全文获取类型
收费全文 | 776573篇 |
免费 | 88011篇 |
国内免费 | 1014篇 |
专业分类
865598篇 |
出版年
2016年 | 8518篇 |
2015年 | 12463篇 |
2014年 | 14642篇 |
2013年 | 20390篇 |
2012年 | 23300篇 |
2011年 | 23912篇 |
2010年 | 15907篇 |
2009年 | 14644篇 |
2008年 | 21163篇 |
2007年 | 21992篇 |
2006年 | 20807篇 |
2005年 | 20009篇 |
2004年 | 19975篇 |
2003年 | 18827篇 |
2002年 | 18529篇 |
2001年 | 33397篇 |
2000年 | 33821篇 |
1999年 | 27068篇 |
1998年 | 9664篇 |
1997年 | 9892篇 |
1996年 | 9314篇 |
1995年 | 8906篇 |
1994年 | 8612篇 |
1993年 | 8637篇 |
1992年 | 22365篇 |
1991年 | 21979篇 |
1990年 | 21457篇 |
1989年 | 20751篇 |
1988年 | 19447篇 |
1987年 | 18469篇 |
1986年 | 17529篇 |
1985年 | 17521篇 |
1984年 | 14495篇 |
1983年 | 12482篇 |
1982年 | 9648篇 |
1981年 | 8940篇 |
1980年 | 8186篇 |
1979年 | 13844篇 |
1978年 | 11266篇 |
1977年 | 10160篇 |
1976年 | 9551篇 |
1975年 | 10930篇 |
1974年 | 11959篇 |
1973年 | 11769篇 |
1972年 | 10764篇 |
1971年 | 9847篇 |
1970年 | 8423篇 |
1969年 | 8294篇 |
1968年 | 7593篇 |
1967年 | 6643篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
Cyclic AMP is not detectable in Clostridium perfringens 总被引:3,自引:0,他引:3
Cyclic AMP was not detected (less than 5 X 10(-9) M intracellular concentration) at any stage of growth or sporulation of two strains of Clostridium perfringens grown with or without methylxanthines. Only Bacillus and Lactobacillus, genera belonging to the same phylogenetic cluster, have previously exhibited undetectable levels of cyclic AMP. 相似文献
892.
In vitro directly micropropagated plantlets from three selected five-year-old Eucalyptus grandis Hill ex. Maiden hybrids were compared to their related half-sib seedlings for growth and growth pattern parameters under greenhouse conditions used for operational seedling production. The oven dry weights were determined from stem, leaf, and root samples collected every 40 days for four times. Relative growth rate, net assimilation rates and shoot:root ratio were calculated. Survival was 98% and 95% for plantlets and seedlings, respectively. Significant differences were observed between parents in terms of shoot and root dry weights and their ratios with similar ranking among plantlets and seedlings, suggesting genetic control over these traits. Plantlets started with significantly higher root: shoot ratios and stem, leaf, root, and total dry weight. Although seedlings had higher relative growth and net assimilation rates, all the initial differences decreased sharply over time. 相似文献
893.
894.
P. H. Baylis 《Cell biochemistry and function》1988,6(3):223-223
895.
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
896.
P Dejours J Armand H Beekenkamp 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1992,315(4):145-150
The pH, the osmolality and the urea and ammonia concentrations in blood, as well as the net urea and ammonia excretions, were studied in the amphibian Xenopus laevis exposed for several weeks to increased osmotic pressure (OP) of the ambient water, as a result of the addition of either NaCl or mannitol to the water. The pH and the ammonia concentration of the blood were independent of the variations of the ambient osmolarity. On the contrary, the blood osmolality and its urea concentration increased markedly when the ambient OP was augmented. The increase of ambient OP by NaCl addition to the medium augmented the urea net excretion and slightly decreased the ammonia excretion. When the increase of ambient OP resulted from the addition of mannitol in the water, excretions of urea and ammonia became negligible. 相似文献
897.
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
898.
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
899.
Detection of genetic variants affecting cattle behaviour and their impact on milk production: a genome‐wide association study 下载免费PDF全文
Juliane Friedrich Bodo Brand Siriluck Ponsuksili Katharina L. Graunke Jan Langbein Jacqueline Knaust Christa Kühn Manfred Schwerin 《Animal genetics》2016,47(1):12-18
Behaviour traits of cattle have been reported to affect important production traits, such as meat quality and milk performance as well as reproduction and health. Genetic predisposition is, together with environmental stimuli, undoubtedly involved in the development of behaviour phenotypes. Underlying molecular mechanisms affecting behaviour in general and behaviour and productions traits in particular still have to be studied in detail. Therefore, we performed a genome‐wide association study in an F2 Charolais × German Holstein cross‐breed population to identify genetic variants that affect behaviour‐related traits assessed in an open‐field and novel‐object test and analysed their putative impact on milk performance. Of 37 201 tested single nucleotide polymorphism (SNPs), four showed a genome‐wide and 37 a chromosome‐wide significant association with behaviour traits assessed in both tests. Nine of the SNPs that were associated with behaviour traits likewise showed a nominal significant association with milk performance traits. On chromosomes 14 and 29, six SNPs were identified to be associated with exploratory behaviour and inactivity during the novel‐object test as well as with milk yield traits. Least squares means for behaviour and milk performance traits for these SNPs revealed that genotypes associated with higher inactivity and less exploratory behaviour promote higher milk yields. Whether these results are due to molecular mechanisms simultaneously affecting behaviour and milk performance or due to a behaviour predisposition, which causes indirect effects on milk performance by influencing individual reactivity, needs further investigation. 相似文献
900.