全文获取类型
收费全文 | 4334篇 |
免费 | 501篇 |
国内免费 | 1篇 |
出版年
2021年 | 56篇 |
2019年 | 40篇 |
2018年 | 54篇 |
2017年 | 37篇 |
2016年 | 81篇 |
2015年 | 113篇 |
2014年 | 139篇 |
2013年 | 158篇 |
2012年 | 202篇 |
2011年 | 190篇 |
2010年 | 145篇 |
2009年 | 122篇 |
2008年 | 175篇 |
2007年 | 176篇 |
2006年 | 140篇 |
2005年 | 155篇 |
2004年 | 150篇 |
2003年 | 153篇 |
2002年 | 145篇 |
2001年 | 95篇 |
2000年 | 98篇 |
1999年 | 87篇 |
1998年 | 54篇 |
1997年 | 56篇 |
1996年 | 48篇 |
1995年 | 48篇 |
1994年 | 46篇 |
1993年 | 52篇 |
1992年 | 82篇 |
1991年 | 69篇 |
1990年 | 81篇 |
1989年 | 78篇 |
1988年 | 80篇 |
1987年 | 72篇 |
1986年 | 61篇 |
1985年 | 64篇 |
1984年 | 63篇 |
1983年 | 52篇 |
1982年 | 59篇 |
1981年 | 57篇 |
1980年 | 39篇 |
1979年 | 59篇 |
1978年 | 45篇 |
1977年 | 37篇 |
1976年 | 52篇 |
1975年 | 55篇 |
1974年 | 67篇 |
1973年 | 80篇 |
1972年 | 57篇 |
1971年 | 35篇 |
排序方式: 共有4836条查询结果,搜索用时 44 毫秒
121.
122.
A linkage study in seven breast cancer families. 总被引:2,自引:1,他引:1
M D Teare M F Santibez-Koref S A Wallace G R White D G Evans L D Burnell M Harris A Howell J M Birch 《American journal of human genetics》1993,52(4):786-788
Seven breast cancer families are examined for evidence of linkage to a site in the region of 17q12-q21, by using five markers. The families constitute a subset of a larger series of familial breast cancer; the seven families were selected because constitutional DNA was available on informative members, either from clinical samples or extracted from paraffin blocks. Two-point lod scores are reported. The maximum lod score, 0.8824, is obtained with marker NM23 at theta = 0. This is clearly not significant in itself; however, when taken in context with evidence from existing reports, it provides support for linkage to this region. 相似文献
123.
Linkage analysis of schizophrenia with five dopamine receptor genes in nine pedigrees 总被引:2,自引:0,他引:2
Hilary Coon William Byerley John Holik Mark Hoff Marina Myles-Worsley Lars Lannfelt Pierre Sokoloff Jean-Charles Schwartz Merilyne Waldo Robert Freedman Rosemarie Plaetke 《American journal of human genetics》1993,52(2):327-334
Alterations in dopamine neurotransmission have been strongly implicated in the pathogenesis of schizophrenia for nearly 2 decades. Recently, the genes for five dopamine receptors have been cloned and characterized, and genetic and physical map information has become available. Using these five loci as candidate genes, we have tested for genetic linkage to schizophrenia in nine multigenerational families which include multiple affected individuals. In addition to testing conservative disease models, we have used a neurophysiological indicator variable, the P50 auditory evoked response. Deficits in gating of the P50 response have been shown to segregate with schizophrenia in this sample and may identify carriers of gene(s) predisposing for schizophrenia. Linkage results were consistently negative, indicating that a defect at any of the actual receptor sites is unlikely to be a major contributor to schizophrenia in the nine families studied. 相似文献
124.
Hilary Simons Morland 《American journal of physical anthropology》1993,91(1):71-82
Mating activity was observed during four breeding seasons in two groups of black and white ruffed lemurs (Varecia variegata variegata) living in lowland rain forest on Nosy Mangabe island, Madagascar. The onset of the May-July breeding season was signalled by behavioral changes in adult males. Males made forays outside their usual home ranges, were more aggressive to other males, and performed appetitive and other sex-specific behaviors more frequently. Females showed receptive and proceptive behaviors during a 1-2 day behavioral estrus. Ruffed lemurs mated monogamously, polyandrously, and polygynously. These observations do not support previous assertions that they live only in monogamous families. Limited evidence suggests females exercised mate choice and may have preferred familiar males. © 1993 Wiley-Liss, Inc. 相似文献
125.
mtDNA variation of aboriginal Siberians reveals distinct genetic affinities with Native Americans. 总被引:44,自引:24,他引:20
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A Torroni R I Sukernik T G Schurr Y B Starikorskaya M F Cabell M H Crawford A G Comuzzie D C Wallace 《American journal of human genetics》1993,53(3):591-608
The mtDNA variation of 411 individuals from 10 aboriginal Siberian populations was analyzed in an effort to delineate the relationships between Siberian and Native American populations. All mtDNAs were characterized by PCR amplification and restriction analysis, and a subset of them was characterized by control region sequencing. The resulting data were then compiled with previous mtDNA data from Native Americans and Asians and were used for phylogenetic analyses and sequence divergence estimations. Aboriginal Siberian populations exhibited mtDNAs from three (A, C, and D) of the four haplogroups observed in Native Americans. However, none of the Siberian populations showed mtDNAs from the fourth haplogroup, group B. The presence of group B deletion haplotypes in East Asian and Native American populations but their absence in Siberians raises the possibility that haplogroup B could represent a migratory event distinct from the one(s) which brought group A, C, and D mtDNAs to the Americas. Our findings support the hypothesis that the first humans to move from Siberia to the Americas carried with them a limited number of founding mtDNAs and that the initial migration occurred between 17,000-34,000 years before present. 相似文献
126.
A systematic survey for the presence of birefringent (anisotropic) structures in rotifers was undertaken. Several common features of rotifers exhibit anisotropism (e.g. trophi & muscles). However, unusual anisotropic crystalline structures (ACS) were found in late stage embryos (i.e. possessing eyespots and trophi, and showing movement). ACS were found in 18 of 26 species of monogonont rotifers (comprising 11 genera of 5 families). In Sinantherina socialis, ACS were present in the lower gut as compact, spherical masses of minute crystals that slowly broke apart and disappeared within 20 hours of hatching. Although several authors have described the existence of refractive bodies in rotifers, to my knowledge this is the first report of their birefringent properties. 相似文献
127.
Regional regulation of glutaminase by phosphate and calcium was examined in the temporal cortex (TCX), striatum (STR) and hippocampus (HIPP) from adult and aged male F344 rats. Phosphate-dependent glutaminase activity in adult rats was significantly lower (35–43%) in the HIPP (100 and 150 mM) and STR (150 mM) compared to PAG activity in the TCX. Phosphate activation in aged rats was 50–60% lower in the HIPP at concentrations greater than 25 mM compared to the aged TCX or STR. PAG activity in the TCX and STR was unaffected by age, but was significantly reduced (30–50%) in the HIPP from aged rats at phosphate concentrations of 25 mM and greater when compared to adult rats. In adult rats at concentrations of CaCl2 above 1 mM, PAG activity was significantly lower (60–75%) in the STR and HIPP when compared to the TCX. In aged rats, PAG activity (1 mM CaCl2) in the HIPP was significantly less (50%) than STR PAG activity in aged rats. Diminished PAG activity was seen only in the TCX (2.5 mM; 32%), and the HIPP (0.5 mM; 25% and 1 mM; 38%) at higher calcium concentrations compared to adult. Phosphate-independent calcium activation of PAG occurred in the HIPP but not in either the TCX or the STR. Addition of phosphate resulted in a synergistic activation of PAG in the STR and TCX, but not in the HIPP. These findings suggest that PAG is regionally regulated by phosphate and calcium, and this regulation is impaired in aged rats. These data also support the hypothesis that isozymes of PAG exist with different regulatory properties.Abbreviation PAG
Phosphate-activated glutaminase
- L-glutamine amidohydrolase
EC 3.5.1.2
- TCX
temporal cortex
- STR
striatum
- HIPP
hippocampus
- F344
Fischer-344 rat 相似文献
128.
Several di-, tri-, and oligopeptides were incubated individually in vitro with rumen fluid from two sheep receiving a mixed grass hay/concentrate diet and with washed cells ofPrevotella (formerlyBacteroides)ruminicola M384 andP. ruminicola B14. The rates of breakdown of most peptides were similar in the rumen fluid from the two sheep. Acidic and proline-containing peptides tended to be more slowly degraded than neutral or basic peptides. The dipeptide at the N-terminus of higher peptides was observed as an early product of hydrolysis, confirming that a dipeptidyl aminopeptidase type of activity was present. The relative rates of breakdown of dipeptides byP. ruminicola were different from that of rumen fluid, but the hydrolysis of higher peptides followed a similar pattern, and dipeptides from the N-terminus were detected as early products. 相似文献
129.
130.