全文获取类型
收费全文 | 9393篇 |
免费 | 734篇 |
国内免费 | 434篇 |
出版年
2024年 | 22篇 |
2023年 | 81篇 |
2022年 | 238篇 |
2021年 | 391篇 |
2020年 | 273篇 |
2019年 | 283篇 |
2018年 | 320篇 |
2017年 | 257篇 |
2016年 | 375篇 |
2015年 | 560篇 |
2014年 | 618篇 |
2013年 | 710篇 |
2012年 | 812篇 |
2011年 | 743篇 |
2010年 | 476篇 |
2009年 | 343篇 |
2008年 | 483篇 |
2007年 | 401篇 |
2006年 | 382篇 |
2005年 | 321篇 |
2004年 | 272篇 |
2003年 | 233篇 |
2002年 | 226篇 |
2001年 | 171篇 |
2000年 | 188篇 |
1999年 | 137篇 |
1998年 | 84篇 |
1997年 | 81篇 |
1996年 | 77篇 |
1995年 | 59篇 |
1994年 | 64篇 |
1993年 | 48篇 |
1992年 | 92篇 |
1991年 | 76篇 |
1990年 | 77篇 |
1989年 | 61篇 |
1988年 | 48篇 |
1987年 | 68篇 |
1986年 | 46篇 |
1985年 | 37篇 |
1984年 | 33篇 |
1983年 | 20篇 |
1982年 | 25篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1975年 | 18篇 |
1973年 | 21篇 |
1972年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Linkage analysis of families with hereditary retinoblastoma: nonpenetrance of mutation, revealed by combined use of markers within and flanking the RB1 gene. 总被引:8,自引:4,他引:4
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)
H Scheffer G J te Meerman Y C Kruize A H van den Berg D P Penninga K E Tan D J der Kinderen C H Buys 《American journal of human genetics》1989,45(2):252-260
Nonpenetrance of the inherited mutation responsible for retinoblastoma has been reported. By DNA analysis in families with hereditary retinoblastoma, it is possible to identify healthy individuals in whom the mutation is nonpenetrant. This requires the use of DNA markers both within and flanking the retinoblastoma gene. We have analyzed the segregation of several markers in 19 families (69 meioses) with hereditary retinoblastoma. In two families a carrier was identified who showed nonpenetrance of the mutation predisposing to retinoblastoma. The intragenic markers were informative in 15 pedigrees. The use of flanking markers from the same chromosomal region caused an increase of the number of informative families to 18. No crossing-over within the gene was observed. In one family an inherited deletion involving one of the RB1 alleles was detected. Our findings emphasize the use of a combination of both intragenic and flanking markers to obtain both the highest reliability of carrier detection in families with hereditary retinoblastoma and an accurate estimate of the frequency of nonpenetrance. 相似文献
62.
Geok -Yong Tan Wai -Koon Tan 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,80(2):258-264
Summary Quantitative inheritance of resistance to Phytophthora pod rot (Ppr) was studied in cocoa hybrid progeny from 12 Trinitario x Amazonian crosses and their reciprocal crosses. The crossing scheme was similar to a factorial design. Disease was assessed by the number and percentage of infected pods on each tree. Highly significant differences due to general combining abilities (GCA) were obtained for all characters, except for the GCA of Trinitario on total pod production. Differences for specific combining ability (SCA) were not significant for all characters. There were no significant differences between reciprocal crosses. The Trinitario clone K82 provided the only source for the hybrid progenies of strong Ppr resistance to the hybrid progenies, while K20 provided moderate resistance. Other parental clones — KA2-101, KA5-201, KEE 2, KEE 5, and KEE 52 — produced progenies which were susceptible to Ppr. It is evident that resistance to Ppr in cocoa is inherited additively. Maternal and cytoplasmic effects were assumed to have no influence on inheritance of resistance. It is also concluded that resistance to Ppr of the kind shown by K82 is likely to be horizontal resistance. Breeding for high-yielding cultivars combined with Ppr resistance is the most effective way of controlling Ppr of cocoa on the crops of growers with small holdings in Papua New Guinea. 相似文献
63.
64.
A DNA helicase (delta helicase) which partially copurifies with DNA polymerase delta has been highly purified from fetal calf thymus. delta helicase differs in physical and enzymatic properties from other eukaryotic DNA helicases described thus far. The enzyme has an apparent mass of 57 kDa by gel filtration and is associated with polypeptides of 56 and 52 kDa by SDS-polyacrylamide gel electrophoresis. Photo-cross-linking of the purified enzyme with [alpha-32P]ATP resulted in labeling of a polypeptide of approximately 58 kDa, suggesting that the active site is present on the larger polypeptide. Unwinding of a partial duplex requires a nucleoside triphosphate which can be either ATP or dATP but not a nonhydrolyzable analogue of ATP. Other ribo- and deoxyribonucleoside triphosphates have little or no activity as cofactors. delta helicase also has DNA-dependent ATPase activity which has a relatively low Km for ATP (40 microM). delta helicase binds to single-stranded DNA but has little or no affinity for double-stranded DNA or single-stranded RNA. Similar to replicative DNA helicases from prokaryotes and the herpes simplex virus type 1 helicase-primase, delta helicase translocates in the 5'-3' direction along the strand to which it is bound and preferentially unwinds DNA substrates with a forklike structure. 相似文献
65.
The inhibition of xanthine oxidase by its reaction product, uric acid, was studied by steady state kinetic analysis. Uric acid behaved as an uncompetitive inhibitor of xanthine oxidase with respect to the reducing substrate, xanthine. Under 50 microM xanthine and 210 microM oxygen, the apparent K(i) for uric acid was 70 microM. Uric acid-mediated xanthine oxidase inhibition also caused an increase in the percentage of univalent reoxidation of the enzyme (superoxide radical production). Steady-state rate equations derived by the King-Altman method support the formation of an abortive-inhibitory enzyme-uric acid complex (dead-end product inhibition). Alternatively, inhibition could also depend on the reversibility of the classical ping-pong mechanism present in xanthine oxidase-catalyzed reactions. 相似文献
66.
Nagilactone E, a norditerpene dilactone isolated from a gymnosperm, Podocarpus nagi (Podocarpaceae), was able to stimulate the growth of cultured cells of Lactuca sativa cv. Grand Rapids at 0.1 g ml-1 but not at 0.01 or 1 g ml-1. Cell wet weight/unit time and cell number/unit wet weight were increased when they were recorded at the end of the 14-day incubation period. Also, the population of cells treated with that concentration of nagilactone E had a higher percentage of cells with shorter cell length compared to the control (untreated). 相似文献
67.
Zhuang G. S. Wang Y. S. Tan M. G. Zhi M. Pan W. Q. Cheng Y. D. 《Biological trace element research》1990,26(1):729-736
In order to study the relationships between trace element concentrations of hair and internal body burdens, a radiochemical NAA technique has been used for determination of the elements As, Cd, and Hg in autopsy samples of liver, kidney-cortex, lung, and hair from 24 male persons who died by accident. High significant positive correlations were observed between the As concentration in hair and in kidney-cortex, and between Cd and Zn concentrations in kidney-cortex. The contents of Cd, both for lung and kidney-cortex, were related to the smoking habits of the subjects.
相似文献68.
David M. Hwang Adam Dempsey Kiat-Tsong Tan Choong-Chin Liew 《Journal of molecular evolution》1996,43(5):536-540
HnifU, a gene exhibiting similarity tonifU genes of nitrogen fixation gene clusters, was identified in the course of expressed sequence tag (EST) generation from a
human fetal heart cDNA library. Northern blot of human tissues and polymerase chain reaction (PCR) using human genomic DNA
verified that the hnifU gene represented a human gene rather than a microbial contaminant of the cDNA library. Conceptual translation of the hnifU cDNA yielded a protein product bearing 77% and 70% amino acid identity to NifU-like hypothetical proteins fromHaemophilus influenzae andSaccharomyces cerevisiae, respectively, and 40–44% identity to the N-terminal regions of NifU proteins from several diazatrophs (i.e., nitrogen-fixing
organisms). Pairwise determination of amino acid identities between the NifU-like proteins of nondiazatrophs showed that these
NifU-like proteins exhibited higher sequence identity to each other (63–77%) than to the diazatrophic NifU proteins (40–48%).
Further, the NifU-like proteins of non-nitrogenfixing organisms were similar only to the N-terminal region of diazatrophic
NifU proteins and therefore identified a novel modular domain in these NifU proteins. These findings support the hypothesis
that NifU is indeed a modular protein. The high degree of sequence similarity between NifU-like proteins from species as divergent
as humans andH. influenzae suggests that these proteins perform some basic cellular function and may be among the most highly conserved proteins.
Correspondence to: C.-C. Liew 相似文献
69.
中国单头螨属一新种(蜱螨亚纲:叶螨科)谭瑞成,鲁素玲(湖南省林业科学研究所长沙410004)(新疆石河子农学院新疆832003)单头螨属AplonobiaWOmersley,1940前足体背毛3对,后半体背毛10对,全部或部分背毛着生在明显结节L,背... 相似文献
70.
Translational control of programmed cell death: eukaryotic translation initiation factor 4E blocks apoptosis in growth-factor-restricted fibroblasts with physiologically expressed or deregulated Myc. 总被引:13,自引:1,他引:12
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
V A Polunovsky I B Rosenwald A T Tan J White L Chiang N Sonenberg P B Bitterman 《Molecular and cellular biology》1996,16(11):6573-6581
There is increasing evidence that cell cycle transit is potentially lethal, with survival depending on the activation of metabolic pathways which block apoptosis. However, the identities of those pathways coupling cell cycle transit to survival remain undefined. Here we show that the eukaryotic translation initiation factor 4E (eIF4E) can mediate both proliferative and survival signaling. Overexpression of eIF4E completely substituted for serum or individual growth factors in preserving the viability of established NIH 3T3 fibroblasts. An eIF4E mutant (Ser-53 changed to Ala) defective in mediating its growth-factor-regulated functions was also defective in its survival signaling. Survival signaling by enforced expression of eIF4E did not result from autocrine release of survival factors, nor did it lead to increased expression of the apoptosis antagonists Bcl-2 and Bcl-XL. In addition, the execution apparatus of the apoptotic response in eIF4E-overexpressing cells was found to be intact. Increased expression of eIF4E was sufficient to inhibit apoptosis in serum-restricted primary fibroblasts with enforced expression of Myc. In contrast, activation of Ha-Ras, which is required for eIF4E proliferative signaling, did not suppress Myc-induced apoptosis. These data suggest that the eIF4E-activated pathways leading to survival and cell cycle progression are distinct. This dual signaling of proliferation and survival might be the basis for the potency of eIF4E as an inducer of neoplastic transformation. 相似文献