全文获取类型
收费全文 | 22700篇 |
免费 | 1565篇 |
国内免费 | 1049篇 |
出版年
2024年 | 54篇 |
2023年 | 301篇 |
2022年 | 643篇 |
2021年 | 1035篇 |
2020年 | 697篇 |
2019年 | 930篇 |
2018年 | 923篇 |
2017年 | 698篇 |
2016年 | 989篇 |
2015年 | 1374篇 |
2014年 | 1557篇 |
2013年 | 1802篇 |
2012年 | 1993篇 |
2011年 | 1861篇 |
2010年 | 1035篇 |
2009年 | 918篇 |
2008年 | 1030篇 |
2007年 | 962篇 |
2006年 | 875篇 |
2005年 | 740篇 |
2004年 | 662篇 |
2003年 | 542篇 |
2002年 | 488篇 |
2001年 | 313篇 |
2000年 | 328篇 |
1999年 | 287篇 |
1998年 | 180篇 |
1997年 | 167篇 |
1996年 | 186篇 |
1995年 | 163篇 |
1994年 | 140篇 |
1993年 | 103篇 |
1992年 | 153篇 |
1991年 | 151篇 |
1990年 | 125篇 |
1989年 | 97篇 |
1988年 | 98篇 |
1987年 | 101篇 |
1986年 | 70篇 |
1985年 | 89篇 |
1984年 | 51篇 |
1983年 | 55篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1975年 | 29篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
861.
862.
Length–weight and length–length relationships of seven fish species from the Ili River and tributaries,northwest China 下载免费PDF全文
Z.‐M. Zhang C.‐X. Xie H.‐P. Ding X.‐F. Ma C.‐J. Liu Y. Guo 《Zeitschrift fur angewandte Ichthyologie》2016,32(1):153-155
Length–weight and length–length relationships were estimated for seven fish species belonging to four families from the Ili River and its tributaries, northwest China. From April to October 2013 and May to October 2014, specimens were collected monthly for a total of 783 specimens. This study presents the first references on LWRs for Diptychus maculates, Gymnodiptychu dybowskii, Perca schrenkii, Silurus meridionalis and Schizothorax pseudoaksaiensis pseudoaksaiensis, and LLRs for G. dybowskii, P. schrenkii, S. meridionalis, S. pseudoaksaiensis pseudoaksaiensis, Triplophysa strauchii and Triplophysa stoliczkai. 相似文献
863.
Ultrasonic Reaction of Bank Vole Males to the Presence of Females Varying in Hormonal Activity 下载免费PDF全文
Joanna Kapusta Małgorzata Kruczek 《Ethology : formerly Zeitschrift fur Tierpsychologie》2016,122(6):468-480
Rodents are known to emit ultrasounds during social interactions. Despite the evidence that ultrasonic vocalizations are emitted during sexual encounters and may play a certain role in sexual selection, only a few studies have investigated this phenomenon, mainly in laboratory rodents. We analysed the ultrasonic calls of bank vole (Myodes glareolus) males from an outbred colony in the presence of females differing in hormonal activity. Sexually experienced males were tested during interactions with naive, ovariectomized, pregnant and post‐partum oestrous females. We found that the males’ ultrasound vocalizations depend on the phase of the bank vole females’ reproductive cycle. During encounters with post‐partum oestrous females the males emitted significantly more ultrasounds, and the total duration of ultrasound vocalization was longer. The presence of post‐partum oestrous females also influenced the type of ultrasounds: the most typical constant‐frequency sounds were significantly shorter, and two additional types of ultrasounds were presented during interactions with females ready to mate: U‐shaped frequency‐modulated sounds and frequency‐modulated upsweep sounds. To our knowledge this is the first evidence that male voles of the subfamily Arvicolinae emit different types of ultrasounds in the presence of females depending on their reproductive stage. We suggest that these ultrasounds may be employed as an attractant during reproductive behaviour and that they are potentially an element of sexual selection. 相似文献
864.
胚胎心率是衡量胚胎新陈代谢速率的重要指标。鸟类的胚胎心率随新陈代谢的增加而呈上升趋势。对早成性鸟类的种间比较发现,胚胎心率平均值随卵重量的增大而减小,卵体积小的种类具有相对较高的胚胎心率。国内有关野生鸟类胚胎心率的研究较少。2014年5~8月,在黑龙江扎龙国家级自然保护区,利用红外胚胎心率测量仪对两种近缘鸟类家燕(Hirundo rustica,n=14)和金腰燕(Cecropis daurica,n=14)的卵胚胎心率及其变化进行了测量与比较。两种燕均在孵卵的第2天开始出现胚胎心率,并随胚龄增加心率呈上升趋势,但在第8天及第11~14天家燕的胚胎心率显著低于金腰燕(第8天:z=﹣2.602,P=0.009;第11天:z=﹣2.497,P=0.013;第12天:z=﹣2.354,P=0.019;第13天:z=3.424,P=0.001;第14天:z=﹣3.380,P=0.001)。家燕卵胚胎日均增长心率(19.0±3.1)次/min,金腰燕卵胚胎日均增长心率(16.1±3.4)次/min,二者差异不显著(z=﹣1.792,P=0.073)。两种燕的胚胎心率与卵容量和卵重均不存在显著相关性[家燕:卵容量(1.73±0.09)cm3,r=0.192,P=0.511;卵重(1.74±0.09)g,r=0.128,P=0.663。金腰燕:卵容量(1.74±0.08)cm3,r=0.040,P=0.891;卵重(1.51±0.09)g,r=0.054,P=0.855]。这可能表明,卵大小和卵重量对家燕与金腰燕的胚胎心率均影响不明显。 相似文献
865.
L. Grijalbo J. M. Becerril O. Barrutia J. Gutierrez‐Mañero J. A. Lucas Garcia 《Plant biology (Stuttgart, Germany)》2016,18(4):695-702
For the first time in the literature, duckweed (Lemna minor) tolerance (alone or in combination with a consortium of bacteria) to spent metal‐working fluid (MWF) was assessed, together with its capacity to reduce the chemical oxygen demand (COD) of this residue. In a preliminary study, L. minor response to pre‐treated MWF residue (ptMWF) and vacuum‐distilled MWF water (MWFw) was tested. Plants were able to grow in both residues at different COD levels tested (up to 2300 mg·l?1), showing few toxicity symptoms (mainly growth inhibition). Plant response to MWFw was more regular and dose responsive than when exposed to ptMWF. Moreover, COD reduction was less significant in ptMWF. Thus, based on these preliminary results, a second study was conducted using MWFw to test the effectiveness of inoculation with a bacterial consortium isolated from a membrane bioreactor fed with the same residue. After 5 days of exposure, COD in solutions containing inoculated plants was significantly lower than in non‐inoculated ones. Moreover, inoculation reduced β+γ‐tocopherol levels in MWFw‐exposed plants, suggesting pollutant imposed stress was reduced. We therefore conclude from that L. minor is highly tolerant to spent MWF residues and that this species can be very useful, together with the appropriate bacterial consortium, in reducing COD of this residue under local legislation limits and thus minimise its potential environmental impact. Interestingly, the lipophilic antioxidant tocopherol (especially the sum of β+γ isomers) proved to be an effective plant biomarker of pollution. 相似文献
866.
A transcriptome‐wide study on the microRNA‐ and the Argonaute 1‐enriched small RNA‐mediated regulatory networks involved in plant leaf senescence 下载免费PDF全文
Leaf senescence is an important physiological process during the plant life cycle. However, systemic studies on the impact of microRNAs (miRNAs) on the expression of senescence‐associated genes (SAGs) are lacking. Besides, whether other Argonaute 1 (AGO1)‐enriched small RNAs (sRNAs) play regulatory roles in leaf senescence remains unclear. In this study, a total of 5,123 and 1,399 AGO1‐enriched sRNAs, excluding miRNAs, were identified in Arabidopsis thaliana and rice (Oryza sativa), respectively. After retrieving SAGs from the Leaf Senescence Database, all of the AGO1‐enriched sRNAs and the miRBase‐registered miRNAs of these two plants were included for target identification. Supported by degradome signatures, 200 regulatory pairs involving 120 AGO1‐enriched sRNAs and 40 SAGs, and 266 regulatory pairs involving 64 miRNAs and 42 SAGs were discovered in Arabidopsis. Moreover, 13 genes predicted to interact with some of the above‐identified target genes at protein level were validated as regulated by 17 AGO1‐enriched sRNAs and ten miRNAs in Arabidopsis. In rice, only one SAG was targeted by three AGO1‐enriched sRNAs, and one SAG was targeted by miR395. However, five AGO1‐enriched sRNAs were conserved between Arabidopsis and rice. Target genes conserved between the two plants were identified for three of the above five sRNAs, pointing to the conserved roles of these regulatory pairs in leaf senescence or other developmental procedures. Novel targets were discovered for three of the five AGO1‐enriched sRNAs in rice, indicating species‐specific functions of these sRNA–target pairs. These results could advance our understanding of the sRNA‐involved molecular processes modulating leaf senescence. 相似文献
867.
868.
Min Cai Yulong Ma Wei Zhang Shiquan Wang Ying Wang Li Tian Zhengwu Peng Huaning Wang Tan Qingrong 《International journal of biological sciences》2016,12(1):42-52
Stroke is the major cause of permanent disability and mortality in China. Apigenin-7-O-β-D-(-6''''-p-coumaroyl)-glucopyranoside (APG) is a glycoside subtype of apigenin and has the antioxidant activity; however, whether and how it plays a neuroprotective role following cerebral ischemia remains unknown. In present study, we adopted the oxygen glucose/reperfusion model in PC12 cells, bilateral common carotid artery occlusion model in C57B6 mice and middle cerebral artery occlusion model in SD rats to observe the therapeutic effects of APG on ischemic stroke. We also discussed the underlying mechanism. Treatment with 0.4 μg/ml or 0.8 μg/ml APG promoted cell viability and proliferation, reduced LDH release and apoptotic cell death levels in PC12 cells. Treatment with 50 mg/kg or 100 mg/kg APG at 30 minutes after reperfusion improved neurological outcomes in vivo, as demonstrated by elevation of neurological scores in both mice and rats. It also increased the number of survival neurons in mice and reduced infarct volume in rats. APG also increased the contents of Mn-SOD and the phosphorylation level of STAT3, elevated the antioxidant activity and reduced oxidative productions. These findings revealed a neuroprotective effect of APG, which possibly induced by the STAT3 phosphorylation-mediated Mn-SOD up-regulation. 相似文献
869.
Conservation and divergence of the cyclic adenosine monophosphate–protein kinase A (cAMP–PKA) pathway in two plant‐pathogenic fungi: Fusarium graminearum and F. verticillioides 下载免费PDF全文
870.