全文获取类型
收费全文 | 465篇 |
免费 | 43篇 |
国内免费 | 23篇 |
专业分类
531篇 |
出版年
2023年 | 2篇 |
2022年 | 29篇 |
2021年 | 18篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 21篇 |
2015年 | 22篇 |
2014年 | 30篇 |
2013年 | 57篇 |
2012年 | 35篇 |
2011年 | 54篇 |
2010年 | 61篇 |
2009年 | 38篇 |
2008年 | 26篇 |
2007年 | 7篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1993年 | 6篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 5篇 |
1971年 | 6篇 |
1968年 | 3篇 |
1963年 | 1篇 |
1954年 | 1篇 |
1951年 | 1篇 |
1950年 | 1篇 |
1937年 | 1篇 |
1929年 | 2篇 |
1928年 | 1篇 |
排序方式: 共有531条查询结果,搜索用时 0 毫秒
11.
Methylparaben induces malformations and alterations on apoptosis,oxidant–antioxidant status,ccnd1 and myca expressions in zebrafish embryos 下载免费PDF全文
Perihan Seda Ateş İsmail Ünal Ünsal Veli Üstündağ Ahmet Ata Alturfan Türkan Yiğitbaşı Ebru Emekli‐Alturfan 《Journal of biochemical and molecular toxicology》2018,32(3)
Methylparabens (MP) are widely used as preservatives in cosmetics, pharmacy, and food industry. Although acute toxicity studies in animals indicated that parabens are not significantly toxic, the effects of chronic exposure under sublethal doses are still unknown and the number of related studies is limited. Our aim was to evaluate the effects of MP on the development of zebrafish embryos focusing on development, locomotor activity, oxidant–antioxidant status, apoptosis, and ccnd1 and myca expressions. The expressions of ccnd1 and myca were determined by RT‐PCR. Lipid peroxidation (LPO), nitric oxide (NO), and glutathione‐S‐transferase (GST) activities were determined spectrophotometrically. Apoptosis was determined using acridine orange staining. Locomotor activity was measured using touch‐evoked movement test. MP exposure increased malformations, LPO, apoptosis, ccnd1 and myca expressions, and decreased GST activities and NO levels compared with the control group. Our findings will lead to further understanding of the mechanism of MP toxicity, and merit further research. 相似文献
12.
13.
MURAT EKICI ZEKI AYTAÇ HASAN AKAN MÜNEVVER PINAR 《Botanical journal of the Linnean Society. Linnean Society of London》2008,157(4):741-747
A new species of Astragalus L., A. trabzonicus (section Onobrychoidei DC.), is described and illustrated from north‐east Anatolia in Turkey. The diagnostic, pollen morphological, and chromosomal characteristics are discussed. A distribution map and conservation status are given. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 741–747. 相似文献
14.
TIMOTHEÜS VAN DER NIET WILLIAM R. LILTVED STEVEN D. JOHNSON 《Botanical journal of the Linnean Society. Linnean Society of London》2011,166(4):417-430
Superficial similarities among unrelated species are often a result of convergent evolution and can cause considerable taxonomic confusion. A case in point is Satyrium eurycalcaratum , described here as a new species, which has been confused with several other Satyrium spp. with similar long‐spurred, white flowers. A phylogenetic analysis, based on molecular data, indicated that S. eurycalcaratum is not closely related to any of the species with which it has been previously confused. A comparative analysis of morphological characters in the seven South African Satyrium spp. with long‐spurred, white flowers showed that each of these, including S. eurycalcaratum , is characterized by a unique combination of traits. Despite the similarity in pollination syndrome characters, such as spur length and flower colour, variation in rostellum structure was particularly pronounced and four distinctive forms were present. There was no phylogenetic signal in patterns of interspecific rostellum variation, as some closely related species had different rostella, whereas some distantly related species shared similar rostellum structures. We therefore conclude that the use of rostellum traits in conjunction with phylogenetic evidence can resolve species delimitations among orchid species that share the same pollination syndrome. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 166 , 417–430. 相似文献
15.
16.
The aim of this study was to determine the first effect of lead on microbial activity in soil. The study was carried out in the soil samples from four different radish (Raphanus sativus L. var. radicula, Brassicaceae) fields along the highway in a district (Kadirli, Osmaniye) of the Eastern Mediterranean Region, Turkey. After the calculation of Pb contents, the Pb amounts of the soil samples were brought up to 50 and 100 mg Pb kg?1 by treatment with Pb(NO 3 ) 2 , and the samples for the carbon and the nitrogen mineralization were incubated under controlled conditions (28°C, constant moist). The carbon mineralization was determined by a CO 2 respiration method for 30 days. The nitrogen mineralization was observed in vitro for 6 weeks. The untreated group was statistically different from the 50 and 100 mg Pb kg?1 treatments in the aspect of the C(CO 2 ) outlet during mineralization (P ≤ 0.05), but difference between the 50 and 100 mg Pb kg?1 treatments was not significant. NH 4 -N and NO 3 -N contents of each soil were shown differences between across treatments. Based on these results, it is possible to conclude that the addition of 50 and 100 mg Pb kg?1 provided a toxic effect threshold for the microbial activity into 30 days. 相似文献
17.
Ülo Niinemets 《Trees - Structure and Function》1998,12(7):446-451
Foliar inclination angles, petiole morphology and dry matter partitioning between assimilative and support biomass were studied
in shade-intolerant Populus tremula L. and shade-tolerant Tilia cordata Mill. along a natural light gradient across the canopy. The leaves of sub-canopy species T. cordata were on average exposed to lower irradiances, and they were also more horizontal with greater blade inclination angles (ϕB, defined as the angle between the leaf fall-line and the horizon; ϕB was positive for the leaves inclined upwards, and negative for the leaves inclined downwards) than those in P. tremula. Seasonal average daily integrated quantum flux density (Q
int, mol m–2 day–1) and ϕB were not related in T. cordata, and only a weak negative effect of Q
int on ϕB was detected in P. tremula. Nevertheless, when both species were pooled, there was a strong negative relationship between Q
int and ϕB, implying that the leaves became progressively vertical with increasing height in the canopy. Interspecific differences in
foliage inclination were mainly related to petiole morphology, in particular to petiole length, rather than to contrasting
biomass investment patterns between assimilative and support tissues within the leaf. It was suggested that more horizontal
leaves, resulting from the species-specific structure of petioles, partly explain the superior performance of shade-tolerant
T. cordata in the understory and the sub-canopy.
Received: 13 November 1997 / Accepted: 6 March 1998 相似文献
18.
JAMES F. HARWOOD KEHUI CHEN HANS‐GEORG MÜLLER JANE‐LING WANG ROGER I. VARGAS JAMES R. CAREY 《Physiological Entomology》2013,38(1):81-88
The reproductive ability of female tephritids can be limited and prevented by denying access to host plants and restricting the dietary precursors of vitellogenesis. The mechanisms underlying the delayed egg production in each case are initiated by different physiological processes that are anticipated to have dissimilar effects on lifespan and reproductive ability later in life. The egg‐laying abilities of laboratory‐reared females of the Mediterranean fruit fly (Ceratitis capitata Wiedmann) and melon fly (Bactrocera cucurbitae Coquillett) from Hawaii are delayed or suppressed by limiting access to host fruits and dietary protein. In each case, this is expected to prevent the loss of lifespan associated with reproduction until protein or hosts are introduced. Two trends are observed in each species: first, access to protein at eclosion leads to a greater probability of survival and a higher reproductive ability than if it is delayed and, second, delayed host access reduces lifetime reproductive ability without improving life expectancy. When host access and protein availability are delayed, the rate of reproductive senescence is reduced in the medfly, whereas the rate of reproductive senescence is generally increased in the melon fly. Overall, delaying reproduction lowers the fitness of females by constraining their fecundity for the remainder of the lifespan without extending the lifespan. © 2013 The Royal Entomological Society 相似文献
19.
20.
JÜRG GERTSCH STEFAN RADUNER KARL-HEINZ ALTMANN 《Journal of receptor and signal transduction research》2013,33(5-6):709-730
Since the discovery that Δ 9-tetrahydrocannabinol and related cannabinoids from Cannabis sativa L. act on specific physiological receptors in the human body and the subsequent elucidation of the mammalian endogenous cannabinoid system, no other natural product class has been reported to mimic the effects of cannabinoids. We recently found that N-alkyl amides from purple coneflower (Echinacea spp.) constitute a new class of cannabinomimetics, which specifically engage and activate the cannabinoid type-2 (CB2) receptors. Cannabinoid type-1 (CB1) and CB2 receptors belong to the family of G protein-coupled receptors and are the primary targets of the endogenous cannabinoids N-arachidonoyl ethanolamine and 2-arachidonoyl glyerol. CB2 receptors are believed to play an important role in distinct pathophysiological processes, including metabolic dysregulation, inflammation, pain, and bone loss. CB2 receptors have, therefore, become of interest as new targets in drug discovery. This review focuses on N-alkyl amide secondary metabolites from plants and underscores that this group of compounds may provide novel lead structures for the development of CB2-directed drugs. 相似文献