全文获取类型
收费全文 | 30151篇 |
免费 | 15715篇 |
国内免费 | 3篇 |
专业分类
45869篇 |
出版年
2023年 | 59篇 |
2022年 | 166篇 |
2021年 | 526篇 |
2020年 | 2296篇 |
2019年 | 3837篇 |
2018年 | 3959篇 |
2017年 | 4231篇 |
2016年 | 4286篇 |
2015年 | 4253篇 |
2014年 | 3959篇 |
2013年 | 4417篇 |
2012年 | 2145篇 |
2011年 | 1829篇 |
2010年 | 3246篇 |
2009年 | 1962篇 |
2008年 | 900篇 |
2007年 | 489篇 |
2006年 | 476篇 |
2005年 | 462篇 |
2004年 | 428篇 |
2003年 | 402篇 |
2002年 | 371篇 |
2001年 | 312篇 |
2000年 | 234篇 |
1999年 | 168篇 |
1998年 | 39篇 |
1997年 | 27篇 |
1996年 | 26篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 20篇 |
1992年 | 29篇 |
1991年 | 28篇 |
1990年 | 16篇 |
1989年 | 21篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1972年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
151.
152.
153.
154.
155.
156.
Julia Spencer Barthold Jobayer Hossain Alicia Olivant‐Fisher Anita Reilly T. Ernesto Figueroa Ahmad BaniHani Jennifer Hagerty Ricardo González Paul H. Noh Jeanne M. Manson 《Birth defects research. Part A, Clinical and molecular teratology》2012,94(11):900-907
BACKGROUND : Genetic and environmental factors likely influence susceptibility to nonsyndromic cryptorchidism, a common disease presenting at birth or in later childhood. We compared cases and controls to define differential risk factors for congenital versus acquired cryptorchidism. METHODS : We compared questionnaire and clinical data from cases of congenital cryptorchidism (n = 230), acquired cryptorchidism (n = 182) and hernia/hydrocele (n = 104) with a group of healthy male controls (n = 358). Potential predictor variables (p < 0.2 in univariable analysis) were included in stepwise multivariable logistic regression models. RESULTS : Temporary (odds ratio [OR], 0.5; 95% confidence interval [CI], 0.4–0.8) or exclusive (OR, 0.6; 95% CI, 0.4–0.9) breastfeeding was reduced and soy formula feeding increased (OR, 1.8; 95% CI, 1.2–2.9) in acquired but not congenital or hernia/hydrocele groups. The highest risk estimates were observed for primary soy formula feeding with limited or no breastfeeding (OR 2.5; 95% CI, 1.4–4.3; adjusted OR, 2.7; 95% CI, 1.4–5.4) in the acquired group. Primary feeding risk estimates were equivalent or strengthened when multivariable models were limited to age greater than 2 years, full‐term or not small for gestational age, or Caucasian subjects. Pregnancy complications and increased maternal exposure to cosmetic or household chemicals were not consistently associated with either form of cryptorchidism in these models. CONCLUSIONS : Our data support reduced breastfeeding and soy formula feeding as potential risk factors for acquired cryptorchidism. Although additional studies are needed, hormonally active components of breast milk and soy formula could influence the establishment of normal testis position in the first months of life, leading to apparent ascent of testes in childhood. Birth Defects Research (Part A), 2012. © 2012 Wiley Periodicals, Inc. 相似文献
157.
Duck‐Oung Jung Dae‐Sup Park Jae‐Kyoung Shim Sukchan Lee Jaeho Pyee Kyeong‐Yeoll Lee 《Entomological Research》2019,49(1):72-77
Mites are one of the serious pests of turfgrass. Our survey of turfgrass fields from 2013 to 2015 in Korea showed that the occurrence of leaf chlorotic symptom has gradually extended to at least 60% of the examined golf courses. We identified the zoysiae mite Aceria zoysiae in most damaged zoysiagrasses. Artificial infestation of A. zoysiae into zoysiagrasses in pots resulted in symptoms of chlorosis and marginal rolling of the leaves within 3 weeks. We firstly determined the nucleotide sequence of mitochondrial cytochrome c oxidase subunit I (COI) and internal transcribed spacer 2 (ITS2) of the nuclear ribosomal DNA region of A. zoysiae. The variations in COI and ITS2 between A. zoysiae and other species of the genus were 20.9%–43.0% and 7.5%–67.3%, respectively, suggesting significant genetic divergence within the genus. Our study provides valuable information for the rapid diagnosis and infestation monitoring of A. zoysiae in turfgrass fields. 相似文献
158.
Ernetti Julia R. Boschetti Joana P. Delazeri Francieli De Bastiani Veluma I. M. Pontes Mariana R. Ribeiro Luisa P. Lingnau Rodrigo Toledo Luís Felipe Lucas Elaine M. 《Hydrobiologia》2020,847(16):3355-3364
Hydrobiologia - Pithecopus rusticus is an endemic amphibian restricted to the type locality, in southern Brazil, and possibly endangered to extinction, due to habitat degradation. However, an... 相似文献
159.
Substantia nigra dopaminergic neurons and striatal interneurons are engaged in three parallel but interdependent postnatal neurotrophic circuits 下载免费PDF全文
Clara Ortega‐de San Luis Manuel A. Sanchez‐Garcia Jose Luis Nieto‐Gonzalez Pablo García‐Junco‐Clemente Adoracion Montero‐Sanchez Rafael Fernandez‐Chacon Alberto Pascual 《Aging cell》2018,17(5)
The striatum integrates motor behavior using a well‐defined microcircuit whose individual components are independently affected in several neurological diseases. The glial cell line‐derived neurotrophic factor (GDNF), synthesized by striatal interneurons, and Sonic hedgehog (Shh), produced by the dopaminergic neurons of the substantia nigra (DA SNpc), are both involved in the nigrostriatal maintenance but the reciprocal neurotrophic relationships among these neurons are only partially understood. To define the postnatal neurotrophic connections among fast‐spiking GABAergic interneurons (FS), cholinergic interneurons (ACh), and DA SNpc, we used a genetically induced mouse model of postnatal DA SNpc neurodegeneration and separately eliminated Smoothened (Smo), the obligatory transducer of Shh signaling, in striatal interneurons. We show that FS postnatal survival relies on DA SNpc and is independent of Shh signaling. On the contrary, Shh signaling but not dopaminergic striatal innervation is required to maintain ACh in the postnatal striatum. ACh are required for DA SNpc survival in a GDNF‐independent manner. These data demonstrate the existence of three parallel but interdependent neurotrophic relationships between SN and striatal interneurons, partially defined by Shh and GDNF. The definition of these new neurotrophic interactions opens the search for new molecules involved in the striatal modulatory circuit maintenance with potential therapeutic value. 相似文献
160.
Lauren E. Hartley‐Tassell Lucy K. Shewell Christopher J. Day Jennifer C. Wilson Randeep Sandhu Julian M. Ketley Victoria Korolik 《Molecular microbiology》2010,75(3):710-730
Campylobacter jejuni is a highly motile bacterium that responds via chemotaxis to environmental stimuli to migrate towards favourable conditions. Previous in silico analysis of the C. jejuni strain NCTC11168 genome sequence identified 10 open reading frames, tlp1‐10, that encode putative chemosensory receptors. We describe the characterization of the role and specificity of the Tlp1 chemoreceptor (Cj1506c). In vitro and in vivo models were used to determine if Tlp1 had a role in host colonization. The tlp1‐ isogenic mutant was more adherent in cell culture, however, showed reduced colonization ability in chickens. Specific interactions between the purified sensory domain of Tlp1 and l ‐aspartate were identified using an amino acid array and saturation transfer difference nuclear magnetic resonance spectroscopy. Chemotaxis assays showed differences between migration of wild‐type C. jejuni cells and that of a tlp1‐ isogenic mutant, specifically towards aspartate. Furthermore, using yeast two‐hybrid and three‐hybrid systems for analysis of protein–protein interactions, the cytoplasmic signalling domain of Tlp1 was found to preferentially interact with CheV, rather than the CheW homologue of the chemotaxis signalling pathway; this interaction was confirmed using immune precipitation assays. This is the first identification of an aspartate receptor in bacteria other than Escherichia coli and Salmonella enterica serovar Typhimurium. 相似文献