全文获取类型
收费全文 | 2774篇 |
免费 | 290篇 |
出版年
2021年 | 34篇 |
2020年 | 21篇 |
2019年 | 33篇 |
2018年 | 28篇 |
2017年 | 25篇 |
2016年 | 40篇 |
2015年 | 83篇 |
2014年 | 102篇 |
2013年 | 130篇 |
2012年 | 124篇 |
2011年 | 136篇 |
2010年 | 76篇 |
2009年 | 79篇 |
2008年 | 114篇 |
2007年 | 122篇 |
2006年 | 106篇 |
2005年 | 100篇 |
2004年 | 78篇 |
2003年 | 84篇 |
2002年 | 80篇 |
2001年 | 78篇 |
2000年 | 82篇 |
1999年 | 74篇 |
1998年 | 42篇 |
1997年 | 40篇 |
1996年 | 38篇 |
1995年 | 33篇 |
1994年 | 21篇 |
1993年 | 22篇 |
1992年 | 45篇 |
1991年 | 51篇 |
1990年 | 51篇 |
1989年 | 60篇 |
1988年 | 45篇 |
1987年 | 51篇 |
1986年 | 42篇 |
1985年 | 38篇 |
1984年 | 39篇 |
1983年 | 49篇 |
1982年 | 35篇 |
1981年 | 21篇 |
1980年 | 25篇 |
1979年 | 40篇 |
1977年 | 30篇 |
1975年 | 24篇 |
1974年 | 25篇 |
1972年 | 33篇 |
1971年 | 21篇 |
1968年 | 26篇 |
1967年 | 22篇 |
排序方式: 共有3064条查询结果,搜索用时 265 毫秒
171.
172.
Faber WD Roberts LS Stump DG Beck M Kirkpatrick D Regan KS Tort M Moran E Banton M 《Birth defects research. Part B, Developmental and reproductive toxicology》2007,80(1):34-48
BACKGROUND: This study was conducted to evaluate the potential adverse effects of whole-body inhalation exposure of F0 and F1 parental animals from a 2-generation reproduction study of ethylbenzene on nervous system functional and/or morphologic end points in the F2 offspring from four groups of male and female Crl:CD (SD)IGS BR rats. METHODS: Thirty rats/sex/group for F0 and 25/sex/group for F1 were exposed to 0, 25, 100, and 500 ppm ethylbenzene for six hours daily for at least 70 consecutive days prior to mating for the F0 and F1 generations. Inhalation exposure for the F0 and F1 females continued throughout mating and gestation through Gestation Day (GD) 20. On lactation days (LD) 1-4, the F0 and F1 females received no inhalation exposure, but instead were administered ethylbenzene in corn oil via oral gavage at dosages estimated to result in similar internal maternal exposure based upon PBPK modeling estimates (0, 26, 90, and 342 mg/kg/day, respectively, divided into three equal doses, approximately two hours apart). Inhalation exposure of the F0 and F1 females was reinitiated on LD 5 and continued through weaning on postnatal day (PND) 21. Survival, body weights, and physical landmarks were assessed in selected F2 offspring. Neurobehavioral development of one F2-generation treatment derived offspring/sex/litter was assessed in a functional observational battery (FOB; PND 4, 11, 22, 45, and 60), motor activity sessions (PND 13, 17, 21, and 61), acoustic startle testing (PND 20 and 60), a Biel water maze learning and memory task (initiated on PND 26 or 62), and in evaluations of whole-brain measurements and brain morphometric and histologic assessments (PND 21 and 72). RESULTS: There were no adverse effects on reproductive performance in either the F0 or F1 parental generations exposed to up to 500 ppm ethylbenzene [Faber et al. Birth Defects Res Part B 77:10-21, 2006]. In the current developmental neurotoxicity component, parental ethylbenzene exposure did not adversely affect offspring survival, clinical condition, body weight parameters, or acquisition of developmental landmarks of the F2-generation treatment derived offspring. There were no alterations in FOB parameters, motor activity counts, acoustic startle endpoints, or Biel water maze performance in offspring attributed to parental ethylbenzene exposure. A few isolated instances of statistically significant differences obtained in the treatment-derived groups occurred sporadically, and were attributed to unusual patterns of development and/or behavior in the concurrent control group. There were no exposure-related differences in any neuropathology parameters in the F2-generation treatment derived offspring. CONCLUSIONS: The no observed adverse effect level (NOAEL) for maternal reproductive toxicity, developmental toxicity, and developmental neurotoxicity in this study was considered to be 500 ppm/342 mg/kg/day ethylbenzene, the highest exposure level tested in the study. 相似文献
173.
Christine R. Beck Claudia M.B. Carvalho Zeynep C. Akdemir Fritz J. Sedlazeck Xiaofei Song Qingchang Meng Jianhong Hu Harsha Doddapaneni Zechen Chong Edward S. Chen Philip C. Thornton Pengfei Liu Bo Yuan Marjorie Withers Shalini N. Jhangiani Divya Kalra Kimberly Walker Adam C. English James R. Lupski 《Cell》2019,176(6):1310-1324.e10
174.
Brendon Conlan Rosemary Birch Celine Kelso Sophie Holland Amanda P. De Souza Stephen P. Long Jennifer L. Beck Spencer M. Whitney 《Plant, cell & environment》2019,42(4):1287-1301
The folding and assembly of Rubisco large and small subunits into L8S8 holoenzyme in chloroplasts involves many auxiliary factors, including the chaperone BSD2. Here we identify apparent intermediary Rubisco‐BSD2 assembly complexes in the model C3 plant tobacco. We show BSD2 and Rubisco content decrease in tandem with leaf age with approximately half of the BSD2 in young leaves (~70 nmol BSD2 protomer.m2) stably integrated in putative intermediary Rubisco complexes that account for <0.2% of the L8S8 pool. RNAi‐silencing BSD2 production in transplastomic tobacco producing bacterial L2 Rubisco had no effect on leaf photosynthesis, cell ultrastructure, or plant growth. Genetic crossing the same RNAi‐bsd2 alleles into wild‐type tobacco however impaired L8S8 Rubisco production and plant growth, indicating the only critical function of BSD2 is in Rubisco biogenesis. Agrobacterium mediated transient expression of tobacco, Arabidopsis, or maize BSD2 reinstated Rubisco biogenesis in BSD2‐silenced tobacco. Overexpressing BSD2 in tobacco chloroplasts however did not alter Rubisco content, activation status, leaf photosynthesis rate, or plant growth in the field or in the glasshouse at 20°C or 35°C. Our findings indicate BSD2 functions exclusively in Rubisco biogenesis, can efficiently facilitate heterologous plant Rubisco assembly, and is produced in amounts nonlimiting to tobacco growth. 相似文献
175.
176.
Shana V. Stoddard Colin L. Welsh Maggie M. Palopoli Serena D. Stoddard Mounika P. Aramandla Riya M. Patel Hong Ma Laurence H. Beck Jr 《Proteins》2019,87(2):136-145
The thrombospondin type-1 domain containing 7A (THSD7A) protein is known to be one of the antigens responsible for the autoimmune disorder idiopathic membranous nephropathy. The structure of this antigen is currently unsolved experimentally. Here we present a homology model of the extracellular portion of the THSD7A antigen. The structure was evaluated for folding patterns, epitope site prediction, and function was predicted. Results show that this protein contains 21 extracellular domains and with the exception of the first two domains, has a regular repeating pattern of TSP-1-like followed by F-spondin-like domains. Our results indicate the presence of a novel Trp-ladder sequence of WxxxxW in the TSP-1-like domains. Of the 21 domains, 18 were shown to have epitope binding sites as predicted by epitopia. Several of the F-spondin-like domains have insertions in the canonical TSP fold, most notably the coiled coil region in domain 4, which may be utilized in protein-protein binding interactions, suggesting that this protein functions as a heparan sulfate binding site. 相似文献
177.
Intrasexual competition is an important selective force that can favor the evolution of honest signals of fighting ability. Research has focused predominantly on male birds, but many female birds also possess plumage ornaments that could mediate the outcome of competitive interactions. We examined the relationship between blue and white structural coloration and aggression in female tree swallows Tachycineta bicolor. Tree swallows are secondary cavity nesters and females show delayed plumage maturation which may be related to intense competition for nest sites. We compared plumage reflectance of second‐year (SY) and after‐second year (ASY) females, and within‐individual changes in plumage reflectance of ASY females in two successive years. We assessed aggression by placing a caged SY female 2 m from the nest box of an ASY female and quantified the ASY female's response in relation to her own plumage coloration. We found substantial differences in plumage reflectance of SY and ASY females, but found that ASY females became greener with duller white coloration in the second year. This may be due to poor weather that made reproduction particularly costly in the first year of the study and suggests coloration is influenced by condition. We found no relationship between dorsal coloration and aggressiveness. Rather, brighter white females spent more time on their nest box and within 2 m of the intruder than females with dull breasts. Our findings suggest that brighter white ASY females may perceive a SY female as less of a threat or that there may be a trade‐off associated with aggression and parental care that is related to white brightness. 相似文献
178.
Lambda-carrageenan, a linear high molecular weight sulfated polysaccharide, has been employed as a chiral selector in capillary electrophoresis for the separation of enantiomers of weakly basic pharmaceutical compounds. The racemic compounds that were enantioresolved included propranolol, pindolol, tryptophanol, laudanosine and laudanosoline. In addition, the diastereomeric pair of cinchonine and cinchonidine were also resolved. Method conditions such as buffer pH, electrolyte concentration, column temperature, and chiral selector concentration were found to be important for improvement of enantioselectivity. © 1996 Wiley-Liss, Inc. 相似文献
179.
Anne Lrke Spangmose Niels Skipper Sine Knorr Tina Wullum Gundersen Rikke Beck Jensen Peter Damm Erik Lykke Mortensen Anja Pinborg Jannet Svensson Tine Clausen 《PLoS medicine》2022,19(4)
BackgroundConflicting results have been reported concerning possible adverse effects on the cognitive function of offspring of mothers with type 1 diabetes (O-mT1D). Previous studies have included offspring of parents from the background population (O-BP), but not offspring of fathers with type 1 diabetes (O-fT1D) as the unexposed reference group.Methods and findingsThis is a population-based retrospective cohort study from 2010 to 2016. Nationally standardized school test scores (range, 1 to 100) were obtained for public school grades 2, 3, 4, 6, and 8 in O-mT1D and compared with those in O-fT1D and O-BP. Of the 622,073 included children, 2,144 were O-mT1D, and 3,474 were O-fT1D. Multiple linear regression models were used to compare outcomes, including the covariates offspring with type 1 diabetes, parity, number of siblings, offspring sex, smoking during pregnancy, parental age, and socioeconomic factors. Mean test scores were 54.2 (standard deviation, SD 24.8) in O-mT1D, 54.4 (SD 24.8) in O-fT1D, and 56.4 (SD 24.7) in O-BP. In adjusted analyses, the mean differences in test scores were −1.59 (95% CI −2.48 to −0.71, p < 0.001) between O-mT1D and O-BP and −0.78 (95% CI −1.48 to −0.08, p = 0.03) between O-fT1D and O-BP. No significant difference in the adjusted mean test scores was found between O-mT1D and O-fT1D (p = 0.16). The study’s limitation was no access to measures of glycemic control during pregnancy.ConclusionsO-mT1D achieved lower test scores than O-BP but similar test scores compared with O-fT1D. Glycemic control during pregnancy is essential to prevent various adverse pregnancy outcomes in women with type 1 diabetes. However, the present study reduces previous concerns regarding adverse effects of in utero hyperglycemia on offspring cognitive function.Anne Lærke Spangmose and colleagues examine the association between school performance and exposure to maternal or paternal type 1 diabetes in utero in Denmark. 相似文献
180.