全文获取类型
收费全文 | 17179篇 |
免费 | 1416篇 |
国内免费 | 8篇 |
专业分类
18603篇 |
出版年
2024年 | 21篇 |
2023年 | 130篇 |
2022年 | 305篇 |
2021年 | 533篇 |
2020年 | 309篇 |
2019年 | 399篇 |
2018年 | 457篇 |
2017年 | 352篇 |
2016年 | 662篇 |
2015年 | 1079篇 |
2014年 | 1159篇 |
2013年 | 1344篇 |
2012年 | 1627篇 |
2011年 | 1457篇 |
2010年 | 930篇 |
2009年 | 773篇 |
2008年 | 1020篇 |
2007年 | 996篇 |
2006年 | 888篇 |
2005年 | 807篇 |
2004年 | 772篇 |
2003年 | 619篇 |
2002年 | 617篇 |
2001年 | 105篇 |
2000年 | 90篇 |
1999年 | 110篇 |
1998年 | 125篇 |
1997年 | 96篇 |
1996年 | 90篇 |
1995年 | 65篇 |
1994年 | 60篇 |
1993年 | 49篇 |
1992年 | 48篇 |
1991年 | 38篇 |
1990年 | 37篇 |
1989年 | 48篇 |
1988年 | 38篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 13篇 |
1976年 | 17篇 |
1974年 | 13篇 |
1968年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Deniselle MC Carreras MC Garay L Gargiulo-Monachelli G Meyer M Poderoso JJ De Nicola AF 《Journal of neurochemistry》2012,122(1):185-195
In the Wobbler mouse, a mutation of the Vps54 protein increases oxidative stress in spinal motoneurons, associated to toxic levels of nitric oxide and hyperactivity of nitric oxide synthase (NOS). Progesterone neuroprotection has been reported for several CNS diseases, including the Wobbler mouse neurodegeneration. In the present study, we analyzed progesterone effects on mitochondrial-associated parameters of symptomatic Wobbler mice. The activities of mitochondrial respiratory chain complexes I, II-III and IV and protein levels of mitochondrial and cytosolic NOS were determined in cervical and lumbar cords from control, Wobbler and Wobbler mice receiving a progesterone implant for 18 days. We found a significant reduction of complex I and II-III activities in mitochondria and increased protein levels of mitochondrial, but not cytosolic nNOS, in the cervical cord of Wobbler mice. Progesterone treatment prevented the reduction of complex I in the cervical region and the increased level of mitochondrial nNOS. Wobbler motoneurons also showed accumulation of amyloid precursor protein immunoreactivity and decreased activity and immunostaining of MnSOD. Progesterone treatment avoided these abnormalities. Therefore, administration of progesterone to clinically afflicted Wobblers (i) prevented the abnormal increase of mitochondrial nNOS and normalized respiratory complex I; (ii) decreased amyloid precursor protein accumulation, a sign of axonal degeneration, and (iii) increased superoxide dismutation. Thus, progesterone neuroprotection decreases mitochondriopathy of Wobbler mouse cervical spinal cord. 相似文献
922.
Närhi K Tummers M Ahtiainen L Itoh N Thesleff I Mikkola ML 《Developmental biology》2012,364(2):149-161
Mammary glands and hair follicles develop as ectodermal organs sharing common features during embryonic morphogenesis. The molecular signals controlling the initiation and patterning of skin appendages involve the bone morphogenetic proteins and Wnt family members, which are commonly thought to serve as inhibitory and activating cues, respectively. Here, we have examined the role of the Bmp and Wnt pathway modulator Sostdc1 in mammary gland, and hair and vibrissa follicle development using Sostdc1-null mice. Contrary to previous speculations, loss of Sostdc1 did not affect pelage hair cycling. Instead, we found that Sostdc1 limits the number of developing vibrissae and other muzzle hair follicles, and the size of primary hair placodes. Sostdc1 controls also the size and shape of mammary buds. Furthermore, Sostdc1 is essential for suppression of hair follicle fate in the normally hairless nipple epidermis, but its loss also promotes the appearance of supernumerary nipple-like protrusions. Our data suggest that functions of Sostdc1 can be largely attributed to its ability to attenuate Wnt/β-catenin signaling. 相似文献
923.
924.
Use of caryophyllene oxide as an antifungal agent in an in vitro experimental model of onychomycosis
Caryophyllene oxide, an oxygenated terpenoid, well known as preservative in food, drugs and cosmetics, has been tested in vitro as an antifungal against dermatophytes. Its antifungal activity has been compared to ciclopiroxolamine and sulconazole, commonly used in onychomycosis treatment and chosen because of their very different chemical structures. So, a new model has been tested, utilizing sheep hoof plates in order to simulate human nails, which are almost unobtainable for in vitro tests. Three protocols were utilized: pre-treatment. simultaneous treatment and post-treatment. Among these, the post-treatment method was the best to simulate antifungal therapy. as it permitted testing and comparing the efficiency of different antifungal drugs.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
925.
Integrated requirement of non‐specific and sequence‐specific DNA binding in Myc‐driven transcription
926.
927.
Diogo Aparecido Lopes Silva Francisco Antonio Rocco Lahr Ana Laura Raymundo Pavan Yovana M. B. Saavedra Natalia Crespo Mendes Sabrina Rodrigues Sousa Roberta Sanches Aldo Roberto Ometto 《The International Journal of Life Cycle Assessment》2014,19(10):1767-1778
Purpose
Sugarcane bagasse is one of the main agro-industrial residues which can be used to produce wood-based panels. However, more investigations related to its environmental performance assessment are needed, focusing on questions such as: Does it provide environmental benefits? What are its main environmental impacts? Could it substitute wood as raw material? Accordingly, this paper presents a life cycle assessment (LCA) study of particle board manufactured with sugarcane bagasse residues.Methods
The cradle-to-gate assessment of 1 m3 of particle board made with sugarcane bagasse (PSB) considered three main subsystems: bagasse generation, bagasse distribution, and PSB production. For the inventory of PSB, dataset from two previous LCA studies related to the conventional particle board production and the ethanol life cycle for the Brazilian context were used. The allocation criterion for the bagasse generation subsystem was 9.08 % (economic base). The potential environmental impact phase was assessed by applying the CML and USEtox methods. PSB was compared with the conventional particle board manufactured in Brazil by the categories of the CML and USETox, and including land use indicators. Finally, two scenarios were analyzed to evaluate the influence of the allocation criteria and the consumption of sugarcane bagasse.Results and discussion
All hotspots identified by CML and USETox methods are mainly related to the PSB production subsystem (24–100 % of impacts) due to heavy fuel oil, electricity, and urea-formaldehyde resin supply chain. The bagasse generation subsystem was more relevant to the eutrophication category (75 % of impacts). The bagasse distribution subsystem was not relevant because the impacts on all categories were lower than 1 %. PSB can substitute the conventional particle board mainly because of its lower contribution to abiotic depletion and ecotoxicity. Regarding land use impacts, PSB showed lower values according to all indicators (38–40 % of all impacts), which is explained by the lower demand for land occupation in comparison to that of the traditional particle board.Conclusions
PSB can replace the traditional particle board due to its better environmental performance. The analysis of the economic allocation criterion was relevant only for the EP category, being important to reduce diesel and N-based fertilizers use during sugarcane cultivation. Regarding the influence of the sugarcane bagasse consumption, it is suggested that the sugarcane bagasse be mixed up to 75 % during particle board manufacturing so that good quality properties and environmental performance of panels can be provided. 相似文献928.
A sex-associated sequence identified by RAPD screening in gynogenetic individuals of turbot (Scophthalmus maximus) 总被引:1,自引:0,他引:1
Luis Vale Rebeca Dieguez Laura Sánchez Paulino Martínez Ana Viñas 《Molecular biology reports》2014,41(3):1501-1509
Understanding the genetic basis of sex determination mechanisms is essential for improving the productivity of farmed aquaculture fish species like turbot (Scophthalmus maximus). In culture conditions turbot males grow slower than females starting from eight months post-hatch, and this differential growth rate is maintained until sexual maturation is reached, being mature females almost twice as big as males of the same age. The goal of this study was to identify sex-specific DNA markers in turbot using comparative random amplified polymorphism DNA (RAPD) profiles in males and females to get new insights of the genetic architecture related to sex determination. In order to do this, we analyzed 540 commercial 10-mer RAPD primers in male and female pools of a gynogenetic family because of its higher inbreeding, which facilitates the detection of associations across the genome. Two sex-linked RAPD markers were identified in the female pool and one in the male pool. After the analysis of the three markers on individual samples of each pool and also in unrelated individuals, only one RAPD showed significant association with females. This marker was isolated, cloned and sequenced, containing two sequences, a microsatellite (SEX01) and a minisatellite (SEX02), which were mapped in the turbot reference map. From this map position, through a comparative mapping approach, we identified Foxl2, a relevant gene related to initial steps of sex differentiation, and Wnt4, a gene related with ovarian development, close to the microsatellite and minisatellite markers, respectively. The position of Foxl2 and Wnt4 was confirmed by linkage mapping in the reference turbot map. 相似文献
929.
Evaluation of live attenuated influenza a virus h6 vaccines in mice and ferrets 总被引:1,自引:0,他引:1 下载免费PDF全文
Chen Z Santos C Aspelund A Gillim-Ross L Jin H Kemble G Subbarao K 《Journal of virology》2009,83(1):65-72
Avian influenza A virus A/teal/HK/W312/97 (H6N1) possesses seven gene segments that are highly homologous to those of highly pathogenic human influenza H5N1 viruses, suggesting that a W312-like H6N1 virus might have been involved in the generation of the A/HK/97 H5N1 viruses. The continuous circulation and reassortment of influenza H6 subtype viruses in birds highlight the need to develop an H6 vaccine to prevent potential influenza pandemics caused by the H6 viruses. Based on the serum antibody cross-reactivity data obtained from 14 different H6 viruses from Eurasian and North American lineages, A/duck/HK/182/77, A/teal/HK/W312/97, and A/mallard/Alberta/89/85 were selected to produce live attenuated H6 candidate vaccines. Each of the H6 vaccine strains is a 6:2 reassortant ca virus containing HA and NA gene segments from an H6 virus and the six internal gene segments from cold-adapted A/Ann Arbor/6/60 (AA ca), the master donor virus that is used to make live attenuated influenza virus FluMist (intranasal) vaccine. All three H6 vaccine candidates exhibited phenotypic properties of temperature sensitivity (ts), ca, and attenuation (att) conferred by the internal gene segments from AA ca. Intranasal administration of a single dose of the three H6 ca vaccine viruses induced neutralizing antibodies in mice and ferrets and fully protected mice and ferrets from homologous wild-type (wt) virus challenge. Among the three H6 vaccine candidates, the A/teal/HK/W312/97 ca virus provided the broadest cross-protection against challenge with three antigenically distinct H6 wt viruses. These data support the rationale for further evaluating the A/teal/HK/W312/97 ca vaccine in humans. 相似文献
930.
Diane Rebourcet Peter J. O’Shaughnessy Ana Monteiro Laura Milne Lyndsey Cruickshanks Nathan Jeffrey Florian Guillou Tom C. Freeman Rod T. Mitchell Lee B. Smith 《PloS one》2014,9(8)
The Sertoli cells are critical regulators of testis differentiation and development. In the adult, however, their known function is restricted largely to maintenance of spermatogenesis. To determine whether the Sertoli cells regulate other aspects of adult testis biology we have used a novel transgenic mouse model in which Amh-Cre induces expression of the receptor for Diphtheria toxin (iDTR) specifically within Sertoli cells. This causes controlled, cell-specific and acute ablation of the Sertoli cell population in the adult animal following Diphtheria toxin injection. Results show that Sertoli cell ablation leads to rapid loss of all germ cell populations. In addition, adult Leydig cell numbers decline by 75% with the remaining cells concentrated around the rete and in the sub-capsular region. In the absence of Sertoli cells, peritubular myoid cell activity is reduced but the cells retain an ability to exclude immune cells from the seminiferous tubules. These data demonstrate that, in addition to support of spermatogenesis, Sertoli cells are required in the adult testis both for retention of the normal adult Leydig cell population and for support of normal peritubular myoid cell function. This has implications for our understanding of male reproductive disorders and wider androgen-related conditions affecting male health. 相似文献