 |
1974年 | 25篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
1.
叉茎管蚜蝇属Tigridemyia与墨管蚜蝇属 Mesembrius和美管蚜蝇属 Mallota形态相似,过去曾被作为后二属的亚属.但此属的雄性外生殖器阳茎的射精管端部4分叉与墨管蚜蝇属和美管蚜蝇属区别明显,因此,其属地位应予肯定.作者在整理中国的食蚜蝇标本时,发现该属1新种,刺腿叉茎管蚜蝇Tigridemyia acanthogemurilis sp.nov,加之过去已记录的1种,我国已知叉茎管蚜蝇属2种.本文描述了新种,并给出了中国已知2种的检索表和形态特征图及其分布.模式标本保存于华南农业大学植保系昆虫标本室. 相似文献
2.
Nutrients are assimilated efficiently by Lymantria dispar caterpillars from the mature leaves of trees in the Salicaceae 下载免费PDF全文
Raymond V. Barbehenn Jennifer Knister Frank Marsik Chelsea Jahant‐Miller William Nham 《Physiological Entomology》2015,40(1):72-81
The efficient aquisition of nutrients from leaves by insect herbivores increases their nutrient assimilation rates and overall fitness. Caterpillars of the gypsy moth (Lymantria dispar L.) have high protein assimilation efficiencies (PAE) from the immature leaves of trees such as red oak (Quercus rubra) and sugar maple (Acer saccharum) (71–81%) but significantly lower PAE from their mature leaves (45–52%). By contrast to this pattern, both PAE and carbohydrate assimilation efficiencies (CAE) remain high for L. dispar larvae on the mature leaves of poplar (Populus alba × Populus tremula) grown in greenhouse conditions. The present study tests two alternative hypotheses: (i) outdoor environmental stresses cause decreased nutrient assimilation efficiencies from mature poplar leaves and (ii) nutrients in the mature leaves of trees in the poplar family (Salicaceae) remain readily available for L. dispar larvae. When poplar trees are grown in ambient outdoor conditions, PAE and CAE remain high (approximately 75% and 78%, respectively) in L. dispar larvae, in contrast to the first hypothesis. When larvae feed on the mature leaves of species in the Salicaceae [aspen (Populus tremuloides), cottonwood (Populus deltoides), willow (Salix nigra) and poplar], PAE and CAE also remain high (68–76% and 72–92%, respectively), consistent with the second hypothesis. Larval growth rates are strongly associated with protein assimilation rates, and more strongly associated with protein assimilation rates than with carbohydrate assimilation rates. It is concluded that tree species in the Salicaceae are relatively high‐quality host plants for L. dispar larvae, in part, because nutrients in their mature leaves remain readily available. 相似文献
3.
Banker plants with Aphidius colemani were tested in greenhouse for control of Myzus persicae on arugula and sweet pepper crops and compared to inoculative releases of parasitoids. Banker plants system consisted of pots of oat (non-crop plant) infested with Rhopalosiphum padi (non-pest herbivore). The non-pest herbivore serves as an alternative host for A. colemani (parasitoid of the target crop pest). In the arugula crop significant differences in the pest population between the two strategies of biological control showed the lowest densities of the pest when introducing the banker plant system. In the sweet pepper crop, there was no difference in the pest population between the two strategies of biological control. 相似文献
4.
5.
Intracellular Development of Enterocytozoon, A Unique Microsporidian Found in the Intestine of AIDS Patients 总被引:2,自引:0,他引:2
Enterocytozoon was 1st described in 1985, in an AIDS patient with intestinal malabsorption and diarrhea. Since then, additional cases of infection with this organism have been observed, but only in individuals with AIDS and malabsorption. Intestinal tissue biopsies were obtained from a 45-year-old man prior to AIDS diagnosis, again nine months later and then at autopsy two months later. When the biopsies were examined electron microscopically, both sets contained the microsporidian parasite. However, the 2nd intestinal biopsy, when wasting was much more severe, contained infection in almost every small intestinal enterocyte examined. The parasite was actively developing, allowing us to detail its life cycle. The parasite is apansporoblastic, polysporous and has characteristics not previously reported in the Microsporida: (1) an electron lucent inclusion not usually seen in Microsporida is prominent and always present; (2) extremely elongated sausage-shaped nuclei occur in the proliferative phase of parasite development; (3) the polar tube development uniquely involves the production of electron dense discs, yet results in the formation of a typical spore; and (4) polar tube development occurs prior to the final division of the multi-nucleate sporont. On the basis of these characteristics, we are placing this genus in a new family, Enterocytozoonidae, n. fam. 相似文献
6.
7.
基于各学科信息作出安全性、有效性和质量可控性方面的综合评价是新药研究评价的灵魂,是一个多学科、多组织参与的综合决策过程。根据新药评价研究的实际工作经验,介绍一个新药临床试验综合评价的逻辑性、结构性的工作思考模式,有助于将不同专业的技术信息和技术结论有机整合,作出科学决策。 相似文献
8.
Abstract Two new species of water mites, Pionopsis (s.s.)longicosta sp. nov. and Pionopsis (s.s.) zhaoi sp. nov. are described in the present paper. This is the first record of the genus of the subfamily Tiphyinae in the family Pionidae from China. 相似文献
9.
山西省异爪蝗属二新种(直翅目:网翅蝗科) 总被引:4,自引:0,他引:4
本文记述在晋南地区采到的异爪蝗属二新种,黑条异爪蝗Euchorthippus nigiliineatus sp.nov.及曲线异爪蝗Eochorthippus sinucarinatus sp.nov. 相似文献
10.
The behaviour of summer and autumn winged forms of the black bean aphid, Aphis fabae Scopoli (Homoptera: Aphididae), was compared on two plants utilized at different stages of the insect’s life cycle. Adult autumn migrants (gynoparae) are monophagous, colonizing spindle (Euonymus europaeus), whereas polyphagous summer winged aphids (alate virginoparae) are associated with a variety of herbaceous plants, including broad bean (Vicia faba). When aphids from a single clone were given access to a spindle leaf and a bean seedling in choice tests, many virginoparae settled and larviposited on both plant species over 24 h. By contrast, gynoparae showed a clear preference for spindle, with 93.5% of settled adults and 98.3% of larvae on this plant species. Close‐up video monitoring showed that gynoparae discriminated beans from spindle within a 5‐min period, whereas virginoparae behaved similarly on both plant species. For gynoparae, the major behavioural difference on the two plants appeared after a brief (epidermal) stylet penetration, with many insects taking flight within a few seconds of stylet withdrawal from bean. Factors detected during stylet insertion by gynoparae must therefore inhibit take‐off on spindle. Electrical recording experiments showed that aphids often punctured a cell membrane during brief probes on both plant species, and intracellular stylet activities always included a waveform associated with ingestion. When gynoparae puncture spindle cells their behaviour is probably modified by intracellular metabolites detected via gustation of ingested epidermal cell sap. These cues may inhibit the take‐off reflex which otherwise follows probing. 相似文献