全文获取类型
收费全文 | 798797篇 |
免费 | 82597篇 |
国内免费 | 257篇 |
专业分类
881651篇 |
出版年
2018年 | 8018篇 |
2017年 | 7652篇 |
2016年 | 10734篇 |
2015年 | 13563篇 |
2014年 | 16173篇 |
2013年 | 23320篇 |
2012年 | 26138篇 |
2011年 | 26940篇 |
2010年 | 18362篇 |
2009年 | 16987篇 |
2008年 | 24013篇 |
2007年 | 24981篇 |
2006年 | 23349篇 |
2005年 | 22446篇 |
2004年 | 22210篇 |
2003年 | 21362篇 |
2002年 | 20873篇 |
2001年 | 34749篇 |
2000年 | 34204篇 |
1999年 | 27593篇 |
1998年 | 10193篇 |
1997年 | 10281篇 |
1996年 | 9846篇 |
1995年 | 9065篇 |
1994年 | 8735篇 |
1993年 | 8760篇 |
1992年 | 22345篇 |
1991年 | 21921篇 |
1990年 | 21376篇 |
1989年 | 20819篇 |
1988年 | 19096篇 |
1987年 | 18328篇 |
1986年 | 17104篇 |
1985年 | 16962篇 |
1984年 | 13935篇 |
1983年 | 12191篇 |
1982年 | 9238篇 |
1981年 | 8360篇 |
1980年 | 7757篇 |
1979年 | 12948篇 |
1978年 | 10204篇 |
1977年 | 9200篇 |
1976年 | 8808篇 |
1975年 | 9817篇 |
1974年 | 10488篇 |
1973年 | 10355篇 |
1972年 | 9479篇 |
1971年 | 8457篇 |
1970年 | 7385篇 |
1969年 | 7256篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
Assignment of the human homologue of Pim-1, a mouse gene implicated in leukemogenesis,to the pter-q12 region of chromosome 6 总被引:2,自引:0,他引:2
Summary Viral leukemogenesis in mice is frequently initiated by proviral activation of a highly conserved cellular gene called Pim-1. Here we report the chromosomal localization of the human homologue by Southern blot analyses of DNAs obtained from human-rodent somatic cell hybrids. The single copy human homologue was assigned to the 6pter-q12 segment. 相似文献
912.
D B Snead A Weltman J Y Weltman W S Evans J D Veldhuis M M Varma C D Teates E A Dowling A D Rogol 《Journal of applied physiology》1992,72(6):2149-2156
We examined the relationships among reproductive hormone concentrations and bone mineral density (BMD) in 43 women runners classified as eumenorrheic (n = 24), oligomenorrheic (n = 8), or amenorrheic (n = 11). Results were compared with a eumenorrheic nonrunner control group (n = 11). Serum 17 beta-estradiol, progesterone, and dehydroepiandrosterone sulfate concentrations were determined in daily blood samples for 21 days, and integrated concentrations (areas under the curve) were calculated. BMD was assessed at the lumbar spine and proximal femur by dual-photon absorptiometry. As expected, 17 beta-estradiol, progesterone, and lumbar spine BMD were higher in the control and eumenorrheic runner groups than in the oligomenorrheic and amenorrheic runner groups (P less than 0.05). Progesterone concentration was significantly correlated with lumbar spine BMD in the eumenorrheic runners (r = 0.61). None of the steroid hormones was significantly related to BMD in the oligomenorrheic/amenorrheic group. The present data suggest that circulating levels of gonadal steroid hormones affect axial BMD in eumenorrheic runners. 相似文献
913.
P S Gromov A M Shandala L I Kovalev S S Shishkin 《Biulleten' eksperimental'no? biologii i meditsiny》1986,102(7):28-30
Fractionation of human erythrocyte membrane proteins was performed using a modification of two-dimensional gel electrophoresis described by P. O'Farrel with isoelectric point plotted against molecular mass. All major erythrocyte proteins, including high molecular weight proteins, such as spectrin and band 3 protein, identified by one-dimensional sodium dodecyl sulfate gel electrophoresis, were visualized by silver staining of two-dimensional gels. All in all about 50 polypeptides were distinguished on two-dimensional electrophoretic patterns. Preliminary protein map was developed. 相似文献
914.
Svetlana A. Semerikova Vladimir L. Semerikov Martin Lascoux 《Journal of Biogeography》2011,38(2):326-340
Aim The main aim of the present study is to infer the post‐glacial history of Abies species from north‐east Asia and to test the hypotheses that coastal Abies populations suffered less from climatic fluctuations during Pleistocene glacial periods than their more continental counterparts, and that Sakhalin was a major area of introgression. Location Natural ranges of the fir species Abies nephrolepis, Abies sachalinensis and Abies holophylla in the Russian Far East, and of Abies gracilis, which is endemic to the Kamchatka Peninsula. Methods Nineteen populations were sampled for allozyme analysis. Seventeen of these populations were also screened for variation at two paternally inherited chloroplast DNA microsatellite loci (cpSSR) and variation at one maternally inherited mitochondrial marker (nad4‐3/4). Finally a subset of 11 populations was analysed with amplified fragment length polymorphism (AFLP). Comparisons were made with already available Abies sibirica data. For all sets of markers, we estimated genetic diversity and differentiation using an analysis of molecular variance (AMOVA). Population clustering was assessed with a Bayesian approach implemented in structure v.2.3. Results Among the three major species, A. sibirica, A. nephrolepis and A. sachalinensis, A. sachalinensis demonstrated the highest cytoplasmic and nuclear diversity and the most continental species, A. sibirica, the lowest. Both nuclear and mitochondrial DNA markers revealed the presence of a transitional zone on Sakhalin Island between A. nephrolepis and A. sachalinensis of south Sakhalin. The structure analysis delivered very clear results confirming the admixed origin of A. sachalinensis, with a genetic contribution from A. nephrolepis. No variation in cytoplasmic markers was found in A. gracilis, suggesting the occurrence of a recent bottleneck. Main conclusions There is a clear reduction of genetic diversity in Abies species from the Pacific coast into the continent. The higher diversity in A. sachalinensis could have two causes: a larger effective population size in the islands due to relatively stable climatic conditions and consequently less pronounced demographic fluctuations in population size and/or hybridization with continental and Japanese populations. Sakhalin Island is a major transitional zone for conifer species. Finally, the fir from Kamchatka, A. gracilis, should be regarded as a separate species closely related to the A. nephrolepis–A. sachalinensis complex. 相似文献
915.
916.
917.
918.
V A Shuklinov 《Tsitologiia》1985,27(3):268-275
The paper reports reasons for a possibility of tumour regression due to selection of low-malignant and differentiating clones. Experimental evidence is provided supporting this view. 相似文献
919.
Malav A. Kapadia 《Inorganica chimica acta》2009,362(9):3292-3298
Coordination polymers of HEAP-ED with La(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III) and Dy(III) metal ions have been synthesized and characterized by elemental analyses, electronic spectra, magnetic susceptibilities, FTIR, NMR, scanning electronic microscopy (SEM) and thermogravimetric analyses. Catalytic activity of selected coordination polymers was examined for pharmaceutical important organic synthesis. Antimicrobial activity of isolated Ln(III) coordination polymers against Escherichia coli, Bacillus subtilis, Staphylococcus aureus (bacteria) and Saccharomyces cerevisiae (yeast) were measured. It was observed from the study that the Ln(III) coordination polymers acted as an efficient and effective catalysts and antimicrobial agents. 相似文献
920.