全文获取类型
收费全文 | 13158篇 |
免费 | 1318篇 |
国内免费 | 8篇 |
专业分类
14484篇 |
出版年
2022年 | 101篇 |
2021年 | 177篇 |
2020年 | 108篇 |
2019年 | 132篇 |
2018年 | 173篇 |
2017年 | 161篇 |
2016年 | 268篇 |
2015年 | 499篇 |
2014年 | 532篇 |
2013年 | 678篇 |
2012年 | 814篇 |
2011年 | 859篇 |
2010年 | 577篇 |
2009年 | 475篇 |
2008年 | 687篇 |
2007年 | 731篇 |
2006年 | 711篇 |
2005年 | 691篇 |
2004年 | 670篇 |
2003年 | 644篇 |
2002年 | 710篇 |
2001年 | 144篇 |
2000年 | 122篇 |
1999年 | 169篇 |
1998年 | 194篇 |
1997年 | 151篇 |
1996年 | 140篇 |
1995年 | 135篇 |
1994年 | 124篇 |
1993年 | 125篇 |
1992年 | 107篇 |
1991年 | 110篇 |
1990年 | 126篇 |
1989年 | 113篇 |
1988年 | 108篇 |
1987年 | 113篇 |
1986年 | 98篇 |
1985年 | 109篇 |
1984年 | 121篇 |
1983年 | 128篇 |
1982年 | 142篇 |
1981年 | 124篇 |
1980年 | 98篇 |
1979年 | 72篇 |
1978年 | 88篇 |
1977年 | 78篇 |
1976年 | 66篇 |
1975年 | 62篇 |
1974年 | 74篇 |
1973年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Mary K. Vaughan Damon C. Herbert George M. Vaughan Frank J. Weaker Anna I. Esquifino Russel J. Reiter 《Chronobiology international》1988,5(2):107-114
In young adult male rats bearing a donor anterior pituitary gland grafted for 3 weeks under a kidney capsule, serum prolactin (PRL) concentrations were elevated and exhibited a rhythm with the highest values in the light phase. Serum PRL in control animals did not exhibit a significant rhythm. Eutopic pituitary PRL content, manifesting a biphasic (12-hr) rhythm with crests during the day and night in controls, exhibited a similar pattern in grafted rats though an overall reduction in pituitary PRL content was seen in the grafted animals. Neither the normal biphasic serum testosterone rhythm nor the normal 24-hr rhythm (nocturnal surge) of pineal N-acetyltransferase activity and melatonin content were altered in the hyperprolactinemic rats. Serum thyroxine (T4) and triiodothyronine (T3) and their free indices (FT4 I, FT3 I) and serum thyrotropin (TSH) were highest during the day in controls and grafted rats and a 12-hr rhythmic component was detected in data for these variables. In the grafted animals, the 12-hr component was reflected in an additional peak at night detectable by testing of means. The overall serum T4 FT4 I, and TSH levels were lower in grafted rats though overall T3 and FT3I levels did not differ between grafted and controls. T3 uptake (T3 U) values were similar between controls and grafted rats, in both cases exhibiting a fall during the night. Changes in serum thyronines could not be explained by changes in serum binding as assessed by the T3U3 and thus may represent changes in thyroidal secretion of T4. The rhythm in serum PRL of grafted rats suggests the presence of rhythmic circulating factor(s) capable of influencing ectopic lactotrophs. The reduced eutopic pituitary PRL content suggests a role for PRL in influencing eutopic lactotrophs in the pituitary-grafted hyperprolactinemic male rat model. Though circulating testosterone and pineal melatonin synthesis were not altered in this model, thyroid function appeared to be so. 相似文献
63.
64.
65.
66.
67.
Proteins that share conserved "zinc finger" motifs represent a class of DNA-binding proteins that have been shown to play a fundamental role in regulating gene expression and to be involved in a number of human hereditary and malignant disease states. We have isolated, characterized, and mapped zinc finger-encoding genes specific to human chromosome 11q to investigate their possible association in the molecular pathogenesis of several disease loci mapped to this chromosome. An arrayed chromosome 11q cosmid library was screened using a degenerate oligonucleotide corresponding to the H/C link consensus sequence of the Drosophila Kruppel zinc finger gene, resulting in the isolation of six putative zinc finger genes. Three of the genes (ZNF123, ZNF125, and ZNF126) were analyzed and shown to contain tandemly repeated zinc finger motifs of the C2-H2 class. All three novel genes were found to be expressed in normal adult human tissues, although the tissue-specific pattern of expression differs markedly. Isolated zinc finger genes were regionally mapped on chromosome 11 using fluorescence in situ suppression hybridization and demonstrated clustering of the genes at 11q13.3-11q13.4 and 11q23.1-11q23.2. Analysis of in situ hybridization to interphase nuclei demonstrated a maximum distance of 1 Mb separating distinct finger genes. This analysis defines two linked multigene families of zinc finger genes to chromosome bands associated with a high frequency of specific translocations associated with malignancies. 相似文献
68.
69.
Calicotyle urolophi n. sp. is proposed for calicotylines found in the cloaca of three stingaree species, Urolophus cruciatus, U. bucculentus and U. paucimaculatus, collected off the southeastern coast of Tasmania. Variations in the soft body parts were observed between specimens taken from U. cruciatus and U. bucculentus but were not considered sufficient for separation into two species. C. urolophi is differentiated from other Calicotyle spp. found in the South Pacific by the configuration of the tubular male copulatory organ, the structure of the intestinal caeca and the arrangement of the vaginae. Amended diagnoses for the subfamily Calicotylinae and the genus Calicotyle are provided. 相似文献
70.
We analyzed data from Section 404 permits issued in California from January 1971 through November 1987 that involved impacts to wetlands and required compensatory mitigation (wetland creation, restoration, or preservation). The purpose of this study was to determine patterns and trends in permitting activity and to document cumulative effects of associated management decisions on the California wetland resource. The 324 permits examined documented that 387 compensatory wetlands (1255.9 ha) were required as mitigation for impacts to 368 wetlands (1176.3 ha). The utility of the data on wetland area was limited, however, since 38.0% of the impacted wetlands and 41.6% of the compensatory wetlands lacked acreage data. The wetland type most frequently impacted (37.8% of impacted wetlands) and used in compensation (38.2% of compensatory wetlands) was palustrine forested wetlands. Estuarine intertidal emergent wetlands had the most area impacted (52.3%) and compensated (62.5%). The majority of the wetlands were small (less than or equal to 4.0 ha in size). Wildlife habitat was the most frequently listed function of impacted wetlands (90.7% of the permits) and objective of compensatory wetlands (83.3%). Endangered species were listed as affected in 20.4% of impacted and 21.0% of compensatory projects. The number of permits requiring compensatory mitigation and the number of impacted and compensatory wetlands increased from 1971 to 1986.Documentation of the details of Section 404 permit decisions was inadequate for the permits we examined. Area information and specific locations of impacted and compensatory wetlands were lacking or of poor quality. Follow-up information was also inadequate. For example, project completion dates were specified in the permit for only 2.2% of compensatory wetlands. Furthermore, less than one-third (31.5%) of the permits required the compensatory wetland to be monitored by at least one site visit. We recommend improved documentation, regular reporting, and increased monitoring for better evaluation of the Section 404 permitting system. 相似文献